CLIMEX parameter values were adjusted iteratively until Ecoclimatic Indices (EI) generated for alligator weed matched the known distribution in South America, and were then fine-tuned to match the exotic distribution in North America (See Figure 1). Values of EI above 10 were accepted for locations favourable to the growth of alligator weed. Moisture stress indices were not used because of growth of the weed in aquatic, swampy and high water table habitats. The parameter values were then applied to predictions of potential distribution in Asia (See Figure 2), Africa and Europe (See Figure 3), and Australia (See Figure 4). CLIMEX predicted with broad accuracy the locations in China where alligator weed grows and suggests that the weed has reached its geographical limit in that country (See Figure 2), thus validating the CLIMEX model of the species. Large parts of Australia (See Figure 4) and Africa (See Figure 3) where alligator weed is not yet present are favourable for growth of the weed, and so are at risk should the weed be introduced.

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Gunter Maywald and Robert Sutherst