those at higher latitudes during the winter months (Nunez 1980). ...... Fuad, Rob Barnes, Massimo Gasparon, Bernie Powell, Doug Ward, Rosemary Niehus, Sue ...
Spatial and Temporal Dynamics of Australian Rainforests Melinda Joy Laidlaw
A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in April 2009 School of Biological Sciences
Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the General Award Rules of The University of Queensland, immediately made available for research and study in accordance with the Copyright Act 1968. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material.
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Statement of Contributions to Jointly Authored Works Contained in the Thesis Chapter 1 - Laidlaw, M. J., Kitching, R. L., Goodall, K., Small, A. & Stork, N. (2007) Temporal and spatial variation in an Australian tropical rainforest, Austral Ecology, 37, 10-20. Roger Kitching was project leader for the biodiversity survey of the Thompson Creek plot and assisted with advice and revision of the manuscript; Kylie Goodall managed and conducted the 2005 resurvey of the Cape Tribulation crane plot and assisted with advice and manuscript revision; Andrew Small assisted manuscript revision and with the identification of tree species on the crane plot in 2000 and on the Thompson Creek plot in 2005; Nigel Stork assisted with advice and revision of the manuscript. The author was responsible for managing the Thompson Creek vegetation survey in 2000 and the remainder of the work. Chapter 2 - Laidlaw, M. J., McDonald, W. J. F., Hunter, R. J. & Kitching, R. L. (In press) Subtropical rainforest turnover along an altitudinal gradient, Memoirs of the Queensland Museum. Bill McDonald assisted with study design, species identification, advice, revision and taxonomic accuracy of the manuscript; John Hunter assisted with species identification, advice and manuscript revision; Roger Kitching was project leader for the IBISCA study and assisted with advice and manuscript revision. The author was responsible for managing the IBISCA vegetation survey and the remainder of the work. Chapter 3 - Laidlaw, M. J., McDonald, W. J. F., Hunter, R. J., Putland, D. A. & Kitching, R. L. (Submitted) The potential impacts of climate change on Australian subtropical rainforest. Bill McDonald assisted with study design, species identification, advice, revision and taxonomic accuracy of the manuscript; John Hunter assisted with species identification, advice and manuscript revision; David Putland assisted with plot establishment and revision of the manuscript; Roger Kitching was project leader for the IBISCA study and assisted with advice and manuscript revision. The author was responsible for managing the IBISCA vegetation survey and the remainder of the work.
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Chapter 4 - Laidlaw, M. J., Richardson, K. S., McDonald, W. J. F. & Hunter, R. J. (In preparation) The determinants of β-diversity in Australian subtropical rainforest. Karen Richardson assisted with study design as well as the application of both survey gap analysis and generalized dissimilarity modelling, advice and manuscript revision; Bill McDonald assisted with study design, species identification, advice and manuscript revision. John Hunter assisted with species identification, advice and manuscript revision. The author was responsible for the remainder of the work.
Statement of Contributions by Others to the Thesis as a Whole The conception and design of the project, implementation and data collection, analysis and interpretation of research data and preparation of four manuscripts in this thesis was undertaken by the author, except where expressed in the statement of contribution by others. Yvonne Buckley advised on thesis structure and commented on chapters. Statement of Parts of the Thesis Submitted to Qualify for the Award of Another Degree None. Published Works by the Author Incorporated into the Thesis Chapter 1 - Laidlaw, M. J., Kitching, R. L., Goodall, K., Small, A. & Stork, N. (2007) Temporal and spatial variation in an Australian tropical rainforest, Austral Ecology, 37, 10-20. Additional Published Works by the Author Relevant to the Thesis but not Forming Part of it None.
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Acknowledgements I am extremely grateful to my supervisors Dr Yvonne Buckley, Dr Bill McDonald and Dr Karen Richardson for their guidance, patience and encouragement. I am greatly indebted to Professor Roger Kitching for sharing with me his knowledge and enthusiasm for rainforest and community ecology and for generously giving me his valued advice and support. I am grateful for the support of the Queensland Department of Environment and Resource Management through the Queensland Herbarium and National Parks and Wildlife Service and the New South Wales National Parks and Wildlife Service. For financial assistance I wish to thank the Rainforest CRC and the Green Mountains Natural History Association. For data, advice, technical assistance and most importantly, their time, I sincerely thank Dr Simon Ferrier, Glen Manion, Dr Anita Smyth, John Hunter, Dr Kristen Williams, Anni Blaxland-Faud, Rob Barnes, Assoc. Prof. Massimo Gasparon, Doug Ward, Rosemary Niehus, Dr Don Butler, Sue Rae, Dr Wayne Rochester, Sarah Boulter, Hugh Nicholson, Nan Nicholson, Dr Gordon Guymer and Stephen McKenna. I would also like to thank Bill Flenady and Andy and Vanessa Quirk for their support of this project. I sincerely thank the many wonderful people who accompanied me in the field with good humour and enthusiasm: Bill McDonald, John Hunter, Stephen McKenna, Kylie Goodall, Wendy Neilan, Rob Price, Lui Weber, Terry Reis, Sarah Boulter, Paul Finn, Richard Pidgeon, Amanda Rasmussen, Cath Leigh, Narelle McCallum, Bethan Haughton, Justin Leigh, Kyran Staunton, Gillian Naylor, Jana Crooks, David Hunt, Sarah Maunsell, David Putland, Tang Yong, Peter Benson, Rohini Mann, Neray McBride, Karen Hurley, Kerry Heise, Brendan Finn, Tom Cotter, Shelly Taylor, Sandy Pollock, Nick Cuff, Scott Whitehead, Dane Lamb and Guy Kennedy. I wish to particularly thank Alice Yeates for giving so generously of her time to help me in the field, and for her friendship. I thank my family for their love and support throughout my PhD, particularly my mother for her constant interest, my father for engineering field equipment and to my whole family for tolerating the constant presence of damp camping equipment. I also wish to sincerely thank my dear friends Melina Gillespie, Kylie Goodall and Sarah Boulter for their constant love and support.
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Abstract The loss of tropical and subtropical rainforest biodiversity due to increasing anthropogenic pressure lends urgency to understanding the processes which drive species coexistence. Without an understanding of how species are distributed across the landscape and how species assemblages change through time, we cannot derive appropriate management regimes for their persistence. This thesis examines the role of deterministic drivers of spatial and temporal dynamics of Australian rainforests and investigates the potential impacts of a changing climate on Australian rainforests. The findings from three studies are presented in four chapters which examine floristic turnover in situ and at catchment, regional and continental scales. Compositional turnover in tropical rainforest following the passage of a category three cyclone was examined both at five years’ post-cyclone recovery and in the context of local and regional spatial turnover. After five years, the forest remained in an active state of recovery with an approximate 30% increase in stems, 5% decrease in basal area and a 16% increase in species richness. Local spatial turnover suggests differential impacts of cyclones over even short distances and overall, a high degree of temporal stability in these rainforests, despite the impact of frequent catastrophic disturbances. Compositional turnover in subtropical rainforest along steep moisture and temperature gradients was investigated and described along an altitudinal transect in subtropical rainforest. The identification of significant modelled climatic and mapped soil variables suggests that moisture stress is an important driver of floristic turnover in these forests. Existing high levels of turnover across tree assemblages from low to mid elevations in subtropical rainforest were identified. Such turnover is greatly reduced at higher elevations. With increasing atmospheric temperatures, the cloud cap is expected to rise and we predict that subtropical rainforest communities which currently sit at the level of the cloud base (800-900m) will experience increasing in situ floristic turnover. Our findings agree with predictions for cloud forests elsewhere: high elevation endemic species will face an increasing risk of extinction as mesic climatic envelopes move upslope out of reach. Baseline data from this study will be used as a benchmark against which to formulate and test hypotheses for climate induced floristic and structural shift. It is also acknowledged that monitoring floristic turnover as a surrogate of shifting climatic envelopes may be confounded both by a lack of knowledge regarding the underlying turnover rates of rainforest communities and by the disparity in temporal scales of tree community turnover and accelerating anthropogenic climate change. 7
Finally, generalized dissimilarity modelling is utilised to combine disparate biological survey data and remotely sensed environmental data to investigate the determinants of floristic turnover at the regional scale. Generalized dissimilarity modelling identified four environmental predictors of βdiversity in subtropical rainforest, all closely linked with moisture stress: radiation of the driest quarter, precipitation of the driest period, slope and aspect. Ten land classes were identified and mapped for the Mt Warning Caldera and may act as appropriate management units for future climate change planning within the region. This thesis has identified a potential threat to the biodiversity of Australian rainforests under a changing climate. Increasing levels of evapotranspiration, moisture stress and an increased return rate and intensity of disturbance are predicted to lead to the upslope movement of species ranges, increasing levels of in situ floristic turnover, and will likely result in the emergence of novel rainforest communities not present under current conditions. The potential for anthropogenic climate change to impact upon native vegetation communities has emphasised the need for the continuation and expansion of monitoring programs and the development of dynamic management regimes. Keywords β-diversity, climate change, cloud, climate, compositional turnover, determinism, distance, environmental surrogacy, soils, topography.
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Table of contents List of figures
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List of tables
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1. General Introduction
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2. Objectives
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3. Summary of chapters
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4. General discussion
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5. References
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6. Chapters
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Chapter 1: Temporal and spatial variation in an Australian tropical rainforest
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Chapter 2: Subtropical rainforest turnover along an altitudinal gradient
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Chapter 3: The potential impacts of climate change on Australian subtropical 85
rainforest Chapter 4: The determinants of β-diversity in Australian subtropical rainforest 7. Appendices
111 133
Appendix 1: Kitching, R. L., Putland, D., Ashton, L. A., Laidlaw, M. J., Boulter, S. L., Christenson, H. & Lambkin, C. L. (Submitted) Detecting biodiversity changes along climatic gradients: The IBISCA Queensland project. Memoirs of the Queensland Museum.
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Appendix 2: Strong, C. L., Boulter, S. L., Laidlaw, M. J., Putland, D. & Kitching, R. L. (In press) The physical environment of an altitudinal gradient in the rainforest of Lamington National Park, southeast Queensland. Memoirs of the Queensland Museum.
