Plant Communities and Their Interrelations with Environmental Factors in the Middle Reaches of the Tarim River

Plant communities were sampled in the lower reaches of t he Tarim River, Xinjiang. The results showed that among the 475 sampled quartets from 19 sites, 23 plant species were identified, which belong to 21 genera in 11 families, most of which have low occurrence freque ncy in quadrats. The most common species of this study, Tamarix ramosi ssima occurred in 17 sites (89.47% of the total investigated sites), fol lowed by Phragmites communis, which occurred in 12 sites (63.15% of the total investigated sites). Populus euphratica and Lycium ruthenicum were fou nd in 11 sites respectively, accounting for 57.89% of the total sites. Quan titative classification (TWINSPAN) and ordination (CCA) methods were used to study the distribution patterns of 23 plant species at 19 sites in this study area. The TWINSPAN analysis identified three site groups. Site group 1 contains 7 sites, which were located in Shazihe transect. Site group 2 contains 5 sites, which were located in Wusman transect. Site group 3 contains 7 sites, which were located in Aqihe transect except for site 10. The site group 3 separated firstly from all the 19 sites by TWINSPAN showed evident difference with other two site grou ps. The 23 plant species could be also divided into 3 ecological speci es groups using TWINSPAN analysis. CCA results were consistent with TW INSPAN results. The distribution patterns of plant species were most str ongly associated with underground water table, soil moisture and soil pH value. To a lesser extent, distribution of species was associated with soil alkalinity, underground water mineralization and altitude. The major en vironmental variables are ground water level and soil moisture, and th e regression model as below respectively: X 1 =-9.5991L + 100.86 (R 2 = 0.6459);X 2 = 1.65W + 43.011 (R 2 = 0.7646). Although the species did not cluster into well-defined groups, loose arrangements of species can be identified which were ass ociated in a similar way with the environmental variables.