Ecological uniqueness of plant communities as a conservation criterion in lake-edge wetlands

Conservation biologists can use several criteria, such as species richness and incidence of range-restricted species, to prioritize allocation of conservation efforts and identify sites of high ecological value. Recently, ecological uniqueness has been proposed as an effective criterion because it allows the identification of species assemblages that are complementary and irreplaceable. This study aims to determine whether the ecological uniqueness of plant communities is an adequate criterion for assessing the conservation value of ecosystems. We used two large datasets of lake-edge wetlands located in southern Quebec (Canada) to achieve this objective. We computed the local contribution to beta diversity (LCBD) as a measure of uniqueness and evaluated its relationship to more common conservation criteria (richness, rarity and specialization of species, as well as site area and connectivity) using Pearson correlations and independent effects. Uniqueness decreased with increasing plant species richness, suggesting a conservation trade-off, whereas it increased with the percentage of rare and disturbance-sensitive specialist species. Highly unique sites were mostly of high conservation value, although the overall integrity of the landscape affected the quality of sites singled out as unique. The species composition of unique sites should be examined closely to determine their conservation value and other criteria should be used in conjunction with uniqueness to identify which set of sites to protect in a given landscape.