祁连山北坡青海云杉中龄林结构随海拔的变化

Altitudinal Changes in Structure of Middle-aged Picea crassifolia Forests on the Northern Slope of the Qilian Mountains

在祁连山北坡中段的大野口流域，沿海拔梯度（2500～3300n1）调查了青海云杉中龄林的结构，并分海拔段（每100m）进行统计。结果表明：1）研究区森林密度较大但树木个体较小，密度、胸径、树高和冠幅直径（平均值±SD）分别为1550±628株·hm-2、13．9±6．2cm、8．1±3．7m和3．3±1．7m。随海拔升高，密度降低、平均胸径和冠幅直径增加，平均树高呈“单峰”变化，峰值在海拔2800～2900m。2）研究区森林的径级组成以小树（DBH：5～12．5cm）和中树（DBH：12．5～22．5cm）为主，树高（H）以6～12m的树木为主。随海拔升高，林内幼树（DBH≤5cm）比例基本稳定，小树比例略有下降，中树比例呈“单峰”变化，峰值在2800～2900m，大树（DBH〉22．5cm）比例增加。胃≤6m的树木比例呈“V”字型变化，在海拔2800～2900m最低，日为6～12m和H〉12m的树木比例均呈“单峰”变化，峰值分别在海拔2600～2700rn和海拔2800～2900m。3）林分高径比介于0．45～0．73，胸高断面积介于7．86～33．32m2·hm-2，随海拔升高两者均呈“单峰”变化，峰值在海拔2800～2900m。分析表明，随海拔升高，青海云杉林的结构呈明显变化，并在中间海拔区（海拔2800～2900m）达到最优。因此，分海拔区段建立森林结构与水文过程的定量关系并进行生态水文模型的参数设置十分必要。

The structures of Qinghai spruce （ Picea crassifolia） forests in Dayekou watershed on the northern slope of Qilian Mountains were studied along the altitude from 2 500 -3 300 m, and the values were calculated with sub - segment elevation （ per 100 m a. s. 1. ）. The results are as follows. （ 1 ） The forest density was high while the trees were relatively small in the study area. The forest density, DBH, H and crown diameter of stands were 1 550 ± 628 trees · hm-2 , 13.9 ±6.2 cm, 8 . 1±＋ 3.7 m and 3.3 ± 1.7 m, respectively. With the elevation increasing, the forest density, the average DBH and the crown diameter decreased. The average H showed a ＂unimodal＂ change. （2） The saplings （DBH 5 - 12.5cm） and middle trees （DBH 12.5 -22.5cm） were predominant in the forests, and the height of trees were about 6 - 12 m. With the elevation increasing, the percentage of seedlings （DBH≤5 cm） in forest showed a basic stability showed a ＂unimodal＂ change, which , the percentage of saplings decreased slightly, the percentage of middle trees peaked at 2 800 - 2 900 m a. s. 1 the percentage of big trees （DBH 〉22. 5 cm） increased. The percentage of the stands （H≤6 m） showed a ＂V＂ shaped change, which the minimum value appeared at 2 800 -2 900 m a. s. l.. The percentages of the stands （H： 6 - 12 m） and the stands （H 〉 12 m） showed ＂unimodal＂ changes, peaking at 2 600 -2 700 m and 2 800 -2 900 m a. s. 1. , respectively. （ 3 ） The ratio of height to diameter ranged from 0.45 - 0.73 and the breast - height basal area ranged from 7.86 33.32 m2 · hm-2, with the elevation increasing, both of them showed a ＂unimodal＂ change, which peaked at 2 800- 2 900 m a. s. 1.. Analysis shows that the stand density, moisture and temperature conditions were leading to the differentiation of the growth in tree diameter and height. The middle segment elevation （2 800 -2 900 m a. s.l. ） is the most suitable area for Qinghai spruce forests distribution in this area.