The Timberline Of Qinling Mountains And Its Response To Climate Change

The IPCC fifth assessment report pointed out that global temperature will continue to become warm, and the development of human society will be impacted. Qinling Mountains is a large mountain nature of the strong transition in the middle of China, it is an imported geography dividing line between the north and south of China, it has an apparent vertical distribution band of climate and vegetation, The timberline is the monitor of climate change.The study on Qinling Mountains timberline plays an exemplary role and prospective significance on the study of climate change and terrestrial vegetation ecosystem changes adaptations. This paper aims to study the trend of temperature variation and regularity under the big background of Qinling Mountains; it would like to study the change status of forest vegetation and the relationship between forest vegetation and climate change in Qinling Mountains. It also tried to find the quantitative relationship between them to predict the impact of future climate change on Qinling Mountains alpine timberline. The following progress and conclusions were obtained:(1)The temperature showed an upward trend, and the mutation happened in the 90’s of the last century in recent 55 years on north-south of Qinling Mountains.On the season, the temperatures in spring and winter were rising more obvious of Qinling Mountains. The temperature increased in North Slope of Qinling Mountains was greater than the extent of the temperature at southern slope in 55 years. The temperatures in summer rendered obvious downward trend at North Slope, and has a slight increase at the southern slope, temperature of the fall rised faster at the southern slope. The temperature showed a declining trend at the area of 74.31% of North Slope former the mutation, the significant temperature increases accounted for 95.2% after the mutation.(2)The average annual precipitation showed no significant decreasing trend in 55-year of Qinling mountains. The annual precipitation mutation happened in 1971 and 1979 at north and south slopes of Qinling.For 55 years, the annual precipitation showed a trend of decrease in the north and south slope of Qinling Mountains. The degree of reduction of the annual precipitation in northern is greater than south slope of Qinling Mountains. The annual precipitation changes rate of the northern slope was -11.339mm/10a, the value in the southern slope was-4.607mm/10a at the south slope. On the season, the precipitation in spring and autumn showed no significant decreasing trend at Qinling Mountains, precipitation in summer and winter has increased gradually. The extent of summer precipitation in the southern slope increased greater than the north Slope, The extent of the increase in winter precipitation was greater than the southern slope of the northern slope; After mutation minimize precipitation decreased.(3) The remote sensing image classification and NDVI data was combined to extract timberline area of Qinling Mountains. It was found that the timberline is sensitive to altitude and climate change.The maximum likelihood method was used to classify the specific timberline zone of Qinling Mountains. Taibai Mountains mainly ranged in 3430-3450m, the timberline height of Niubeiliang, Bingjingding and Guangtoushan Mountain mainly distributed in about 2600-2700m.Tai Baishan timberline area’s average annual temperature change rate was 0.428 ℃/10a, the annual temperature change rate Niubeiliang timberline was 0.25℃/10a, Bingjingding timberline’s annual temperature change rate was 0.362℃/10a, The annual temperature change rate of Guangtoushan timberline was 0.298℃/10a;The temperature mutations points were occurred in 1998,1990,1993 and 1990 at Taibai Mountains, Niubeiliang Mountains, Bingjingding area and Guangtoushan timberline. Nearly 33 years, the overall area of Taibai Mountains, Niubeiliang, Guangtou Mountain, Bingjingding timberline vegetation area had some reduced in 1980-2013 years as temperatures rose. The temperature at Taibai mountains timberline area increased by 2 ℃ as a whole; The temperature isotherm in 1980 and 2013 are nearly coincidence at timberline area of Guangtou Mountains and Niubeiliang mountains.(4) NDVI showed an upward trend at the typical timberline area of Qinling Mountains, it mutated to 2005 of Qinling Mountains’NDVI in 33-years, NDVI mutations point at Taibai Mountains timber was 2009NDVI showed an upward trend at Qinling Mountains in 1982-2013, the change rate was 0.036/10a. Nearly 32 years, the area of NDVI increased significantly accounting for 52.45% in total of Qinling mountain, the region increased no significant accounted for 39.75%. NDVI mutations point occurred in 2005.NDVI increased rate at timberline of Taibaishan, Niubeiliang, Guangtou Mountain, Bingjingding were 0.014/10a,0.042/10a,0.017/10a,0.02/10a during the year of 1998-2013. NDVI mutations point at Taibai Mountains timber was 2009.While it showed many mutation points at the timberline area due to the effect of human.(5) NDVI of Qinling mountains and the timberline area were sensitive to climate change, the correlation between temperature and NDVI was significantly higher than the correlation between precipitation and NDVI.It showed positive and negative response between the year max NDVI and the temperature in different period, but it showed significant positive correlation with the temperature of July. The vegetation at timberline area was mainly significantly influenced by winter low temperature. The temperature in Jan. to Mar. was significantly positively related to the NDVI in Mar. at the timberline of Taibai Mountains. The NDVI of Apr.. Jun. and Aug. showed significantly positive to the temperature in Jan. at Niubeiliang timberline. The temperature in Feb. had a significant correlation to NDVI in Apr..(6) The growth of vegetation could inhibit when the temperature reaches a certain critical temperature. The max NDVI of year in the part region of Qinling mountains will be restrained when the average temperature in July exceeded 21.51 ℃ in Qinling mountains, while the vegetation at timberline of Taibai mountains were controlled by low temperature.It had the best correlation of July temperature and annual maximum NDVI of Qinling Mountains.21.51 C is critical temperature of July temperatures produce inhibitory effects on NDVI at Qinling Mountains. By using the threshold value analysis:the threshold range of April NDVI influenced by the temperature of before 12 months is-4.45℃--1.05℃ of Taibai Mountain timberline.(7) The predict of future NDVI changes in timberline area of Qinling Mountains based on BP neural network, when the temperature variation rate in future 3 years exceed 0.3℃/10a,the vegetation in timberline will be badly effect.Using the BP neural network model to forecast the future NDVI changes of Qinling Mountains and timberline area, the vegetation growth status will drop under the condition of temperature variation rate raised 0.4 ℃ overall the whole Qinling Mountains. When the temperature change rate reaches 0.2℃/10a, the NDVI in the next three years will drop. The annual NDVI probably began to decline in the next three years of Guangtou mountain under the condition of regional temperature change rate reaches 0.1 ℃, it shows that the temperature rising will affect mutual adjustment of future climate-vegetation ecosystem.