Benchmarks of fallen timber and man's role in nature: Some evidence from eucalypt woodlands in southeastern Australia

Forest Ecology and Management 261 (2011) 2149–2156

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Benchmarks of fallen timber and man’s role in nature: Some evidence from eucalypt woodlands in southeastern Australia Vic Jurskis ∗ Forests NSW, 6 Cocks Lane, Eden, NSW 2551, Australia

a r t i c l e

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Article history: Received 25 January 2011 Received in revised form 28 February 2011 Accepted 9 March 2011 Available online 1 April 2011 Key words: Fallen timber Aboriginal economy Biodiversity Human ecology Wilderness

a b s t r a c t 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. © 2011 Elsevier B.V. All rights reserved.

1. Introduction Fallen timber is regarded as a key natural component contributing to biodiversity, nutrient cycling, soil and water protection and carbon sequestration in temperate ecosystems (e.g. Harmon et al., 1986; Woldendorp et al., 2002; Killey et al., 2010). It is widely considered that fallen timber has been depleted since European settlement of the New World and Australia, impacting negatively on biodiversity (e.g. Harmon et al., 1986; MacNally et al., 2001; MacNally and Parkinson, 2005; MacNally and Horrocks, 2007; Manning et al., 2007; Eyre et al., 2010; Killey et al., 2010). However this is difficult to substantiate due to a lack of studies assessing distribution and dynamics of fallen timber in Aboriginal ecosystems. Natural conditions in the New World and Australia are those that applied before European settlement but quantitative data on natural loads of fallen timber are unavailable (e.g. Allen et al., 2002; Hessburg et al., 2005; Gibbons et al., 2008). Data have been gathered from stands that appear minimally disturbed by human activity on the assumption that they reflect natural conditions (e.g. Harmon

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et al., 1986; Robinson, 1997; MacNally et al., 2001; McElhinney et al., 2006; Gibbons et al., 2008; Eyre et al., 2010; Killey et al., 2010). However this assumption is clearly incorrect because human activities shaped ecosystems globally over many millennia and profound changes occurred when those activities were terminated or modified (e.g. Allen et al., 2002; Sherman et al., 2008; Szabo, 2010; St Clair and Jurskis, in press). Furthermore ‘undisturbed’ stands were generally unsuitable for agricultural development and are therefore unrepresentative of stands that were selected for agriculture (e.g. Croft et al., 1997; Jurskis, 2002, 2009; Keith, 2004; Department of Environment and Heritage, 2006). Eucalypt woodlands and forests occur on the northern, eastern and southwestern continental margin of Australia and most of Tasmania. Woodlands mostly occur on subdued terrain where mean annual rainfall is less than 750 mm whilst forests mainly occupy rougher terrain in higher rainfall zones nearer the coast (Hall et al., 1970). Grassy woodlands occupy relatively fertile valleys and plains whereas shrubby woodlands occur on sandy or stony rises (Keith, 2004). Grassy woodlands were mostly developed to form the ‘sheep and wheat belts’ of southeastern and southwestern Australia whilst most shrubby woodlands and forests have been retained as native vegetation (e.g. Keith, 2004). Australian explorers and naturalists described ecosystems that had been shaped by about 50,000 years of Aboriginal manage-

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ment (Pyne, 2003; St Clair and Jurskis, in press). The explorers detailed understoreys, ground conditions, visibility and obstructions to travel, so presence/absence of accumulated fallen timber can be assessed and compared against contemporary quantitative data on fallen timber and contemporary observations of obstructions to travel (Jurskis, 2009). However historical information on natural loads and dynamics of fallen timber in eastern Australia has been largely dismissed in the recent literature (e.g. MacNally and Parkinson, 2005; Gibbons et al., 2008; Killey et al., 2010) and the extent of Aboriginal burning has again been questioned (Mooney et al., 2010). Evidence of human economy including firewood collection, burning, grazing by domestic stock and/or cut stumps has been used to create indices of disturbance and benchmarks have been derived from stands with low indices (e.g. McElhinney et al., 2006; Gibbons et al., 2008; Eyre et al., 2010). Also models of the natural dynamics of fallen timber have failed to incorporate human economy (e.g. Harmon et al., 1986; Killey et al., 2010) resulting in high benchmarks and proposals to augment fallen timber in conservation reserves so as to increase their carrying capacity for various biota (e.g. MacNally et al., 2001; MacNally and Horrocks, 2007; Killey et al., 2010). This raises questions of which biota and habitat elements should have priority if biodiversity is to be maintained or enhanced, and how this can best be done (e.g. Jurskis, 2002; Jurskis et al., 2003; Ford et al., 2009). The three earliest extensive explorations of grassy eucalypt woodlands were carried out by Oxley (1820), Sturt (1833) and Mitchell (1839) whilst the woodlands were still under traditional aboriginal management and before feral cattle had any impact. Jurskis (2009) analysed these explorers’ records to describe the pre-European landscape and provide context for an environmental assessment of current forestry management in south western New South Wales. This region has been the focus of several benchmarking studies of fallen timber and vegetation structure (Robinson, 1997; MacNally et al., 2001; Lunt et al., 2006; Gibbons et al., 2008, 2010). The current analysis compares these against the historical information and also compares current data from similar woodlands around Yass Plains (McElhinney et al., 2006; Manning et al., 2007; Killey et al., 2010) against the original description by Hume and Hovell (Bland, 1831). Detailed historical information on ecosystem ‘transitions’ consequent to European settlement (Mitchell, 1848; Wallis, 1878; Curr, 1883; Howitt, 1891; Donovan, 1997; Noble, 1997) is also used to judge the validity of proposed benchmarks and models.

