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People proliferated across Australia, which was then a part of Sahul, from about 40 000 years ago when megafauna finally disappeared long before the Last Glacial Maximum. The so called ‘blitzkrieg’ hypothesis proposes that megafauna were extinguished by Aboriginal hunting. It is argued, either that there were some changes in vegetation and fire regimes as a consequence, or that fire regimes and vegetation were largely unaffected by human arrival. However, there is an alternative view that Aboriginal burning changed the vegetation so that megafauna had insufficient food resources to sustain them. We aimed to resolve this debate by examining the published palaeological and historical evidence. This evidence indicates that Aboriginal burning initially turned much biomass into charcoal, reducing browse, changing vegetation and causing megafaunal extinctions. It created ecosystems whose health and safety depend on constant human input of mild fire. Mild burning of these anthropogenic landscapes consumes relatively little biomass and produces relatively little charcoal. Although burning by people has typically been regarded as an ecological disturbance, the historical evidence, together with traditional Aboriginal knowledge, suggests that it is actually maintenance, essential to sustain our natural environment. We conclude that people can reinstate resilient, healthy and safe landscapes irrespective of climate change.

There is a concept in fire ecology that some natural (pre-European) fire regimes were dominated by infrequent high intensity fires ignited by lightning. In Australia, some ecologists extend this to most or all ecosystems across the landscape. They regard contemporary human burning or prescribed burning as an unnatural disturbance that threatens biodiversity. Their particular concern is the potential extinction of slow maturing obligate seeders by frequent fire. However, a completely different picture emerges from study of Australia’s ecological history and prehistory. There is ample evidence that Australian vegetation was shaped by thousands of years of frequent mild burning by Aborigines. Infrequent, high intensity lightning fires affected only small areas of wet forests in refuges that were physically protected from mild fires. We present a case study of ecosystems on the Sydney sandstones to demonstrate that a regime of infrequent high intensity wildfires since European settlement has caused structural changes and reduced spatial diversity. This has put many fire dependent plants at a competitive disadvantage and increased their susceptibility to disease. We argue that biodiversity, ecosystem health, and fire safety are threatened by lack of frequent mild fire. Ecological theory should build on ecological history. Australia is fortunate in having comprehensive historical records of Aboriginal burning against which paleoecological data can be calibrated. We emphasize the importance of using historical information to interpret ecological studies and inform fire management.

Fallen timber is widely considered to be a key element of ecosystem structure and function that is critical to maintenance of biodiversity. This concept is closely linked to ideas of wilderness and old growth. ‘Conventional wisdom’ is that fallen timber has been drastically depleted from natural levels by human activity. However natural conditions reflect interactions of Aborigines with their environment, and fallen timber as well as broadcast fire was critically important to Aboriginal economies in the New World and Australia. Quantitative historical data are not available, so it is necessary to use qualitative historical information to describe natural loads and dynamics of fallen timber. A comparison against detailed historical descriptions of woodlands under Aboriginal management in Australia indicates that benchmarks from ‘undisturbed’ examples of the same types of vegetation are generally inflated. The ecological history of grassy woodlands since European settlement shows that proposed ‘restoration’ measures will favour common and widespread biota at the expense of rare and endangered species. No correlation of biodiversity with fallen timber has been demonstrated for grassy eucalypt ecosystems. Globally, conservation strategies that minimize human activity have generally failed because resilience of ecosystems and ancient trees has been reduced and rare species have been lost. The concept of wilderness has little application outside the unpeopled continent of Antarctica.

On the western rivers and plains of southern New South Wales, relatively small areas of forests remain in a semi-natural condition and conservation reserves are lacking. Severe drought stress in recent decades after two centuries of European management has raised issues about how best to manage these forests and, if necessary, restore them. The region was explored between 1817 and 1836. Settlers, foresters and ecologists described changes as Aboriginal culture was displaced, domestic stock, feral animals and exotic plants were introduced, rabbits were controlled, rivers were regulated, and grazing was reduced. The Aboriginal ecosystems were different to the new red gum ( Eucalyptus camaldulensis ) and white cypress ( Callitris columellaris ) forests which lack resilience. Trees, saplings, fallen timber, shrubs and parasitic plants have accumulated in recently ‘undisturbed’ sites and these features are now promoted as benchmarks for conservation. However, human activity including watering, thinning, firewood collection, grazing and/or burning may aid restoration whereas non-intervention may allow continuing degradation. This historical ecology and recent palaeoecology provide insights to conserving grassy woodlands globally.

