Tamm review: The impact of forest tent caterpillar defoliation on maple fitness and syrup production

The forest tent caterpillar ( Malacosoma disstria Hübner) is a major defoliator of sugar maple ( Acer saccharum Marsh.) stands, with recurrent outbreaks that can impact tree growth and health, while posing a significant challenge as well to the maple syrup industry. Severe and prolonged outbreaks can weaken trees, potentially reducing growth rates and increasing their susceptibility to secondary stressors, such as other pests and diseases, with possible implications for long-term stand biomass productivity. This review examines the effects of defoliation on sugar maple physiology, focusing on sap exudation dynamics, sugar concentration, and tree health. It also explores the potential compounding effects of tapping during outbreak years and the role of starch reserves in tree survival. Additionally, we provide broader perspectives on sugarbush management strategies, such as species composition and stand structure adjustments in mitigating forest tent caterpillar damage and spread. Future research should aim to deepen our understanding of the physiological effects of defoliation to support the establishment of clear guidelines for tapping defoliated trees as well as explore adaptive silvicultural strategies to increase sugarbush resilience in the face of recurrent outbreaks of the forest tent caterpillar. • Sap yield and sugar content response to defoliation have limited empirical evidence. • Defoliation alters carbohydrates annual dynamics in maples. • Early defoliation impacts differ from late-season leaf loss.