Australia State of the Environment Report 2001 (Theme Report)
Prepared by: Dr Jann Williams, RMIT University, Authors
Published by CSIRO on behalf of the Department of the Environment and Heritage, 2001
ISBN 0 643 06749 3
Biodiversity Issues and Challenges (continued)
Disturbance Regimes and Biodiversity (continued)
The Third Assessment Report from the Intergovernmental Panel on Climate Change (IPCC) was due to be released in mid 2001, and the Summaries for Policy Makers for the three working groups were released in early 2001 (IPCC 2001). This report and the regional climate projections released by the CSIRO in May indicate that Australia can expect to be generally warmer and drier, but with increased floods and storm surges. Australia's natural systems will have difficulty adapting, with vulnerable areas including the Great Barrier Reef, alpine ecosystems, wetlands and riverine systems and woodlands.
Climate change will affect biodiversity and it presents serious challenges for management aimed at conserving biodiversity. Several potential changes arising as a result of climate change (Table 35) will directly and indirectly affect biota. The degree of adverse climatic effects depends on the ability of the system to adapt to climate change.
|Changing weather patterns|
|Increased number, range and severity of cyclones|
|Changes in rainfall and run-off|
|Changes in cloudiness|
|Inundation of coast lines|
|Coastal recession changes in coastal vegetation (e.g. salt marshes)|
|Storm surge levels|
|Increased drowning of reefs|
|Changing fishery production|
|Hydrology and water resources|
|Increased erosion due to wind and water|
|Changes in ground water recharge and salinity|
|Increased salinity of streams|
|Greater probability of large and damaging floods|
|Changes in soil moisture during the growing season|
|Changes in extent and duration of snow cover|
|Shifts in bioclimatic zones|
|Changes in the distribution and abundance of native flora and fauna|
|Local and regional extinction of species|
|Increased plant growth due to CO2fertilisation|
|Increase in diseases|
|Increased frequency of natural hazards such as bush fires|
|Reduced grain production capacity in southern Australia|
|Increased year-to-year crop variability|
|Reduced production due to increases in cloudiness|
|Reduced yields of warm temperate crops due to less winter chilling.|
Source: after Williams et al. (1994).
The difficulties in predicting the effects of climate change arise because:
- detailed regional forecasts of potential changes in climate have only emerged recently
- understanding of the potential response of biota and ecological systems to these changes is limited.
Regional forecasts of climate change [BD Indicator 7]
The Atmosphere Report provides a detailed discussion of forecasts of climate change under an enhanced greenhouse effect. By 2030, most of Australia will be warmer by 0.4 to 2.0C. For 2070 the warming is 1.0 to 6.0C (estimates for 2030 and 2070 are subject to spatial variation). In summer and autumn, projected rainfalls for most of Australia are-10% to +10% by 2030 and -35% to +35% by 2070 and tend towards an increase. In winter and spring, most locations tend towards decreased rainfall and are estimated at-10% to +5% by 2030 and-35% to +10% by 2070 (CSIRO 2001). Soil moisture changes are expected as a result of changes in rainfall characteristics and evaporation. Higher average temperatures are likely to increase evaporation. The global increase in sea level is expected to be between 9 and 88 cm by 2100, or 0.8 to 8.0 cm per decade.
The potential responses of biodiversity to climate change can be considered in terms of changes in the distribution and abundance of taxa, species performance, and interactions between species which have implications for the structure and function of ecosystems (IPCC 1998). The potential ecological trajectories induced by climatic change encompass processes over the entire range of magnitudes from the level of leaf physiology to biome physiognomy and distribution. At least two conceptual views of biome response to climatic change have been proposed: ecotones gradually shifting in space, or ecosystems rapidly undergoing change over large areas in response to catastrophic disturbance such as drought (IPCC 1998). The view of gradually shifting ecotones in space arises largely from an emphasis on demographic processes, whereas the concept of catastrophic change arises largely from an emphasis on ecosystem function (water and nutrient) processes. These two models present different images of future change and biosphere responses.