2. Dynamics and distribution of fallen timber in eastern Australia 2.1. Historical observations European settlement was established at Sydney Cove in 1788 and did not extend beyond the Cumberland Plain until Blaxland, Lawson and Wentworth found a route to the west through the precipitous Blue Mountains in 1813. George Evans extended this route from the central tablelands to the Western Slopes in 1815. Subsequently Oxley, Sturt and Mitchell were successively employed by the Colonial Government to describe the environment, assess the potential for development and identify suitable access through the Murray Darling Basin. Between 1814 and 1822 Hume was instrumental in developing access south west from Sydney to the eastern edge of Murrumbidgee section of the Basin. In 1824 he joined Hovell in an expedition from the southwestern limit of European settlement near Goulburn and crossed the Yass Plains on the commencement of the first overland journey to Port Phillip (Melbourne).

Howitt was an explorer, naturalist and anthropologist, Fellow of the Geological Society, Fellow of the Linnaean Society and magistrate. He described the impact of European settlement on the grassy woodlands of the Gippsland Plains in eastern Victoria. Curr was the first pastoralist to settle on the Murray. He was a keen naturalist and anthropologist who recorded details of Aboriginal culture and changes in the landscape after settlement. Wallis was the Victorian Parliamentary Secretary for Agriculture who compiled foresters’ reports on the natural state of river red gum (Eucalyptus camadulensis) ecosystems and changes under European management. Australian Aborigines frequented grassy eucalypt ecosystems, routinely carried fire and used it for heating, cooking, hunting, signaling, fighting, celebrating and managing vegetation (e.g. Oxley, 1820; Sturt, 1833; Mitchell, 1839, 1848; Curr, 1883; Howitt, 1891). They burnt substantial quantities of firewood and also used fallen timber in construction and decoration and burnt it in broadcast fires (Jurskis, 2009). Most dead wood in grassy eucalypt ecosystems was burnt by grass fires (Mitchell, 1848; Howitt, 1891). Under Aboriginal management, fires also felled trees and consumed litter, seedlings, ground layer vegetation, shrubs and saplings (Oxley, 1820; Sturt, 1833; Mitchell, 1839, 1848; Curr, 1883; Howitt, 1891). The early explorers for the Colonial Government travelled with heavily laden pack horses (Oxley, 1820) or with packhorses and bullock carts carrying tonnes of supplies and equipment and also with flocks of sheep (Sturt, 1833; Mitchell, 1839). On New South Wales’ southwestern slopes and plains they reported obstructions to their travels on 107 occasions, however they were not obstructed by fallen timber except when travelling by boat (Oxley, 1820; Sturt, 1833; Mitchell, 1839; Jurskis, 2009). Curr (1883) remarked that hunting with hounds in river red gum woodlands involved “but little jumping and no falls” and noted that after the hunt, riders actively sought fallen timber to try out their horses. In other regions, Oxley (1820) remarked twice on fallen timber. He described a eucalypt woodland at the head of the Manning River system as “country perfectly open though much covered with fallen timber”, however “the great number of fallen trees was in some measure accounted for by the men observing about a dozen trees on fire near this (Aboriginal) camp, no doubt the more easily to expel the opossums, rats and other vermin which inhabit their hollows”. Whilst traversing a rainforest plateau at the head of the Apsley River system, Oxley (1820) found “our progress much impeded by the vast trunks of fallen trees in a state of decay”. He called this a “truly primeval forest” and there are no other references to primeval forest in his journal. In the mountainous regions surrounding the Australian Alps, Hume and Hovell were only thrice impeded by fallen timber in “thick forest”, “scrub” and “almost impenetrable brush” (Bland, 1831). Yass plains were a centre of Aboriginal culture contributing hundreds of people to regional Aboriginal gatherings in the mid 1800s (Wesson, 2000). In 1824 Hume and Hovell described the red gum (E. blakleyii) – yellow box (E. melliodora) woodlands around the plains as “a country affording good pasturage for cattle, thinly wooded and well watered” (Bland, 1831). By contrast they described the forested (AUSLIG, 1990) Mundoonen Range as “poor land but thickly timbered”. From the top of the range Hovell had a “pleasing view of” (Yass) “plains skirted by fine extensive forest” (Bland, 1831). ‘Forest’ was woodland or open woodland in current terminology (Jurskis, 2009) and Hume and Hovell obviously took pleasure in traversing these woodlands with six men, a spare horse and bullock, a cart drawn by four bullocks and another drawn by two horses, the carts carrying more than a tonne of supplies and equipment (Bland, 1831). They were not obstructed by fallen timber, understoreys, saplings or dense forest. Mitchell (1848) was obstructed on 7 occasions by fallen timber in tropical acacia scrubs. Once he noted: “Our carts had been so much jolted about and shaken, in crossing the dead timber yester-

