August 1999
The effects of current forestry practices on species distribution
At the end of April, Scientists for Sustainability launched a discussion on the scientific evidence behind recently reported claims that current forestry practices threaten massive species extinctions.
In launching the topic, Dr Peter Attiwill, the project’s Principal Investigator, said that while there is no record of species extinction through sound management of our native forests for timber production, the scientific community rightly insists that we deal with uncertainty about the threat of extinction by taking a precautionary approach to management. In response, Mr Peter Robertson from the Conservation Council of Western Australia posed a series of questions about that statement. His questions and our answers, which were composed after consultation with scientists who participate in the Scientists for Sustainability Forum, are re-printed below.
Peter Attiwill, Principal Investigator, and Jane Fewings, Project Coordinator
Scientists for Sustainability
4 August 1999
- Does your statement include both local extinction and global (total) extinction of species?
SFS Replies
- How do you define ‘sound’ forest management ?
SFS Replies
- Where may one see sound forest management in practice?
SFS Replies
- What species have become extinct as a result of unsound forest management?
SFS Replies
- Are any species undergoing population declines or local extinctions as a result, in whole or in part, of forest management practices?
SFS Replies
- If this is the case, do those practices automatically become unsound or are there other criteria?
SFS Replies
- Is it possible, as some independent scientists claim, that there may be many species which although not yet extinct have already lost their viability as a result of (sound or unsound) forest management practices (extinction debt) ?
SFS Replies
- Does the SFS have any form of peer review in terms of what it publishes, and if so, what form does this take?
SFS Replies
- Does your statement include both local extinction and global (total) extinction of species?
SFS: Yes. In relation to global extinctions, Briggs and Leigh (1992) concluded that no plant species had been made extinct as a result of forestry operations in contrast to the 44 plant species made extinct by agriculture and the 34 species made extinct by grazing. They listed 436 endangered plant species, of which 10 were threatened by forestry activities and 151 by vegetation removal or replacement due to agriculture or development. Recher and Lim (1990) concluded that about 20 forest-dwelling fauna have become extinct since European settlement but the Resource Assessment Commission (1992) found these extinctions to be more a consequence of land clearing than of commercial forestry. Armstrong and Abbott (1995) concluded that the Western Australian state forests retain an almost complete set of native vertebrate and plant species One vertebrate species is absent from Western Australian state forests (Lewin’s water rail) but as it inhabited swamps rather than areas subject to logging, Christensen (1997) is reluctant to ascribe the extinction to forestry. Calver and Dell (1998a, 1998b) concluded that forestry practices in the south-west forests of Western Australia may be implicated in the conservation status of only one mammal species and of no bird species. However, they reached that conclusion with caution, in view of limited data.
With regard to local extinctions, we feel that it is essential to comment first on the use of the term. Extinction means the elimination of a taxon (Allaby 1994) - a ‘condition that arises from the death of the last surviving individual of a species, group or gene, globally or locally’ (Begon et al 1996). At what point does a local change in species’ composition become a local extinction of one species? It is clear to us that the question is both definition-dependent and scale-dependent, at scales both of length and time. As with the concept of minimum viable population, at what spatial scale does the concept of local extinction apply: ‘is it a patch within a metapopulation or the entire metapopulation’ (Crawley 1997)? And how can we predict ‘the population size and genetic attributes of a population that will allow it to persist decades or centuries into the future’ (Crawley 1997)?
A further problem to do with the time-scale of local extinction is how permanent is the elimination? The theory of local extinction has been applied to islands (MacArthur & Wilson 1967), and to forests where selective logging may remove one or two tree species over a large area (eg. Crawley 1997). Since in both cases the rate of immigration may be low, the elimination of a species may either be final or sufficiently long-lasting as to rank as a local extinction.
In summary, we suggest that the term ‘local extinction’ has no self-evident meaning unless the scales of time and space at which it has been assessed are explicit. We looked at the evidence provided for recently reported claims of local extinctions due to forestry. The first is Barry Traill’s study (1991), conducted over 1986 to 1989, in two box-ironbark forest blocks near Chiltern in North-Eastern Victoria, which found that four bird species (Powerful Owl, Barking Owl, Owlet nightjar and Sacred kingfisher) and the Common ringtail possum were absent from a 80 hectare block which had been subject to selective, licensed logging for posts and to illegal firewood collection and live-tree removal. He concluded that the removal of nearly all mature trees from this block, resulting in a lack of hollows, has limited the distribution of these species. This is an example of unsound forest management. Whether the absences observed in a single site in the 1980s will persist over time and be able to be described as local extinction will depend on the extent to which past mismanagement of the box-ironbark forests of North-East Victoria is redressed.
