The synchronized and intermittent reproduction of forest trees is mediated by the Moran effect, only in association with pollen coupling

Abstract

1 Coupled map models for the dynamics of individuals' energy reserves have shown that large between-year fluctuation in tree seed crops can occur in a constant environment and that reproduction can be synchronized over the whole forest if fruit production is limited by the availability of outcross pollen. 2 In this paper we examine the effects of the environmental fluctuation experienced by different individuals. The reactive changes in annual productivity and the reproductive threshold are accounted for by an additional term in the energy reserve dynamics. 3 If individuals show chaotic seed production, strongly correlated environmental fluctuations (the Moran effect) failed to produce a high positive correlation in seed production across the forest in the absence of pollen limitation. Regardless of the high nonlinearity of resource dynamics, a large correlation was maintained when both pollen limitation and correlated environmental fluctuation occurred. 4 We derived a regression formula for the degree of synchronization when pollen coupling occurred only on a local scale. The correlation coefficient of seed crops between distantly located individuals decreases with the resource depletion coefficient, but it increases with the strength of pollen limitation, the standard deviation of environmental noise, and the correlation of environmental noise between different trees.