TREE SEED PRODUCTION AND FOOD CONDITIONS FOR RODENTS IN AN OAK WOOD IN SOUTHERN ENGLAND

Seed production and seed losses were monitored in an oak (Quercus robu r) wood in southern England between 1975 and 1988. In addition to acor ns, seeds from several large beech (Fagus sylvatica) and sweet chestnu t (Castanea sativa) trees which occurred within the wood, and from the understorey of hazel (Corylus avellana) trees, were also monitored. T he seeds from these four tree species are all subject to heavy predati on by rodents, as well as other seed-eaters such as birds and insects. Seed fall tended to be irregular and three years, 1976, 1985 and 1987 were considered oak mast years. There were too few years with large a corn crops-to examine whether resource depletion in these years result ed in poor crops in subsequent years. There was no correlation in seed production between the four tree species which does not agree with on e of the predictions of the predator satiation theory of masting behav iour. The effects of weather on seed production were investigated but few significant correlations were found. In general the results tended to support previous findings. Between 1980 and 1982 a serious outbrea k of Tortrix moth caterpillars occurred within the wood and may have a ffected acorn production. A negative relationship was found between oa k defoliation and acorn production in the subsequent year. The loss of seeds from the forest floor was initially rapid and in 9 years no see ds survived into the following year and food conditions were poor for granivores. In 3 of the remaining 4 years acorns survived well into sp ring and early summer providing good food conditions for forest rodent s through to the times when alternative food supplies became available . Although oak trees contributed most seed energy in good years, the o ther tree species, especially beech, became important when acorn produ ction was poor. Predispersal losses due to predators were frequently h igh and averaged 80 per cent, 40 per cent, 38 per cent and 33 per cent in hazel, sweet chestnut, oak and beech respectively. On average, haz el nuts tended to fall first, some 6 weeks before acorns which tended to be the last seeds to fall of the four tree species. Knopper galls a nd weeviled acorns fell earlier than sound acorns. A key-factor analys is indicated that a failure to mature, predispersal predation and inse ct infestation from weevils and Knopper galls contributed equally to c hanges in numbers of acorns among years.