ABSTRACT
This chapter defines terms associated with tree risk in the urban environment, explores options for systematic evaluation of trees, outlines one commonly used system and briefly discusses risk mitigation. Trees can pose a variety of risks, which are categorized into two basic groups: conflicts and structural failures. The chapter focuses primarily on structural failures. A primary goal of tree risk assessment is to provide information about the level of risk posed by a tree over a specific time period. The two primary approaches to risk assessment are quantitative and qualitative. Each has advantages and limitations, and each may be appropriate with different objectives, requirements, resources, and uncertainties. Both the quantitative and qualitative approaches are valid when applied properly with reliable data and valid assumptions. Tree risk assessments can be conducted at different levels and may employ various methods and tools. Three levels of tree risk assessment have been defined: limited visual; basic; and advanced.