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List of figures Chapter 1 Figure 1
Location of Australasian one hectare rainforest plots
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Figure 2
Dbh size classes of individuals surveyed at Cape Tribulation in 2000 and 2005
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Figure 3
Height classes of individuals surveyed at Cape Tribulation in 2000 and 2005
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Figure 4
(a) Mean dbh of species represented by 10 or more individuals surveyed at Cape Tribulation in 2000 and 2005
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(b) Mean height of species represented by 10 or more individuals surveyed at Cape Tribulation in 2000 and 2005
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(c) Abundance of species represented by 10 or more individuals surveyed at Cape Tribulation in 2000 and 2005
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(d) Basal area of species represented by 10 or more individuals surveyed at Cape Tribulation in 2000 and 2005 Figure 5
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Bray-Curtis dissimilarity dendrogram of Australasian rainforest survey plots based on floristic composition (dbh ≥10cm)
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Figure 1
The location of 20 20 x 20m quadrats along the IBISCA Queensland transect
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Figure 2
Bray-Curtis dissimilarity dendrogram of altitudinal groups based on floristic
Chapter 2
composition Figure 3
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SSH MDS ordination of altitudes based on floristic composition with minimal spanning tree and biplot of selected associated climatic variables identified by the MCAO significance test
Figure 4
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SSH MDS ordination of altitudes based on species composition with minimal spanning tree and biplot of selected associated soil variables identified by the MCAO significance test
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Chapter 3 Figure 1
Decline in richness with increasing altitude. Data are means (and standard errors) from four 20 x 20 m plots per altitude
Figure 2
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Dendrogram displaying classification of established and juvenile canopy and subcanopy tree community floristic composition recorded from 20 plots at Lamington National Park, south-east Queensland, showing membership of sites to altitudinal groups
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Figure 3
Three dimensional SSH MDS ordination of established and juvenile canopy and subcanopy tree communities recorded at ≤ 700m asl with biplot of selected significant species (MCAO ≤ 1%)
Figure 4
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Three dimensional SSH MDS ordination of high altitude communities and established and juvenile canopy and subcanopy tree communities recorded at ≤ 700m asl with biplot of selected significant extrinsic variables (MCAO ≤ 1%)
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Figure 5
Species accumulation curves for each altitude along the transect
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Figure 6
Mean Bray-Curtis dissimilarity between established and juvenile communities at each altitude
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Chapter 4 Figure 1
(a) Satellite image (Landsat) of the Mt Warning Caldera
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(b) Location of 29 biological survey sites, 28 selected via SGA and one arbitrarily located on rhyolite geology
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Figure 2
The GDM process
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Figure 3
Change in environmental dissimilarity after the selection of 30 survey sites using survey gap analysis
Figure 4
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The GDM model: the predicted ecological distance from four transformed environmental predictors of floristic compositional turnover on the Mt Warning Caldera. Each point represents a site-pair and the line represents the optimal 1:1 fit
Figure 5
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A 10-class classification of the Mt Warning Caldera derived from predicted floristic and environmental dissimilarities
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List of tables General Introduction Table 1
The contributions to β-diversity by environmental heterogeneity, distance, and their combined effect in rainforest studies
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Chapter 1 Table 1
Floristic and structural data for one hectare vegetation plots in Queensland and Papua New Guinea
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Chapter 2 Table 1
Two-way table of twelve species groups recorded for four altitudinal groups. Altitudes at which species were recorded are marked with an asterisk. Species significantly associated with altitudinal groups (MCAO ≤1%) are identified
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Chapter 3 Table 1
Floristic summaries for trees ≥5cm dbh summed for four plots established at each of five altitudes
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Chapter 4 Table 1
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Site locations within the Mt Warning Caldera
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1. General Introduction Rainforests are superbly complex systems which support in excess of half of global terrestrial biodiversity (Wilson 1992). This diversity is due to the ability of hundreds, and potentially thousands, of species to compete for limited resources and coexist within homogeneous habitats (Tilman 1999). What causes compositional turnover and why are some species spatially clumped rather than being evenly distributed? Much progress has been made in recent years in testing hypotheses of species coexistence through the establishment of long term permanent forest plots (Plotkin et al. 2002; Burslem et al. 2001). However, understanding the myriad of interactions which makes this possible is a challenging and ongoing quest for rainforest ecologists (Baker & Wilson 2003; Volkov et al. 2003; Plotkin et al. 2002; Whitfield 2002). Knowledge of the mechanisms from which biodiversity arises will influence how we approach conservation, complementarity and reserve design (Whitfield 2002). This quest is now of particular urgency if we hope to insulate rainforest communities, and biodiversity at the global scale, from the worst impacts of anthropogenic climate change. Although we know much about the capabilities of rainforests to support high α-diversity (species richness) (Leigh et al. 2004; Makana et al. 2004; Condit et al. 2002; Laidlaw et al. 2000; Oatham & Beehler 1998; Terborgh & Andresen 1998; Ashton 1976, 1964; Paijmans 1970), less is known about the patterns and processes which drive β-diversity, or compositional turnover with distance (Chave & Leigh 2002; Condit et al. 2002; Whittaker 1972). Understanding the determinants of spatial floristic turnover, and how this changes over time, are fundamental to the study of diversity and to the field of plant ecology as a whole (Chave 2008; Condit et al. 2002; Dale 1999; Nekola & White 1999; Greig-Smith 1979). The study of vegetation dynamics is the recounting of multispecies patterns over space and time (Law et al. 2009). The neighbourhood in which a plant grows will, in part, determine its spatial distribution, so dynamics must be considered at the community level and in a temporal context (Law et al. 2009). The relative roles of environmental conditions and dispersal limitation have formed one of the central studies in vegetation dynamics (Ricklefs & Schluter 1993). Where geographic distance is the most important predictor of compositional turnover, the community is likely to be dispersal limited (Chust et al. 2006; Condit et al. 2002). Alternatively, where plant establishment is limited, turnover in environmental variables is likely to be the dominant driver of compositional turnover (Tuomisto et al. 2003). Studies of seedling communities show that communities can be both dispersal and establishment limited, although the timing of dispersal limitation appears to be of critical importance (Norden et al. 2007). 13
Floristic turnover is influenced by processes such as dispersal, speciation and disturbance (Mouquet & Loreau 2003; Tuomisto et al. 2003; Condit et al. 2002). Such dispersal-assembly theories of species coexistence emphasise community demographics and limits to seed dispersal in shaping species composition and turnover (Chave 2008; Bell 2001). In Hubbell’s theoretical neutral community, all individuals within broadly defined functional groups are considered ecologically equivalent in their probability of reproduction, recruitment and mortality (Dalling et al. 2009; Whitfield 2002; Hubbell 2001, 1997) irrespective of environmental heterogeneity (Potts et al. 2004), providing resources are not too limiting (Chave 2008). Differences in relative species abundance is thus due to population biology mechanisms of speciation, extinction, dispersal and ecological drift (Volkov et al. 2005; Volkov et al. 2003). Increasing floristic dissimilarity with increasing distance between survey points is expected as a result of limited seed dispersal and speciation (Chave & Leigh 2002). Although this has been demonstrated by some authors under particular conditions of scale (Chave 2004; Phillips et al. 2003; Condit et al. 2002), many studies have pointed to the importance of environmental heterogeneity in accounting for floristic turnover in rainforest communities (Jabot et al. 2008; Chust et al. 2006; Phillips et al. 2003; Duivenvoorden et al. 2002; Ruokolainen & Tuomisto 2002). Other studies have found evidence of turnover influenced by both dispersal-limited and niche-based processes (Potts et al. 2004; Plotkin et al. 2002). Null models such as Hubbell’s neutral theory (Hubbell 2008) are, however, useful tools for the progression of community dynamics and can be complementary with other theories (Legendre et al. 2009). The importance of dispersal-assembly is acknowledged but not explored directly in this thesis. Instead, this study investigates deterministic processes as drivers of spatial and temporal dynamics. Niche-assembly theories of species turnover suggest that some sites are unsuitable at some times, for certain species (Plotkin et al. 2002). Niche theory predicts (Gentry 1988, 1982; Whittaker 1972; Ashton 1976, 1964) that species are distributed according to constraints placed on them by their environment (physiological filters) and competition for limited resources (biotic filters) (Chave 2008). These physiological filters restrict the establishment of species without suitable adaptations (Chave 2008; Tuomisto et al. 2003; Condit et al. 2002; Ashton & Hall 1992) and may include moisture, soil nutrients, radiation and warmth (Queenborough et al. 2007; Austin et al. 1996). This specialisation of species along resource gradients in multidimensional ecological space is an important mechanism supporting species coexistence in rainforest communities (Kitajima & Poorter 2008) and results in identifiable, repeated and mappable patterns in the landscape.
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Moisture The amount of moisture available to plants will depend on a number of factors in addition to the amount and timing of rainfall events, including air temperature, air movement, humidity, the waterholding capacity of the soil and the degree of runoff and groundwater movement (Kirkpatrick & Nunez 1980). Together, these variables determine the amount of moisture available within an ecosystem and will help determine the type and abundance of vegetation able to grow in a location (Woodward & Williams 1987). Although annual rainfall inputs are vital in determining the distribution of many species, for others, it is the seasonal distribution of this rainfall that will determine their range (Salisbury 1926). Rainforest is largely restricted to regions with high levels of annual rainfall and with no prolonged dry season. This forest type reaches its maximum potential in areas of high and evenly distributed rainfall (Richards 1964). Rainforest can occur in areas outside of these broad conditions, however, if cloud and fog or other environmental or edaphic factors are able to compensate for lower rainfall (Richards 1964). Where a cloud cap is common, moisture inputs and humidity are higher, solar radiation is lower and as a result, evaporation is approximately 30% lower than at lower altitudes (Pendry & Proctor 1996). As a result of this occult precipitation and low evaporation, plant groups such as epiphytes and bryophytes thrive in these moist environments (Pendry & Proctor 1996). Spatio-temporal variation in rainfall within a rainforest can be considerable, even over small distances. Local topography and canopy structure in itself are also able to enhance the spatial patchiness of rainfall events by the enhancing of convection or upwind/downwind effects of local changes in altitude (Chappell et al. 2001). Canopies intercept some rainfall before it reaches the ground and it is lost to the atmosphere as ‘wet-canopy-evaporation’ (Chappell et al. 2001). Chappell et al. (2001) found strong diurnal patterning in rainfall events in Borneo due to a majority of rainfall events occurring between 2 and 4pm in the afternoon which was associated with highly localised convective rainfall cells (cumulus clouds) resulting in spatially heterogeneous rainfall. Where moisture loss exceeds that available from the soil, due to the evaporative power of the atmosphere or resistant texture of the soil, a plant will become permanently wilted (Salisbury 1926). Laurance et al. (2009) found for the Amazon rainforest that broad scale tree mortality was caused by drought events and were not confined to particular topographic positions (Laurance et al. 2009). These rainfall anomalies were associated with ENSO events in the Amazon (Laurance et al. 2009). Droughts are likely to become more common as the frequency and intensity of ENSO events increases (Nepstad et al. 2004). As a result, many rainforests may experience increasing moisture stress into the future. 15
Nutrients Gradients in soil nutrient availability are a principal cause of compositional turnover in vegetation communities (Walker & del Moral 2003; Kitayama & Mueller-Dombois 1995). Plants require both macronutrients (eg. iron (Fe), nitrogen (N), phosphorus (P), potassium (K), sulphate (S), calcium (C) and magnesium (Mg)) and micronutrients (manganese (Mn), Zinc (Zn), copper (Cu), (Mo), boron (B) and chlorine (Cl)) to survive (Larcher 1980). As different species have different nutritional requirements, both in terms of amount and proportion, the presence and quantity of different nutrients in an ecosystem will determine their distribution. For example, climbing plants generally require higher levels of soil nutrients than non-climbing species (Salzer et al. 2006). In general, rainforest soils tend to be highly leached, acidic, either red or yellow in colour, high in loam or clay fractions and rich in aluminium (Richards 1964). Soil pH generally decreases with increasing altitude (Pendry & Proctor 1996). Soil organic matter is generally restricted to the surface layers and also declines with increasing altitude, largely due to the slower decomposition rates associated with cooler temperatures (Proctor et al. 2007) and increased waterlogging of the soil (Pendry & Proctor 1996). Torn et al. (2005) found that decomposition rates were fastest on sites of high soil fertility. Some species of rainforest tree which grow on poor soils form a fine surface root mat in order to take advantage of nutrients from the leaf litter (Luizão et al. 2007). Calcium, magnesium, manganese and zinc were found to be removed from the leaf litter at a faster rate where a root mat was present (Luizão et al. 2007). Nutrient cycling tends to occur more quickly in moist environments through faster rock weathering and leaching of soil elements (Kitayama & Mueller-Dombois 1995). Hydrological and nutrient cycles are particularly closely linked in rainforest ecosystems (Luizão et al. 2007; Brunijnzeel 1991). Gentry (1988) found that in the neotropics, species richness generally increased along with soil nutrient levels and rainfall. Rainfall can carry with it significant amounts of nutrients (Chuyong et al. 2004; Schroth et al. 2001) and can wash additional nutrient deposits collected on leaves through to the forest floor (Germer et al. 2007). Heath and Huebert (1999) found that cloud water is also a significant source of nutrient deposition with up to 50kg of nitrogen per hectare, per year being deposited in Hawaiian montane rainforest. These nutrient inputs may drive decomposition in the leaf litter at the start of a wet season (Chuyong et al. 2004). Soil microbial activity is also closely linked with moisture (Zhang & Zak 1995).
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Radiation The availability of light within a rainforest is highly variable, both in space and time (Turnbull et al. 1993) and is often limiting to plant growth (Yates et al. 1988). These differences in radiation will in turn result in differences water balance and edaphic characteristics (Kirkpatrick & Nunez 1980; Galacia et al.1999) and help drive compositional turnover. High levels of high-intensity visible radiation or UV can cause photodestructive effects in plants such as photooxidation of chloroplast pigments (Larcher 1980). The sunlight which reaches the rainforest floor may constitute as little as 2% of that received by the canopy and is largely received by understorey plants in the form of transient sunflecks (Chazdon & Fetcher 1984). The amount of radiation received at a site will depend on the latitude of the site, the angle of the slope and its aspect (Holland & Steyn 1975) and the degree of cloud cover (Larcher 1980). At the equator, day length generally varies little throughout the year and as a result of this lack of seasonality, daily oscillations in climate between day and night are important (Larcher 1980). At higher latitudes, however, day length and thus temperature, can vary greatly throughout the year (Larcher 1980). Differentiation between regions based on the amount of solar radiation received will create gradients in the amount of light available, the degree of heating, the humidity and the amount of available moisture (Kirkpatrick & Nunez 1980). With increasing altitude, the amount of radiation increases due to the shorter distance from the sun and the lower level of air turbidity for the radiation to pass through (Larcher 1980). According to Flenley (1995), the physiognomic features of montane forest such as stunted growth forms, small, thick leaves and the presence of leaf compounds such as flavonoids, can be simulated through the exposure of vegetation to high levels of UV-B light. The incidence and physical properties of cloud cover will also have a dramatic impact on the level of radiation reaching the ground (Nunez 1980). Through upwards reflection from low clouds, Flenley (1995) believes that montane forest may be exposed to up to 70% higher insolation than lower altitude forest. . In mountainous terrain, radiation must be calculated for a sloping surface (Nunez 1980) and aspect considered (Galicia et al. 1999). The duration and intensity of radiation received by a slope influences both temperature and moisture regimes and in turn, floristic composition and plant growth (Holland & Steyn 1975). Radiation generally increases with slope angle (Galicia et al. 1999). This is complicated, however, by the effects of shadow (Nunez 1980) as slopes may receive less solar radiation and thus be moister than nearby horizontal areas (Lindenmayer et al. 1999). A northerly slope of 30º at a latitude of 30º experiences radiation levels equivalent to a horizontal point approximately 5º further north (Holland & Steyn 1975). For individuals growing where 17
rainfall is limited, water stress will be greater for individuals growing on slopes receiving higher levels of radiation than for members of the same species on shaded slopes (Holland & Steyn 1975). Holland and Steyn (1975) have found that at middle latitudes, a slope steeper than 15-25º will not only experience a different radiation and thermal regime than from a nearby horizontal point, but will also be exposed to diminished soil water storage capabilities. In Australia, north-facing slopes will receive the highest levels of radiation, while southern slopes are often in shadow, particularly those at higher latitudes during the winter months (Nunez 1980). Kirkpatrick and Nunez (1980) found that there were strong links between vegetation patterns and total annual solar radiation when adjusted for topographical shading, cloud and the sky view factor. They found that north-west slopes supported more xeric vegetation than those slopes facing due north, where insolation levels were highest (Kirkpatrick & Nunez 1980). This same result was found in California by Pinder et al. (1997), where, in the northern hemisphere, the most xeric vegetation was found high on steep, south-western slopes where insolation was high and the soil was well drained. Conversely, the most mesic vegetation was found on south-east slopes (or northeast in the case of Pinder et al. (1997)), not southern slopes with the lowest insolation (Kirkpatrick & Nunez 1980). This suggests that it is possibly the combined effects of high levels of solar radiation coupled with high evapotranspiration rates in the afternoons on north-west slopes creating such vegetation patterns (Kirkpatrick & Nunez 1980). In a study by Galicia et al. (1999), in mountainous regions in Mexico, solar radiation was highest on the top section of gentle slopes and on the bottom section of southern slopes. The lowest levels of solar radiation were received by the bottom sections of northern slopes (Galicia et al. 1999). Temperature Plants are essentially ectothermic and any heat produced via chemical processes is quickly lost to the atmosphere (Sutcliffe 1977). As such, the distribution of plant communities is, at some scales, regulated by ambient temperature (Sutcliffe 1977). Processes such as photosynthesis, respiration and evapotranspiration, carbon, water and nutrient cycles are closely linked to temperature (Ricotta & Avena 1997). The responses of plants to temperature differs both within and between communities (Turnball et al. 2005). All species have an optimal temperature range beyond which growth ceases (Sutcliffe 1977). This range is likely to be wider for survival than it is for reproductive success (Sutcliffe 1977). Both above and below a species’ cardinal temperatures, performance declines towards a lethal limit (Larcher 1980).
