Ecologists have recently interpreted patterns of phylogenetic distance among coexisting species as indicative of processes aff ecting community assembly during forest succession. We investigated plant community phylogenetic structure along a successional gradient in New Guinean lowland rain forest. We surveyed all trees with diameter at breast height Ն 5 cm in nineteen 0.25 ha plots representing younger secondary, older secondary, and primary forest. We estimated plant community phylogeny from

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... bcL gene sequences to quantify change in phylogenetic structure during succession. Mean phylogenetic distance among co-occurring trees increased with total basal area per plot, a proxy for forest age. Signifi cant phylogenetic clustering was detected in secondary forest whereas primary forest was signifi cantly over-dispersed relative to null expectations. We examined the sensitivity of these patterns to various methods of branch length estimation and phylogenetic uncertainty. Power to detect community phylogenetic patterns when equal branch lengths were assumed was weak in comparison to direct molecular and time-calibrated measures of divergence. Inferred change during forest succession was also robust to phylogenetic uncertainty so long as temporal information was incorporated in estimates of divergence. Th e observed patterns are consistent with processes of environmental fi ltering during tropical forest succession giving way to other processes in primary forests including density-dependence.