RECONSTRUCTED JULY TO SEPTEMBER NDVI OF PAST 565 YEARS IN BALUNTAI REGION OF CENTRAL TIANSHAN MOUNTAINS BASED ON PICEA SCHRENKIANA
The Normalized Difference Vegetation Index(NDVI)is crucial for analyzing vegetation dynamics and its response to climate;however,for the Tianshan Mountains,the current short-term NDVI datasets are too short to reflect long-term trends in vegetation.Therefore,in this study,a total of 86 cores(1 to 2 cores per tree)were taken from 49 Picea schrenkiana trees in the Baluntai region(42.80°～42.83° N,86.45°～86.47° E)in the summer of 2020.Then,a tree-ring width chronology was developed after cross dating.The time span of the reliable chronology was 1455～2020,the expressed population signal(EPS)of the chronology samples was greater than 0.85,the average correlation among trees for the common overlap period among series(Rbar)was greater than 0.6,and the chronology signal-to-noise ratio(SNR)was 155.73.The Baluntai standard(STD)chronology showed a significant correlation with the observed NDVI derived from NOAA polar-orbiting satellites from July to September(r=0.69,n=39,p＜0.001).Subsequently,we reconstructed the variations in the July to September NDVI in the study area over the past 565 years(i.e.,1455～2019 A.D.).The reconstruction accounted for 46％of the variation in the NDVI from July to September during the calibration period(1981～2019 A.D.).The results showed that the study area experienced five periods of high vegetation cover(1460～1473 A.D.,1542～1577 A.D.,1724～1749 A.D.,1842～1 873 A.D.,and 1988～2019 A.D.)and eight periods of low vegetation cover(1492～1541 A.D.,1577～1595 A.D.,1707～1723 A.D.,1750～1784 A.D.,1806～1841 A.D.,1873～1890 A.D.,1904～1925 A.D.,and 1944～1987 A.D.).Furthermore,vegetation growth peaked during 1988～2019.Comparisons with other studies revealed spatial heterogeneity in NDVI fluctuations.The vegetation of the middle Tianshan Mountains has exhibited an increasing trend over the past three decades,while that of the West Tianshan Mountains has shown a declining trend.Precipitation is the main factor influencing the NDVI in this study area,where precipitation is primarily influenced by anomalies in sea surface temperature(SST)and teleconnection patterns.Specifically,increased SSTs in the Indian Ocean combined with positive phase East Atlantic(EA)teleconnections can lead to an increase in precipitation in the Tianshan Mountains,thereby promoting vegetation growth.The Baluntai NDVI reconstruction indicates that the NDVI observation data in recent decades may underestimate the impact of precipitation on vegetation in the Tianshan Mountains.However,our study area is not sufficient to represent the entire Tianshan Mountains,and more studies are needed in the future to better understand the dynamics of vegetation growth change in the Tianshan Mountains.This study provides basic data for future dynamic evolution prediction of vegetation in the Tianshan Mountains.
NETL
NSTL
万方数据