The second source of recent local extinction claims of which we are aware is research on arboreal marsupials and owls in Australia’s south-eastern forests, particularly the Yellow-bellied glider in Victoria’s Central Highlands region. We looked at five studies on the Yellow-bellied glider, other arboreal marsupials and owls published between 1991 and 1999.
A study by Milledge, Palmer and Nelson (1991) of Yellow-bellied gliders at large owl sites in Mountain Ash forests in the Victorian Central Highlands showed that this species has a strong preference for old-growth forest. Yellow-bellied gliders were found at 31 out of 70 sites in old-growth forests (44.3% of sites) compared with 5 out of 60 sites in 50- to 80-year old regrowth forest (8.3% of sites). The glider appeared to make little use of young forest even where stags or scattered old trees, apparently suitable for nest and den sites, were available. Milledge and colleagues concluded that the strong relationship of the glider to old-growth stands probably related to factors additional to hollow availability such as a high diversity of eucalypts which provide food sources at different times of the year and the glider’s foraging requirements. They argued that their results suggest that "conversion of tracts of old-growth Mountain Ash forest to a series of stands younger than 80 years will cause substantial reductions in the densities of the Sooty owl and Greater glider and the likely loss of the Yellow-bellied glider".
Kavanagh and Bamkin (1995) surveyed numbers of nocturnal forest birds and mammals at 200 sites in south-eastern New South Wales to determine their distribution in relation to logging. They compared large areas of unlogged forest with large areas containing both logged and unlogged forest, which they felt might provide more biologically meaningful results for species with large home ranges than focussing on individual logged or unlogged patches. They noted that the Yellow-bellied glider may be difficult to conserve in the context of intensive wood production in view of its large home range, its requirements for large hollows in old trees and its foraging habits but found no significant association between the glider and logging. They suggested, however, that because of the species’ diet and the spatio-temporal availability of food, the effects of logging might become more apparent during the second half of the cutting cycle.
Goldingay and Possingham (1995) suggested that the Yellow-bellied glider should be used as a target species for preserving forest ecosystems, because its range extends along the eastern and southern coast from far north Queensland to just inside the South Australian border, encompassing the entire length of forests along the Great Dividing Range, and because it is strictly arboreal, unlikely to cross open ground and unable to disperse among patches of suitable habitat in the absence of trees. They used computer modelling in a preliminary population viability analysis to determine the minimum habitat areas that would contain viable populations ( populations that had 95% probability of persistence after 100 years). Their simulation model indicated that a population containing approximately 150 glider groups is needed for species viability. They suggested that the area required for a minimum viable population (MVP) depends on the suitability of the habitat but varies between 9750 hectares where all the habitat is suitable (150 glider groups multiplied by the 65 hectares of the largest average home range per group) to between 18,000 to 35,000 hectares where only a proportion of forest is suitable. The intermediate value was based on a study by Braithwaite (1983) in Eden, NSW which found 54% of forest occupied in those forest blocks where most Yellow-bellied gliders were recorded and the largest area estimate was based on the 1991 and the 1995 studies referred to above. Goldingay and Possingham (1995) concluded that a sound conservation strategy for forest ecosystems would encompass large areas of reserved forest within several areas across the landscape to provide some security against wildfire, disease or predation affecting all areas simultaneously. (Note: while Population Viability Analysis (PVA) is a very useful tool for alerting us to potential problems, these are models which do not have empirical certainty.)
Lindenmayer (1994) presented a synthesis of the key findings of an array of studies which have been used to predict the likely impacts of timber harvesting on arboreal marsupials at different scales in the south-eastern Australian forests. He concluded that the management regime current in 1994 may threaten the long-term persistence of several species of arboreal marsupials because of various effects of the prevailing silvicultural system (clearfelling followed by high intensity burns). He recommended a range of remedial actions: a modification of present clearfelling techniques to ensure a larger amount of vegetation on logged sites (it was suggested that "more than 20%" of forest be treated by a modified silviculture), the permanent exclusion of logging on more stands of existing regrowth montane ash forests, and the expansion of the national park system.
