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Variations Of Vegetation And Its Influence Factors In The Arid Region Of The Central Asia From2000to2012

Posted on:2015-01-03Degree:MasterType:Thesis
Country:ChinaCandidate:H J XuFull Text:PDF
GTID:2250330431451187Subject:Biogeography
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The arid region of the Central Asia is located in the hinterland of the Eurasian continent which is the largest arid region of and warm temperature climatic zone in the northern hemisphere. Under the control of the westerly circulation, it is very sensitive to climate change due to its vulnerable ecological environment. It usually impresses us with arid environment, sparse vegetation and frequent sand activities. The harsh environment profoundly restricts the sustainable development of regional economy and society. Over the last decade, it experienced by rising temperature, decreasing precipitation and increasing human activities. How do warm and dry climate and intensive human activities impact on spatial-temporal variations of vegetation growth? What is the process and mechanisms of climate and human activities impacted on vegetation growth? These questions are still unknown.Based on monthly MODIS NDVI datasets, along with monthly gridded air temperature and precipitation data, land use and land cover data during2000-2012, the spatial pattern and spatial-temporal variations of vegetation growth in the arid region of the Central Asia were analyzed using a variety of mathematical statistics such as trend analysis, correlation analysis, multiple linear regression analysis and residual analysis according to the scientific issues above-mentioned. On the other hand, the lag effects of vegetation growth in response to temperature and precipitation change, the relationships among vegetation growth, temperature and precipitation, the contribution rates and mechanisms of climate change and the impact of human activities on vegetation growth were discussed. The results showed as follows:1. The longitudinal distribution pattern of vegetation activities in the arid region of the Central Asia was characterized as weak in the west and east, and strong in the middle, and with the direction from west to east, vegetation activities weakened. The latitudinal distribution pattern of vegetation activities was characterized as weak in the south and strong in the north, and with the direction from south to north, vegetation activities firstly kept stable and then gradually strengthened. The topographic distribution pattern of vegetation activities was characterized as weak in the high elevations and strong in mid-low elevations. With the increase of slope, vegetation activities gradually weakened and it had no significant relationships with aspect change.2. The temporal variations of vegetation growth in the arid region of the Central Asia over the last decade showed that, the yearly maximum vegetation NDVI (NDVImax) experienced an insignificant degradation trend at a rate of-0.3%/a (p>0.05). Especially after2007, the deterioration of vegetation growth condition continued. The forest was the most dramatically changed vegetation types, followed by the wetland and grassland, and the shrubland was the most stably changed vegetation. The spatial variations of vegetation growth in the arid region of the Central Asia over the last decade showed that, the vegetation restoration and degradation area accounted for about18.68%and43.56%of the study area, and the significant vegetation restoration and degradation area percentage occupied about2.30%and9.16%of the study area. The vegetation degradation area was mainly distributed in the Ural River downstream, Turgay Plateau, Kazakh Hills, southern West Siberian Plain, northwestern Hindu Kush Mt., Altai Mt., western Tianshan Mt., northern Alatau Mt., mid-upper reaches of Ili River and Aydin Lake Basin. The vegetation restoration area was mainly distributed in the surrounding area of Aral Sea, eastern Balkhash Lake, upper reaches of Irtysh River, southern Junggar Basin, oases in Tarim Basin, Qilian Mt.and Helan Mt.3. The vegetation growing season average temperature in the arid region of the Central Asia showed a significant increasing trend at a rate of+0.11℃/a (p<0.01) and it accelerated after2005over the last decade. The temperature significant increasing area was mainly distributed in the western and central Kazakhstan, northwestern Uzbekistan, surrounding area of Balkhash Lake, mid-upper reaches of Ili River and Qilian Mt. The vegetation growing season accumulated precipitation showed a significant decreasing trend at a rate of-2.61mm/a (p<0.05) over the last decade. The overall precipitation was less than normal since2005. The precipitation mainly increased in Qilian Mt.and western Pamirs. Significantly reduction area of precipitation was mainly distributed in Western Kazakhstan, surrounding area of Balkhash Lake, Altai Mt. and northern Taklimakan Desert.4. The lag time of vegetation growth in response to temperature variation was about one month, while the lag time did not significantly exist for vegetation growth to precipitation in the arid region of the Central Asia. The sensitivity of vegetation growth to temperature and precipitation varied with different vegetation types. The shurbland was more sensitive to climatic factors, followed by grassland, wetland and forests. Vegetation growth had the most significant negative correlation with average temperature from May to June, and it also had the most significant positive correlation with accumulated precipitation from April to July. The significant negative and positive correlation area between vegetation growth and temperature occupied about 24.93%and0.48%of the vegetated lands. The negative correlation area between vegetation growth and temperature was mainly distributed in the Caspian Lowlands, Turgay Plateau, Turgay Depression, western Kazakh Hills, western Balkhash Lake, Syr Darya River Basin, Ili River Basin, southern Turkmenistan, western Pamir, Irtysh River Basin and central Tianshan Mt. The positive correlation area between vegetation growth and temperature was mainly distributed in lowlands and high mountains. The significant positive and negative area between vegetation growth and precipitation occupied about24.85%and0.52%of the vegetated lands. The positive correlation area between vegetation growth and precipitation was mainly distributed in the Turgay Depression, Kazakh Hills, Irtysh River Basin, River, mid-upper reaches of Ili River, Syr Darya and Amu Darya River downstream, northern Tianshan Mt. and Qilian Mt. The negative correlation area between vegetation growth and precipitation was mainly distributed in the oases of Tarim Basin.5. The degradation of vegetation growth in the arid region of the Central Asia over the last decade was affected by temperature increase and precipitation decrease. The warm and dry climate had stronger influence on vegetation growth in low than high altitude areas. The contribution rates of temperature, temperature and precipitation, and precipitation to vegetation growth were24.92%,14.48%and28.97%respectively. The effects of precipitation on vegetation growth mainly reflected in its increase of soil moisture. Influence of temperature on vegetation growth had two aspects. On one hand, high temperatures led to higher plant respiration than photosynthesis; On the other hand, rising temperature led to enhanced evapotranspiration which caused soil drought, and vegetation growth was restricted.6. The contribution rates of human activities to vegetation growth in the arid region of the Central Asia over the last decade were about31.61%, in which the positive and negative effects of human activities to vegetation growth were about77.82%and22.18%. Positive effects of human activities on vegetation growth occurred in northwestern China, northern Kazakhstan and western Tianshan Mt. due to a series of implementation measurements related to the ecological environment such as farmland reclamation in deserts and conversion of farmland to forests and grassland. Negative effects of human activities on vegetation growth concentrated in central and southeastern Kazakhstan, southeastern Turkmenistan and Altai Mt. because of forest harvesting, farmland abandonment, urban construction, overgrazing and fire.
Keywords/Search Tags:the arid region of the Central Asia, vegetation growth condition, distribution pattern, spatial-temporal difference, climate change, human activities
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