Mast seeding in Abies balsamea, Acer saccharum and Betula alleghaniensis in an old growth, cold temperate forest of north-eastern North America

1 Several hypotheses have been put forward to explain the phenomenon of mas ting or mast seeding, i.e. the supra-annual, periodic production of a large number of seeds in long-lived plants. Some of these hypotheses deal with t he proximate causes of masting (e.g. the climate hypothesis) but others are concerned mostly with ultimate, evolutionary explanations (e.g. the pollin ation efficiency hypothesis). 2 The seed production of three tree species, Abies bulsamea, Acer saccharum and Betula alleghaniensis, was followed over a 7-year period in an old-gro wth, cold temperate forest of north-eastern North America. The main objecti ves were to determine the extent of interannual variations in seed producti on, to investigate the relationship between viable and potential seed crop and crop efficiency, and to explore the effects of climate on seed producti on. 3 Potential and viable seed production varied significantly among years for all three species. However, the timing of dispersal remained the same rega rdless of the level of seed production. 4 Seed rain was spatially less heterogeneous in years of high seed producti on, suggesting that most trees were reproducing in such years. 5 Over the 7-year period, there was a significant concordance among species in their viable seed crop and crop efficiency, but not in their potential seed crop. Crop efficiency was positively correlated to potential seed crop for Abies and Betula, but not for Acer. 6 High seed production was related to warm, dry conditions in the spring of the previous year (i.e. at reproductive bud initiation) but to a moist sum mer in the year of seed maturation. 7 Masting in these three species thus appears to be controlled by several f actors, including climate and pollination efficiency.