Small rainfall events: An ecological role in semiarid regions.

Small precipitation events account for a large proportion of the precipitation received in semiarid regions, and their potential ecological importance has previously been ignored. We investigated the effect of a small rainfall event (5 mm) upon Bouteloua gracilis, the dominant grass species of the central and southern Great Plains of North America. An effect of a small event on leaf water potential and leaf conductance to water vapor was observed in less than 12 h and lasted for up to two days.The remarkable short response time of Bouteloua gracilis to a rainfall stimulus enables this species to utilize small events and, therefore, may influence its persistence as a dominant species in the steppe region.We proposed response times to be one of the major species characteristics determining capacity for utilizing different portions of the water resource of the region. We suggest that small precipitation events are ecologically significant and a qualitatively distinct resource for ecosystems in semiarid regions.