Study on stem radial growth of Castanopsis hystrix in Guangxi

Objective  To evaluate the diurnal and seasonal variation characteristics of the stem radial growth of Castanopsis hystrix, explore the influencing factors of the radial growth and their action mechanisms, enrich the observational data on the stem radial growth dynamics in the south subtropical region of China, and improve the predictability of the stem radial growth of C. hystrix under global climate changes.

Method  The stem radial growth variation of C. hystrix in different differentiation classes were studied using dendrometers, and the meteorological environmental factors were measured simultaneously. The relationships between stem radial growth and meteorological environmental factors were analyzed.

Result  The monthly mean diurnal variation cycles of the stem radial growth over a full year were all summer patterns, and the stem radial variation peak, valley and amplitude of dominant tree were significantly greater than those of intermediate tree and suppressed tree. The stem radial culmulative growth of C. hystrix showed an S-shaped curve. The stem radial culmulative growth of the dominant tree (7 138 μm) was the largest, followed by intermediate tree (2 466 μm), and the smallest was that of the suppressed tree (267 μm). The maximum stem radial growth rate and occurrence time were significantly different among different trees. The maximum stem radial growth rates of dominant tree, intermediate tree and suppressed tree were 46.14, 12.21, 1.70 μm·d^–1respectively, appearing on the 146th, 163th and 190th days in a year, respectively. The main growth period of the dominant tree was the 59th to the 331th day in a year, while that of the intermediate tree was the 73th to the 317th day. The suppressed tree did not have main growth period. The results of Pearson correlation coefficient, principle component analysis and partial correlation analysis indicated that the meteorological environmental factors affecting the stem radial growth of dominant tree over the main growing period mainly included daily average relative air humidity (RH), daily precipitation (P) and 20 cm-depth daily average soil moisture content (φ_s20), while the meteorological environmental factors affecting the stem radial growth of intermediate tree mainly included daily relative air humidity , daily precipitation , 20 cm-depth daily soil moisture content , and daily average radiation(SR). The models of daily stem radial increment (SRI) for dominant tree and intermediate tree were expressed as: SRI = 0.955RH + 1.909P −418.406 φ_s20, (R² = 0.525); SRI = −0.002SR + 1.101RH + 1.139 P − 579.751 φ_s20, (R² = 0.342), respectively.

Conclusion  The monthly mean diurnal variation cycles of the stem radial growth of dominant tree, intermediate tree and suppressed tree are the same. The stem radial culmulative growth, the maximum stem radial growth rate and occurrence time, and the responses to the meteorological environmental factors are significantly different among different sample trees.