The Spatial Pattern Of Tetraena Mongolica-Nitraria Tangutorum Community And Its Feedback Mechanism In Western Ordos Plateau

Tetraena mongolica, monotypic genus of Zygophyllaceae, is the super xerophyte and the relic and endemic shrub of the Mediterranean Sea. There was only a small part of them distributing in the world, mainly aggregating in the north western part of Ordos Plateau, the south of Kubuqi Desert and the foothill of Zhuozi Mountain, it is a special shrub endemic to the west of Ordos Plateau and its distributed area is very small, belongs to second-class national conserved plant. Since the construction of the Wuhai city and the development of economy have resulted in desertification, the quantity and size of its population are still decreasing.In this paper, the spatial pattern and its transformation of T. mongolica community after N. tangutorum invaded were discussed by method of point pattern analysis, and research sites were choosed through the density of T. mongolica and N. tangutorum., the preliminary results were got as following:(1) After analyzing the quantity of the T. mongolica and N. tangutorum we concluded that during the succession, the mortality of T. mongolica and the average value of crown size increased, the density of T. mongolica diminished,seedling and immaturity were diminished, the population of Tetraena mongolica inclined to old-growth. The invasion of Nitraria tangutorum had serious effects on the succession of the community of T. mongolica, the community of T. mongolica had degraded obviously.(2) we concluded from the analysises of Ripley's L function and pair-correlation function that after the invasion of N. tangutorum, T. mongolica aggregated because of the drastic competition between species, and sand burying made the population of N. tangutorum extend rapidly and then become the dominant population, N. tangutorum sand mounds and inter-mound space were even wider, so the N. tangutorum sand mounds distributed regularly at low scale, a series of factor, such as shortage of soil moisture,heterogeneity of soil elements and T. mongolica seed dispersal influenced by sand mounds, affected the development of T. mongolica,, so there were significantly negative correlation between T. mongolica and N. tangutorum, the community of Tetraena mongolica had degenerated obviously.(3) After analyzing the mark correlation function of T. mongolica, N. Tangutorum and their ineraction, we concluded that along with the succession after invasion of N. tangutorum, ?the conspecific competition of T. mongolica became weaker as well as the conspecific competition of N. tangutorum and interspecific competition between T. mongolica and N. tangutorum became enhanced. The population of T. mongolica evolved from small patch and high density into big patch and low density as well as the population of N. tangutorum evolved from small patch and low density into big patch and high densityEven though the biological characters and ecological adaptability of plants were important reasons which cause N. tangutorum invading into T. mongolica community and its succession, some man-made factors such as the decline of water table and the desertification were important matters. Therefore, this factors should be take into account to make sound protection strategies for the endangered plant T. mongolica.