Maintain trees and remove hazards to reduce severity or extent of wind and ice damage

Storm damage from wind and ice can be particularly problematic in urban areas because of the risk to life and property, and both could become more severe because of changes in climate. When an urban forest undergoes severe disturbances such as strong wind and ice storms, downed limbs and trees can result in loss of electric service, displacement of families and businesses, and blockage of emergency vehicles. Structural pruning can mitigate these safety and infrastructure issues by fostering mechanically strong branch structure. Although intensive hazard management is common in developed areas, it may also take place in urban natural areas where individual tree management is necessary or possible, such as in high-use areas or near infrastructure. Even when trees are maintained, however, some limb and tree failure can occur. Promptly removing these hazards can help mitigate the severity of the disturbance and associated negative public reaction.

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, and injuries or fatalities to human beings. From 1995 to 2007, there were 407 tree-related human fatalities in the United States. 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. 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. 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).