Masting in Buxus balearica: assessing fruiting patterns and processes at a large spatial scale

Masting consists of the synchronous highly variable seed production among years by a plant population. We studied spatiotemporal variation in fruit production in ten populations of Buxus balearica (six in the Balearic Islands and four in the Iberian Peninsula) from 2001 to 2004 in the light of masting. In some of them we assessed, by means of both observational and experimental data, the relationship between fruit production and some abiotic variables, the role of previous reproduction, the ‘‘pollination efficiency’’ and the ‘‘predator satiation’’ hypotheses, as well as the consequences for seedling density and survival. Fruit production in B. balearica showed substantial between-year variation, especially in island compared to mainland populations. Correlative evidence indicated that this variation and its geographic pattern were related to differences between regions in rainfall variability, cost of reproduction and the degree of ambophily. We found no indication of predator satiation. However, experimental tests failed to support many of our results, namely a negative effect of previous reproduction on future flowering in island populations and lower pollen limitation with increasing flower production. We therefore warn against exclusive reliance on correlations when testing hypotheses related to masting. In addition, seedling recruitment increased after some episodes of high fruit production but probably additional factors had a role in recruitment, suggesting that mast events not always translate into increased reproductive success. Although a limited time series only allows considering B. balearica as showing ‘putative’ masting, weather and pollination-related processes are good candidates for further exploration of fruiting patterns and processes at a large spatial scale.