Impact of small rodents on tree seeds in temperate and subtropical forests, China.

A study was conducted in a temperate forest located at Donglingshan Mountains from 1999 to 2001 and in a subtropical forest located at Dujiangyan region from 2000 to 2002, both in China, to investigate the impact of small rodents on tree seeds in these forests. The rodent-dispersed tree species included in the study were Quercus liaotungensis and Prunus armeniaca in Donglingshan and Q. variabilis, Q. serrata, Castanopsis fargesii and Camellia oleifera in Dujiangyan. From 1999 to 2001, 171 individuals of small nocturnal rodents were trapped in 900 trap nights in the Donglingshan forest, while from 2000 to 2002, 228 small nocturnal rodents were captured in 2250 trap nights at the Dujiangyan forest. In both forests, seed production of the tree species varied among years. Nearly 100% of the tin-tagged seeds were harvested (i.e., removed or consumed in situ) by small rodents within 1 or 2 weeks after release at seed stations. The proportion of seed removal versus consumption in situ varied significantly among seed species, seasons, years and stands. Results indicated that rodents prefer to remove large seeds or high value seeds. Post-removal seed fate can be sorted into three categories: (1) cached, including buried intact in the soil by rodents or deposited intact on the surface; (2) eaten, leaving only tin tags and seed fragments; and (3) missing with their true fates unknown. In both forests, scatterhoarding by small rodents was very common, but the proportion of the cached seeds varied among the seed species, years and stands. Seeds were often recovered from caches within several days and transported to new cache sites or eaten near cache sites. The amount of seed recaching by rodents was higher in subtropical forest than that in temperate forest. Seeds with a hard hull or higher nutritional value were recached more frequently than seeds with a soft hull or lower value. In both forests, small rodents made caches with similar numbers of seeds. For all species in both forests, 76-100% of primary caches and nearly 100% of higher order caches (i.e. secondary and tertiary caches) contained only one seed. In both forests, over 80% of cached seeds for all seed species were dispersed less than 20 m from the seed stations. More than 70 and 60% of all cached Q. liaotungensis and other tree species seeds, respectively, were deposited under shrubs in the Donglingshan and Dujiangyang forests. In both forests, tagged seeds with a hard hull (e.g. P. armeniaca) or high caloric value (e.g. C. oleifera and Q. variabilis) were more likely to survive and establish seedlings than tagged acorns of other studied species.