A blome-scale assessment of the impact of invasive alien plants on ecosystem services in South Africa

This paper reports an assessment of the current and potential impaets of invasive alien plants on selected ecosystem servies in South Africa. We used data on the current and potential future distribution of 56 invasive alien plant species to estimate thier impact on four serveies (surface water runoff, groundwater recharge, livestock production and biodiversity) in five terrestrial biomes. The estimated reductions in surface water runoff as a result of current invasions were > 3000 million m(3) (about 7% of the national tatal), most of which is form the fynbos (shrubland) and grassland biomes; the potential reductions would be more than eight times greater if invasive alien plants were to occupy the full extent of their potential range. Impacts on groundwater recharge would be less severe, potentially amounting to approxiately 1.5% orf the estimated maximum reductions in surface water runoff. Reductions in grazing capacity as a result of current levels of invasion amounted to just over 1% of the potential number of livestock that could be supported. However, future impacts could increase to 71%. A biodiversity intactness index (the remaining proportion of premodern populations) ranged form 89% to 71% for the five biomes. With the exception of the fynobos biome, current invasions have almost no impact on biodiversity intanctness. Under future levels of invasion, however, these intanctness values decrease to around 30% for the savanna, fynbos and grassland biomes, but to even lower values (13% and 4%) for the two karoo biomes. Thus, while the current impacts of invasive alien planets are relatively low (with the exception of those on surface water runoff), the future impacts could be very high. While the errors in these estimates are likely ot be substantial, the predicted impacts are suffiently large to suggest that there is serious cause for concern. (C) 2007 Elsevier Ltd. All rights reserved.