Spatiotemporal variation in seed dispersal and recruitment near and far from Pinus halepensis trees

Spatiotemporal variation in the wind-generated dispersion pattern of Aleppo pine (Pinus halepensis) seeds was examined by placing seed traps up to 110 m away from a small, isolated stand in Israel during six successive dispersal seasons. Subsequent recruitment was surveyed two years later. Of the 5487 seeds, 97% were trapped ≤20 m from the nearest adult tree. Seasonal dispersal curves were consistently right-skewed and leptokurtic. The inverse power law and the negative exponential model accounted for a similar fraction of the variation in the number of dispersed seeds at different distances (79-86% and 76-88%, respectively). Seed dispersal rates varied significantly among seasons. Eighty saplings (3-5 yr old) became established during the three years of the study, most within 15 m of the nearest canopy, some farther away, and none directly under the tree canopies. The estimated probability of seed survival to sapling stage increased significantly with increasing distance from adults, as predicted by the escape hypothesis. Winds varied significantly between seasons, generating significant interseasonal variation in seed deposition patterns far from, but not near to, adult trees. Coefficients of variation of seed dispersal rates were lower near adult trees than farther away. Both Moran's I correlograms and partial Mantel tests revealed interseasonal consistency in seed deposition patterns for the total study area and for the area near adult trees but showed considerable variation farther away. We suggest that the low spatiotemporal variation near adults and the high variation far away act to intensify the effects of predation (by increasing the efficiency of predators near adults and reducing it far away) and competition (by increasing the intensity of seedling competition near adults and reducing it far away) in structuring the observed survivorship curve predicted by the escape hypothesis.