In the Eden area in NSW, Australia, low fertility granitic surface soils were sampled from 156 sites and analysed for pH, organic C, total N, total P, available P, exchangeable bases and exchangeable Al. Fifty eight of these sites were also sampled to a depth of 40 cm. Time since fire ranged from 1 to 39 years and was used in the analysis as a surrogate for fire frequency. No information was available on fire intensity. No significant relationships were found between time since fire and P or base cations. However, the quantities of organic matter and total N (kg ha−1), and the C/N ratio were significantly related to both time since fire alone and to the combination of time since fire and soil total P. Based on these relationships, it was estimated that there were average net increases of between 11 and 21 kg N ha−1 year−1 in surface soil, the actual quantity depending on the level of soil total P. There was little change in N in the initial 10 years after fire and there was a peak in N accumulation about 24 years after fire. The C/N ratio and surface soil pH decreased with time since fire. Accumulation of N and reductions in pH and C/N ratio were studied further in a small scale paired plot analysis. The repeatedly burnt plots had lower levels of both litter and understorey and the overstorey trees generally had healthier crowns than in the unburnt plots. The differences between the repeatedly burnt and the unburnt plots matched the models developed from the general survey. There were no significant changes in the C/N ratio, but the unburnt sites had higher levels of extractable mineral N and the relationships between the mineral N and the C/N ratio for burnt and unburnt sites were statistically significant. The quantities of extractable mineral N in the unburnt soils (2.3 kg N ha−1) were about twice the levels in the burnt soils (1.2 kg N ha−1). The pH of the surface soil (4.4 in 1:1 water) in the regularly burnt area was higher than in the unburnt area (pH 4.1) and the exchangeable aluminium also differed (0.62 c mol−1 in the burnt area and 1.3 c mol−1 in the unburnt). The combined data indicate that changes occur in forest soils when there is a long period of exclusion of fire. It is suggested that these changes generally lead to secondary changes, such as in pH and availability of other elements such as aluminium. The study highlights a number of issues including the rates of inputs of N to the system and the question of N saturation and its long term interaction with plant species. It is hypothesised that reduced burning leads to increased N availability and other soil changes which negatively impact on tree health.

Decline and dieback of eucalypts have been attributed to an exotic pathogen, various native organisms, climatic factors and agricultural or urban pollution. Where particular biotic or abiotic factors could not be singled out, they have been regarded as predisposing, inciting or contributing factors in ‘diseases of complex etiology’. Ongoing monitoring of eucalypt decline during recent droughts in eastern Australia, together with extensive one-time observations across temperate Australia, provided opportunities to further examine some hypotheses of decline and dieback that were largely based on retrospective investigations. Episodes of dieback can be distinguished from the process of chronic decline. Dieback episodes were associated with natural climatic extremes whereas chronic decline was associated with human management. Decline of forests in nature reserves was associated with exclusion of fire and grazing, while decline of rural trees was mostly associated with pasture improvement. Trees growing low in the landscape on soils with poor drainage and aeration were especially predisposed to decline. It appears that chronic abiotic stress causes tree decline when the function of roots is impaired by changes in soils. Climatic extremes can accelerate chronic declines associated with human management. A variety of pests, ‘pathogens’ and parasites can take advantage of trees that are stressed by environmental changes, especially eutrophication. Similarities between diebacks and declines in the Atlantic and Pacific regions suggest a simple unifying concept of tree decline and dieback. The implications for management of forest health are discussed.

Summary Fire was an integral part of the Australian environment before European settlement. The conventional view of fire as a ‘disturbance’, and the misconception that ‘natural succession’ occurs in the absence of ‘disturbance’ to eucalypt ecosystems, cause much confusion about eucalypt forest decline. Natural fire regimes stabilised eucalypt ecosystems so that they were self sustaining, whereas post-European interference has substantially changed the environment, initiating unnatural ecosystem processes. Eucalypts are declining whilst many of their arbivores and competitors are proliferating. The same types of changes have been reported in other parts of the world, especially North America. A more realistic approach to ecology can provide simple and operationally feasible solutions to eucalypt decline, but the confusion makes these solutions politically difficult.

Summary Increases in populations of mistletoes were observed in undisturbed eucalypt forest near Eden, New South Wales. Repeated counts in an ecological research area showed that there were large increases in mistletoes over 13 years. Populations of mistletoes quadrupled in areas that had few or no prescribed burns. Mistletoes doubled in areas that were patchily burnt by fires of generally low intensity six times in 13 years, but this increase was not statistically significant. Hypotheses advanced to explain the perceived proliferation of mistletoes in rural lands cannot account for the increases in undisturbed forests. However, the results of this study are consistent with a general hypothesis of tree decline in rural lands and forests caused by chronic abiotic stress. Unnatural exclusion of low intensity fire may impair the health of eucalypt forests and cause outbreaks of pests, pathogens and parasites. Populations of mistletoes or other parasites could readily be monitored as indicators of ecological ...

