Interactions of local and regional processes: Species richness in tussock sedge communities

Grime's model of plant species richness was used as a basis for examining h ow local and regional processes interact in the regulation of the species r ichness of vascular plants growing on individual Carer stricta (tussock sed ge) tussocks in New Hampshire, USA. We first used a correlational study of 71 tussocks in five marshes to examine the relationships between species ri chness and standing crop + leaf litter biomass. We found humped (unimodal) relationships with a wide variation in peak species richness per tussock am ong sites. Then, using a factorial design involving 167 tussocks in three m arshes, we performed Carer stricta standing crop removals, leaf litter remo vals, and seed additions to examine how these factors interacted to influen ce species richness. The results of both studies supported Grime's model, w hich implies that the magnitude of local competitive effects on plant speci es richness is dependent on regional propagule availability.