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Low temperatures can cause injury by limiting or halting vital plant physiological processes and, at extremely low temperatures, cause the death of the plant (Woodward 1990). In general, the incidence of frost resistance in plants increases with latitude (Bannister 2003) and according to Sutcliffe (1977), is the single most important factor limiting the global distribution of some plant groups. Catastrophic freezing events can have long lasting effects on patterns of species dominance in a community due to differential levels of frost tolerance among species (Read & Hill 1988). A species’ tolerance to low temperatures does not, however, reduce their ability to successfully compete in warmer climates (Read 1990). Species adapted to temperate conditions are able to reach maximum growth under colder conditions than their tropical counterparts (Cunningham & Read 2003). Cunningham and Read (2002) report that temperate rainforest species are able to sustain maximum net photosynthesis rates over a wider range of growth temperatures than tropical rainforest species and suggest they may fair better under global warming scenarios than many tropical species. In general, tropical rainforest is restricted to regions where annual mean temperature does not drop below 20ºC (Richards 1964). High temperatures can injure a plant by causing it to lose moisture from high transpiration rates, by respiration rates outstripping the photosynthetic rate at high temperature causing the plant to starve to death (Clark et al. 2003) and through the denaturation of protoplasm and a decrease in protoplasmic streaming (Larcher 1980, Sutcliffe 1977). Laurance et al. (2009) found in the Amazon, however, that increasing daytime maximum temperatures were strongly correlated with increasing tree growth rather than causing reduced plant growth due to high respiration rates. Where a species’ distribution is limited by temperature, it is more likely that it is impacting upon a species via water relations (Salisbury 1926). Thus, where water availability is low either due to hot, dry conditions or due to the freezing of soil moisture during frost, a plant can experience excessive transpiration and eventually, death (Salisbury 1926). Temperature at a site is likely to be determined by a range of environmental factors (Ashcroft et al. 2008) such as latitude, altitude, topography and soil characteristics (Salisbury 1926). Annual mean temperatures decrease and seasonal and diurnal temperature ranges increase with distance from the equator (Bannister 2003). Diurnal temperature ranges at low latitudes increase sharply with altitude, thus on tropical mountains, diurnal temperature ranges can be far more extreme than seasonal temperature ranges (Bannister 2003). With increasing latitude, the sun is at a lower angle at midday and delivers less heat than in the tropics (Sutcliffe 1977). At high altitudes, warm air expands and cools approximately 1ºC for every 160m rise (Sutcliffe 1977). Soil temperatures tend to be more spatially variable than air temperature (Ashcroft et al. 2008). In a study of the forests of 19
southeastern NSW, Austin et al. (1996) found that mean annual temperature was best able to predict species richness at a site. Temperature also affected the way that species richness responded to rainfall (Austin et al. 1996). When only rainforest trees were examined, temperature and topography were found to be of almost equal importance in explaining species richness (Austin et al. 1996). Despite the availability of new technologies to assist in the identification of patterns in floristic turnover such as satellite data and climate models, we still do not fully understand the drivers of rainforest β-diversity. Environmental heterogeneity alone has been shown to explain between 6% and 42% of floristic turnover in rainforest communities worldwide (Table 1) (Legendre et al. 2009; Chave 2008; Chust et al. 2006; Phillips et al. 2003; Balvenera et al. 2002; Duivenvoorden et al. 2002). Geographical distance between sites shows high collinearity with environmental variation and can explain between 10% and 29% of floristic turnover (Table 1) (Chave 2008; Chust et al. 2006; Phillips et al. 2003; Balvanera et al. 2002; Duivenvoorden et al. 2002). Geographical distance and environmental heterogeneity together, however, have been shown to explain only up to 24% of floristic turnover in tropical rainforest (Chust et al. 2006; Balvanera et al. 2002; Duivenvoorden et al. 2002) and up to 65% in the subtropical rainforest of China (Table 1) (Legendre et al. 2009). The degree to which geographical distance and environmental heterogeneity are able to explain variation in floristic composition will depend on the scale of observation and on the community being studied (Balvanera et al. 2002), however, the amount of unexplained floristic turnover in rainforest remains considerable, at up to 59% (Chave 2008; Chust et al. 2006; Duivenvoorden et al. 2002). Understanding this unexplained component is an ongoing challenge in rainforest ecology.
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Table 1: The contributions to β-diversity by environmental heterogeneity, distance, and their combined effect in rainforest studies
Contribution to compositional turnover (%) Study
Balvanera et al. 2002
Chust et al. 2006
Duivenvoorden et al. 2002
Location
Scale
Plot size
Mexico
2.4 Ha
30 x 100m
Panama
53 plots, 0.32-6 Ha
variable
Panama
64 Ha
1 Ha
Legendre et al. 2009
China
24 Ha
20 x 20m
Phillips et al. 2003
Peru
0.88 Ha
2 x 50m
Method Canonical correspondence analysis Mantel tests on distance matrices and canonical analysis Steinhaus coefficient of similarity and multiple regression Principal coordinates of neighbour matrices (PCNM) Monte Carlo randomisation tests and multiple regression of distance matrices
Environment
Distance
Environment + distance
42
19
7
10-12
22-27
13-18
7
10
24
6
29
65
40
10
-
The time scales required to understand rainforest dynamics can exceed the working life of researchers. Therefore, to better understand the spatial and temporal dynamics of Australian rainforests and apply this to practical, on-ground action, a multifaceted approach has been taken in this study. The role of disturbance in driving regional scale floristic turnover was examined through the post-cyclone recovery of an existing tropical rainforest plot. The environmental drivers of floristic turnover were investigated through the establishment of floristic inventory plots, which provide both a ‘snap-shot’ in time of current drivers of β-diversity and a benchmark against which future resurveys can be compared. The direction and environmental drivers of in situ floristic turnover were explored and extrapolated through the recruiting tree community in subtropical rainforest. Finally, GIS and modelling tools were combined to allow immediate conservation planning and management action to be taken, despite lacking a complete understanding of the deterministic drivers of β-diversity.
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2. Objectives The objective of this thesis was to investigate the spatial and temporal dynamics of Australian tropical and subtropical rainforests as drivers of floristic diversity. Spatial dynamics were examined via compositional turnover and structural variation between forests at local, regional and continental scales (Chapter 1), through the a priori identification of deterministic processes affecting niche assembly along environmental axes known to accentuate compositional turnover (Chapters 2 and 3) and through the regional scale investigation of β-diversity using both biological survey and remotely derived environmental data (Chapter 4). Temporal dynamics were examined by monitoring secondary succession following a major natural disturbance (Chapter 1), through the use of the recruiting tree community to examine future floristic turnover (Chapter 3), and through the use of adjacent climates as a surrogate for climatic shifts over time (Chapter 2 and 3). 3. Summary of chapters The four chapters contained in this thesis examine rainforest dynamics at a progression of increasing spatial scales from temporal in situ turnover, to turnover at the catchment, regional and continental scales. Chapter 1 investigates the temporal dynamics of tropical rainforest by tracking its floristic and structural recovery following cyclone disturbance. The association between spatial and temporal turnover is also explored by placing these results in a regional context. Chapter 2 examines the climatic, topographic and edaphic determinants of altitudinally distributed structural formations of subtropical rainforest. This chapter provides the baseline description of floristic assemblages along the altitudinal transect and will serve as the point of reference against which future surveys can be compared. Chapter 3 examines floristic shift within subtropical rainforest by investigating differences between the established and juvenile canopy and subcanopy tree communities along an altitudinal gradient. The potential impacts of a rising cloud cap on high altitude cloud forests are also explored. Chapter 4 examines a new methodology for studying spatial turnover in data poor communities and identifies land classes from remotely sensed and biological survey data for planning at the regional scale. A brief summary of each of these chapters in provided below.
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Chapter 1: Temporal and Spatial variation in an Australian tropical rainforest The structure and floristics of a 0.95 hectare lowland tropical rainforest plot at Cape Tribulation, Queensland, are described following surveys conducted both 18 months and five years after the passage of a category three tropical cyclone. Temporal, in situ compositional turnover and spatial compositional turnover at catchment to continental scales in tropical rainforest were examined. Floristic and structural changes in the time following the cyclone suggest that the study site is still in an active stage of post-cyclone recovery, however, local variation in structure and floristic composition exceeded that exhibited by a single plot, despite severe cyclone damage. Spatial variation in the impacts of cyclone damage in these forests, and the resulting high degree of patchiness, is suggested as a regional scale surrogate for intermediate disturbance regimes. These results suggest that the lowland rainforests of Cape Tribulation are highly adapted to frequent catastrophic disturbance and remain floristically and structurally stable at the regional scale over time. Chapter 2: Subtropical rainforest turnover along an altitudinal gradient Spatial turnover in subtropical rainforest structural formations and species assemblages along a steep gradient of temperature and moisture was examined via an altitudinal transect extending from 300m to 1100m above sea level. Four altitudinal groups were identified and closely reflect the spatial distribution of recognised structural formations in the region. Twelve species groups were identified along the transect and the environmental determinants of their distribution are discussed. Multivariate analysis was used to examine the influence of climatic, edaphic and topographic gradients on vegetation and to identify species groups able to be used as indicators of floristic shift along these axes. The floristic composition of extant communities will be used as a baseline against which future changes in these forests can be assessed. Chapter 3: The potential impacts of climate change on Australian subtropical rainforest The temporal dynamics of subtropical rainforest tree communities were examined through investigation of in situ turnover using recruiting tree species. A stepwise upslope progression of tree species was anticipated as an indicator of a warming and/or drying climate. Instead, what was found was a dissociation between established and juvenile tree communities at mid to low altitudes. Moisture stress during annual dry seasons and periodic drought are suggested as potential drivers of this floristic shift. We suggest that this compositional turnover is mitigated at high altitudes by high inputs from moisture-laden maritime trade winds. Contact with the cloud cap is expected to decrease, however, as a result of increasing atmospheric and sea surface temperatures, thus
23
potentially increasing the incidence of moisture stress in these forests. These results have important implications for future monitoring and management under climate change scenarios. Chapter 4: The determinants of β-diversity in Australian subtropical rainforest An understanding of β-diversity, the spatial distribution of biodiversity, is necessary for conservation management. This is confounded, however, by the fine scale spatial turnover of floristic composition within subtropical rainforest and the relative paucity of biological survey data at the regional scale. This chapter explores a relatively new technique for combining biological survey data with remotely sensed environmental data to investigate the determinants of compositional turnover and define land classes relevant to management agencies. Climatic variables associated with moisture stress, as well as slope and aspect, were identified as significant in determining floristic turnover between survey sites. Ten land classes were identified and mapped across the study region, which may assist in conservation planning and management of these forests. 4. General discussion Australian rainforest communities may be relatively small in area, however, the biodiversity they maintain through high levels of species coexistence across space and time make them a priority for research and conservation. The findings from this thesis suggest that niche assembly models of species coexistence alone cannot account for the high level of floristic diversity observed in Australian rainforests. Further study of the determinants of spatial and temporal rainforest dynamics as drivers of species coexistence will need to address the large unexplained portion of all studies attempting to uncover the drivers of β-diversity. It could be suggested either that we are overlooking or underestimating the importance of something fundamental in our understanding of plant interactions with their environment, such as the role of ectomycorrhizae or edaphic variables. There is, as Terborgh et al. (1999) suggests, ‘a vast difference between saying that biological mechanisms do not exist, and saying that we do not fully understand what they are’. Alternatively, the interactions between the myriad of factors determining any individual of any species’ presence in a location at a particular time is extremely complex and is, at the community level, irreducible. The impact of future local species extinctions on these complex interactions are also unknown. Future work on the spatial and temporal dynamics of Australian rainforests in this region must incorporate the role of dispersal, stochasticity and other components of neutral models of species coexistence. Studies testing the relative importance of deterministic and stochastic process to 24
floristic turnover in tropical rainforests have shown that both are likely to be significant in determining species distributions, even across strong environmental gradients (Chave 2008; Cannon & Leighton 2004; Condit et al. 2002, 2000; Wright 2002). Current dispersal assembly theories overlook species physiological traits, whilst niche assembly theories underestimate the role of dispersal and stochasticity in distributional patterns (Chave 2008, 2004). Such approaches may help to close the gap on the ‘unexplained’ component of rainforest β-diversity. Mountain tops have served as important repositories of genetic diversity through prior climatic fluctuations and are now under threat from a rapidly changing climate. As yet we cannot quantify the contribution of cloud water on the Mt Warning Caldera and what climate data we do have is from sparsely distributed weather stations which are only capable of recording vertical precipitation. A research priority will be to stratify fog detectors and other climate sensors both horizontally throughout the region, and vertically within the different strata of the forest. The ongoing monitoring of the existing 49 subtropical survey sites on the Mt Warning Caldera, the Cape Tribulation crane and Thompson Creek sites in the wet tropics and other permanently marked plots up and down the coast, should be considered a priority for detecting floristic shifts. A set of testable hypotheses against which the results of future monitoring can be compared should also be formulated. The publication or release of long term datasets such as the 40 years of seedling dynamics data collected at Lamington National Park would allow the results from this study and others to be better placed into temporal context. Establishment of large scale dynamics plots such as those established by the Smithsonian Tropical Forests Institute (Losos & Leigh 2004) would allow Australian researchers the opportunity to become more active in the study of rainforest dynamics and diversity. Two 25 hectare plots are currently being established in the wet tropics bioregion of Queensland and an equivalent in the subtropics would be extremely beneficial. It must be acknowledged that, even as we investigate the deterministic causes of compositional turnover, our climatic systems and its myriad correlates are also on the move. Researchers are challenged by time lags associated with working with long lived species, interactions between climate and soil forming processes and the time taken for research to inform policy. Functional groups such as canopy epiphytes may be able to serve as a miner’s canary for moisture stress in Australian rainforests due to their faster generation times and detachment from soil water reservoirs. The use of new tools such as survey gap analysis and generalized dissimilarity modelling may allow the better direction of new surveys and the efficient use of existing biological datasets to identify land classes for management. Any future planning and management regimes for Australian
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Turnbull, M. H., Doley, D. & Yates, D. J. (1993) The dynamics of photosynthetic acclimation to changes in light quantity and quality in three Australian rainforest tree species, Oecologia, 94, 218228. Volkov, I., Banavar, J. R., He, F., Hubbell, S. P, Maritian, A. (2005) Density dependence explains tree species abundance and diversity in tropical forests, Nature, 438, 658-661. Volkov, I., Banavar, J. R., Hubbell, S. P. & Maritan, A. (2003) Neutral theory and relative species abundance in ecology, Nature, 424, 1035-1037. Walker, L. R. & del Moral, R. (2003) Primary succession and ecosystem rehabilitation, Cambridge University Press, Cambridge. Whitfield, J. (2002) Neutrality versus the niche, Nature, 417, 480-481. Whittaker, R. H. (1972) Evolution and measurement of species diversity, Taxon, 21, 213-251. Wilson, E. O. (1992) The diversity of life, Harvard University Press, Cambridge. Woodward, F. I. (1990) Global change – translating plant ecophysiological responses to ecosystems, Trends in Ecology and Evolution, 5, 308-311. Woodward, F. I. & Williams, B. G. (1987) Climate and plant distribution at global and local scales, Vegetatio, 69, 189-197. Wright, S. J. (2002) Plant diversity in tropical forests: a review of mechanisms of species coexistence, Oecologia, 130, 1-14. Yates, D. J., Unwin, G. L. & Doley, D. (1988) Rainforest environment and physiology, Proceedings of the Ecological Society of Australia, 15, 31-37. Zhang, Q. & Zak, J. C. (1995) Effects of gap size on litter decomposition and microbial activity in a subtropical forest, Ecology, 76, 2196-2204.
