VERTEBRATE PREDATION ON HOLM OAK, QUERCUS-ILEX, ACORNS IN A FRAGMENTED HABITAT - EFFECTS ON SEEDLING RECRUITMENT

Rodent and avian consumption of Helm Oak, Quercus ilex, acorns were ex amined in central Spain during two high-production seasons, 1990-1991 and 1993-1994, in 1 and 3 large stands and in 6 and IO small stands (0 .2-12 ha) respectively, to study the effects of vertebrate predation o n seedling recruitment. Previous data indicate that wood mouse abundan ce is much higher in small stands. Tree size, frequency of acorn-beari ng oaks and acorn abundance were similar in the two sizes of forest st ands. Overall acorn consumption was 33.7 times higher in the small sta nds compared to that in the large stands in 1991, and 3.1 times larger in 1994. Consumption of acorns by mice in the small stands was 49 and 95 times greater than that by birds in the first and second year, res pectively. Seedling recruitment was significantly higher in the large stands in both study seasons. Regeneration by ramets was roughly simil ar in small and large stands in both seasons. Thus, predation by mice was apparently responsible for the failure of sexual reproduction in t he small stands. The results suggest that vegetative regeneration migh t be the prevalent reproductive method of Helm Oaks in small forest tr acts. (C) 1997 Elsevier Science B.V.