The effect of soil and climate on the growth and survival of A. saligna and A. cyclops seedlings on a mountain gradient in Villiersdorp, South Africa.

Very few studies have simultaneously considered the effect of climate change and invasive species on ecosystems, and there is a great need for research in this field. Considered in isolation, climate change, invasive species and habitat destruction are the greatest threats to ecosystem functioning. It is believed that by causing disturbances in ecosystems (i.e. creating niches and lowering community resistance), climate change may increase the invasive ability of alien species. To determine the possible success of invasive alien species, we need to determine which factors (i.e. soil; climate; dispersal ability) could work together to facilitate or hinder their spread in a changing climate. Using two invasive alien species, Acacia cyclops and Acacia saligna, this study attempts to determine which factors (i.e. soil and climate) affect their survival and growth. This was done by means of reciprocal transplants using an environmental gradient as a proxy for different climatic conditions. A. saligna showed no significant response to soil type, whilst A. cyclops showed increased survival and growth on fynbos soil. Survival of A. saligna was affected by its position on the gradient, i.e. climate, but its growth once established was not affected. A. cyclops showed significant differences in both survival and growth due to climate. It is suggested that A. saligna is more likely to invade mountain Fynbos under future climate change scenarios: soil type will not be a barrier to its spread, and decreased rainfall may cause lowland conditions to become too dry. A. cyclops is more drought tolerant and will most likely be able to maintain its range in the lowlands. Since many other factors not included in this study are likely to be synergistic with climate change, further studies of this nature are encouraged.