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day, that I resolved to keep along the river bank this day . . . there was less fallen timber, as the natives had been accustomed there to make their fires, and roast the mussles of the river, and other food.” Also “The fallen timber of the brigalow (Acacia harpophylla) decays very slowly, and is not liable to be burnt, like most other dead wood in open forests, because no grass grows amongst the brigalow, as in open forests.” (Mitchell, 1848). Curr (1883) remarked that Australia had “over a great portion of its area, the inestimable advantage of being ready for immediate use without the outlay of a sixpence” He originally described ‘firestick farming’ (Curr, 1883) and the terminology was ‘reinvented’ by Jones (1969) a century later. Howitt (1891) noted that Aboriginal fires “tended to keep the forests open, and to prevent the open country from being overgrown, for they not only consumed much of the standing and fallen timber, but in a great measure destroyed the seedlings which had sprung up since former conflagrations”. Aboriginal burning was very extensive. Mitchell (1839) stated: “On the highest mountains, and in places the most remote and desolate, I have always found on every dead trunk on the ground, and living tree of any magnitude also, the marks of fire”. Charles Darwin wrote “The woodland is generally so open that a person on horseback can gallop through it; . . . In the whole country I scarcely saw a place without the marks of fire;” (Darwin, 1845). 2.2. Changes in dynamics Removal of Aboriginal fire had profound impacts (Mitchell, 1848; Wallis, 1878; Curr, 1883; Howitt, 1891; Donovan, 1997; Noble, 1997). Mitchell (1848) reported that “The omission of the annual periodical burning by natives, of the grass and young saplings, has already produced in the open forest lands nearest to Sydney, thick forests of young trees, where, formerly, a man might gallop without impediment, and see whole miles before him. Kangaroos are no longer to be seen there; the grass is choked by underwood”. By 1901, a Royal Commission found that this process had severely reduced carrying capacities over large parts of the Western Division of New South Wales as there was insufficient herbage to feed stock or carry fire (Noble, 1997). Curr (1883) attributed “the baked, calcined, indurated condition of the ground so common to many parts of the continent, the remarkable absence of mould which should have resulted from the accumulation of decayed vegetation, the comparative unproductiveness of our soils, the character of our vegetation and its scantiness, the retention within bounds of insect life” to Aboriginal burning. He observed increases in soil organic matter, and the initiation of widespread eucalypt decline after burning ceased (Curr, 1883). Howitt (1891) gave many examples of changes in the landscape after settlers “dispossessed the Aboriginal occupiers” who had “unintentionally prepared it, by their annual burnings, for our occupation”. He noted that large tracts of Gippsland became overgrown by saplings and shrubs so that it was difficult to ride over formerly open grassy country. Plagues of leaf eating insects erupted to “threaten the very existence of the red-gum” (Howitt, 1891). Scrubs replaced woodlands, grasslands and reedbeds, and were subsequently thinned to create forests or developed into forests by self-thinning (Wallis, 1878; Jacobs, 1955; AUSLIG, 1990; Donovan, 1997; Jurskis, 2009). Sedimentology and palynology have corroborated the historical ecology. Strong positive anomalies in charcoal deposition across Australia occurred on two occasions about the time of Aboriginal and European settlement. Following these peaks, deposition declined under Aboriginal management and under recent prescribed burning (Mooney et al., 2010, Figs. 2 and 5, p. 10). Sediment cores on the Murray River floodplain confirm historical accounts of woody thickening, increases in organic matter and

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Fig. 1. ‘Protected’ stand of Blakeley’s red gum – yellow box showing woody thickening, declining red gum and accumulating dead timber.

