Remote Sensing-based Identification Method And Driving Force Analysis Of Forest Ecosystem Degradayion In North China

The northern forest ecosystem is an important forest resource in China.However,due to the early rough development model and the fragile ecological environment,the forest ecosystem was severely damaged.After that,it was improved under the projects of Three North Shelterbelt,Returning Farmland to Forestry and Grass,and Beijing-Tianjin-Hebei Wind and Sand Control Project.However,with the change of the whole climatic conditions and the interference of afforestation and other factors,it is necessary to understand and grasp the current status of the forest.This article uses a trend analysis method based on full time series and based on time series changes to understand the spatial distribution of the health status of northern forest ecosystems,and conduct field surveys of degraded forest ecosystems.The regional scale driving force analysis method was used to explore the contribution rate of meteorological factors and human factors to vegetation growth,and the single factor driving force analysis method based on survey data was used to discuss the contribution rate of natural environmental factors,forest elements and human disturbance factors to forest health.In order to scientifically manage the health of the forest ecosystem,the study found: 1.The years of significant mutations in the forest ecosystem NDVI on each sub-climatic zoning of the study area are concentrated in 2004-2013.The area of the significant mutation grid is the largest in 2009,and the cumulative cumulative percentage of the mutation grid is in the middle III south temperate zone> I north Temperate>II medium temperate.From the overall view of the study area,there is spatial heterogeneity in the health of the forest ecosystem before and after the mutation.Before the mutation(from 2000 to 2009),the areas of significant improvement were mainly concentrated in the southern temperate zone of III,and the areas of significant degradation were concentrated in the intermediate temperate zone of II and the northern temperate zone of I;after the mutation(2009 to 2018),the areas of significant improvement were mostly distributed in II.The temperate zone and the northern temperate zone of I are markedly degraded in the southern temperate zone of III.From the perspective of the type of forest ecosystem,degradation mainly occurs in broad-leaved forests,accounting for 1.75% of the total forest area,and improvement areas are also located in the broad-leaved forest areas,accounting for 20.42% of the total area.2.The identification method based on time series mutation established in this paper is more accurate than the traditional identification method based on long time series to accurately identify the dynamic changes of forest ecosystem.3.Different forest types have different responses to environmental factors and human disturbance factors.Coniferous forests(Pinus sylvestris var.mongolica and Larch)in the survey site are positively correlated with temperature and precipitation;birch trees(mainly birch)in broad-leaved forest are negatively correlated with temperature and positively correlated with precipitation.In coniferous forests,Pinus tabulaeformis and the upper,middle and lower layers of soil water content showed a negative correlation,while larch showed a positive correlation;broad leaves(birch and chestnut)were negatively correlated with the soil water content of each layer.Coniferous forests(Pinus tabulaeformis and Larch)are suitable in slightly acidic and neutral soils,and there is no significant difference in the p H of the upper,middle and lower soils;the p H of the birch and the upper,middle and lower soils are negatively correlated(p H: 4.5 ~7.5),the optimal p H is 5.5;the chestnut has a positive correlation with the upper soil p H and a negative correlation with the middle and lower soil p H.The optimal planting density of coniferous forests and broad-leaved forests has an optimal range.Among them,the optimal planting density of coniferous forests is about 1650 plants/ha,and the optimal planting density of broad-leaved forests is about 1100 plants/ha.From the perspective of human disturbance factors,proper felling is helpful for the growth of denser larch and birch trees,but it has side effects on Chinese pine;in addition,the impact of roads,coniferous and broad-leaved forests respond The trend is the same,the longer the distance from the road,the better the growth.4.The climate factor in the regional scale provides a positive contribution rate for vegetation dynamics,but the contribution rate is not high,and the contribution rate is mostly 25%.The contribution rate of human activity factors to the dynamic changes of vegetation is higher than that of meteorological factors,and the contribution rate in most regions is 100%.However,human activities are dominated by negative contribution rates in cities,and urban vegetation is destructive.