Spatio-temporal Evolution Of Ecological Conditions In Coastal Areas Of China And Its Influential Factors

Global climate change seriously affects the diversity,stability and balance of ecosystems,resulting in changes in global ecological conditions.It not only affects the changes of human living environment,the development of agricultural production,social progress and economic development,but also has an important impact on ecosystems such as forest ecosystems and water resources.This study took the coastal areas of mainland China(CAMC)with high economic and urbanization development as the research area.Based on land use/cover change(LULC)data and Normalized Difference Vegetation Index(NDVI)data set,the temporal and spatial characteristics of ecological conditions from 1980 to 2015 were analyzed.Using ecological grade index(EG_i)evaluation method and Mann-Kendall trend analysis method,this study explored the differences between the ecological conditions obtained by the two methods.At the same time,K-means clustering analysis method was used to explore the regional differences of ecological conditions in 116 prefecture-level cities in the study area.Besides,combined with elevation(DEM)data,distance from the coast data and vegetation types data,the elevation,sea-land gradient characteristics and different vegetation types characteristics of ecological conditions in CAMC were analyzed.Based on meteorological data(temperature and precipitation),socio-economic data(GDP and population),the driving factors of ecological conditions were explored through partial correlation analysis.In addition,as an important agricultural production area in our country,we should actively understand the impact of agricultural activity intensity(such as fertilization,irrigation,etc.)on vegetation in CAMC.And further explored the relationship between regional ecological conditions and economic development.The main conclusions of this study are as follows:(1)Based on the regional ecological conditions reflected by LULC data,the ecological grade index of CAMC increased from 4.60 in 1980 and 1990 to 4.61 in 2015.The ecological grade index is a negative index,that is,the larger the ecological grade index value,the worse the ecological condition.Therefore,the ecological conditions in CAMC was basically stable but slightly worsened.The spatial distribution of ecological conditions in CAMC were roughly bounded by the Hangzhou Bay,with high in the south and low in the north.At the same time,the ecological conditions in CAMC had obvious vertical zone characteristics,which presented a"rising-falling-rising"pattern with the increase of elevation.The land-sea gradient characteristics of the regional ecological conditions were obvious,too.As it gets farther and farther away from the coastline,the ecological conditions presented a"high-low-high-low"pattern.The two characteristics of the ecological conditions were mainly affected by the area proportion changes of land use types and human activities.K-means clustering analysis showed that the cities with good ecological conditions were mostly distributed in the south,while the cities with moderate and poor ecological conditions were mostly distributed in the north.(2)Based on ecological conditions reflected by NDVI,33.71%areas of CAMC showed a significant trend of greening(vegetation restoration)and 8.88%showed a significant trend of browning(vegetation degradation).Compared with the annual NDVI greening rate of 0.0006/a(p<0.01),the vegetation greening rate in spring in CAMC was higher at 0.0021/a(p<0.01).This may be related to the early stimulation of photosynthetic rate and promotion of vegetation growth under the background of global warming.However,the minimum rate of greening in summer in CAMC was 0.0006/a(p<0.01).This indicated that the NDVI data set synthesized by the maximum value synthesis method may not be sufficient to reflect the growth status of vegetation in CAMC.In addition,greening was dominant at lower and middle elevations as the accelerated nitrogen deposition driven in cultivated plants enhanced vegetation growth.However,browning mainly occurred at high elevation with the warming temperature that may exacerbate moisture stress to plants.Socioeconomic factors,such as economic production and human populations,were the most important factors for vegetation changes.Besides,the agricultural intensity and land use/cover change also had influence on vegetation variations.The contribution of climate conditions to the vegetation browning or greening in CAMC was limited.K-means clustering analysis showed that the cities with good ecological conditions were mostly distributed in the south and some areas of Liaoning and Hebei provinces.While the cities of with moderate ecological conditions were mostly distributed in the south of Hebei province,the middle of Shandong province and the north of Zhejiang province.(3)By standardizing EG_i and NDVI of the study area,the comparative analysis showed that NDVI was generally higher than EG_i in CAMC,with the distribution area accounting for 97%.However,the proportion of distribution area with EG_i higher than NDVI was small,only accounted for 0%-1%.This phenomenon reflected the uncertainty of ecological conditions based on EG_i and NDVI.For example,the assignment of EG_i to different land use types was greatly influenced by human subjectivity.K-means clustering analysis showed that the ecological conditions in the south of CAMC was better than that in the north,which is consistent with the analysis of ecological conditions in the first and second parts.The development of cities in CAMC should further optimize the industrial structure,improve the efficiency of resource utilization,and promote the coordinated development of economic and environmental conditions.