Geoscience Reference
In-Depth Information
from Asia and New Guinea and with many endemic species that have evolved
in
situ
. Endemicity is especially high in groups such as terrestrial mammals (87 per
cent), flowering plants (92 per cent), fish (90 per cent), reptiles (93 per cent),
frogs (94 per cent) and birds (45 per cent) (Steffen et al., 2009). Many of these
species have narrow geographic and climatic ranges. Over 50 per cent of eucalypt
species, for example, have climatic ranges that span less than 3°C of mean
annual temperature, and approximately 25 per cent span less than 1°C (Hughes,
Cawsey and Westoby, 1996). While factors other than climate are likely to play
a role in limiting the ranges of most species, restricted distribution is a key factor
predisposing species to increased vulnerability from rapid environmental change.
The risk of negative impacts on species from rapid future change may, in some
regions, be somewhat mitigated by the species' pre-adaptation to the episodic
nature of the Australian climate. Rapid climatic swings - from cyclonic or
monsoonal depressions causing flooding to prolonged drought, especially across
the arid and semi-arid regions - have acted as strong selective pressures on
species to evolve opportunistic life styles and other features that confer resilience
to extreme conditions (Steffen et al.,
2009). Overall, it is generally considered
that the dynamics of many Australian ecosystems are more driven by these
episodic, extreme events and disturbances than are ecosystems in many other
regions of the world (Orians and Milewski, 2007).
Australia's unique dominance of infertile soils will also influence future climate
impacts. The combination of deep weathering during the Late Cretaceous
and Tertiary periods, the long period of relative geological stability and the
limited extent of recent (Quaternary) glacial activity has produced soils largely
depleted of phosphorus and nitrogen (Attiwill and Leeper, 1987). Low levels of
phosphorus and nitrogen, in particular, are associated with an evergreen, sclero-
phyllous flora, characterized by hardened, long-lived leaves (Specht and Specht,
1999), and are important factors also controlling growth rates in animals (Orians
and Milewski, 2007).
Low soil fertility has two important consequences for understanding future
climate change impacts. Firstly, low nutrients are likely to limit the fertilization
effect of rising atmospheric CO
2
although the lack of experimental data on the
responses of Australian vegetation growing in native soils to elevated CO
2
limits
quantification of this effect (see Hovenden and Williams, 2009). Secondly,
vegetation growing on low nutrient soils tends to have higher flammability,
via a complex set of interacting feedbacks, and the interaction of fire and soil
fertility acts to maintain distinct vegetation boundaries in many environments
(Lehmann and Hughes, in review). Australia is characterized by high fire
frequency, with some regions burning annually. The expected increase in fire
danger weather, especially in the south east, is expected to be one of the most
significant drivers of future ecological change (Williams et al., 2009a).
The topography of the Australian continent also has important consequences for
the distribution of species and their future adaptive capacity. Australia is the flattest
of all continents, with 99 per cent of the landmass less than 1,000 metres above sea
level, and with few summits exceeding 2,000 metres. This topography has important
