Assessing Climate–Wildfire Effects on Alaskan Boreal Forest Using Ground‐Truth Surveys and NASA Airborne Remote Sensing

ABSTRACT Aim Alaska's boreal forest is experiencing increasingly severe fires, droughts, and pest attacks that may destabilize carbon sequestration. Our aim was to understand boreal forest resilience to changing wildfire regimes using remote‐sensed datasets validated with ground‐truthing (GT). Location Five recently burned boreal forest sites (2010–2019) near Fairbanks, Alaska. Methods We used four AVIRIS‐NG hyperspectral image datasets (425 spectral bands at 5‐nm intervals; 3.5 × 43 km average swath) imaged by NASA in 2017–2018 during the Arctic‐Boreal Vulnerability Experiment (ABoVE). Spectral analysis included fire fuel loads and random forest (RF) models constructed from key bands to describe common pre‐ and postburned vegetation classes. Models were validated with 89 GT plots inside the AVIRIS scenes. GT included tree stem densities, understory cover, soil characteristics, radial growth of 51 spruce trees from cores, and visual damage assays of 668 conifers and deciduous trees. Results Spectral evidence of high fuel loads in 2017 pre‐dated a 2019 wildfire. Post‐GT local models described vegetation more accurately than pre‐GT, but accuracy decreased when spectral rulesets were broadened to increase overall classification. Soil temperature, basal area, slope, elevation, and tree density varied widely; thaw depth, soil moisture, moss cover, and canopy height varied mainly by vegetation class. Invasive species and thermokarst were insignificant. Deciduous seedlings were abundant in postburned sites; however, conifer seedling densities were similar to unburned forest. Upland spruce radial growth showed earlier drought sensitivity than lowland spruce. Conclusion Spectral analysis revealed fire vulnerability in some areas; however, local and temporal spectral variation presented challenges to accurately classify vegetation in AVIRIS scenes. GT suggests that recovering forests near Fairbanks may lack sufficient conifer recruitment to replace existing stands. Sites with stable seasonal thaw may offset drought stress under global warming.