连续放牧对沙质草地植被盖度、土壤性质及其空间分布的影响

在科尔沁典型沙质草地,设置不同放牧强度的4块样区:重牧区、中牧区、低牧区和封育对照区。连续放牧4年后,通过统计学分析及方差均值比、秩相关系数和分维数等方法,分析了植被平均盖度、多样性指数和土壤颗粒组分、土壤养分含量(有机碳和全氮)在各样区的变化及其空间分布。结果表明,(1)沙质草地的植被平均盖度、多样性指数均随放牧强度的增加而降低,植被平均盖度对放牧的反应比多样性指数更为敏感,变化幅度更大;植被在各样区均为聚集分布,但随聚集程度随放牧强度的降低而降低;(2)不论放牧强度大小,植被平均盖度在4个样区均受到土壤养分的制约作用,而土壤颗粒组分对植被的影响随放牧强度的降低逐渐减弱;(3)通过比较植被平均盖度和土壤某些指标在4个样区的分维数值认为,在科尔沁沙质草地,放牧强度应保持在低牧水平,更高的放牧强度将导致植被和土壤特征的空间分布格局产生大的改变,可能导致沙漠化。

Soil Characteristics and Spatial Pattern of Vegetation After Successive Grazing in Horqin Sandy Land,Inner Mongolia

Four plots with different grazing intensities,i, e. high grazing(6 sheep · hm-2,H),moderate graz-ing(4 sheep · hm-2,M),light grazing(2 sheep · hm-2,L) and control(0 sheep · hm-2,C) were settled in korqin sandy pasture. After four years of successive grazing, average coverage and diversity index of vegetation, content of soil granule, organic carbon and total nitrogen were measured respectively in 4 plots by sampling. Through the analysis of classical bio - statistics, ratio of variance to mean(s2/X), rank correlation coefficient and fractal dimension, the main results were drawn as follows.- (1)With increasing of grazing intensity, both average coverage and diversity index of vegetation declined, while the degree of aggregate distribution of vegetation enhanced remarkably. (2)Despite the grazing intensity, average vegetation coverage was always limited by soil nutrients. The influence of soil granule content on average vegetation coverage would be descended accompanying with decreasing of grazing intensities. (3)By comparing the fractal dimension(D) of average vegetation coverage,soil granule and soil nutrient content in 4 plots,it was suggested that grazing at light intensity would give less,even no influence on , while more intense grazing (like H and M) would change the spatial pattern of vegetation and soil characteristics apparently, thus resulting in desertification in Korqin sandy pasture.