Biodiversity
Theme commentary
Steven Cork, Land & Water Australia and CSIRO
Paul Sattler, Paul Sattler Eco-consulting Pty Ltd
Jason Alexandra, Alexandra and Associates Pty Ltd
prepared for the 2006 Australian State of the Environment Committee, 2006
Pressures on biodiversity
The major pressures
Climate change and habitat modification are the leading drivers of biodiversity decline worldwide (Thomas et al 2004; Millennium Ecosystem Assessment 2005a, b). In Australia, climate change will be one of the major pressures on biodiversity in the next few decades. Direct habitat loss through vegetation clearing is expected to decrease due to legislation to curtail it in most states and territories, but the remaining pressures are powerful: the legacy of past clearing together with the direct impacts on habitat and native species of total grazing pressure, altered fire regimes, and introduced species.
There are few systematic and quantitative data on trends in any of these pressures at a national scale, but the weight of evidence about their effects makes it clear that they are still having substantial impacts on a wide range of biodiversity. In the absence of quantitative data, one way to gauge which pressures are most significant nationally is expert opinion. In NLWRA (2002), which assembled information and opinion from more than 40 of Australia’s leading ecologists and experienced conservation managers, the five most frequently recorded threatening processes perceived to be pressures on a range of biodiversity assets assessed across all bioregions and subregions were:
- total grazing pressure
- weeds
- feral animals
- changed fire regime
- habitat fragmentation.
- Other less frequently reported pressures include:
- vegetation clearing (particularly eastern Australia)
- changed hydrology and salinity (changed flows, increases or decreases in ground water)
- pollution (including sediment and nutrient pollution of rivers, wetlands, estuaries and coastal waters).
| Threatened Species (see caption for difference between columns)* |
Threatened Ecosystems | Riparian Zones | DIWA** wetlands | |
|---|---|---|---|---|
| Feral animals Changed fire regimes Grazing pressure Exotic weeds Other Increasing fragmentation Vegetation clearing Changed hydrology Pollution Pathogens Firewood collection Salinity |
Vegetation clearing Grazing pressure Feral animals Changed fire regimes Increasing fragmentation Changed hydrology Exotic weeds Pollution Salinity |
Grazing pressure Feral animals Exotic weeds Changed fire regimes Increasing fragmentation Vegetation clearing Changed hydrology Salinity Firewood collection |
Grazing pressure Exotic weeds Feral animals Changed hydrology Increasing fragmentation Changed fire regimes |
Grazing pressure Exotic weeds Feral animals Changed hydrology Pollution Salinity |
* For columns 1, 3, 4 and 5 the ranking was based on the number of IBRA subregions reporting the threat. For column 2 the ranking was based on numbers of species per subregion reported to be threatened
**DIWA = Directory of Important Wetlands in Australia
These pressures have greater impacts in Australia, compared with other parts of the world, for several reasons:
- Australia has experienced high rates of recent land use change , with approximately half of all clearing and land development for agriculture occurring in the last 30 years (Dunlop et al 2002; Dunlop 2003). This has altered the extent, quality and patterns of habitat and changed fundamental hydrological and other processes
- Australia has high rates of diversity and endemism, with many plants and animals adapted to specific climates: many species could face challenges adapting to expected climate change
- Australian biodiversity is adapted to fluctuating patterns of fire frequency and intensity , and water availability , both of which are being altered by human activities;
- Altered erosion rates and nutrient status of soil and water systems are impacting on plants and animals adapted to this continent’s old and nutrient-poor soils and on species adapted to low nutrient riverine, estuarine and coastal ecosystems
- Australia, with its 300 million years of geographic isolation and separate evolution, has been protected from biotic invasions . It is increasingly being exposed to exotic species due to increased globalisation of trade and movement of people.
In the following section, comment is made on these major pressures individually, but it should be born in mind that they are not independent. They often interact to increase one another’s impact, and they should not be dealt with individually. This is why landscape-scale responses to biodiversity decline, discussed later, are extremely important.
Land clearing
Recognition of the impact of clearing Australia's native vegetation is not new. As long ago as 1892, Samuel Dixon expressed concern to the Royal Society of South Australia (Dixon 1892) about the destruction of the forests, balding of hills, increased flooding and loss of indigenous flora.
