| Present, the surface environment present an ever-worsening trend in many areas of the world. How will the surface environment change? What are the relationships between the surface environment changes and hydrological-weather factors? All above problems have been paied close attention from scientific communities and governments, already become a hot topic for International Geosphere Biosphere Program (IGBP) in the research of global changes.Horqin sandy land was a beautiful and exuberant grassland in history, after hundred years grassland degeneration and desertification has already become one of four big sandy land in our country, whatever in the whole world or our country, the variation of the surface environment had many typical and representative natures. How will the surface environment changing trend and characteristics go on? What are the relationships between the changes of the surface environment and hydrological-weather factors? These are scientific communities want to learn urgently at present.The paper take Horqin sandy land as regional study area, in this study area have carried out researches about the changes of vegetation ecotype, elm growth and the relationships between the surface environment changes and hydrological-weather factors, and chosen two areas which can represent the landform, terrain, vegetation and hydrological-weather conditions in Horqin sandy land, namely general study area (Agula town) and principal study area (Agula testing-station). The paper based on 17 remote sensing image data from 1987 to 2006 and lots of vegetation and hydrological-weather data which by collecting, surveying and testing in two study areas, with translating the remote sensing image and arranging the hydrological-weather data, have carried out researches about the inter- and inner-annual changes of the surface environment and the relationships between the surface environment changes and hydrological-weather factors in general and principal study areas. From analysis, gained four main conclusions as follows:Regional study area:(1) For hygrophytes, mesophytes, mesoxerophytes and xerophytes, the buried depth of groundwater table were respectively from 0.45m to 1.66m, from 0.95m to 2.20m, from 2.20m to 4.59m and from 3.45m to 7.45m; the water content of surface soil of root structure were respectively from 2.70% to 25.54%, from 0.80% to 13.32%, from 0.41% to 2.25% and from 0.28% to 0.44%; the water content of root structure were respectively from 5.59% to 54.80%, from 3.59% to 9.19%, from 0.71% to 3.59% and from 0.16% to 0.78%. At the same time, for hygrophytes and mesophytes, mesoxerophytes and xerophytes, there were two transition response ranges of buried depth of groundwater table respectively from 0.95m to 1.66m and from 3.45m to 4.59m; there were two transition response ranges of water content of surface soil of root structure respectively from 2.70% to 13.32% and from 0.41% to 0.44%; there were two transition response ranges of water content of root structure were respectively from 5.59% to 9.19% and 0.71% to 0.78%.(2)The annual ring index had three biggest correlation coefficients with rainfall of July, the annual precipitation and the total evaporation of August and September are respectively +0.605, +0.595 and -0.459, namely the elm growth changes present an increasing trend with the increase of precipitation and present a decreasing trend with the increase of evaporation. From these ruslts, established elm standard annual table and rebuilded the sequence of precipitation and evaporation from 1906 to 1951, from certification, the sequence had fairly good reliability for actual practices.General study area:(1)During 1987~2006 the area of farmland, forest, the land of resident and road, alkaline-saline land, low-covered degree grassland and the fixed and partly fixed sandy land respectively increased from 26.65, 1.02, 1.878, 38.71, 120.30 and 104.84km2 to 74.79, 2.832, 4.585, 94.91, 201.79 and 203.21km2. The six types of surface environment in inter-annual presented a gradually increasing trend. The area of bush forest, water surface, high-covered degree grassland, fixed sandy land,bare sand dunes and middle cover degree grassland respectively increased from 53.26, 30.80, 49.38, 321.24, 59.70 and 116.94km2 to 42.63, 16.50, 32.88, 103.86, 18.48 and 128.36km2. The six types of surface environment in inter-annual presented a gradually decreasing trend. All types of surface environment in the course of mutual transformation. It indicated that the surface environment presented an ever-worsening trend for a long time, but changed for the better condition close to recent two years.(2)In the course of inter-annual changes of average value of NDVI, from 1987 to 1994 was a rising stage and from 1994 to 2002 was decreasing stage, afterwards presented a rising trend. As a whole, the inter-annual changes of the average value of NDVI presented a decreasing trend, namely the changes of surface environment presented a worsening trend, but changed for the better close to recent two years.(3)All types of area changes of the surface environment had different degrees correlations with 9 major kinds of hydrological-weather factors, about 2～28 hydrological-weather factors influenced the changes of surface environment and had certain orders according to the size of correlation coefficients, with the fluctuation of these factors, all types of area changes of the surface environment presented different response modes. As a whole, the influences of rainfall, relative humidity, maximum temperature, minimum temperature and average wind speed went throughout the whole course of early, initial and flush period of vegetation growth.