WATER TABLE AND THE DESERT RIPARIAN FOREST COMMUNITY IN THE LOWER REACHES OF TARIM RIVER,CHINA

Aims Intensive utilization of water resources in the Tarim River watershed during the past five decades has reduced flows in a 320-km section in the lower reaches, drying lakes and lowering groundwater levels. This has degraded Populus euphratica forests over large areas, reducing biodiver-sity and impairing ecosystem structure and function. Our objectives are to study ecological responses of the natural vegetation to changes in the water table and determine the water table depth needed for the survival of desert riparian forest. Methods We divided water table depths into a gradient of six levels based on annual mean groundwa-ter level and sampled vegetation plots for each of the six levels. We analyzed niche characteristics and species diversity of the primary populations for the six water table levels. Important findings With an increase of groundwater depth, the niche breadth of plant populations in-creases approximately monotonically, reaching a maximum at a groundwater depth of 4–6 m, after which the niche breadth decreases. Niche overlap is the smallest and plant species abundance highest at groundwater depth of 4–6 m. The Hill species diversity index showed highest species diversity with groundwater depth of 2–4 m, followed by 4–6 m and then 0–2 m. At groundwater depth 6 m, diversity is low and the diversity curve becomes smooth. Therefore, to restore the degraded vegetation in the lower reaches of Tarim River, the groundwater depth should be at least 6 m, with 4–6 m in most areas and 2–4 m in some areas near the water course.