The clearing of native vegetation has been recognised as one of the biggest threats to Australia’s biodiversity in previous state of the environment theme reports (Saunders et al 1996; Williams et al 2001). Since SoE2001, significant reforms to vegetation management have occurred in Queensland, New South Wales and, very recently, Tasmania (Table 5).
| Jurisdiction | Reforms |
|---|---|
| Australian Capital Territory | Stronger emphasis on biodiversity and vegetation management through land management agreements on all rural leases |
| New South Wales | Commitment to end broadscale clearing and clearing of protected regrowth vegetation |
| Northern Territory | Commitment to control the clearing of native vegetation across all tenures |
| Queensland | Commitment to protect all threatened vegetation communities and phase out clearing of remnant vegetation by 2006 |
| South Australia | Commitment to achieve a net gain in native vegetation quality and extent |
| Tasmania | Commitment to protect all threatened forest and non-forest vegetation communities and maintain at least 95 per cent of the 1996 native forest estate on public land |
| Victoria | Native vegetation management framework in place to achieve a net gain in native vegetation cover |
| Western Australia | Environmental Protection Act 1986 now protects native vegetation |
Source: DEH(2004b)
The effects of these reforms are not yet evident. Declines in rates of land clearing are not evident in the data available for this assessment (see Tables 6–7 and Figures 1–4), and clearing in Queensland continues at a high level as part of a phase out programme. Overall there was a nett loss in ‘forest’ between 1973 and 2004 due to land clearing of about 7.5 million hectares. Clearing has resulted in high death rates for a range of fauna and flora species in this 2001–06 reporting period, but there has been insufficient monitoring to allow conclusions about the impacts on the long-term viability of populations.
| State or territory | Number of hectares cleared each year | |||
|---|---|---|---|---|
| 2001 | 2002 | 2003 | 2004 | |
| New South Wales | 72 420 | 64 073 | 64 068 | 110 858 |
| Northern Territory | 1 325 | 1 510 | 1 718 | 5 751 |
| Queensland | 288 257 | 215 131 | 192 390 | 219 961 |
| South Australia | 9 929 | 8 438 | 8 064 | 12 329 |
| Tasmania | 7 369 | 10 432 | 12 260 | 13 717 |
| Victoria | 10 454 | 13 058 | 13 640 | 23 407 |
| Western Australia | 29 795 | 34 599 | 35 231 | 38 704 |
Source: ERIN (2005); International definition of forest is defined as vegetation that has at least 20 per cent canopy cover, is two metres tall and has a minimum of 0.2 hectares. It does not distinguish between native and non-native woody vegetation. The analysis includes land that has been cleared more than once during the period
| State or territory | Number of hectares cleared each year | |||
|---|---|---|---|---|
| 2001 | 2002 | 2003 | 2004 | |
| New South Wales | 63 610 | 74 852 | 76 483 | 115 373 |
| Northern Territory | 4 206 | 5 264 | 6 323 | 9 076 |
| Queensland | 99 844 | 115 373 | 108 339 | 117 173 |
| South Australia | 18 465 | 15 517 | 15 419 | 18 636 |
| Tasmania | 12 753 | 12 517 | 12 527 | 11 374 |
| Victoria | 40 293 | 36 816 | 35 531 | 49 311 |
| Western Australia | 63 214 | 57 050 | 56 498 | 50 247 |
Source: ERIN 2005
Source: ERIN 2005
Source: ERIN 2005
While recent developments may make broadacre vegetation clearing itself of less concern as a direct pressure nationally than it was at SoE2001 (although it remains a significant pressure in some parts of Australia), the legacy of past clearing is a major ongoing pressure. Once vegetation communities and their associated animals and other organisms have been fragmented and disturbed by clearing they become susceptible to other pressures such as insects, weeds, overgrazing, compaction, salinisation, and changed fire regimes (Saunders et al 1996; Williams et al 2001). In particular, changed hydrology may underlie increasing salinisation for many decades (see Murray–Darling Basin Commission 2003b).
For vegetation communities, these pressures can result in a decline in health, increased susceptibility to diseases, failure of regeneration, and even plant death. As many vegetation communities on fertile soils have been preferentially and extensively cleared, these communities are generally under-represented in protected areas, and remnants outside reserves are under particular threat. Recent work in South Australia and Western Australia raises fears that direct removal of paddock trees, coupled with a lack of regeneration, will lead to a near-complete loss of paddock trees from many rural landscapes in the future (Saunders et al 2003; Carruthers and Hodder 2005).
