| Vegetation dynamic is the important research content of land resources and environmental changes. Based on the remote sensing technology and the image data of time series from 1999 to 2009 in SPOT VEGETATION, spatial distribution and the characteristics of dynamics of vegetation among Yangtze river Basin were analyzed through kinds of mathematical methods.The average NDVI image map obtained by using mean value method showed the average condition of the spatial distribution of Yangtze river vegetation by using slope analysis, Mann-kendall trend analysis, CVA, and Hurst index R/S analysis. Math operations on-the NDVI time sequencing of each year,season and month were done,the research on the characteristics of Yangtze river vegetation's dynamic, and the NDVI spatial distribution characteristic of different vegetation, watershed, water system division was done as well. The results showed:(1) The whole Yangtze River basin vegetation was in good condition. And the average NDVI value per year from 1999 to 2009 was smaller than 0.1. Non-vegetatioon area was up to 1.8% in the whole basin. High vegetation whose NDVI value was between 0.5-0.65 accounts for 47.4% of the whole watershed area, and the middle-high vegetation whose NDVI value was higher than 0.65 accounted for 31.7% of the whole watershed area. On the seasonal level, high vegetation was the main vegetation in spring and autumn, high vegetation was the main vegetation in summer as well, and the middle vegetation was the main vegetation in winter. On the month level, the middle, middle-high vegetation accounted for 88% of the whole watershed area. In February, the condition of vegetation was the wrost, and the area whose NDBVI value each year was higher than 0.5 accounted the least proportion, which was less than 9%. The trend of whole spatial distribution was that vegetation in south was more than that in north, that in east was more than that in west. The area with little NDVI value per year mainl located in Qinghai to the Yangtze river headwaters, large lakes in the middle and lower reaches of the Yangtze Rive rand nearby large and medium-sized cities.(2) The NDVI change curve appeared unimodal within a year, February had the minimum value, the curve dropped after July got the maximum value. April gained the greatest growth based on last month March, while October dropped most sharply. The curve's appearance diversed from different streams/ water systems/ elevation/ vegetation forms, it was bimodal in water systems of down streams, particularly for farmland in down reaches, the double-humped curve peaked in April and August, and had a lower value in between in June; while the whole Yangtze River Basin peaked in July, in middlestream and downstream area the curve peaked in August. It was implied that growing season was delayed in East part compared to West.(3) For interannual change, the vegetation cover enhanced obviously in Yangtze River Basin as a whole in the last 11 years, the slope for annual NDVI change trend line was 0.0059, increased 0.0649 for 11 years, amplified 14.25% from 1999. Summer and Autumn contributed much more for improved vegetation cover ratio, seasonal NDVI increased 0.070 and 0.067, account for 11.92% and 13.75% for 1999. There were general increasing trend for four main vegetation forms with farmland increased most remarkable, amount to 0.079, up to 17.17% gaining rate; at the elevation of 500-1000m, NDVI gaining rate was 17.94%, increased 0.092, topped in the 6 elevation classes; among 12 water systems, only Tai lake basin showed decline trend.(4) Space distribution of change trend (slope image) demonstrated that annual NDVI increased in most areas of Yangtze River Basin, around 92.3% pixels showed increasing trend, compared with 7.7% pixels that decreased which indicated ecological benefit from vegetation restoration such as " Shelterbelt Construction project of the Yangtze River "and "Natural Forest Protection Programme"。Where NDVI value declined scattered in the source region, up-middle streams of Jinsha river, north of Min-Tuo river basin, part of Chiang-nan hilly region and certain urban areas. Through F-test, classified change trend image was obtained, which showed percentage of nosignificant chang area was 39.4%, scattered significant increased area 18.5%, while 42.1% area in the whole basin where NDVI was increased extremely significant. For four seasons, NDVI extremely remarkable increased area accounted for 51.1%,42.1%,35.5% and 9.8% separately. Among 12 monthes, April NDVI enhanced most vigorously, about 43.5% area increased extremely significant in this month, while December had the least significant increased area which accounted only for 4.5%.(5) Change Vector Analysis method was used to analyse the change intensity during 1999-2009,1999-2004 and 2004-2009 those three time slot by calculate the values of‖Δp‖. The result showed that more than half of the pixels values belonged to the low change grade. According to the transition matrix, the change intensity during 2004-2009 was less than that of 1999-2004.The analysis of spacial variablility of‖Δp‖in 1999-2009 illustrated that:downstream >middlestream >upstream sort by the value of‖Δp‖; for 12 water systems, Wujiang river >upstream of the mainstream>Tai lake area (which were the top three areas), and Jinsha river had the least value of‖Δp‖; the value was relatively high in elevation of 500-1000m and rather low in elevation of more than 4000. For the four main vegetation form, farmland >bushwood >forest > grassland sort by the values.There were positive correlation between value of‖Δp‖and-human activities such as vegetation afforestation, rural activity and urbanization.(6) The result of Mann-kendall Analysis was much the same with slope analysis method, especially in dividing the change by significance or not, but there was about 10% deviation in percentage of extremely significance areas. It has the advantage of choosing significant levels adaptively according to the Z values of the whole data. Z value was the calculated result of the NDVI time series by Mann-Kendall Analysis method, its characteristics of spatial division illustrated that:increasing trend in downstream annual average NDVI time series was not significant, so was Jinsha river and Min-Tuo water systems, and the decreasing trend in Tai lake water system demonstrated nosignificance; the increasing of NDVI in elevation of more than 4000m was not remarkable; grassland either; the rest streams/ water systems/ elevations/ vegetation forms demonstrated significant increasing trend in 0.1 significant level with the threshold value 1.64.(7) Hurst Index indicated annual average NDVI time series was not mere random walk but biased, with self similarity and longtime dependency. The average Hurst value was 0.8344 in the whole basin, while the average value in different streams/ elevation/ vegetation forms were all above 0.75, which demonstrated that the change trend of NDVI were continuable. The hurst index was higher in downstream compared to up/middle streams; Hanjiang river> middlestream of the mainstram> downstream of the mainstream (top three) among 12 water systems; difference among elevation was less remarkable, elevation of 500-1000m had the maximum while elevation above 4000m had the least value; for 4 vegetation form, farmland >bushwood >forest >grassland sorted by Hurst index value. Hurst value may relate to regular agricultural activities.Conclusions of this research may provide as certain reference and evidence for Ecological Environment protection and construction, Land Resources management and policy, and may also help with the Sustainable Development of population, resource, environment and economy. |
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