六盘山南坡华北落叶松人工林冠层LAI的坡面尺度效应

叶面积指数(LAI)是评价森林的生长、结构及众多服务功能的重要参数,受坡面上环境条件变化影响而有坡面变化与尺度效应,对此需要深入理解和精细刻画。在六盘山半湿润区香水河小流域选择了33年生华北落叶松人工林的一个斜坡长480.6m、水平长398.2m的东南坡向的典型坡面,在整个坡面上建立了宽30 m的调查样带,均匀分为空间连续的16个样地,在2014年生长季中期测定了林冠层LAI,并分析其坡面变化规律。结果表明:林冠层LAI存在明显的坡面差异,其坡面平均值为3.11,变化在2.66—3.49,变幅为0.83,变异系数为0.09;LAI总体上随着从坡顶向下的坡长增加呈波动性增大趋势,在坡面中部(水平坡长188.45 m时)达到最大,之后稍微减小。森林冠层LAI存在着坡面空间尺度效应,即冠层LAI的顺坡滑动平均值(Y_1)随水平坡长(X,m)增加而逐渐增大,平均每100 m升高0.12,其回归关系式为:Y_1=-2×10~(-8)X~3+8×10~(-6)X~2+5×10~(-4)X+2.6523,(R~2=0.99);各样地LAI与整个坡面平均值的比值(Y_2,小数)随水平坡长(X_1,m)增加呈现为波动性的非线性变化,其回归关系式为:Y_2=-9×10~(-9)X_1~3+2×10~(-6)X_1~2+1×10~(-3)X1+0.829,(R~2=0.78),可基于此式将特定坡位样地的实测LAI推算整个坡面的估计值。造成研究坡面上LAI坡位变化的主要原因是不同坡位(海拔)样地的气温与土壤含水量的差异。

The slope scale effect of canopy LAI of Larix principis-rupprechtii plantation at the south side of Liupan Mountains

The leaf area index (LAI) is an important parameter for the evaluation of forest growth, stand structure, and numerous ecological services. It is necessary to understand and quantify the LAI variation with site conditions and its spatial scale effect on slopes. In this study, one representative southeast-facing slope covered by 33-years-old Larix principis-rupprechtii plantation was selected in the small watershed of Xiangshuihe within the semi-humid region of Liupan Mountains, northwest China. This slope has slope length of 480.6 m and a corresponding horizontal length of 398.2 m. A survey transect with a width of 30 m was set up on the whole slope, and sixteen stand plots were set up continuously within this survey transect, this means that the plots covered all different slope positions from slope top to slope foot. The canopy LAI in the middle of growing season of 2014 was measured and the spatial variation of LAI on the slope was analyzed. The results showed that there is a remarkable difference in canopy LAI among the different slope positions. The mean LAI on the whole slope was 3.11, with a variation range of 2.66-3.49, a difference of 0.83, and a coefficient of variation of 0.09. The variation of LAI along lowering slope positions showed a trend of firstly increase, reaching its maximum at the middle slope (at the horizontal slope length of 188.45 m), and thereafter a slight decrease. The canopy LAI showed a slope scale effect, i.e., the moving average of LAI (Y₁) increases gradually with the increasing horizontal slope length (X, m) from slope top, with an mean rate of 0.12 per 100 m. The corresponding relation to express this scale effect on the studied slope is Y₁=-2×10^-8X³+8×10^-6X²+5×10^-4X+2.6523(R²=0.99). The ratio of plot LAI to the whole slope average (Y₂) varies nonlinearly along the horizontal length of plots from slope top (X₁, m), with the relation of Y₂=-9×10^-8X³₁+2×10^-6X²₁+1×10^-3X₁+0.829(R²=0.78). This relation can be used to estimate the slope mean LAI from the LAI measured at certain slope position. The slope variation of LAI mentioned above is mainly caused by the difference of air temperature and soil moisture among the plots with different slope position and elevation.