Spatiotemporal variation of vegetation coverage in Qinling-Daba Mountains in relation to environmental factors
The Qinling-Daba (Qinba) Mountains,a key ecological zone of terrestrial ecosystem,has experienced a significant change of vegetation coverage in recent years,which is characterized by rapid climate change.Using MODIS-NDVI dataset,the current study investigated the patterns of spatiotemporal variation of vegetation coverage in the Qinba Mountains during the period 2000-2014.In addition,possible environmental factors affecting this variation were identified.Sen+Mann-Kendall model and partial correlation analysis were used to analyze the data,followed by the calculation of Hurst index in order to analyze future trends of vegetation coverage.The results of the study showed that (1) the Normalized Difference Vegetation Index (NDVI) of the study area revealed a significant increase during 2000-2014 (linear tendency 2.8％/10a).During this period,a stable increase was detected before 2010 (linear tendency 4.32％/10a),followed by a sharp decline after 2010 (linear tendency-6.59％/10a).(2) In terms of spatiotemporal variation,vegetation cover showed a "high in the middle and low in surroundings" pattern.High values of vegetation coverage were mainly found in the Qinba Mountains of Shaanxi Province,while low values of vegetation coverage were mainly observed in Longnan,Tianshui,and Gannan prefectures occupied by arable land.(3) The area covered with vegetation was larger than the degraded area,accounting for 81.32％ and 18.68％ of the total area,respectively.Piecewise analysis revealed that 71.61％ of the total study area showed a decreasing trend in vegetation coverage during 2010-2014,of which,the extremely significant and significant decrease accounted for 6.38％ and 3.45％,respectively.(4) The reverse characteristics of vegetation coverage change were stronger than the same characteristic in the Qinba Mountains.Some 46.89％ of the entire study area is predicted to decrease in future,while 34.44％ of the total area will follow a continuous increasing trend.(5) The change of vegetation coverage was mainly attributed to the deficit of precipitation.At the same time,vegetation coverage during La Nina years was larger than that during E1 Nino years.Statistical analysis showed that positive and negative anomaly pixels accounted for 28.37％ and 71.63％,respectively during E1 Nino years and 80.48％ and 19.52％,respectively during La Nina years.(6) Human activities can induce ambiguous effects on vegetation coverage:both positive effect (through the implementation of the ecological restoration project) and negative effect (through urbanization) were observed.
NETL
NSTL
万方数据
维普
