Establish reserves to maintain ecosystem diversity

Although urban areas are highly developed, some natural areas may remain to serve as reserves. Reserves are traditionally defined as natural areas with little to no harvest activity that do not exclude fire management or other natural disturbance processes. In a highly fragmented urban area, this definition may need to be adjusted to reflect the realities of what is possible on small tracts of land surrounded by development.

Promoting species and structural diversity is as important in urban forests as in nonurbanized forest landscapes, if not more so. Urban areas are highly susceptible to introduction of nonnative pests and pathogens and often exhibit high occurrence of invasive plant species. Urban forests have been decimated because of a lack of species diversity in the face of pest introductions. Widespread acknowledgement of this problem has led to guidelines focused on diversification of the urban forest. However, urban areas contain difficult sites, and only a limited set of tree species may be able to tolerate the conditions of many of these sites. Species and structural diversity are especially important as a climate adaptation strategy because urban habitats (both natural areas and urban land uses) are likely to be stressed in the future in many ways, some of which will be unforeseeable. A diverse set of species, carefully selected to match the urban environment, will be more likely to maintain adequate forest cover and ecosystem services under a changing and increasingly variable climate.