Temporal And Spatial Dynamics Of Forest Greenness Anomaly And Its Driving Factors

Meteorological events(e.g.droughts,windstorms,etc.)can affect the growth of forests by affecting the physiological processes of trees or by direct physical damage,leading to a reduction in forest leaf area over a certain period of time.Here,we employ multiple satellite observations to investigate the negative deviation of the forest leaf area index(LAI)from the average state and refers to this phenomenon as greenness anomaly.Since the implementation of afforestation and national greening policies in China,forest cover and LAI have increased rapidly.At the same time,the proportion of planted forests in the forest area has also increased significantly,but artificial forests are more sensitive to extreme events than natural forests as they are more prone to forest greenness anomalies.Therefore,explore the spatial distribution,trends of forest greenness anomalies and their dominant drivers in China is beneficial to provide references for policymaking community.Based on this,this paper used various remote sensing and meteorological data(i.e.LAI,land cover data,meteorological data,forest fire hot-spot data)to analyze the forest greenness anomalies from 2003 to 2018,and further explored the spatial-temporal trend of forest greenness anomalies.To investigate the impact of different disturbance types on forest greenness anomalies by combining drivers such as droughts and windstorms,and to reveal the impact of extreme weather events on China’s forests.Results showed that:(1)China’s forest greenness anomalies increased significantly from 2003 to 2018,as evidenced by a significant increase in the overall area of greenness anomalies and an increase in the intensity of them in some regions of southern China.From the perspective of the spatial patterns,there was a significant increase in the area of forest greenness anomalies in the southwest,central and southern regions,and the intensity of forest greenness anomalies in south-central China increased significantly.These results indicate that the enhancement of forest greenness anomalies in China is generally dominated by the southern region.(2)The intensity of greenness anomalies increases with the frequency of greenness anomalies,and there is a sudden increase in the intensity of anomalies with increasing frequency.However,the spatial distribution of extreme greenness anomalies and very high frequency greenness anomalies do not overlap,and the highest intensity of greenness anomalies occur in the region where moderate frequency greenness anomalies occur.(3)The spatial distribution of wind-driven forest greenness anomaly intensity shows a spatial pattern of high in the southern,northern and eastern regions and low in the middle and western regions.The areas with a high frequency of forest greenness anomalies are mainly concentrated in the southeastern and northeastern coastal areas.The intensity and area of forest greenness anomalies under the influence of windstorms did not showed significant changes between 2003 and 2018.The intensity of greenness anomalies that dominated by drought showed obvious spatial patterns,with higher in northeast and southwest of China and lower in other regions.The spatial distribution of greenness anomaly also exhibited distinct spatial patterns that higher in the south and lower in the north,and the anomaly frequency was concentrated in the southwest of China.The forests were gradually affected by drought during the period 2003-2018.Both the intensity of forest greenness anomalies and the area of greenness anomalies under the influence of drought showed an increasing trend.(4)Forest greenness anomalies in different regions of China are dominated by a few extreme climatic events.Drought-dominated areas are concentrated in northern Yunnan Province,where droughttriggered fires have a more serious impact on greenness anomalies in the northern of the Greater Hinggan Mountains.Areas dominated by windstorms are mainly distributed in the southern coastal areas of Fujian Province,most of Taiwan Province,northern Hebei Province and northern Inner Mongolia.(5)The drought sensitivity of different forest types being the highest in broadleaf forest,followed by coniferous and mixed forests.This is mainly due to the dominant role of drought intensity in the performance of forest anomalies compared to vegetation sensitivity,with different forest types having an inconsistent distribution of drought sensitivity and overall greenness anomalies during drought.