Vegetation Dynamics And The Relationship With Environmental Factors In Ordos Region

The formation and development of vegetation are closely related to environmental factors. Different environmental factors lead to diversity of vegetation distribution, while diverse vegetation distribution can also affect the environmental factors. It can reveal the inner mechanism and process between vegetation and environmental factors from exploring vegetation-environment relationship. It can provide the basis for understanding and utilizing human environment, and achieving the sustainable development. In this paper, we completed two vegetation maps of1987and2007based on Landsat TM. Combined field survey date in2007, on one hand we summarized vegetation dynamics during this20years periods; on the other hand, we analyzed the relationship between vegetation dynamics and environmental factors using DCA multivariate analysis.The main results during the20years (1987-2007) are as follows:(1) Overall, zonal vegetation (typical steppe, desert steppe) area, showed a little decrease, non-zonal vegetation (sand vegetation, wetland vegetation) area was increased, and other types (residential, farmland, plantation areas, bare sand and water bodies, etc.) area did not change significantly;(2) Typical steppe area reduced from835,800hectares in1987to598,500hectares in2007; desert steppe area reduced from1,270,200 hectares to921,700hectares; steppe desert area reduced from854,500hectares to701,400hectares. While the annual precipitation did not change significantly during this time. It indicated that other factors may drive vegetation change in addition to climate change, such as vegetation restoration, desertification control and other ecological construction activities in recent years. The increase of sand vegetation area may lead to the reduce of typical steppe and desert steppe area. Steppe desert vegetation area increased slightly, it probably due to area increase of shrub planted;(3) Sandy vegetation area increased from2,340,000hectares in1987to3,402,400hectares in2007. The main reason was Ordos government has taken various sand control measures. Some sand plant, such as artificial Salix, was cropped in sand. It lead to bare sand changed to sand vegetation. Low wetland vegetation area decreased from717,200hectares in1987to439,700hectares in2007. It mainly because groundwater level declined. It further lead to some mesophyte plants lost their habitats and finally caused low wetland vegetation area reduced.(4) The total number of landscape patches changed from3295in1987to54570in2007. The rapid increase of patches number reflected that landscape fragmentation degree tended to increase. It also certified human activity enhanced in Ordos region.(5) DCA ordination showed that zonal vegetation distribution has a great relationship with soil factor(moisture and salt content)and the thermal effector; low-wetland vegetation distribution is mainly affected by the soil factor, sandy vegetation is mainly reflected the degree of sandy matrix flow.