CAUSES AND CONSEQUENCES OF MAST SEED PRODUCTION OF FOUR CO-OCCURRING<i>CARPINUS</i>SPECIES IN JAPAN

To test two hypotheses for mast fruiting, i.e., (1) pollination efficiency and (2) pre-dispersal predator satiation, we investigated annual fluctuation in seed production and demography from flower to seed of four Carpinus species (family Betulaceae). We monitored flowering, seed production, and seed fall for seven years (1987–1993) for Carpinus laxiflora, C. tschonoskii, C. japonica, and C. cordata, which co-occur in a temperate deciduous forest, Ogawa Forest Reserve, central Japan. We also monitored the seasonal development of pistillate aments in 1995. These Carpinus species are known to show highly synchronized, fluctuating annual seed production. Total seed production (the sum of sound seeds, seeds suffering predation, empty seeds, and immature seeds) was proportional to the quantity of staminate aments and was synchronized among the four species during the observation period. The percentage of mature seeds (the sum of sound seeds and seeds suffering predation) out of the total seed production was positively correlated with annual staminate ament production. This result supports the pollination efficiency hypothesis. The observation that most ovaries in this study did not fall after the pollination season and grew into normal, mature-sized seeds irrespective of fertilization (empty or not) also supports the hypothesis. The percentage of seeds suffering predation by insects significantly decreased in relation to sound seed production, suggesting that predator satiation also operated for these Carpinus species. If the four species have common seed predators (possibly some curculionid species), mutually synchronized fluctuation of seed production among them would be effective for escaping from pre-dispersal predation.

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