Problems of placing boundaries on ecological ...

Aust. J. Bot., 2000, 48, 511–530

Problems of placing boundaries on ecological continua — options for a workable national rainforest definition in Australia A. J. J. LynchAC and V. J. NeldnerB A

Environment Australia, GPO Box 787, Canberra, ACT 2601, Australia. Present address: Department of Geopgraphy and Environmental Studies, University of Tasmania, based at Division of Botany and Zoology, Australian National University, Canberra, ACT 0200, Australia. B Present address: Queensland Herbarium, Brisbane Botanic Gardens, Mt Coot-tha Road, Toowong, Qld 4066, Australia. C Corresponding author; email: [email protected]

Abstract. Options for a new definition of, and key for, rainforest in Australia are provided. The definitions take a national perspective, and are based on the ecological characteristics of rainforest species and some structural and floristic characteristics. Rainforest plant species are defined as those adapted to regenerating under low-light conditions experienced under the closed canopy or in localised gaps caused by recurring disturbances which are part of the natural rainforest ecosystem, and are not dependent on fire for successful regeneration. Three definitions are provided which differ in the extent of inclusion of transitional and seral communities. The first definition recognises communities such as mixed forests as transitional to rainforests and therefore as separate communities. The second definition includes a minimal component of emergent non-rainforest species in rainforest in the recognition that the main floristic component and functioning of the communities cannot be distinguished. The third definition includes the late successional stages of transitional and seral communities in rainforest on the presumption that such communities include non-rainforest species which are close to senescence, and that these communities are essential for the long-term conservation of rainforest in areas where rainforest is vulnerable and subject to major disturbance, particularly by fire. The first definition is concluded to be the least ambiguous and arbitrary, and enables a consistent approach to rainforest management. Recognition of mixed forests as a distinctive and mappable vegetation type should be incorporated in a comprehensive conservation strategy inclusive of all ecosystem developmental stages. Introduction The recognition of forest types is important for land management agencies as it provides a basis for development of forest management policies and strategies. Although there have been several attempts to construct a nation-wide vegetation classification (Moore and Perry 1970; Specht 1970; Carnahan 1976; Beadle 1981; AUSLIG 1990; RAC 1992), different systems for classifying and describing forest vegetation have been developed by various forest management agencies in Australia to suit their own situations. The lack of common understanding across the country about the vegetation classification systems being used in different States, or between different agencies within single States, became particularly evident in the early stages of the Comprehensive Regional Assessment of forests (the Deferred/Interim Forest Assessment process) (Sun et al. 1997). Why an encompassing definition is needed One of the primary conservation objectives stated in the National Forest Policy Statement (CoA 1992) is to protect native forest communities, on the basis of principles of © CSIRO 2000

comprehensiveness, adequacy and representativeness (hence the acronym CAR). As a general criterion, 15% of the pre1750 distribution of all forest communities in Australia should be protected in a CAR conservation system (JANIS 1996). Subsequently, problems have been highlighted in the definition of ‘forest community’, in general, and the specific regional communities, in particular. While many States and territories have developed regional vegetation classifications, national consistency of conservation levels and regional assessment requires the equivalence of communities across all the regions. A vegetation type that exemplifies many of the classification difficulties is rainforest. Rainforests have been recognised as different from the typical eucalypt-dominated forests from early settlement, with terms such as ‘brush’ and ‘scrub’ applied to rainforests (Adam 1992; Ryan et al. 1995). They have been treated almost completely separately from other vegetation types (Carnahan 1976). Rainforests have been defined and classified locally (e.g. Jarman and Brown 1983; Jarman et al. 1984 in Tasmania; Floyd 1990 in New South Wales; Russell-Smith 1991 in the Northern Territory); however, the general definition of rainforest per se has been 10.1071/BT97022

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disputed legally and through formal inquiries (Adam 1992). Current terminology and popular image reflect the origins of rainforest studies being based on tropical vegetation. The aesthetic appeal of rainforests is heavily marketed and promoted in coffee-table books (e.g. Figgis 1985) and tourist brochures, and the emphasis is usually on tropical and subtropical rainforest. Part of the appeal of these communities is that they contrast so strongly with the arid and semi-arid communities that dominate the Australian continent. This image has been promoted photographically in conservation campaigns, resulting in an emotive public response to the issue of rainforest conservation. The high biological diversity, structural complexity and aesthetic appeal of tropical rainforests in particular, together with the presence of unique animals, such as the cassowary (Casuarius casuarius), have also contributed to rainforest being given a high priority in the consideration of maintenance of biodiversity and conservation planning. An encompassing definition of rainforest has proven elusive, and even broad definitions have not been immune to criticism (Adam 1992). Confusion and lack of precision have developed about the term ‘rainforest’ as well as about ‘sclerophyll forest’(Johnston and Lacey 1984), and several vegetation classifications based on combinations of physiognomy, structure and function for major divisions in the classifications have avoided the term ‘rainforest’ completely (e.g. Fosberg 1967; UNESCO 1973; Johnston and Lacey 1984). With increasing competition for rainforests as a conservation and economic resource, they can be and have been defined in terms most advantageous for conservation or economic purposes (Jarman and Brown 1983). Importantly, comparison and analysis of most communities regarded as rainforest in Australia is made between regions or nationally, with regional analyses often taking into account the floristic composition of the communities (e.g. Webb et al. 1967a, 1967b; Busby 1984; Russell-Smith 1991). Internationally, comparisons tend to focus more at the formation class, subclass or group level (Appendix), since equivalent formations in different parts of the world tend to be composed of different floras (UNESCO 1973). In Australia, ‘rainforest’ is used as an all-embracing term that includes both the evergreen types along the moist eastern coast of the Australian mainland and in Tasmania, and the increasingly deciduous types in the more strongly seasonal northern areas (Hopkins et al. 1984). Rainforest is patchily and widely distributed, being recorded in all States except South Australia, and in many Australian territories, for example Christmas Island. Associated with this wide geographical and environmental range is significant variability in the structure, physiognomy and floristics of Australian rainforests. Features that may have diagnostic or descriptive value at one extreme of the range are not useful elsewhere (Hopkins et al. 1984). This demonstrates the degree to which a national definition must be both general and regionally specific. Consequently, any nationally applicable definition of rainforest

A. J. J. Lynch and V. J. Neldner

should not only consider the distinctiveness of rainforest from other vegetation types, but also attempt to recognise the inherent variability, both floristically and structurally, recorded in regional community typologies. While necessarily originating from an ecological perspective, anthropogenic and operational considerations mean that a national definition must also account for the management implications for, and community values attributed to, rainforest. The importance of rainforest in Australia Palaeobotanical studies have shown that present rainforests are remnants of the oldest extant vegetation formation in Australia, with ancestors of most component taxa dating back to the Cretaceous or early Tertiary, at least at the generic level. For this reason, they have major historical and scientific significance (Kershaw 1992). The extant tropical rainforests contain eight of the 14 primitive angiosperm families recognised by Takhtajan (1969) (Webb and Tracey 1981a), while the extant temperate rainforests of Tasmania contain several primitive gymnosperms and angiosperms (Barlow 1981; Hill 1990). From a conservation perspective, rainforests are recognised as important for the maintenance of biodiversity. Globally, rainforests cover only 5% of the land area, but contain at least half of the world’s species of terrestrial plants and animals (Grainger 1980). Australian rainforests contain 60% of the families of vascular plants on the continent, including eight families and 103 genera that are endemic (Webb and Tracey 1981a; Floyd 1990), while about 17% of all Australian bird species occur in rainforests (Frith 1979). The rainforests of the wet tropics of Queensland cover only 0.18% of the area of the continent, but contain about 30% of Australia’s marsupial and frog species and 62% of its butterfly species (AHC 1986). Five of the 13 centres of plant diversity identified for Australia by the World Wide Fund for Nature and the International Union for the Conservation of Nature (WWF and IUCN 1994–95) are dominated by rainforest, while a further three have rainforest components. On a global basis, rainforests are threatened ecosystems (cleared at a rate of 0.52 ha s–1, Bellamy 1992), while in Australia, rainforests have been specifically targeted for research and conservation through the National Rainforest Conservation Program. Kirkpatrick (1992), however, regards them as one of the best-reserved ecosystems in Australia. The current extent and types of rainforest in Australia The current distribution of rainforest and rainforest taxa within these forests is both a product of long-term climatic and edaphic sifting of the flora, and the effects of short-term disturbance events (Adam 1992). In Australia, rainforest currently extends from the tropics at 10°S in northern Australia to the cool temperate zone at 44°S in southern Tasmania.

