半干旱黄土丘陵区人工林叶面积特征

 该文通过对黄土丘陵区4个密度的刺槐（Robinia pseudoacacia）人工林、3个密度的侧柏（Platycladus orientalis）人工林生长季叶面积变化的研究，揭示了不同密度林分叶面积生长与林分密度的关系；通过对灌木生长季叶面积变化的研究，建立了灌木柠条(Caragana korshinskii)、沙棘（Hippophae rhamnoides）和紫穗槐（Amorpha fruticosa）叶面积与叶鲜重、枝条基径的经验公式，为半干旱区灌木生长调查提供了一种方便、快捷的方法。结果表明：1）刺槐和侧柏各密度林分的单株林木叶面积和叶面积指数均在9月达到最大值，其中刺槐林叶面积指数峰值可达到10.5，侧柏峰值可达到3.2；灌木柠条、沙棘和紫穗槐叶面积和叶面积指数都在8月份达到各自的最大值，柠条、沙棘和紫穗槐的叶面积指数峰值分别为1.1 95、1.123和1.882；2）刺槐叶面积与叶鲜重具有极显著相关的幂函数关系，侧柏、柠条、沙棘、紫穗槐叶面积与叶鲜重具有极显著相关的线性函数关系，其中柠条枝条基径与叶面积还具有极显著相关的幂函数关系，沙棘、紫穗槐枝条基径与叶面积还具有极显著相关的线性函数关系；3）黄土丘陵区，由于林地土壤水分条件的限制，承载力有限。人工林进入生长盛期后， 不同密度刺槐和侧柏林分叶面积指数趋于一致，与最初的造林密度和现存密度没有关系。在不同密度的刺槐和侧柏林分间，单株叶面积与其林分密度成反比。在对上述结果分析的基础上得出：黄土丘陵区，由于林地土壤水分条件的限制，承载力有限。该文所研究的刺槐和侧柏各林分均已达到了当地土地承载力的上限，基于提高单株林木质量的考虑，建议刺槐林郁闭后的密度不超过833株&;#8226;hm^-2，侧柏则不超过1 111株&;#8226;hm^－2。如以全林分生物量为目标，林分密度也可适当减小。

LEAF AREA CHARACTERISTICS OF PLANTATION STANDS IN SEMI-ARID LOESS HILL-GULLY REGION OF CHINA

Aims Our objectives are to explore the relationship of leaf area and stand density and determine a convenient way to measure stand leaf area. Methods Using direct and indirect methods during the growing season (from May to October) of 2004, we measured seasonal variation of the leaf area of tree and shrub species: Robinia pseudoacacia stands with four densities (3 333,1 666, 1 111 and 833 plants per hm²), Platycladus orientalis stands with three densities (3 333, 1 666 and 1 111 plants per hm²), Caragana korshinskii, Hippophae rhamnoidesand Amorpha fruticosa . We developed formulas for leaf area by correlating leaf fresh weight, diameter of base branch and leaf area. Important findings Maximum leaf area and leaf area index (LAI) occurred in September for trees and August for shrubs. There is a significant power relation between leaf area and leaf fresh weight for Robinia pseudoacacia, significant linear relation between leaf area and leaf fresh weight for P. orientalis, C. korshinskii, H. rhamnoides and A. fruticosa, significant power relation between leaf area and diameter of base branch for C. korshinskii, and significant linear relation between leaf area and diameter of base branch for H. rhamnoides and A. fruticosa. After the planted vegetation in Loess hilly-gully region enters into a rapid growth stage, the LAI of R. pseudoacacia stands with different densities converge and LAI is not affected by initial or current density. This was also observed for P. orientalis stands. However, the leaf area of individual trees is negatively linearly related with stand density. Robinia pseudoacacia stands and P. orientalis stands have reached their maximum bearing capacities in the Loess hilly-gully region as a result of limited soil water. Therefore, to improve the quality of individual trees, we recommend stand densities not exceed 833 and 1 111 plants per hm² for R. pseudoacaciaand P. orientalis, respectively. To improve the quality of entire stands, we suggest reducing the density a little.