Delays in peak physiological activity may reduce resource acquisition as trees recover from wildfire

Few studies have investigated how mature trees recover physiologically from wildfire damage, and none have comprehensively linked tree hydraulics with belowground function. Uncovering mechanistic links between rates of above- and belowground recovery is necessary for improving predictions of forest resilience and carbon dynamics following wildfire. We coupled continuous measurements of tree water flow and soil CO₂ efflux with detailed physiological measurements of above- and belowground function following a mixed-severity wildfire. We found that mature Pinus ponderosa trees with up to 85% canopy and stem damage resumed physiological functioning by the second growing season post-fire. However, these trees also exhibited delayed peak water uptake (relative to less-burned trees) that coincided with summer heat and drought. Our results suggest fire damage may prevent the critical timing in which peak physiological function overlaps with optimal growing conditions (e.g., moisture and nutrient availability). As a result, we suggest the degree of root and microbial damage should be assessed along with observed aboveground damage to more effectively predict tree recovery potential. While significantly damaged trees resumed typical hydraulic function within two years, observed delays in peak water uptake could require higher water and nutrient use efficiency to maintain carbon sequestration rates.