Offset measures and development projects : the conservation of protected species under the EU Birds and Habitats Directives. Conservation Biology 27: 1335–1343

Biodiversity offsets are intended to achieve no net loss of biodiversity due to economic and human development. A variety of biodiversity components are addressed by offset policies. It is required that loss
of protected species due to development be offset under the EU Habitats and Birds Directives in Europe. We call this type of offset a species-equality offset because the offset pertains to the same species affected by the
development project. Whether species equality can be achieved by offset design is unknown. We addressed this gap by reviewing derogation files (i.e., specific files that describe mitigation measures to ensure no net
loss under the EU Habitats and Birds Directives) from 85 development projects in France (2009–2010). We collected information on type of effect (reversible vs. irreversible) and characteristics of affected and offset
sites (i.e., types of species, total area). We analyzed how the type of effect and the affected-site characteristics influenced the occurrence of offset measures. The proportion of species targeted by offset measures (i.e., offset species) increased with the irreversibility of the effect of development and the conservation status of the species affected by development (i.e., affected species). Not all effects on endangered species (International Union for Conservation of Nature Red List) were offset; on average, 82% of affected species would be offset. Twenty-six percent of species of least concern were offset species. Thirty-five percent of development projects considered all affected species in their offset measures. Species richness was much lower in offset sites than in developed sites even after offset proposals. For developed areas where species richness was relatively high before development, species richness at offset sites was 5–10 times lower. The species-equality principle appears to have been applied only partially in offset policies, as in the EU directives. We suggest the application of this principle through offsets is highly important for the long-term conservation of biodiversity in Europe.

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