毛乌素沙地南缘沙漠化临界区域土壤水分和植被空间格局

应用地统计学和经典统计学方法,对毛乌素沙地南缘沙漠化临界区域土壤水分和植被特征的空间分布格局及其相互关系进行研究,结果表明: 0-5 cm和5-10 cm土壤水分符合指数模型,10-15 cm土壤水分和植物群落物种数、植被盖度、植被密度都符合球状模型;0-5 cm土壤水分、植物群落物种数和植被盖度都具有强空间自相关性,5-10 cm、10-15 cm土壤水分和植被密度都具有中等程度的空间自相关性;从牛枝子群落到黑沙蒿群落,各层土壤水分与植物群落物种数之间具有相似的空间格局,都呈先升高后降低的变化趋势,而植被盖度和植被密度呈逐渐减小的变化趋势;0-5 cm土壤水分与植物群落物种数之间具有显著的正相关,是制约植被物种空间分布的关键因素。

Spatial pattern of soil moisture and vegetation attributes along the critical area of desertification in Southern Mu Us Sandy Land

The critical area of desertification in Southern Edge of Mu Us Sandy Land is a clear example of a grassland undergoing the process of desertification. Accordingly, studying this process at this site will be important in revealing the underlying mechanisms of grassland desertification in general. We employed several statistical and geostatistical methods to quantify spatial pattern of soil moisture, plant species richness, vegetation coverage, plant density, and moisture/vegetation correlations. Soil moisture was measured at 0-5, 5-10, and 10-15 cm depths. Soil moisture varied moderately at all three depths, and the same as vegetation attributes. Coefficients of variation ranged from 0.33 to 0.89, decreasing with soil depth. Semivariograms of soil moisture at 0-5 and 5-10 cm were best described by an exponential model, whereas those of species richness, vegetation coverage, plant density and soil moisture at 10-15 cm were best described by a spherical model. Values of nugget and sill increased with soil depth, as did random and total variation. Soil moisture at 0-5 cm, species richness, and vegetation coverage exhibited strong spatial autocorrelation, with 99.9, 81.3, and 77.1% of total variation found within autocorrelation distances of 27.5, 216.9, and 255.7 m, respectively. Plant density and soil moisture at 5-10 and 10-15 cm were less spatially auto-correlated, with 64.6, 63.2, and 59.8% of total variation found within autocorrelation distances of 214.4, 500.5, and 510.9 m, respectively. Ecological processes affecting soil moisture at 0-5 cm exerted their effects at finer spatial scales, whereas those affecting species richness, vegetation coverage and plant density operated at somewhat broader spatial scales. Ecological processes affecting soil moisture at 5-10 cm and 10-15 cm did so over still broader scales. Spatial pattern of soil moisture at all depths and plant species richness exhibited strong spatial regularity, generally increasing and then decreasing along the transect. In contrast, vegetation coverage and plant density decreased gradually along the transect. Soil moisture at 0-5 cm was strongly and positively correlated with plant species richness, indicating that surface moisture may be a predominant factor for determining the distribution of plant species in the critical area of desertification. Vegetation coverage was significantly, positively correlated with both plant density and richness, exhibiting an intimate association among vegetation characteristics. However, neither vegetation coverage nor plant density were significantly correlated with soil moisture at any depth, suggesting that soil moisture at surface layers was not a crucial factor for vegetation growing in this area. This study is the basis for further study on the mechanisms of desertification and the relationship between vegetation and soil properties. Furthermore, results of this study have great scientific and practical significance for prevention and mitigation of desertification.