Diverse associations and proximate effects of weather on Madagascar reproductive phenology

Abstract

How plants respond to weather seasonality is a fundamental evolutionary question that is particularly relevant to understand as climate change alters weather patterns across the globe. Although temperature and light conditions primarily cue flowering in temperate plants, the weather cues that tropical plants use to regulate their phenological cycles are lesser known. We studied the weather‐related ultimate causes of flowering and fruiting patterns in six woody perennial species found in the evergreen lowland humid forests of southeastern Madagascar by investigating the associations between biweekly weather (i.e. rainfall, temperature and insolation) and species‐level flowering and fruiting phenology. We then developed process‐based models to identify the potential proximate weather cues that these species use to regulate their flowering time. Given the region's strong rainfall seasonality, we hypothesised that the reproductive timing of these species would mainly be constrained by water availability. These species flowered asynchronously, at different times of the year and after a variety of weather conditions, including drought, cool temperatures, warm temperatures and low light. The flowering and fruiting patterns of only two species suggested that water stress constrained their phenology in support of the water limitation and optimal time of germination hypotheses. The flowering patterns of these six species did not align with the insolation limitation hypothesis, providing no evidence to suggest that light stress constrained their phenology. Cool temperature was most likely a proximate flowering cue for only one of these perennial tropical species, which contrasts with the ubiquitous influence that low temperatures have on temperate flowering phenology. Light limitation most likely influenced the flowering time of two species, paralleling the photoperiod flowering cues that some temperate plants use. The timescales at which these potential flowering cues operated were species‐specific, spanning 1–7 months. Synthesis. The diverse associations we identified between weather and flowering patterns suggest that the phenology of these perennial tropical plants evolved in response to different selective pressures and will likely have variable responses to climate change.