Seed and microsite limitations mediate stochastic recruitment in a low-diversity prairie restoration
Recruitment of species into plant communities requires the arrival of viable propagules to coincide with the availability of suitable microsites for establishment. Accordingly, the rarity of recruitment events due to seed and/or microsite limitations may constrain the establishment, diversity, and spatial distribution of species in plant communities, thus potentially mediating stochastic recruitment—herein described as probabilistic and unpredictable patterns of species establishment over space that can emerge in the absence or in spite of environmental heterogeneity. To examine this premise, we applied a gradient of propagule pressure, using 37 native forb species, to plots subjected to disturbances of varying intensity in a low-diversity grassland restoration in Eastern Kansas, USA. We monitored establishment for three years, assessing the effects of propagule pressure and disturbance on sown species stem density, richness, composition, and community dissimilarity. Seed limitation was the primary constraint on species richness in this grassland, but both propagule pressure and disturbance had positive, interactive effects on stem density. Increased propagule pressure enhanced recruitment and reduced community dissimilarity among disturbance treatment replicates, thus tempering stochastic recruitment. High propagule pressure led to compositional divergence among disturbance treatments, indicative of deterministic species sorting. These results suggest that seed limitation and stochastic recruitment have important implications for beta diversity and spatial structuring of plant community species compositions, acting to (1) generate and maintain beta diversity by producing stochastic spatial variation in species composition among environmentally similar localities; while concurrently (2) limiting beta diversity by constraining the expression of niche-based species sorting in response to environmental heterogeneity.
KeywordsBeta diversity Disturbance Microsite limitation Propagule pressure Seed addition Stochastic
Funding was provided by Prairie Fork Trust and the University of Kansas Ecological Reserves, with support from NSF Grant # 0950100 and the Madison and Lila Self Graduate Fellowship. Bernadette Kuhn and Joel Harvester provided invaluable field assistance. Matthew Albrecht, Ford Ballantyne IV, Adam Smith, and three anonymous reviewers provided insightful comments to improve this manuscript.
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