Understanding the effects of rainfall pattern on the plant interactions is a prerequisite for anticipating the effects of climate change on communities and ecosystems. Effects of a change in growth-season rainfall pattern were tested on individual performances, and the interaction between arid land plants. Simulated rain events were applied either as two rains of 20 mm, or as four rains of 10 mm, on natural vegetation of steppe rangelands in Nasr-Abad, Yazd, Iran. Phenotype responses were assessed by measuring the density of annuals and current year growth of perennials. Facilitation effects were assessed by comparing density of annuals in open space and within the sub-canopy of perennials. Competition between perennials was tested using target-neighbour designs. Effects of rain size were more significant than rain frequency. There were linear increases in performances of both annuals and perennials, as the magnitude of pulse sizes increased linearly from zero (control), to 10 and 20 ml per event. Larger rain events led to a shift in relationships between annual and perennials from facilitation to no interactions, and a change in the interaction between perennial plants from no relationship to the competition. Accordingly, arid land plant communities showed some potential to buffer the short time effects of climate change, which may occur as variations in the intra-annual rainfall pattern.

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