Assessing environmental services and disservices of urban street trees. an application of the emergy accounting

The urban green infrastructure (UGI), with special focus on street trees, is a very complex engineered ecosystem which plays an important role in generating ecosystem services and, if improperly managed, a number of dis-services to be prevented. This study applies the Emergy Accounting method to the cost and benefit evaluation, in order to establish a non-monetary “supply-side” assessment framework capable to assign an environmental value to each kind of services provided by urban forests and other green infrastructures. Further, the study classifies urban street tree integrated valuation framework into ecosystem services, avoided cost for human health and biodiversity damage, growing/maintenance cost and ecosystem dis-services. In a like manner, the interaction among the three different component flows in street tree ecosystems (costs, benefits and associated dis-services) are compared by means of a ternary diagram. Taking the case of the street ecosystem in Beijing, China, eleven typical urban tree species, including oak, maple, Chinese ash and linden, are selected for services and dis-services evaluation. Results show that, in general, UGI provides a large number of services to urban population, but it may also generate dis-services affecting human health, well-being and biodiversity when tree selection, location and management is not accurate. Results may help improve management practices which enhance the overall ecosystem service provision by urban forests not only in Beijing as case study but also in other cities by means of appropriate management.