For both plants and animals, fragmentation of large areas of habitat into smaller pieces means that fewer species can be accommodated in the new ‘islands’. In addition, fragmentation can slow or prevent the mixing of genes among individuals in populations, which can result in inbreeding that reduces the reproductive fitness and long-term health of populations. It is estimated, for example, that even after cessation of clearing in the Mount Lofty Ranges of South Australia, 16 species are likely to go extinct within 200 years due to past impacts (Westphal et al 2003). Available data also report declines in a range of bird species in other parts of Australia (Olsen et al 2006) At present there are few studies of genetic fitness and health of Australia’s biodiversity, although with the increasing capacity through high-speed genetic profiling, research into genetic impacts for some species will be more feasible in coming years.
Clearing in the past has been much higher in some vegetation types than others (NLWRA 2002; and also Table 8; Figure 5). In general, policy frameworks have not been in place to determine the environmental risks and costs, such as of loss of ecosystem services, of clearing in each area (for example, the loss of carbon sequestration and artesian aquifer recharge associated with clearing of marginal rangelands in the Desert Uplands of Queensland). In terms of both planning and state of the environment reporting, there is a need for better assessment processes that assess the trade-offs between development, biodiversity impacts, and implications for ecosystem services at scales relevant to the processes involved; those tradeoffs should also be made much clearer than they are now.
| Major vegetation group | Estimated pre-1750 area (kmē) | Area remaining (kmē) | Percentage remaining | Percentage of remaining vegetation in reserves |
|---|---|---|---|---|
| Rainforest and vine thickets | 53 469 | 35 200 | 65.8 | 54.4 |
| Eucalyptus tall open forest | 40 801 | 35 344 | 86.6 | 33.6 |
| Eucalyptus open forest | 394 280 | 272 121 | 69.0 | 22.7 |
| Eucalyptus low open forest | 4 726 | 3 952 | 83.6 | 35.1 |
| Eucalyptus woodlands | 1 362 263 | 892 920 | 65.5 | 8.1 |
| Acacia forests and woodlands | 495 059 | 408 632 | 82.5 | 8.8 |
| Callitris forests and woodlands | 40 278 | 32 296 | 80.2 | 6.1 |
| Casuarina forests and woodlands | 166 303 | 149 262 | 89.8 | 18.5 |
| Melaleuca forests and woodlands | 106 057 | 99 561 | 93.9 | 10.1 |
| Other forests and woodlands | 80 772 | 72 414 | 89.7 | 9.9 |
| Eucalyptus open woodlands | 498 663 | 458 905 | 92.0 | 6.2 |
| Tropical eucalypt woodlands/grasslands | 115 503 | 112 481 | 97.4 | 12.8 |
| Acacia open woodlands | 320 981 | 314 040 | 97.8 | 7.6 |
| Mallee woodlands and shrublands | 387 230 | 271 529 | 70.1 | 36.8 |
| Low closed forest and tall closed shrublands | 25 819 | 16 278 | 63.0 | 30.5 |
| Acacia shrublands | 865 845 | 851 274 | 98.3 | 10.0 |
| Other shrublands | 157 530 | 123 464 | 78.4 | 18.7 |
| Heath | 9 256 | 8 071 | 87.2 | 44.1 |
| Tussock grasslands | 559 850 | 525 888 | 93.9 | 3.0 |
| Hummock grasslands | 1 368 861 | 1 367 973 | 99.9 | 9.9 |
| Other grasslands, herblands, sedgelands and rushlands | 67 977 | 64 810 | 95.3 | 17.2 |
| Chenopod shrublands, samphire shrubs and forblands | 447 239 | 436 801 | 97.7 | 12.6 |
| Mangroves | 9 664 | 9 325 | 96.5 | 33.1 |
| 7 578 427 | 6 562 541 | 86.6 | 11.5 |
* except for the NSW component, where most data are from 1997
Sources: National Vegetation Information System (NVIS) Stage 1, Version 3.0 Major Vegetation Groups, DEH, Canberra. URL: http://www.deh.gov.au/erin/nvis/mvg/index.html; and DEH (2006) Australia’s Native Vegetation 2006, Australian Government, Canberra.
Large-scale restoration of habitat is required to offset the effects of past clearing and ongoing degradation of the woodlands of south-eastern and south-western Australia. Revegetation programmes have been supported by local, state and Australian governments and have been notably implemented by non-government organisations such as Landcare and Greening Australia. To assess the effectiveness of these responses, detailed data are needed to show where the actions are taking place, which vegetation and animal associations are being targeted, how the actions affect the connectivity of habitat, how populations are responding, and how changed hydrological regimes may be restored in some locations. As emphasised elsewhere in this commentary, plans are required that identify the specific priorities for different places and different elements of biodiversity around Australia.
