Effects of microhabitat patchiness on patterns of seed dispersal and seed predation of Cercocarpus ledifolius (Rosaceae)

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Abstract

Structural heterogeneity of habitats is thought to influence spatial patterns of seed dispersal and of seed survival, two critical processes influencing seedling recruitment. Using the wind-dispersed tree Cercocarpus ledifolius in northeastern Utah, USA, we investigated patterns of initial seed arrival, seed survival, and longer-term seed accumulation among four structurally distinct microhabitats (beneath Cercocarpus, Juniperus, and woody shrubs, and in open interspaces). Initial density of seedfall into seed traps was generally greater beneath Cercocarpus than in the remaining microhabitats, which did not differ from one another. Patterns of initial seedfall density appear to be more affected by distance from a seed source than by the physical structure of the microhabitat. The total numbers of seeds arriving in a microhabitat type, however, likely differ greatly among sites due to large differences in the relative abundances of microhabitat types. Experiments with 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 fewest accumulated seeds and beneath C. ledifolius had the most. The redistribution of the seed shadow through time is likely a consequence of both secondary seed movement over winter and the disproportionately high levels of post-dispersal seed predation in open microhabitats. By following seeds through multiple phases of early recruitment, we demonstrated that seed distributions and the processes affecting seeds are heterogeneous in space and temporally dynamic. These findings are important for understanding processes leading to the ultimate quantity and patterning of adult plant populations.

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