Quantity Analysis On Species Diversity Of Desert Plant Communities In The Lower Reaches Of Tarim River, Xinjiang

Based on the field investigation data in 2005 and on July to October in 2006 of six transects and 38 plots of flow-breaking region in lower reaches of Tarim River(Tahe) and of three transects and 12 plots of non flow-breaking region in middle reaches of Tarim River, this paper studied on the diversity and structural characters of desert plant communities by riverside with application of Multivariate Statistical Method. The conclusions are shown as following:1 During the period of field investigation, there were super plants of 13 families and 24 species in middle reaches of Tarim River and 10 families and 15 species in lower reaches of Tarim River. 2. By employing some models such as species-area curve, researches on the minimum sample size of plant communities in middle and lower reaches of Tarim River indicated :①When P including 50%,80% and 90% plant species, the minimal sample area should be 418m2,1702m2 and 2656 m2 in lower reaches and 1129 m2,5112 m2 and 7493 m2 in middle reaches.②With the distance from river increasing, the variation curve of the minimal sample area in lower reaches tended to"U", while the size in middle reaches showed some aggrandizing tendency.3. Studies on the individual quantity characters of plant communities in lower reaches of Tarim River showed: With the distance from river increasing, the correlation between quantity of species and buried underground level, density and buried underground level, coverage and frequency of herb and buried groundwater level, all of them was not significant. The correlation between arbor and shrub coverage and buried groundwater level, the minimal area and buried groundwater level was characterized"S"and logarithmic curve respectively. In order to describe the correlation between restoration of vegetation in transportation riverside and buried groundwater level correctly, the proper sampling method and sample quantity should be explored. 4. Studies on the compatibility among main species of plant communities in middle and lower reaches of Tarim River showed:①Association of species collectivity in lower reaches was positive but not significant. There did not existed significant or extremely significant, positive or negative correlation among most species in lower reaches.②Association among main species of plant communities in middle and lower reaches was compared, of which significant and irrelative was 29.1% and 71% in middle reaches,13.6% and 69.7% in lower reaches. Species Association varied spatially, which indirectly reacted the adaptability of horizontal structural characters of communities and different species to environmental conditions. 5. Ordered quadrate clustering was used to classify 14 species in lower reaches and 11 species in middle reaches of Tarim River which important value were over 0.01:①Vegetation could be classified 3 communities and 7 groups in lower reaches, while 2 communities and 7 groups in middle reaches.②The classification results of plant communities in lower reaches analyzed by Ordered quadrate clustering or TWINSPAN had extremely significant correlation. However, the improper sample classified accounted for 6% by former, 21% by latter, which indicated that Ordered quadrate clustering was better than TWINSPAN with respect to desert vegetation by riverside.③Based on FA ordination to vegetation in lower reaches, it concluded that both of distribution of plant communities and species composition closely correlated with soil moisture content, level and pH value of groundwater.6. Studies on the diversity indexes of plant communities in middle and lower reaches of Tarim River resulted:①The diversity indexes of arbor and shrub in middle and lower reaches was obviously higher than that of herb.②The richness index of communities in lower reaches was relied on that of shrub layer and herb layer. Both diversity indexes and richness index were higher in some region where groundwater level was high, lower on the contrary.③Studies on the relationship between species diversity and structural characters of communities showed: With species diversity increasing, individual density of plants tended to ascend linearly. The increment of individual average height and vegetation coverage were also related with increasing of species diversity..7. Studies on the relationship between species diversity of plant communities in lower reaches of Tarim River and environmental factors showed:①Based on combination of Correlate Analysis, Principal Component Analysis and Regression Analysis, the ordination of importance of environmental factors to community diversity was: buried groundwater level>pH value of groundwater>total salinity>soil moisture content of 60㎝ layer>mineral. level②According to results of Cluster, it indicated that the correlation between buried groundwater level and diversity was significant at 7 scale, the correlation between the other factors and diversity was significant at 1～4 scale. The buried groundwater level was the most important environmental factor influencing community diversity.