Options for a workable national rainforest definition

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High annual rainfall is an important climatic factor delimiting rainforest distribution. Estimates of upper limits include over 3600 mm per annum (p.a.) in the wet tropics of Queensland (Webb and Tracey 1981b) and about 3500 mm p.a. in western Tasmania (Busby and Brown 1994). Lower estimates of annual requirements range from 1270 mm (Baur 1957) and 1200 mm (Read 1992) to 1000 mm (Busby and Brown 1994), while discontinuous patches may occur in eastern Australia, north of severe frosts (to about 30°S) and to about the 600-mm isohyet, and in northern Australia to about the 800-mm isohyet (Webb and Tracey 1981b). Nix (1991) modelled the potential distributions of rainforest in Australia on the basis of bioclimate (indices of temperature and precipitation characteristics) and soil nutrient status. Eight primary rainforest types were identified, grouped into three main thermal regimes (Table 1). The bioclimate envelopes indicate that Australian rainforests occupy a wide range of temperature and precipitation attributes. Also, altitude may substitute for latitude, given that mesotherm climate rainforests occur at progressively higher elevations northward from Victoria to north-east Queensland (Nix 1991). Effective rainfall is indirectly modified by other climate factors such as cloud cover, humidity regime, wind, temperature and mist (Hitchcock 1977). Topographic position and aspect affect solar insolation, wind exposure, humidity (including cloud trapping), light and temperature. These factors can result in rainforest occurring on southern aspects but not northern, for example, in the Liverpool Ranges of

Table 1.

Some bioclimatic attributes of primary rainforest types in Australia grouped by thermal regime (Nix 1991)

Thermal regime

Table 2.

New South Wales (Hitchcock 1977), or as small, isolated, fire-protected pockets of lower annual rainfall in deeply incised lowland areas or on south-east-facing steep hillslopes in eastern and south-eastern Tasmania (Neyland 1991). Estimates of the area of rainforest in Australia (Table 2) and in individual states (e.g. Tasmania, Table 3) differ substantially, depending on the definition of rainforest and the methods and mapping coverages used to derive the area estimates. The difference between the estimates for the area of rainforest in Tasmania determined by the Australian Forestry Commission (AFC) (1975) and that of Kirkpatrick and Dickinson (1984) was attributed to the use of a different threshold of crown cover for eucalypts in the rainforest definition (Miller 1984) and different height thresholds (Hickey et al. 1993). The value from Hickey et al. (1993) was derived from 1 : 25 000-scale forest-type coverage as compared to the other published maps at 1 : 500 000 scale, and was claimed to be the most accurate (Hickey et al. 1993). The extensive distribution of rainforest in Australia can be subdivided spatially, with the various types of rainforest being broadly correlated with factors of latitude, altitude and coastal proximity. Four rainforest types were described on a floristic basis by Beadle and Costin (1952) — tropical, subtropical, monsoon and temperate — whereas Webb (1968, 1978) used physiognomy and floristics of the understorey to determine three major rainforest types: (1) vine forests characterised by robust woody vines (lianes);

Primary rainforest group

Rainforest type

Annual mean temp.

Coldest month mean min. temp.

Megatherm

1–3

Tropical

≥24°C

>10°C

549 to > 5000

Mesotherm

4–6

Subtropical– warm temperate

∼18°C (range 14–22°C)

>5°C (range 0–5°C)

Similar to megatherm

Microtherm

7, 8

Cool temperate

4–14°C

–3 to 1°C

719 to > 3000

Estimates of area of rainforest by political regions (AFC 1975; Baur 1989; RAC 1992)

Table 3. Estimates of area of rainforest in Tasmania Source

State/territory AFC (1975) Northern Territory New South Wales Tasmania Queensland Victoria Western Australia

36 800 300 300 456 100 1 068 000

Total

1 861 200

A

Annual mean precipitation

A A

Area of rainforest (ha) Baur (1989) RAC (1992) 38 000 226 100 711 500 1 237 200 13 300 2 000

147 000 328 000 754 000 1 175 000 41 000

2 228 100

2 445 000

No estimate of rainforest area provided.

A

AFC (1975) Kirkpatrick and Dickinson (1984) Baur (1989) Kirkpatrick and Brown (1991) RAC (1992) Hickey et al. (1993) Tasmanian CRA (CoATas 1997)

Area (ha) 456 100 656 210–765 100 711 500 602 000 754 000 563 120 597 880

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(2) fern forests in which tree ferns and terrestrial ferns are conspicuous and vines are generally wiry and slender; and (3) mossy forests characterised by an abundance of epiphytic bryophytes. Tropical and subtropical rainforests occur in northern and eastern Australia in the wetter, coastal areas as far south as New South Wales. Monsoon rainforests occur in northern and north-western Australia in the seasonally dry coastal and subcoastal regions. Temperate rainforests occur in eastern and south-eastern Australia: warm temperate in New South Wales and Victoria, and cool temperate in Victoria and Tasmania with a few outliers in New South Wales and Queensland (Webb and Tracey 1981a; Young and McDonald 1987). Dry rainforests are predominantly a variation of tropical/subtropical rainforest and are present in fire-protected sites in subcoastal and inland areas across northern and eastern Australia (Gillison 1987; Cameron 1992). The vine forests are largely confined to the tropical and subtropical ecofloristic zones, while fern and mossy forests are concentrated in the temperate zones and restricted to high altitudes in the tropics. The total area of rainforest in Australia has been estimated by Webb and Tracey (1981a) for three categories of rainforest type (i.e. subformation, Table 4). No estimates were provided for the monsoon rainforest patches in the Northern Territory and Western Australia, dry rainforests in inland Queensland, or for rainforest in Victoria. Recent inventories of vegetation have improved estimates of rainforest extent in specific regions (e.g. Cape York Peninsula); however, a valid, updated estimate of rainforest extent awaits comprehensive surveys across all relevant areas of Australia and a consistently applied definition. Table 4. Estimates of area by type of rainforest (Webb and Tracey 1981a) Type

Area (ha)

Tropical rainforest (north of Ingham, Queensland) Subtropical and warm temperate rainforest (Mackay, Queensland, to Eden, New South Wales) Cool temperate rainforest (Tasmania)

759 000 609 000 456 100

Past definitions of rainforest As originally defined by Schimper (1903), the term ‘rainforest’ was applied to evergreen, hygrophilous forests with lianas and epiphytes growing in the lowland tropics. Schimper acknowledged that rainforest could extend to temperate regions with a mild winter, rainfall of at least 1200 mm p.a., and lacking a dry season. This definition has been widely accepted in treatments of tropical rainforests (e.g. Whitmore 1984; Richards 1996). Schimper also defined monsoon forest as forest that is more or less leafless during the dry season, usually with a canopy lower than that of rainforest, rich in woody lianes and herbaceous

epiphytes, but poor in woody epiphytes. In Australia, the term ‘monsoon forest’ has been applied to rainforest vegetation occurring in tropical regions, independent of the leaf-fall phenomenon (Russell-Smith 1991). International vegetation classifications have been derived from attributes of structure and function (e.g. Fosberg 1967) or physiognomy and structure (e.g. UNESCO 1973) in attempts to avoid ecological and social relationships as well as regional floristic differentiation. A disputable limitation of such classifications is, however, that terms in common use, such as rainforest, can include forest, woodland, scrub and mangrove communities incorporating broad-leaved, needleleaved (and other coniferous) and deciduous species. This one term therefore can apply to many categories, even at the formation group level (e.g. UNESCO 1973 categories: tropical ombrophilous forest, tropical and subtropical semi-deciduous forest, subtropical ombrophilous forest, mangrove forest, temperate and subpolar evergreen ombrophilous forest, winter-rain evergreen broad-leaved sclerophyllous forest, tropical and subtropical evergreen needle-leaved forest, and temperate and subpolar evergreen needle-leaved forest, as well as evergreen needle-leaved woodland and cold deciduous scrub). It is also necessary to extend such classifications at the regional level to incorporate floristics and distinguish regional variation. Webb and Tracey (1981b) noted that the UNESCO classification does not include categories matching many of the Australian rainforest types. In Australia in the 1950s and 1960s, rainforests at the national level were variously defined by Beadle and Costin (1952), Webb (1959, 1968) and Baur (1965). These definitions considered aspects of structure and floristics, concentrating on the diversity of life-forms and structural complexity to distinguish rainforest from non-rainforest (Table 5). The uppermost canopy was generally a dense, closed forest, while lianas and epiphytes were usually present. Baur (1965) extended these generalisations to include a hygrophilic nature, floristic affinities with the Antarctic flora and an absence of eucalypts. These definitions were limited in application nationally, however, as they implicitly exclude communities dominated by deciduous species (e.g. monsoon and dry rainforests), communities lacking lianas (e.g. those in the temperate zone), or having sclerophyllous elements (e.g. Acacia spp.). Forests with a more open canopy, such as scrub rainforest and subalpine rainforest found throughout western Tasmania (Cullen 1991), were also excluded. Specht (1970, 1981) developed a vegetation classification on the basis of the structure of the community, by using the life-form, projective foliage cover and height of the tallest stratum. Communities with deciduous canopy species were classified on the basis of foliage projective cover at the time of maximum leaf development (Specht 1970). Difficulties with the application of Specht’s classification to rainforest are related to the definition of the upper stratum and the significance of emergents above the canopy, particularly eucalypt


species, and the apparent synonymy of closed-forest and rainforest in the classification. While a closed canopy is a key feature of most rainforest communities, not all closed-canopy communities are rainforest or are dominated by species generally considered to be rainforest species (e.g. mangrove closedforests). In addition, not all rainforest communities have a closed canopy, most specifically the ephemeral canopies Table 5. Author(s)

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dominated by deciduous species occurring in tropical Australia (Russell-Smith 1991), and some cool temperate rainforests in Tasmania, including scrub rainforest and subalpine rainforest (Jarman and Brown 1983). Rainforests on very rocky substrates frequently have a very open canopy. A proposed system for the classification of tree-dominated vegetation in Australia by Johnston and Lacey (1984) was

Several definitions of Australian rainforest and problems with their application to Australian rainforests

Definition

Schimper (1903) Forest which is ‘evergreen, hygrophilous, and at least 30 metres high, rich in thick-stemmed lianas, and in woody as well as herbaceous epiphytes’.

