Changing Characteristics Of Vegetation Growth And Its Response To Spring Phenology And Climate In Cross-Border Areas Of China,North Korea And Russia

Vegetation phenology accurately models the dynamics of plant ecosystems and reflects vegetation growth to a certain extent.The relationship between spring phenology and vegetation growth needs to be further explored as the advancement of spring phenology will affect vegetation growth by influencing the length of the vegetation growing season,which in turn affects vegetation growth and thus terrestrial ecosystem productivity and carbon sink function,but also exacerbates summer drought,which may reduce vegetation growth.The cross-border area of China,North Korea,and Russia is located in Northeast Asia,a region where the borders of China,North Korea,and Russia meet,and is a special ecological barrier functional area,which has a certain guarantee and buffer role for the border ecological security of the three countries.The region is widely distributed in mountainous areas,with diverse vegetation types and high coverage,and has an obvious vertical distribution pattern of vegetation.However,there are few studies on the relationship between vegetation dynamics and climate in the cross-border region of China,North Korea and Russia,and the influence process of spring phenology on the stages of vegetation growth still needs to be effectively explained.In this paper,the spring phenology of vegetation was evaluated from 2001 to 2020 using the polynomial maximum method based on the MODIS NDVI dataset with the effect of snow removed,taking the cross-border region of China,North Korea and Russia as an example.The vegetation growth in different growing season periods was defined as the current monthly NDVI average.The spatial and temporal distribution characteristics of spring phenology and vegetation growth were also analyzed based on the Sen trend analysis and MK trend test methods,and the response relationships between vegetation growth and spring phenology and climate factors in different growing season periods were investigated using the partial correlation analysis method.The following conclusions were drawn from the study.(1)The multi-year spring phenology averages in the cross-border areas of China,North Korea and Russia in the past 20 years were mainly between the 90 th and 120 th days,accounting for 90.4% of the study area.There is a clear heterogeneity in spatial distribution,with late spring phenology in the eastern part of the study area in the Sikhot Mountains and the Changbai Mountains,and early spring phenology in the eastern side of Liaoning Province,China,and the area near the Yellow Sea Province,Korea.In addition,79% of the regions showed an early spring phenology trend(19.75% of which were significant).The spring phenology of the whole region advanced at the rate of-0.17 days/year(P>0.05).Areas with late spring phenology showed a delayed trend,while on the contrary,areas with early spring phenology showed an early trend.(2)The vegetation growth in the cross-border areas of China,North Korea and Russia in the last 20 years was the lowest in the first month of the growing season,and the vegetation growth was mainly between 0.3 and 0.6,accounting for 87.6% of the whole study area.Vegetation growth was highest in the fourth month of the growing season,with vegetation growth concentrated between 0.8 and 0.9.At the regional scale,vegetation growth in all three subregions of China,Korea,and Russia showed an increase followed by a decrease as the growing season period progressed.Vegetation growth in most areas showed an increasing trend.In all three subregions,the rate of increase of vegetation growth decreased and then increased as the season progressed.The increase rate reached the maximum in the sixth month of the growing season.(3)The main factors influencing the vegetation growth in different periods of the growing season in the Sino-Russian transboundary region differed.From the first to the third month of the growing season,the increase in vegetation growth was mainly due to the advancement of spring phenology,while from the fourth to the sixth month of the growing season,it was mainly due to the increase in temperature.The situation was the same on the Chinese side.The main factors of vegetation growth in the first three months of the growing season in Korea were spring phenology,temperature and radiation,and the fourth to the sixth months of the growing season were temperature.In Russia,the main control factors for vegetation growth in the first three months of the growing season were spring phenology,while the fourth to sixth months of the growing season were temperature,precipitation,and air temperature,respectively.(4)The influence of spring phenology on vegetation growth fluctuates and decreases as the growing season progresses.Spring phenology promoted vegetation growth from the first to the fifth month of the growing season in the cross-border areas of China,Korea and Russia,but suppressed vegetation growth in the sixth month of the growing season.This study adds to the vegetation growth in the cross-border region of China,North Korea and Russia,and further clarifies the extent of spring phenology and climate influence on the dynamic process of vegetation growth,which not only provides a reference for vegetation growth simulation models,but also further increases the understanding of how climate affects vegetation ecosystems and,to a certain extent,improves the understanding of ecosystem carbon cycling.