Effect of soil type and climatic conditions on the growth and flowering phenology of three Oxalis species in the Western Cape, South Africa.
Generally, invasive plant species have wide environmental tolerance that enables them to exploit various climatic conditions and soil types, allowing them to invade new habitats easily. In the Cape Floristic Region, South Africa, the diversity of flowering plants can in part be ascribed to variation in these habitat characteristics that limit their distribution. Climate change has been predicted to bring warmer and drier conditions to the region, with possible influences on the climatic barriers that influence species distributions. We tested the effects of soil type and climate on the growth and flowering of the non-weedy Oxalis tomentosa, and the two weedy species Oxalis purpurea and Oxalis pes-caprae on an altitudinal gradient. The three species, all native to the region, exhibit a range of tolerances to environmental conditions: the first is habitat specific whereas the others are both well-known indigenous weeds that have wider tolerance. The results showed that O. purpurea tolerates a variety of conditions well, whereas O. pes-caprae is more restricted by soil type, but would potentially profit from future climatic changes. O. tomentosa, when removed from its native habitat, was stressed under all conditions. These results suggest that habitat-restricted species will be threatened if the predicted level of climate change occurs, while invasive weeds will profit. Studying species responses to different environmental conditions is essential in determining future distributions.