Flowering Asynchrony and Temporal Mate Restriction in Tropical Peat Swamp Forest Trees

ABSTRACT Many tropical rainforest tree species exhibit high flowering asynchrony, with individuals differing in how often, when, and for how long they flower. Over short timescales, asynchrony is known to restrict both the quantity and diversity of outcrossing partners, affecting reproductive success and the genetic diversity of offspring. However, longer‐term effects of flowering asynchrony on mating opportunities remain poorly understood, particularly for long‐lived, iteroparous tropical trees. For instance, it is not known whether an individual tree's flowering phenology is consistent over time, such that the same conspecific individuals repeatedly flower together; this could result in assortative mating, or exclude some tree pairs from reproducing together. We analyzed 18 years of flowering records from 50 tree species in a Bornean tropical peat swamp forest to quantify within‐species (intraspecific) flowering asynchrony. For a subset of 24 bisexually‐flowering species with larger sample size (from which dioecious species were excluded because the sex of individuals was unknown), we evaluated whether the same conspecific individuals flower together across years, then extrapolated predictions of lifetime mate restriction from the observed accumulation of co‐flowering partners. We found high intraspecific flowering asynchrony, and most species showed a significant tendency for the same individuals to co‐flower across years. However, patterns of intraspecific variation in phenology rarely resulted in predictions of lifetime mate restriction between conspecific pairs. Exceptions were several species that flowered infrequently, i.e., with multi‐year intervals between species‐level flowering events, in which phenological mismatch did exclude many potential pairings.