Monitoring Spatio-temporal Pattern Of Ecosystem Functional Types Based On Landsat Time Series Data

The energy flow,circulation of materials and informational linkage constitute the basic function of the ecosystem.Ecosystem function is an essential component of biodiversity.Compared to the structural and compositional characteristics of ecosystem,ecosystem functions sometimes respond faster to the environmental changes,thereby they are regarded as one of the most sensitive indicators in global ecosystem change monitoring.Ecosystem functional types(EFTs)are defined as land surface areas with similar response to environmental conditions and ecosystem processes,which reflect the spatial heterogeneity of ecosystem functions.EFTs provide an important basis for assessing the impact of environmental and anthropogenic changes on terrestrial ecosystems.Satellite remote sensing provides the effective technical approach to identify and monitor EFTs changes at regional scale.In this study,based on the Landsat time series remote sensing images,taking an typical area of the western Songnen Plain,Northeast China that is sensitive to global changes as an example,the key indices and their derived variables of ecosystem functional classification were selected and calculated.An identification method of ecosystem functional types based on modified Fuzzy C-Means(FCM)clustering algorithm is proposed to classify the ecosystem functional types in the study area.The spatial heterogeneity and variation of ecosystem function in the last 10 years were analyzed,and the relationship between ecosystem functional types and structural types was revealed.Firstly,Landsat satellite remote sensing images in the growth season(April to October)of 2008 and 2017 were used to retrieve Albedo,Land Surface Temperature(LST)and Normalized Difference Vegetation Index(NDVI)and regarded as the key indicators for ecosystem functional classification.The mean,maximum,and range of each index were calculated,characterizing the ecosystem functional features of carbon gains,energy and water balance.Secondly,the Self-organizing Map(SOM)was used to obtain the clustering centers based on the ecosystem function index parameters images.The obtained clustering centers of SOM were input into the FCM clustering algorithm as the initial clustering centers,and ecosystem functional types in 2008 and 2017 were identified for the study area.The change of EFTs' diversity patterns was analyzed by Shannon-Wiener index and Simpson's diversity index.Finally,we discussed the consistency and difference relationship between EFTs and land cover types by using Correspondence Analysis(CA).The results showed that the SOM and FCM clustering method could be used to accurately identify the EFTs at finer scales based on the ecosystem functional parameters of energy and matter exchange extracted from Landsat data.From 2008 to 2017,the spatial heterogeneity characteristics of ecosystem functions in the study area were significantly different,and EFTs' diversity increased over past 10 years.The same EFTs might corresponded to a variety of land cover types,while a structural types presented different energy and material exchange characteristics.There was a complex correspondence between the functional and structural types of ecosystems.The quantitative identification of EFTs and monitoring and analysis of spatial pattern change of ecosystem function in the temperate semi-arid and semi-humid typical region would provided basic information and reference basis for understanding regional ecosystem functional diversity and ecosystem service integrity,developing strategies for natural resource management and biodiversity conservation,and assessing environmental and anthropogenic impacts.