declines of herbaceous taxa after European settlement (Kenyon and Rutherfurd, 1999). Aboriginal burning (rather than climate change or hunting) had a key role in megafaunal extinctions (Miller et al., 2005; Prideaux et al., 2007), the development of eucalypt woodlands (Kershaw et al., 2002) and their maintenance (Kenyon, 2005). Grazing sometimes served as an ecological analogue for fire by removing vegetation and nitrogen, thus maintaining stable soil conditions and open stands of healthy old trees (Jurskis, 2008, 2009, Fig. 2; Turner et al., 2008; St Clair and Jurskis, in press). However the ecological history has been repeated over the last three decades in eastern Australia as prescribed burning has declined, grazing, thinning and firewood collection have been excluded from new conservation reserves, and thinning on private lands has been regulated with consequent increases in woody thickening, high intensity fires and eucalypt decline (Jurskis et al., 2003; Jurskis, 2005). Many recent studies have confirmed various parts of the process including accumulation of soil N, reduced C:N ratios and increased acidity and availability of aluminium and manganese with time since fire (Turner and Lambert, 2005; Turner et al., 2008); consequent changes in eucalypt physiology and increased folivory (Jurskis et al., 2011); as well as increases in other pests, parasites and diseases of eucalypts contributing to chronic decline (Jurskis, 2005; Jurskis et al., 2005; Sinclair, 2006) and woody thickening including shrub encroachment, decline of herbaceous, seasonally flammable understoreys and a change from breezy, sunny microclimates to shady, damp and still conditions (e.g. Birk and Bridges, 1989; Rose, 1997; Lunt, 1998; Jurskis, 2002; Lunt et al., 2006; Gleadow and Narayan, 2007; Price and Morgan, 2008; York, 2000). Only one of these studies measured fallen timber and it found that large logs were associated with unburnt stands (York, 2000). Red gum – yellow box woodlands are particularly prone to decline (Landsberg et al., 1990). Fig. 1 shows a stand that has been ‘protected’ from grazing and firewood collection for 16 years and displays these features. Woodlands are defined as stands of trees with less than 30% canopy cover whilst forests have more than 30% cover (AUSLIG, 1990). Woodlands that have been ‘protected from disturbance’ are developing into forests. For example, canopy cover averages 27% across red gum – yellow box stands in the region around Yass Plains and ranges up to 57% for ‘minimally disturbed’ stands (McElhinney et al., 2006). All types of woodland assessed by Gibbons et al. (2008, 2010) had tree densities typical of forests (104–614 stems ha−1 ) and an order of magnitude higher than pre-European woodlands

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(Jurskis, 2009). However most trees were small (<40 cm dbh) whilst densities of larger trees (average 27 ha−1 Gibbons et al., 2008, Table 5) were typical of stand densities in Aboriginal woodlands (∼30 ha−1 Wallis, 1878; Donovan, 1997; Lunt et al., 2006; Jurskis, 2009) confirming that woody thickening had occurred after human economy was excluded. In addition to living trees there were many dead trees contributing to the production of fallen timber. For example, 29% of large (>60 cm dbh) standing trees in red gum – yellow box woodlands were dead (Killey et al., 2010). 2.3. Contemporary observations Loads of fallen timber have been variously reported by weight or volume with or without estimates of moisture content and decay (Woldendorp et al., 2002). Air dry densities of the solid wood of woodland eucalypts typically range from about 0.8 to 1.2 Mg m−3 (Bootle, 1983). Contemporary observations of fallen timber loads are stated hereunder as published and it can be assumed that the weight and volume units are broadly comparable. Robinson (1997) reported that an ‘undisturbed’ stand of river red gum on the Murray River contained 125 Mg ha−1 of fallen timber and this is commonly cited as a benchmark for river red gum (e.g. MacNally et al., 2001; MacNally and Parkinson, 2005). MacNally et al. (2001) reported average loads of fallen timber in river red gum forests of 20 Mg ha−1 and maximum loads of 90 Mg ha−1 . They proposed ‘restoration targets’ of 40–50 Mg ha−1 . In red gum – yellow box woodlands, Manning et al. (2007) reported average loads of 34 m3 ha−1 and maximum loads of 247 m3 ha−1 , Gibbons et al. (2008) estimated a benchmark of 8 m3 ha−1 and Killey et al. (2010) estimated a benchmark of 7–12 m3 ha−1 of branchwood only. McElhinney et al. (2006) reported mean fallen timber loads of 11 m3 ha−1 (range <1–24 m3 ha−1 ) and this was not significantly different from scribbly gum (E. rossii) – red stringybark (E. macrorhyncha) forest (15 m3 ha−1 ). Benchmarks have been estimated at 4–9 m3 ha−1 for other eucalypt woodlands on New South Wales’ southwestern slopes and plains, and 9 m3 ha−1 for cypress (Callitris glaucophylla) woodlands (Gibbons et al., 2008). Gibbons et al. (2008) reported that fallen timber decreased where there was evidence of firewood collection. Overstorey cover, midstorey cover, litter cover, tree regeneration and stocking of small trees (<40 cm dbh) decreased with grazing and browsing by domestic stock and feral animals, and stocking of small trees also decreased as the number of cut stumps increased (Gibbons et al., 2008). In eucalypt forests in southern Queensland, Eyre et al. (2010) found that loads of fallen timber averaged 22 m3 ha−1 . They regarded frequent burning by graziers as a profound disturbance that reduced loads of fallen timber from 33 m3 ha−1 to 14 m3 ha−1 . Grazing and burning were also reported to reduce shrub densities (Eyre et al., 2010). Woldendorp et al. (2002) reviewed estimates of fallen timber in Australian ecosystems, reporting mean loads of 22 Mg ha−1 in four eucalypt woodlands and 51 Mg ha−1 in fourteen dry eucalypt forests. Moore et al. (1967) reported 56 Mg ha−1 from a single stand of brigalow (Acacia harpophylla) forest. In grassy blackbutt (E. pilularis) forest, York (2000) found that long unburnt plots were characterized by a greater number of large logs than repeatedly burnt plots. Hamilton et al. (1991) found that a low intensity prescribed burn in a messmate (E. obliqua) forest reduced fallen timber by 73%. In contrast, Bridges (2005) reported that prescribed burning had limited or negligible impact on loads of fallen timber in three studies in dry eucalypt forest. Harmon et al. (1986) suggested that burning increases the rate of accumulation of fallen timber, whereas Woldendorp et al. (2002) recognized that burning may increase or decrease loads of fallen timber in different circumstances.

