Relative importance of available energy, environmental heterogeneity, and seed availability for seedling emergence on a limestone pavement

Abstract

Environmental heterogeneity at fine spatial scales is expected to be especially important in determining community patterns at seed germination and establishment stages. I compared seedling and adult species richness patterns in relation to environmental gradients by adding seeds from 39 species across an elevation gradient, unimodally related to species richness on a limestone pavement. Environmental variables linked to habitat fertility (“available energy”), within-plot spatial or temporal variability (“environmental heterogeneity”), and spatial coordinates were evaluated as contributors to richness patterns using variance partitioning. Variables related to available energy explained most of the variance in species richness for adults and seedlings in sown plots; pure spatial variation, shared variation between energy and heterogeneity variables, and other shared fractions explained more of the variance in seedling richness in unsown plots. Seedling density and richness increased with sowing, but the relative increase differed along the elevation gradient; relative increase in richness was greatest at the lowest and highest elevations. Limited seed dispersal from parent plants may result in seedlings colonizing less favorable microsites in unsown plots, whereas sowing resulted in greater explained variance owing to environmental factors, and lower variance attributable to space alone, indicating that appropriate species are more able to reach suitable microsites. While many experimental studies have revealed associations between microsite characteristics and species-specific recruitment responses, seed limitations in natural communities can contribute to the spatial structure of seedling communities and mask environmental control of seedling species richness.