The Response Of Vegetation-soil-soil Fauna To Desertification In The Western Of Ordos Plateau

Desertification is the first of the top ten problems that impact the earth environment. Based on the review of the evolvement about the concept of desertification and the status quo about studying on desertification, the thesis analyzes the deficiency existing in current research that is deficient in the responses of plant and soil to the land desertification. The thesis combine the TM image, the field survey of plant community and the test of soil physical and chemistry on the scale of district and ecological system in the western of Ordos plateau that is the desert-grassland biome transition zone. Based on the district desertification monitoring, the thesis had been analysis the change of Stipa breviflora community and Caragana stenophylla community , soil degradation and soil fauna community. All together,the response of plant community, soil and macro soil fauna to land desertification had been analysed. The study not only has the important value in theory but also provides scientific basis for the control of district land desertification.The result of study showed that the land desertification was very serious and deteriorating gradually.The average desertification rate was about 80% and the area proportion of wind-eroded land, water-eroded land and salinized soil was about 65:10:5. The average growth rate every year is 0.35%. The area of wind-eroded land and salinized soil showed a increasing tendency, but the water-eroded land did a decreasing tendency, its average rate every year was 0.36%, -0.06% and 0.97%, respectively. Most of wind-eroded land was light-desertification and moderate-desertification, and that was moderate-desertification and heavy-desertification for water-eroded land, and that is extreme-desertification for land salinized soil. The desertification index is the lightest degree in 1989, and the most seriousdegree in 2005. It often comes about the conversion of no-desertifcation and desertification land to cause desertification degree increasing. The serious land desertification in study area from 1989 to 2005 was the effect of climate warming and drying and irrational human activies.The results showed that plant communities in study area had the response to the land desertification. With the progress of desertification, the total species number and species abundance showed a decreasing trend. The biomass of above-ground significantly decreased, and it is equivalent to 20-25% of the mid-20th century at extreme-desertification stage. The results showed that the biodiversity indexes decrease overall, community structure become simpler. Artemisia frigida, Caragana tibetica,Artemisia ordosica may be the indicator to the serious degradation of Stipa breviflora community, and Stipa plareosa,Corispermum mongolicum,Oxytropis aciphylla and Convolvulus ammannii to the serious degradation of Caragana stenophylla community.The results showed that soil water content reduced, bulk density and hardness increased gradually, the content of clay decreased and the sand increased with the process of desertification. Soil organic matter, total nitrogen, total phosphorus, available nitrogen and phosphorus were reducing quickly with the more serious of desertification degree. But the change of soil organic matter content, total nitrogen and available were the most serious. The correlation analysis showed that the soil physics and chemistry properities were strongly correlated with the vegetation properities. So we can concluded that the soil degradation was closely related to vegetation degradation caused by land desertification.The results showed that the dominant groups of soil macrofauna were Scarabaeidae and Formicidae larva, the common groups were Araneae, Chrysomelidae larva, Diptera larva, Tenebrionidae, Scarabaeidae and Cydnidae. With the increasing of land desertification degree, the groups and individuals of soil macrofauna in Stipa breviflora community and Caragana stenophylla community all reduced gradually. But the significant difference appeard manily in the heavy-desertification stage. Shannon-Wiener index, Pielou index and abundance index all gradually reduced, Simpson index contraried. But the biodiversities of Caragana stenophylla community had not show clear regularity. Gradient analysis showed that the distribution of desertification habitats and soil mcrofauna communities had reflected the vegetation degradation and soil degradation caused by land desertification. So we can conclude that the response of vegetation,soil and soil macrofauna to alnd desertification will affect the stability of ecolosystem structure and function.The beginning of desertification process are soil organic matter and nutrition’s changes which affect other physical and chemical properties of soil and vegetation growth.And then the changes will affect soil macrofauna community. In turn vegetation and soil macrofauna community will influence or change physical and chemical properties of soil. In a word vegetagation, soil and soil macrofauna community intact and mutal restrict with each other. The three factors co-determine the desertification process. So the responses of vegetagation–soil–soil macrofauna community to desertification will influence the stability of structure and function in soil ecological system and then affect ecological system security absolutely .