Study On Temperature And NPP Reconstruction Of Qinling Mountains Based On Tree Rings

As an important geographical boundary of China,Qinling is particularly sensitive to the response of tree growth to climate change.It is of great significance to study the climate change in Qinling to understand the global climate change and mechanism.In the existing research,the Qinling Mountains are generally the study of climate single point reconstruction.The width of the tree rings is generally used as a proxy for climate agents to directly correlate with climatic elements.However,there are few researches on temperature reconstruction on the whole surface of Qinling Mountains.There are few studies on the use of tree-ring width index as validation index for simulating NPP in ecosystems.In the study,we applied a revised PPR?point-by-point regression?method to obtain the search coefficient chart based on the weighted average values of the temperature-related coefficients and the search circles.The tree-ring width chronologies significantly correlated with the air temperature of the meteorological stations in the Qinling Mountains region were selected to reconstruct the average temperatures from February to April during 1835 to 2013 in 32 meteorological stations.Considering the variations between the north and south slopes,the reconstructed sequences of the meteorological stations were interpolated by the Kriging based on DEM.The average values of the reconstructed sequence of the meteorological stations were used as the historic temperatures from February to April during the latest 200 years in the Qinling Mountains region.Because Mt.Taibai Mountain is the highest peak of the Qinling Mountains and the most sensitive area to climate change,this paper selects the Mt.Taibai Mountain area of Qinling Mountains as the research area.In this paper,the Biome-BGC model was used to simulate the Net primary productivity?NPP?of the Larix chinensis forest ecosystem during 1960—2013.The relationship between NPP value and climatic factors as well as the response of Larix chinensis radial growth to climate change were analyzed.The conclusions are as follows:?1?During the recent 200 years,the Qinling Mountains region had experienced four colder periods:1835¹869,1874¹886,1918¹925 and 1960¹998;three warmer periods which were 1887¹917,1926¹959 and 1999²013.?2?Wavelet analysis indicates that there were multi-scale cycles such as 2 to 3 years,2 to 5years,7 to 11 years and 11 years in the reconstructed sequence.The overall trend of temperature change in the North-south slope of Qinling Mountain is consistent from late winter to early spring and 1959 is the turning point.?3?The temperature in north slope changed more sharply than whichin the south slope before1959,while the more severe opposite characteristic was showed after 1959.The interpolation results show that the temperatures of the Qinling Mountains were significantly affected by the topographic factor.The range of temperature about 1?in the colder period is lower than which in the warmer period.In addition,there was a rising trend of the lowest temperatures in the warmer period.The interpolation results show significant differences between the north and south slopes.The ranges of temperature in north slope were declining trend?except the period of 1960 to 1998,the range of temperature change was 16.57??,while there was no significant change in the south slope.?4?The Biome-BGC model was used to simulate the Net primary productivity?NPP?of the Larix chinensis forest ecosystem during 1960—2013.The relationship between NPP value and climatic factors as well as the response of Larix chinensis radial growth to climate change were analyzed.The results showed that the average NPP of Larix chinensis on the northern slope at Mt.Taibai Mountain was 305.33 g C m^-22 a^-1,320.71 g C m^-22 a^-1on the southern slope during 1960-2013 years.The NPP values of both north and south slope increased.The rising rate of the northern slope(0.47 g C m^-22 a^-1)was lower than that of the southern slope(1.29 g C m^-22 a^-1).However,the range of NPP fluctuation was larger at the lower limit of the distribution of Larix chinensis.The NPP value of the Larix chinensis of the northern slope decreased gradually with the increase of the altitude.On the northern slop,the NPP amplitude of the low altitude was higher than that of the high altitude,while the southern slope showed no obvious change.?5?The simulated NPP values of most sampling points were consistent with the inter annual variation trend of tree-ring width index,and the correlation was significant.The correlation between the simulated NPP and the meteorological factors showed that the connection between the growth and the temperature of the growth season was significantly higher than that of the precipitation,indicating that temperature in the growing season was the limiting factor of the growth of the Larix chinensis.As a result,the tree-ring data could be used to validate simulation results based on Biome-BGC model..Climate change,as an important factor,controls the habitat of Larix chinensis.Therefore the growth of Larix chinensisas well as the changes of NPP are heavily influenced.