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4.3. Vulnerabilities and Potential Impacts for Key Sectors
4.3.1. Ecosystems
Summary: In responding to climate change, Australasia's biota may face a
greater rate of long-term change than ever before. They also must respond in
a highly altered landscape fragmented by urban and agricultural development.
There is ample evidence for significant potential impacts. Alterations in soil
characteristics, water and nutrient cycling, plant productivity, species interactions
(competition, predation, parasitism, etc.), and composition and function of
ecosystems are highly likely responses to increases in atmospheric CO2 concentration
and temperature and to shifts in rainfall regimes. These changes would be exacerbated
by any increases in fire occurrence and insect outbreaks.
Aquatic systems will be affected by the disproportionately large responses
in runoff, riverflow and associated nutrients, wastes and sediments that are
likely from changes in rainfall and rainfall intensity and by sea-level rise
in estuaries, mangroves, and other low-lying coastal areas. Australia's Great
Barrier Reef and other coral reefs are vulnerable to temperature-induced bleaching
and death of corals, in addition to sea-level rise and weather changes. However,
there is evidence that the growth of coral reef biota may be sufficient to adapt
to sea-level rise. Our knowledge of climate change impacts on aquatic and marine
ecosystems is relatively limited.
Prediction of climate change effects is very difficult because of the complexity
of ecosystem dynamics. Although Australasia's biota and ecosystems are adapted
to the region's high climate variability (exemplified in arid and ENSO-affected
areas), it is unclear whether this will provide any natural adaptation advantage.
Many species will be able to adapt through altered ecosystem relationships or
migration, but such possibilities may not exist in some cases, and reduction
of species diversity is highly likely. Climate change will add to existing problems
such as land degradation, weed infestations, and pest animals and generally
will increase the difficulties and uncertainty involved in managing these problems.
The primary human adaptation option is land-use management-for example,
by modification of animal stocking rates in rangelands, control of pests and
weeds, changed forestry practices, and plantings along waterways. Research,
monitoring, and prediction, both climatic and ecological, will be necessary
foundations to human adaptive responses. Active manipulation of species generally
will not be feasible in the region's extensive natural or lightly managed ecosystems,
except for rare and endangered species or commercially valuable species. In
summary, it must be concluded that some of the region's ecosystems are very
vulnerable to climate change.
4.3.1.1. General
Climate is a primary influence not only on the individual plant, animal, and
soil components of an ecosystem but also on water and nutrient availability
and cycling within the ecosystem, on fire and other disturbances, and on the
dynamics of species interactions. Changes in climate therefore affect ecosystems
both by directly altering an area's suitability to the physiological requirements
of individual species and by altering the nature of ecosystem dynamics and species
interactions (Peters and Darling, 1985). In addition, biota face an environment
in which the rising atmospheric CO2 concentration also will directly affect
plants and soils.
The rate of climatic change may exceed any that the biota have previously experienced
(IPCC 1996, WG II, Chapter A and Section 4.3.3). This rate of change poses a
potentially major threat to ecosystem structure and function and possibly to
the ability of evolutionary processes, such as natural selection, to keep pace
(Peters and Darling, 1985). Although many of the biota and ecosystems in the
region have adapted to high climate variability (exemplified in the region's
arid and ENSO-affected areas), it is unclear whether this will provide any advantage
in adapting to the projected changes in climate.
Furthermore, in contrast to the case of climate change over geological time
scales, today the region's biota must respond in a landscape that has been highly
modified by agricultural and urban development and introduced species (Peters,
1992). Considerable fragmentation of habitat has occurred in Australasia's forests,
temperate woodlands, and rangelands. In the short term, land-use changes such
as vegetation clearance are likely to have a much greater bearing on the maintenance
of conservation values than the direct effects of climate change on biodiversity
(Saunders and Hobbs, 1992). In the longer term, however, climate change impacts
are likely to become increasingly evident, especially where other processes
have increased ecosystem vulnerability (Williams et al., 1994).
Australasia's isolated evolutionary history has led to a very high level of
endemism (plants and animals found only in the region). For example, 77% of
mammals, 41% of birds, and 93% of plant species are endemic (see Annex D). As one of the 12 recognized "mega-diversity" countries (and the only
one that is an OECD member), Australia has a particular stewardship responsibility
toward an unusually large fraction of the world's biodiversity. Many of New
Zealand's endemic bird species are endangered. Species confined to limited areas
or habitat, such as Australia's endangered Mountain Pygmy Possum (Burramys parvus)-which
is only found in the alpine and subalpine regions of southeast Australia (Dexter
et al., 1995)-may be especially vulnerable to climate change.
Certain ecosystems have particular importance to the region's indigenous people,
both for use as traditional sources of food and materials and for their cultural
and spiritual significance. Selected climate change impacts on Australian Aborigines
and New Zealand Maori are considered in Sections 4.3.3.1
and 4.3.4.2 respectively.
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