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6. Chapters Chapter 1 Laidlaw, M. J., Kitching, R. L., Goodall, K., Small, A. & Stork, N. (2007) Temporal and spatial variation in an Australian tropical rainforest, Austral Ecology, 37, 10-20. Chapter 2 Laidlaw, M. J., McDonald, W. J. F., Hunter, R. J. & Kitching, R. L. (In Press) Subtropical rainforest turnover along an altitudinal gradient, Memoirs of the Queensland Museum. Chapter 3 Laidlaw, M. J., McDonald, W. J. F., Hunter, R. J., Putland, D. A. & Kitching, R. L. (Submitted) The potential impacts of climate change on Australian subtropical rainforest. Chapter 4 Laidlaw, M. J., Richardson, K. S., McDonald, W. J. F. & Hunter, R. J. (In preparation) The determinants of β-diversity in Australian subtropical rainforest.
35
36
Chapter 1 TEMPORAL AND SPATIAL VARIATION IN AN AUSTRALIAN TROPICAL RAINFOREST
MELINDA LAIDLAW1, ROGER KITCHING2, KYLIE GOODALL2 ANDREW SMALL3 AND NIGEL STORK4 1
Cooperative Research Centre for Tropical Rainforest Ecology and Management, School of
Biological Sciences, The University of Queensland, St Lucia, Qld, 4072. 2
Cooperative Research Centre for Tropical Rainforest Ecology and Management, Griffith School of
the Environment, Griffith University, Nathan, Qld, 4111. 3
GHD Pty. Ltd., Cairns, Qld, 4870.
4
Cooperative Research Centre for Tropical Rainforest Ecology and Management, James Cook
University, Cairns, Qld, 4870. Abstract This study describes the floristics and structure of a 0.95 hectare lowland tropical rainforest plot at the Australian Canopy Crane Research Facility at Cape Tribulation, Queensland. Five years of post-cyclonic change in forest floristics and structure following the passage of Tropical Cyclone ‘Rona’ in February 1999 are examined. The 2005 survey of the Cape Tribulation Crane plot found 680 stems of 82 species ≥ 10 cm dbh, an increase of 30.3% in stems and 16.4% of species in the five years since the previous survey. The most important families were Meliaceae, Euphorbiaceae, Lauraceae, Myrtaceae and Apocynaceae and the most important species were Cleistanthus myrianthus, Alstonia scholaris, Myristica insipida, Normanbya normanbyi and Rockinghamia angustifolia. Temporal floristic and structural variation suggests that the crane site remains in an active stage of post-cyclonic recovery. Local and regional variation in tropical rainforest is examined in comparison with both lowland plots established nearby, and mid-elevation plots located elsewhere in north Queensland at Eungella, Paluma and the Atherton Tablelands. These plots are placed in a broader Australasian context along with lowland rainforest plots at Baitabag and Oomsis, Papua New Guinea. Local spatial variability in floristics and structure at Cape Tribulation exceeded the variation exhibited by a single plot over a period of five years, despite the impact of Cyclone Rona. The rainforests of Cape Tribulation constitute a relatively unique floristic community when observed in an Australasian context. Variation in rainforest community composition across the region shows the importance of biogeographic connections, the impacts of local topography, environmental conditions and disturbance history. Keywords: Cape Tribulation, cyclone, floristics, structure, tropical rainforest 37
Introduction Human impacts are beginning to change environmental conditions around the world (Feeley et al. (2007). Some studies have observed recent increases in above ground biomass in tropical forest regions (Gloor et al. 2009; Baker et al. 2004; Phillips et al. 2002, Phillips et al. 1998), whilst others have observed declines (Chave et al. 2008, Feeley et al. 2007, Clarke 2002) or fluctuations between these states over time (Chave et al. 2003). Understanding how these changes will impact upon highly diverse rainforest communities is critical (Malhi & Phillips 2004). Linking changes in tropical forests to causal mechanism is difficult however (Lewis et al. 2004). Much of the evidence for this increased biomass has come from the monitoring of up to 17 large-scale forest plots, most 25-50 hectares in size, and from many smaller forest plots across the tropical world. To date there is little comparable baseline information from Australia’s tropical rainforests let alone data on the way they are changing. Some evidence suggests that Australian tropical forests may be responding differently to climatic extremes than other rainforests. A recent study in the Wet Tropics Bioregion showed that flowering and seedling recruitment behaviour in Australian species did not match expectations generated from studies in the neotropics (Connell & Green 2000). In another recent Australian study (Edwards & Krockenberger 2006), seedling survival across the 2002 El Nino event was extremely low; 64% percent of the individuals and 30% of the species that were recorded in 2001 were no longer present at the end of 2002. Those species that were removed were among the rarest in the community. These estimates are much greater than that reported from previous work in Panama, where most seedlings survived the El Nino drought (Engelbrecht et al. 2002). The impacts of cyclones and hurricanes on forest floristics, structure and dynamics have been investigated worldwide. Studies in Puerto Rico, the Virgin Islands, South Carolina, Jamaica and the Yucatan Peninsula in the two years following Hurricane Hugo (1989) showed that defoliation was the most common form of damage suffered by forest trees, with uprooting and snapping of boles more likely to impact on tall and large diameter trees (Brokaw & Walker 1991, Gresham et al. 1991, Walker 1991, You & Petty 1991). This result was also recorded in Taiwan (Mabry et al. 1998). It was found that Hurricane Hugo impacted some species consistently more than others (Gresham et al. 1991), however, this was not the case in Taiwan (Mabry et al. 1998). Despite a large loss of canopy cover as a result of this event (Brokaw & Grear 1991), tree deaths were relatively low, ranging from 4-7% (Walker 1991; You & Petty 1991). Importance rankings of species were also found not to have changed following Hurricane Hugo (Brokaw & Walker 1991). The increase in understorey light from gap formation and defoliation resulted in increased seedling density from seeds and increased recruitment of understorey individuals to larger size classes (Brokow & Grear 1991). The passage of Cyclone Larry in north Queensland in 2006 showed that 38
species with leaves resistant to petiole breakage were more likely to have broken branches than those which experienced higher levels of leaf stripping (Gleason et al. 2008). This may suggest that the loss of leaves during a cyclone may reduce surface area and thus, wind damage (Gleason et al. 2008). This study aims to investigate in-situ turnover in floristic composition following the passage of a Category 3 Tropical Cyclone (Rona) in February 1999 and compare this with floristic turnover observed with geographical distance at the local, regional and continental scales. This study focussed on approximately one hectare of lowland tropical rainforest beneath the arc of the Australian canopy crane near Cape Tribulation in North Queensland over a five year period (from 2000 to 2005). Elsewhere, Ticehurst et al. (2007) present further analysis of the impact of Cyclone Rona on the crane area and surrounding forest. The floristics of the canopy crane are also compared with a series of seven rainforest plots, some located relatively close to the crane plot and others on a latitudinal gradient from 50 to 210S. This analysis provides some measure of the variation in vegetation structure and floristics in tropical forests in the Australasian region. Methods Vegetation Survey The Cape Tribulation Canopy Crane Research Facility is located in lowland tropical rainforest at 16°06'20"S 145°26'40"E and at approximately 50 m elevation. It lies within a semi-enclosed coastal basin formed by ridges running east-west to an upland massif (Grove et al. 2000). Environmental conditions recorded at the site are reported in Freiberg and Turton (2007). In 1998, a Leibherr 91EC industrial T-crane was established on the site to facilitate canopy access by researchers (Stork 2007; Stork & Cermak 2003). Installation was carried out by helicopter in order to minimize canopy disturbance. In 2000, a circular vegetation plot was established directly below the 55 m radius of the crane jib, encompassing an area of 0.95 of a hectare (Cape Tribulation Survey 2000). All stems with a diameter at breast height (dbh) of 10 cm or more were tagged, numbered and mapped. Their diameters were measured at 1.3 m from the ground on the uphill side of the bole. Tree heights were obtained by locating the crane bucket at the top of each tree and dropping a tape measure to the ground beside each stem. These stems were identified by consultant botanists and by staff at the research facility and the taxonomic work of Henderson (2002) should be consulted for all species authorities. This survey methodology was repeated in 2005 and new recruits to the ≥ 10 cm size class were included in the survey (Cape Tribulation Survey 2005).
39
Additional one hectare plots were established elsewhere near the crane plot (Thompson Creek) and in other tropical forests in the region. In most cases, a standard 100 m x 100 m plot was established with markers delineating each 10 m x 10 m quadrat within the plot. All stems with a dbh ≥5 cm were tagged and numbered. The diameter of each tagged individual was measured at 1.3 m from the ground on the uphill side of the bole. Each individual was then surveyed for height, identified to species and its position within the plot mapped. All individuals were counted in the quadrats where they were rooted, regardless of the projection of the crown. Any coppice stems with a dbh ≥ 5 cm were included as separate individuals. Where trees possessed buttress roots, the dbh was measured directly above these roots. If an irregularity occurred in the bole at 1.3m, the dbh was measured directly below this point. These plots form part of a larger comparative study of rainforest plots on a transect stretching from south-east Queensland to southern Vietnam. Some of these results have been published (Small et al. 2004, Laidlaw et al. 2000). For others (including several of those described in this paper) the results are hitherto unpublished (but see Laidlaw in preparation; Laidlaw 1999). In the comparative analyses presented here, we have screened this data to give information for stem diameters ≥10 cm so that the results will be comparable with data from the crane plot. Analysis For each plot we have calculated values for both family, generic and species richness (the simple taxon count, s), species evenness, and the Shannon Index value (H'). For evenness and diversity we used the standard formulae found in Magurran (1988). We calculated basal areas, family importance values (FIV) and an individual value index (IVI) for each species. We calculated the FIV's using the formula of Mori et al. (1983), namely: FIV = relative diversity + relative density + relative dominance where: relative diversity = number of species in the family/the plot total relative density = number stems in the family/the plot total relative dominance = basal area of the family/plot total basal area. The IVI values were calculated using the formula of Cottam and Curtis (1956), namely IVI = (relative density + relative dominance + relative frequency) x 100 where: relative frequency = number of times a species occurs/total quadrats relative density = number stems of the species/the plot total relative dominance = basal area of the species/plot total basal area. 40
The pattern analysis program PATN™ (Belbin 1993) was used to determine the relationship among all eight survey sites based on the presence or absence of tree species ≥10 cm dbh. A Bray Curtis dissimilarity dendrogram based on quantitative data was produced to examine community variation between the crane site and other lowland plots established nearby, mid-elevation plots located elsewhere in north Queensland (Eungella, Paluma and the Atherton Tablelands) and lowland rainforest plots established at Baitabag and Oomsis, Papua New Guinea (Figure 1).
Baitabag
Papua New Guinea
Oomsis
Cape Tribulation & Noah Creek
Cairns Atherton Paluma Eungella
Brisbane
Australia
Figure 1 Location of Australasian one hectare rainforest plots Results Summaries of the results from all four lowland sites surveyed in the Daintree Region (three at Cape Tribulation, including the 2000 and 2005 surveys at the crane site and Thompson Creek, and one at Noah Creek) are presented in Table 1 together with those from the three other tropical Queensland plots (Eungella, Paluma and the Atherton Tableland) and the two lowland plots for New Guinea (Oomsis and Baitabag). More detailed results from the 2005 survey of the crane plot are presented as Appendix 1.
