The phenology of temperate plants is vulnerable to climate change. Yet, the phenological responses of tropical plants to climate change are still unclear. In this study, temporal trends (1973–1999) of four phenological events (budburst, growing season, flowering and flowering duration) were studied among 21 plant species in Xishuangbanna Tropical Botanical Garden (south-western China). Fourteen species (67%) showed significant phenological trends during the study period. Seven species (33%) presented delaying trends in budburst (average 1.4 d y−1) and such trend was more likely to be presented in those that started budburst earlier in the dry season. Four species (19%) showed trends of extension in growing season (average of 3.5 d y−1). These vegetative events appeared to be mainly influenced by increasing temperature. Rainfall showed little effects directly, however, the effects of temperature seemed to largely depend on the moisture condition. Flowering duration of five species (24%) was shortened by average 2.1 d y−1 which was most likely to be the result of the decline in sunshine duration during the rainy season. Our results suggest that the phenology of tropical plants has changed significantly in response to the regional climate change but these reactions are somewhat different from those of temperate plants.

Trees growing in a seasonally tropical dry forest, with its characteristic 5–7-mo rainless interval, possess a variety of physiological adaptations to drought, the most common being leaf abscission. At the Estacion Biologia de Chamela in western Mexico, we experimentally examined the relationship between one-time experimental irrigation ranging as 0 (control) to 200 mm, and (1) the degree of bud burst (and, for a single species, flowering), and (2) the formation of a false ring. Additionally, we used long-term records at a nearby meteorological station to determine the probability of a rain event exceeding a particular intensity (mm). For our seven species (particularly the two most common species: Cordia alliodora and Piptadenia constricta), we found that the degree of budburst and leaf extension was a function of irrigation intensity. In no case, however, did we find false rings, or indeed any indication of cambial activity initiated by the irrigation event. Further, there was no effect of intensity on subsequent relative growth rate in the following wet season. While sufficient rainfall (200 mm) to cause full leaf deployment is rare, nonetheless we estimate that a canopy tree in the study area would experience an event of this magnitude at least a few times per century. In any case, it will have no effect on the reliability of annual rings in this biome, nor any effect on diameter growth in (at least) the following year.

Several physiological processes controlling tree phenology remain poorly understood and in particular bud dormancy. Many studies have emphasised the action of chilling temperatures in breaking dormancy. However, the effect of the preceding summer temperatures has rarely been investigated although there is some evidence that they may be involved in the settlement and intensity of dormancy as well as cold acclimation. In this paper, thermal time to budburst in relation to the duration of chilling outdoors, preceding summer temperatures and forcing temperatures was studied by outdoors experiments in seedlings of Platanus acerifolia, Vitis vinifera, Quercus pubescens and Castanea sativa. Results showed that temperatures of the preceding summer had no significant effect on the timing of budburst, P. acerifolia and Q. pubescens showed a very weak response to the duration of chilling, and the phenological characteristics of each species were found to be adapted to the climate conditions of its own geographical area. The phenological model used in this study explained 82–100% of the variance of the data without taking into account summer temperatures. Thus, although summer temperatures may be well involved in the intensity of dormancy and cold hardiness, they do not significantly affect budburst and therefore may not need to be considered in phenological models for predicting budburst.