干旱地区山地荒漠草原阴坡植物群落空间异质性

Spatial heterogeneity of the north slope's plant communities in the mountain desert grassland of the arid region

在样线调查基础上 ,以 Shannon- Wiener指数 ,群落盖度 ,DCA排序轴为区域化随机变量 ,应用半方差、分形分析等方法 ,对干旱地区山坡植物群落空间异质性进行了研究。结果表明 ,在整个山坡尺度上植被格局的空间异质性不大 ,小尺度上植被格局的空间异质性较大 ,尺度依赖性较强 ,不同群落类型的空间格局不同 ,随尺度变化的规律也不一样。严重放牧干扰强烈影响干旱山地植物群落的空间格局 ,生境中的牧道格局 ,斑块格局使山坡植物群落多样性空间异质性更加复杂 ,牧道效应是导致群落空间格局周期性振荡的重要因子。去势对应分析 (DCA)排序第一轴特征值体现了综合生态因子对群落格局作用的结果 ,DCA第二轴半方差变化包含了大量信息 ,其变化具有周期性。群落多样性空间格局强烈影响着干旱山地生态系统的各种生态学过程 。

The spatial heterogeneity of ecology lies in its ubiquity as a feature of ecosystem. It has drawn more attentions in the research of ecosystem processes in recent years. The arid mountainous regions of northwest parts of China are considered as the sensitive ecological zones to affect environment of China. However, the ecosystem functions of those areas have been adversely affected by some reasonless activities of mankind, such as overgrazing, mining and digging up the roots of herbs etc. Therefore, a better understanding of the hierarchical structure of the ecosystem, particularly in its heterogeneity is necessary to learn the arid mountainous ecosystem functions as a whole. The study was conducted at the Xiangshan mountain, Zhongwei County, Ningxia Hui Autonomous Region (37°15′ N, 105°31′ E). It has a typical continental climate, with a stronger sunshine and a shorter growing period of native vegetations. The altitude ranges from 1300 to 2100m. The types of vegetations are mainly desert-rangeland and semi-desert-rangeland i.e. Caragana roborovskyi, Lagochilus ilicifolius, Convolvulus tragacanthoides, Stipa bungean, Heterapappus altaicus, Artemisia ordossica, Artemisia frigida. Where a special goat-Zhongwei goat is found who produces a kind of valuable fur. The three 100 m long sampling lines were selected along the north slope of the mountain from the bottom to the top. The total of 100 plots (1m×1m) were measured on each sampling line. The number of plant species, species density and coverage of every plot were investigated. Base on the principle of geostatistics, three independent variables including Shannon-Wiener index(H), coverage, axes of DCA (Detrended Corresporndence Analysis), were employed to examine characteristic of spatial heterogeneity of the arid mountain by using the semi-variance function and the fractal dimension methods. The result showed that in the whole large scales of the north slope the spatial heterogeneity of vegetation pattern was less obvious than what was shown in the small scales. Thus a scale-dependent was reflected in the small scales . The spatial pattern of herbage community and brushwood community was different. Moreover, their variation trends were also different depend on the scales size. The spatial pattern of plant communities was adversely affected greatly by overgrazing disturbance in the arid mountains. The grazing activities and speckle spatial pattern of the habitat led to the complex of the community diversity and spatial heterogeneity in the mountains. The spatial variations of herbage community diversity showed a periodical fluctuation in several scales of 7m or 8m, 11m or 12m, 16 or 17m. The variation breadth ranged from 6m～7m, which was similar to the trend of density variation of the grazing-path. Thus the periodical variation of the herbage community diversity would be caused by variations of the grazing-path density from the bottom to the half way up the mountain. The grazing-path impact was an important factor that led to the community spatial pattern to be periodic oscillation. So it would be necessary to study further in the future to discuss the relationship between the grazing-path impact and the periodic fluctuation of the pattern of community. The trend of the brushwood community spatial variation was not obvious compared to the herbage community, this would be explained by these two reasons : (1) The plot area (1m^2) investigated was smaller in the brushwood community, which would not reflect characteristics of the community diversity; (2) The spatial variation of brushwood community diversity was resulted from speckle pattern of habitats. The data from the first axis of the detrended correspondence analysis (DCA) indicated that community spatial patterns were influenced by many factors. The semi-variance variation of the second axis of DCA has shown a periodical fluctuation.Therefore, intensity grazing disturbance was a driving force to form the spatial heterogeneity of the ecological structure. This activity was also a main factor that was able to e