Lindenmayer, Cunningham and McCarthy (1999) quantified relationships between the presence/absence of four species of arboreal marsupials (Mountain brushtail possum, Greater glider, Leadbeater’s possum and Yellow-bellied glider) and attributes of landscape surrounding each of 166, 3 ha field sites surveyed for these animals in the mountain ash forests of the Central Highlands. None of the landscape variables used was statistically significant for the first three species but there was a significantly higher probability of the Yellow-bellied glider occurring in old-growth forest, on northerly and westerly aspects and in either flat or steep terrain. Like Milledge et al, Lindenmayer and colleagues considered that the old-growth association in the mountain ash forest is due to the glider’s feeding requirements. While the glider utilises an assemblage of different tree species in other forest types in which it is found, in the monotypic mountain ash forests food resources are more abundant in old-growth. They concluded that differences between old and young mountain ash forests in flowering intensity and the levels of bark production and decortication may explain the virtual absence of the glider from landscapes that did not support stands of old-growth mountain ash forest. They noted that all remaining stands of old-growth have been protected from logging since 1991 and that the largest and most continuous areas of old-growth are contained in national parks. Referring to Goldingay and Possingham (1995) they considered that remaining patches of old-growth within areas of forest available for timber production are not large enough to support viable Yellow-bellied glider populations, even though these patches are protected from logging. They concluded that the Yellow-bellied glider is rare in forests used for timber production, and will continue to be rare unless strategies are employed to expand the area of old-growth.
Finally, in relation to the Yellow-bellied glider, we looked at the Commonwealth government’s prescriptions for its management as prepared by the Australasian Marsupial and Monotreme Specialist Group (Maxwell et al 1996). The Group noted that the principal threats to its conservation are habitat reduction and alteration through land clearing for agriculture and timber harvesting. The Group believes it will suffer declines in density with the removal of old-growth elements from unlogged forests or from previously lightly-logged forests. It recommends that the states manage for its persistence over its natural range through reservation of large areas of forest containing old, hollow trees, coupled with links to other protected areas by corridors no less than 200m wide, establishing monitoring programs, especially of the isolated populations, and those in areas where timber harvesting is part of forest management and, in forest management areas, by retaining trees suitable for sap-sites and robust mature eucalypts which provide an adequate nectar foraging resource.
The study by Lindenmayer, Cunningham and McCarthy (1999) appears to be the source of the statement by the National Biodiversity Council (The Age, Melbourne 26/4/99) that the Yellow-bellied glider’s virtual absence from timber production forests in the Central Highlands is evidence of a local extinction due to logging. However such a statement does not necessarily follow from the research cited above. Timber production is limited to regrowth forest in the Central Highlands. The Yellow-bellied glider does not utilise monotypic mountain ash regrowth forest. The term ‘local extinction’ implies more than a temporal absence of a species from a particular patch of forest. It implies that the habitat left vacant will never be recolonised by the species in question. The claim that the Yellow-bellied glider has been made ‘locally extinct’ in certain areas of the mountain ash forests of the Central Highlands, whether you call them timber production forests or regrowth forests, is based on the expectation that management will never allow these areas to develop the structural elements on which the Yellow-bellied glider depends.
This expectation leads the National Biodiversity Council to consider that government policy on species conservation is ineffective(The Age, Melbourne 26/4/99). As you know, Australia’s national forest policy obliges the commonwealth, state and territory governments to "manage for the conservation of all species of Australia’s indigenous forest fauna and flora throughout those species ranges" (Commonwealth of Australia, 1992). Victoria’s Flora and Fauna Guarantee Act 1988 commits management agencies to guaranteeing "that all of Victoria’s flora and fauna can survive, flourish and retain their potential for evolutionary development in the wild" (Government of Victoria. 1999). The Central Highlands Forest Management Plan (Victoria, DNRE, 1998) reiterates that "conservation of species and communities across their natural range is fundamental to sound nature conservation". We assess the effectiveness of such policy in answer to question 3 below.
- How do you define ‘sound’ forest management ?
