放牧对大针茅草原建群种与优势种空间分布关系的影响

为探讨放牧下大针茅草原建群种大针茅(Stipa grandis)和优势种羊草(Leymus chinensis)及糙隐子草(Cleistogenes squarrosa)种群空间分布特点及关系,本实验以内蒙古自治区锡林郭勒盟毛登牧场大针茅草原建群种大针茅、优势种羊草和糙隐子草为研究对象,通过野外试验,以地统计学为基础,采用半方差函数、分形维数及克里格插值法,分析了围封(CK)和放牧(G)样地大针茅、羊草及糙隐子草种群小尺度空间分布关系。结果表明:围封样地大针茅、羊草及糙隐子草植株密度分别为10.94株/m~(2 )、12.95株/m~(2 )、13.60株/m~(2 ),放牧样地植株密度分别为16.84株/m~(2 )、48.28株/m~(2 )、28.63株/m~(2 ),放牧显著增加大针茅、羊草及糙隐子草种群密度(P0.05);半方差函数进行模型拟合发现,大针茅、羊草及糙隐子草种群空间分布函数关系均符合高斯模型;通过对空间分布函数关系分析,围封和放牧样地结构比为G (93.3%) CK(60.4%),表明放牧样地大针茅种群空间分布主要受结构性因素影响,而围封大针茅种群则受随机性因素影响较大;围封和放牧样地分形维数值为CK(1.796) G(1.361),表明放牧样地大针茅、羊草和糙隐子草所形成的空间分布格局相比围封样地较为复杂,大针茅空间分布对羊草和糙隐子草空间分布的依赖性较弱;通过立体图分析,在放牧利用过程中,羊草处于中低密度时,及糙隐子草处于高密度时,均与大针茅种群间的关系从围封中的竞争关系变为放牧过程中的亲和关系,可见放牧导致种间关系改变。

Effects of grazing on spatial distribution relationships among constructive and dominant species in the Stipa grandis steppe

A study was conducted to determine the effects of grazing on spatial distribution characteristics and relationships of constructive species (Stipa grandis) and dominant species (Leymus chinensis and Cleistogenes squarrosa) in the S. grandis typical steppe of Xilinguole, Inner Mongolia. Based on geostatistics, the semi-variance function, fractal dimensions, and kriging interpolation methods were used to analyze the spatial distribution of S. grandis, L. chinensis, and C. squarrosa on the small scale in all treatments. The results showed that the population density of S. grandis, L. chinensis, and C. squarrosa were higher in the grazing treatment (G) than in the enclosure (CK) (P < 0.05), which were 10.94, 12.95, and 13.60 plant/m² in the CK, and 16.84, 48.28, and 28.63 plant/m² in the grazing treatment, respectively. The model was fitted by the semi-variance function, the spatial distribution functions of S. grandis, L. chinensis, and C. squarrosa populations were all consistent with the Gaussian model in the CK and grazing treatment. According to the relationship analysis of the spatial distribution, the structure ratio was 93.3% in the grazing treatment and 60.4% in the CK, which indicates that the population distribution of S. grandis was affected by structural factors in the grazing treatment and was influenced by random factors in the CK. The fractal dimension values of the CK and grazing treatment were 1.796 and 1.361 respectively. This means the spatial distribution patterns of S. grandis, L. chinensis and C. squarrosa in the grazing treatment were more complex than that in the CK, and the spatial distribution of S. grandis is less dependent on L. chinensis and C. squarrosa. The three-dimensional map analysis showed that the relationship of mid-low density of L. chinensis and high density of C. squarrosa changed from a competitive relationship in the CK to an affinity in the grazing treatment with S. grandis. Therefore, grazing may change the inter-species relationship.