SOUTH-EASTERN AUSTRALIA. Trent Penman. 1. Forest Science Centre, NSW Department of Primary Industries. Beecroft, NSW, Australia. 2. Bushfire ...
EFFECT OF FOREST MANAGEMENT PRACTICES ON UNDERSTOREY COMMUNITY COMPOSITION IN DRY SCLEROPHYLL FORESTS IN SOUTH-EASTERN AUSTRALIA Trent Penman 1 Forest Science Centre, NSW Department of Primary Industries Beecroft, NSW, Australia 2
Bushfire Co-operative Research Centre East Melbourne, Victoria, Australia Doug Binns Forests NSW Coffs Harbour, NSW, Australia Rod Kavanagh Forest Science Centre, NSW Department of Primary Industries Beecroft, NSW, Australia INTRODUCTION Impacts of management practices on native forest plant and animal communities have been the subject of ongoing and often heated debate. The focus is primarily on the harvesting of timber and prescribed burning, although few long term data are available for either practice. Fires have the ability to consume the above ground biomass however the extent to which this occurs is related to the intensity of the fire. Post-fire regeneration occurs via germination of the soil seed bank or re-sprouting from lignotubers or from epicormic buds in some tree species. Obligate seeders and some re-sprouting species can experience localised extinctions if the fire interval is less than the time to maturation, (e.g. Keith 1996). However, most studies in Australian ecosystems regarding the impacts of fire are based on frequent high intensity wildfires and little has been published regarding the long term impacts of repeated prescribed burning. Timber harvesting can result in dramatic changes in overstorey structure and cover resulting in changes to the levels of light, moisture and temperature experienced by understorey vegetation species. (e.g Loyn et al. 1980). Concerns have been raised that these changes may adversely affect understorey floristic diversity. However, studies conducted within dry sclerophyll forests in Australia to date have found no impact of harvesting on understorey communities (e.g. Dickinson and Kirkpatrick 1987). In this paper, we examine the medium term impacts (approx. 15 years) of repeated prescribed burning on the understorey communities in logged and unlogged dry sclerophyll forest in south-eastern Australia.
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METHODS The study was conducted in the Eden Burning Study Area (EBSA) located in south-eastern Australia. The EBSA is approximately 1080 hectares of dry Eucalyptus forest with a floristically diverse understorey. In 1986, 18 operational-sized coupes (~ 30 ha) were randomly assigned to one of six management regimes – unlogged unburnt, unlogged routinely burnt, unlogged frequently burnt, logged unburnt, logged routinely burnt and logged frequently burnt. All activities were conducted according to operational standards. Initial vegetation measurements were taken prior to any anthropogenic disturbance in 1986 and then at approximately five year intervals thereafter. In each coupe, 12 vegetation plots were established using random bearings and distances. Shrub and ground vegetation within a 5.64m radius of the plot centre was recorded. Several multivariate statistical approaches were used to examine the effects of the imposed management regimes on the vegetation communities. Non-metric Multidimensional scaling (nMDS) was used to visually examine the data, PERMANOVA (Anderson 2001) was used to examine the effect of the imposed management regimes and ANOSIM (Clarke 1993) was used to examine temporal changes. RESULTS AND DISCUSSION No clear groupings of sites were apparent after 13 years following initial disturbances (Figure 1). The PERMANOVA analysis also found few meaningful differences between the imposed treatments. This is most likely a result of the heterogeneity (i.e. patchiness) of both the fire and logging treatments. Differences between the results from wildfire studies and this study may also be related to the fact that prescribed burns were of a much lower intensity than wildfires. However, a significant shift in plant community structure over time was observed and this occurred independently of treatment (Figure 2). It is likely that this represents a broad scale response throughout the study area, such as an effect of time since the last wildfire (e.g. Gill 1999).
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Figure 2: Differences in community structure over time using the R-statistic from ANOSIM (Clarke 1993).
Figure 1: nMDS results for the vegetation measurement in 2001. LF, logged frequent burn; LR, logged routine burn; UF, unlogged frequent burn; UR, unlogged routine burn.
SUMMARY AND CONCLUSIONS Repeated prescribed burning in dry sclerophyll forests was not associated with the negative effects predicted for understorey plant species from related research involving wildfires. Logging operations did not have a detrimental effect on the species richness and plant abundance in understorey vegetation communities. Changes in community structure may be related to successional changes associated with the times since the last wildfire. LITERATURE CITED Keith, David (1996). Fire-driven extinction of plant populations: A synthesis of theory and review of evidence from Australian vegetation. Proceedings of the Linnean Society of New South Wales 116, 37-78 Anderson, M.J. (2001). A new method for non-parametric multivariate analysis of variance. Austral Ecology 26, 32-46 Clarke, K.R. (1993). Non-parametric multivariate analyses of changes in community structure. Australia Journal of Ecology, 18, 117-143. Loyn, R. H., Macfalane, M. A., Chesterfield, E. A., and Harris, J. A. (1980). Forest utilisation and the flora and fauna of the Boola Boola State Forest in south-eastern Victoria. (Forest Commission of Victoria: Victoria.) Gill, M. A. (1999). Biodiversity and bushfires: an Australia-wide perspective on plant-species changes after a fire event. In 'Australia's Biodiveristy - Responses to fire: Plants, birds and invertebrates'. (A. M. Gill, J. C. Z. Woinarski, and A. YorkEds. ) pp. 9-53. (Department of the Environment and Heritage: Canberra.) Dickinson, K J M and Kirkpatrick, J B (1987). The Short-Term Effects of Clearfelling and Slash-Burning on the Richness Diversity and Relative Abundance of Higher Plant Species in Two Types of Eucalypt Forest on Dolerite in Tasmania Australia. Australian Journal of Botany 35, 601-616.
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