Abstract: Post-fire stand, water balance, and hydrology are critical factors influencing vegetation recovery after a wildfire. Fire severity, and the amount of fire-induced tree mortality influence post-fire vegetation water cycling, as the rate of water movement from the soil to the atmosphere, depends upon the amount of live vegetation cover in the wake of wildfire. We examined the influences of fire severity on diurnal plant evapotranspiration (ET) rates, as measured by sapflow, by installing a network of 45 tree sapflow meters across the fire severity gradient of the 2011 Horseshoe Two Fire in the Chiricahua Mountains of southeastern Arizona. Unlike many high-severity fire sites, post-fire ET was high at shrub-land sites at high fire severity burns. In this study, post-fire ET was driven by plant species composition and forest stand structural complexity. The more drought-sensitive pines display a peak in transpiration early in the day during the peak of photosynthesis, closing their stomata midday as a water conservation strategy. Cypress and oaks maintain high sap velocity through sundown, demonstrating multiple peaks throughout the day. Our results suggest that plant functional traits and stomatal regulation of gas and water exchange play critical roles in explaining post-fire forest recovery trajectories. The ability of the cypress and oaks to keep their stomata open throughout the day and high transpiration rates may be a key mechanism explaining their success on high-severity sites relative to pines. These results provide key information for predicting post-fire plant communities and forest water cycling under future environmental change.
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