SFS: We define sound forest management as the planned management of a forest for any or all of its values (recreation, biodiversity, timber, water etc) so that the consequences of management on forest biota and ecosystem processes across landscapes are minimised over time. Sound forest management is responsive to new information as it becomes available. Thus, while it is impossible to expect that there will be no effects of a particular management practice at all scales and at all times, ‘sound’ forest management will attempt to incorporate changes over time and space so that their effects are minimised, will respond to new information by adapting management practices and monitoring their effects and will account for uncertainty.
What new information is needed? Obviously we have to set priorities, and that has happened through the normal, peer-review funding processes available to all scientists. An example of setting priorities for research and using the information to change management procedures is the work on Leadbeater’s possum in Victoria. It is up to us, as ecologists, to set the priorities for research in forest ecology. In terms of the current debate, this will only come about through the open and unbiased assessment of the effectiveness of management. It is only by this continuous, interactive process between management and research that the obvious goals set by Calver and Dell (1998a, 1998b) can be met - namely: to determine the effectiveness of current management practices in minimizing impacts on the biota, while at the same time identifying remedial actions and setting research priorities.
- Where may one see sound forest management in practice?
SFS: The maintenance of species distribution across or throughout known ranges is one indicator of sound forest management. To assess the extent to which policy on species distribution is being achieved in practice in the Central Highlands (the region at the centre of localised extinction claims in south-eastern Australia) and whether the results of research on the Yellow-bellied glider and threatened species have been incorporated into management prescriptions we looked at the relevant regional forest agreement and the biodiversity assessment prepared as part of the Central Highlands FRA process (Commonwealth of Australia, 1997), the Central Highlands Forest Management Plan (Victoria, DNRE, 1998), action plans prepared under Victoria’s Flora and Fauna Guarantee Act 1988 (Victoria, DCE, 1995), and the recommendations of the Victorian silvicultural systems project (Campbell 1997).
The principal strategy for species conservation in the Central Highlands is long-term reservation of large areas of forest representing the range of ecological vegetation classes. In total, 85,000 hectares of ash-eucalypt forest are in conservation reserves and special protection zones. About a quarter of the conserved ash-eucalypt forest is old-growth. This area meets the size criterion suggested by Goldingay and Possingham (1995) for the Yellow-bellied glider and all conservation reserves are connected by special protection zones at least 200m wide, as recommended by the Australasian Marsupial and Monotreme Specialist Group (Maxwell et al 1996). The national park system has been expanded by about 60% since 1994. Timber harvesting is excluded from all old-growth forest in the Central Highlands region, and this is important for water production and species such as the Yellow-bellied glider. It is important to note also that the 1939 bushfires have resulted in 82-84% of ash type forests in the Central Highlands being essentially even-aged regrowth. The extensive salvage logging of the ash forests after the bushfires is suspected to have exacerbated the current extensive areas of regrowth forest where there are few hollow-bearing trees.
Species-specific strategies are in place for the Powerful, Sooty and Masked owls, Leadbeater’s possum, the Spot-tailed quoll, and stream- or wetland-dependent fauna - specifically the Spotted tree frog, the Large-footed myotis and the Baw-Baw frog. The persistence of these species outside reserves is managed largely through a system of timber production-free zones of varying sizes catering for known habitat, suitable habitat and known breeding sites.
Alteration of forest structure through timber harvesting is ameliorated by prescriptions which set minimum standards for reservation of riparian and vegetation corridors, link protected areas and reserves with wildlife corridors, retain habitat trees and all ash eucalypts originating before 1900 in timber harvesting coupes and which retain and protect biologically significant habitats. In addition, systems which modify the effects of clearfelling are being trialed, for example the ‘understorey islands’ system in which heavy machinery is kept out of zones within coupes which are being clearfelled to improve the survival of understorey species. Such modifications enable ‘clearfelling’ as a silvicultural system to be differentiated from ‘improved clearfelling’ which is claimed to have more favourable outcomes for flora and fauna conservation (Campbell 1997).
The loss of hollow-bearing trees is listed as a threatening process under Flora and Fauna Guarantee Act 1988. The Central Highlands RFA obliges Victoria to develop an action plan as a priority. The report of the Victorian silvicultural systems project, established to evaluate alternative silvicultures under experimental conditions recommends ‘judicious’ development of an integrated block level mosaic of natural and specialised and intensive wood production systems to improve fauna conservation (Campbell 1997). The report states that "it should be possible to develop a silviculture that conserves indigenous vertebrate species over a large proportion of their natural range in Mountain Ash forest" subject to the control of other threatening processes such as disease and predation (Campbell 1997).