3. Fallen timber and biodiversity MacNally et al. (2001) found no difference in total populations or species richness of birds, reptiles or amphibians according to loads of fallen timber in river red gum forests, however the most depauperate avifaunas were at two sites with the highest loads of fallen timber (60 Mg ha−1 ). Adding large quantities of fallen timber to small areas (1 ha) increased average species richness of birds from 2.5 to 2.9 species, probably by drawing birds in from surrounding areas with less fallen timber (MacNally and Horrocks, 2007). Densities of three birds (white-plumed honeyeater Lichenostomus penicillatus, western brown treecreeper Climacteris picumnus picumnus, yellow rosella Platycercus elegans flaveolus) and yellowfooted antechinus (Antechinus flavipes) increased with the additions (MacNally and Horrocks, 2007). They are common and widespread species that are not listed under New South Wales’ threatened species legislation. In red gum – yellow box woodland, species richness of beetles was higher under trees than next to logs and species composition was different (Barton et al., 2009). In blackbutt forest, species richness of understory plants and ants was higher in burnt areas with less fallen timber but there were more litter dwelling invertebrate taxa in unburnt areas with more fallen timber (York, 1999, 2000; Jurskis et al., 2003). However the quantity of fallen timber was not a significant factor explaining the species richness of ants and its effect on other taxa was not tested (York, 2000). None of the taxa are rare. I am unaware of any other direct studies of the relationship between fallen timber and biodiversity in grassy eucalypt ecosystems.

4. Discussion Studies of fallen timber have assumed that absence of human economy reflects natural conditions and the dramatic impacts of removal of Aboriginal fire have been uncritically dismissed (e.g. Wright, 1982; Griffiths, 2002; Jurskis, 2002, 2009). Ecological history shows that these assumptions are generally incorrect and that human intervention is necessary to maintain natural conditions because it has been a factor in their evolution (Allen et al., 2002; Jurskis, 2002, 2005, 2009; Bond, 2005; Hessburg et al., 2005; Turner et al., 2008; Attiwill and Adams, 2008; Ford et al., 2009; St Clair and Jurskis, in press; Jurskis et al., 2011). Historical records demonstrate that fallen timber did not accumulate in grassy ecosystems under Aboriginal management in Australia because it was consumed by Aboriginal people and their broadcast fires. Fallen timber accumulated in watercourses, rainforests and other dense shady stands where infrequent severe fires produced much fallen timber. Reports from North America (e.g. Harmon et al., 1986; Hessburg et al., 2005) suggest a similar pattern. Although fallen timber is widely considered to underpin biodiversity, a connection has not been demonstrated for grassy eucalypt systems. In contrast, loss of biodiversity with lack of fire and woody thickening has been demonstrated in several studies (Yates and Hobbs, 1997). Yates and Hobbs (1997) nominated chronic decline of eucalypts as an indicator of woodland degradation but had nothing to say about fallen timber. Exclusion of human economy promotes chronic decline of established trees (Curr, 1883; Howitt, 1891; Noble, 1997; Jurskis, 2008, 2009). Declining trees produce more fallen timber than healthy trees (e.g. Killey et al., 2010, Table 8), and dead trees contribute substantial quantities when they fall. Killey et al. (2010) suggested that dead trees can remain standing for long periods of time. This is true of large open grown trees, however small subdominant trees that ‘self-thin’ in denser stands are unbalanced and defective and fall quickly (pers. obs.). In a Nature Reserve in the Australian Capital Territory, Killey et al. (2010) found

