Spatial-temporal Changes Of Vegetation And Responses To Temperature In Taibai Mountain

Taibai Mountain, the peak of Qinling Mountains, locates in the middle hinterland of Qinling Mountains, and the ridge line of Qinling Mountains walks through the Taibai Mountain. Based on Taibai Mountain Nature Reserve as the study area, and remote-sensing images in 1988,2000,2006 as the information source and site survey, we implemented supervised classification to the vegetation of study area, and studied the spatial and temporal variation of different landscape vegetation and the alpine timberline of Taibai Mountain. Then, based on NDVI datas of Taibai Mountains Nature Reserve which derived from remote sensing we analyzed the spatial-temporal changes of vegetation index for different vegetation zones during the past 30years, as well as their responses to temperature. The studies of vegetation variation in different levels in Taibai Mountain nature reserve, which not only reveal the responses to temperature in forest ecological system in Taibai Mountain under the global warming, but also can provides typical case for the response of climate change on forest ecological system, and provide theoretical support of biodiversity conservation and warter source protection. We arrive at some conclusions and progresses as follow:(1)Spatial-temporal changes of different landscape vegetation in Taibai MountainThe area of vegetation types in Taibai Mountain nature reserve had undergone changes certaintly, during of past 22 years from 1988 to 2009. Larix chinensis forest, shrub meadow, birch forest and non-forest land are presented increase tendency, while abies fargesill and oak forest are presented decrease tendency. The trend of alpine non-forest land mainly transfer to shrub meadow and shrub meadow transfer to Larix chinensis forest, which showed shrub meadow have the trend of extending to non-optimum growth range and Larix chinensis forest have the trend of intruding shrub meadow.In addition, elevation is the biggest factor of impacting the variation of vegetation inTaibai Mountain nature reserve, and the vegetation in upper altitude is more sensitive to changes in temperature than the lower latitude's, which made the optimum growth range of shrub meadow and abies fargesill have shifted upward, and the upper limits and the lower limits of Larix chinensis forest's optimal growth range have somewhat expanded, while the distribution range of birch forest and oak forest have shifted downward during the past 22 years. All these changes explain that the temperature have affected then alpine vegetation of Taibai Mountai. Slope and aspect have little effect to the variation of vegetation.(2) dynamic changes in the alpine timberline of Taibai Mountain The timberline of Taibai Mountain have 42.74% presented upward trend and have 25.79% changeless trend in the region during of past 22 years; Based on the analysis of NDVI changes in three alpine timberline samples, we concluded that NDVI changes in three samples remarkably. The pixels where NDVI significantly increased account for 29.88% of the total pixles of sample area, especially in the edge of Larix chinensis forest and shrub medow. Climate warming did affect alpine timberline.(3) The spatial-temporal changes of vegetation of Taibai Mountain Nature ReserveThe results showed that the area where the average NDVI in May was higher than 0.2 accounts for 89.5% of the total Taibai Mountain, but because the elevation difference is very apparent, vegetation index NDVI value also showed obvious vertical difference, and the value of NDVI is generally over 0.2 for the low altitude regions while ranges from 0.2 to 0.5 for the high altitude regions, which indicate a larger area's vegetation protection be very good.No changes was found in about 56% of total pixles, while the pixles where NDVI increased and decreased significantly during the past three decades account for 23.87% and 19.39%.(4) Responses of vegetation index to regional temperature change of Taibai MountainThe annual average temperature of Taibai Mountain region show clear ascendant trend, and the linear increase trend for 0.35℃/10a; Vegetation NDVI is more sensitive to changes in temperature along with the elevation of the rise, and the vegetation in upper altitude is more sensitive than the lower latitude's. With the elevation of the rise, in the same vegetation, the ratio of significant positive correlation of vegetation index and temperature gradually higher than the ratio of significant negative correlation.