Problems with definition Excludes rainforest with canopies less than 30 m high; excludes rainforests lacking lianes but rich in ferns and/ or bryophytes; excludes deciduous canopies.

Beadle and Costin (1952)

Structure used to delimit major formations, such as Excludes rainforest with open canopies; excludes rainforests lacking sclerophyll forest, woodland and rainforest. The formations lianes; excludes rainforests with xerophytic dominants. were divided into associations and alliances on the basis of the floristics of the dominant stratum. The rainforest formation was described as a ‘closed community dominated by usually mesomorphic meso- or mega-phanerophytes forming a deep, densely interlacing canopy in which lianes and epiphytes are invariably present, with mesomorphic subordinate strata of smaller trees, shrubs and ferns and herbs’. It was divided into four subformations: temperate, subtropical, tropical and monsoonal rainforests.

Webb (1959)

‘Rainforest, excluding its transitions, is essentially a Excludes rainforest with simply structured canopies; excludes closed forest, with closed-spaced trees generally arranged rainforest with simple floristic composition; excludes herb-rich in several more or less continuous storeys, the uppermost rainforests. of which (the canopy level) may be even or uneven. Rainforest is distinguished from other closed-canopy forests by the prominence of life-forms, such as epiphytes and lianes, by the absence of annual herbs on the forest floor, and by its floristic complexity’.

Baur (1965)

Rainforest is ‘a closed moisture-loving community of trees, usually containing one or more subordinate storeys of trees and shrubs; frequently mixed in composition; the species typically, but not invariably, broad-leaved and evergreen; heavy vines (lianes), vascular and non-vascular epiphytes, stranglers and buttressing often present and sometimes abundant; floristic affinities mainly with the Antarctic or Indo-Malaysian floras; eucalypts typically absent except as relics of an earlier community’.

Excludes rainforest with open canopies; cool temperate rainforests are not typically broad-leaved; monsoonal rainforests are not evergreen; cool temperate rainforests do not typically include lianes, stranglers or buttressed roots; eucalypt presence (up to 50% projective foliage cover) in a canopy of typical rainforest species should not exclude the community from being considered rainforest.

Fosberg (1967)

Multistratal evergreen forest (rainforest) is tall, multistratal, orthophyllous or top of canopy sclerophyllous closed-woody vegetation 5 m or more tall; epiphytes and lianes usually common, e.g. Dipterocarp forest (Malaya, Borneo).

Applies predominantly to tropical rainforest.

Specht (1970, 1981)

Based solely on structural and physiognomic attributes, no definition for rainforest, but generally it equates with closed forest and low closed forest.

Excludes open-canopy rainforests; no specific definition for rainforest per se.

Dale et al. (1980) ‘The rainforests are defined as closed, broad-leaved forest vegetation with a continuous tree canopy of variable height, and with characteristic diversity of species and life-forms. The ecological definition of rainforest includes transitional and seral communities with sclerophyll emergents that are of similar botanical composition to mature rainforests in which sclerophylls are absent.’

Excludes rainforest with open canopies; excludes rainforest with simple or ‘non-characteristic diversity’ floristic composition; includes all transitional and seral communities.

Jarman and Brown (1983)

Excludes wet-gully communities in Tasmania and most rainforest communities in other states that are dominated by other taxa.

Vegetation dominated by species of Nothofagus, Eucryphia, Atherosperma, Athrotaxis, Lagarostrobos, Phyllocladus or Diselma.

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Table 5. (continued) Author(s)

Definition

Rainforest Technical Committee (1986)

‘Rainforest is defined ecologically as closed (> 70% Excludes rainforest with open or deciduous canopies; excludes projective foliage cover) broad-leaved forest vegetation with rainforest with simple or ‘non-characteristic diversity’ floristic a continuous rainforest tree canopy of variable height, and composition; includes transitional and seral communities. with a characteristic diversity of species and life-forms. Rainforest includes closed transitional and seral communities, with emergent eucalypts that are of similar botanical composition to mature rainforests in which eucalypts are absent. Rainforest canopy species are defined as shadetolerant tree species which are able to establish below an undisturbed canopy, or in small canopy gaps resulting from locally recurring minor disturbances, such as isolated windthrow or lightning strike, which are part of the rainforest ecosystem. Such species are not dependent on fire for their regeneration.’

CFL (1987)

‘Rainforest is defined ecologically as closed broad-leaved Excludes rainforest with open canopies; excludes forest vegetation with a more or less continuous rainforest transitional and seral communities identified tree canopy of variable height, and with a characteristic in alternative regional definitions. composition of species and life-forms. Rainforest canopy species are defined as shade-tolerant tree species which are able to regenerate below an undisturbed canopy, or in small canopy gaps resulting from locally recurring minor disturbances, such as isolated windthrow or lightning strike, which are part of the rainforest ecosystem. Such species are not dependent on fire for their regeneration.’

AUSLIG (1990)

‘In structural terms, Australian rainforests are a dense Rainforest canopies not always diverse; non-rainforest formation of diverse tree types, floristically distinct from communities may also contain epiphytes, lianes, mosses, ferns. the surrounding eucalypt forests. Rainforests are distinguished from other closed forests by the presence of growth forms such as epiphytes, lianes, mosses and ferns. Of course, there are many transitional types and mixtures of sclerophyll and rainforest species.’

Walker and Hopkins (1990)

Used the definition of Webb (1959, 1968, 1978), Webb et al. (1970, 1976)

based on a hierarchy of intrinsic attributes of physiognomy, floristics and spatial occupancy. This system avoided the implication of environmental attributes in terms such as ‘rainforest’ by the categorisation of the rainforests of Webb and Tracey (1981a) with the Malaysian and Antarctic elements of the Australian flora or the relict subelement of the Gondwanic element of Nelson (1981), including mangroves (Johnston and Lacey 1984). However, it separates communities dominated by conifers, palms, and phyllodial and cladodial species into separate classes. This distinction is contentious in regions such as Tasmania owing to the regional prominence of coniferous species in communities locally classified as rainforest (see Jarman and Brown 1983) including the phyllocladial celery-top pine (Phyllocladus aspleniifolius). Walker and Hopkins (1990) devised a separate classification for rainforest and non-rainforest communities. They followed the classification of rainforest in Webb (1978), but also used many of the structural/physiognomic features of Webb’s classification (Webb 1959, 1968, 1978; Webb et al. 1970, 1976) for their rainforest classification. While some individual

Problems with definition

stands may fall between existing categories, Webb’s classification provides an appropriate framework for discussion of rainforests at a national scale (Adam 1992). The Webb structural types have been successfully related to the forest formations of Whitmore (1984) and the UNESCO (1973) world formation groups by Kershaw and Whiffen (1989), and earlier rainforest nomenclatures by Winter et al. (1987) (Table 6). The species diversity of most rainforest communities, together with the high proportion of species with localised or disjunct distributions suggests that a physiognomic or structural approach (e.g. Table 7) may be used more adequately than floristics to quantify the variation in rainforests. The key to Webb’s (1978) forest types is based primarily on leaf-size categories of the canopy trees, and secondly on liana/epiphyte/fern/palm/sclerophyll characters and canopy/trunk/ stem attributes. Webb’s classification provides a framework for national comparison of communities, by matching of formation or subformation levels to the structural/physiognomic units. At the regional scale, further delimitation is necessary by use of floristics (Adam 1992).


