六盘山叠叠沟华北落叶松人工林叶面积指数的时空变化特征

摘要

在具有半干旱气候的宁夏固原六盘山区叠叠沟小流域,于2009年整个生长季内(5-10月)监测了典型阴坡坡面上的华北落叶松人工林不同坡位的7个样地的林冠层、林下灌木层和草本层的叶面积指数(LAI)的数量变化和季节动态.结果表明:(1)华北落叶松不同样地的林冠层LAI随坡位升高的变化趋势基本上是逐渐减小,从坡下部的1.52～2.95减少到坡顶部的0.15～0.27;林下灌木层LAI是先增加后减小,从坡下部的0.05～0.06增加到坡中上部的0.73～1.01后再减小到坡顶的0.19～0.30;草本层的LAI,随坡位上升不断增加,从0.18～0.36增加到0.19～0.75.(2)林冠层和草本层的LAI季节变化趋势都呈先上升、达到最大值后再下降的单峰曲线.在生长季初期(5-6月),林冠层LAI,的增长比草本的快,而在生长季中期(7-8月)却比草本层的慢,这是南温度和土壤水分条件及根系层深度差别共同决定的.(3)随着林冠郁闭度增加,林冠层的LAI几乎线性增大;灌木层LAI随林冠郁闭度增加先增大后逐渐减小,在0.5左右达到最大值,在0.9以后几乎为零;草本层LAI随林冠郁闭度增加缓慢线性减小,从0.74降到0.35;灌草层(灌木加草本)LAI在林冠郁闭度0.4～0.5时最高并超过林冠层的LAI,在0.6以后急剧减少并开始低于林冠层LMI;总LAI随林冠郁闭度增加先急剧增加,在郁闭度0.6～0.8之间保持最大且相对稳定,之后轻微下降.%From the observation of 1eaf area index ( LAI ) of 7 Larix principis-rupprechtii plantation plots at 3 layers ( tree canopy, shrubs and herbage) on the north slope in the vegetation period ( May-Oct. ) of 2009, the change of LAI along slope position, the vertical composition of LAI and its seasonal variation were studied at the semi-arid watershed of Diediegou, which locates at Liupan Mountains of Northwest China. The results showed: 1 ) The LAI of tree canopy decreased basically with rising slope position, from 1.52-2.95 at slope foot to 0. 15-0.27 at slope top; the LAI of shrubs layer increased at first and then decreased with slope position, from 0. 05-0.06 at slope foot to 0.73-1.01 at up-middle slope and 0. 19-0.30 at slope top; while the LAI of herbage layer increased slowly, from 0. 18-0.36 at slope foot to 0.19-0.75 at slope top. 2) The seasonal variation of LAI of tree canopy and herbage layers showed the same tendency, i.e. a one-peak curve of increase and then decrease with time. However, the LAI of tree canopy layer grew faster than that of herbage layer in the early vegetation period ( May-Jun. ) and slower than that of the herbage layer in the middle vegetation period (Jul. - Aug. ), due to the integrated result of varying temperature and soil moisture as well as the root depth difference between trees and grasses. 3) With increasing tree canopy density, the LAI of each vegetation layer responded differently. The tree canopy LAI nearly linearly increased with canopy density; the LAI of shrubs layer increased at first and then decreased, with a maximum when the canopy density was about 0.5 and decreased to nearly zero when canopy density above 0.9; the LAI of herbage layer decreased gradually, from 0.74 to 0.35; the LAI of undergrowth ( shrubs plus herbage) reached its maximum value and higher than tree canopy LAI when canopy density varied between 0.4-0.5, but decreased rapidly and lower than canopy LAI when canopy density above 0.6; the total LAI of all the 3 layers increased at first with rising canopy density, reaching its maximum and keeping relatively stable when canopy density was 0.6-0.8,and then slightly decreased with rising canopy density.