Cape Tribulation Surveys 2000 and 2005 The first Cape Tribulation survey (2000) was 18 months after the passage of Cyclone Rona. At this time, approximately 16 % of stems ≥ 10 cm under the canopy crane had been recorded as dead, some of which were killed by the cyclone's passage (Grove et al. 2000). These dead stems are not included in the following analyses. In 2000, the Cape Tribulation crane plot supported 522 stems ≥ 10 cm dbh. These stems were from 32 families, 57 genera and 73 species of trees. Shannon Index was 3.49 with an evenness of 0.81. The five most important families were Meliaceae, Euphorbiaceae, Lauraceae, Myrtaceae and Apocynaceae. The most important species were 41
Cleistanthus myrianthus (Euphorbiaceae), Alstonia scholaris (Apocynaceae), Normanbya normanbyi (Arecaceae), Myristica insipida (Myristicaceae) and Acmena graveolens (Myrtaceae). The reassessment of the Cape Tribulation crane plot in 2005 showed that the stem count had increased by 30.3% (158 individuals, Table 1). Shannon Index increased slightly to 3.59 but the evenness remained the same (0.81). An additional 12 species, 11 genera and two families were recorded in 2005 that were not present in 2000. Two of the 'new' species were the non-strangling figs Ficus copiosa (n=1) and F. variegata (n=3). Two species (Dysoxylum latifolium (Meliaceae) and Polyosma hirsuta (Grossulariaceae)) recorded in 2000 and originally represented by only one individual, were no longer present in 2005. Despite these changes, the Bray Curtis index of dissimilarity was extremely low at 0.15. The most important families (FIV) did not change between measurements although species importance values (IVI) did change due to shifts in species abundances. Twenty-eight species (33.7%) were recorded only as singletons and six species (7.2%) as doubletons in 2005. This is very similar to the survey in 2000 where there were 27 (36.9%) were singletons and four species (5.5%) were doubletons. In 2000, the mean diameter of trees ≥ 10 cm dbh was 0.25 m (± SE 0.008). The two largest individuals were a Dysoxylum papuanum (Meliaceae) (1.49 m) and a Syzygium sayeri (Myrtaceae) (1.45 m). The mean height of trees ≥10 cm dbh was 15.9 m (± SE 0.27) and the tallest individual in 2000 was a Cryptocarya mackinnoniana at 32.6 m. The total basal area of the plot was 39.84 m2. In 2005, the mean dbh of trees ≥10cm dbh on the crane plot was 0.22 m (± SE 0.56). The individual with the largest dbh was a Ficus destruens (Moraceae) (1.34 m). The largest non-fig individual was a blackbean, Castanospermum australe (Fabaceae) (1.26 m). The two largest individuals recorded in 2000 were no longer present in the 2005 survey. The mean height of trees ≥10 cm dbh was 15.85 m (± SE 0.23). The tallest individual was an Argyrodendron peralatum (Sterculiaceae) at 34.6 m. The large Cryptocarya mackinnoniana recorded in 2000 was not located in 2005. The basal area of the plot decreased by 1.81 m2 to 38.03 m2 (Table 1). The frequency of stems in all dbh size classes ≥ 10 cm and ≤ 50 cm dbh increased from 2000 to 2005 (Figure 2). The greatest increases were in the 10–15 cm dbh size class. Individuals with a dbh of over 50 cm decreased. The frequency of individuals in all height classes increased between 2000 and 2005 (Figure 3). The greatest increase was in the 10-19.9 m size class. The structural changes in species represented by 10 or more individuals (n=16) across the two surveys has been examined. The mean dbh increased in some species, and decreased in others 42
(Figure 4a). Decreases may have been due to the delayed loss of large individuals as a result of Cyclone Rona, or by other mortality factors. Two-sample T-tests assuming unequal variances found that none of the changes in mean dbh were significant. Changes in the mean heights of the same 16 species were also examined and again responses varied from species to species (Figure 4b). A two-sample T-test assuming unequal variances found only one significant result. The black palm, Normanbya normanbyi (Arecaceae) was found to have increased significantly in height (t = 3.46, df = 97, P < 0.001) from a mean of 15.24 (± SE 0.59) to a mean of 17.93 (± SE 0.49). A comparison of the abundances of the same 16 key species between 2000 and 2005 were made. A majority of species were found to have increased in abundance (Figure 4c). The greatest increases were by Cleistanthus myrianthus (Euphorbiaceae), Myristica insipida (Myristicaceae) and Rockinghamia angustifolia (Euphorbiaceae). Three species declined in abundance: Acmena graveolens, Cardwellia sublimis and Dysoxylum papuanum - all canopy species. The basal area of these 16 key species was examined and again showed some variability in response (Figure 4d). Although a majority of species increased in basal area, five species lost total basal area. These were Antirhea tenuiflora, Acmena graveolens, Cardwellia sublimis, Dysoxylum papuanum and Syzygium sayeri. For Acmena graveolens, Cardwellia sublimis and Dysoxylum papuanum this is readily explained by the concomitant drop in the number of individuals on the plot. This is not the case for the remaining two species. The mean height and dbh of Antirhea tenuiflora (Rubiaceae) decreased along with the total basal area suggesting that the species has suffered some mortality of its larger individuals, but the species is now recovering as evidenced by increased numbers in the smaller size classes. Syzygium sayeri (Myrtaceae), however, experienced a decrease in the mean dbh, an associated decrease in total basal area for the species, but an increase in mean height and abundance. This suggests either a rapid reach for the canopy by midstorey individuals, or, possibly, an error in the initial height survey. Local variation in vegetation in the region of the crane plot is evident in our comparisons of the 2000 data with that from a 2001 survey made by Griffith University (Thompson Creek). The 2000 crane site data was used in order to minimize the time difference between the two data sets. Although separated only by a small creek line, the two plots are quite different in character. The Thompson Creek plot supported 339 more stems, 3 more families, 19 more genera and 45 more species ≥10 cm dbh than the crane plot (Table 1). The Bray-Curtis index of dissimilarity between the two plots was 0.62. Despite this, the Thompson Creek plot had a considerably lower total basal area (32.67m2), 7.17 m2 less than the crane plot. The Thompson Creek plot was more diverse, with a Shannon Index of 3.64, although less even (E = 0.76). The most important families on the 43
Table I. Floristic and structural data for one hectare vegetation plots in Queensland and Papua New Guinea Lowland rainforest, Queensland, Australia Cape Tribulation Cape Tribulation Crane Plot 2005 Thompson Creek
Cape Tribulation Crane Plot 2000 Location Elevation (m asl)
16°06.333S, 145°26.667E 50
16°06.333S, 145°26.667E 50
16°06.333S, 145°26.667E 50
16°08.529S, 145°25.786E 50
522 73 39.84 3.49 0.81 57 32
680 82 38.03 3.59 0.81 63 34
861 118 32.67 3.64 0.76 76 35
974 166 4.15 0.81 125 62
FIV1† FIV2 FIV3 FIV4 FIV5
Meliaceae Euphorbiaceae Lauraceae Myrtaceae Apocynaceae
Meliaceae Euphorbiaceae Lauraceae Myrtaceae Apocynaceae
Lauraceae Euphorbiaceae Arecaceae Myrtaceae Proteaceae
-
IVI1‡ IVI2 IVI3 IVI4 IVI5
Cleistanthus myrianthus Alstonia scholaris Normanbya normanbyi Myristica insipida Acmena graveolens
Cleistanthus myrianthus Alstonia scholaris Myristica insipida Normanbya normanbyi Rockinghamia angustifolia
Macaranga subdentata Licuala ramsayi Normanbya normanbyi Cleistanthus myrianthus Endiandra microneura
-
Stems ≥ 10cm dbh Species ≥ 10cm dbh Basal area (m2) Shannon Diversity (H') Evenness (E) Genera richness Family richness
Eungella Location Elevation (m asl)
FIV1 FIV2 FIV3 FIV4 FIV5 IVI1 IVI2 IVI3 IVI4 IVI5
Mid-elevation rainforest, Queensland, Australia Paluma Atherton Tableland
21°01.07 S, 148°36.70 E 720
18°57.28 S , 146°10.84 E 1000
17°06.00 S, 145°37.08 E 686
1194 40 55 2.87 0.78 28 19
1064 68 64.87 3.59 0.85 48 27
687 92 49.57 3.73 0.82 61 27
Lauraceae Myrtaceae Elaeocarpaceae Arecaceae Cunoniaceae
Lauraceae Myrtaceae Elaeocarpaceae Icacinaceae Rutaceae
Lauraceae Elaeocarpaceae Monimiaceae Myrtaceae Euphorbiaceae
Apodytes brachystylis Cryptocarya leucophylla Acmena resa Sloanea macbrydei Brackenridgea nitida
Sloanea australis Daphnandra repandula Litsea leefeana Beilschmiedia bancroftii Syzygium trachyphloium
Stems ≥ 10cm dbh Species ≥ 10cm dbh Basal area (m2) Shannon Diversity (H') Evenness (E) Genera richness Family richness
Archontophoenix alexandrae Cryptocarya sp.1 Elaeocarpus largiflorens Sloanea macbrydei Cryptocarya densiflora
Lowland rainforest, Papua New Guinea Oomsis (Laidlaw et al . in Baitabag (Laidlaw et al . in preparation) preparation) Location Elevation (m asl)
6º 41' S, 146º 48' E 65
145º 47' E, 5º 08' S 100
484 97 27.54 3.96 0.86 64 37
453 111 26.35 4.13 0.88 74 36
FIV1 FIV2 FIV3 FIV4 FIV5
Moraceae Meliaceae Myristicaceae Ulmaceae Lauraceae
Rubiaceae Meliaceae Moraceae Sapotaceae Euphorbiaceae
IVI1 IVI2 IVI3 IVI4 IVI5
Medusanthera laxiflora Celtis latifolia Ficus sp. Myristica globosa Myristica subalulata
Pimelodendron amboinicum Pouteria lobianum Horsfieldia irya Pometia pinnata Erythrospermum candidum
Stems ≥ 10cm dbh Species ≥ 10cm dbh Basal area (m2) Shannon Diversity (H') Evenness (E) Genera richness Family richness
† Family Importance Value ranked from 1 to 5 ‡ Individual Value Index ranked from 1 to 5
44
Noah Creek
Thompson Creek plot were Lauraceae, Euphorbiaceae, Arecaceae, Myrtaceae and Proteaceae, three of which were also important on the crane plot. The most important species were Macaranga subdentata (Euphorbiaceae), Licuala ramsayi (Arecaceae), Normanbya normanbyi (Arecaceae), Cleistanthus myrianthus (Euphorbiaceae) and Endiandra microneura (Lauraceae). Forty-four species (37.3%) were recorded only as singletons and 20 species (16.9%) were recorded as doubles. These forests are amongst the most diverse in Australia, with over half of the species recorded on the crane plot in 2005 (57.3%) being endemic to Australia and 56.1% are endemic to Queensland. More specifically, 45.1% of species are endemic to Northern Queensland (Cook and North Kennedy pastoral districts) and 20.7% of species are endemic to Cape York (Cook pastoral district). Many species are shared with our neighbouring regions: 40.2% with New Guinea, 20.7% with Melanesia, 19.5% with Malesia, 0.09% with Asia, 0.04% with the Pacific Islands and 0.01% with New Zealand/Antarctica (Henderson 2002). Three species ≥ 10 cm dbh are listed as rare under the Queensland Biodiversity Conservation Act 1992. These are Cleistanthus myrianthus (Euphorbiaceae) (n = 90), Pseuduvaria froggattii (Annonaceae) (n = 1) and Austromuellera trinervia (Proteaceae) (n = 5). All three species are restricted in Australia to Cape York, however, Cleistanthus myrianthus also occurs in Malesia and Papua New Guinea (Henderson 2002). As this species is the most dominant recorded on the crane site, it should be considered as a survey plot of high conservation value. Other North Queensland Plots The most direct comparison with the two Cape Tribulation plots is that from Noah Creek, a refugial lowland forest about 11 kms due south of Cape Tribulation. It is evident from the results summarized in Table 1 that this is a much richer site both in terms of its family, generic and species richness than either of the two Cape Tribulation plots. There were almost 60 additional species and almost twice as many families found within the Noah Creek hectare than at the richest of the more northerly plots. This accords with its 'special' status as a supposed glacial refugium and suggests, further, that it may be much more protected from cyclonic depredations than the Cape Tribulation sites.
45
300
2000
Frequency
250
2005
200 150 100
>0.6
>0.55-0.6
>0.5-0.55
>0.45-0.5
>0.4-0.45
>0.35-0.4
>0.3-0.35
>0.25-0.3
>0.2-0.25
>0.15-0.2
0
>0.1-0.15
50
Dbh size class (m)
Figure 2
Dbh size classes of individuals surveyed at Cape Tribulation in 2000 and 2005
Frequency
450 400
2000
350
2005
300 250 200 150 100
30-39.9
20-29.9
10-19.9
0
1.2-9.9
50
Height class (m)
Figure 3
Height classes of individuals surveyed at the Cape Tribulation crane site in 2000 and 2005
46
Three other tropical Australian plots (Eungella, Paluma and Atherton Tablelands) are presented in table 1 and described elsewhere (Laidlaw 1999). All three are at higher elevations than the Cape Tribulation plots and are all at more southerly latitudes. In terms of species richness they show a gradual northerly increase from 40 species at the most southerly site, Eungella (which is also at the highest elevation) to 92 species at the Robson Creek site on the Atherton Tablelands. This gradual northerly enrichment continues when the richer of the two Cape Tribulation plots is added. These patterns are reflected with only minor modifications in the values of generic and family richness. The crane plot is richer than all but the Atherton Tablelands plot (and, we note above, appears to be on an increasing temporal trend in that regard). When relative abundance is considered, the trends are not so clear. Shannon Index values are clearly lower at the Eungella plot and higher at the Noah Creek plots, but hover around the 3.6 mark for all other plots. The dominant families differ markedly across plots. All three upland plots (Eungella, Paluma and the Atherton Tablelands) feature Lauraceae, Myrtaceae and Elaeocarpaceae in their top 4 ranked families. In contrast the two Cape Tribulation plots, although including Lauraceae and Myrtaceae in their top-ranking families, add Euphorbiaceae (which also ranks fifth on the Atherton Tablelands plot). As would be expected with these widely separated plots, there is no overlap among the topranked species. Basal area at each of the southerly plots exceeds that recorded in either of the Cape Tribulation sites. The Papua New Guinea Plots The two lowland plots from Papua New Guinea are remarkably similar in measures of diversity and structure to the Cape Tribulation plots (Laidlaw et al. in preparation) with an average species richness value of 104 (cf. 105 for the Cape Tribulation sites), a generic richness value of 69 (cf. 70 for Cape Tribulation) and a family richness value of 36.5 (cf. 34 for Cape Tribulation). Shannon Index and evenness values were also very similar. Basal area at the Papua New Guinea sites was even lower than at the Cape Tribulation sites, almost certainly because of historical human use of the sites for shifting agriculture. The most important families in the Papua New Guinea sites showed some overlap with one or other of the Cape Tribulation sites (eg. Meliaceae, Lauraceae, Euphorbiaceae) but also include other families which are much less important in the Australian sites (eg. Ulmaceae). Again we had no expectation that important species would be shared and these expectations were born out.
