Biodiversity in Australian Forest Ecosystems

John W. Turnbull

Abstract

Australia is one of the most biologically diverse countries in the world and the conservation of biodiversity is one of the greatest challenges facing its natural resource managers.

Since European settlement in 1788 approximately half of Australia's forests have been cleared for agricultural or urban development or severely modified. There are currently about 34 million hectares classified as forest. Forest biodiversity is still being eroded by land clearing and by some inappropriate forest management practices. These practices lead to forest fragmentation and habitat modification which impact negatively on plants and animals. Areas of `dieback' in some highly disturbed eucalypt ecosystems are evidence of such effects.

Since the 1960s there has been increasing community pressure to broaden the focus of management of forests from wood production to integrated management for wood production and conservation. The public attitude reflects concern for the ecological values of forests, including biodiversity. The challenge and goal of much of the research in progress is to develop management practices which combine maintenance of high levels of biodiversity in wood production forests. Plantations and conservation reserves are considered as complementary strategies to optimize wood production and biodiversity conservation. Major efforts are in progress to modify forest policies and practices and to develop conservation strategies to better maintain biological diversity in forests. An example of changes in forest management following research is given from the State of Victoria. The extent to which the new practices are fully adopted and implemented and monitored will determine their contribution to the conservation of forest biodiversity.

Keywords: Biodiversity, Australian forests, forest conservation.

Introduction

Australia is one of the most biologically diverse countries in the world and the conservation of biodiversity is one of the greatest challenges facing its natural resource managers. As in many other parts of the world, the forestry profession has always considered itself to be an up holder of forests values and supportive of actions to manage forests on a sustainable basis. Yet there is a public perception that foresters are driven by a desire to satisfy the wood demands of a timber industry that has little regard for long-term conservation of the environment. For some years now the forestry profession in Australia has been under siege and forest management and related land use decisions are surrounded by controversy, conflict, confusion and confrontation (Squire 1993, Vanclay 1993).

At the United Nations Conference on Environment and Development (UNCED) in Rio de Janeiro in June 1992 Australia signed the international convention on Biological Diversity. This obligation is supported by a National Forest Policy Statement (Commonwealth of Australia 1992). It commits Australia to a policy of sustainable forest management on both public and private lands. It remains a point of some controversy whether the use of native forests for wood production can be made compatible with the conservation of biodiversity in the forests.

There are many definitions of the concept of biodiversity and some these have been reviewed by Boyle (1994). Australia's National Forest Policy Statement defines biological diversity as "a concept encompassing the diversity of indigenous species and communities occurring in a given region, it includes `genetic diversity', which reflects the diversity within each species; `species diversity', which is the variety of species; and `ecosystem diversity', which is the diversity of different communities formed by living organisms and the relations between them. Conservation of biodiversity involves a regional approach to land management and strives to maintain natural processes and evolutionary potential across the natural ranges of flora and fauna (Scotts 1994).

This paper provides an overview of biodiversity in Australia forest ecosystems, the evolutionary forces that have shaped it and the impact of human settlement on it. Policy changes affecting forests, and development of more appropriate forest management practices to conserve biodiversity are described.

Biodiversity in Australian Biota

The unusual characteristics and biogeographic affinities of Australia's biota are the result of the interplay of tectonic movement, climatic change and biotic dispersal (Cox and Moore 1993). Australia is an ancient land mass which has been isolated for some 60 million years since it separated from the southern super-continent of Gondwanaland and began its drift northwards. During this long period of isolation great changes occurred in the climate and soils which were important in the evolution of the modern fauna and flora. The outcome has been a distinctive flora and fauna with many unique features and a very high level of endemism.