Summary Eucalypt dieback is widespread throughout Australia and affects an increasing range of species. In addition to salt, a 1993 study listed 13 types of insects, five types of fungi, five kinds of vertebrate animals, four climatic perturbations and a parasitic plant that had been implicated as major agents of dieback in southeastern Australia. Repeated defoliation by insects has usually been identified as a major factor in rural and forest diebacks, while mesic understorey development is often an important feature of forest diebacks. Different mechanisms of initiation and reinforcement have been proposed to account for many different forms of dieback. High rates of folivory leading to both rural and forest diebacks, have been related either to high resource availability and tree vigour or to low resource availability and tree stress. A simple model of eucalypt dieback is proposed to account for both rural and forest dieback, including an increasing range of ‘susceptible’ species and sites. It associat...

Assessments of the conservation status of koalas and trends in their population have been based on mostly unstated false assumptions about their pre-European status and on notions that either they were naturally regulated by their predators, chiefly Aborigines and dingoes, or that they somehow ‘self-regulated’ their fecundity. Closer examination of their ecological history suggests that frequent mild burning by Aborigines maintained eucalypt forests having fewer, mostly healthy trees, fewer young trees, canopies comprising mostly hard and dry leaves with low nutrient content, and, consequently, very few koalas. European explorers did not see them because they were solitary animals occupying large home ranges. After burning was disrupted, koalas responded to increased food resources in dense new growth of eucalypts and in stressed trees continually turning over new foliage. An export skin industry flourished. When their food resources were depleted by clearing or ringbarking of new growth and/or death of declining stands during droughts, koalas crashed back to low levels. Koalas continue to irrupt and decline through much of their range according to changing land management. Wildlife managers should re-assess their status and their management from a clear historical and ecological perspective.

A report in Wildlife Research, that koalas are extinct in most of the Eden region as a result of climate change, logging and clearing, is mistaken. Its recommendation, that logging should cease in a climate refuge where, supposedly, the last koalas persist, has been adopted by Government. Koalas are unlikely to benefit. It would be better to conduct radio-tracking studies of koalas in this area and in the wider region to inform their future management.

Summary A survey conducted by playing pre-recorded calls of a male koala and listening for responses was used to further assess the distribution of koalas in south-eastern New South Wales. Fourteen koalas were recorded from 388 sample sites. This detection rate (4%) was low compared to detection rates in north-eastern New South Wales. Insufficient data were generated to allow analysis of koala distribution in relation to environmental variables. The koalas were scattered through the region on various land tenures. The results suggest that conclusions regarding the distribution of koalas, based on previous records, may reflect uneven survey effort. The data from this survey and from other contemporary sources show the continued presence of koalas at localities where they had previously been reported as extinct. It is concluded that a low density koala population persists in the regional forests and that purported evidence of decline in the population is unconvincing. There were no significant differences i...

Summary Height and diameter equations were developed using the Chapman-Richards function for 30 species in the regrowth forests of southeast New South Wales. These species included all commercial species of eucalypts and non-commercial small tree species of acacia and allocasuarina in the region. To improve prediction accuracy, the mean height and mean diameter of 50 largest regrowth trees/ha were incorporated in a modified Chapman-Richards function: where H and D represent total tree height in m and diameter at breast height in cm, H50 and D50 are the mean height and mean diameter of 50 largest trees/ha in m and cm respectively, a, b, c and d are parameters. Detailed evaluation of prediction accuracy through resampling showed that the incorporation lead to unbiased and more precise prediction for tree height and stem volume of most species and for stand volume of the regrowth forests. The common practice of calibrating height prediction from species-specific individual tree height-diameter equations agai...

Summary Old tree retention during logging results in irregular regrowth forests, for which growth and yield information are urgently required by forest managers in Australia. Using data obtained from 30 stands through random sampling in regrowth Eucalyptus fastigata forests on the south-east tablelands of New South Wales, equations were developed to determine the yield of the regrowth stands in relation to old tree density. The predicted regrowth stand volume for stands without any old trees increased from 253m3ha1 at age 20 to 623m3ha−1 at age 80 for the most productive site, from 253m3ha1 to 339m3ha−1 for the average site and from 84m3ha−1 to 206m3ha−1 for the least productive site. As old tree density increases from 0 to 100 trees ha−1 the percentage reduction in regrowth stand volume increases from 0 to 66%. As a result of past fire and logging disturbances, the old trees had a wide range of crown conditions, with many having a small and sparse crown, but not a large healthy primary crown. A clear und...

Summary Two studies of foraging preference of the smoky mouse at the same site in south-eastern NSW reached distinctly different conclusions. The first found that the smoky mouse foraged on relatively bare exposed slopes but not in heath. The second study concluded that the smoky mouse foraged and nested in heath. This article examines the sampling strategies and results in terms of vegetation patterns and nest locations. It concludes that the results of the second study reflected the placement of traps in relation to nests rather than foraging preferences. It also questions another conclusion of the second study, that it may be necessary to reserve large areas of undisturbed vegetation to conserve the smoky mouse. This conclusion was not supported by the data presented.

Studies of frequent burning in eucalypt ecosystems show that accumulation of N in the absence of fire drives changes in their composition, structure and function.