517

Table 6. Structural/physiognomic rainforest types of Webb (Webb 1959, 1968, 1978; Webb et al. 1970, 1976) as related to earlier rainforest nomenclature (modified from Winter et al. 1987) Structural type

Other names

Complex mesophyll vine forest (CMVF) Mesophyll vine forest (MVF) Semi-deciduous mesophyll vine forest (SDMVF) Semi-deciduous notophyll vine forest (SDNVF) Evergreen notophyll vine forest (ENVF) Simple semi-evergreen notophyll vine forest (SSENVF) Simple semi-evergreen notophyll vine thicket (SSENVT) Deciduous vine thicket (DVT) Complex notophyll vine forest (CNVF) Notophyll vine forest (NVF) Simple notophyll evergreen vine forest (SNEVF)

Araucarian notophyll vine forest (ANVF) Araucarian microphyll vine forest (AMVF)

Tropical rainforest Tropical rainforest Tall monsoon forest Monsoon forest Monsoon forest Monsoon forest Monsoon forest Monsoon forest Subtropical rainforest Subtropical rainforest Subtropical rainforest, warm temperate rainforest coachwood forest Hoop-pine rainforest Hoop-pine rainforest

Low microphyll vine forest (LMVF) Semi-evergreen vine thicket (SEVT)

Dry rainforest Bottle-tree scrub

Microphyll fern forest (MFF) Microphyll fern thicket (MFT) Nanophyll fern forest (NFF) Nanophyll mossy forest (NMF)

Warm temperate rainforest Warm temperate rainforest Cool temperate rainforest Cool temperate rainforest beech forest/myrtle forest

Nanophyll fern thicket (NFT) and mossy thicket (NMT)

Cool temperate rainforest beech forest/myrtle forest

Table 7.

Physiognomic attributes used by Webb (1978) to quantify rainforest variation

Attribute

Descriptors

Height and depth of canopy closure

Prominence of tree layers, evenness of canopy, presence and type of emergents, regularity of distribution of trunks of upper canopy trees, crown shapes, vertical extension of crowns in relation to length of trunk

Leaves

Size, shape, texture, periodicity of leaf-fall

Trunks

Texture and colour of bark, extent of covering by epiphytes, cauliflory, stilt roots, spreading surface roots, club-like base

Special life-forms or growth-forms

Types of palm-like, fern-like, pandan-like, banana-like, bamboo-like, grass-like plants; stranglers; banyans; thorns, prickles and hooks; robust, slender and wiry vines; types of epiphytes and their vertical extension

The current Commonwealth definition of rainforest includes forest where the tallest tree layer consists of nonrainforest species in their latter growth stages (late mature and overmature), which emerge above a closed canopy dominated by rainforest species (CoA 1997). By specifying the growth stages of emergent non-rainforest species, the definition can be applied by using aerial photograph interpretation or field inspection to determine the developmental stage of mixed forest. Determining the growth stage of many noneucalypt sclerophyll emergents (e.g. Lophostemon confertus, Syncarpia glomulifera) is not, however, practical from aerial

photographs or other remote sensing. The growth stage of these species can be estimated from stand characteristics and/or by an examination of canopy form (CoA 1997). Regional rainforest classifications Regional vegetation classifications have often been developed with specific vegetation types in mind and for particular purposes by using specific attributes. Their context is therefore important when equating classifications developed in different regions for different purposes. Regional classifications often have a floristic basis. However, the high degree of

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latitudinal and local diversity within Australia makes their extension beyond the region of derivation inappropriate. Full species floristic classifications that use numerical methods have been attempted in several areas: north-east Queensland and Cape York (Webb et al. 1967a, 1967b); the Nightcap Range, northern New South Wales (Williams et al. 1973); north-east Queensland (Williams and Tracey 1984); Victoria and Tasmania (Busby 1984); Tasmania (Jarman et al. 1994); the Northern Territory (Russell-Smith 1991); the Kimberley (Kenneally et al. 1991); and inland dry rainforest of north Queensland (Fensham 1995). The complexity of the datasets in the species-rich rainforests and the time needed to collect and identify full floristic data have limited the development of regional floristic-based rainforest classifications. Phytosociological methods have been useful in the cool temperate rainforests (e.g. Busby 1984) because of their low vascular plant species diversity (Adam 1992). The datasets used did not, however, include the lichen or bryophyte flora, which is rich and diverse in cool temperate Australian rainforests (Adam 1992; Busby and Brown 1994). Non-vascular plants outnumber vascular plants by at least five to one in Tasmanian rainforest communities, and at any single site the difference in diversity between the two groups is even more pronounced (Jarman et al. 1991). In Tasmania, for example, the rainforest classification (Jarman and Brown 1982, 1983; Jarman et al. 1984, 1987) is based on floristic composition and the regeneration processes of key species. Rainforest in Tasmania is defined floristically as vegetation dominated by species of Nothofagus, Eucryphia, Atherosperma, Athrotaxis, Lagarostrobos, Phyllocladus or Diselma (Jarman and Brown 1983). It comprises forest with trees greater than 8 m in height, as below this height the distinction between tree and shrub form is indistinct for a number of rainforest dominants which occur with stunted growth form in alpine treeless habitats, and because rainforest may grade into subalpine or alpine vegetation. Jarman et al. (1991) subsequently decreased the height threshold to 5 m. In Victoria, rainforest was defined on a theoretical and structural basis by the Department of Conservation, Forests and Lands (1987) with a characteristic composition of species and life-forms. Rainforest canopy species were defined as shade-tolerant tree species able to regenerate below an undisturbed canopy or in small canopy gaps and not dependent on fire for regeneration (CFL 1987). A working definition was also supplied that identified dominant rainforest canopy species and specifying minimum spatial configurations of suitable stands of trees for mapping from aerial photographs and ground survey. A later, comprehensive definition of rainforest in Victoria of Cameron (1992) was structured into ecological, floristic and structural–physiognomic criteria, with the ecological components having priority over the other components. Primary and secondary rainforest species that significantly contribute to the canopy or are emergent above the canopy in


the three types of rainforest in Victoria were listed by Cameron (1992) as part of the definition. The definition of Cameron followed from proposed definitions by the Ecological Society of Australia (Dale et al. 1980) and the Rainforest Technical Committee (1986) which included closed transitional and seral communities, with emergent sclerophylls or eucalypts, respectively, that are of similar botanical composition to mature rainforests lacking sclerophylls or eucalypts, respectively. The Victorian government definition of rainforest (CFL 1987) has remained the official position and was used in the East Gippsland and Central Highlands Proposed Forest Management Plans (CNR 1995b; DNRE 1996b). Working definitions for field identification of rainforest were also derived. The working definitions identified cool-temperate and warm-temperate character species and specified that rainforest in both regions should generally be at least 0.4 ha or that streamside linear strips should be at least 20 m wide and 100 m long (CNR 1995b; DNRE 1996b). The ecosystems or ecological vegetation classes (EVCs) identified in these Forest Management Plans were also used in the ecosystem assessment of the respective Regional Forest Agreements. In East Gippsland, there were four rainforest EVCs (cool temperate, warm temperate, warm/cool overlap and dry), while in the Central Highlands only cool temperate rainforest was present (CVRFASC 1996, 1997). In addition, gallery rainforest is now recognised and described in Victoria by Peel (1999). Rainforest is protected in these regions in dedicated reserves, special protection zones and through the Code of Forest Practices (DNRE 1996a), which also utilises the CFL (1987) rainforest definition. By contrast, in New South Wales, forest types were defined for forest management on the basis of structural distinctiveness with selected floristic attributes (Baur 1965; Forestry Commission of NSW 1989), and the four rainforest subforms (subtropical, warm temperate, cool temperate, dry) were intuitively divided into 24 types on the basis of the floristics of key commercial species. It was stated, however, that the dry forest subform would probably not be called rainforest in a worldwide classification (Forestry Commission of NSW 1989), presumably because of the discontinuous or absent upper canopy containing deciduous or xerophytic species. Studies in the Northern Territory by Russell-Smith (1991) and Bowman et al. (1991) defined a broad working definition of rainforest as not being dominated by Eucalyptus, Melaleuca or mangrove species (Bowman 1992) although many of the monsoon types recognised by Russell-Smith (1991) included species of Melaleuca, Acacia and Callitris. Bowman et al. (1991) described these forests as monsoon forests with floristic affinities to humid rainforests. They occur as small patches scattered throughout the north-west Australian eucalyptdominated savannah and form a floristic and structural continuum along a moisture gradient (Bowman et al. 1991; Russell-Smith 1991; Bowman 1992). Russell-Smith referred