47
48
2000 and 2005 Dysoxylum papuanum
Licuala ramsayi
Cardwellia sublimis
Key Species
30
25
15
10
5
0 Syzygium sayeri
20
Syzygium sayeri
2005
Cryptocarya murrayi
2000
Cryptocarya murrayi
Wrightia laevis (subsp. millgar)
Dysoxylum papuanum
Licuala ramsayi
Cardwellia sublimis
Acmena graveolens
Cryptocarya mackinnoniana
Argyrodendron peralatum
Antirhea tenuiflora
Endiandra microneura
Rockinghamia angustifolia
Myristica insipida
Normanbya normanbyi
Alstonia scholaris
Cleistanthus myrianthus
Mean dbh (m) 0.7
Wrightia laevis (subsp. millgar)
Key Species Acmena graveolens
Cryptocarya mackinnoniana
Argyrodendron peralatum
Antirhea tenuiflora
Endiandra microneura
Rockinghamia angustifolia
Myristica insipida
Normanbya normanbyi
Alstonia scholaris
Cleistanthus myrianthus
Mean height (m)
0.8 2000
2005
0.6
0.5
0.4
0.3
0.2
0.1
0
Figure 4
(a) Mean dbh of species represented by 10 or more individuals surveyed at Cape Tribulation in
2000 and 2005
(b) Mean height of species represented by 10 or more individuals surveyed at Cape Tribulation in
Dysoxylum papuanum
Licuala ramsayi
Cardwellia sublimis
4
3.5
Syzygium sayeri
Cryptocarya murrayi
Argyrodendron peralatum
Antirhea tenuiflora
Endiandra microneura
Rockinghamia angustifolia
Myristica insipida
Normanbya normanbyi
Alstonia scholaris
Cleistanthus myrianthus
Syzygium sayeri
Cryptocarya murrayi
Wrightia laevis (subsp. millgar)
Dysoxylum papuanum
Licuala ramsayi
Cardwellia sublimis
Acmena graveolens
Cryptocarya mackinnoniana
Key Species
Wrightia laevis (subsp. millgar)
Key Species Acmena graveolens
Cryptocarya mackinnoniana
Argyrodendron peralatum
Antirhea tenuiflora
Endiandra microneura
Rockinghamia angustifolia
Myristica insipida
Normanbya normanbyi
Alstonia scholaris
Cleistanthus myrianthus
Basal area (m2 ) Abundance
100 90 2000
80 2005
70
60
50
40
30
20
10
0
2000
2005
3
2.5
2
1.5
1
0.5
0
(c) Abundance of species represented by 10 or more individuals surveyed at Cape Tribulation in
2000 and 2005
(d) Basal area of species represented by 10 or more individuals surveyed at Cape Tribulation in
2000 and 2005.
49
Site Classification The Bray Curtis (BC) dissimilarity metric based on presence/absence data for all species ≥10cm dbh showed that the PNG plots shared very few species with the Australian plots (BC = 1), although there was overlap between the two (Baitabag and Oomsis, BC = 0.73). Of the Australian plots, Eungella and Paluma shared several species (BC = 0.82) but shared few species with the more northerly plots (BC = 1). The crane plot and the Thompson Creek plot were the most closely related (BC = 0.59), and both were closely associated with the Noah Creek plot (BC = 0.70). Atherton fused with the Daintree plots (Cape Tribulation, Noah Ck and Thompson Ck) at a Bray Curtis dissimilarity of 0.89 (Figure 5).
Site
Bray-Curtis Dissimilarity
Figure 5 Bray-Curtis dissimilarity dendrogram of Australasian rainforest survey plots based on floristic composition (dbh ≥10 cm) Discussion Recently Graham (2006) described the basic structure of 20 0.5ha rainforest plots that were established between 1971 and 1980 and have been resurveyed several times since. Unfortunately, data on the changes to the floristics of the site during that time have not yet been published and are unavailable for comparison. In this respect we believe that our study is probably unique in Australian rainforest studies, being the first published account of such floristic changes over a five year period. It is clear from the comparison of the two surveys of the crane plot that the site is still in a very active stage of post-cyclonic recovery. Several large trees, apparently healthy in 2000 did not appear in the survey in 2005. This could represent ‘normal’ processes of ageing and mortality but it seems more likely that these represented delayed mortality following the 1999 cyclone. These losses no doubt help explain the almost 5% decline in basal area, even though there has been substantial recruitment of smaller stems (total stems: 2000, 522; 2005, 680). 50
Turton and Stork (2008) analysed the frequency and intensity of tropical cyclones crossing the wet tropical coast (Cooktown–Ingham) over the period 1858-2006 according to the Australian Cyclone Severity Scale. Their data suggest that a weak cyclone (Australian System: Category 1-2) is likely to cross the wet tropical coast with a frequency interval of about five years, compared with a frequency of about 15 years for a moderate to severe cyclone (Category 3) and about 75 years for a very severe cyclone (Category 4-5). Coastal areas are much more heavily and frequently damaged than inland areas. It is likely that the Daintree lowlands are constantly being affected by cyclones and therefore, are in a constant state of recovery. How representative is the crane site of the local vegetation? The Thompson Creek site is only a few metres to the north of the crane site. It was selected to provide details on vegetation which would be useful to future work using the crane without compromising work on the crane site through generating human ‘traffic’. Yet at the time of the survey, this site appeared to be quite different with 861 stems ≥ 10 cm dbh of 118 species compared with the 522 stems of 73 species on the crane site itself. There are several possible explanations for this. Firstly, it has a different general aspect to the crane site (south-east rather than east-north-east) which may, in turn have led to a differential impact at the time of Cyclone Rona. Furthermore, it has a section which includes an area of disturbance approaching a forest edge and this may have led to a greater representation of secondary species within the inventory (and also no doubt accounts in part for the lower basal area on the Thompson Creek plot). Ticehurst et al. (2007) have shown that the impact of Cyclone Rona on the crane site and surrounding area was very variable with some areas heavily impacted and others, some just a few metres away, much less so. One consequence of the patchy impact of cyclones has been to produce an exceptional ecological heterogeneity within the forest. This no doubt acts, on a larger scale, in a way comparable to within-forest intermediate disturbance regimes. The mosaic of patches of forest exhibiting various degrees of post-cyclonic recovery is no doubt a strong contributory factor to the overall ecological diversity of the Daintree lowland ecosystems. This having been said, it is also evident that some forest patches are much less cyclone-prone than others. The Noah Creek site is much more diverse than either of the Cape Tribulation sites and exhibits little evidence of disturbance. This is no doubt due in part to local topography which may ‘steer’ cyclone paths around the valley. We have little doubt that this is one reason why the Noah Creek valley (and others such as Oliver and Cooper Creek) have maintained their status as postglacial vegetation refuges over millennia. Comparable areas showing few signs of recent cyclonic impact are also apparent north of Cape Tribulation where there are to be found areas with trees of truly impressive basal area (eg. Emagen Creek). 51
The Bray Curtis dissimilarity metric shows clearly that at the species level the two Cape Tribulation sites group together and are progressively more distant ‘sisters’ to the Noah Creek site and Atherton Tablelands site (Figure 5). This ‘North Queensland’ grouping represents a set of sites which, to varying degrees, share considerable numbers of tree species. The other two groupings are the two more southerly Queensland sites (Paluma and Eungella) and the two New Guinea sites (Baitabag and Oomsis). Again this reflects varying degrees of co-occurrence of species within a grouping. Very few species are shared cross groupings. The most parsimonious explanation for the patterns seen in the dendrogram (Figure 5) is simply that inter-site distance gradually diminishes the number of shared species between sites. Other patterns emerge at the supra-species level. In analyses at the generic level (Kitching et al. 2004) it was demonstrated that the Thompson Creek site at Cape Tribulation showed lower values for a so-called ‘Gondwanic Index’ in which genera from families with stereotypical Australian distributions were compared with a set with Papuasian distributions. The mid-elevation sites of Atherton Tableland and Eungella showed high values (indicating a greater representation of ‘Australian’ genera), the New Guinean sites an even lower value indicating a (not unexpected) preeminence of genera from Papuasian families. These vegetation patterns were also reflected in pattern analyses of Diptera and underscores the existence of biogeographic connections between lowland rainforest in Australia and New Guinea. The Daintree lowland rainforests are of such high biological significance that it will be of considerable value to continue re-surveys of the trees on the crane plot at five-yearly intervals so that the processes of post-cyclonic recovery can be further monitored and interpreted. The current vegetation data on the crane site is based on a survey using a 10 cm dbh cut-off. We have data from the Thompson Creek plot down to a 5 cm cut-off. It will be valuable to re-survey the crane plot at least to the level of 5 cm dbh and a re-comparison with the Thompson Creek plot made. It would be of considerable value in understanding tree demographics if a subset of 10 x 10m plots on both the crane and Thompson Creek sites were surveyed for seedlings at least of the dominant species. This would allow genuine population dynamic interpretations to be made for key species during post-disturbance recovery. Given the very clear regional heterogeneity of vegetation it will require more information before better interpretations of forest dynamics can be made in the Daintree lowlands. This area is of immense conservation and iconic value and we recommend strongly that a network of one-hectare plots be established between Daintree and Bloomfield, of which the crane plot is part. The state of 52
our taxonomic knowledge is now such that these plots could be established with relatively little effort. Finally, it is noteworthy that nowhere in the Australasian region are there long term forest dynamic plots larger than one ha. The utility of 25-50 ha forest dynamic plots has been well demonstrated (Chave et al. 2003, Condit et al. 1996, Hubbell and Foster 1983) and addresses some of the problems in highly patchy forests. The creation of a 25 or 50 ha lowland rainforest plot in the Daintree would allow comparisons with the 17 others that have been created in other parts of the tropical world. Acknowledgements The authors wish to thank staff and volunteers involved in vegetation surveys conducted at Cape Tribulation in 2000, 2001 and 2005. Sincerest thanks go to the late Richard Cooper, Martin Frieberg, Guy Vickerman, Karen Hurley, Griffith University and James Cook University volunteers, DIWPA participants, Queensland National Parks and Wildlife Service, staff of the Australian Canopy Crane and The Rainforest CRC. References Baker, T. R., Phillips, O. L., Malhi, Y., Almeida, S., Arroyo, L., Di Fiore, A., Erwin, T, Higuchi, N., Killeen, T. J., Laurance, S. G., Laurance, W. J., Lewis, S. L., Monteagudo, A., Neill, D. A., Vargas, P. N., Pitman, N. C. A., Silva, J. N. M. & Martínez, R. V. (2004) Increasing biomass in Amazonian forest plots. Phil. Trans. Roy. Soc. Lond. B. 359, 353-365. Belbin, L. (1993) PATN: Pattern analysis package technical reference. CSIRO, Sydney. Brokaw, V. L. & Grear, J. S. (1991) Forest structure before and after Hurricane Hugo at three elevations in the Luquillo Mountains, Puerto Rico. Biotropica. 23, 389-392. Brokaw, V. L. & Walker, L. R. (1991) Summary of the effects of Caribbean hurricanes on vegetation. Biotropica. 23, 442-447. Chave, J., Condit, R., Muller-Landau, H. C., Thomas, S. C., Ashton, P. S., Bunyavejchewin, S., Co, L. L., Dattaraja, H. S., Davies, S. J., Esufali, S., Ewango, C. E. N., Feeley, K. J., Foster, R. B., Gunatilleke, N., Gunatilleke, S., Hall, P., Hart, T. B., Hernández, C., Hubbell, S. P., Itoh, A., Kiratiprayoon, S., LaFrankie, J. V., Loo de Lao, S., Makana, J. R., Noor, M. N. S., Kassim, A. R., Samper, C., Sujkumar, R., Suresh, H. S., Tan, S., Thompson, J., Tongco, M. D., Valencia, R., 53
Vallejo, M., Villa, G., Yamakura, T., Zimmerman, J. K. & Losos, E. C. (2008) Assessing evidence for a pervasive alteration in tropical tree communities. PLOS Biol. 6, 455-462. Chave, J., Condit, R., Lao, S., Caspersen, J. P., Foster, R. B. & Hubbell, S. P. (2003) Spatial and temporal variation of biomass in a tropical forest: results from a large census plot in Panama. J. Ecol. 91, 240-252. Clark, D. A. (2002) Are tropical forests an important global carbon sink?: revisiting the evidence from long-term inventory plots. Ecol. Applic. 12, 3–7. Condit, R., Hubbell, S. P., Lafrankie, J. V., Sukumar, R., Manokaran, N., Foster, R. B. & Ashton, P. S. (1996) Species-area and species-individual relationships for tropical trees: a comparison of three 50-ha plots, J. Ecol. 84, 5449-562. Connell, J. H. & Green, P.T. (2000) Seedling dynamics over thirty-two years in a tropical rain forest tree. Ecology. 81, 568-584. Cottam, G. & Curtis, J. T. (1956) The use of distance measurement in phytosociological sampling. Ecology. 37, 244-248. Edwards, W. & Krockenberger, A. (2006) Seedling mortality due to drought and fire associated with the 2002 El Niño in a tropical rain forest in North-East Queensland, Australia. Biotropica. 38, 16-26. Engelbrecht, B. M. J., Wright, S. J., & De Steven, D. (2002) Survival and ecophysiology of tree seedlings during El Niño drought in Panama. J. Trop. Ecol. 18, 569-579. Feeley, K. J., Wright, S. J., Supardi, M. N. N., Kassim, A. R. & Davies, S. J. (2007) Decelerating growth in tropical forest trees, Ecol. Lett. 10, 461-469. Freiberg, M. & Turton, S. M. (2007) Importance of drought on the distribution of birds nest fern, Asplenium nidus, in the canopy of lowland tropical rainforest in north-eastern Australia, Austral Ecology, 32, 70-76.