Large-scale changes in the distribution of species and biomes has occurred. However, the anticipated changes in global climate are expected to occur at a rate most biologists acknowledge as simply too fast for evolutionary processes, such as natural selection, to keep pace (Table 36). Such constraints on the ability of species to adapt to their rapidly changing habitat could substantially increase their probability of extinction. In addition, landscape fragmentation related to human activities will markedly limit the opportunity for some species to migrate. It has been suggested that habitat destruction and climate change will act together, setting the stage for greater rates of extinction than when considering human encroachment alone (IPCC 1998).
|Pinus strobus||Late Holocene||5|
|Corylus spp.||Early Holocene||10|
|Picea glauca||Late Pleistocene||2-3|
Source: after Williams et al. (1994).
The intrinsic ability of a species to colonise will depend on its ecological characteristics, including reproductive rate, viability and growth, the way it disperses, and its ability to tolerate inbreeding. Species disperse at different rates, which may result in dramatic alterations of the species composition of all biological communities. The biology of a species will be crucial in determining the rate at which it can respond to climate change. A species can extend its geographical range only if humans move it, or by natural processes individuals disperse to, and establish in, areas beyond their current distribution.
Physical constraints of a locality will restrict migration and increase vulnerability. For species on small offshore islands, southernmost coasts, the northern boundary of the central Australian desert, the tops of mountains, riparian zones, and forest remnants separated by urban development, there may be no migration options. Soil differences, inadequate rainfall, or excessive wind may also prove to be barriers to migration (IPCC 1998). Conversely, changes in temperature and rainfall may remove an existing barrier to migration, such as frost.
The physiological adaptations of most species to climate are conservative, and it is unlikely that most species could evolve significantly in the time allotted by the coming warming trend. Most of the available data on the effects of elevated carbon dioxide levels on vegetation have been derived from short-term treatments in controlled environments. Many of these studies report increased growth rates (particularly of C3species), although there have been striking interspecific variations in responses to higher temperatures and carbon dioxide levels (IPCC 1998).
The ability of plant communities to accommodate climate change will be influenced by plant-soil-soil moisture interactions (IPCC 1998). This relationship among soil, soil moisture, vegetation and climate needs to be better understood in order to project responses.
Disturbance regimes are often a main factor in determining the suitability of habitat for species and, hence, will be of major importance in facilitating turnover from one species or vegetation type to another in response to climate change. Studies in other countries have identified the importance of altered fire regimes under climate change for a range of ecosystems. Fires are also integral in the dynamics of most Australian ecosystems. Therefore, the response to disturbance regimes must be considered when predicting ecosystem dynamics. Changes in climate and fuel dynamics will affect future fire regimes. Factors such as ignition sources will also be important.
In natural ecosystems, the timing of plant fruiting and flowering, which at least in the tropics is largely determined by the temporal distribution of droughts and rainy periods, may be adversely affected if rainfall patterns change. Most research efforts into the affect of elevated carbon dioxide levels do not include an examination of the plant's reproductive responses, despite their importance to ecosystem function.
As well as the effect on plants, pollinators may be affected by climate change. This can be expected to have significant consequences for plant reproduction. Long-lived species such as established trees might show a muted response to climate change, exhibiting substantial time lags assuming they are not significantly altered by other human activities or by catastrophic disturbance. Disturbances such as fire, however, will create opportunities for more rapid change by reducing the inertia of, at least, established forests. Even if adults of a species can tolerate changes in climate, their ability to produce propagules and the ability of those propagules to recruit to maturity may be adversely affected. Many Australian animals, particularly birds such as the Yellow-tailed Black Cockatoo (Calyptorhyncus funereus), are relatively long-lived. Without knowledge of the fecundity of these species, the presence of adults in a population may not be a reliable guide to the longer term persistence of a population or the species (IPCC 1998).