As the Australian continent became drier in the mid-Miocene (15M years BP) grassland expanded and favoured marsupials which were present in greater numbers than in the modern fauna. Pressure from the marsupial browsers perhaps contributed to the evolution of high levels of protective toxic biochemicals in present shrubs and trees. The kangaroos and wallabies are the most diverse of these grazers but the primitive Gondwanic stocks of marsupials radiated into a great variety of forms. Marsupial equivalents of rats, mice, squirrels, anteaters, rabbits, cats and bears all have a superficial resemblance to their placental counterparts and occupy similar ecological niches (Cox and Moore 1993). Eisenberg (1981) has noted that 20% of Australian mammalian genera are arboreal and suggests that this high percentage compared to the limited area of forest may be due to a much extensive tree cover in the distant past. Currently among the land vertebrates there are 686 endemic species including 89% of marsupials, 70% of birds and 88% of reptiles (Common and Norton 1992). Much of Australia's biota remain undescribed, especially the invertebrates. Despite this, invertebrates constitute 95% of known species of fauna (York 1994) and arthropods may represent 70% of forest biodiversity (Recher et al. 1994).

The most significant events shaping the evolution of Australian flora took place during the Tertiary period (3-65 million years ago) and the Quaternary period (present to 3 million years ago). During the early Tertiary it is
probable that Australia was uniformly humid with a warm seasonally-wet climate, a set of conditions that favoured the development of lateritic soils which still persist in tropical areas and in the arid zone. Laterisation reduced an already-low soil fertility level by progressively fixing phosphorus in insoluble iron and aluminium complexes. Weathered laterites added to poor sandy soils derived from sandstones and granite. Beadle (1966, 1981) suggests that such soil changes directed the primary evolution of the Australian flora and many elements of the modern flora have adaptations enabling them to survive and grow on very infertile soils.

Fossil evidence indicates mesophytic communities dominated by temperate rainforest covered much of Australia in the early Tertiary. Increased aridity and greater climatic variability fragmented the temperate rainforests and these formations became generally restricted to moister enclaves in eastern and southern Australia. The modern flora therefore is primarily Gondwanic in origin. It comprises a relatively stable relict group taxa confined mainly to rainforests and comparable to species on other southern continents and another group which is derived from these rainforest elements. This group has undergone rapid evolutionary change from rainforest types towards scleromorphy from intense competition on the highly weathered and nutrient deficient soils of the ancient land surface (Barlow 1981). As a consequence, adaptive traits facilitating survival and reproduction under various natural environmental stresses have been acquired. The derived element includes the genera Acacia and Eucalyptus which dominate many communities outside the rainforest.

This evolutionary development resulted in a distinctive Australian flora, with many genera endemic to the region and areas of great species diversity in the southeast and extreme southwest of the continent. About one-third of the seed-bearing plant genera (566 genera out of 1700) are endemic (Boland et al. 1984). At a higher taxonomic level, almost all angiosperm families in Australia occur widely in other parts of the world. In this sense, the Australian flora is a typical segment of the world flora and the special character of Australian plants has to be explained in terms of the geography and environment in which they have evolved
(Barlow 1981).

Human Impact on Forest Biodiversity

Consideration of the biodiversity of Australian forests at the landscape level cannot be made without reference to the impact of the actions of Aborigines and Europeans that have modified the extent and composition of the resource. The Aborigines began to move into Australia at least 50,000 years ago and it is claimed
(eg. Singh et al. 1981) that their use of fire for hunting and other purposes contributed to vegetation changes. Pollen analysis suggests the more fire sensitive trees, such as casuarinas, have been partially replaced by the more resistant eucalypts during the past 100,000 years. However, compared to the impact of Europeans over 200 years the Aboriginal impact must be considered insignificant.

Since European settlement in 1788 approximately half of Australia's forests have been cleared or severely modified. There are currently about 34 million hectares classified as forest (RAC 1992). In the late nineteenth century and early twentieth centuries deforestation was rapid. Forests were viewed as a hindrance to settlement and their agricultural possibilities were viewed with great optimism (Vanclay 1993). Rapid expansion of the wheat, sheep and dairy industries in the south and sugarcane cultivation in the north resulted in massive clearing. Rates of deforestation are still high in many areas. The current annual national rate is
0.2-0.3% (RAC 1992). Patterns of clearing have not been consistent across forest ecosystems with greater clearing on accessible lowlands and on the more fertile soils, so there has been uneven impact on different forest types and their biodiversity. For example, the coastal lowland eucalypt forest from Sydney to southern Queensland has been heavily cleared and is poorly represented in reserves (Resource Assessment Commission, RAC, 1992). The combined southeastern dry eucalypt forest, the central coast eucalypt forest and northeastern eucalypt forests occupy 12.5 million ha of which only a little over 10 percent occurs in conservation reserves (Norton and May 1994).

