Stem radial growth in response to microclimate in an Asian tropical dry karst forest

Abstract

Relationships between environmental factors and stem radius variation at short temporal scales can provide useful information regarding the sensitivity of tree species' productivity to climate change. In this study, we used automatic point dendrometers to continuously record day-to-day stem radius variations of two evergreen (Alphonsea monogyna and Celtis philippensis Blanco) and two deciduous (Lagerstroemia villosa, Garuga floribunda var. gamblei) broadleaves species growing in a tropical karst forest in Xishuangbanna, Yunnan, southwest China. Daily stem radius increments were extracted from dendrometer traces, and were correlated with environmental variables recorded from nearby standard meteorological stations. The results indicated that stem radial growth of the four species initiated from late dry season (middle April), speeded in rainy season (July to August) and slowed down after October. Daily stem radius increments of the four species correlated positively with relative humidity (RH) and rainfall (Rain), while correlated negatively with daily maximum temperatures (Tmax), vapor pressure deficit (VPD) and photosynthetic active radiation (PAR). Rainfall and moisture availability during early growth season (May–June) was important for stem radius growth of the four studied species. Stem radial growth rates of two deciduous species (L. villosa, G. floribunda var. gamblei) declined significantly during short-term drought events occurred during late April and late May to early June, then recovered quickly after one or more rainfall events, which indicated a more sensitive response to climatic factors as compared with evergreen species. These results provide evidences for studying and predicting tree growths and forest productivities in the tropical karst forests under future climate change.