© 1993 by Institute of Chartered Foresters
Tree Seed Production and Food Conditions for Rodents in an Oak Wood in Southern England
School of Biological Sciences, Queen Mary and Westfield College London, E1 4NS, England
Seed production and seed losses were monitored in an oak (Quercus robur) wood in southern England between 1975 and 1988. In addition to acorns, seeds from several large beech (Fagus sylvatica) and sweet chestnut (Castanea sativa) trees which occurred within the wood, and from the understorey of hazel (Corylus avellana) trees, were also monitored. The seeds from these four tree species are all subject to heavy predation 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 acorn crops to examine whether resource depletion in these years resulted in poor crops in subsequent years. There was no correlation in seed production between the four tree species which does not agree with one of the predictions of the predator satiation theory of masting behaviour. 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 outbreak of Tortrix moth caterpillars occurred within the wood and may have affected acorn production. A negative relationship was found between oak defoliation and acorn production in the subsequent year.
The loss of seeds from the forest floor was initially rapid and in 9 years no seeds survived into the following year and food conditions were poor for granivores. In 3 of the remaining 4 years acorns survived well into spring and early summer providing good food conditions for forest rodents through to the times when alternative food supplies became available. Although oak trees contributed most seed energy in good years, the other tree species, especially beech, became important when acorn production was poor. Predispersal losses due to predators were frequently high 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, hazel 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 and weeviled acorns fell earlier than sound acorns. A key-factor analysis indicated that a failure to mature, predispersal predation and insect infestation from weevils and Knopper galls contributed equally to changes in numbers of acorns among years.
Received 27 October 1992.
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