宁夏六盘山香水河小流域华北落叶松人工林乔木层生物量的坡面变化和尺度效应

生物量受坡面环境条件变化影响而有坡面变化与尺度效应。本文在六盘山半湿润区的香水河小流域选择了33 a生华北落叶松人工林的一个斜坡长480 m,水平长398 m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年生长季中期调查不同坡位的样地生物量,分析其坡面变化规律。结果表明:生物量存在明显的坡位差异。坡面生物量t·hm^-2平均值为118.59,其变化范围为96.19 139.18,变幅为42.99,变异系数为0.12;随着离坡顶距离的增加,生物量总体上呈现先升高后降低的变化趋势,在坡面的中上部(水平坡长为87.71 m)达到最大。生物量存在坡面空间尺度效应,即随着相对坡长(X₁)的增加,生物量的顺坡滑动平均值(Y₁)先增大后减小,其回归关系式为:Y₁=23.004X₁³-60.834X₁²+31.786X₁+123.43(R²=0.84),坡面尺度效应表现为每100 m水平坡长生物量变化的数值为6.12 t·hm^-2;各样地生物量与整个坡面平均值的比值(Y₂,小数)随相对坡长有很好的非线性关系,基本上呈先增加后下降、后趋于稳定的变化趋势,其关系式为Y₂=1.722 6X₁³-2.844 5X₁²+1.033 8X₁+1.000 1(R²=0.57),可基于此将特定坡位样地的生物量换算成整个坡面的估算值。造成生物量坡面变化的主要原因是太阳辐射和光照时间随海拔的变化等多种因素造成的。

The Variation of Biomass of Larix principis-rupprechtii Plantation along Slopes and It's Scale Effect in the Xiangshuihe Watershed of Liupan Mountains of China, Ningxia

In this study, one representative slopes covered by the 33-year-old Larix principis-rupprechtii plantation were selected in the small watershed of Xiangshuihe within the semi-humid region of Liupan Mountains, northwest China. Sixteen stand plots were set up continuous along the slope positions of slope top. The biomass was measured in the middle of growing season in 2014. The results showed that the mean biomass on the slope was 118.59 t/hm², with a range of 96.19 139.18 t/hm², and the variation range of 42.99 t/hm² and the coefficient of variation was 0.12. The variation pattern of biomass along slope positions was shown a trend of first increase then decrease, reached the maximum at the middle-upper slope(horizontal slope length is 87.71 m). The biomass existed the slope scale effect. It was found that the moving averaged biomass (Y₁) increases gradually with the increasing relative horizontal length (X₁) of slope section from slope top. The relationship to express this scale effect on the shady slope is Y₁=23.004X₁³-60.834X₁²+31.786X₁+123.43(R²=0.84).The slope average of biomass increased 6.12 t/hm² per 100 m increase in the slope length on the slope. The ratio of plot biomass to the slope average (Y₂) varies nonlinearly along the relative horizontal distance of plots from slope top (X₁), with the relation expressed as Y₂=1.7226X₁³-2.8445X₁²+1.0338X₁+1.0001(R²=0.57), This relation can be used to calculate the slope mean biomass from the biomass measured at certain slope position. The slope variation of biomass mentioned above is mainly caused by the comprehensive effect of solar radiationand duration of sunshine with the change of elevation along the slope.