Spatial concordance between seed rain and seedling establishment in bird‐dispersed trees: does scale matter?

Abstract

Summary 1 We explored whether seedling recruitment was spatially predicted by seed rain (spatial concordance) at different scales (microsite, microhabitat and site) in the bird-dispersed trees Crataegus monogyna, Ilex aquifolium and Taxus baccata, in temperate secondary forests in north-west Spain. 2 We propose that both spatial concordance within each scale and consistency of concordance patterns across scales are dependent on differences between seed rain and post-dispersal processes in the partitioning of spatial variance at each scale. 3 We measured the density of dispersed seeds, the percentage of post-dispersal seed predation by rodents and the density of emerged first-year seedlings at sampling stations distributed throughout five microhabitats (under canopies of parental trees and in open gaps) and four localities over two seasons. 4 Seed rain density of all tree species varied most at the microhabitat scale, but microsite and site differences accounted for most of the spatial variance in post-dispersal seed predation and, especially, in seedling establishment. 5 All three species showed concordance between seed rain and seedling establishment at the microhabitat scale, because strong patchiness in avian-generated seed rain overrode the slight uncoupling effects exerted by the more homogeneous post-dispersal processes. Seed rain was also a good predictor of recruitment of Ilex and Crataegus at the microsite scale, but, for Taxus, the rather homogeneous dispersal across microsites contrasted with the heterogeneous post-dispersal losses. At the site scale, only Taxus showed a positive trend of concordance. 6 Concordance patterns were maintained from microsite to microhabitat in Crataegus and Ilex, and from microhabitat to site in Taxus. Low-variance allocation to the site scale at the seed rain stage precluded complete consistency in Crataegus and Ilex. 7 Positive responses of recruitment to seed dispersal depended on both species and scale, resulting in a complex template for dispersal-limitation effects on metapopulations and communities.