The geographical distribution of many parasitic species are limited by the distributions of potential host species or by environmental constraints on the parasite's rates of development (IPCC 1998). The effect of changing climate will depend, therefore, to some extent on the response of the host to the altered conditions. Where members of the parasite community are important in mediating competition between hosts, this may lead to further changes in the structure of the host community and the possible extinction of particularly susceptible hosts.
If the temperature increases significantly, parasites and disease will do well as they are by definition organisms that colonise and exploit, particularly in relation to stressed individuals on the edge of their environmental range. The details of where and when these changes will occur, and what effect they may have on the distribution and abundance of species, are relatively poorly understood (IPCC 1998). Predictive models have focused principally on species important from an economic perspective, such as the cattle tick.
Human-induced changes to climate and habitat could dramatically increase the frequency of invasions by organisms from outside their current biogeographical boundaries. Therefore, planning for the movement and invasion of species into new areas is essential. However, understanding the consequences of global change on species invasions requires a much better understanding of the community and ecosystem roles of individual species.
Changes in hydrology associated with climate change may have serious implications for wetland biota. Although some aquatic plants are able to survive water fluctuations, it is unknown how wetland biota will respond to the potentially major changes in rainfall and subsequent run-on and run-off characteristics. Several migratory birds that utilise Australian wetlands may also be affected if wetland dynamics alter under climate change. Potential changes to wetlands resulting from climate change will be aggravated by the modification of wetlands through draining, fragmentation and rising water tables (IPCC 1998).
The responses to climate change of the large, arid, ephemeral lake systems of interior Australia are difficult to predict. Although these systems already experience significant seasonal and interannual variations, and the associated ecosystems are attuned to this high variability, their resilience to long-term change in the frequency and intensity of events is less certain. Significant water level changes may occur for non-ephemeral lakes in dry evaporative drainages or small basins where, at present, evaporation is comparable with rainfall inputs.
Estuaries and coastal wetlands have survived historical rises in sea level, usually by migration landward; salt marshes and mangroves have survived where the rate of sedimentation approximates the rate of local sea level rise; beaches have grown or decayed according to changes in prevailing winds and seas; and coral reefs have demonstrated the capacity to grow vertically in response to past rises in sea level. However, these past rates of adaptation may be insufficient for the higher rates of future rises in sea level, and in many cases landward migration will be blocked by human infrastructure, such as causeways, flood protection levees, and urban development, leading to a reduction in the area of the delta or mangrove (IPCC 1998).
Coral reefs and atolls in the region, and in neighbouring South Pacific countries, are among the most sensitive environments to rises in sea level and climate change, through potential inundation, flooding, erosion, saline intrusion and death of corals. Coral bleaching and decline from prolonged increases in seawater temperature can inhibit their capacity to grow at the rates required by sea level rise. Managing reef ecosystems such as the Great Barrier Reef may be more problematic as a result of climate change.
Increased sea temperatures seem to be the main concern, rather than sea level rise per se. The potential sensitivity of coral reef ecosystems to climate change was demonstrated in 1998 when a global episode of coral bleaching showed that many reef corals live near the limits of their thermal tolerance. Where corals bleached, sea temperatures were several degrees above normal summer values and were some of the highest on record. Climate change is believed to be a major threat to coral reefs and could be a major driver of change across one of the most productive ecosystems on earth (AIMS 2000).
Minimising the effects of climate change [BD Indicator 22]
The international community is engaging in considerable scientific research to deepen understandings of climate change. Australian scientists are prominent in many areas, with the focus on developing models of regional climates and carbon sequestration (through the CRC for Greenhouse Accounting). Research on the direct effects of climate change on biodiversity is relatively limited, with some work underway on the response of different organisms to elevated carbon dioxide levels.
SoE (1996) presented modelling results that illustrated changes in the potential distribution of several species under different climate change scenarios (Dexter et al. 1995). More recently, modelling has demonstrated similar effects on different species (Figure 30). These studies show the potential for significant effects on native species under the current models for climate change.
