Understanding how intra-annual stem growth responds to atmospheric and soil conditions is essential for assessing the effects of climate extremes on forest productivity. However, it is unclear to what extent species growth patterns and climate responses are aligned within a community.
In a study published in New Phytologist, researchers from Xishuangbanna Tropical Botanical Garden (XTBG) and their collaborators from Wageningen University and Research studied intra-annual stem growth and its climatic drivers for 14 common tree species in a montane, subtropical forest with a monsoon climate. They aimed to identify the role of atmospheric conditions and soil moisture in driving intra-annual stem growth variation – both timing and magnitude – of a tree community in a montane subtropical forest.
The researchers monitored stem growth at 10-min resolution of 27 trees belonging to 14 species over five years in a subtropical evergreen broadleaf forest at the Ailao Mountains. They quantified diel and seasonal stem growth patterns, verified to what extent observed growth patterns are consistent across study species and tested underlying climatic drivers.
They found that seasonal growth patterns were mainly driven by temperature and VPD in this tree community, and that stem growth during the day mainly occurred before dawn associated with low vapour pressure deficit (VPD). The species largely differed in absolute stem growth rates, but diel and seasonal growth patterns were strikingly similar. Trees mainly grew before dawn when VPD was low.Over a year, trees mainly grew during May–August when climate conditions were warm and moist.
Growth–climate analyses at various temporal scales confirmed that atmospheric conditions (VPD and temperature) strongly determined when stem growth occurred during the day and the year. However, the rate of stem growth was mainly determined by temperature, and much less by moisture conditions. Temperature not only favoured stem growth at the seasonal scale but also increased diel growth rate when moisture availability permitted growth.
"We present one of the first community-level studies of intra-annual stem growth in a species-rich forest," said FAN Zexin of XTBG.
The study was supported by the National Natural Science Foundation of China and the China Scholarship Council.

Contact
FAN Zexin Ph.D Principal Investigator
Key Laboratory of Tropical Forest Ecology, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Mengla, Yunnan 666303, China
E-mail: fanzexin@xtbg.org.cn 

First published: 22 September 2023

Ailaoshan subtropical forest. (Image by XTBG)