to Schimper’s (1903) definition of monsoon forest, i.e. a ‘climatic formation which is more or less leafless during the dry season, especially toward its termination, is tropophilous in character, usually less lofty than the rainforest, rich in woody lianas, rich in herbaceous, but poor in woody epiphytes.’ Russell-Smith indicated the relevance of the definition in Australia to rainforest vegetation occurring in tropical regions, although it should be applied independent of leaf-fall phenomena. Transects across the savannah monsoon forest boundary indicate a lack of fidelity in many tree species; however, there are significant differences in the abundance of tree species in the savannah and rainforest (Bowman 1992). Defining rainforest species The term ‘hygrophilous’ is often applied in rainforest definitions. It has a range of meanings in dictionaries of biological terms: ‘growing in or preferring moist habitats’ (Allanby 1994); living ‘in damp environments with either free water or high humidity’ (Meagher 1991); or thriving ‘in plentiful moisture but is not aquatic’ (Lawrence 1989). Since sclerophyllous and drought-adapted plants also require high humidity and plentiful moisture at least for short periods for successful seedling establishment, this term has not been used in this paper to describe rainforest species. The image portrayed of rainforest plants is of tall trees with broad, soft, luxuriant leaves. Schimper (1903) introduced the term ‘sclerophylly’ to the ecological literature, and Diels (1906) was the first to use it in Australia to describe the vegetation of south-west Western Australia. Its use and definition in Australia has changed significantly over time (Seddon 1974), so that now its meaning is unclear and imprecise. Species such as Araucaria cunninghamii exhibit sclerophyllous characteristics, yet function as, and are generally regarded as, rainforest species. Callitris intratropica is an emergent above a closed rainforest canopy in some rarely burnt areas in northern Cape York Peninsula (Neldner and Clarkson, in press); however, it requires major disturbance to enable regeneration at these sites, and hence is not a rainforest species. Allosyncarpia ternata is regarded as a rainforest species dominating an anomalous type of rainforest in the Northern Territory, even though A. ternata is a Myrtaceous tree and exhibits many sclerophyllous characteristics (Russell-Smith 1991; Bowman 1992). Similarly, a shrubland dominated by Acacia shirleyi has also been recognised in the Northern Territory as an anomalous evergreen, sclerophyll rainforest type (Russell-Smith 1991; Bowman 1992). The sclerophyllous nature of some rainforest leaves is discussed by Webb (1978), and sclerophyllous leaves were regarded as characteristic of many tropical rainforests (Richards 1996). Hence, the adoption of sclerophyllous or xeromorphic characteristics is not a consistent attribute on which to distinguish rainforest species. The definition of a rainforest species is based on the species’ ability to regenerate (either vegetatively or from

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seed) under an undisturbed canopy or in areas of localised disturbances which are part of the natural rainforest ecosystem (e.g. windthrow, flooding). This definition was proposed by Jarman and Brown (1983), extending the implied definition of Webb and Tracey (1981b) that rainforest species can regenerate under a well-developed or slightly disturbed canopy. The essential meaning of the Jarman and Brown definition has been used in many of the other definitions (e.g. Cameron 1992; Peel 1999). The type of regeneration at a particular site depends on the size of the canopy gap and the extent of exposure of mineral soil, i.e. the size and intensity of disturbance. Small gaps, caused by the collapse of old trees or local windthrows, are rapidly filled by expansion of existing crowns of adjacent trees or by the growth of suppressed trees. Larger gaps from lightning strikes or violent storms provide suitable conditions for the establishment and growth of early secondary and at least some pioneer species (McDonald 1996). Localised disturbance should be considered an integral part of the rainforest environment and a strong influence on species diversity (Webb and Tracey 1981b). Primary subtropical and tropical rainforests thus comprise mosaics of regenerating units, termed microseres (Hopkins 1981), resulting from continual production of gaps of varying sizes by natural disturbances. The structural and floristic composition of these forests is therefore as much determined by their disturbance regimes as by variations in climate, soil and topography (McDonald 1996). Regeneration in the relatively species-poor temperate rainforests involves fewer groups of species and fewer phases than that of complex rainforests (Read and Hill 1985). The dominant angiosperms in the southern rainforests are capable of continuous regeneration with self-replacement, as are the Tasmanian coniferous dominants in open situations. In mature closed forests, however, these conifers require major disturbance for establishment and recruitment (Busby and Brown 1994). Many rainforest species have the ability to regenerate after fire: Nothofagus cunninghamii can regenerate after moderate fire from lignotuberous burls (Ashton 1981); Acmena smithii develops a lignotuber and the bark protects vegetative buds from low-intensity fires (Adam 1992); and a large proportion of the flora of the Northern Territory rainforest is capable of vegetative reproduction after fire (Russell-Smith and Dunlop 1987). In northern Queensland, Stocker (1981) recorded 74 species coppicing from stumps and 10 producing root suckers in an area of complex notophyll vine forest (CNVF) that had been felled and burnt. In a severely storm-damaged CNVF in southern Queensland, Olsen and Lamb (1988) reported vegetative regrowth in 35 of the original 44 tree species. Similarly, Unwin et al. (1988b) recorded widespread regrowth in lowland tropical rainforest trees in northern Queensland 40 days after severe cyclonic damage. A survey of rainforests in Tasmania after two major fires found that most vascular species regenerated but that sclero-

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phyll species tended to dominate (Barker 1991). The large component of sclerophyllous species in recently burnt rainforest also caused the vegetation to be more pyrogenic than mature rainforest (Barker 1991). The frequency of fire and the actual intensity of individual fire events are both important in determining the long-term survival of rainforest taxa. Some species that occur in rainforest may also occur typically in fire-prone vegetation, including Leptospermum lanigerum, L. scoparium, L. nitidum, Melaleuca squarrosa and Acacia melanoxylon. Leptospermum lanigerum was listed as a rainforest species by Gilbert (1970–71), and Jarman and Brown (1983) suggest that it, and L. nitidum and M. squarrosa, may regenerate in canopy gaps in implicate rainforest on infertile substrates. Leptospermum grandiflorum has been reported in Victorian rainforests (Howard 1981). Acacia melanoxylon has been listed as a rainforest constituent in New South Wales and Victoria (Francis 1951; Howard and Ashton 1973). In Tasmania, A. melanoxylon may regenerate in canopy gaps in rainforest (Pannell 1992). Jarman and Brown (1983), however, suggest that there is only a narrow spatial overlap in distribution for species occurring in rainforest and in other communities in Tasmania. Generally, rainforest species do not require catastrophic fire or major disturbance to regenerate successfully. This definition therefore excludes most species of Eucalyptus, Allocasuarina, Casuarina and Melaleuca, all species of Callitris except C. macleyana and most Acacia and Lophostemon species. It can be argued, however, that some species of Acacia and L. confertus may function as rainforest species in some situations and not in others. Lophostemon confertus may occur as a canopy dominant over a rainforest understorey in New South Wales. This species can regenerate from seed after fire, but can also persist under conditions of low light and colonise landslip areas (Floyd 1990). Floyd considered this species to be a rainforest species on steep slopes but a non-rainforest tree in fire-prone situations. Acacia melanoxylon also has been included as an important rainforest tree in New South Wales and Victoria (Francis 1951), but is considered as a seral species by Howard (1981). Acacia melanoxylon is a rainforest species (can regenerate successfully and persist at the site) in situations such as riverine rainforests and swamps, where the flooding disturbance is a natural and frequent part of the ecosystem. However, in situations of catastrophic disturbance, e.g. landslides, A. melanoxylon is a transient species that occurs for one generation after the disturbance but does not persist at the site unless there is continued disturbance. In the wet tropics of Queensland, A. aulacocarpa, A. cincinnata, A. mangium and possibly Corymbia torelliana may behave as rainforest species in some situations. Welchidendron longivalve is a widespread canopy tree in the monsoon rainforest of Cape York Peninsula, but also occurs as a scattered subcanopy tree in eucalypt woodlands (Neldner and Clarkson, in press). The status of some species, for example A. melanoxylon, in rainforest is therefore unclear, because they also occur in more sclerophyllous vegetation. These species may be regarded as true rainforest species, early seral stage species, or oppor-


tunistic mobile species that are able to exploit recurring local disturbances in the rainforest (Jarman and Brown 1983). Communities related to rainforest Mangroves While some authors have treated mangrove communities as a special form of tropical rainforest (e.g. Whitmore 1984; Adam 1992), they have traditionally been treated as separate communities in Australia. Despite sharing many families with rainforests, mangroves are characterised by their special adaptations to the intertidal environment, including morphological adaptations such as pneumatophores in Avicennia, knee roots in Bruguiera and stilt roots in Rhizophora, and physiological adaptations to the saline conditions. Mangrove communities are generally species poor, frequently being dominated by only one or two species. The total Australian mangrove flora consists of only 40 species (Adam 1992). While epiphytic orchids and ant plants are present in northern Queensland mangroves, lianes, mosses and ferns (life-forms prominent in most rainforests) are generally rare. In the public perception as well as for research and management, the mangroves are more closely associated with wetlands and fisheries management. Mixed forests — are they rainforests? In general, rainforest boundaries in northern Australia are sharp, while further south there are extensive communities with closed canopies of rainforest species below tall eucalypts (Ash 1988; Cameron 1992). Extensive areas of mixed forest occur in Tasmania (nearly 200 000 ha or 20% of Tasmanian wet forests, Hickey and Savva 1992) with substantial areas in the Central Highlands of Victoria, significant areas on the Errinundra Plateau in East Gippsland (470 ha, Radic et al. 1985), and other large areas in New South Wales and Queensland. The term mixed forests was first used by Gilbert (1959) for Tasmanian cool temperate rainforest–sclerophyll (eucalypt) forest. On an ecological basis, mixed forests with a species composition characteristic of a recognised rainforest community, but including sclerophyllous emergents or dominants, may be representative of a seral community transitional to rainforest. Without further catastrophic disturbance (e.g. intense fire, cyclone, landslip), the non-rainforest elements progressively die out (this process may take 100–350 years), leaving behind a mature rainforest (Gilbert 1959; Jackson 1968; Mount 1979). The mixed forests of Victoria are generally regarded as being successional to rainforest in the absence of fire, with rainforest being the climatic equilibrium vegetation type on most high-rainfall sites (Read 1992). The formerly extensive mixed forests of the Errinundra Plateau in East Gippsland could be regarded as ecologically seral rather than ecotonal, given their extensiveness and lack of rapid variation on an environmental gradient (Cameron 1992). However, some Victorian mixed-forest communities were suggested by