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that 30% of small (<30 cm dbh) trees in red gum – yellow box ‘woodlands’ were dead. Accumulation of fallen timber is an indicator of malfunction in grassy ecosystems. A human role in shaping natural ecosystems, even over relatively short periods, and the consequences of excluding it appear to be well recognized in Eurasia (e.g. Gustavsson et al., 2007; Partel et al., 2007; von Oheimb and Brunet, 2007; Sherman et al., 2008; Szabo, 2010). Szabo (2010) found that a lowland Czech woodland remained relatively stable in structure for nearly six centuries under human management but changed dramatically when it was reserved for nature conservation with minimal human intervention. Plant diversity declined sharply with structural changes (Szabo, 2010). Historical ecology can provide a more realistic view of natural conditions than ‘scientifically rigorous’ studies based on false premises (Jurskis, 2002; Laris, 2008). Szabo (2010) recognised the value of qualitative historical information to assess natural conditions where no quantitative data are available and noted that the reliability of historical information can be assessed according to its source and the purpose for which it was recorded (Szabo, 2010). Early Australian explorers and naturalists studied the dynamics of Aboriginal fire and provided the richest testimony anywhere in the world of the function of fire in Aboriginal economies and ecosystems (Pyne, 2003). Oxley, Sturt and Mitchell were employed by the Colonial Government to describe the Aboriginal environment, assess the potential for development and identify suitable access. They systematically recorded all their difficulties and obstructions and it is clear that they were never obstructed by fallen timber in grassy eucalypt ecosystems under Aboriginal management (Jurskis, 2009). Historical records of changes to these ecosystems after European settlement disrupted Aboriginal culture were corroborated by recent scientific investigations. Mooney et al. (2010) found that post-European charcoal deposition rates declined under recent prescribed burning regimes but unaccountably dismissed historical records of frequent and extensive burning by Aborigines on the basis of low pre-European deposition rates. Gibbons et al. (2008, 2010) uncritically dismissed historical information about vegetation structure as tainted by subjectivity and pecuniary interest, qualitative and unsystematic. They suggested that diameter distributions of trees in eucalypt woodlands and open forests should have the reverse J form typical of unmanaged stands. However history shows that stands with high densities of small eucalypts were rare until Aboriginal management was removed (Mitchell, 1848; Wallis, 1878; Curr, 1883; Howitt, 1891; Donovan, 1997; Noble, 1997; Jurskis, 2009, Table 3) and historical data for stand densities are consistent with data from remnant pre-European stands (Jurskis, 2009), cadastral survey records (Lunt, 1997) and stump counts (Lunt et al., 2006). Aboriginal broadcast fire controlled recruitment of trees and shrubs in grassy ecosystems. Later on, domestic stock or rabbits performed a similar role in some areas. Current average loads of fallen timber in dry eucalypt forests of 51 Mg ha−1 (Woldendorp et al., 2002) are similar to loads in brigalow scrub (56 Mg ha−1 Moore et al., 1967). The distinction remarked upon by Mitchell (1848) has disappeared. Similarly, the distinction between open woodlands and dense forests around the Yass Plains (Bland, 1831) is disappearing and loads of fallen timber are similar (McElhinney et al., 2006). There are no quantitative records of fallen timber in Aboriginal ecosystems, other than presence/absence of loads sufficient to obstruct explorers’ travels. However this information together with historical records of the dynamics as influenced by Aboriginal economy can be used to infer natural loads. The roles of fire and Aboriginal people as consumers of fallen timber have not previously been assessed in any detail (e.g. Harmon et al., 1986; Woldendorp et al., 2002; Allen et al., 2002; Hessburg et al., 2005). The few recent studies of the impact of low inten-

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Fig. 2. River red gum forest growing on a site occupied in 1842 by reedbeds. ‘Framed’ by a pre-European woodland tree.

