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Gansu Agricultural University (2002)

Study on the Variation Mechanism of Landscape Pattern of Desertification Land and the Assessment of Desertification Degree in Hexi Corridor

XuDangHui

Titre : Study on the Variation Mechanism of Landscape Pattern of Desertification Land and the Assessment of Desertification Degree in Hexi Corridor

Auteur : XuDangHui

Grade : Master Thesis 2002

Université : Gansu Agricultural University

Résumé
Based on the investigation material of sandy desertification land of Hexi corridor, Gansu province in 1996 and images of middle and lower reaches of Shule river basin, landscape pattern indices, transition matrix of patches and land desertification synthesis value were calculated. The variation mechanism of landscape pattern of desertification land in Hexi corridor and middle and lower reaches of Shule river basin and desertification degree of 19 counties, cities or regions in Hexi corridor were analyzed and discussed on the basis of landscape ecological theory and method. The results and conclusions are summarized up as follows:1. The variation mechanism of landscape pattern of desertification land in Hexi corridor(1) The variation trend of landscape diversity index shows that in Hexi corridor, landscape diversity index and evenness index increased in past 50 years. Landscape diversity index increased from 2.454 to 2.489 and evenness index increased from 0.685 to 0.694 from 1949 to 1995, which indicates that the landscape heterogeneity enhanced. Comparing landscape diversity index and evenness index of five periods in three basins, the minima were in Shule river basin whose maxims carne to 2.204 and 0.615 respectively in 1970, the maxims were in Hei river basin whose minima appeared 2.642 and 0.737 respectively in 1949, which indicates that the landscape heterogeneity in Hei river basin was higher than in Shule river basin.(2) The variation trend of landscape isolation index shows that the landscape isolation index of man-made landscape types such as special utilized land, farmland and forest land decreased in Hei river basin and Shiyang river basin from 1949 to 1995, which decreased 0.120, 0.035, 0.051 and 157.800, 0.350, 0.270 respectively. But in Shule river basin, which increased 0.005, 0.026 and 0.029 respectively. On the other hand, landscape isolation index of remained natural landscape types such as flowing sand dune, semi-flowing sand dune and gobi had a decreasing trend in three basins. Analysis results show that the relationship between landscape isolation index and human activity intensity is complex, which is reflected from two aspects:3(a) For those man-made landscape types, landscape isolation index shows an inverse relationship with human activity intensity in the basins effected intensively by human activity, shows a positive relationship in the basins impacted weakly by human activity, (b) For those remained natural types, the relationship between landscape isolation index and human activity is inverse.(3) The variation trend of landscape patch fragmentation index shows that in Shiyang river basin, Hei river basin and overall Hexi corridor, the landscape patch fragmentation index increased. In 1949, they were 0.0037, 0.0036 and 0.0009 respectively, and in 1995, the’ were 0.021, 0.0065 and 0.0024 respectively, which shows that the landscape patterns were fragmenting in those regions, this was contrary to the analysis results of mean patch area. But in Shule river basin, this index decreased, in 1949, it was 0.0023 and in 1995, it was 0.0003, which means that the landscape fragmentation degree descended, this coordinates with the results obtained from the mean patch area. Therefore, in order to measure landscape fragmentation degree, the landscape patch fragmentation index results should be taken as a reference index and not as a sole or major index.2. The variation mechanism of landscape pattern in middle and lower reaches of Shule river basinThe area percentage of sandy land, wind eroded land and saline-alkali land to the total in 1990,1994 and 1999 were 57.1%, 60.1% and 63.6% respectively. The transition rate of grassland with low coverage to sandy desert was 1300hnr/a, shrub land to grassland with low and high coverage were 672hm2/a and 908hnr/a respectively in the period of 1990-1994.

Mots clés : Hexi corridor Desertification land Landscape pattern Variation mechanism Desertification assessment

Présentation (Dissertation topics)

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