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Urban ecosystems are the areas where built infrastructure covers a large proportion of the land surface but the main source of ecosystem services provision is the green infrastructure. This provision is very much dependent on the particular combination of green spaces such as parks or vegetation belts and paved areas such as buildings and streets. The spatial arrangement of these elements is an important parameter which could be used for the assessment of the ecosystem condition in the urban areas. An integrated index of spatial structure is proposed which incorporates built types and land cover from the Local Climate Zones (LCZ) concept with urban ecosystems' classes developed on the basis of MAES typology. An algorithm has been developed for index generation using an urban ecosystems' database and remote sensing data. The index is used to define vegetation cover in urban ecosystems and assess their condition as a part of the assessment framework. It is also applied in the assessment of several ecosystem services through quantification of ecosystem services' indicators or as an indicator in a complex assessment. The results show that, although most urban ecosystems in Bulgaria are assessed as moderate and good condition, very few of them have very good condition and about 3.5% have very bad condition. The highest scores are defined for urban green areas while the lowest are for transport networks. The use of an integrated index in urban ecosystem services' assessment is represented by examples for global and local climate regulation. The results are used to develop maps of ecosystem services supply capacity for selected cities. The overall analysis indicates that the urban ecosystems in Bulgaria have a moderate to good capacity for local climate regulation and moderate to low capacity for global climate regulation. The integrated index of spatial structure provides an appropriate basis for characterisation and assessment of the urban ecosystems condition and ecosystem services following the requirements of the EU Biodiversity Strategy and the MAES process. The proposed approach enables the internal heterogeneity of the urban ecosystems at national level to be defined, this being one of the main challenges in studying urban ecological systems.
