Reproductive phenology in a lowland dipterocarp forest and its consequences for seedling recruitment
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We carried out weekly surveys of flower and seed rain and annual censuses of seedling recruitment and survivorship using a network of 336 sampling locations in a mapped 50 ha plot of lowland dipterocarp forest in Peninsular Malaysia. The study ran between August 2001 and September 2006 and included four general flowering (GF) events of varying magnitudes. With the analysis of time series auto cross correlation, we found that 50.8% and 74.6% of the 126 study species exhibited supra annual flowering pattern and flowering synchrony with dipterocarp species in genus Shorea section mutica, respectively. Moreover, many of the supra annual species were synchronized in their flowering with species of the genus Shorea section mutica, which are the classical signature GF species. Flowering periodicity was significantly related to dispersal modes, the types of rewards offered by fruits to dispersers, and growth forms. However, fruiting periodicity was only related to reward types. The relationship of phenological patterns and functional traits supports the hypothesis of predator satiation, but also the hypothesis that species in the upper and lower canopy layers have different microclimatic triggers for flower induction. Among Shorea species there was no evidence of staggered flowering, but there was significant fruiting synchrony. Published methods using the flowering pattern of Shorea species in the section mutica to estimate floral induction time did not yield consistent dates for induction (5 or 7 weeks before the appearance of the first flower in Shorea macroptera, the first Shorea species to flower in a given GF season), but these methods assume that all species have the same trigger. Mortality was more strongly and negatively density dependent during the transition from seed-to-established seedling that during the transition from established seedling to yearling. However, we detected no difference in density dependence among various phenological groups. We also found no compensation in the strength of density dependence between the two sequential transitions. The loss in species diversity over time, as measured by Fisher’s ±, was greater in the seed-to-established seedling transition than in the established seedling-to-yearling transition. The one cohort of seeds produced in a non GF year lost more species diversity and evenness than the GF cohorts, and it remained in the lowest in diversity and evenness after the second year.