Cameron (1992) to represent a disclimax resulting from a history of repeated disturbance by wildfire and, therefore, to be in dynamic equilibrium with a contemporary environment of recurrent disturbance. Most Victorian Nothofagus forests were found by Howard (1973 in Read 1992) to be structurally immature and lack the reverse-J size-class structure indicative of continuous regeneration in Tasmanian rainforests. Howard ascribed the difference to higher fire frequency in Victoria. Since the mid-Tertiary, rainforest extent in Australia has contracted markedly (Martin 1990; Kershaw 1992). Research based on the pollen record has shown that the distribution of rainforest has increased and decreased dramatically in the past 200 000 years (e.g. Kershaw (1985) in northern Queensland). Vegetation boundaries are dynamic and will continue to move in the landscape under the influence of long-term climatic and short-term disturbance effects. The perception of mixed forests is dependent on the timeframe taken. A static timeframe would tend to place such communities as a distinct vegetation type, whereas a longterm timeframe would consider the vegetation type against its presumed ecological processes and successional regime. Taking a long-term view, if the vegetation was expected to develop into rainforest proper in the absence of major disturbance, then it could be recognised as a transitional stage to a rainforest-climax community. This could be extended to the absurd lengths that some buttongrass moorlands in western Tasmania could be regarded in the long-term as potential or seral rainforest (Brown 1992; Kirkpatrick 1992) in the same way that post-fire regeneration of Victorian cool temperate rainforest and sclerophyll forest may pass rapidly through closed herbland, heathland, closed heathland, scrub, lowforest or closed-forest stages (Cameron 1992). For long-term conservation, preservation of communities in all transitional stages, including related disclimax communities, is desirable to maintain ecological and evolutionary processes for all dependent biota. The geographic position of these transitional stages will move across the landscape over time. In many areas, community boundaries are stable and in balance with the prevailing environmental and disturbance regimes, whereas in other areas there are rapid changes in community structure and floristics. Those communities that are adversely affected by the current disturbance regime should constitute a higher conservation priority, given the likelihood of them becoming increasingly fragmented and disturbed and taking into account their low rates of migration. Floyd (1990) described six forest types that form a continuous gradation from a rainforest to a eucalypt-dominated forest: (1) canopy composed exclusively of rainforest trees; (2) canopy of rainforest species with large, scattered, emergent Eucalyptus or Lophostemon; (3) overstorey of large Eucalyptus or Lophostemon overtopping a closed canopy of well-developed rainforest species; (4) canopy of entirely Eucalyptus or Lophostemon above a subcanopy of rainforest species expected to replace the upper canopy in the absence of fire;

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(5) canopy of Eucalyptus or Lophostemon above a subcanopy of rainforest species not expected to replace the upper canopy because of unfavourable conditions including exposure and seasonally low moisture levels; and (6) canopy composed entirely of Eucalyptus with no rainforest species in the understorey. While Floyd acknowledged that forests should be classified according to the direction in which they were developing, he predicted that ecologists and environmentalists would classify (1), (2) and (3) as rainforest with (4) as transitional to rainforest, but that foresters and sawmillers would define (1) as rainforest but (2), (3) and (4) as sclerophyll forest under a logging regime that would favour regeneration of Eucalyptus and Lophostemon. Difficulties with these species being considered rainforest species also relate to the capability of both to regenerate after fire (Floyd 1990). The delimitation of rainforest and mixed forests from sclerophyll forests has caused major conflict between forestry and conservation groups. A policy for these mixed forests could take one of three options. These mixed-forest communities could be considered to be: (1) non-rainforest; (2) communities transitional to rainforest; or (3) distinctive vegetation types/communities. (1) Mixed forests as non-rainforest In many previous studies, mixed forests have been regarded as mixtures of rainforest and sclerophyll forest elements and excluded from the definition of rainforest (e.g. Francis 1951; Gilbert 1959; Webb 1959; Webb and Tracey 1981a). Jarman and Brown (1983) state that lowland mixed forests in Tasmania may be equally considered as mature eucalypt forest or as immature rainforest. In production forests, mixed forests are regarded as having a lower economic value than managed eucalypt forest because of the slower growth rate of eucalypts in mixed forests as they approach the overmature to senescent stages. However, the value is increasing for speciality rainforest timbers, which are unobtainable from pure rainforest owing to explicit prescriptions preventing logging (Busby and Brown 1994). Eucalypt emergents are typically used to identify ecotonal or seral characteristics. This policy approach has prevented forests with ecotonal or seral characteristics from being classified as rainforest, despite their exhibition of many of the characteristics of more typical rainforest communities. (2) Mixed forests as communities transitional to rainforest In the definition of Dale et al. (1980), all transitional and seral communities with a similar floristic composition to mature rainforest are classed as rainforest. Structural attributes have also been used to divide mixed forests into rainforest and non-rainforest. Arbitrary threshold values have been used for the crown cover of sclerophyll elements present in the canopy and below which the community is

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classed as rainforest. A major point of contention has been the quantification of an acceptable proportion of sclerophyll species, particularly eucalypts, in the canopy. Mixed forests have been classified as rainforest when the cover of eucalypts is less than 40% in New South Wales (Floyd 1990), between 10 and 50% in Victoria (CNR 1995a), and as low as 5% (AFC 1975) and 10% (Kirkpatrick and Dickinson 1984) in Tasmania (Hickey et al. 1993). Clearly, there has been no consistency in the thresholds applied. Importantly, even if there was agreement on the threshold, the accurate measurement of crown cover in the field is very difficult and time consuming, particularly in mixed forests. Rather than adopting arbitrary percentages of non-rainforest canopy emergents to distinguish between rainforest and mixed forest, the Commonwealth (COA 1997) definition recognises mixed-forest communities as transitional to rainforest, with the latter stages of these mixed forests (as evidenced by the older growth stages of non-rainforest emergent tree species) having a high probability of developing a canopy composed entirely of rainforest species in the next phase of forest succession within the next 50–100 years. (3) Mixed forests as distinctive vegetation types Rainforest occurs in a variety of successional stages (Webb 1986; Cameron 1992); however, mixed forests are generally recognised as mature rainforest only where the floristics are essentially the same. The presence of occasional remnant sclerophyll emergents in secondary rainforest does not alter its status as mature (Webb 1992). Similarly, Cameron (1992) distinguished transitional (ecotonal), seral and disclimax rainforest vegetation but considered mixed forest as primary or mature rainforest where the sclerophyll overstorey is emergent, not continuous. The recognition of mixed forests as distinct vegetation types allows maximum flexibility in their management. The management of mixed forests can be addressed regionally, taking into consideration the rarity of the rainforest and mixed-forest communities, the relative extent of clearing and/or disturbance, and their vulnerability to disturbance (both short-term, e.g. fire, and long-term, e.g. climate change). Mixed forests have been mapped as separate vegetation map units in some areas. For example, vine forests with emergent Acacia species (Tracey 1982, types 12a–d) and combinations of Eucalyptus and Acacia species (Tracey 1982, types 13a–e) have been mapped in the wet tropics area of northern Queensland by Tracey (1982), and on Cape York Peninsula by Neldner and Clarkson (in press) (units 26 and 27). Other mapped mixed forests in northern Queensland include vine forests with Syncarpia glomulifera emergents (Tracey 1982, types 13e and f) and Callitris intratropica (Neldner and Clarkson, in press, unit 25). At the drier extent of rainforest, mixed forests of softwood species overtopped by Acacia harpophylla emergents have been mapped in


