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

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2.4.1.3 Australia The distribution of rubber vine in Australia was determined from information from the PestInfo project (Queensland Department of Natural Resources) (Figure 2.5). Of note are the scattered infestations in the southwest of Queensland. This area is subject to a large annual and diurnal range of temperature. On average, it receives less than 300 mm of rain. However, the averaging process masks the extremely variable nature of the rainfall, which includes infrequent major flooding events. 2.4.2 Ecology of rubber vine Rubber vine occurs naturally in arid areas wherever there is an abundance of water. This apparent contradiction is explained by the plant’s life strategy. Rubber vine appears to be a ruderal, stresstolerator. This adaptive strategy is apparent in its high seed production, and its ability to quickly take advantage of a small amount of moisture for germination and subsequent development of a taproot. This taproot and an ability to store starch during favourable growing conditions enable the plant to tolerate a great deal of drought and cold stress. Stress tolerance is a mechanism for avoiding competition. There is some suggestion that rubber vine is a poor competitor under warm, moist conditions. There are claims that it is shade-intolerant and, under natural conditions, the species is limited to open areas and the margins of forested areas. Thus, whilst rubber vine is capable of growing very well in hot, moist conditions, it may not be able to invade undisturbed moist tropical communities. Rubber vine has existed in a creek at Gatton west of Brisbane, which receives a great deal of frost, but microclimatic effects in the creek may have protected this patch from significant frost damage. In this model it is assumed that the plant is frost sensitive based on other reports. By comparing the range of the organism with climate surfaces we are able to directly infer the response of the population to the climate variables, as opposed to the short-term response to weather sequences. Due to its coarse geographic scale, the world distribution can only be used for a coarse verification of the model. Ideally, the Australian distribution would only used for validation of the model. However, because of the limited opportunity to infer the climate preferences of rubber vine from the distribution in Madagascar, it was necessary to include consideration of the Australian distribution of the plant in building the model. The use of reported physiological responses of the plant to weather conditions is complicated by the relationship between short-term weather variables and long-term climate averages. The parameters used in the rubber vine CLIMEX model are shown in Table 2.2. 14
3 Results Experience with ecological analyses at the CRC for Tropical Pest Management has shown that it is invaluable to investigate the broad response of any species, using the CLIMEX model, before proceeding to detailed biological observations or modelling. The CLIMEX results define the climatic context into which detailed observations can be placed. Therefore CLIMEX was applied to each of the woody weeds prior to building the mechanistic model of prickly acacia. These results were also found to be useful as a validation tool to check the results of the simulation modelling. 3.1 Prickly acacia distribution using CLIMEX 3.1.1 Current Climate The current analysis indicates that the potential distribution of prickly acacia may be greater under current climatic conditions than previous analyses have indicated (Carter 1989). The basic shapes of the predicted distributions are however fairly similar. The potential distribution under current climatic conditions includes most of Queensland, a considerable amount of the Northern Territory and Western Australia, and a small amount of South Australia and New South Wales (Figure 3.1). The potential distribution greatly exceeds the current distribution, highlighting the desirability of effective strategies that constrain the dispersal of the plant into new areas. Figure 3.1 Current and potential distribution of prickly acacia under current climatic conditions. 15
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: Due to its coarse geographic scale,
Page 25 and 26: Figure 3.2 CLIMEX Climate suitabili
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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