sity fires in Australia are equivocal (e.g. Hamilton et al., 1991; York, 2000; Bridges, 2005). However it is clear that woody thickening in the absence of fire alters microclimatic conditions and ground vegetation, reducing the flammability of fallen timber (Mitchell, 1848; York, 2000; Jurskis et al., 2003). The equivocal evidence from contemporary eucalypt ecosystems is likely a consequence of variable degrees of woody thickening. For example, after a breezy and sunny microclimate was restored by selective logging (51% stocking retained) in an ‘undisturbed’ coastal forest, a low intensity prescribed burn reduced the weight of fallen timber by 39% (Bridges, 2005) even though it was mostly relatively green logging debris. The residual stand retained a forest structure (101 stems ha−1 , Bridges, 2005), indicating the potential for broadcast burning to remove a large proportion of fallen timber from natural woodlands with drier climates and grassy understories. Consumption of fallen timber and broadcast burning were critically important to Aboriginal culture and economics. On the single occasion when Oxley (1820) was obstructed by fallen timber on land, the lack of evidence of human economy prompted him to declare it a “truly primeval forest”. In contrast, 41% of the remnant ‘woodlands’ and forests studied by Gibbons et al. (2008, 2010) had no evidence of fire and only 2% had evidence of recent fire. Studies of fallen timber in purported woodlands were in fact conducted in forests developing in a landscape starved of fire (e.g. ACT Government, 2004; Jurskis, 2009). Eyre et al. (2010) suggested that frequent burning by graziers was a disturbance that reduced loads of fallen timber and shrub densities. Historical information indicates that suppression of fire is a disturbance (e.g. Attiwill and Adams, 2008) and that absence of firewood collection and broadcast burning must result in accumulation of unnaturally high loads of fallen timber. For example, the data presented by Eyre et al. (2010) indicate that exclusion of fire from a dry eucalypt forest increased loads by 136%. The commonly cited benchmark (125 Mg ha−1 ) for fallen timber in river red gum is based on a single purported old growth stand in Millewa State Forest (Robinson, 1997). However historical records show that this site had no trees prior to European settlement. In 1842 Curr (1883) described it as follows: “on one side of us we saw extensive reed-beds intersected by the Murray, which (an unusual feature in colonial rivers) flowed here almost without banks, and on the level of the plain”. Mitchell (1839) noted the absence of fallen timber from reedbeds in the same region after spending a miserable frosty night with no fire. The purported old growth forest (Fig. 2) developed after European settlement (as a consequence of fire suppression and reduced flooding after river regulation) and is much denser and less resilient than the Aboriginal woodlands described

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by Curr as follows: “The other half of the circle was occupied by open, grassy forest land”. The difference is quite evident in the form and the health of the trees (e.g. Fig. 2; Jurskis, 2009, Fig. 2). Aboriginal woodlands contained low spreading trees at densities from about 6 to 30 ha−1 and were easily trafficable (Oxley, 1820; Bland, 1831; Sturt, 1833; Mitchell, 1839; Wallis, 1878; Curr, 1883; Howitt, 1891; Donovan, 1997; Jurskis, 2009) whereas vehicular access in current ‘minimally disturbed’ stands is usually impeded by fallen timber, small trees and undergrowth (pers. obs., Figs. 1 and 2, McElhinney et al., 2006, Fig. 8c). Remnant woodland stands whose natural structure and health have been maintained by grazing and burning of fallen timber are still easily trafficable (e.g. Lunt et al., 2006, Figs. 6 and 8; Jurskis, 2009, Fig. 2). Killey et al. (2010) suggested that production of fallen timber has been reduced as a consequence of thinning to promote pasture. However there are currently 21 large trees ha−1 in red gum – yellow box woodlands (Gibbons et al., 2008; Killey et al., 2010) and this is typical of pre-European tree densities for temperate eucalypt woodlands (Wallis, 1878; Croft et al., 1997; Lunt, 1997; Lunt et al., 2006; Jurskis, 2009). Aboriginal management maintained native pastures that were suitable for immediate occupation by European graziers (Bland, 1831; Curr, 1883; Howitt, 1891). Thinning by pastoralists has typically removed most new growth and some established trees as did Aboriginal burning and hunting practices (Jurskis, 2009). The lowest benchmark in the literature for fallen timber in grassy eucalypt ecosystems was 4 m3 ha−1 in ‘relatively unmodified’ white box (E. albens) ‘woodland’ with about 20% canopy cover and 188 live trees ha−1 including 16 large (>60 cm) live trees and an additional unspecified number of dead trees (Gibbons et al., 2008, Tables 5 and 6 and Fig. 1). There were 34 hollow bearing trees per hectare, but only 16 large live trees (Gibbons et al., 2008), suggesting that there were many large dead trees. This ‘benchmark’ reflects a forest rather than a woodland structure, absence of firewood collection, fire, and any ecological analogues for fire; production of fallen timber by large trees at natural densities; and additional production by many large dead trees and dense stands of small trees that were not a feature of the Aboriginal environment. It clearly represents very much reduced consumption and increased production of fallen timber compared to Aboriginal woodlands.

