Response of daily stem radial growth of Platycladus orientalis to environmental factors in a semi-arid area of North China

The daily stem radial growth of P. orientalis during the main growing period in semi-arid areas of North China is mainly limited by moisture availability. Finer resolution studies of tree stem radial growth on short temporal scales can be useful for exploring the main environmental variables that trigger radial growth. The objective of this study was to determine the most important environmental factors that impact the intra-annual radial growth of Platycladus orientalis (Linn.) Franco in a semi-arid area of North China. The stem radial growth of P. orientalis was studied daily during the growing season (May to October 2013) using high-resolution automatic point dendrometers. Our results showed that the daily stem radial increment (SRI) of P. orientalis during the main growing period was primarily impacted by relative air humidity, precipitation, vapor pressure deficit and daily maximum air temperature. Those environmental factors mainly influenced the moisture availability to the trees, thereby affecting their daily stem radial growth. The rapid release of stem radial growth was observed when heavy precipitation events occurred after a drought period. The maximum stem growth rate of P. orientalis was observed in early August and was regulated by soil water content in the summer; this was regarded as an adaptation to the local climate conditions. Our results have further implications for sensitivity analyses of tree growth to climate changes in semi-arid areas.