Dynamics of stem radial growth of Picea meyeri during the growing season at the treeline of Luya Mountain, China
芦芽山林线白杄生长季径向生长动态

Aims As an important ecological boundary, treeline ecotone is sensitive and vulnerable to external environmental changes, and tree growth at treeline is strongly constrained by the harsh environment. Our objectives were to analyze the characteristics of the stem radial growth of Picea meyeri during the growing season at the treeline of Luya Mountain, Shanxi, China and investigate the main environmental factors affecting radial growth. Methods From May to September 2009, an automatic point dendrometer was used to continuously monitor stem radial growth of P. meyeri. Environmental factors were measured by instruments synchronously. Important findings The daily variation pattern, i.e., reversible stem shrinking (day) and swelling (night), was controlled by the daily course of tree transpiration. The cumulative radial variation of P. meyeri during the growing season could be divided into three distinct periods: 1) stem rehydration, 2) stem rapid growth, and 3) stem dehydration contraction. During different growth periods, the major environmental factors controlling the stem radial growth were different. Soil water content, soil temperature, soil temperature and water content were the main environmental factors corresponding to the above mentioned three growth periods, respectively. Soil temperature determined the initiation of stem radial growth of P. meyeri. Photoperiod could act as the constricting factor for the growth rate of P. meyeri at the treeline. The maximum growth rate of P. meyeri occurred in late June, around the time of maximum day length (summer solstice), which may be a survival strategy to avoid frost damage during cold winter conditions at treeline.