Pinus kesiya var. langbianensis (Szemao pine), a regional subspecies of Pinus kesiya, is distributed naturally in the humid and sub-humid areas of Yunnan Province, southwestern China. Due to its rapid growth rate, vigorous germination, and high productivity of quality wood and resins, Szemao pine is one of the main timber plantation species in the tropical and subtropical areas of Yunnan. Despite of its economic and ecological importance, little is known about its intra-annual growth dynamics and responses to climatic factors. 

Researchers from Xishuangbanna Tropical Botanical Garden (XTBG) studied seasonal dynamics and climatic determinants of stem radius changes of Pinus kesiya var. langbianensis in the Ailao Mountains, SW China. 

Based on five-year high-resolution dendrometer data (2012–2015 and 2017),  they found that the stem radial growth of Szemao pine mainly occurred during early March to October, with highest growth rates during May to June. 

The results demonstrated that stem increment of Szemao pine primarily related to precipitation and humidity, and confirmed that sufficient water supply, especially during the early growing season, is crucial for maintaining tree water status, as well as xylem cell production and cell enlargement. 

"Our study reveals that moisture availability plays a major role for tree growth of P. kesiya var langbianensis in the Ailao Mountains, southwest China", said Prof. FAN Zexin , first author of the study. 

"Our results are fundamental to better understand the growth performance and carbon sequestration capacity of this economically important species under future climate change", added Dr. FAN. 

The study entitled "Intra-Annual Radial Growth of Pinus kesiya var. langbianensis is Mainly Controlled by Moisture Availability in the Ailao Mountains, Southwestern China" has been published in Forests.  

Monitoring radius growth of Szemao pine in the Ailao Mountains (Image by FAN Zexin)