Do United States protected areas effectively conserve forest tree rarity and evolutionary distinctiveness?

Because forest tree species face serious threats including insect and disease epidemics, climate change, and forest fragmentation and conversion, prioritizing species and forests for conservation is an essential management goal. This paper describes a species prioritization approach that incorporates both the rarity of species, because of the increased vulnerability associated with rare species, and their evolutionary distinctiveness (ED), a measure of evolutionary originality. Rarity and ED scores, and scores for the two combined, were calculated for 352 North American forest tree species. A weak but significant phylogenetic signal was associated with species rarity. The scores were used to weight species importance values on approximately 130,000 forest inventory plots across the conterminous United States. The resulting plot-level estimates of conservation value were employed to identify geographic hotspots of forests with high conservation value, and to assess whether forests with protected status effectively conserve rarity and ED. Rarity hotspots were detected in California, the Southwest, central Texas, and Florida. Hotspots of ED included locations along the Pacific Coast, in the Northern Rockies, and in scattered eastern locations. Protected forest areas across the United States effectively conserve ED, but not rarity. In fact, rarity was lowest in areas with the highest protection, and highest in areas with no or unknown protected status. Multiple-use protected areas had higher ED, but not rarity, than restricted-use protected areas. Protected area effectiveness varied across the country. Such spatially explicit assessment approaches can help determine which forests to target for monitoring efforts and pro-active management activities.