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 (Halpin 1997). 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 (Dreistadt et al. 1990, McKinney 2002). Urban forests have been decimated because of a lack of species diversity in the face of pest introductions (Poland and McCullough 2006, Santamour 2004). Widespread acknowledgement of this problem has led to guidelines focused on diversification of the urban forest (Santamour 2004). 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 (Whitlow and Bassuk 1987). 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 (Gill et al. 2007, Kirshen et al. 2008). 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.