Geoscience Reference
In-Depth Information
distributions and abundance of invasive species, with flow on effects to native
communities (O'Donnell et al.,
2012).
Just as some climates will disappear entirely and new climates without
analogue will appear (Williams and Jackson, 2007), so too will some ecological
assemblages disappear, to be replaced by new ones. The potential for ecological
transformation can be illustrated, in a simplistic way, by considering the results of
climate modelling described by Whetton et al. (2013,
Chapter 2
, this volume),
who modelled analogous climates in a Four Degree World for a number of major
centres in Australia. A comparison of the vegetation typical of those locations,
with that currently supported in the regions with analogous climates, provides
a crude assessment of the potential scope of future transformation. Consider for
example, the rich tropical rainforest of the Cairns region, one of the most biodi-
verse areas in the continent. Under a mid-range rainfall scenario in a Four Degree
World, the closest climate analogue to Cairns is Weipa, Queensland. Under
the hottest and driest scenario, the closest analogue is Jabiru in the Northern
Territory, while there were no Australian analogues found under the least hot,
wettest scenario (see Whetton et al., 2013,
Chapter 2
, this volume). The Weipa
district typically supports open forest dominated by stringybark eucalypts, while
the vegetation of Jabiru is classified as savannah woodland. While these two
regions certainly support extensive biodiversity, their level of species richness
and endemism is considerably less than that supported by tropical rainforest.
An Australia-wide analysis of potential changes in vegetation classes and plant
community composition using mid- (A1B) and high-range (A1FI) emissions
scenarios for 2050 and 2070 predicts dramatic changes in the structure and
composition of vegetation communities with a general decline in environments
favouring trees and an increase in open woodlands, chenopod shrublands and
grasslands (Dunlop et al., 2012). It is worth noting, however, that this analysis
used only a single Global Circulation Model (CSIRO Mk3.5), and did not
include potentially critical factors such as rising atmospheric CO
2
, altered distur-
bance regimes and hydrology.
A number of reviews have identified those regions in Australia likely to be
most vulnerable to loss of species and ecosystem function from climate change
impacts and potentially to regime shifts (
Table 4.1
). Features that may confer
increased susceptibility of these ecosystems include restriction of distribution of
either the ecosystem in general, or of a high proportion of species, high exposure
to factors such as increased sea level and changed fire regimes, those geographi-
cally limited in their capacity to shift, and those already under the most threat
from fragmentation, reduction in environmental flows and invasive species.
Key drivers of transformation will be changes in fire regimes, intensification of
extreme events such as droughts, heat waves and tropical cyclones, and changes
in hydrology (see Braganza et al., 2013,
Chapter 3
, this volume). Confidence in
these projections is stronger for those ecosystems in coastal regions (where sea
level rise is relatively well modelled) and in the south east and south west of
Australia, where rainfall projections from climate models are more consistent.
