Pressures on our land

Habitat loss via vegetation clearance, mostly for agricultural expansion, is the most important cause of native vegetation decline and species extinctions.

Almost immediately after European settlement, large-scale native vegetation clearance for agriculture occurred, with the highest rates of clearance in those areas where soils were best suited to agriculture. Climate change has since become a major threat for the future of remaining native vegetation.

Historically, high levels of native vegetation clearance have occurred in SA, particularly in the southern parts with higher average rainfall. While unregulated clearance came to an end in 1983, there is still incremental clearing of remaining native vegetation. Together with the legacy of historical clearance, and in the absence of large-scale restoration of habitat, this will continue to result in the extinction of species into the future. 

Clearing of native vegetation is now largely controlled through the Native Vegetation Act 1991, with exemptions allowing for clearance under specified conditions, including for permitted landuse changes. Some illegal clearance also still takes place.

According to data reported by the Native Vegetation Council, and shown in Figure 42, there has been an average of about 200 reports of illegal clearance since 2004. The highest number of reports (about 50 per year) are from regions such as the Adelaide and Mount Lofty Ranges that already has reduced and fragmented remnant native vegetation. These areas have comparatively higher population densities and, therefore, a possibly higher detection rate.

The information provided does not include the extent or condition of the vegetation affected by the reported illegal clearance which, if it did, would improve reporting on trends.

Vegetation clearance approved under the Native Vegetation Act 1991 and its regulations average almost 3,000 ha and 1,500 trees a year, as shown in Figure 43.

Following the introduction of the Native Vegetation Regulations 2003, the range of activities and development able to be assessed under the Regulations has broadened. This resulted in a higher proportion of matters approved under the Regulations rather than formal clearance applications under section 28 of the Native Vegetation Act.

The Native Vegetation Regulations 2017 further relaxed the requirements for formal approval by expanding the categories of permitted clearance. The increased scope of exemptions makes reporting on the total extent of clearing more difficult as these are not recorded. It also increases the need for compliance to distinguish between permitted and illegal clearance.

The cumulative impacts of land uses and management practices on the environmental values of SA’s native vegetation is a concern also because the majority of the remaining native vegetation is outside of formal protected areas.  

This ongoing fragmentation of remaining vegetation reduces its viability and ability to provide adequate habitat for birds and other species relying on it. Fragmentation also increases exposure to threats at the edges from pest plants, animals and pathogens.

South Australia’s climate has always been characterised by huge seasonal variability and many species are adapted to this. However, accelerated climate change is likely to alter the distribution and abundance of native and exotic species, including expanding some species’ distribution. It will also change the spatial and temporal distribution of land use and other drivers of environmental change (such as fire management and invasive species).

These impacts from climate change, together with the effects of flood, drought and other weather patterns, will progressively alter the landscape. Changes in mean annual temperatures and heatwaves, increasing frequency of droughts, and changes in rainfall amount and seasonality are likely to lead to shorter growing seasons and more intense bushfires that will change habitats and species distributions.

The tropical zone (the area between 30° latitude on either side of the equator) is expanding at an unprecedented rate. At the edge of the expanding tropics is a dry subtropical zone that is also shifting poleward. This implies a likely shift of the dry hot climatic conditions of SA’s arid inland into the currently more temperate southern parts. It is estimated that the dry subtropics may expand by as much as 30% by 2100. This will have dire consequences for native plant species, which will have nowhere to move to, given the barrier presented by the Southern Ocean.

The key driver here is the expansion of arid/subtropical highs that are pushing southern cold fronts off the southern coast – the main driver of winter rainfall in southern Australia. This has already changed the climate of southwest Western Australia, and we are beginning to see it here in SA.

One of the direct consequences of a drier climate is the reduction of soil bacterial and fungal diversity and abundance. When soils dry out, plant cover and soil organic carbon content decline which, in turn, affects bacteria and fungi living in the soil. As a high level of microbial diversity is linked to higher plant productivity and soil fertility, climate change will negatively impact on the key ecosystem functions in soils that are vitally important for habitat health and global food production.

Parts of Australia are projected to become unsuitable for 30–60% of species across all groups as a result of predicted climate change. Currently, with the pledged levels of emissions, half of all birds and reptiles, two-thirds of mammals and nearly 80% of amphibians will disappear. For plants, the figure is 60%, which would radically change ecosystems across the region.  

