Seed Bank Survival and Dynamics in Sprouting and Nonsprouting Arctostaphylos Species

Abstract

-Members of the chaparral genus Arctostaphylos regenerate after fires either by obligate seeding or facultative sprouting. To test the hypothesis that sprouting species differ from nonsprouting species, we compared flower, fruit and seed production and changes in soil seed densities between sprouting (S) and nonsprouting (NS) Arctostaphylos species during 18 months. We estimated postdispersal seed predation experimentally by comparing seed banks that excluded vertebrate predators with seed banks that excluded no predators. We determined changes in unmanipulated, naturally occurring seed banks during the same time period. Production of inflorescences, infructescences and fruit did not differ significantly between A. canescens (NS) and A. glandulosa (S). Densities of whole and damaged seeds were consistently higher in seed banks of A. glandulosa than in A. canescens seed banks, but densities of viable seeds were lower in A. glandulosa seed banks. In two additional pairs of Arctostaphylos species examined, total and viable seed bank densities were higher for nonsprouting species than sprouting species. Densities of experimentally enclosed seed banks did not change during 18 mo, whereas unenclosed, experimental seed banks decreased by 60% (A. canescens) and 53% (A. glandulosa) in 5 mo. Similarly, densities of naturally occurring seed banks decreased by 29% (A. canescens) and 14% (A. glandulosa) in 11 mo. Postdispersal seed predation was important in reducing the survival of seeds in soil seed banks, whereas senescence and decay were not. However, there was no consistent relationship between sprouting and nonsprouting in these Arctostaphylos species.