south-central Queensland (Neldner 1984, unit 7). By delineating mixed forests as separate communities, their spatial extent and relationship to pure rainforest communities are clearly illustrated. This can greatly assist in planning appropriate management for specific locations. The mixed forests units can be subdivided at a later stage if the rainforest definition or policy is changed. In some regions, such as Victoria, rainforest is rare and vulnerable to fire, and hence it is important to reserve some of the mixed forests to ensure persistence of rainforest in the long term, and also of mixed forest as an entity in itself. Cameron (1992) states that rainforest conservation in Victoria is largely dependent on the successful protection of the rainforest ecotone and its sclerophyll forest buffer from disturbance by fire. This is also the case in heavily fragmented landscapes such as coastal Queensland and New South Wales, where large areas of undisturbed rainforest no longer exist. Webb and Tracey (1994) state that certain plant species are restricted to ecotones (mixed forests), for example, Endiandra floydii (W. J. F. McDonald, pers. comm.), and hence these deserve consideration as ecological entities in their own right. Burgman and Ferguson (1995) suggest that mixed forest be classified separately from other forest types in Victoria and that management procedures be implemented to ensure the preservation of all forest values within it. Mixed forest is now recognised as a distinct Ecological Vegetation Class in Victoria by the Department of Natural Resources and Environment. The Forest Management Plan for the East Gippsland Forest Management Area (CNR 1995b) states that prescriptions will be developed to ensure that at least 90% of the mixed-forest vegetation class is protected. Rainforest is not, however, always vulnerable to disturbance. In parts of northern Queensland, there has been widespread expansion of rainforest into wet eucalypt forests because of less frequent burning than the pre-European Aboriginal fire regime (Unwin 1989). Harrington (1996) states that, since the 1940s, more than 70% of the Eucalyptus grandis and 55% of the E. resinifera open forests in the Wet Tropics Management Area have been invaded by rainforest species. This phenomenon was also reported by Neldner and Clarkson (in press) on Cape York Peninsula. In this region, wet eucalypt forests need interventive management to persist, as rainforest communities have been favoured by the recent actions of humans and are out of equilibrium with the pre-European regime. In this case, mixed forests may need to be burnt to maintain the relatively restricted wet sclerophyll forests. In Tasmania also, mixed forests probably require active management if the full expression of their successional range is to be maintained (Brown et al. 1987). Long logging rotations, i.e. 200 years, are probably required to allow for the perpetuation of mixed forest, as standard rotation lengths of 80–100 years may result in the local elimination of at least some rainforest species (Hickey 1994). Without disturbance, mixed forests may be eventually replaced by rainforest


through the senescence of the eucalypt emergents (Gilbert 1959; Jackson 1968; Mount 1979). Mature rainforest needs no such treatment to persist, and for this reason, mixed forest and wet sclerophyll forest could be regarded as distinct from rainforest (Brown 1992). Proposed options for a national definition of rainforest A nationally applicable rainforest definition must incorporate the structural and environmental parameters applicable across the continent and the biogeographic affinities of the flora. As highlighted in the preceding discussion, there are a number of problems in existing rainforest definitions. This paper attempts to resolve some of these problems, and proposes three definitions of rainforest that could be applied across Australia. The first definition forms the basis for all three definitions, with additional qualifying criteria included in the second and third definitions. Definition 1 Rainforest in Australia is a tree-dominated plant formation, where the tallest tree layer is usually1 closed (with a projective foliage cover of greater than 70%) and greater than 5 m in height. Rainforest also includes tree-dominated plant formations where the tallest tree layer is not closed (projective foliage cover of less than 70%) and the canopy is less than 5 m high, but the tallest trees are rainforest species. (**Additional qualifying criteria for Definitions 2 and 3). Rainforest plant species are adapted to regenerating in the low-light conditions experienced under the closed canopy or in localised gaps caused by recurring disturbances which are part of the natural rainforest ecosystem2, and are not dependent on fire for successful regeneration. The closed-canopy mangrove communities are specially adapted to the intertidal zone, and should be considered a distinct formation. Additional qualifying criteria for Definition 2 **The ecological definition of rainforest includes transitional (ecotonal) and seral (secondary or mixed) communities with a minimal (to be defined — somewhere between 5 and 50%) component of emergent non-rainforest species, where the community is of similar botanical composition to mature rainforests in which non-rainforest species are absent. Additional qualifying criteria for Definition 3 **The ecological definition of rainforest includes the late successional stages of transitional (ecotonal) and seral (secondary or mixed) communities with emergent non-rainforest species in their older growth stages, where the community is of similar botanical composition to mature rainforests in which non-rainforest species are absent.

1

Widely accepted exceptions include the deciduous ‘dry’ and monsoonal rainforests of northern Australia, communities on rocky sites where the canopy is more open, and montane environments in Tasmania. In these types, the canopy is open but dominated by rainforest tree species. 2 These disturbances include windthrow, landslip, flooding, lightning strike and endemic forest diseases.

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It is recognised that localised classifications with a floristic basis will be necessary for application of the definition in regions or states. However, the regional definitions need to be related to a national rainforest definition for consistency across the continent. A key is provided in Fig. 1 to enable rainforest communities to be systematically distinguished. The original application of the term ‘rainforest’ to tropical, evergreen wet forests accorded largely with the biogeographic evolution of most rainforest dominants and many understorey species from the Gondwanan flora about 50 million years before present. This ‘relict’ subelement of the Australian flora includes species of cool, moist semitropical habitats, generally with close relatives in New Zealand, New Caledonia and South America (Nelson 1981). The ‘autochthonous’ subelement and ‘intrusive’ element are also present in rainforests, but to a lesser extent. As a consequence, it is generally accepted that rainforest communities are dense forests, i.e. tree-dominated with a closed canopy. In some regions, rainforest communities grade into other communities, such as montane heaths in Tasmania, and so a canopy height limit of 8 m was nominated by Jarman and Brown (1983) and later reduced to 5 m by Jarman et al. (1991), to distinguish these vegetation types. A canopy height limit of 5 m is used in the definitions proposed in this paper to be consistent with the National Forest Policy Statement (CoA 1992). Some rainforest communities have a more open canopy (projective foliage cover < 70%). These include the deciduous ‘dry’ and monsoon rainforests of northern Australia, communities on rocky sites where the canopy is more open, and the montane rainforests in Tasmania. They also include rainforest where the tallest tree layer is a more open layer of rainforest emergents above a closed canopy, for example, many complex mesophyll rainforests. The structure of many littoral rainforests in northern Australia can vary from sclerophyll heath and scrub through to layered open forest and closed forest, and sclerophyll species are generally present (Webb and Tracey 1994). Another vegetation type that has a similar ecology to ‘typical’ rainforest is the ‘wet gully’ communities in Tasmania dominated by species such as Olearia argophylla, Pomaderris apetala and Notelaea ligustrina (Cullen 1991). These species can also regenerate without disturbance (Kirkpatrick 1989), and were considered by Cullen (1991) to be rainforest species. Wet-gully communities extend to drier regions than do other rainforest types in Tasmania, but are usually confined to moist topographically protected sites or sites with a high degree of fire protection (Cullen 1991). These wet gully rainforests are not encompassed by the rainforest definition of Jarman and Brown (1983), which only includes vegetation dominated by species of Nothofagus, Eucryphia, Atherosperma, Athrotaxis, Lagarostrobos, Phyllocladus or Diselma, because the floristic dominants are not listed as rainforest species. The wetgully rainforests are, however, included in the definition proposed here.

Fig. 1. Key to identify rainforests in Australia.* A tree is defined as a woody plant more than 5 m tall with a single stem or branches well above the base. + Some components of mixed forest are included in rainforest under Definitions 2 and 3. Under Definition 2, forests where the canopy cover of non-rainforest tallest trees is less than a threshold, are included as rainforest. Under Definition 3, forests where the non-rainforest emergents are in their older growth stages are included as rainforest.

524 A. J. J. Lynch and V. J. Neldner


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should be protected, by using various approaches ranging from reservation to prescription management (JANIS 1996). Rainforests are generally regarded as being vulnerable to fire. However, some rainforest species and communities have poorer regenerative capacities than others. The JANIS (1996) paper makes specific reference to Athrotaxis selaginoides rainforest as an example of a vulnerable forest ecosystem, since it is highly susceptible to further destruction by fire and has a limited ability to reinvade burnt areas (Brown 1988; Gill 1996). The perceived vulnerability of a community has important implications for the reservation level required under JANIS (1996) (15% for most communities, > 60% if vulnerable). An example is the extensive lowland rainforests of Tasmania, which have a high sensitivity to fire, poor seed dispersal of many canopy species, and an inability to grow in intervening dry corridors (Read 1992). It could be argued, however, that the extensive areas of contiguous rainforest in western Tasmania, much of which is in conservation reserves, would ensure their long-term persistence. The question of whether the CRA process will provide adequate mechanisms for the reservation of rainforests may be influenced by the high cultural, aesthetic and historical values placed on these communities. The East Gippsland CRA Environment and Heritage Report (CVRFASC 1996) lists three of the four rainforest Ecological Vegetation Classes as either rare or vulnerable, and all four are afforded 100% protection on public land through reservation and code of practice requirements (Table 8). As the mixed forests have not been separately mapped during this process, but can occur within the wet forest, damp forest, and montane damp forest EVCs, it is impossible to determine precisely how well they are reserved. Dry rainforest is considered to be vulnerable (category V2, where threatening processes have caused the following: significant changes in species composition; loss or significant decline in species that play a major role within the ecosystem; or significant alteration to ecosystem processes). The dry rainforests are fire sensitive, and vulnerable to damage from grazing, weed invasion and land clearance (CVRFASC 1996).

