Ponderosa pine dispersal and recruitment: the role of seed-caching rodents

Abstract

Seed-caching rodents are important agents of dispersal for many plant species and understanding the factors that determine spatial patterns of seed dispersal are critical for understanding plant recruitment and demographics. Although ponderosa pine has traditionally been viewed as a wind dispersed pine, I found that rodent seed-caching behavior could be advantageous to ponderosa pine for several reasons. First, rodents cached seeds in contact with mineral soil which enhances germination. Second, rodents cached seeds with a layer of litter that may protect seedlings from mortality due to frost heaving by acting as insulation. Third, rodents doubled the dispersal distance (compared to wind) of ponderosa pine seeds which could increase escape from distance-dependent mortality, increase the probability of colonizing open habitats, and increase the probability that seeds arrive in suitable microsites. Finally, rodents non-randomly placed seed caches near rocks, where seedlings had higher survival, and near downed wood, where seedlings may benefit from fire-resistant "hot beds" following surface burns. Taken together these data suggest that rodents may act as directed dispersers of ponderosa pine seed and could enhance germination and recruitment about background levels.