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Gleason, S. M., Williams, L. J., Read, J., Metcalfe, D. J. & Baker, P. J. (2008) Cyclone effects on the structure and production of a tropical upland rainforest: implications for life-history tradeoffs, Ecosystems. 11, 1277 – 1290. Gloor, M., Phillips, O. L., Lloyd, J. J., Lewis, S. L., Malhi, Y., Baker, T. R., López-Gonzalez, G., Peacock, J., Almeida, S., Alves de Oliveiras. A. C., Alvarez, E., Amaral, I., Arroyo, L., Aymard, G., Banki, O., Blanc, L., Bonal, D., Brando, P., Chao, K. J., Chave, J., Dávila, N., Erwin, T., Silva, J., Di Fiore, A., Feldpausch, T. R., Freitas, A., Herrera, R., Higuchi, N., Honorio, E., Jiménez, E., Killeen, T., Laurance, W., Mendoza, C., Monteagudo, A., Andrade, A., Neill, D., Nepstad, D., Núñez Vargas, P., Peñuela, M. C., Peña Cruz, A., Prieto, A., Pitman, N., Quesada, C., Salomão, R., Silveira, M., Schwarz, M., Stropp, J., Ramírez, F., Ramírez, H., Rudas, A., Ter Steege, H., Silva, N., Torres, A., Terborgh, J., Vásquez, R., & van der Heijden, G. (2009) Does the disturbance hypothesis explain the biomass increase in basin-wide Amazon forest plot data? Global Change Biology. 15, 2418-2430. Graham, A.W. (2006) The CSIRO rainforest permanent plots of North Queensland. Site, structural, floristic and edaphic descriptions. Cooperative Research Centre for Tropical Rainforest Ecology and Management, Cairns. Gresham, C. A., Williams, T. M. & Lipscomb, D. J. (1991) Hurricane Hugo wind damage to Southeastern U. S. coastal forest tree species. Biotropica. 23, 420-426. Grove, S. J., Turton, S. M. & Siegenthaler, D. T. (2000) Mosaics of canopy openness induced by tropical cyclones in lowland rain forests with contrasting management histories in north-eastern Australia. J. Trop. Ecol. 16, 883-894. Henderson, R. J. F. (2002) Names and distribution of Queensland plants, algae and lichens. Queensland Herbarium, Brisbane. Hubbell, S. P. & Foster, R. B. (1983) Diversity of canopy trees in a neotropical forest and implications for conservation. In: Tropical Rain Forest: Ecology and Management (eds T. C. Whitmore, A. C. Chadwick & A. C. D. Sutton) pp 25-41. The British Ecological Society, Oxford. Kitching, R. L., Bickel, D., Creagh, A. C., Hurley, K. & Symonds, C. (2004) The biodiversity of Diptera in Old-world rainforest surveys: a comparative analysis. J. Biogeogr. 31, 1185-1200. 55
Laidlaw, M. J., Olsen, M., Kitching, R. L. & Greenway, M. (2000) Tree floristic and structural characteristics of one hectare of subtropical rainforest in Lamington National Park, Queensland. Proc. Royal Soc. Qld. 109, 91-105. Laidlaw, M. J. (1999) Variation in rainforest vegetation along a latitudinal gradient, (BSc Honours Thesis). Griffith University, Brisbane. Laidlaw, M. J., Kitching, R. L., Damas, K. & Kiapranis, R. (In preparation) Tree floristic and structural attributes of two lowland rainforest plots in Papua New Guinea. Lewis, S. L., Malhi, Y. & Phillips, O. L. (2004) Fingerprinting the impacts of global change on tropical forests. Phil. Trans. R. Soc. Lond. B. 359, 437-462. Mabry, C. M., Hamburg, S. P., Lin, T. C., Horng, F. W., King, H. B. & Hsia, Y, J. (1998) Typhoon disturbance and stand-level damage patterns at a subtropical forest in Taiwan. Biotripica. 30, 238250. Magurran, A. E. (1988) Ecological Diversity and its Measurement, Princeton University Press, Princeton. Malhi, Y. & Phillips, O. L. (2004) Tropical forests and global atmospheric change: a synthesis. Phil. Trans. R. Soc. Lond. B. 359, 549-555. Mori, S. A., Boom, B. M., De Carvalino, A. M. & Dos Santos, T. S. (1983) Ecological importance of Myrtaceae in an eastern Brazilian wet forest. Biotropica. 15, 68-70. Phillips, O.L., Malhi, Y., Vinceti, B., Baker, T., Lewis, S. L., Higuchi, N., Laurance, W. F., Núñez V. P., Vásquez M. R., Laurance, S. G., Ferreira, L. V., Stern, M., Brown, S., Grace, J. (2002) Changes in the biomass of tropical forests: evaluating potential biases. Ecol. Applic. 12: 576-587. Phillips, O.L., Malhi, Y., Higuchi, N., Laurance, W. F., Nuñez V. P., Vásquez M. R., Laurance, S. G., Ferriera, L. V., Stern, M., Brown, S., and Grace, J. (1998) Changes in the carbon balance of tropical forest: evidence from long-term plots. Science. 282: 439-442.
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Small, A., Martin, T., Kitching, R. L. & Khoon Meng, W. (2004) Contribution of tree species to the biodiversity of a one hectare plot of Old-World rainforest, Brunei, Borneo. Biodivers. Conserv. 13, 2067-2088. Stork, N. E. (2007) The Australian tropical forest canopy crane: new tools for new frontiers, Austral Ecol. 32, 4-9. Stork, N. E. & Cermak, M. (2003) Australian Canopy Crane: getting on top of the World's last biological frontier. In: Studying Forest Canopies from Above: the International Canopy Crane Network (eds Y. Basset, V. Horlyck & S. J. Wright) pp. 108-114. Smithsonian Tropical Research Institute, Panama. Ticehurst, C., Phinn, S. & Held, A. (2007) Using multi-temporal digital elevation model data for detecting canopy gaps in tropical forests due to cyclone damage: an initial assessment. Austral Ecol. 32, 59-69. Turton, S. M. and Stork, N. E. (2008) Impacts of Tropical Cyclones on Rainforests in north-eastern Australia. In: Living in a Dynamic Tropical Forest Landscape (eds N. E. Stork & S. L. Turton). Blackwell, Oxford. Walker, L. R. (1991) Tree damage and recovery from Hurricane Hugo in Luquillo Experimental Forest, Peurto Rico. Biotropica. 23, 379-385. You, C. & Petty, W. H. (1991) Effects of Hurrican Hugo on Manilkara bidentata, a primary tree species in the Luquillo Experimental Forest of Peurto Rico. Biotropica. 23, 400-406.
57
Appendix 1. Species (dbh ≥10cm dbh) recorded on the Cape Tribulation crane plot in 2005
Species
Family
Abundance
Acmena graveolens
Myrtaceae
16
Acmenosperma claviflorum
Myrtaceae
3
Aglaia tomentosa
Meliaceae
1
Alstonia scholaris
Apocynaceae
60
Antirhea tenuiflora
Rubiaceae
17
Archindendron ramiflorioum
Mimosaceae
1
Archontophoenix alexandrae
Arecaceae
5
Argyrodendron peralatum
Sterculiaceae
17
Austromuellera trinervia
Proteaceae
5
Brombya platynema
Rutaceae
8
Canarium vitiense
Burseraceae
1
Canthium sp. (Whitfield Range)
Rubiaceae
3
Cardwellia sublimis
Proteaceae
14
Castanospermum australe
Fabaceae
8
Celtis paniculata
Ulmaceae
1
Chisocheton longistipitatus
Meliaceae
1
Citronella smythii
Icacinaceae
1
Cleistanthus myrianthus
Euphorbiaceae
90
Cryptocarya grandis
Lauraceae
7
Cryptocarya hypospodia
Lauraceae
1
Cryptocarya mackinnoniana
Lauraceae
17
Cryptocarya murrayi
Lauraceae
11
Doryphora aromatica
Monimiaceae
3
Dysoxylum alliaceum
Meliaceae
7
Dysoxylum arborescens
Meliaceae
8
Dysoxylum oppositifolium
Meliaceae
2
Dysoxylum papuanum
Meliaceae
12
Dysoxylum parasiticum
Meliaceae
8
Dysoxylum pettigrewianum
Meliaceae
9
58
Elaeocarpus grandis
Elaeocarpaceae
5
Elaeocarpus bancroftii
Elaeocarpaceae
1
Emmanosperma cunninghamii
Rhamnaceae
1
Endiandra insignis
Lauraceae
1
Endiandra leptodendron
Lauraceae
9
Endiandra microneura
Lauraceae
23
Endiandra sankeyana
Lauraceae
1
Eupomatia laurina
Eupomatiaceae
1
Fagraea cambagei
Gentianaceae
2
Ficus copiosa
Moraceae
1
Ficus destruens
Moraceae
1
Ficus variegata
Moraceae
3
Ganophyllum falcatum
Sapindaceae
1
Garcinia warrenii
Clusiaceae
3
Gardenia ovularis
Rubiaceae
1
Gillbeea adenopetala
Cunnoniaceae
6
Gmelina fasciculiflora
Lamiaceae
1
Gomphandra australiana
Icacinaceae
3
Lepidozamia hopei
Zamiaceae
1
Licuala ramsayi
Arecaceae
14
Litsea leefeana
Lauraceae
4
Macaranga subdentata
Euphorbiaceae
2
Mallotus mollissimus
Euphorbiaceae
9
Medicosma fareana
Rutaceae
3
Musgravea heterophylla
Proteaceae
8
Myristica insipida
Myristicaceae
54
Myristica globosa subsp. muelleri
Myristicaceae
1
Neonauclea glabra
Rubiaceae
1
Niemeyera prunifera
Sapotaceae
7
Normanbya normanbyi
Arecaceae
55
Palaquium galactoxylon
Sapotaceae
5
Polyscias australiana
Araliaceae
2
Pouteria obovoidea
Sapotaceae
3
Premna serratifolia
Lamiaceae
1
Prunus turneriana
Rosaceae
1 59
Pseuduvaria froggattii
Annonaceae
1
Rhodamnia sessiliflora
Myrtaceae
1
Rockinghamia angustifolia
Euphorbiaceae
37
Semecarpus australiensis
Anacardiaceae
4
Siphonodon membranaceus
Celastraceae
1
Synima cordierorum
Sapindaceae
6
Syzygium cormiflorum
Myrtaceae
3
Syzygium erythrocalyx
Myrtaceae
5
Syzygium gustavioides
Myrtaceae
8
Syzygium kuranda
Myrtaceae
3
Syzygium sayeri
Myrtaceae
11
Tetrasynandra laxiflora
Monimiaceae
3
Toechima erythrocarpum
Sapindaceae
3
Toona ciliata
Meliaceae
1
Trema tormentosa var. viridis
Ulmaceae
1
Viticipremna queenslandica
Lamiaceae
2
Wrightia laevis (subsp. millgar)
Apocynaceae
12
Xanthophyllum octandrum
Xanthophyllaceae
6 680
60
Chapter 2
SUBTROPICAL RAINFOREST TURNOVER ALONG AN ALTITUDINAL GRADIENT MELINDA J. LAIDLAW1,2, WILLIAM J.F. MCDONALD3, R. JOHN HUNTER4 & ROGER L. KITCHING5 Running head: Subtropical rainforest turnover Laidlaw, M.J., McDonald, W.J.F., Hunter, R. John & Kitching, R.L. (In press) Subtropical rainforest turnover along an altitudinal gradient, Memoirs of the Queensland Museum, ****. ISSN *** 1
Biodiversity and Ecosystem Sciences, Department of Environment and Resource Management,
Indooroopilly, Qld, 4068, Australia. 2
The University of Queensland, School of Biological Sciences, St Lucia, Qld, 4072, Australia.
3
Queensland Herbarium, Department of Environment and Resource Management, Toowong, Qld,
4066, Australia. 4
Lowanna, NSW, 2450, Australia.
5
Griffith School of the Environment, Griffith University, Nathan, Qld, 4111, Australia. ABSTRACT
The rainforests of south-east Queensland and northern New South Wales are highly diverse, floristically and structurally complex. This diversity is due, in part, to regional variation in soil and parent geology, climate and topography. Patterns in regional species composition were identified along an altitudinal transect from 300 to 1100m elevation in Lamington National Park, south-east Queensland. This study also relates subtropical rainforest composition to soil variables and to the environmental correlates of altitude, namely temperature and moisture. Twenty-nine climatic and nine soil variables were correlated with floristic variation between altitudes. Twelve species groups were also identified from the 282 vascular plant species recorded along the transect. These baseline data will form the benchmark against which future changes in the forest can be monitored. The use of adjacent altitudes as surrogates for adjacent climates can also provide a useful insight into the potential impacts of a changing climate. KEYWORDS: altitudinal gradient, climate change, compositional turnover, subtropical rainforest, surrogacy.
