EXOTIC WOODY WEEDS Use of simulation models to predict future ...

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3.1.2 Impact of Climate Change The overall impact of climate change on the potential distribution of prickly acacia in Australia, as estimated by the CLIMEX Ecoclimatic Index and its growth and stress components, will be to increase the climatically suitable range poleward and inland (Figure 3.2,a). The area of ‘highly suitable’ habitat extends further north, south and west under the higher precipitation, and more water-use-efficient scenarios (Figure 3.2,e-f). All scenarios show a poleward increase in range in response to rising temperature. When conditions include increased temperature, decreased precipitation, and no increase in water use efficiency (Figure 3.2, b) there is a slight contraction of the ‘highly suitable’ habitat toward the eastern coast compared with present climatic conditions. However, even moderate reductions in evapotranspiration (E t ) resulting from increases in water use efficiency (Figure 3.2, a-c) may be able to compensate for a 10% reduction in precipitation. The marked effect of increasing water use efficiency upon the projected distribution of different habitat suitability zones demonstrates that the model is highly sensitive to this parameter. The uncertainty that it introduces to the analysis means that studies of the effect of increased CO 2 on the water use efficiency of prickly acacia at the stand level may be warranted. The distribution of the CLIMEX growth index for prickly acacia (Figure 3.3) indicates the relative growth potential. The area of highest growth potential under current climatic conditions is centred near Rockhampton, and extends in a coastal arc from the northern part of Western Australia clockwise across and down to mid-New South Wales (Figure 3.3, a). A comparison of the Ecoclimatic Index (Figure 3.2) and the Growth Index (Figure 3.3) shows how the area in which the plant could grow far exceeds the area in which it can persist and reproduce. The expected increases in temperature, rainfall and water use efficiency associated with climate change result in a large-scale expansion of the areas with highest projected growth potential. The areas of moderate to small growth potential increase toward the centre of the continent under the same climate scenarios. These findings are reflected in the two components of the growth index, the temperature index (Figure 3.5), and the moisture index (Figure 3.4). The cold stress due to frost intolerance is restricted to the southern highlands of the Great Dividing Range (Figure 3.6). The area of this unsuitable zone is reduced considerably by a 2 °C increase in global temperatures. The area that receives sufficient heat for pod development is increased by about 200 km in a poleward direction (Figure 3.7). The change is fairly uniform along the southern boundary of the threshold, except for the highlands of the Great Dividing Range where frost occurrence is presumed to prevent the plant from persisting. The additional area at risk of invasion is considerable. There appears to be a small amount of wet stress in northern Australia under current climatic conditions (Figure 3.8, a). There is little impact of climate change on the distribution of this stress. The combination of slight increases in wet stress, and a coincident reduction in the moisture index are enough to reduce the climatic suitability of small patches of northern Australia under each of the scenarios that include a 10% precipitation increase (Figure 3.8, e-g), and the highest water use efficiency scenario with a reduction in precipitation (Figure 3.8, d). 16
Figure 3.2 CLIMEX Climate suitability (Ecoclimatic Index) for prickly acacia under different climate scenarios. $ &XUUHQW FOLPDWH % R & LQFUHDVH LQ WHPSHUDWXUH GHFUHDVH LQ SUHFLSLWDWLRQ (W & R & LQFUHDVH LQ WHPSHUDWXUH GHFUHDVH LQ SUHFLSLWDWLRQ (W ' °& LQFUHDVH LQ WHPSHUDWXUH GHFUHDVH LQ SUHFLSLWDWLRQ (W ( R & LQFUHDVH LQ WHPSHUDWXUH LQFUHDVH LQ SUHFLSLWDWLRQ (W ) R & LQFUHDVH LQ WHPSHUDWXUH LQFUHDVH LQ SUHFLSLWDWLRQ (W * R & LQFUHDVH LQ WHPSHUDWXUH LQFUHDVH LQ SUHFLSLWDWLRQ (W 17
Page 1 and 2: EXOTIC WOODY WEEDS Use of simulatio
Page 3 and 4: Foreword In 1995 the National Green
Page 5 and 6: Contents Foreword .................
Page 7 and 8: Executive Summary Climate change is
Page 9 and 10: 1 Introduction Broad scale invasion
Page 11 and 12: 2 Methods A two-phased approach was
Page 13 and 14: In addition to the spatial data set
Page 15 and 16: Table 2.2 Prickly acacia and rubber
Page 17 and 18: Climate Change Climate Biophysical
Page 19 and 20: Mitchell Grass Downs. This provides
Page 21 and 22: Due to its coarse geographic scale,
Page 23: 3 Results Experience with ecologica
Page 27 and 28: Figure 3.4 CLIMEX Moisture Index (M
Page 29 and 30: Figure 3.8 CLIMEX Wet Stress (WS) f
Page 31 and 32: 3.2 Rubber vine distribution using
Page 33 and 34: Figure 3.12 CLIMEX Climate suitabil
Page 35 and 36: Figure 3.14 CLIMEX Moisture Index (
Page 37 and 38: Figure 3.18 CLIMEX Wet Stress (WS)
Page 39 and 40: 3.3 Prickly acacia population dynam
Page 41 and 42: Table 3.3 Sensitivity of upland bas
Page 43 and 44: 30 Cordillo Downs (SA) Upland Bioma
Page 45 and 46: economy. The value of the biomass w
Page 47 and 48: 5 Implications The principle object
Page 49 and 50: 7 References Aikman, D.P. and Watki
Page 51: Sutherst, R. W., Maywald, G. F., Yo

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