Estimates of the forest cover remaining in Australia are relatively inaccurate. Those given in Table 1 are based primarily on data from RAC (1992).

The extent to which the forests have been modified by logging, fire management or other activities is unknown but an estimated 16.25 million ha of unlogged forest and woodland exists (RAC 1992). In 1991 about 8.8 million ha of public forests were in conservation reserves of which about half had not been logged (RAC 1991). Of the remaining forest area there is over 11 million ha of privately owned forest subject to little management control.

Table 1. Estimated area of major native forest types in Australia.

Species Diversity

There are over 15,000 vascular plant species in Australia (Common and Norton 1992) and about 2500 of these are trees. Of these about half are rainforest species. Mangroves, one of the many rainforest formations, are extensive and rich in species by world standards. There are over 500 species of Eucalyptus and about 900 species of Acacia in the sclerophyllous forests and woodlands. Conversely, conifers, with less than 40 species, are relatively poorly represented in the flora. They include a few genera with species commercially important for forestry such as Araucaria and Callitris.

At the species level there are many taxa of plants with very restricted natural occurrences which have an uncertain future (Specht et al. 1974) for example, although no eucalypt species has become extinct due to human intervention, natural populations of 57 species were found to include so few individuals that they are threatened with extinction within 10-50 years if current land use and other causal factors continue to operate (Briggs and Leigh 1988).

While some mammals, birds and at least one reptile have become extinct in Australia (Recher and Lim 1990), there is no evidence that any animal species has yet become extinct due to forest management practices. Nevertheless, recent wildlife research has shown a decline in many forest dependent species and the potential for extinctions at local, regional and national scales if current logging regimes continue (Scotts 1994). Loss of habitat due to the clearing of forests for agriculture and changes in the quality of habitat as a result of harvesting of old growth forests and their replacement by regrowth managed on short rotations are impacting adversely on forest fauna (Recher et al. 1987).

Habitat fragmentation can have serious disruptive effects on forest ecology. It makes for easier access by exotic predators such as feral cats, dingoes and foxes, which can impact negatively on native fauna (May 1994), and it may affect bird occurrences (Loyn 1987) and insect dynamics (Landsberg et al. 1990). The consequences of habitat fragmentation and modification may not become obvious until there is ecosystem breakdown and extinctions occur. Species and groups of fauna particularly sensitive to such disturbance include forest owls, Yellow-bellied Glider, Glossy Black Cockatoo and certain forest bats (Scotts 1994).

Most assessments of species at risk in forests have been focused on the larger animals and the impact of forest management practices and logging on reptiles, amphibians and invertebrates is not well-documented (Lunney 1991). Any negative effects on invertebrates are likely to influence decomposition and nutrient cycling, and disrupt food chains and host-predator patterns. Recher et al. (1994) suggest that such changes are already evident in some highly disturbed eucalypt ecosystems.

It seems unlikely that it will be possible to deal with conservation of biodiversity on a species by species basis. The very nature of biodiversity suggests policies and practices must be developed based on holistic, ecosystem level perspectives. However a case can be made for special measures to protect species known to be already rare or endangered.

Genetic Diversity

Expansions and contractions of communities in response to climatic fluctuations have left disjunct, relict species and populations amongst the present vegetation associations. Many of the species in the modern flora have experienced a variety of environmental conditions and clearly have needed a wide ecological amplitude to survive. The gene pools must have undergone considerable sorting and selection during these perturbations leading to the evolution of new species and a high overall genetic variability in the more-widespread species.

