Environmental influence on canopy phenology in the dry tropics

Inter-annual variation in the timing of leaf flush peak was well predicted by models based on air relative humidity or vapour pressure deficit or global radiation (root mean square error = 0.5 month and R2 = 0.8). Inter-annual variation of leaf fall peak was also significantly predicted by models based on atmospheric variables (temperatures or maximum value of vapour pressure deficit) however with weaker relationships (root mean square error = 0.7 month and R2 = 0.7). By contrast, models based on upper soil water availability or rainfall did not predict either leaf flush or leaf fall inter-annual variation. It appears that inter-annual variation of canopy phenology is mainly tuned to atmospheric conditions. Such behaviour maximizes the duration of high photosynthetic activity below a threshold of evaporative demand.