Assessment of the effect of water-table depth on riparian vegetation along the middle and lower reaches of the Manasi River, Northwest China

The Manasi riparian zone in northwestern China has become a survival habitat for numerous native plant species and requires urgent protection owning to rapid expansion of farmland. The critical factor affecting the growth of desert riparian vegetation in arid regions is recognized to be groundwater, but in this region the threshold of water-table depth for riparian species has been rarely studied. To determine the association between species and their major growth factors and to ascertain the water-table depth threshold, this study employed field investigation, a logarithm distribution model and canonical correspondence analysis. According to the findings, (1) the water-table depth largely regulates the species distribution; (2) from the results of the logarithm distribution model, the water-table depth appropriate for herbs is 1-1.5 m and for shrubs it is 2-4 m, and a water-table depth of less than 6 m could satisfy the growth requirement of major species; (3) species diversity peaks at the water-table depths of 2-3, 3-5, and 2-4 m for herbs, shrubs and all species, respectively; (4) the frequency of appearance of Phragmites communis (grass herb) and Tamarix chinensis (deciduous shrub) was not as sensitive to depth to water table. To reconstruct a riparian zone, Phragmites communis and Tamarix chinensis could be planted in areas with water-table depth of less than 3 m and 2-5 m, respectively. These results may contribute to suitable policy regarding vegetation restoration.

Automated summary

The distribution of plant species in the Manasi riparian zone is largely influenced by the depth of the water table, with appropriate depths for herbaceous plants being 1-1.5 meters and for shrubs being 2-4 meters. Water table depths less than 6 meters can satisfy the growth requirements of major species. Suitable water table depths can increase species diversity, and the grass herb Phragmites communis and deciduous shrub Tamarix chinensis are not sensitive to water table depth, allowing for planting in various depth ranges.