Effect of groundwater depth on riparian plant diversity along riverside-desert gradients in the Tarim River

Abstract

Riparian plant diversity is sensitive to changes in groundwater in arid regions. However, little is known about how plant diversity responds to changes in environment along riverside-desert gradients in riparian ecosystem. Our objectives were to (i) identify riparian plant diversity along riverside-desert gradients in Tarim desert riparian forests, (ii) analyze the impact of environment variables on plant diversity, (iii) determine the optimum groundwater depth for different plant life-forms. Six transects 90 quadrats (with each size 100 m × 100 m) distributed vertically to river bed along riverside-desert gradients ~30 km in length were surveyed. At each quadrat, the morphological features of riparian plant communities were measured, and the groundwater depth, soil water, soil salinity, soil nutrient were also monitored at same sites. Three distinct vegetation communities were identified based on cover and richness in the tree, shrub and herb layers: the riparian zone, the transitional zone and the desert margin zone. Twelve species were indicators of the three vegetation communities. Riparian plant diversity was influenced by groundwater depth, distance from river, soil moisture content, soil salinity and soil nutrient by redundancy analysis. In response to groundwater depth, the optimal groundwater depths for species diversity, evenness and shrub cover were 2.8, 2.7 and 3.7 m, respectively. Therefore, maintaining high plant diversity requires managers to ensure stable groundwater depth for different plant life-forms rather than for some of them.