Many pressures and threats that affect native vegetation have been identified. The principal threats are land clearing, grazing (by feral and domestic animals), altered fire regimes, weeds, Phytophthora cinnamomi and climate change. These threats lead to other threats such as fragmentation, altered hydrology, soil salinity and lack of regeneration. Minimising these threats is considered vital to the long-term viability of native vegetation and its associated biodiversity in Australia 36. At a property level, pressures can include vegetation clearance, weed invasions, altered fire and grazing regimes, spray drift and the removal of dead woody material. Managing these threats often requires priorities to be made. When considering the conservation value of a site, the significance is highest where there are threatened species present or the vegetation is in very good condition. Assessing and managing the condition of native vegetation, and how threatened species can be managed, are covered in Question 3.

Agriculture and the Environmental Imperative 37 provides technical discussions of some of the major environmental problems confronting land managers and planners in dryland farming regions of Australia. It reviews the biophysical mechanisms responsible for environmental problems and takes the social and economic factors that influence these problems and their solutions into account. A range of topical issues is covered including: water quality and quantity; integrating conservation and agricultural production; soil salinity, acidification and structure decline; pesticides; natural resource policy; and farm and ecosystem management. State of the Environment reports at the Commonwealth, State and local levels also provide a regular snapshot of some of the key pressures on natural resources.

The following section briefly reviews resources that document the impact of clearing and altered grazing and fire regimes on native vegetation. These threats have been selected because they are high on the list of pressures that cover large areas. Further information on the impact of these and other threats such as climate change on native vegetation can be found in Native Vegetation and Regional Management 38. The main focus of this property-scale directory is to point to resources on the sustainable management of native vegetation and how it can be integrated into farm businesses. In line with this, the planning and management resources provided in Question 3 are designed to remove or minimise pressures on native vegetation. The management of dryland salinity, which is another significant threat to native vegetation, is covered in Dryland Salinity: On-Farm Decisions and Catchment Outcomes 39.

Understanding the effects of clearing

Clearing is considered the greatest threat to native vegetation and its associated biodiversity  and has thus received considerable attention 40  41. Often the debate centres around the question “how much vegetation is enough?” The answer depends on the management goals of a property owner. The amount of vegetation needed to conserve all native species on a property, for example, is likely to be different to the amount needed to provide shade and shelter for livestock. Research projects aiming to address these questions are described in Native Vegetation and Regional Management  42.

Rates of broadscale clearance are now reasonably well documented at the national 43 and regional scale 44, particularly through the use of satellite imagery. Wide-spread vegetation clearing has principally occurred in the higher rainfall zones of southern and eastern Australia, often in response to government policies on land use. Certain vegetation types such as temperate eucalypt woodlands and grasslands have been cleared more than others 45, and in some regions have almost completely disappeared.

Temperate Eucalypt Woodlands: A review of their status, processes threatening their persistence and techniques for restoration 46  tries to develop solutions for the management of these vegetation types. Habitat loss is said to represent the main effect of widespread clearing and grazing, with associated impacts on woodland flora and fauna. A number of native species have gone extinct in these woodlands and many are considered threatened. Many other species are said to have experienced regional and local population declines. Ongoing threats to temperate woodlands are: further clearing, rising saline water tables and increased inundation, inappropriate livestock grazing, nutrient enrichment, soil structural decline, altered fire regimes and exotic weed invasion.

The direct impacts of the act of clearing have recently been studied in the report Impacts of Land Clearing on Australian Wildlife in Queensland. 47 The authors calculated that between 1997 and 1999, each year approximately 100 million native animals, birds, and reptiles died and an estimated 190 million trees were lost due to broadscale clearing of remnant vegetation. They state that broadscale land clearing often leads to many species being pushed into decline that culminates in the elimination of local and regional populations. This process follows a predictable path – rapid death of individuals, local and regional extinction of populations, and finally, total extinction of a species (Figure 3). The impacts are discussed in relation to mammals, birds, reptiles and remnant trees.