(While we have concentrated on fauna here we have also looked at research on vegetation recovery after logging, and can report that concerns are held for some understorey species in wetter forests, particularly ferns and epiphytes and can discuss the management actions suggested by this research as well, if you wish).
- What species have become extinct as a result of unsound forest management?
SFS: As far as we know, one tree species has become extinct due to past overcutting rather than intentional removal for non-forestry purposes (the Red Cedar in sub-equatorial rainforest, as a result of selective logging - but this was uncontrolled exploitation, rather than any form of management). If you consider the permanent clearing of forest for agriculture or development purposes as unsound forest management, although, again, it would be quite incorrect to consider uncontrolled clearing as any form of management, then see Briggs and Leigh (1992) and Recher and Lim (1990) for examples. As noted above, Christensen (1997) cites the extinction of one vertebrate species in Western Australian state forests (Lewin’s water rail) but as it inhabited swamps rather than areas subject to logging, he is reluctant to ascribe the extinction to forestry.
- Are any species undergoing population declines or local extinctions as a result, in whole or in part, of forest management practices?
SFS: Populations of the Yellow-bellied glider in Western Victoria may not be viable due to discontinuities of habitat, whether or not forestry-related (Menkhorst 1995). There are many non-forestry-related threatening processes such as predation or competition from introduced species or disease which may be exacerbated by forest management practices such as the building of roads. ‘Sound’ forest management would attempt to minimise known effects, be sensitive to new information as it becomes available and account for uncertainty.
- If this is the case, do those practices automatically become unsound or are there other criteria?
SFS: We repeat that sound forest management would attempt to minimise known effects, be sensitive to new information as it becomes available and account for uncertainty. It follows that unsound forest management does not apply what is known and ignores new information.
- Is it possible, as some independent scientists claim, that there may be many species which although not yet extinct have already lost their viability as a result of (sound or unsound) forest management practices (extinction debt) ?
SFS: Yes, it is possible, whether or not some ‘independent’ scientists claim. The possibility of long-term or cumulative effects of current forest management practices will always exist, no matter what the practice. Management must therefore be able to demonstrate that current practices account explicitly for uncertainty. We believe that there have been many significant steps towards dealing with uncertainty over the past few years. Efforts to establish comprehensive and representative reserve networks have been a practical step towards minimising risk to biodiversity. The need for forests outside reserves to contribute to sustainability of biodiversity at regional scales has been accepted, and a range of measures, from species-specific management prescriptions to strategies to counter threatening processes to whole groups of species have been or are being developed. The demands of some researchers for less intensive timber harvesting and the active recruitment of old-growth within timber production areas have been partially satisfied in Victoria by management acceptance of the need for a range of treatments of differing intensity across the landscape. Such experimentation with the system, together with monitoring programs, should allow continuous modification of decisions and management practices. The adequacy of current experimentation and monitoring is the subject of debate, but nevertheless the fact that we have been able to point to the results of previous research being put into practice offers some encouragement.
We would also like to question your use of the term ‘independent scientists’. Are scientists independent only if their research is funded by disinterested parties, or only if the results of their research are published in independent, peer- reviewed publications, or only if they have never been involved in forest research? We believe we have searched the peer-reviewed literature thoroughly in providing these responses. We have found no evidence for loss of viability other than that quoted above. However, we readily acknowledge that we may have missed something; in particular, we would be most interested to see the data on which your ‘independent’ scientists claims are based.
We feel that the categorization of scientists as independent or otherwise is entirely driven by perceived political outcomes. Rather than taking the moral high-ground through aggressively and often pompously asserting bias on one side or the other, the debate will progress only when all parties concentrate on the quality of basic data and the merits of the analysis and interpretation of the data.
- Does the SFS have any form of peer review in terms of what it publishes, and if so, what form does this take?
SFS: Articles which appear on our website, and no doubt on many other websites, may or may not have been peer-reviewed (eg. articles or features in newspapers). The Forum on our website is open to all scientists who are involved with forest research. Through this process we aim to help scientists to produce manuscripts that will be suitable for submission to peer-reviewed journals.
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