At present, the only data available on replacement of vegetation at a national scale are very broad. These data do not distinguish between native and introduced plants; they also include plantations, with variable value for biodiversity, and woody weeds. Revegetated areas take many decades to develop structure and other elements of habitat quality required to sustain plant and animal populations. Thus, numbers of individual plants and animals do not increase as quickly in replaced vegetation as they declined during clearing.
Nevertheless, recent research indicates that in landscapes that have been predominantly cleared and grazed, revegetation can have a significant impact on fauna (Lindenmayer et al 2003). Programmes to encourage the protection of regrowth in key areas remain viable opportunities to secure some threatened ecological communities and the return of vegetation to overcleared landscapes. This can be a much more cost-effective approach than replanting in some landscapes where natural regenerative capacity remains. Other effective responses involve the fencing and special management of remnants.
Invasive organisms
Invasive organisms are animals, plants or diseases that have entered Australia from elsewhere, either as deliberate or accidental introductions, and many cause economic, social or environmental harm (Australian Biosecurity Group 2005).
These species have diverse modes of action, routes of introduction and spread, and geographic range among invasive organisms (Reddiex et al 2004; Australian Biosecurity Group 2005;. There are more than 2800 exotic weeds, 25 mammals, 20 birds, four reptiles, 34 fish, 100–400 invasive marine species, and unknown numbers of other invertebrate species and diseases. The CSIRO estimates that Australia gains 20 new pests or diseases each year (CSIRO 2004).
In Australia, exotic pests like feral cats, foxes and rabbits are considered a primary cause of past extinctions of animal species and a potent source of ongoing pressure. Examples include the recent arrival of the Cane Toad (Bufus marinus) in relatively undisturbed parts of the Top End , and the devastating reduction in Quoll (Dasyurus spp) numbers.
The impacts of habitat alteration can be magnified by invasive organisms. The two Australia Bird Atlas surveys reviewed by Garnett et al (2002) show increases in habitat modification and the relative abundance of introduced bird species correlated with decreases in native bird abundance and distribution. The highest abundance of introduced bird species, principally exotic species, occur in the extensively modified parts of south-east Australia and eastern Tasmania where they now make up 15 per cent of all species (NLWRA 2002).
Diseases have posed threats, and will pose new threats, to both plants and animals, especially in an increasingly globalised world (Millennium Ecosystem Assessment 2005b). A prime example is the devastating impacts of Phytophthera cinnamomi on native vegetation (Australian Biosecurity Group 2005).
Although there are few data on economic costs of marine and freshwater pests, invertebrates and diseases generally, the annual costs of weeds and feral vertebrates alone (more than $4 billion) outstrip the cost of dryland salinity (more than $200 million) several-fold (Agtrans Research and Dawson 2005; Australian Biosecurity Group 2005.
| Sector | Economic activity low | Economic activity moderate | Economic activity high |
|---|---|---|---|
| Costs of control and losses in output | |||
| Agriculture | 3442 | 3927 | 4420 |
| Costs of control only: no losses in output | |||
| Natural environment | 20 | 20 | 20 |
| Public authorities | 81 | 81 | 81 |
| Indigenous lands | 3 | 3 | 3 |
| Commonwealth research | 8 | 8 | 8 |
| Total | 3554 | 4039 | 4532 |
Source: Sinden et al (2004)
In the past, management of invasive organisms has focused on identifying the magnitude of the impacts and on control strategies for impact minimisation (for example, the Bureau of Rural Science’s vertebrate pest series). Approaches to managing invasive organisms often have been applied without attention to monitoring the effectiveness of past responses or to experimental design (Reddiex et al 2004).
Since SoE2001, increased attention has been given to protecting Australia from the threat of new invasive plant species, with a focus on the routes of invasions and integrated legislation, policies, plans and processes that aim to enhance national biosecurity. A recent analysis of weed introductions concluded that ornamental horticulture (the gardening industry) exceeds all other industries in terms of introducing new plants species, including many agricultural and environmental weeds (Australian Biosecurity Group 2005).
A number of gaps in Australia’s suite of responses to invasive organisms have been identified, including: gaps in quarantine laws; inadequate early warning surveillance; mismatches between laws in different states; inadequate contingency plans for environmental weeds, pests and diseases; inadequate approaches to integrated control of agricultural and environmental pests; inadequate funding for controlling environmental invasive species; inadequate protocols to decide priorities and who pays; poor sharing of information; and lack of community awareness (Australian Biosecurity Group 2005). The deliberate spread of some aggressive introduced pasture species and the lack of protocols for their use as part of pastoral development remains a key biodiversity issue.
