special issue - URBANISTICA INFORMAZIONI | 1 As regards the United Nations Convention on Biological Diversity, ratified by Italy by Law no. 1994/124, an ecosystem is “a dy- namic complex of plant, animal and micro- organism communities and their nonliving environment interacting as a functional unit”. Ecosystem goods and services, univo- cally defined as “ecosystem services”, repre- sent the benefits human populations derive, directly or indirectly, from ecosystem func- tions (Costanza et al., 1997). When trying to assess the ecosystem ser- vices of natural resources the usual vision is always based on qualitative approaches. We all know how important the environmental services are and that they are worth protect- ing and restoring. But it is really difficult to compare the costs, which can be easily re- vealed in monetary terms, to the benefits, which are always in the abstract world of ideas. Actually, it is impossible to compare apples to oranges. It would be of huge util- ity for planning and managing to have tools that bridge this gap. A quantitative approach is needed for a bet- ter spatial planning and a more efficient management of natural resources. It has to be emphasized that the Strategic environmental assessment (SEA) of Manage- ment plans (MPs) for Natura 2000 sites has to be regarded as an assessment exercise con- cerning not merely a single node of the eco- logical network (that is, a single Natura 2000 site), but rather the network as a whole. SEA can be defined as a formal, systemic and comprehensive process in which environ- mental impacts produced by a policy, a plan or a program and by its alternatives (if any) are assessed. Such process mainly centers around the preparation of a written report, whose outcomes must be made available in the public domain and incorporated in the decision-making process (Thérivel et al., 1992). In this conceptual framework, SEA is not a simplistic and sectoral descriptive analysis of the impacts that the implemen- tation of the policy, plan or program would produce on environmental resources. Rath- er, it is a process that must be intertwined with the definition, approval and imple- mentation of the policy, plan or program, hence with its strategic dimension (Brown & Thérivel, 2000; Kørnøv & Thissen, 2000). In other words, SEA is ontologically entwined with the decision-making process, in which – since the very first stages – sustainability goals must be integrated with goals aiming at social and economic development. This also means that SEA is intrinsically connected to sustainability because it estab- lishes environmental-protection related ob- jectives, and therefore it acts as a sustainabil- ity-oriented plan which becomes part of the planning process itself. As a consequence, the SEA of a spatial plan also comprises the continuous verification of the compliance of the policy, plan or program to environmen- tal objectives that are not, or should not be, different to those pursuing economic and social development. This is of particular im- portance with reference to the definition of conservation measures, including the prepa- ration of MPs, as SEA can help integrate sus- tainability within MPs objectives and can be Sessione speciale Ecosystem services and urban and regional planning 01. Corrado Zoppi, Ignazio Cannas, Sabrina Lai Ecosystem services and urban and regional planning