The international trade in live plants is a major pathway for the introduction of invasive tree pests and pathogens, resulting in environmental and economic damage. Many recently introduced pests and diseases were not known to be harmful, or unknown to science, and were not regulated before they invaded, indicating that the current system to identify harmful species does not provide sufficient protection from invasions by alien pests and pathogens. A novel way of identifying potentially harmful organisms for regulation is by monitoring European trees planted in regions that export plants to Europe. The Action will 1) establish a global network of scientists and regulators in countries where sentinel nurseries could be established from seed or where there are botanical gardens or arboreta with exotic trees, 2) develop common protocols for the monitoring and identification of pests and 3) explore ways to regulate the establishment of such nurseries and the use of data collected through them. This Action will also bring together detailed information about the international trade in trees and the environmental value of native trees in Europe. The Action will produce written, electronic and workshop outputs, as well as at least five short-term scientific missions per year.