MASTING IN ANIMAL-DISPERSED PINES FACILITATES SEED DISPERSAL

Abstract

Masting increases the efficiency of wind pollination and satiates seed predators, but there is little evidence that masting facilitates seed dispersal by animals. Masting in pines was studied over three field seasons by simulating seed crops in synchrony (mast years, autumn 1998 and 1999) or out of synchrony (non-mast year, autumn 2000) with the local population. Rodents removed simulated wind-dispersed Jeffrey pine (Pinus jeffreyi) and sugar pine (Pinus lambertiana) seeds significantly more rapidly in mast years than in the non-mast year. Radioisotopes were used to follow the fates of individual pine seeds taken from three source trees. Rodents cached nearly all experimental seeds in mast and non-mast years, making 562 caches in 1998, 510 caches in 1999, and 1034 caches in 2000. Mean dispersal distances of seeds in primary caches were 5.9 and 4.6 m (28.6% and 22.1%) farther in the two mast years than in the non-mast year. Rodents often excavated cached seeds and moved them to new sites (secondary caching). During mast years, some seeds were found in as many as three cache sites, but during the non-mast year, the level of secondary caching approximately tripled, with some seeds being found in five or six separate cache sites. Large seed crops were associated with reduced secondary caching of seeds, reduced seed consumption, and greater seed survival in the following spring. Animal-mediated seed dispersal may be a selective force, along with predator satiation and increased efficiency of wind pollination, driving temporal variation in seed production in some large-seeded pines.