Impacts Of Climate Change On Vegetation In Qilian Mountains From2000to2011

At present, more and more evidences indicate that global climate is in a period of rapid change, and there were significant change especially in the last decade. What influence can rapid change climate bring to vegetation which is a sensitive part of terrestrial ecosystem? There were many studies having reported that climate warming as the main feature of climate change has led to remarkable changes in vegetation growth. However there were large regional differences for those variations. Therefore, still more evidences on regional scales are needed for us to fully understand the impacts of climate change on vegetation ecosystems. At the same time, it is vital for us to understand the influence of climate change on vegetation at present to predict climate change in the future as well as its impacts on ecology environment. On the basis of above background of scientific study, the spatial pattern and the spatio-temporal variability of temperature and precipitation as well as vegetation in the Qilian Mountains (QLM) from2000to2011was studied based on MODIS NDVI datasets and records (comprising the mean monthly temperature and monthly precipitation) of37meteorological stations in the study areas. The method of correlation analysis was utilized to analyse the impacts of climate change on regional vegetation. Then, the connection between vegetation variation and topography factors (elevation, slope, aspect, etc.) was researched. On the basis of diverse vegetation types sample regions, the interannual variation of main vegetation types in QLM from2000to2011was researched. There was heterogeneity of responses of different regional vegetation to climate change. Moreover, the phenology of grassland from2000to2011was researched on the site scale to discuss the spatial pattern and the spatio-temporal variability of phenology of grassland (including vegetation green-up onset date (GUD) and dormancy onset as well as the length of growing season). The impacts of temperature and precipitation on grassland was transformed to potential green-up onset date, which was employed to discuss the effects of climatic factors (containing temperature and precipitation) on green-up onset date of grassland. On the basis of above analysis, the main conclusions of this paper are as follows:There was a distinct increasing trend for average annual temperature and annual precipitation in the QLM from2000to2011with an significant increase in temperature in September and that in precipitation in August and October respectively. The temperature in the edge of QLM was higher than that in the middle-western mountainous areas. The precipitation decreased gradually from eastern to western QLM.In addition, we found that vegetation with higher mean NDVI value from May to September were mainly distributed in the vertical zone (2700—3600m), on the side (NE41°—SE120°) of the mountain, with lower slope (10°—14°). The overall trend for vegetation was ameliorated with changing rate (0.003/year and-0.018/year respectively) during2000-2011. There were26.71%ameliorated vegetation and2.27%degenerated vegetation respectively. The ameliorated vegetation mainly located at western and southern adge of QLM, while the vegetation degradation distributed at middle-eastern QLM dominantly.The areas with ameliorated vegetation predomiantly distributed in vertical zones (2700—3600m and3900—4500m) on the shady side (SW220°—E60°) of the mountain with lower slope, while that degradation dominantly appears in vertical zone (2500—3100m) on the sunny side (NE85°—SE190°) of mountain with higher slope.There was different interannual variation trend for different types of vegetation in QLM from2000to2011. There was an amelioration trend for cropland and desertied grassland as well as alpine meadow, in contrast, that for grasslands, shrub and broadleaf forest, needleleaf forest as well as submountain shrub and meadow is not significant.The mean GUD and dormancy onset as well as length of growing season for grassland in QLM during the period from2000to2011were98days,266days,168days respectively. The grassland in the southwestern and middle stations turned green-up later than that in the northern and southeastern stations. The dormancy onset for grassland for the northern and middle as well as southwestern stations was comparatively earlier. The growing season length for grassland in northern stations was much longer, while that for grassland in southwestern and middle stations was comparatively short. Along with elevated altitude, GUD for grassland got delayed, while, length of growing season for grassland shortens. However there was no distinct connection between dormancy onset and altitude.GUD for64.7%of the stations were advanced with the rate (7days per decade), however dormancy onset for64.7%of the stations were delayed with the rate (8days per decade). The growing season length for grassland in82.4%of the stations were delayed with the rate (10days per decade). There was an obvious advanced trend for stations with high altitude, however there were no distinct relation between the trends of dormancy date and growing season length and altitude.The growth of vegetation in the ameliorated areas was mainly controlled by precipitation (from May to August) and mean temperature (from April to August), on the contrary, that of vegetation in the degradation areas was primarily restrained by average temperature (from April to September). The distinct spatial heterogeneity of vegetation variation was controlled by the background hydrothermal conditions, which was mainly influenced by climate change and topography factors as well as local hydrological conditions. There was a close connection between the growth of main vegetation types and precipitation in the study area, while temperature was the vital climatic factor for some special vegetation types (such as alpine meadow and needleleaf forest) which located at the region with high altitude or sufficient water resource.GUD in70.6%stations was chiefly influenced by precipitation. Those were mainly controlled by temperature distributed at middle QLM. The GUD of grassland in the areas with low attitude was mainly controlled by precipitation, however, dominant element for those in the areas with high attitude depend on local moisture and thermal conditions principally. Meanwhile, there was a close relationship between GUD and precipitation at the stations with high HAI. Contrarily, the main climatic factor is temperature for GUD in the stations with low HAI was temperature.