Establish or encourage new mixes of native species

Future conditions in urban areas are likely to become especially extreme, with higher peaks in temperature and moisture than might be seen in nonurban landscapes. However, considerable uncertainty exists in what future conditions will be, especially at the site level. Thus, encouraging new mixtures of native species and regionally, but not locally, native species in forest communities and plantings could help these systems adapt and maintain ecological function. This approach could also discourage invasion by exotic invasive species. Managers may need to prioritize diversity (both in terms of species as well as functional groups and phylogenetic lineages) over historical species combinations to increase community resilience.

Urban areas already contain a broad mixture of species that come from outside of the area. Because these species evolved in different climates, they will probably have very different tolerances to future climate conditions. In the urban landscape, fostering species transitions is less a question of whether to assist migration of species from other geographies; this is already a common occurrence. Instead, it is more about deciding when and where to incorporate species into forests and plantings in different habitats and land uses. These species could be nonnative taxa or species that are regionally native, that is, those from the same region but not currently growing at that particular location. In addition to increasing the climatic resilience of the urban landscape, urban forests could also facilitate the migration of species that will be favored under future climate to new habitats at or beyond the edges of their current range.