黄土丘陵区油松水土保持林生长过程与直径结构

Growth process and diameter structure of Pinus tabulaeformis forest for soil and water conservation in Loess Plateau hilly regions

应用标准木树干解析法,研究了黄土丘陵沟壑区阴坡和阳坡两种21年生（密度为2222株.hm-2）油松林分的生物量、林木生长过程和直径结构.结果表明：两种林分树高、林木直径和材积生长过程明显不同,阴坡林分的生物量、生长状况和直径结构优于阳坡林分.两种林分树高速生期出现在9~13年生之间,13年生以后,阴坡林分的生长量明显高于阳坡林分（21年生时,前者的连年生长量约在0.26m·a^-1,后者在0.1m.a-1左右）.两种林分的胸径生长量在13年生以后明显降低,但阴坡林分的降幅明显小于阳坡林分;17年生以后,前者的连年生长量明显大于后者（21年时,前者约在0.46m·a^-1,后者只有0.27m·a^-1左右）.两种林分单株材积生长量在13年生之前差异较小,13年生之后,阴坡林分的连年生长量明显大于阳坡林分（21年生时,前者为0.0023m3·a^-1,后者只有0.0015m3·a^-1）.两种林分直径分布都呈现顶峰左偏（林分密度偏大）的现象,但阴坡林分的偏度系数（SK为0.75）小于阳坡林分（SK为1.03）、而峰度系数（K为1.05）大于阳坡林分（K为0.94）,说明阳坡林分密度偏大的程度大于阴坡林分.

Through stem analysis of sample trees, the biomass, growth process, and diameter structure of two 21 years old Pinus tabulaeformis forests growing on the shady and sunny slopes in Loess Plateau hilly and gully regions were investigated. The results showed that there were distinct differences between these two forests in their tree height, diameter at breast height （DBH）, and timber volume. The forest biomass, growth status, and diameter structure on shady slope were superior to those on sunny slope. The fast-growing period of tree height all appeared in the period of 9-13 years, and after 13 years, the annual increment of tree height was larger in shady slope forest than in sunny slope forest, with the increment in the 21^st year being 0. 26 and 0. 1, respectively. The DBH growth of the two forests was declined greatly after 13 years, but the decrement was obviously less in shady slope forest than in sunny slope forest. After 17 years, the annual increment of DBH growth was larger in shady slope forest than in sunny slope forest, with the values being 0. 46 cm · a^-1 and O. 27 cm · a^-1 , respectively in the 21^st year. Before 13 years, there was little difference in the increment of timber production between the two forests, but the increment after 13 years was larger in shady slope forest than in sunny slope forest, with the values of 0. 0023 m^3 and 0. 0015 m^3, respectively in the 21^st year. The summit of DBH distributioncurve was all partial to left, but the skewness of shady slope forest （SK = 0. 75） was lower than that of sunny slope forest （ SK = 1.03 ）,and the kurtosis of shady slope forest （K = 1.05 ） was higher than that of sunny slope forest （K = 0. 94）, indicating that sunny slope forest had a larger stand density than shady slope forest.