Heatwaves are already causing mass die-offs, and models suggest that the current changes will result in both gradual and sudden collapses of biological systems. This will affect our health, food security and economies. This means we need to protect larger and more diverse areas and all their biomes, which is a massive challenge since we are already struggling to agree on mitigation measures, as illustrated by the scale of land clearing and habitat loss on the east coast of Australia. South Australia is part of a country with the worst recent extinction record in the world and a country that stands to benefit the most by what we do about these issues.

Plants

Pest animals

Bushfires can have massive economic, social and environmental impacts. Plants have evolved in conjunction with fire, and many plants have developed strategies enabling them to resist or even use fire to their own advantage. Eucalyptus species provide good examples of epicormic re-sprouting (from buds on the trunk), which enables rapid recovery following fires.

While fires can threaten human life and cause extensive damage to crops and infrastructure, the impacts on native species are heavily context dependent and fire is a vital process in many ecosystems.

The risk to native vegetation depends on fire frequency, extent and severity, and on the specific vegetation communities’ adaptation capacity, for example, thick fast-growing bark sprouting from surviving tissue and recruitment from seeds.

The SA Government undertakes prescribed burns to reduce the risk of fire on human safety and assets, as well as for ecological outcomes, such as regenerating fire-dependent plants.

Burning for ecological purposes makes up less than 10% of prescribed burning. There is a high degree of uncertainty about how best to use fire to meet conservation goals. This results from the responses of a range of species to fire remaining poorly understood and documented, as well as, of those known, the differences in responses by species to fire.

In the Environment, Resources and Development Committee of Parliament’s report on its inquiry into SA’s biodiversity, the committee recommended that fire management plans and operations need to include greater consideration of the impact of fire on biodiversity. The committee also recommended a shift in focus from managing single fires on public land to consideration of cumulative effects across the landscape.

Soil erosion is the highest priority threat to SA’s soils. Approximately 6.2 million ha (60% of cleared land) of agricultural land are inherently susceptible to wind erosion, and 3.3 million ha (32%) are susceptible to water erosion.

Most of the erosion risk is due to cropping practices, such as tillage and stubble burning. Grazing management is also an important factor, especially in dry years and droughts. The highest risks associated with grazing occur in late summer and autumn, when feed availability and the cover of annual crop and pasture residues is declining. – 2013 SOER Report

While soil erosion has steadily declined due to improvements in farming practices such as no-till sowing and stubble retention, soil losses still occur with extreme wind or rainfall events and after severe or prolonged drought and bushfires.

After erosion, soil acidity is the second highest threat to the sustainable management of agricultural soils in SA (Figure 44). Approximately 2 million ha (20%) of agricultural land are affected by soil acidity.

Many soils in SA’s higher rainfall areas are naturally acidic. Soil acidification can be accelerated by agricultural practices, including removal of alkaline products, such as grain, hay and wool off the paddock, use of ammonium-containing or ammonium-forming fertilisers and leaching of nitrogen derived from legume plants or fertilisers. Sandy textured soils and higher levels of production also tend to lead to higher acidification rates.

The consequences of untreated, highly acidic soils include:

• reduced growth and production of most agricultural plants
• increased soil salinity due to increased drainage of rainfall to groundwater
• increased leaching of iron, aluminium and some nutrients leading to contamination of surface and groundwater
• structural breakdown of the soil.

Dryland salinity occurs when salts in soils are brought close to the surface by a rising watertable. Historical clearance of native vegetation and its replacement with annual crops and pastures has resulted in higher groundwater levels. In 2000, approximately 360,000 ha of land in SA were affected by dryland salinity, which is 2.3% of all land in the agricultural zone.

Approximately 200,000 ha of the Upper South East are afflicted, making it the most severely affected area of SA. With the completion of the Upper South East Dryland Salinity and Flood Management Program, the drainage network has reduced the risk of salinity over an area of more than 100,000 ha. According to some views, part of this benefit could have been achieved at less environmental cost (for example from drainage into the Coorong) through more extensive planting of deep-rooted native species and perennials, such as Lucerne.  

The future impact and risk of dryland salinity will depend largely on future rainfall patterns, climate change, nature of the groundwater system and effectiveness of interventions to slow or halt a rise in groundwater. For most of SA, the overall risk is expected to decline in line with the predicted decline in long-term average rainfall.

The remaining concern is with areas of shallow groundwater where periodic short-term recharge can cause soil salinity. Localised seepage is increasing in Mallee dune-swale landscapes due to greater recharge resulting from increased control of summer weeds in annual cropping systems. Management options include large-scale adoption of perennial plant systems and re-planting of key areas with deep-rooted natives.