Reproductive Phenology of a Seasonally-Dry Dipterocarp Forest in Southern Thailand

Abstract:

Our understanding of the proximate and ultimate factors that shape reproductive phenology in dipterocarp forests comes exclusively from studies of everwet, general flowering forests. This study, for the first time, examines the reproductive phenology of a dipterocarp-dominated forest in a seasonally-dry region in Southeast Asia. We monitored flowering and fruiting monthly for 1344 trees (>300 spp.) in a seasonally-dry forest in Khao Chong, Thailand from 2001-2009, and assessed frequency, duration, seasonality, and synchrony of reproduction. Reproductive phenology of the Khao Chong forest was more similar to tropical forests in other seasonally-dry parts of the tropics than it was to dipterocarp forests in everwet regions of Southeast Asia, despite being more phylogenetically similar to the latter. The Khao Chong forest exhibited annual reproduction, with peak flowering occurring at the end of the dry season, and peak fruiting occurring early in the wet season. The majority of species and individuals also reproduced annually, including some species that are known to be “general flowering” in everwet climates. Short periods of drought appeared to be the cue that initiated flowering in early flowering species, while species flowering later in the dry season may have responded to either drought or low temperature. Over the eight years of our study, we observed a decline in the proportion of individuals reproducing each season. This decline appeared to be associated with a shorter dry season due to a later onset of continuous drought, suggesting that changing climate in the region may have significant impacts on plant reproduction and recruitment.