There are existing financial, legal, and natural barriers preventing improvements to the urban forest, and such challenges may become more severe as the climate, politics, and economy change. Addressing these challenges and forecasting their impacts will be a complex but necessary component of sustainable urban forest management (SUFM). The main impacts affecting HRM’s urban forest include impacts to aquatic systems and watershed health, climate change, conflicts with infrastructure, development, imperviousness, invasive species, lack of knowledge, ownership, peri-urban forests and the urban-rural gradient, redevelopment, and species and age-class diversity. Protecting the health and integrity of urban watersheds constantly intertwines with the management of the urban forest. Perhaps the most critical relationship is the role of forested riverbank (riparian) buffer zones in protecting aquatic systems. Forested riparian buffers regulate flooding, reduce the impacts of sedimentation, erosion, and nutrient loading on watercourses, regulate the temperature of adjacent watercourses, and provide important wildlife habitat.
Climate change is a major threat to HRM’s urban forest and urban forests around the world, and is a key source of uncertainty in urban forest management. Potential climate change impacts include more frequent and severe storms and hurricanes, drier and hotter growing seasons (a stressor for urban trees), more invasive pests, and warmer winters with a higher occurrence of damaging freeze-thaw cycles. Moreover, the warming climate is changing the range of tree species, which is shifting northward (and higher in altitude in some places). This will influence the types of trees that can survive in HRM. The two principal concepts related to managing a resource in a changing climate are mitigation and adaptation. Adaptation refers to management actions that reduce the vulnerability of systems to the changing climate by adapting the system to anticipated future conditions and likely impacts. Adaptation is much more important for reducing the threat of climate change to the urban forest than mitigation.