Can we protect forests by harnessing variation in resistance to pests and pathogens?

Our natural and commercially planted forests are currently facing an unprecedented threat from pests and pathogens. On the principle that 'prevention is better than cure', the policies and practices that influence forest management must aim to prevent epidemics rather than to fight them once they are established. Vigilance and strict security at national borders aim to prevent entry of pests and pathogens but experience shows us that this does not achieve total exclusion. Consequently, to improve the long-term resistance and resilience of tree populations to infection or herbivory, a more realistic and scientific approach may be to understand and use the resistance mechanisms that are naturally present in trees. Resistance trait variation may be genetically controlled and heritable. Populations therefore have the potential to respond to the selective pressure imposed by attack and, if the management and environmental conditions are right, adapt. This review outlines the mechanisms that trees use to defend themselves, the genetic and environmental control of these mechanisms, the subsequent phenotypic variation that we observe and how best to measure and use this to develop and maintain resilient tree populations. In order to ensure a more sustainable and stable future for commercial and native tree species there is a need to incorporate these approaches into forest management globally through collaboration between foresters and scientists and increased investment in relevant research trials.