Figure 30: Changes in the distribution of the Swift Parrot (Lathamus discolor), under various scenarios of climate change
Scenario 1, present day;
Scenario 2, small temperature increase, no rainfall changes;
Scenario 3, large temperature increase, small rainfall increase; and
Scenario 4, large temperature increase, large rainfall increase.
Source: Chapman and Milne (1998)
Much of the focus on minimising the effect of climate change has attempted to stabilise greenhouse gas emissions. Because of the global threats imposed by climate change, these approaches have also been undertaken at an international level. Australia became a party to the United Nations Framework Convention on Climate Change (UNFCCC) in 1992. The Convention aims to stabilise emissions of greenhouse gases at a level that would prevent dangerous human-induced interference with the climate system.
The UNFCCC has led to the Kyoto Protocol, agreed in December 1997. The Protocol aims, inter alia, to enhance the energy efficiency of national economies, protect and enhance sinks and reservoirs of greenhouse gases, promote sustainable forms of agriculture, limit and/or reduce emissions of greenhouse gases, and remove economic instruments that undermine such outcomes. The Protocol outlined emission targets for developed countries, with Australia having a target of restricting greenhouse gas emissions for 2008 to 2012 to an increase of 8% over 1990 levels. To date, Australia has submitted two reports (Commonwealth of Australia 1994, 1997) on its commitments under the Convention and these reports were reviewed by independent committees appointed by the UNFCCC Secretariat.
Some mitigation actions that are promoted by Australia to meet greenhouse gas emission targets could have considerable effects on biodiversity, especially those related to carbon sinks. For example, the potential for vegetation clearance to be reduced to maintain carbon sinks could have a positive impact. Clearing of native vegetation is a major source of emissions in Australia and accounts for 13 to 18% of the total annual emissions. Significant reduction in, or elimination of vegetation clearing, would remove of one of Australia's most serious threats to biodiversity, and would help meet international greenhouse gas commitments. Similarly, biodiversity will benefit both directly and indirectly from measures to improve national energy efficiency and put agriculture on a sustainable footing.
In calculating net emissions of greenhouse gases for 2008 to 2012, Australia is likely to be allowed to count the removal of carbon dioxide from the atmosphere to sinks such as vegetation and soils. The sequestration (or storage) of carbon into vegetation and soil sinks is one way to reduce net emissions of greenhouse gases. These sinks have the potential to be linked in with carbon 'credit' schemes that provide a basis to make carbon a tradeable commodity. Under such schemes, vegetation has a quantifiable value as a carbon store, irrespective of its value for biodiversity, and may provide stronger investment incentives for landscape revegetation.
Carbon sequestration schemes have focused mainly on plantation trees in Australia, although other opportunities exist to sequester carbon by adopting changes in land use. One example is the retirement of land from conventional agriculture, and promoting the thickening of understorey vegetation of native grasses and woody shrubs, which in turn become carbon sinks. These types of activities and strategies may benefit biodiversity if biodiversity conservation is treated as an integral or strong complementary aim. Revegetation strategies can markedly change the biophysical and ecological processes of a region and help reverse habitat degradation (e.g. lowering water tables and the affects of salinity). However, poorly conceived strategies of this nature may be as bad for biodiversity as many current threats and human activities.
Despite the benefits for carbon sequestration and climate change, the planting of large areas with tree monocultures can have serious socioeconomic, as well as biodiversity, implications (e.g. Gill & Williams 1996). In many regional areas, the rapid growth of the plantation industry is changing employment opportunities and investment strategies and requires the upgrading of road infrastructure and networks for use by heavy transport.
Overall, the future of much of the biodiversity of the Australia is threatened by climate change. Australian governments must adopt enhanced measures to achieve genuine and significant reductions in greenhouse gas emissions and prevent human activities that seriously compound the potential effects of climate change on biodiversity.