Analysis Of The Degenerated Mechanism Of Haloxylon Ammodendron Populations In Gurbantunggut Desert

Vegetation degradation has occurred in many arid areas around the world in the current. The northern part of Xinjiang is located in central Eurasia, is a typical inland arid areas in the moderate temperate zone. Haloxylon ammodendron belong to perennial shrub-like small trees of Chenopodiaceae plants which are constructive species in Gurbantunggut Desert. It played a very important role for the prevention of sand dune movement and the sustainable development of the northern Xinjiang economic zone. However, Large-scale degenerated Haloxylon ammodendron forest has occurred in the western part of Gurbantunggut Desert In recent years. Why did this phenomenon happen? It is very urgent to seek out the degenerated reasons in order to make scientific and reasonable measures for ecological restoration. Therefore, Based on the investigation of characteristics of degenerated Haloxylon ammodendron populations, soil physical-chemical properties and groundwater level, we analyzed the degenerated reasons of H. ammodendron populations in the western part of Ggurbantonggut Desert. The conclusions as follows:(1),Most of the soil was severe or extremely saliferous in the study area. The salt accumulation of soil surface was in serious condition, with clear salt crust.(2),The species composition of these community was very single and most of the plots were Haloxylon ammodendron only. The trees were sparse with largh plant spacing, in addition, the branches and leaves have less overlapped among individuals. Furthermore, there were lots of dead but not fallen Haloxylon ammodendron trees with black-brown color in the study area.(3),The average coverage was 11.58% in study area, it has a greater decrease with compare to the average coverage of 25% in early 80s of the last century. The seedlings were sparse and the age structure diagram indicated that the Haloxylon Ammodendron populations were in declining. In addition, the plots were divided into soil plain and tempered ups and downs sand dune by different habitats. The analysis showed that the spatial distribution of Haloxylon Ammodendron populations belonged to the cluster distribution.(4),There were very significant negative correlation between individual viability of Haloxylon Ammodendron and the surface (0-40 cm) and the middle (40-80 cm) soil electrical conductivity (r =-0.79, P=0.0000; r=-0.32, P=0.009), and also were very significant positive correlation between individual viability and the lower (80-120 cm) soil water content (r=0.54, P=0.0000). Although the relationship between soil organic matter, Cl-, SO42-, pH and individual viability of Haloxylon Ammodendron were not significant, however, it is possible that all the physical-chemical factors were collaborative to affect the growth of plants.(5),The survival index and coverage of Haloxylon Ammodendron populations were significantly correlated with groundwater level (r2=0.40, P=0.007; r2=0.46, P=0.004). With the increase of groundwater level, the survival index, coverage was significantly reduced. This showed that the groundwater level played a very important role in the growth and survival of Haloxylon Ammodendron populations.