The importance of occasional droughts for afroalpine landscape ecology

Abstract

The paper presents climatic and plant ecological data for unusually severe dry-season conditions on Mt. Elgon (Uganda/Kenya) and the Bale Mountains (Ethiopia). There is clear evidence that plants are exposed to desiccation stress during high-altitude droughts, which occur on average every 7-10 y in the study sites. Although high vapour-pressure deficits and consequently high potential evapotranspiration led to conspicuous wilting of several plant species, no lethal damage was observed and plant communities maintained increased flowering activity under drought conditions. Moreover, highest outposts of ericaceous vegetation were regularly found on thin soil covering rocky outcrops, where water stress apparently is high. Probably more important than direct water stress are the extensive fires occurring under drought conditions, which cause large-scale replacement of woody vegetation by grasslands. Additional consequences of drought include adverse conditions for seedling stablishment.