(4)Relative humidity was the most influential factor to the area changes of surface environment, the HFII(Hydrological-Weather Factors Influential Index) was 0.161; rainfall occupied the second place, the HFII was 0.150; the third one was evaporation, the HFII was 0.131. That show clearly, in arid area, water condition was the key restrictive factor to the changes of surface environment, it's contrary factor-evaporation was another key restrictive factor, these phenomenon accorded with the characteristics of arid area, the worsening conditions of the surface environment mainly bringed about by the multi-years dry climate.(5)Rainfall and evaporation was the impetus factors to the changes of average value of NDVI, which will present a decreasing trend from 2007 to 2012, it indicates that the surface environment will increasingly worsen during this period; and it will present an increasing trend from 2013 to 2020, it indicates that the surface environment will change for the better.(6)In the initial stage of vegetation growth, because of rainfall was comparatively rare, the growth of vegetation mainly depended on absorbing groundwater by root system, accordingly the buried depth of groundwater table was increasingly shallow and the average value of NDVI was more bigger. A little fluctuation of buried depth of groundwater table on May will make the average value of NDVI occur greater changes. Meanwhile, with the different ranges of buried depth of groundwater table on May and July, NDVI presented three response ranges were respectively from 0.145 to 0.3, from 0.3 to 0.5 and from 0.5 to 0.582, there were transient ranges of buried depth of groundwater table in these response ranges.Principal study area:(1) The inner-annual variation of farmland, bush forest land, alkaline-saline land, high-covered degree grassland and fixed sandy land presented a parabola trend. The inner-annual variation of water surface, low-covered degree grassland, fixed and partly fixed sandy land, bare sand dunes presented a little inverted parabola trend. The other forest land nearly had no changes in 2006, the inner-annual changes of middle -cover degree grassland presented an increasing trend.(2)The inner-annual changes of maximum and average value of NDVI presented a parabola trend, on August 24 the NDVI was maximum of 0.707, on October 27 the NDVI was minimum of 0.302.(3)In the stage of May 22 to August 24, all types area of surface environment changed and transformated each other with the changes of hydrological-weather factors and had close response relationships. From August 24 to November 27 presented inverted response relationships.(4)The average value of NDVI of all types of surface environment presented a parabola trend, the average value of NDVI of high-covered degree grassland was maximum of 0.3006; the mixed land of alkaline-saline and high-covered degree grassland occuied the second place, the value was 0.1098; bare sand dunes was the last factor, the value was 0.0682.(5)The inner-annual changes of rainfall and the value of NDVI had the same trend, it was the most influential factors and influenced the whole course of vegetation growth. The value of NDVI decreased with the increase of evaporation and increased with the increase of sunshine hours. The value of NDVI correspondingly increased with the increase of relative humidity of 0m, 2m and 3.5m, it indicated that the different height of water condition influenced the whole course of vegetation growth. Samely, a little fluctuation of buried depth of groundwater table on May will make the average value of NDVI occur greater changes, it played a key role for vegetation growth. However during June to August, the state of vegetation growth was in good condition, the cardinal number was stable, so the growth of vegetation was less dependent on the buried depth of groundwater table. Meanwhile, when the value of NDVI were respectively from 0.125 to 0.3, from 0.3 to 0.5 and from 0.5 to 0.612, which had respectively corresponding ranges of buried depth of groundwater table from May to July, and had a part of transition ranges. The value of NDVI gradually decreased with the wind speed increase. If the ground temperature was higher, it would suppress the vegetation growth and reduce good vegetation cardinal number, if the ground temperature increased on August, the vegetation growth would be suppressed and the value of NDVI also reduced. To October, the temperature gradually deduced, so vegetation growth need higher soil temperature environment, from analysis, if various layers of ground temperature were higher, the value of NDVI were more bigger, the most influential layer of ground temperature located at 5cm. In the flush period of vegetation growth, the average temperature in various spatial layers should be not too high, otherwise was disadvantageous to vegetation growth. On August the value of NDVI was influenced by soil evaporation, especially 0~20cm soil evaporation, with the increase of soil evaporation, the soil moisture was insufficient, the root system of vegetation could not receive supplement of moisture content, the NDVI would be reduced.Whatever inter-annual or inner-annual changes of surface environment mainly responded to changes of hydrological-weather factors, especially the changes of rainfall, relative humidity, evaporation and temperature et al. As a whole, the surface environment presented an ever-worsening trend for a long time, has a part of undulation, especially has changed for the better close to recent two years, but will still continue to worsen in next 6 years, afterwards it will lasting better, all above phenomenon result from the continuous drought and future wet of climate, certainly, in which include partial influence from the human beings.
|
PDF Full Text Request