EFFECTS OF MICROHABITAT PATCHINESS ON PATTERNS OF SEED DISPERSAL AND SEED PREDATION OF CERCOCARPUS-LEDIFOLIUS (ROSACEAE)

Structural heterogeneity of habitats is thought to influence spatial p atterns of seed dispersal and of seed survival, two critical processes influencing seedling recruitment. Using the wind-dispersed tree Cerco carpus ledifolius in northeastern Utah, USA, we investigated patterns of initial seed arrival, seed survival, and longer-term seed accumulat ion among four structurally distinct microhabitats (beneath Cercocarpu s, Juniperus, and woody shrubs, and in open interspaces). Initial dens ity of seedfall into seed traps was generally greater beneath Cercocar pus than in the remaining microhabitats, which did not differ from one another. Patterns of initial seedfall density appear to be more affec ted by distance from a seed source than by the physical structure of t he microhabitat. The total numbers of seeds arriving in a microhabitat type. however, likely differ greatly among sites due to large differe nces in the relative abundances of microhabitat types. Experiments wit h tethered seeds indicated that overall levels of post-dispersal seed predation were low. However, seed loss in 1995 differed significantly among microhabitats, with open microhabitats generally having greatest seed loss. Patterns of accumulated seeds on the ground, in the litter , and in the soil showed greater differences among microhabitats than did patterns of initial seed arrival. Open microhabitats had the fewes t accumulated seeds and beneath C. ledifolius had the most. The redist ribution of the reed shadow through time is likely a consequence of bo th secondary seed movement over winter and the disproportionately high levels of post-dispersal seed predation in open microhabitats. By fol lowing seeds through multiple phases of early recruitment, we demonstr ated that seed distributions and the processes affecting seeds are het erogenous in space and temporally dynamic. These findings are importan t for understanding processes leading to the ultimate quantity and pat terning of adult plant populations.