Abstract
Ecological restoration of degraded riparian Tugai forests is a key driver to combat desertification in arid regions. Previous studies have focused mainly on changes in groundwater as the underlying mechanisms of Tugai forest’s decline. We evaluated species composition and diversity of Tugai forest and their relationship to groundwater, soil salinity, and soil nutrient. Using 73 quadrats (100 m × 100 m) from 13 transects located perpendicularly to river in the upper reaches of the Tarim River. Eighteen plant species belonging to sixteen genera and eight families were recorded, and the dominant species included Populus euphratica, Phragmites communis, and Tamarix ramosissima. Three P. euphratica stand ages were detected: young stand, mature stand, and old stand. There were significant differences in species diversity, groundwater depth, groundwater salinity, distance from the quadrat to the river channel, soil moisture content, pH, electrical conductivity, total salt, Cl−, SO42−, Ca2−, Mg2+, Na+, K+, soil organic carbon, and soil organic matter across the stand ages. Seven species were identified as indicators of the three stand ages. Redundancy analysis indicated that the Tugai forest diversity indices were negatively correlated with groundwater depth, groundwater salinity, and distance from the river, and positively associated with electrical conductivity, total salt, pH, Cl−, SO42−, CO32−, soil organic matter, soil organic carbon, and soil moisture content. Plant diversity was the highest at 3–6 m groundwater depth, followed by 0–3 m and then 6–9 m, with the lowest recorded at > 9 m. The appropriate groundwater depth for herbs was about 1–4 m, whereas the depth for trees and shrubs was about 3–6 m. The groundwater depth < 6 m was deemed suitable for the growth of desert riparian forests. This results provide a scientific reference for the ecological restoration and protection for Tugai forests in arid areas.
Highlights
Desertification is the serious land degradation at arid, semi-arid and dry sub-humid areas [1], which constitute the largest terrestrial ecosystem, collectively covering 41% of the Earth’s land surface and supporting over 38% of the human population [2]
Eighteen plant species belonging to eight families and sixteen genera were detected in the upper reaches of the Tarim River, which is similar to that of the Syr Darya and Amu Drya rivers [45], which harbor large areas of Tugai forest [7]
Our results indicated that the importance value of P. euphratica in the Tarim River was the highest, followed by T. ramosissima and P. communis
Summary
Desertification is the serious land degradation at arid, semi-arid and dry sub-humid areas [1], which constitute the largest terrestrial ecosystem, collectively covering 41% of the Earth’s land surface and supporting over 38% of the human population [2]. Tugai forests almost exclusively consist of the tree species P. euphratica [7] Among these areas, the largest natural P. euphratica forest is in the Tarim Basin of China, which accounts for > 50% of the global P. euphratica forests [8]. As a natural barrier to desert expansion, these forests provide valuable ecosystem services, including biodiversity maintenance, protection from sandstorms, moderation of desertification, regulation of oasis climate, forest soil fertilization, maintenance of ecosystem balance, and the most importantly, they prevent desertification in arid regions [8, 9]. Tugai forest degradation is often accompanied by large changes in the spatial pattern of soil resources and vegetation [12], which have been linked with alterations in the structure and functioning of ecosystem leading to its desertification [13]. Determining the species diversity of Tugai forests is crucial for Tugai forest restoration and combat desertification in arid regions [7]
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