Assessing intraspecific phenological synchrony in zoochorous trees from the monsoon forests of northern Australia

Abstract

Intraspecific synchrony in the phenology of tropical forest trees has implications for satiation of browsers and seed predators, pollination, dispersal and interpreting plant responses to environmental cues and stresses. Community phenological studies have been constrained in their consideration of these issues by the lack of concise quantitative measures of intraspecific synchrony. We propose a novel application of Colwell's predictability indices to overcome this deficiency. Its application is demonstrated by evaluating the leaf and reproductive phenologies of 8–16 individuals of each of 20 monsoon forest tree species from northern Australia monthly for 30 mo. The indices yielded substantial additional information over that provided by summaries averaged amongst conspecifics. Marked intraspecific asynchronies in leaf flush or flowering occurred in five evergreen species and two deciduous fig species, and were associated with prolonged individual commitments to these states. Five partly deciduous species exhibited marked intraspecific variation in the seasonal extent of leaf loss. We interpret the observed variation in intraspecific synchrony in terms of contrasting water-use and pollination strategies. The synchronicity indices are concise and robust to small and variable sample sizes, and may thus enhance studies of species-rich assemblages.