It has been noted that public resources committed to invasive organisms appear to be small, particularly compared with expenditure on other natural resource management issues, the economic and environmental impacts of invasives compared with other issues, and the relatively high benefit-cost ratios reported from analyses of research and development on invasive organisms (Agtrans Research and Dawson 2005).
The Australian, state and territory governments have commenced a major review to identify and correct strategic gaps in Australia’s response to invasive organisms . This includes development of a National Framework to Prevent and Control Invasive Species, a National Biosecurity Strategy, a revision of the National Weeds Strategy, development of a new National Pest Animal Strategy, and progress to implement the National System for the Prevention and Management of Introduced Marine Pests. In early 2005, the Australian Government agreed to remove 4000 known weeds not yet present in Australia from the permitted list under the Quarantine Proclamation 1998. Because of the costs of invasive organisms and the risks they could pose to Australia’s diversity of ecosystems, it would be prudent to go further and place the burden of proof on proponents of any new introductions, with new species planned for introduction being considered potentially invasive until proven benign.
Fire
See also: Living in a land of fire
‘Burn grass’ is as ancient as time itself. The burning of country was handed down to our people from the Dreamtime. ‘Burn grass’ takes place after the wet season when the grass starts drying off. The country tells you when and where to burn. To carry out this task you must know your country (Yinirrakun-April Bright 1995).
To grow flowers in Blackheath, Australia,
set fire to your fields. Let flame
singe the delicate dust-seeds
of native shrubs. Soon they sprout,
on ground bare, as if hoed.
Bright petals follow,…
but not one has a name that Shakespeare knew… (O’Connor 1990)
Both quotes, from widely different backgrounds, tell of fire as a natural phenomenon and its importance in the evolutionary history of Australia. Recent research confirms the conventional wisdom that different types of country and different species of plants and animals require different fire regimes. This approach is reflected in the Ecological Society of Australia’s call for informed use of fire as a management tool and in approaches adopted by the various state agencies responsible for fire.
Australia’s capacity to monitor fire has increased greatly over the last decade and this is now done at a range of scales; although the data available on the incidence and intensity of fires across Australia and the areas burned (see Tables 12 and 13 and
Figure 6) do not allow national conclusions on the overall impacts on biodiversity . In 2003, there was more than 25 000 unplanned grass or bush fires in Australia that burnt more than 67 million hectares. In the five years to 2003, approximately eight per cent of the Australian land area was burnt each year; this is in contrast to the tropical savannas (north of 21 degrees South) where approximately 77 per cent of the area is burnt each year.
| State or territory | Number of unplanned grass and forest fires | Estimated area burnt (ha) |
|---|---|---|
| Australian Capital Territory | 94 | 157 000 |
| New South Wales | 2 500 | 1 464 000 |
| Northern Territory | 2 886 | 38 400 000 |
| Queensland | 2 778 | 8 000 000 |
| South Australia | 1 311 | 2 610 000 |
| Tasmania | 1 500 | 58 000 |
| Victoria | 3 000 | 1 300 000 |
| Western Australia | 11 515 | 15 545 000 |
Source: Ellis et al (2004)
Figure 6: Area of forest in Australia burned due to wildfire and fuel reduction burns, 1995–2004
Source: AGO (2005)
To illustrate some of the impacts of fire, examples of different fire regimes are given from the forests and woodland of the southern Australia and the tropical savannas.
South-eastern Australia has experienced several major bushfires in recent years, including the extensive alpine fires of 2003. Because such large alpine and subalpine areas were burnt in one event, this could have resulted in major impacts on plants and animals, including several nationally threatened fauna species and rare plants and sensitive vegetation communities (such as peat bogs). Additional impacts can result from the thousands of kilometres of heavy-vehicle tracks and fire lines that create opportunities for species invasion .
While fires appear to result in significant change to landscapes in the higher rainfall parts of south-eastern Australia, there is evidence of irregular but episodic fires in both the historical records and in the patterns of vegetation responses to fire (for example, fire sensitive ash species Eucalyptus regnans and Eucalyptus delegatensis). There is a strong tendency for major fires to be associated with periods of below average rainfall (for example, 1939, 1983 and 2003).