Much focus and discussion has been on broadscale clearing that can affect large areas in a relatively short period. The collection of individual trees for firewood can also contribute to clearing, with recent Bushcare Firewood Conferences 48 highlighting some issues associated with the firewood industry and the large demand in cities for firewood for heating. Like most pressures on native vegetation, it is the scale of the activity that is important. With nearly six million tonnes of firewood being collected each year, the impact on native vegetation is great. Even though most of the trees are dead, they still contribute to habitat for native animals and are eventually incorporated back into the soil. At property level, firewood collection for personal use is likely to have much less of an effect, depending on how much native vegetation is remaining and firewood is collected.

Figure 3: The direct and indirect impacts of broadscale clearance of native vegetation on animal species.



Source: Cogger H, Ford H, Johnson C, Holman J, Butler D (2003) ‘Impacts of Land Clearing on Australian Wildlife in Queensland.’ WWF Australia, Sydney, NSW.

Altering fire and grazing regimes

Fire is a natural element that has helped shape the environment and been one of the driving forces in the evolution of native plants and animals in Australia. The importance of fire in the ecology and management of Australian ecosystems has been identified in several recent books 49  50  51. The components of a ‘fire regime’ are the type, frequency, season and intensity of a fire experienced at a specific site. Fires can be too frequent, not frequent enough, too hot, too cool or at the wrong time to benefit native vegetation.

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There is ongoing debate about what constitutes an ‘appropriate’ fire regime for conservation of native vegetation 52. The impact that fires have on life and property adds another dimension. Current fire regimes, which have changed since the arrival of Europeans, have been implicated in local extinctions of several vascular plant species across Australia and inappropriate fire regimes have been associated with 19 plant species threatened with extinction at State or Federal level 53. The decline and loss of woody plant species under frequent fires has led to changes in habitat structure that has a flow-on effect on the persistence of other species. Even the long-term absence of fire, as in many isolated remnants in southern and eastern Australia, can be a threat to native plant species that need fire for germination and establishment. In the rangelands, changes to fire regimes have led to a change in the type and extent of vegetation types across broad landscapes 54. They have also changed characteristics within most vegetation types, altering vegetation structure and floristic composition over very large areas. An understanding of the response of native plant species or groups to fire regimes is an important component of management at the property level. Tools for managing fire at this scale are provided in Question 3.

Native herbivores including kangaroos and wallabies, possums and insects, have grazed native vegetation for millennia. Added to these, we now have domestic livestock, and feral animals such as goats and rabbits. Managing the total grazing pressure on both native and exotic vegetation is therefore a key issue. Landholders know that there are grass and shrub species that change in abundance under different grazing pressures – some plants are ‘decreasers’ under grazing, while others are ‘increasers’. In the pastoral zone, the Biograze project has shown that this pattern applies to most types of plants and animals 55. Furthermore, some decreasers are so sensitive that they occur only where there is negligible grazing pressure. Areas with very light grazing pressure are usually far from water points, so species that are very sensitive to grazing may show severe decline. Managing kangaroos as part of total grazing pressure in the rangelands has been covered in Living with Kangaroos 56.

In the Northern Tablelands of NSW, where native pastures make an important contribution to the fine wool industry, the effects of grazing, fertiliser use and cultivation on species richness of native ground-layer vegetation have been investigated 57. Significantly higher native species richness was recorded at sites that had never been grazed or infrequently grazed and lacked a history of cultivation or fertiliser use. Reduced native species richness and increased exotic species richness were linked to higher grazing intensity and fertiliser inputs. In Tasmania, the response of native plant species to sheep grazing has shown to be variable, with some species declining and others now requiring some grazing in the absence of fire 58. These examples demonstrate that grazing pressures on native vegetation can be reduced by careful pasture and stock management. Sustainable grazing can also help address issues such as the amount of groundcover and reduce the potential for erosion from wind and water. Grazing management is further explored in Question 3, with a number of useful management and monitoring resources highlighted.