Spatiotemporal variation in acorn production and damage in a Spanish holm oak (Quercus ilex) dehesa

摘要

Aim of study: There is a lack of knowledge about spatio-temporal patterns of acorn production in dehesas, especially regarding the influence of different agents causing acorn damage. We examined the spatial and temporal variability on acorn productionand damage in four stands within a dehesa farm in 1997, 1998 and 1999. Area of study: The study was carried out in a 1800 ha dehesa farm of Caceres province, western Spain. Material and methods: Acorns were sampled by means of seed traps placed in the canopy of six holm oak trees per stand. Acorns collected were counted and assessed for damage by Curculio weevils, Cydia moths and the bacterial pathogen Brenneria quercina. Main results: Mean acorn production for the whole study period was 44.60 acorns m~2, which did not vary significantly either among stands or among years. The variability among individual trees was very high (0-300 acorns nr2). The rate of infestation by Curculio was 7.64± 10.72%, by Cydia was 1.76 ±3.33%, whereas 10.29± 16.12% ofacorns were infested by Brenneria. We found no significant spatial differences, but the rates of acorn loss by insects varied among years. These rates were independent of annual acorn production and there was no correlation among damages by different pests, except between Curculio and Cydia in two crop years. Research highlights: It can be concluded that acorn crops are synchronized at the within-farm level and that the temporal variation in acorn damages can be independent of crop size.