CACHE SITE SELECTION BY CHIPMUNKS (TAMIAS SPP) AND ITS INFLUENCE ON THE EFFECTIVENESS OF SEED DISPERSAL IN JEFFREY PINE (PINUS-JEFFREYI)

The effectiveness of Jeffrey pine (Pinus jeffreyi) seed dispersal perf ormed by seed-caching yellow pine chipmunks (Tamias amoenus) and lodge pole chipmunks (Tamias speciosus) was compared to that of wind dispers al in the Sierra Nevada of western Nevada. Wind-dispersed seeds typica lly fall under or near the parent tree. Chipmunks removed 90 and 97% o f 1064 radioactive seeds from each of two simulated wind-dispersed see d shadows in less than 24 h. ''Wind-dispersed'' seeds were deployed wi thin 12 m of the two ''source'' trees, but chipmunk caches were found from 2-69 m from the trees. Chipmunks carried nearly all seeds away fr om source trees, greatly reducing the density of seeds under and near source trees. Caches contained from 1-35 seeds and most were buried 7- 21 mm deep. Chipmunks cached in open bitterbrush shrubland with minera l soils much more than expected and cached in closed-canopy Jeffrey pi ne and lodgepole pine forests with thick needle litter much less than expected. Many Jeffrey pine seedlings and saplings grow in the bitterb rush habitat and few grow in the pine forests. Ten and 20% of the orig inal caches survived until April, the time of seed germination, at the two sites. The movement of wind-dispersed seeds is random relative to environmental variables important in seedling survival, and the wind in coniferous forests cannot quickly bury seeds. The quality of seed d ispersal rendered by chipmunks was superior to that provided by the wi nd because the chipmunks quickly harvested seeds on the ground, moved them away from source trees, and buried them in the ground in habitats and microhabitats where they were more likely to establish new seedli ngs. The increased quality of seed dispersal provided by animals relat ive to the wind may help explain why over twenty species of pines have evolved seeds and cones that are adapted for dispersal by seed-cachin g animals.