Burn Severity as a Driver of Multi‐Year Increases in Gross Primary Production and Solar‐Induced Fluorescence Following a Wildfire in Arctic Tundra

While climate‐driven increases in wildfires are altering the composition and function of Arctic ecosystems, the impact of burn severity on longer‐term changes in community composition and ecosystem fluxes remains less understood, creating uncertainty in estimates of the biome's carbon storage capacity. Here, we used field and remote sensing observations from the 2007 Anaktuvuk River Fire on Alaska's North Slope to explore post‐fire changes in gross primary production (GPP) and solar‐induced fluorescence (SIF). A key goal was to develop a mechanistic understanding of the relationships between burn severity, active layer thickness, post‐fire plant functional type composition, and GPP, using SIF to explore these linkages at a landscape scale. We measured GPP using eddy covariance flux towers at sites with high and moderate burn severity and at a nearby unburned control site. In high burn severity areas, GPP increased by 38 ± 19% and SIF increased by 48 ± 34% 11–15 years after the fire compared to unburned controls. A positive correlation across space between SIF and post‐fire shrub cover within the fire perimeter ( r = 0.38, p < 0.01) suggests that shrub expansion (43 ± 22%) was a key driver of the observed pattern of SIF enhancement. Post‐fire shrub cover, in turn, was positively correlated to active layer thickness ( r = 0.33, p < 0.01) and burn severity ( r = 0.76, p < 0.01). Our findings suggest that more frequent and severe Arctic wildfires could accelerate shrub dominance and increases in photosynthesis, trends that are already being driven by climate warming.