One response arising from these fires has been the increased prescription burning for fuel reduction and for asset protection. Despite various prescriptions for burning regimes, the use and management of fire across Australia’s diverse ecosystems will remain controversial. Therefore the most substantive issues are not the area burnt but the area subjected to well-developed fire management plans that include biodiversity conservation objectives, and the need for monitoring and reporting systems to track biodiversity responses. An example is in parks in the Northern Territory, which have fire monitoring programmes that are designed to measure biodiversity trends (Edwards et al 2003).
In much of the northern savannas, there is now a higher incidence of extensive, hot, late, dry season fires, with marked environmental costs. These fires are of much higher intensity and of greater scale than traditional burning practices by Indigenous peoples. Instead of a patchwork of burnt and unburnt country, important habitat refuges are easily lost leading to a loss of regional biodiversity.
| Year | Area (million hectares) |
Percentage of total land area fire affected | Percentage of fire affected area that is tropical savanna1 |
|---|---|---|---|
| 1997 | 48.3 | 6.3 | 86 |
| 1998 | 26.3 | 3.4 | 92 |
| 1999 | 60.0 | 7.8 | 86 |
| 2000 | 71.5 | 9.3 | 65 |
| 2001 | 80.1 | 10.4 | 84 |
| 2002 | 63.8 | 8.3 | 63 |
| 2003 | 31.6 | 4.1 | 85 |
1 Defined by the Department of Land Information, for the purposes of monitoring fire-affected areas, as being the area north of 21°S and east of 120°E.
Source: Western Australian Department of Land Information (2004)
In contrast, in the wet tropical environments with an average of more than 1500 millimeters of rainfall each year-on Cape York Peninsula and in the Wet Tropics bioregions-massive habitat changes are still occurring due to the decreasing incidence of fire, largely caused by fuel removal by cows. Grasslands have mostly disappeared under shrubs and trees, and wet sclerophyll communities have been significantly invaded by rainforest causing the loss of habitat for many species (Stanton 1995). The reintroduction of regular fire into these systems, and possibly hotter fires to ensure penetration, is required.
In the drier 500–800 millimetre rainfall belt, some Acacia communities such as Brigalow (Acacia harpophylla), Gidgee (Acacia cambagei) and the botanically diverse vine thickets are sensitive to fire. The introduction of exotic pasture species such as Buffel Grass (Cenchrus cillaris) can carry fire into these fire retardant but fire sensitive communities, causing their loss. Likewise, introduced Gamba Grass (Andropogon gayanus), which grows to four metres high, in the Top End has caused such fuel loads that even the structure of eucalypt woodlands may be threatened (Bowman 1999; CSIRO 2002).
In some agricultural and pastoral regions, fire has been excluded for social and economic reasons. There often is a reticence by the community to allow the use of fire because of threats to safety and property, and because the short-term loss of pasture is considered economically undesirable. In places this has led to invasion by woody shrubs, which causes the loss of ground cover and sometimes creates conditions where controlled use of fire as a management tool to control woody shrubs cannot be used due to the lack of grassy biomass (fuel) in the ground layer (Noble et al1990).
Fire was recognised in 1999 as a main threatening process for many rare, vulnerable and endangered Australian birds (Woinarski 1999) and this situation has not improved.
The long history of the withdrawal of traditional burning practices has allowed radical changes to occur to the structure and floristics of many habitats. In some places, the return to traditional burning is not possible. In contrast, in large parts of northern Australia and across our rangelands, the adoption of burning practices based on the combined experience of traditional ‘grass burn’ and scientific knowledge is essential to achieve sustainable management for biodiversity (Latz 1995).
The adoption of appropriate fire regimes could be one of the most cost-effective tools for biodiversity management across large parts of Australia Williams et al (2001) identified a tension between management of fire for biodiversity protection versus other management objectives in much of Australia. Some progress has been made since SoE2001 towards resolving this dilemma, with the publication of several guidelines based on research on the fire ecology of a range of species. The application of a technical understanding of fire regimes and their impacts on different ecosystems to protect biodiversity as part of ongoing land management remains a key challenge. This will involve much greater investment in research and in community understanding of appropriate fire regimes than currently exists. Finally, fire frequency and intensity, and the probability of uncontrollable fires, are likely to change significantly with climate change (see below).
