Alter forest structure or composition to reduce risk or severity of wildfire

Risk of wildfire is likely to increase in urban natural areas in much the same fashion as in nonurban forests. However, due to their location in the wildland-urban interface, these areas are of especially high priority in risk reduction. Developed landscapes in the wildland-urban interface may incorporate somewhat different principles of risk reduction through altering forest structure and composition, such as the Firewise methods of creating defensible space around structures and using less-combustible landscaping (see http://www.firewise.org).

Climate change may increase the likelihood and risk of severe disturbances, which will have significant effects on urban trees. Urban tree failures can cause severe property damage, electric outages (Simpson and Van Bossuyt 1996), and injuries or fatalities to human beings. From 1995 to 2007, there were 407 tree-related human fatalities in the United States (Schmindlin 2009). In developed urban sites, these potential impacts make it essential for risk to be managed at the individual tree level. Factors such as tree form, size, condition, species, wind speed, pruning, and wood material properties affect tree resistance to storm damage (Duryea et al. 2007, Francis 2000, King 1986, Putz et al. 1983). Urban foresters must balance the risk of tree failure, including the danger to people and property, with the loss of benefits when shade trees are removed. This is especially important for large trees, which provide greater benefits and take a long time to replace (Miller 1997). Priorities are somewhat different in urban natural areas, where avoiding risk is more associated with minimizing disturbances that are potentially devastating to tree communities, especially those that could affect urban population and the built environment (e.g., fires spreading from natural areas).