Masting in Buxus balearica : assessing fruiting patterns and processes at a large spatial scale Amparo La ´zaro, Anna Traveset and Marcos Me ´ndez La ´zaro, A., Traveset, A. and Me ´ndez, M. 2006. Masting in Buxus balearica : assessing fruiting patterns and processes at a large spatial scale.  Oikos 115: 229  240. 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. A. La ´zaro (amparo.lazaro@umb.no) and A. Traveset, Inst. Mediterra ´neo de Estudios Avanzados (C.S.I.C.-U.I.B.), c/ Miquel Marque ´s no. 21, ES-07190 Esporles, Baleares, Spain.  M. Me ´ndez, A ´ rea de Biodiversidad y Conservacio ´n, Univ. Rey Juan Carlos, c/ Tulipa ´n s/n., ES-28933 Mo ´stoles, Madrid, Spain.  AL also at: Norwegian Univ. of Life Sciences, Dept of Ecology and Natural Resources Management, PO Box 5003, No-1432 Aas, Norway. Mast seeding (masting hereafter) consists of the syn- chronous highly variable seed production among years by a plant population (Kelly 1994). A continuum exists from annual reproduction through unsynchronized supra-annual reproduction to strict masting (Kelly 1994, Herrera et al. 1998), depending on the degree of synchrony achieved in the originally chaotic fluctuation in fruit production by individual trees (Koenig et al. 2003). Patterns of annual variation in seed production have been mainly investigated at the plant population level, and only rarely at the individual level (but see Herrera 1998, Rees et al. 2002, Koenig et al. 2003). The ecological and evolutionary significance of mast- ing (Kelly 1994, Kelly and Sork 2002) revolves around the following two groups of hypotheses: (1) the ‘‘resource matching’’ hypothesis, which proposes that plants Accepted 20 June 2006 Subject Editor: Pia Mutikainen Copyright # OIKOS 2006 ISSN 0030-1299 OIKOS 115: 229  240, 2006 OIKOS 115:2 (2006) 229