Spatiotemporal Variation Of Vegetation Phenophase And Its Response To Climate Change In Micang Mountains

Phenology is a phenomenon that organisms appear in annual cycle under the influence of environment,which is of great significance to understand the relationship between vegetation and climate.This paper explored the spatiotemporal variability of vegetation phenophase and its response to climate changes in Micang Mountains,a classic example of Qinling-Daba Mountains,China.Based on the MODIS NDVI data from 2003 to 2018,the vegetation phenological parameters of the Micang Mountains were obtained by the Savitzky-Golay filtering method and the dynamic threshold method.The Theil Sen slope and Mann-Kendall trend test,combined with vegetation types,were used to analyze quantitatively the temporal and spatial variation of phenophase.Sensitivity method and partial correlation method were used to analyze the relationship between phenology and climate.The main conclusions are as follows.(1)The results showed that the start of the growing season(SOS)ranged mainly from 80^th to 125^th day,and it delayed with the increasing elevation about 0.6 days every100 m.The end of the growing season(EOS)ranged mainly from 250^th to 300^th day.The length of the growing season(LOS)ranged mainly from 130 to 210 days.The EOS and LOS had 2000 m boundary with the elevation changes,except for low-altitude areas where the phenophase fluctuated greatly affected by human activities.The phenophase below it significantly delayed or shortened with the elevation,and the phenological changes above it tended to be gentle.The SOS showed an advanced trend with-0.47 d/a,accounting for 74.03%of the total area,and significantly advanced area accounted for15.01%(P<0.1).The EOS showed an early trend totally with an advanced range of-0.22 d/a,and only 4.91%of the area passed the significance test(P<0.1).The LOS slightly extended with a rate of 0.26 d/a and the area with an extended trend accounts for53.25%.The SOS of evergreen forest vegetation was later than that of deciduous forest vegetation in the same vertical belt.The advanced trends of SOS in grassland and evergreen broad-leaved shrub forest were the most obvious,and their changed rates were-0.80 d/a and-0.71 d/a,respectively.The most obviously advanced trend of EOS appeared in the coniferous and broad-leaved mixed forest and deciduous broad-leaved forest.(2)In the spring(March,April and May)climate change in Micang Mountains,the temperature in March increased most obviously,with an increase range of 0.09?/a.The effective precipitation in April showed an increasing trend in the past 16 years,with a larger change range of 0.22 mm/a.The sunshine in spring was decreasing,and the sunshine hours in March decreased the most,which was-0.86 h/a.In the climate change of late summer and early autumn(August,September and October),the average temperature in August increased most obviously,which was 0.12?/a.The interannual variation of effective precipitation in late summer and early autumn showed a decreasing trend,with the largest decrease in September.The sunshine hours in August showed an increasing trend with the largest variation range of 3.82 h/a,while the sunshine hours in September and October showed a decreasing trend.(3)The correlation between vegetation SOS and meteorological factors in May was weak.There was a strong negative correlation between vegetation SOS and temperature in March,sunshine in March and effective precipitation in April.The results showed that temperature and sunshine in March and effective precipitation in April were the main meteorological factors affecting vegetation growth.The correlation between vegetation EOS and sunshine in August,temperature in September,effective precipitation and sunshine in October was strong,and the response of EOS to meteorological factors in October was particularly significant.The results showed that sunshine and effective precipitation are the main influencing factors of vegetation EOS,and the influence of temperature is relatively weak.(4)The vegetation SOS was highly sensitive to the meteorological factors in March and April.In March,the SOS advances by 0.17 days for every 1?increase in temperature,and the SOS advances by 0.07 days for every 10 hours increase in sunshine hours.In April,the SOS advances by 0.24 days for every 1?increase in temperature,and the SOS advances by 0.25 days for every 1 mm increase in effective precipitation.The sensitivity of vegetation EOS to temperature in September,effective precipitation in October and sunshine in October was the highest.In September,the EOS was advanced 0.14 days for every 1?increase in temperature.In October,for every 1 mm increase in effective precipitation,the EOS advances by 1.16 days,and for every 10 hours increase in sunshine hours,the EOS delays by 0.15 days.