Scatter-hoarding rodents disperse seeds to safe sites in a fire-prone ecosystem

Abstract

Fire can potentially decimate soil seed banks, even for species that are abundant in fire-prone areas. Many plants, like the widespread and dominant members of the genus Arctostaphylos in the fire-prone California Floristic Province, have seeds that (i) have no clear adaptions for dispersal and (ii) experience lethal fire temperatures if present on or near the soil surface. In this study, we aim to resolve these juxtaposed observations by mechanistically determining how one species, Arctostaphylos patula, is dispersed. To distinguish among dispersal modalities and determine the seed shadow, deposition patterns, and the conditions under which seeds germinate, we employed full-shrub exclosure treatments to monitor fruit removal, used a mark-relocation technique by radioactively labeling seeds, identified dispersers using motion-sensor cameras, and surveyed seedlings following fire to relate natural germination patterns to measured patterns from our experiment. Seed removal from exclosure treatments that allowed rodents access to shrubs was higher than those that prevented rodent access to shrubs, and cameras at radioactively labeled-seed stations failed to detect the presence of any other disperser; thus implicating rodents as the primary disperser of A. patula seeds. This evidence is corroborated by our finding from tracking radioactively labeled seeds that the depth at which rodents bury seeds completely overlaps with the depth from which we observed seedlings germinate following two fire events. Our study extends the boundary of what is understood as a scatter-hoarding seed dispersal syndrome and identifies a mechanism that allows populations of Arctostaphylos to exist in spite of recurrent fires that can be lethal to seeds and hazardous to plant populations.