It is inevitable that clearance of forests will have resulted in some loss of genetic diversity in forest plants and animals. There is also potential contamination of natural gene pools through seeding of cutover eucalypt forests with seed brought in from other localities (Pederick 1976) and outbreaks of eucalypt `dieback' diseases have killed susceptible species in a wide range of habitats (Eldridge et al. 1993).

The extent and implications of loss of genetic diversity remains obscure. It is generally considered that a high level of genetic variation may provide a buffer against extinction, although a single catastrophe can eliminate a population irrespective of its genetic make up. The size of a population needed to minimize the probability of extinction while retaining substantial variability in natural populations is the subject of considerable debate. Tree breeders generally accept that while the majority of genetic information in a species can be represented byrelatively few trees, quite large populations are required to protect the total gene pool. The question of how many trees provide a representative sample of the gene pool and how they are spatially distributed is a key issue for devising appropriate conservation strategies. In Australia, where there are so many tree species, research has been directed at developing general strategies for in-situ conservation of genetic resources.

There are many ways to evaluate genetic variation but the genetic structure of populations of Australian trees and their breeding systems were little known until the application of allozyme markers began in the late 1970s (eg. Brown et al. 1975). Since then isozyme studies have been used to determine the distribution and levels of genetic diversity within and between populations of species of Eucalyptus (Moran and Hopper 1987, Prober et al. 1990), Acacia (Moran et al. 1989 b), Casuarina (Moran et al. 1989 a) and Grevillea (Harwood et al. 1992). Fewer studies have been made in rainforest species (eg. Moran et al. 1990, Shapcott 1993).

Diversity data from a number of the Australian tree studies were reviewed by Moran (1992). He concluded that tree species in Australia generally have high levels of allozyme variation compared to other organisms. Species with extensive geographic distributions have the highest levels of variation. Most of the genetic variation is within populations but species with disjunct occurrences have greater genetic variation between populations (Moran and Hopper 1987). However, relatively low levels of variation were found in Acacia mangium (Moran et al. 1989 b) possibly due to the species being reduced to small refugia during the Pleistocene by sea level changes, in the A. holosericea complex (Moran 1992) where outcrossing may not be the primary breeding system, and in Lagarostrobus franklinii (Shapcott and Harris 1994) possibly due to small founder populations.

The optimal procedure to conserve genetic diversity would be to conserve all types of biological communities in very large reserves but this is impractical for many dispersed communities and their constituent species. Based on these allozyme studies it is possible to suggest general or specific conservation strategies to conserve high levels of genetic diversity. For example, a conservation strategy has been defined for Eucalyptus globulus using a combination of results from morphological and molecular genetic studies (Vaillancourt et al. 1994). The establishment of "genetic reserves" for particular species in production forests has also been advocated (Pederick 1976).

Conservation of Biodiversity

Since the 1960s there has been increasing community pressure to broaden the focus of management of forests from wood production to integrated management for wood production and conservation. The public attitude reflects concern for the ecological values of forests, including biodiversity, and their potential for recreation, tourism and other non-wood production purposes. It has become clear that forest biodiversity management is not just a biological issue but a social issue. Conservation of biodiversity will require decisions on the use of resources and economic trade-offs, it will also require recognition of people's values and attitudes and an appreciation of the role of ethics (Namkoong 1992, Aslin 1994). In response to this community pressure, national parks and other conservation reserves have been expanded and large areas of forest have been included in UNESCO World Heritage Areas in Queensland and Tasmania.

The debate over forest conservation was initially focused on the tropical rainforests. In 1971 only half of rainforest formations were represented in conservation areas of some kind but this situation improved to almost 90% by 1979 (Specht 1981). Nevertheless representation of rainforest ecosystems in national parks was inadequate with the principal deficiency in the coastal lowland forests where there was increasing encroachment from agricultural expansion and urban development (Webb 1987). Under great pressure from non-government organisations such as the Australian Conservation Foundation, the Federal Government nominated north Queensland rainforest for World Heritage listing and legislated to stop commercial forestry in the area. It is estimated that over 80% of the original tropical rainforests remain and their conservation seems assured although how to manage the biodiversity is an issue. In 1993 the Australian Government established a Cooperative Research Centre for Tropical Rainforest Ecology and Management with a biodiversity research program to enable greater research an animal and plant diversity in the tropical rainforests. With tropical rainforests secured, the focus of public attention turned to the extensive eucalypt-dominated forests of southeastern Australia which are the country's principal native forest resource.

