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Seed dispersal and recruitment limitation at large spatial scales in northern hardwood forest fragments.
McEuen, Amy1, 2, Curran, Lisa3, 1 University of Michigan, Ann Arbor, MI2 Present address: Wilkes University, Wilkes-Barre, PA3 Yale University, New Haven, CT
ABSTRACT- Despite increasing evidence of seed limitation in forest ecosystems, data on spatial patterns of seed availability at large (>1ha) spatial scales remain sparse. We monitored seed rain in five northern hardwood fragments in Michigan for two years (40m spacing, n = 114). Of the 37 woody plants sampled (n = 98,032 mature seeds), only three had widespread seed availability within all sites containing resident sources (seed in >70% of traps in each fragment). Seed colonization, measured as the percentage of traps within a fragment receiving seed, differed based on dispersal vector, with animal-dispersed species hitting fewer traps than wind-dispersed, even after adjusting for lower seed production. High colonization percentages (>70%) were found for light-seeded, high-fecundity species (Betula papyrifera, Betula alleghaniensis) at low source densities and distributions (<0.15m2 basal area*ha-1 and <4% plots containing mature individuals), but only occurred for heavy-seeded, lower-fecundity species (Acer rubrum, Fraxinus pennsylvanica, Tilia americana) when source densities and distributions were high (>0.7m2 basal area*ha-1 and >19% plots containing mature individuals). Heavy-seeded wind-dispersed species and animal-dispersed species also showed evidence of recruitment limitation, with seedling presence associated with seed presence for Carpinus caroliniana, Fagus grandifolia, Prunus avium, and Tilia americana. No seed dispersal into fragments was detected for Acer rubrum, Betula alleghaniensis, or Tsuga canadensis, despite high seed colonization levels (>50%) in fragments with resident sources, suggesting these species can be seed-limited at larger spatial scales. Our results confirm the importance of seed dispersal to forest dynamics and suggest seed availability plays a significant role in determining variation in plant community composition across scale.
Key words: seed dispersal, northern hardwood forests, seed size, recruitment limitation