Do Changes in Monoterpenes and Non-Structural Carbohydrate Reserves Signal Post-Fire Vulnerability in Pines?

Wildfires are increasingly affecting boreal conifer forests, altering their chemical defences and carbohydrate reserves in ways that may affect their susceptibility to subsequent herbivore threats. We quantified monoterpenes and non-structural carbohydrates in the phloem of lodgepole pine across three treatments (unburned, burn-year, one-year post-fire) to identify fire-induced chemical changes and their temporal dynamics. Monoterpene concentrations rose sharply immediately following the fire but declined after one year. Non-structural carbohydrates showed compound-specific responses: starch and sucrose concentrations reduced post-fire, with partial recovery of sucrose, while glucose increased, and fructose exhibited a delayed response. Multivariate analysis revealed sucrose, starch, and specific monoterpenes as key compounds distinguishing the treatments. Elevated monoterpene concentrations immediately post-fire likely decreased susceptibility to insects; however, the subsequent decline in defences and accumulation of sugars suggest the emergence of a distinct post-fire window of increased vulnerability. These findings improve our understanding of fire-induced chemical shifts and can help predict forest vulnerability to interacting biotic stressors under a changing climate.