Relationship between Species Diversity of Herbaceous Plants in the Shelterbelt and Environment Factors

Abstract

Many researchers have focused on the close relationship between species diversity and ecosystem stability. The Taklimakan Desert is a mobile desert with various dunes. Climate in the desert is characterized by the extreme aridity,low vegetation coverage and a few survival salt-tolerant desert plants. So,herbaceous plants grow only in the bottom of dunes under the conditions of high temperature,drought and high saline environment. As the longest desert highway in the world,the Tarim Desert Highway in Xinjiang of China is 436 km in length and covers an area of 3 128 hm2. The shelterbelt along the highway with average width of 2-6 km is irrigated with salty groundwater. Shrubs of the shelterbelt are Haloxylon,Tamarix and Calligonum plants. Herbaceous plant species have been notably increased since the shelterbelt was planted,and the herbaceous plant coverage has been over 40% along some highway sections. A stable windbreak and sand-fixation system has been formed by the shrub layer and herbaceous plant layer. Previous researches focused on sand-fixing efficiency,micro-climate benefits,physical and chemical properties of soil,changes of plant growth and transpiration along the shelterbelt in the Taklimakan Desert. To date,there are no the papers focusing on the change of species diversity of the artificial ecosystem yet. In this paper,the spatial differentiation of herbaceous plants is researched,and the relationship between species diversity and environmental factors is analyzed. In the study,10 sample plots were delimited along the Tarim Desert Highway shelterbelt,3 sample lines,100 m in length and perpendicular to the highway,were set in each sample plot,and 10 to 14 sub-plots (5 m×5 m) were delimited between the sample lines. Number,coverage and richness of herbaceous plants and corresponding environment factors,such as groundwater level,groundwater electrical conductivity and mineralization,soil electrical conductivity,average range of tree crown of shrub layer and shade density,were recorded and surveyed comprehensively. Sample altitude was measured by GPS; groundwater level was measured with self-made electronic water level meter; shrub crown diameter was measured with steel tape; shade density of shrubs and coverage of herbaceous plants were measured by ocular estimate; groundwater samples in the study area were collected and analyzed in laboratory,their electrical conductivity and mineralization were measured by conductivity gauge; soil samples were collected at soil depths of 0-10 cm and 10-30 cm and analyzed in laboratory,and their conductivity was measured by conductivity gauge. Main indices included the richness index,important value index,average vegetation coverage in the plots,Shannon-wiener diversity index (H'),Simpson diversity index (D') and Sorensen similarity index. The results are as follows:(1) There were less herbaceous plants and their species in the Tarim Desert Highway shelterbelt; these herbaceous plants were composed of 13 species in 12 genera and 8 families. Most of the plants belonged to Chenopodiaceae and Compositae families,and many of them were perennial; (2) Some plant communities were consisted of the scarce species,but many ones are composed of single families; (3) Under different groundwater levels,the electrical conductivity of topsoil,distribution of herbs and species diversity were quite different; (4) The species diversity of herbaceous plants was closely correlated to groundwater level,groundwater electrical conductivity and topsoil electrical conductivity. The correlation coefficients between Shannon-Wiener index and groundwater level,groundwater electrical conductivity,electrical conductivity of soil at depth of 0-10 cm were 0.72,0.63 and 0.69,and those between Simpson index and groundwater level,groundwater electrical conductivity,topsoil electrical conductivity were 0.65,0.61 and 0.69,respectively. The coverage of herb community and the diversity index were increased with the raise of groundwater depth. Therefore,the study results can provide the basal information for conserving plant species diversity,improving the stability of the ecosystem,maintaining the unblocked desert highway traffic,and supplying the gap of herbaceous plant diversity in the shelterbelt along the desert highway.