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

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observations that some graziers do not consider prickly acacia a problem, and others regard it as a net asset (Mackey 1996a; March 1995). The simulated effect of changing the livestock pattern using herds with different proportions of sheep and cattle was investigated using the DYMEX model under a series of climate change scenarios. 2.4 Rubber Vine Rubber vine Cryptostegia grandiflora Roxb. ex R. Br. was introduced into Australia prior to 1875 as a garden ornamental in several mining towns in north Queensland. The plant spread rapidly and by the early 1900’s had established major populations around Charters Towers, Chillagoe, Georgetown and Rockhampton. It continued to spread and now occupies areas throughout most of Queensland (Figure 2.5). In moist regions it can form extensive infestations, smothering native vegetation. At xeric southern and western locations it is generally found in isolated clumps at moist microsites, or has been deliberately cultivated. # Cooktown # Cairns # Boulia # Rockhampton Quilpie# # Charleville # Hungerford Brisbane # 1999 Department of Natural Resources Strategic Control Line Sparse rubber vine Dense rubber vine Figure 2.5. Australian distribution of rubber vine. Source adapted from Pestinfo system, DNR. Rubber vine has attained weed status due to its ability to form dense monospecific stands that smother native vegetation, especially in riparian habitats. The resulting reduction in biodiversity has caused concern from a conservation perspective. Rubber vine has also attracted criticism because these dense infestations cause reductions in domestic livestock production due to its dominance of the otherwise productive riparian habitat. There are also concerns about the potential for stock poisoning because rubber vine contains several toxic compounds. Four sources of information were used to predict the biotic performance of rubber vine in Australia: its published distribution in the country of origin, Madagascar, its published worldwide distribution, the current distribution of rubber vine in Australia, and finally, some published data on the physiological performance of rubber vine with respect to some climatic factors. The native range of an organism is the most important source of information for CLIMEX analyses. 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. 12
Due to its coarse geographic scale, the world distribution by country information 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 lack of knowledge of the exact climate preferences of rubber vine to some climate variables, 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. 2.4.1 Present distribution of rubber vine 2.4.1.1 Worldwide The global distribution of rubber vine is shown in Figure 2.6. It is primarily tropical, but extends into equatorial and sub-tropical regions. Figure 2.6 Worldwide distribution of rubber vine (Jenkins 1944; Tomley 1995). Shaded areas indicate countries with rubber vine, not actual territory occupied. 2.4.1.2 Madagascar The climate of Madagascar in the natural range of rubber vine is characteristically dry tropical with a highly pronounced summer bias in the rainfall. It is important to note that Madagascar is a relatively small landmass, and has a limited amount of climatic variation. This means that rubber vine probably cannot fully express its climatic preferences. This limitation is most likely to be evident in the ability of the plant to survive drier climates than are present in Madagascar because the end of the climatic gradient across the range of rubber vine is limited by sea. The existence of the congeneric Cryptostegia madagascariensis Decne. within the northern range of Cryptostegia grandiflora provides a complication in the analysis. In Madagascar there is a distinct north-south rainfall gradient along the western coast. It is likely that C. madagascariensis is better able to tolerate the wetter conditions to the north, and outcompetes C. grandiflora. In the absence of this competition it is likely that C. grandiflora could persist in moister conditions than it has been noted occupying in Madagascar. 13
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: Mitchell Grass Downs. This provides
Page 23 and 24: 3 Results Experience with ecologica
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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