Grazing
Grazing affects biodiversity in a range of ways, including direct removal of some species, changes in the relative proportions and mixtures of species in ecosystems such as grasslands, shrublands and woodlands, alteration to habitat in mid-and lower storeys of forests and grasslands, altered fire regimes, and impacts on soil structure and water infiltration. Total grazing pressure is considered to be the most significant threat to a range of biodiversity elements, including threatened ecosystems across Australia ( Table 4). Very large reductions in extent of all native grasslands have occurred since 1750 ( Table 4).
| Bioregion | Pre-1750 (ha) | Extant (ha) | Proportion remaining (%) |
|---|---|---|---|
| Brigalow Belt South | 270 000 | 25 000 | 9.26 |
| Flinders Lofty Block | 1 500 000 | 5 000 | 0.33 |
| Murray-Darling Depression | 440 460 | 1 244 | 0.28 |
| Riverina | 2 750 000 | 26 871 | 0.98 |
| South East Coastal Plain | 60 000 | 25 | 0.04 |
| South Eastern Highlands | 450 000 | <22 500 | <5.00 |
| Tasmania | 80 098 | 13 617 | 17 |
| Victorian Volcanic Plain | 220 073 | 2 291 | 1.04 |
| Total | 5 770 631 | 96 548 | 1.67 |
Source: Carter et al (2003)
The impact of grazing is often disproportionately higher on the more fertile, alluvial parts of the landscape, riparian zones beside watercourses, and on important refugial habitats.
The Biograze project concluded that, although native species generally appear to be surviving in grazed rangeland areas, some are so sensitive that they occur only where there is negligible grazing pressure. Such sites are typically a long way from water points; a factor increasing the impacts of total grazing on these sites is the number of water points developed to spread pasture utilisation. While there has been talk of incentives to protect ungrazed parts of properties through fencing and restriction of new watering points, there are few examples of this being put into practice. The conversion of bore drains to poly pipe with controlled watering facilities in some rangelands also offers the opportunity for better ecological management.
In some marginal rangelands, such as parts of the Mulga Lands, the poor economics of wool production and high kangaroo populations have conspired against the possibility of country being spelled and ecosystems restored.
Management of total grazing pressure is critical to achieving biodiversity conservation and sustainable landscape management. In large parts of Australia’s rangelands, the prevailing tenures are pastoral leases. Revision of conditions of pastoral leases in a number of the states and territories in the next decade presents a unique opportunity for the introduction of requirements that more accurately can specify sustainable grazing regimes and the protection of multiple values.
No coordinated Australia-wide monitoring programme exists for the rangelands, despite their enormous social, environmental and economic contribution; efforts to establish a comprehensive monitoring system have been slow. A number of major reports have recommended the comprehensive monitoring of the rangelands, including the impacts of grazing on biodiversity and landscape function. These reports include: National Principles and Guidelines for Rangeland Management (Commonwealth of Australia 1999); Rangelands – Tracking Changes (NLWRA 2001b); and Biodiversity Monitoring in the Rangelands: A Way Forward (Smyth et al 2003). Progress on monitoring in the rangelands is reported in Watson 2006.
Changed hydrology
Hydrology is the study of the properties, distribution, and effects of water on the earth's surface, in the soil and underlying rocks, and in the atmosphere. Impacts of changed hydrology on biodiversity include deteriorating water quality, reduced water availability, altered flow regimes in waterways, and the rising of watertables due to clearing of native vegetation and the movement of salts to surface layers of soil and waterways (Williams et al 2001).
Despite steps to reverse drivers of changed hydrology, large areas of cropping and grazing land, remnant native vegetation, wetlands, streams and associated ecosystems are at risk from dryland salinity (Keighery 2000; Briggs and Taws 2003) (see Table 135).
| State | Current | 2020 Prediction | 2050 Prediction |
|---|---|---|---|
| New South Wales | 7 000 | 32 700 | 81 000 |
| Victoria | 6 000 | 11 800 | 24 300 |
| Queensland | not assessed | not assessed | 92 000 |
| South Australia | 18 000 | 22 000 | 25 000 |
| Western Australia | 600 000 | 710 000 | 1 800 000 |
| Total | 631 000 | 776 500 | 2 022 300 |
Source: NLWRA (2000)
Salinity and altered environmental flows threaten wetland ecosystems as well as a range of other aquatic and terrestrial species, including groundwater-dependent species such as terrestrial vegetation and wetlands that rely on groundwater during key phases of their lifecycles (Fensham 2006) and a range of life that exists in karstic, cave, porous and fissured aquifers and about which very little is known (Sinclair Knight Merz 2001; Humphreys 2006).
In October 2000, A National Action Plan for Salinity and Water Quality in Australia was released by the Australian Government. More recently, the National Water Commission was established to improve water management across Australia, including its use for environmental outcomes.
