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

More documents

Recommendations

Info

2.3.1.2 Australia The present distribution of prickly acacia in Australia was gauged from several sources: Prickly acacia is present in much of Queensland and in isolated pockets of the Northern Territory, New South Wales, and at one location in South Australia (Figure 2.2). The Australian distribution information was used primarily as a means of validating the model. Figure 2.2 Occurrence records of prickly acacia, Acacia nilotica ssp. indica, in Australia Influence of Climatic Factors on Distribution. Prickly acacia has a wide tolerance of rainfall. It occurs in areas receiving less than 230 mm y -1 and in areas receiving more than 1 500 mm y -1 . It is reported to be intolerant of frost, but it can grow in areas where the mean monthly temperature of the coldest month is 16 °C and it can withstand temperatures up to 50 °C. A minimum threshold thermal accumulation each year (degree-days) may be necessary for seed production, so the length of the growing season was tested to see if it could govern the poleward limit of this species. The parameters used in the CLIMEX models are shown in Table 2.2. 6
Table 2.2 Prickly acacia and rubber vine parameter values used in the CLIMEX model Index Parameter Rubber vine Prickly acacia Temperature DV0 15 18 DV1 25 25 DV2 37 37 DV3 43 45 PDD 1985 1200 Moisture SM0 0.1 0.045 SM1 0.3 0.2 SM2 1 1.2 SM3 1.3 1.5 Cold Stress TTCS 2.5 2.5 THCS 0.2 0.2 Heat Stress TTHS 43 45 THHS 0.25 0.05 Dry Stress SMDS 0.1 0.045 HDS 0.0025 0.025 Wet Stress SMWS 1.35 1.5 HWS 0.017 0.02 2.3.1.3 Influence of non climatic factors on distribution The climatic factors discussed above will generally determine the outermost bounds of a species’ potential distribution. Within the areas defined as climatically suitable there will be other factors that determine whether a species is found in a particular area. The effects of some of these non-climatic factors are discussed below. Prickly acacia appears to be able to grow on all soils excepts very sandy soils. Landlocked drainage channels allow populations to persist in areas that would otherwise be climatically unsuitable due to a lack of soil moisture. As prickly acacia takes approximately five years to mature, any disturbance regime that destroys the shrubs, and recurs every five years or less will prevent its widespread recruitment. Similarly, a fire regime of intensive burns every five years or less may prevent recruitment of prickly acacia, depending upon the intensity of the fires and the size structure of the population of prickly acacia. Seed germination rates are markedly increased where seeds are scarified by passing through the gut of cattle. In the absence of seed dispersal by cattle it is unlikely that prickly acacia will actively invade and establish in new areas in densities that will cause significant reductions in pasture production. The procedure for estimating the climatic requirements of prickly acacia was firstly to fit the predicted distribution to the known distribution outside of Australia. Where prickly acacia was noted growing in Australia outside of the area predicted to be climatically suitable, based upon its overseas distribution, 7
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: In addition to the spatial data set
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 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

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?