Greater diurnal temperature difference, an overlooked but important climatic driver of rubber yield

Abstract

The increase of rubber demand has led to rapid expansion of rubber plantations from optimal environments in the humid tropics of Southeast Asia into suboptimal environments in montane mainland Southeast Asia. Nevertheless, rubber yields can be surprisingly high in sub-optimal environments. This paper investigates climatic factors which contribute to the higher than expected rubber yields in a suboptimal environment in Jinghong, Yunnan, Southwest China. Two mathematical analysis methods were used to relate climate to rubber yield and dry matter content: partial least square regression and classification and regression tree models were used. Greater diurnal temperature difference was found to increase dry rubber yield, and has been previously overlooked as an explanatory factor. Average temperatures below 25.7°C, and more sunshine hours in the day before tapping, were also found to significantly improve dry rubber yield, although more sunshine hours during the month prior to tapping were found to reduce rubber yield. Lower relative humidity was found to increase dry rubber content of latex and increase yield. Greater diurnal temperature difference and more sunshine hours in a day before tapping facilitate photosynthesis and rubber formation. Lower relative humidity reduces the water content in the latex, thus increasing dry rubber content of the latex.In summary, this study finds that lower average temperature (within certain thresholds), greater diurnal temperature difference in both a day and a month before tapping, more sunshine hours in a day before tapping and lower sunshine hours in a month before tapping are the most important factors which promote dry rubber yield, and lower relative humidity in the day prior to tapping is the most important factor in determining dry rubber content of latex. Diurnal temperature difference has not been previously investigated as a driver of rubber yield. The case study site has a greater diurnal temperature difference than many other main rubber producing areas, which may contribute to explaining why rubber yields in Jinghong are higher than might be expected in a sub-optimal environment.