Modelling of the future impact of vegetation clearing in the Queensland part of the Murray-Darling Basin shows that, for some groundwater flow systems, there could be a tenfold increase in salinity during the next 50 years (Murray-Darling Basin Commission 2003a). This finding establishes the finite timeline-or window-for catchment-wide management strategies to be put in place to keep the salt down in the soil profile. Once the salt reaches the surface or appears in the streams of the Brigalow Belt it will be too late to address the issue effectively and prevent substantial impacts (John Williams pers. comm. 2005).
Climate change and climate variability
Variability in climate is a characteristic of many Australian environments, to which native species have adapted in their evolution. There is now scientific consensus of profound changes in both average climate and the extremes and timing of the components of climate in coming decades.
In SoE2001, climate change was identified as a serious emerging threat to biodiversity that needed to be adequately documented, better understood and managed (Williams et al 2001). More recent Australian (Howden et al 2003, Krockenberger et al 2003) and international (Thomas et al 2004) aassessments suggest that climate change is among the most significant emerging pressures on biodiversity.
Although the capacity to attribute changes in biodiversity in the recent past specifically to climate change is limited, a few convincing examples are emerging. These include the encroachment by snow gum (Eucalyptus pauciflora) into subalpine grasslands and higher elevations, and shifts in ranges of vertebrates in the Alps over the thirty-year period to 1999.
Changes in climate are likely to induce rapid change in the conditions that determine the numbers and distribution of Australian native species, as well as weeds and other invasive organisms, in coming decades. While the ability to predict impacts of climate change in the future is still developing, the predicted changes strongly underline the need for adequate institutional responses to deal with a range of direct and indirect impacts on biodiversity.
Direct and indirect impacts of climate changes on biodiversity include physiological effects on species (such as a failure of alpine species to cope with increased summer temperatures, a failure of native plants to cope with changed water availability), altered interactions within communities and ecosystems (such as increased or decreased competitive ability of native versus introduced plants as increased temperatures and elevated carbon dioxide levels encourage increased growth rates, changes in food availability and predator-prey relationships, changes in the structure of habitat and cover, and the movement of species to new areas), altered stream flows, and changes in the severity and frequency of natural events such as bushfires (Pittock 2003).
Credible analyses suggest that there will be major changes in biodiversity due to changes in climate in coming decades. For example, predicted increases in temperatures could result in serious population declines in half of Australia’s butterfly species, loss of all suitable bioclimates for more than a third of vertebrates in southeastern Australia, and major changes in the Australian tree flora, depending on how closely current ranges reflect climatic limits (Hughes 2003). Climate change is likely to result in significant shrinking or total loss of habitat for those Australian species dependent on cool, high-altitude climatic zones such as those in Victoria’s alpine regions or in high altitudes in the Wet Tropics. Alterations to rainfall patterns and hydrological cycles-affecting wetlands, river ecosystems and estuaries-will have repercussions for aquatic biodiversity, including fish, and for migratory birds that depend on wetlands for breeding (Pittock 2003).
Adapting to climate change will require integrated policy, in which biodiversity issues are not addressed in isolation from other policy issues. For example, biodiversity responses will need to be developed and applied along with other natural resource management and industry policies, such as those addressing drought impacts and the need for more public investment in water resource infrastructure.
A decade ago, the impacts on biodiversity of climate change were seen as a distant threat that did not warrant urgent policy attention; this was partly due to sparse evidence. Conservation planning today needs to take account of climate change. Since 1996, climate change has been listed by some jurisdictions as a ‘key threatening process’ (for example, New South Wales in 2000 and the Australian Government in 2001). Despite these listings and a growing body of global scientific evidence about both climate change and its impacts on biodiversity, only limited attention has been given in Australian biodiversity conservation policy and practice to the impacts of climate change (Howden et al 2003). A National Biodiversity and Climate Change Action Plan (Natural Resource Management Ministers Council 2005) was released in 2005 with the aim of addressing many of the policy, research and development issues identified above, but responsibilities and funding for implementation are as yet unclear.
Pressures rarely act alone
It is worth reiterating that these pressures are all interrelated. The information that is currently available indicates that regions with the most intense agricultural and urban development tend to have the most species, habitats and ecological communities in decline. For example, more than 40 per cent of nationally listed threatened ecological communities and more than 50 per cent of threatened species occur in urban fringe areas (Yencken and Wilkinson 2000). Considerable biodiversity impacts also have occurred in Australia’s arid lands where species such as small mammals, often persisting in extreme conditions, have succumbed to pervasive threats from changed fire regimes and grazing pressure across large areas.