| Vegetation plays an important role in regulating the balance of the ecological carbon cycle and the climate system.Monitoring vegetation distribution,changing trends and driving factors can reveal the relationship between vegetation and atmospheric,soil and other ecological factors.The land surface pattern of Longitudinal Range Gorge Region(LRGR)with towering mountains and deep valleys arranged vertically side by side has significant effects on physical environments and eco-geographical differentiation in Southwest China.Based on the MODIS EVI,combined with vegetation map,meteorological data and DEM data,through the techniques of the trend line analytical method,grey correlation analysis,and correlation analysis,the temporal and spatial changes of vegetation EVI is studied in the LRGR during 2001-2015.Results show the following conclusions:(1)The mean annual EVI of vegetation in the LRGR is 0.36.The spatial distribution of vegetation EVI is increasing from north to south.The value of EVI in Dehong County,Simao County and the southwestern of Lincang County are high.The low value of EVI is mainly distributed in the northern of Nujiang County,the western of Changdu County,and the southwestern of Ganzi Prefecture.There are similar spatial distribution characteristics of EVI in different seasons,and some differences in the isolated region.In addition,the EVI of vegetation in the LRGR in each season shows a decreasing trend with increasing altitude.(2)The EVI value in the LRGR fluctuated slightly,with a range of 0.30 to 0.34.The degraded areas of the annual mean vegetation EVI are mainly scattered in Nujiang Prefecture and the southern of Dali County.The increased areas are mainly distributed in the west of Lincang County and the east of Wenshan County.In addition,the change trend of EVI in different seasons is insignificantly decreased.The largest area of the EVI in summer,autumn,and spring showed a degenerative,unchanged,and increased trend respectively.The change trend of the EVI is totally different in different elevation intervals.(3)There is a time-delay effect on response between the EVI and climatic factorsin the LRGR.The EVI has a good correlation with air temperature at the same time series and the precipitation at the previous time series both in the spring and the growing season.The summer vegetation EVI has the closest relationship with precipitation in the same period,while air temperature is lagging by two months.In the autumn,the air temperature and the precipitation both show a lag of two months.(4)The EVI of mean annual,growing season,summer and air temperature are roughly negatively correlated,mainly distributed in Nujiang County,the eastern of Lijiang County and the northern of Dehong County;and positively correlated with precipitation,mainly distributed in the northwestern part of Dali County,the eastern part of Lincang County and the southern of Chuxiong.The EVI shows a negative correlation with air temperature and precipitation in spring.The correlation between autumn vegetation EVI and air temperature and precipitation is weak.(5)The change of vegetation EVI in LGRG mainly affected by non-climate driving factors.The climate-driven area of the vegetation EVI accounts for 11.05%,in which there are 5.26% and 3.21% area impacted by air temperature and precipitation respectively.The strongly driven of air temperature and precipitation combined is distribute sporadically in the study area.In general,the influence of climatic factors on the growth of EVI in different seasons from strong to weak is summer,growing season,spring and autumn. |
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