Tasmania's 600,000 ha of temperate rainforest and one million ha of wet eucalypt forest occupy 82% of the forested area present at European settlement of the island. About 40% of the forests are on private land, 24% are in reserves or Recommended Areas for Protection, 7% are subject to a 10 year moratorium on logging until conservation evaluations are made and the remaining 30% are Multiple Use Forest subject to logging (Brown 1994). The Tasmanian Wilderness World Heritage Area reserves almost one-quarter of the State's tall wet eucalypt forest, and about half of the higher plant flora. The forests are in a succession from moorland to temperate rainforest and if managed to exclude fire will eventually form a climax rainforest dominated by non-eucalypts (Balmer 1994). There is on-going debate as to the best management practices and utilisation of the forest resources, including biological diversity.

More contentious is the large area of public and private eucalypt forest being subjected to woodchipping. A large part of the eucalypt forests being logged currently is for woodchip production for export to Japan. The remainder is for sawn timber for the domestic Australian market. It is argued by conservationists that forest management practices such as clear felling in large coupes or short logging cycles are ecologically unsustainable and that logging in native forests should be stopped. Some contend that the domestic demand for most wood products could be met from plantations and this would be the most effective means of maintaining the ecological integrity of the native forests (eg. Clark 1994). The forest industry counters with the view that the reserve system is already adequate and that current management practices are sustainable.

The forestry profession considers there is potential for the eucalypt forests to contribute benefits of wood products to the Australia community, particularly recognising that increasing wood imports places pressure on the forests of other countries. They also recognise the need for plantations and the conservation of representative forests in reserves managed in such a way as to maintain biological diversity and ecological processes ( Drielsma 1993, Squire 1993, Johnson et al. 1994).

Policies and Biodiversity

In recent years there have been several national inquiries into forestry which have produced baseline data and policy recommendations relevant to the sustainable use of forests and maintenance of biodiversity. In 1984, the Federal Government developed, after wide consultations, the National Conservation Strategy for Australia. The agreed objectives of the Strategy were to:

• maintain essential ecological processes and life support systems;
• preserve genetic diversity;
• ensure the sustainable utilisation of species and ecosystems; and
• maintain and enhance environmental qualities.

The Resource Assessment Commission (RAC) was established in 1989 to advise the Federal Government on options for the use of Australia's natural resources, and their relative values to the community consistent with the requirements of sustainability.

The RAC concluded that the "management of the forest estate to achieve a sustainable, marketable and relatively even flow of products will always remain difficult and controversial". A key concept for forest management is `ecologically sustainable development (ESD)' which has as its basis the need to optimize the material and non-material benefits accruing to the community from all forest uses, in accord with the principles of equity for both current and future generations. It was defined as development that `meets the needs of the present without compromising the ability of future generations to meet their own needs'. The RAC identified three tiers to ESD, as applied to forests, maintenance of ecosystem processes and species (biodiversity), ensuring that forests are optimally used for the present and future generations (social equity) and that use of forest provides economic benefit to the community (RAC 1992).

Other enquiries included the Ecologically Sustainable Working Group (1991) and the National Plantations Advisory Committee (1990). In response to the findings of these bodies a National Forest Policy Statement was formulated and signed by all Governments. The new Policy provides a framework for a move to ecologically sustainable forestry (Commonwealth of Australia 1992). The approach is based on a dedicated system of reserves which are to be representative and comprehensive. In addition the Policy outlines a process for upgrading the forest reserve system to cover all lands by 1997. It proposes the reserve system be complemented by enhanced off-reserve management which will undoubtedly require modification of the forest management practices in forests used for wood production. Management practices should follow the `precautionary principle'. The implementation of the policy will be substantial step forward in Australia's compliance with the UNCED Convention on Biological Diversity.

