Biodiversity Impact Assessment of roads: an approach based on ecosystem rarity Davide Geneletti * Department of Civil and Environmental Engineering (DICA), University of Trento, Via Mesiano, 77, 38100 Trento, Italy Received 1 July 2002; received in revised form 1 November 2002; accepted 1 November 2002 Abstract Biodiversity has become one of the central environmental issues in the framework of recent policies and international conventions for the promotion of sustainable develop- ment. The reduction of habitat worldwide is currently considered as the main threat to biodiversity conservation. Transportation infrastructures, and above all road networks, are blamed for highly contributing to the decrease in both the quantity and the quality of natural habitat. Therefore, a sound Biodiversity Impact Assessment (BIA) in road planning and development needs to be coupled to other commonly considered aspects. This paper presents an approach to contribute to BIA of road projects that focuses on one type of impact: the direct loss of ecosystems. The first step consists in mapping the different ecosystem types, and in evaluating their relevance for biodiversity conservation. This is based on the assessment of ecosystem’s rarity. Rarity is a measure of how frequently an ecosystem type is found within a given area. Its relevance is confirmed by the fact that the protection of rare ecosystems is often considered as the single most important function of biodiversity conservation. Subsequently, the impact of a road project can be quantified by spatially computing the expected losses of each ecosystem type. To illustrate the applicability of the methodology, a case study is presented dealing with the assessment of alternative routes for a highway development in northern Italy. D 2002 Elsevier Science Inc. All rights reserved. Keywords: Biodiversity; Ecosystem; Road; Rarity; Space occupation; Impact 0195-9255/02/$ – see front matter D 2002 Elsevier Science Inc. All rights reserved. doi:10.1016/S0195-9255(02)00099-9 * Tel.: +39-0461-882685; fax: +39-0461-882672. E-mail address: davide.geneletti@ing.unitn.it (D. Geneletti). www.elsevier.com/locate/eiar Environmental Impact Assessment Review 23 (2003) 343 – 365