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INTRODUCTION The subtropical rainforests of south-east Queensland and northern New South Wales are a living link to our botanical past. They support subtropical through to cool temperate biota and have done so throughout the climatic fluctuations of the Late Tertiary and Quaternary (Adam, 1987). This continuity of climate has allowed the persistence of primitive plant families (Winteraceae, Eupomatiaceae, Annonaceae, Trimeniaceae, Monimiaceae, Atherospermataceae and Lauraceae) which have undergone little evolutionary change since Gondwanan times (McDonald, In press; Floyd, 1990a). These rainforests also host 42 genera of primitive angiosperms and gymnosperms (Floyd 2008), relictual and endemic species, as well as rare and threatened flora (McDonald, In press). Subtropical rainforest is particularly well represented in Australia and extends from approximately 21°-35° latitude (based on the prominence of notophyll and microphyll canopy leaves) (Webb, 1959). These forests have been described and classified under various schemes at both continental (Webb, 1978, 1968, 1959) and state levels (Sattler & Williams, 1999; Baur, 1964). Lamington National Park supports several structural types of rainforest, three of which were examined in this study and described below. The approximate equivalents between classification schemes are also included below. Araucarian Complex Notophyll Vine Forest (ANVF) (Webb, 1978, 1968, 1959)/Qld Regional Ecosystem (RE) 12.8.4 (Sattler & Williams, 1999)/Dry rainforest (Floyd, 1990b; Baur, 1964). This structural form occurs on basalt soils on the northern and western slopes of the Lamington Plateau and on shallow rocky soils on steep slopes. ANVF is a subtype of the more extensive complex notophyll vine forest (CNVF) dominant in the region. It differs from other forms of CNVF in supporting emergent hoop pine, Araucaria cunninghamii. This structural type is tolerant not only of a lower annual rainfall, but a marked dry season between spring and early summer (McDonald & Whiteman, 1979). Complex Notophyll Vine Forest (CNVF) (Webb, 1978, 1968, 1959)/RE 12.8.3 and 12.8.5 (Sattler & Williams, 1999)/Subtropical rainforest (Floyd, 1990b; Baur, 1964). CNVF occurs on basalt soils and Lamington National Park supports some of the most extensive and best developed stands of this rainforest type in the region. It is both floristically and structurally complex. There are two broad subtypes, the distributions of which are associated with altitude. Warm subtropical CNVF/RE 12.8.3, generally occurs below 600 – 700m asl, particularly in valleys. This forest type can grade into ANVF on steep slopes and on drier aspects (McDonald & Whiteman, 1979). Cool subtropical 62
CNVF/RE 12.8.5 generally occurs at altitudes above 600m – 700m, although a broad ecotone of high floristic diversity between these two subtypes can occur (Laidlaw et al., 2000). All forms of CNVF support robust and woody lianes, a diverse community of vascular epiphytes, canopy species with plank buttresses and compound, entire leaves, as well as other life forms such as palms and climbing aroids (Pothos longipes) (Webb, 1959). Microphyll Fern Forest (MFF) (Webb, 1978)/RE 12.8.6 (Sattler & Williams, 1999)/Cool temperate rainforest (Floyd 1990b; Baur, 1964). MFF occurs on the high plateaus and mountain tops at altitudes over 1000m. Rainfall at this altitude is supplemented by the interception of water from clouds that occur frequently with onshore winds (Floyd, 2008). This forest is typically dominated by Nothofagus moorei (Nothofagaceae), a species whose extent has contracted and moved south and upslope, along with cold and wet microclimates (Hopkins et al., 1976; Webb, 1964). These forests are without plank buttress forming species or woody lianes. Instead, they support prolific mossy epiphytes, tree and ground ferns and tree species with simple, toothed leaves (McDonald & Whiteman, 1979). The distribution of these three structural types of rainforest at Lamington National Park are known to be correlated with the environmental features of topography (particularly aspect), climate, soil nutrient status, soil depth and moisture content (Adam, 1987; Hopkins et al., 1976; Webb, 1969, 1968). The response of species groups to these environmental variables is complex and interactions between them are likely (Adam, 1987). It can be very difficult to attribute rainforest distribution to any one factor, however, general trends can be identified. Broadly speaking, CNVF (and subtypes) occur in a mesothermal environment with annual mean maximum temperatures of 18 - 22°C and an annual mean minimum of 5°C. By comparison, MFF is found in a microthermal environment with an optimum annual mean maximum temperature of 10 - 12°C and an annual mean minimum of 0°C (Floyd, 1990a; Adam, 1987). Such microthermal conditions in the study region are restricted to altitudes over 1000m and to elevated gullies, where cold air drainage allows the downslope extension of these conditions. The downslope extension of MFF, under appropriate moisture regimes, is likely restricted by either intolerance of higher temperatures (Fraser & Vickery, 1939), or by the superior competitive ability of CNVF species (Dolman, 1982). The upslope extension of CNVF is restricted by its susceptibility to frost events tolerated by species such as Nothofagus moorei (Adam, 1987; Dolman, 1982). The moisture regime is a result of the complex interaction between precipitation, aspect, slope, soil parent material and soil depth (Adam, 1987). ANVF occurs where annual rainfall ranges between 63
660-1100mm, CNVF is found where it exceeds 1300mm, while MFF is found where annual rainfall is over 1750mm, with the input of up to an additional 50% of this annual rainfall from fog drip (Floyd, 2008, 1990a; Hutley et al., 1997; King 1980; Fisher & Timms, 1978). Rainfall seasonality is also important. ANVF is able to withstand a pronounced dry season. CNVF requires a largely uniformly distributed rainfall with a summer peak when evaporative potential is highest and MFF requires consistently moist conditions from both rainfall and regular contact with cloud and fog (Floyd, 2008, 1990a). The availability of these moisture inputs to rainforest species also depends quite strongly on the geological history of the region. The volcanic strata underlying Lamington National Park were laid down in three major series of eruptions emanating from Mt Warning to the south. The Beechmont Basalt is overlain by the Binna Burra Rhyolite and scattered pyroclastic vents, which was then capped by the later Hobwee Basalt (Stevens, 1976). The current erosion caldera is a result of the differential weathering of these strata for 20 million years (Willmott, 1992). Basalts generally weather to red krasnozem soils which are fine textured with a high water holding capacity, acidic and low in soil nutrients, except for those stored in the surface horizons (Beckmann & Thompson, 1976). Subtle differences in basalt chemical composition, differential weathering characters and age of weathering surfaces, in conjunction with varied topography and the resulting microclimate has resulted in a wide variety of soil types even on this one geology (Beckmann & Thompson, 1976). The multiple basalt flows and their subsequent weathering has also resulted in step and bench sequences down the slopes (Turner, 1976) and associated variations in soil depth. According to Webb (1959), edaphic factors can be just as important in determining community composition and distribution as climatic variables. However, this is a complex interaction and equally for some structural types, edaphic factors are dominated by climate. A forest type which is highly competitive on poor soils under favourable climatic conditions, may be able to tolerate suboptimal rainfall only on richer soils (Adam, 1987). Similarly, CNVF may be able to tolerate poorer soils if rainfall is sufficient and there is no dry season (Adam, 1987). High rainfall may also be able to compensate for poorer soils in some cases such as in sheltered, fire protected sites (edaphic compensation) (Floyd, 1990a; Webb, 1969, 1959). Subtropical rainforest distribution is greatly impacted by topography (Adam, 1987). Aspect is more important at this latitude than in tropical rainforests, where the sunlight received annually is similar between northerly and southerly aspects. On the shortest day in winter at Lamington National Park, the sun shines for 10.25 hours (flat plane) and reaches a maximum altitude of 38.42° (Cornwall et 64
al., 2009). This low altitude means that much of the forest on southerly slopes and enclosed gullies receives far less than 10 hours of sunlight per day. The forests tucked below the inner rim of the caldera may receive no direct sunlight at all for extended periods through winter. The southern and eastern aspects are also protected from drying northerly and westerly winds in late winter and spring and from direct solar radiation in the heat of summer, where the midday sun sits almost directly over the forest at an altitude of 85° (Cornwall et al., 2009; Floyd, 2008). Erosion gullies shelter rainforest from fire, frost and damaging winds, as well as being sites of higher soil nutrients and moisture (Floyd, 2008, 1990). Soils also vary significantly between ridges and valleys, generally becoming deeper, higher in soil nutrients and moisture downslope (McKenzie et al., 2004). However, on steep slopes, erosion and leaching of soil nutrients may be pronounced (Floyd, 2008). This study aims to identify current patterns in species composition in the subtropical rainforest communities of south-east Queensland and to relate these patterns current climatic and edaphic conditions through the establishment of an altitudinal transect. Similar transects have been established for the assessment of rainforest structure, productivity and composition elsewhere (Borneo – Ashton 2003, Kitayama & Aiba 2002, Aiba & Kitayama 1999; Mexico – Vázquez & Givnish 1998; Costa Rica - Lieberman et al. 1996; Brunei – Pendry & Proctor 1996). This baseline will allow changes in floristic composition and their environmental correlates to be tracked over time and will serve as the essential benchmark against which resurveys of the forest will be compared. In addition, we use the current climatic envelopes of adjacent altitudes as a surrogate for climatic variation over time and identify species and groups for which predicted future climatic changes may prove challenging. This transect samples the response of vegetation along two major environmental axes along which human influenced climate is predicted to shift, temperature and moisture. MATERIALS AND METHODS Twenty permanently marked 20m x 20m vegetation survey plots were established in August 2006 in the Canungra Creek catchment of Lamington National Park, south-east Queensland, Australia (Figure 1) (see Kitching et al. Submitted (Appendix 1) for site description). Dispersed 0.04 hectare plots were chosen as appropriate for linking floristics with discrete environmental variables in this highly topographically variable region following a detailed pilot study investigating the implications of using five different sizes, shapes and configurations of plots. A fully surveyed one hectare plot was divided into 100 x 25m (n=4), 50 x 50m (n=4), 50 x 10m (n=20), 20 x 20m (n=25) and 10 x 10m (n=100) subplots. Data was collected on slope, aspect, degree of rock outcropping 65
Figure 1. The location of 20 20 x 20m quadrats along the IBISCA Queensland transect and soil pH and cation exchange were measured for the 100 10 x 10m plots and then averaged for larger plots. Bray-Curtis dissimilarity was used to examine floristic differences between the plots in each of these five different configurations and principal axis correlation (PCC) (Belbin et al., 2003) was used to calculate the correlation between the resulting groups of plots and the measured environmental variables. Monte-Carlo permutation tests (Belbin et al., 2003), (MCAO) were used to test the significance of the relationship between plot groups and measured environmental variables. On inspection of these results, 20 x 20m plots were chosen as they reduced the perimeter to internal area ratio, minimised the chance of crossing soil and climatic boundaries and showed the strongest relationship with discrete soil and climatic variables. Four 20 x 20m plots were located at each altitude at a distance of no less than 400m in an attempt to capture a degree of the variation at each altitude, and to maintain an achievable scale for the project and its participants. These plots sample several structural types (Webb 1959) of subtropical rainforest vegetation at five altitudes: 300m, 500m, 700m, 900m and 1100m. Four plots were established at each of these altitudes, with a minimum distance of 400m along the contour between replicates, and the data for each altitude pooled. This was done in place of establishing large plots at each altitude, which previous studies (Laidlaw et al. 2000) have shown must be at least 80 x 80m in size before an asymptote is achieved in the species accumulation curve. The plots were located ≥ 50m from permanent water and away from recent disturbance, however, this was more difficult at 300 and 500m due to the steep terrain lower in the catchment. All plots were positioned on basic Cainozoic volcanic rocks (Beechmont and Hobwee basalts). Soil samples were collected from each 66
plot, air dried and analysed for pH, conductivity and nutrient status. Soil analysis techniques are described in Strong et al. (In Press) (Appendix 2). The transect traverses a steep moisture and temperature gradient, where lower altitudes generally experience hotter and drier conditions, while upland sites generally experience colder and moister conditions. These trends can be strongly influenced by aspect. The establishment of all survey plots within a single catchment and, as far as possible, maintaining a common north-north-westerly aspect, attempts to reduce this variation. All established trees ≥ 5cm diameter at breast height (dbh: measured at 1.3m height or directly above buttresses or below bole deformities) were numbered and measured for diameter and height and were identified to species by the Queensland Herbarium (see Bostock and Holland (2007) for species authorities). Multi-stemmed species were treated as separate individuals wherever stems were ≥ 5cm dbh. Where vines and epiphytes obstructed the bole, these were gently lifted to allow accurate dbh measurement. All other vascular species on each plot were identified and given a cover score. Multivariate analyses were conducted on data pooled across four 20 m x 20 m plots per altitude. The pattern analysis software WinPATN (Belbin et al., 2003) was used to examine the association between altitude and floristic composition along the transect. The Bray-Curtis dissimilarity metric (Bray & Curtis, 1957) was applied to presence/absence data and used to determine the floristic dissimilarity between altitudes. A two-step procedure, based on the Bray-Curtis dissimilarity metric (Belbin et al., 2003), was used to examine the relationships between species based on the altitudes at which they were recorded. The groups resulting from both associations are displayed in a twoway table. The data were classified using unweighted pair group arithmetic averaging (UPGMA) (β value = -0.1). Semi-strong hybrid multidimensional scaling ordination (SSH MDS) was used to depict the association between altitudes based on their floristic composition in two-dimensional space (Belbin et al., 2003) using a dissimilarity cutoff value of 0.9. SSH is superior over other multidimensional scaling programs as it increases reliability through reducing the weighting of input distances by fitting them to output distances and is more flexible in its data handling capabilities than other ordination methods (Belbin et al., 2003). Minimum spanning trees are used to display the floristic links between pairs of altitudes surveyed along the transect. Principal axis correlation (PCC) (Belbin et al., 2003) was used to calculate the correlation between sampled altitudes in ordination space and selected intrinsic (species) and extrinsic (climatic, edaphic and topographic) variables for the transect. Thirty-five climatic variables were modelled using the Bioclim climate modelling package (Houlder et al., 2000), applied to an 80m digital elevation model. A Monte-Carlo permutation test (Belbin et al., 2003), (MCAO) was used to test the 67
significance of the relationship between altitudinal groups, their constituent species and extrinsic variables. MCAO randomly assigned values of variables to objects in the ordination plot and ran a principal axis correlation (1000 permutations) in order to evaluate the 'robustness' of the PCC results (Belbin 2004). Biplots of these significant extrinsic variables were overlaid on the ordination. RESULTS Recorded from the 20 plots along the transect were a total of 282 species, including 1218 tree stems (≥5cm dbh) of 115 species, 90 genera and 37 families (including one species of tree fern and one species of tree palm). The study also recorded 10 species of shrub, 59 species of vine, 18 species of herb, 13 species of ground fern, 13 species of orchid, 17 species of epiphyte (including 15 ferns and one climber). The remaining 37 species recorded are understorey tree species (