The conservation of forest communities — are rainforests a special case? Support for the total protection of rainforest has been put forward by The Australian Rainforest Conservation Society (ARCS 1995) and The Wilderness Society. This approach has been argued on the basis of the antiquity of rainforest, its currently restricted distribution in comparison to its historical coverage, its high species diversity and refugial characteristics, and its vulnerability to disturbance, particularly by fire. The current Comprehensive Regional Assessment (CRA) of forests being conducted in five states of Australia has, as part of its objectives, the establishment of a comprehensive, adequate and representative (CAR) reserve system for all forest communities. As a general criterion, 15% of the pre1750 distribution of all forest communities in Australia should be protected in a CAR conservation system (JANIS 1996). The CRA process endeavours to examine regional biodiversity at the population, species and community/ecosystem level. The principle of comprehensiveness requires the full range of forest communities across the landscape to be adequately (maintaining ecological viability and integrity) reserved (CoA 1992; JANIS 1996). The reserve system designed should be representative, i.e. reasonably reflect the biotic diversity of the communities across their geographic and environmental ranges (CoA 1992; JANIS 1996). These principles are being applied by using biodiversity, old growth and wilderness criteria. Forest ecosystems need to be recognisable in the field, be able to be mapped (at the recommended scale of 1 : 100 000), and be able to have their pre-1750 distribution modelled or mapped (JANIS 1996). Other criteria of flexibility in decision-making on a regional basis, and rarity and vulnerability of species and ecosystems are also being applied. The flexibility criterion is applied on a case-by-case basis and may mean a lower reservation level than 15% for some extensive and relatively uniform ecosystems. For vulnerable ecosystems (reduced to 30% or less of their pre-1750 area, or sensitive to threatening processes), a higher level of reservation is applied (at least 60% of remaining extent). All remaining occurrences of rare or endangered ecosystems

Table 8.

Protection levels and rarity criteria met by rainforest Ecological Vegetation Classes in East Gippsland (CVRFASC 1996)

Ecological Vegetation Class

Percentage of remaining area protected

Criterion

Cool temperate rainforest

62 (additional 38% protected by Code)

Patch sizes generally less than 100 ha

Warm temperate rainforest

57 (additional 41% protected by Code, 2% on private land)

Patch sizes generally less than 100 ha

Warm/cool temperate rainforest overlap Dry rainforest

50.5% (additional 49.5% protected by Code) 100

Total area generally less than 1000 ha (i.e. 11 ha)

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The East Gippsland rainforests are very well conserved. This is not surprising since the East Gippsland Forest Management Plan (CNR 1995b) has an objective of reservation of rainforest and mixed forests. Even without this policy, however, a high reservation target would have been required for the rainforest communities in East Gippsland because of their rarity and vulnerability. Only cool temperate rainforest occurs in the Central Highlands. Almost all (99.9%) of the pre-European extent of this rare ecosystem is still present, with 44% conserved, 55% protected in State Forest and other reserves, and only 0.8% unprotected (CVRFASC 1997). A high proportion (97%) of wet forest also remains relative to its pre-European extent, with 29% reserved and 19% in State Forest Special Protection Zones (CVRFASC 1997). In the Tasmanian CRA, the mixed forests were not mapped separately because of inconsistencies in the foresttype mapping and the impossibility of accurately mapping their pre-European distribution. They were included as the later stage in the successional continuum of the wet-forest units. Representation of the mixed forests was examined within the wet-forest units across regions, and substantial areas of mixed forest were proposed for reservation on the basis of them representing the old-growth stage of the wetforest communities (minimum of 60% of existing old growth area is required under JANIS (1996)). Of the seven rainforest types in the Tasmanian CRA, four were classified as vulnerable, and all were reserved to levels greater than that required under the predetermined reservation criteria (CoATas 1997). Conclusions Three options for a new definition of rainforest in Australia are provided, which endeavour to encompass the full range of the vegetation type occurring in Australia, and are based on the ecological characteristics of rainforest species and some structural and floristic characteristics. A key is provided to facilitate the identification of rainforest and other related vegetation communities. The definitions differ in their treatment of mixed forest. The first definition excludes mixed forest from mature rainforest. The second definition classifies mixed forest with rainforest although a threshold for the component of emergent non-rainforest species has not been specified. The third definition includes the late successional stages of mixed forest with emergent non-rainforest in their older-growth stages as rainforest, where the community is of similar botanical composition to mature rainforests in which non-rainforest species are absent. The core of each of the three definitions is stated in Definition 1, and reflects an unambiguous, clearly applicable and non-arbitrary definition of mature rainforest. The other two definitions are fraught with the difficulties of previous definitions. Inclusion of some mixed forests as rainforest on the basis of the proportion of the cover of sclerophyll species in the canopy has been arbitrary and inconsistent. Thresholds have been determined regionally and have been influenced


by economic or cultural perspectives. Similarly, inclusion of an undefined threshold in terms of growth stages is also arbitrary and ambiguous. Mixed forests are recognised as being transitional or seral to rainforests. They include communities which border rainforest, communities which are successional to rainforest, and disclimax communities in a dynamic equilibrium with a contemporary environment of recurrent disturbance. Such distinctions may not be accessible without detailed site investigations. Many of these communities may in the longterm become rainforests and it cannot be assumed that fire disclimax forests will not reach maturity (Webb 1992). The inclusion of mixed forests strictly within either rainforest or sclerophyll forest does not resolve the debate between many conservationists and forestry agencies over rainforest management. For the purposes of nature conservation and optimal biodiversity, as many different stages as feasible of the total rainforest development series should be conserved within a region (Webb 1992). Therefore, the recognition of mixed forest as a distinctive vegetation type, as mapped in areas of Queensland, facilitates this management objective and shifts the debate to one explicitly of degree of management of mixed forest. This distinction allows maximum flexibility in managing mixed forests while enabling a consistent approach to management of rainforest. The current Comprehensive Regional Assessment of Australian forests aims to conserve the full range of forest communities across the landscape. The procedures for assessing the conservation criteria established through the CRA process should ensure that the long-term conservation needs of rainforest are adequately covered. The CRA process should also address the conservation of mixed forests as well as possible given their current standard of data and mapping. Further work on defining and mapping a variety of growth stages of these communities may, however, be an appropriate direction for future resources and may further improve their likelihood of long-term viability. Acknowledgments The authors acknowledge the constructive comments on various drafts of this manuscript and provision of additional information by colleagues at Environment Australia: Sean Cadman, Jane Coram, Bruce Cummings, Geoff Dyne and Andrew Taplin; and at the Queensland Herbarium: Trevor Clifford, Rod Fensham, Laurie Jessup and Bill McDonald. References Adam P (1992) ‘Australian rainforests.’ (Clarendon Press: Oxford) AFC (Australian Forestry Council) (1975) FORWOOD. Report of the Forestry and Wood-based Industries Development Conference, 1974. (Australian Government Publishing Service: Canberra) AHC (Australian Heritage Commission) (1986) ‘Tropical rainforests of north Queensland — their conservation significance.’ (Australian Government Publishing Service: Canberra) Allanby M (Ed.) (1994) ‘The concise Oxford dictionary of ecology.’ (Oxford University Press: Oxford)


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Manuscript received 12 March 1997, accepted 26 August 1998

Appendix Vegetation classification units (from Fosberg 1967) Units of vegetation can be classified at differing levels of rank. A combination of features of structure (the arrangement in space of the components of vegetation, e.g. life-form, stratification and spacing, leaf characters) and function (features that suggest special adaptation to present or past environmental situations, e.g. protective mechanisms, means of resistance to fire, xeromorphy) can be used for maximum objectivity, suitability for comparative analysis and simplicity. Lowest level units must necessarily be floristic; however, floristic criteria do not permit broad enough correlations at higher levels. The primary basis for division can be the spacing of the visible portions of the vegetation to form three primary structural groups of closed vegetation, open vegetation and sparse vegetation or desert. The next level, of formation class, is based on habit and stature, i.e. the structural components of height and life-form, and may contain formation subclasses (e.g. UNESCO 1973). The next lowest level, formation group, is

characterised by the nature of the dominant layer, i.e. whether it is evergreen, deciduous or visibly seasonally dormant. The formation rank is based on the physiognomy of the dominant growth form, with emphasis on leaf texture and features such as thorniness, succulence and graminoid habit. Subformations are a further subdivision made by using similar characters to formations. The basis of classifications varies between vegetation typologists, as indicated in the two examples. While Carnahan (1976) defined vegetation types in terms of physiognomy and floristics, Sochava and Lukicheva (1964 in Carnahan 1981) defined their mapping units of formations or formation groups by using physiognomy, floristics, ecology and geography. The UNESCO (1973) system is primarily physiognomic with some environmental features; however, Carnahan (1981) suggests that the system is not very appropriate for Australian vegetation because of the dominance of a few distinctively Australian genera, i.e. Eucalyptus, Acacia and Triodia.

Classification unit

Example 1 (Fosberg 1967)

Example 2 (UNESCO 1973)

Primary structural group Formation class Formation subclass Formation group Formation Subformation

Closed vegetation Forest — Deciduous forest Dry season deciduous forest — e.g. most monsoon forests

— Closed forest Mainly deciduous forest Temperate and subpolar evergreen needle-leaved forest Evergreen forest with rounded crowns With evergreen sclerophyllous understorey

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