Study On Peak Phenology Of Vegetation Growth And Its Influence On Vegetation Productivity In Inner Mongolia

Vegetation phenology refers to the natural phenomenon of plants affected by climate or other environmental factors,and is the most sensitive and accurate indicator of climate change.GPP(Gross Primary Production)is the total amount of organic matter produced by green plants absorbing atmospheric CO2 through photosynthesis,which drives the seasonal and interannual changes of atmospheric CO2 content,reflects the productivity of terrestrial ecosystems under natural conditions,and plays an important role in the global carbon cycle.In this study,the data of MOD13A2,MOD17A2H and meteorology(temperature,precipitation,sunshine hours)were used,and the method of Logistic curve curvature extremum of cumulative NDVI,the fitting method of univariate sixth polynomial and time series harmonic analysis were used to extract the Start of Growing Season(SOS),Peak of Season(POS)and peak of vegetation.Furthermore,the effects of the greening period and meteorological factors in Inner Mongolia on the peak phenology of vegetation growth and annual total productivity were discussed,and the main driving factors for the changes of the peak phenology of vegetation growth and annual total productivity were identified.The research results show that:(1)The average annual peak of vegetation growth in Inner Mongolia was 0.52.The peak value of vegetation growth decreased gradually from northeast to southwest.The change of vegetation growth peak value was obvious,and the trend was mainly increasing,and the annual increase rate was 0.004(P<0.01).The peak value of vegetation growth in Inner Mongolia mainly fluctuated from 0.46(2001)to 0.56(2012),and fluctuated greatly.In most areas of Inner Mongolia(92.8%),the peak period of vegetation growth mainly ranged from 195th to 235th days,that is,from mid-July to late August,and the average peak period of vegetation growth was 214.2 days.Spatially,the peak growth period is gradually delayed from northeast to southwest.The peak period of vegetation growth in Inner Mongolia showed an insignificant advance trend,and the advance slope was 0.005 days/year.Precipitation is the main factor affecting the peak value of vegetation growth in Inner Mongolia.It is positively correlated with spring precipitation,summer precipitation and pre-seasonal precipitation,negatively correlated with summer temperature and pre-seasonal temperature,and negatively correlated with sunshine duration in spring,summer sunshine duration and pre-seasonal sunshine duration.The peak value of vegetation growth in Inner Mongolia was positively correlated with the return to green,that is,with the delay of return to green,the peak value of vegetation growth would increase.The peak vegetation growth period was positively correlated with spring temperature,summer temperature and pre-seasonal temperature,and was mainly affected by the scale of the first two and six months of the season,but negatively correlated with spring precipitation,pre-seasonal precipitation,summer sunshine duration and pre-seasonal sunshine duration.The peak period of vegetation growth in Inner Mongolia was positively correlated with the greening period,accounting for about 77.1%of the total area.(2)There was a significant spatial difference in vegetation productivity in Inner Mongolia,which decreased gradually from northeast to southwest,and the average productivity was 2.66kg C/(m~2a).The annual total productivity increased significantly(P<0.01),the annual increase rate was 0.035kg C/(m~2a).The vegetation productivity of forest,grassland,farmland and shrub increased.The vegetation productivity in Inner Mongolia was negatively correlated with annual mean temperature and summer temperature,and positively correlated with spring temperature.There was no significant difference between the vegetation productivity and autumn temperature.The vegetation productivity in Inner Mongolia is positively correlated with annual total precipitation,spring precipitation,summer precipitation and autumn precipitation,that is,the increase of precipitation will improve the vegetation productivity.The vegetation productivity in Inner Mongolia was negatively correlated with annual total sunshine duration and summer sunshine duration,and there was no significant difference between the vegetation productivity and spring sunshine duration and autumn sunshine duration.There was a positive correlation between vegetation productivity and greenness.(3)In Inner Mongolia,the vegetation productivity was positively correlated with the peak vegetation growth,and the area with extremely significant positive correlation accounted for 86.9%of the total area,while the vegetation productivity was mainly negatively correlated with the peak vegetation growth period,that is,with the delay of the peak vegetation growth period,the vegetation productivity decreased.From the perspective of different vegetation types,the peak growth periods of forest,grassland,farmland and shrub are positively correlated with productivity,while the peak growth periods of forest,grassland,farmland and shrub are negatively correlated with productivity.