5. Management of grasslands, woodlands and open forests Since the mid 20th Century there has been a global upsurge in nature reserves and conservation strategies based on exclusion of human intervention (Szabo, 2010). These strategies have typically failed because a few species including pests, parasites and diseases of trees as well as dense shading or shade tolerant vegetation have proliferated at the expense of many others, whilst nutrient cycling processes, microclimates and ecosystem structures have been altered and resilience has been lost. Examples come from a wide range of North American forests where human burning was stopped (e.g. Allen et al., 2002; Hessburg et al., 2005; St Clair and Jurskis, in press), European woodlands and grasslands where grazing, mowing and/or timber harvesting were stopped (Gustavsson et al., 2007; von Oheimb and Brunet, 2007; Spitzer et al., 2008; Szabo, 2010), Chinese alpine meadows where burning by graziers was stopped (Sherman et al., 2008) and Australian eucalypt woodlands where grazing and burning were stopped (Jurskis, 2005, 2009; Close et al., 2009; Price and Morgan, 2009). New South Wales legislation lists White Box Yellow Box Blakeley’s Red Gum Woodland (box – gum woodland) as an Endangered Ecological Community (EEC) and the EEC Profile states that grazing and collection of firewood and other fallen timber are threats to this community (Department of Environment and Conservation,

2005). Exclusion of these activities and ‘protection from disturbance’ are nominated as priority actions for recovery. In contrast, the Commonwealth listing of box – gum woodlands as critically endangered recognizes that burning, grazing and/or slashing can play a positive role in conserving biodiversity and reducing fire risk by controlling weeds, physically dominant native grasses and overstorey ‘regeneration’ (Department of Environment and Heritage, 2006). However the Commonwealth has no direct role in the management of box – gum woodlands. Ninety two percent of Australian box – gum grassy woodlands has been cleared since European settlement (Department of Environment and Heritage, 2006) and many reserved remnants are thickening into forests. There are many extinct or endangered species associated with grassy woodlands and five of seven broad types of grassy woodland in New South Wales are EECs (Keith, 2004). Augmentation of fallen timber and exclusion of ‘disturbance’ to encourage woody thickening are not logical conservation measures because common species associated with dense forests and accumulations of fallen timber may replace rare species associated with open grassy ecosystems and/or large old spreading trees (Allen et al., 2002; Jurskis, 2002; Jurskis et al., 2003; Waldron et al., 2008; Ford et al., 2009). Different invertebrate assemblages are associated with fallen timber compared to open grassy groundlayers (York, 1999, 2000; Barton et al., 2009). As reserved remnant woodlands turn into forests and grassy forests turn into shrubby forests, they will be favoured at the expense of species dependent on woodlands. On New South Wales’ southwestern slopes the threatened superb parrot (Polytelis swainsonii) is associated with scattered large hollow woodland trees, particularly Blakely’s red gum, and patchy herbaceous ground layers (Department of Environment and Conservation, 2005; Manning et al., 2006), habitat features which decline in the absence of fire or some ecological analogue for fire. On New South Wales’ Northern Tablelands, the endangered Hastings River mouse (Pseudomys oralis) is found only in open grassy forest maintained by grazing and burning and not in dense ‘protected’ forests where there are high numbers of the common and widespread brown antechinus (Antechinus stuartii) and bush rat (Rattus fuscipes) (Tasker and Dickman, 2004). In non-floodplain river red gum woodlands, species richness of the naturally diverse ground layer is reduced by woody thickening (Price and Morgan, 2008, 2010) and in East Gippsland the critically endangered orchid Prasophyllum correctum occurs only in red gum woodlands within railway reserves where frequent burning reduces grass competition and increases reproduction of orchids (Coates et al., 2006). The eastern brown treecreeper (Climacteris picumnus victoriae) which is listed as threatened in New South Wales was lost from two eucalypt woodlands after they were ‘protected’ from grazing, burning and firewood collection and consequently suffered structural changes including woody thickening (Ford et al., 2009). Structural changes after removal of human intervention have affected ecosystems around the world, reducing plant diversity and endangering fauna. For example, the extent of longleaf pine (Pinus palustris) woodlands in the southeastern United States has been reduced by 97% and the eastern diamond backed rattler (Crotalus adamanteus) which relies on open grassy habitat is imperiled as a consequence (Waldron et al., 2008). In North America various combinations of thinning and burning are now being widely used in adaptive management and monitoring programs to restore diversity, resilience and fire safety (e.g. Allen et al., 2002; Hessburg et al., 2005; St Clair and Jurskis, in press).

6. Conclusions Quantitative data are not available for natural loads of fallen timber and undisturbed stands are not a suitable reference. Qualitative

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