Shrubs facilitate pine colonization by controlling seed predation in dry Mediterranean dwarf shrublands

Abstract

Spatial association between pine recruitment and shrubs is widely observed in dry environments and often associated with physical facilitation provided by the shrub, alleviating seedling drought stress. However, shrubs may also facilitate recruitment by sheltering seeds from granivores. In this study we investigated the influence of shrub-related microsites on post-dispersal pine seed survival in dry Mediterranean shrubland. We present a novel approach investigating the survival of single seeds in the context of long-distance wind dispersal. In four dry shrubland sites of central Israel, we placed seeds of Pinus halepensis in different microsites associated with Sarcopoterium spinosum shrubs: under canopy, at two margins and in between shrubs. We monitored the seed persistence monthly, replacing seeds removed by granivores. We also compared seed survival in burned vs. unburned areas. Logistic regression showed that seeds placed under shrubs had significantly higher survival rates than elsewhere. In unburned sites survival was higher than in burned sites and remained higher under shrub canopies. We show that these effects were substantial by considering the length of the season through which seeds need to persist. We conclude that shrubs constitute an important facilitator for Pinus halepensis colonization in dry shrubland through their positive effect on seed survival.