Impact of Current Forest Management Practices on Biodiversity

In response to community attitudes and changes in government policies, efforts are increasing in Australia to modify forest practices to better address the maintenance of biological diversity. How to achieve this and to convince the community at large that the native forests can be managed wisely, profitably and sustainably is a major challenge.

The Resource Assessment Commission concluded that there was no environmental basis for discontinuing management of forests for timber production. Provided strict codes of harvesting practice are adopted, wood production can be compatible with other values such as recreation, water quality and wildlife conservation (RAC 1992, Attiwill 1994). Nevertheless a statement from the International Temperate Forest Biodiversity Conference in Canberra 1994 stressed that `a number of management practices used in Australia's temperate native forests potentially threaten the long-term viability of biodiversity'. The key to integrating production and conservation seems to lie in determining appropriate harvesting regimes and in increasing community involvement in identifying management strategies which are economically and ecologically sustainable. Comprehensive programs of research on forest biodiversity which have started need to be well-coordinated and expanded. They need to bring together those with research skills of plant and animal ecology, genetics, economics, social sciences and forest management.

Forest managers have been responding to pressures to make their practices more environmentally acceptable. Numerous research projects are underway in various agencies to develop and implement new practices, prescriptions, standards and guidelines. The following example is from Victoria.

Timber harvesting in Victoria is conducted under a Code of Forest Practices and associated prescriptions designed to regenerate eucalypts, protect flora, fauna, water and other values. Traditionally there has been a mosaic of clear felled coupes for timber production combined with unharvested reserves for conservation of biota.

The State Government has a number of policy objectives which support ecologically sustainable forestry practices and the conservation of biodiversity and other values. These are set out in the Timber Industry Strategy; Flora and Fauna Guarantee Strategy; Code of Forest Practices and the National Forest Policy Statement. Lindenmayer (1994) has suggested considerable conflict between policies which try to maximise the conservation of biodiversity and wood production, and permit forest practices such as intensive and extensive clear felling. He suggests long-term Government commitments to supply sawlogs and pulpwood make it difficult for forest managers to modify logging practices even those which are known to be detrimental to fauna. Despite the criticisms, there has been a major effort to develop alternative silvicultural systems which minimize impact on biodiversity.

Extensive cooperative and multidisciplinary studies (Value Adding and Silvicultural Systems Program) have been undertaken since 1986 to provide information on the environmental impacts of forest management practices (Squire 1993). The Silvicultural Systems Project (SSP) aims to develop more environmentally sensitive systems of silviculture, especially for flora and fauna management (Burgess and Cherry 1994). The results already indicate that from a fauna conservation viewpoint the size, shape and spatial distribution of silvicultural disturbances across the forest landscape are as important as the habitats they produce (Mueck et al. 1994). The Silvicultural Systems Project is expected to develop operationally feasible options to optimize plant and animal biodiversity in timber production areas. For the long term conservation of some animal species such as Leadbeater's Possum (Gymnobelideus leadbeateri), which is virtually confined to the montane ash forests designated for timber production, it has been suggested that it will be necessary to reserve 50-100 ha patches of forest and allow them to grow through to ecological maturity (> 250 years) (Lindenmayer and Possingham 1994).

In addition to the SSP research, Forest Management Plans are being developed with the `holistic approach needed to conserve biodiversity while providing a stable environment for a sustainable timber industry' (Thompson et al. 1994). For example the East Gippsland Forest Management Area covers 1.2 million ha of temperate eucalypt forest in eastern Victoria and the key strategies in its plan are (1) representative conservation of vegetation types and old growth forest, (2) conservation guidelines for threatened or sensitive fauna, such as the Masked Owl and Long-footed Potoroo.

Some improved management practices are already included in the Code of Forest Practices and will feature in new Forest Management Plans but breaches of these prescriptions have reduced their effectiveness in initiating the effects of logging on forest fauna (Lindenmayer 1994). The extent to which the new practices are fully adopted and implemented and monitored will determine their contribution to the conservation of forest biodiversity.

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