TREEPACT - The Impacts of Insects and Pathogens in Urban Contexts in a Changing Climate

Urban trees and forests contribute greatly to society and human well-being. A healthy canopy cover of the urban forest (i.e. all trees within an urban area) is vitally important to help cities adapt to raising temperatures. The urban forest can also provide important opportunities for recreation, sources of food, ornamental resources, carbon sequestration, and valued landscapes. Hence, in recent years, the greening of towns and cities has received prominence in many parts of the world, including the expansion of urban tree canopy cover. However, the ability of urban trees to make these contributions is increasingly threatened by growing incidences of disturbances, including tree pests / pathogens, storms, droughts, and fire. Climate change frequently exacerbates such disturbances as they can weaken trees and make them more susceptible to disturbances, creating complex interactions. TREEPACT focuses on tree pests /pathogens. Urban trees can be affected by a wide range of native and non-native pests / pathogens, including invertebrates, bacteria, viruses, fungi, and vertebrate pests. Prominent examples are the fungal pathogen Phytophthora ramorum, the oak processionary moth (Thaumetopoea processionea), canker stain (Ceratocystis platani), and the Asian long-horned beetle (Anoplophora glabripennis). These may affect trees through defoliation, boring, staining, or loss of branches; they may also cause tree mortality or have negative impacts on human health (e.g. dermatitis). Pest / pathogen outbreaks may also affect the ability of trees to contribute to climate mitigation and adaptation, especially their capacity to cool the urban temperature, and their ability to help mitigate against soil erosion, landslides and flooding. Weakened trees are also more susceptible to the effects of increased wind damage and fire under climatic changes. Climate change, evolving international trade, and declining biodiversity are likely to further increase the risks posed by tree pests / pathogens. Trees stressed through droughts can be particularly vulnerable to pests and diseases. Therefore, a thorough assessment and quantification of tree pest / pathogen impacts, risk perceptions and responses in the urban context is key to achieving science-based outcomes for effective urban green space, tree, and forest policy and management. The results will be valuable to urban policymakers, planners, managers, and researchers and will help to climate proofing European cities through a healthy tree canopy cover.
Urban trees need to be better protected and supported, especially in times of climate change, in order to be able to continue to contribute to a healthy urban environment and human well-being.