Wildfire severity reshapes remotely sensed surface temperature and vegetation phenology in a Western Cascades forest ecosystem

Daniel M Griffith , Christopher J. Still, Matt Betts, Amelia Fitch, Hannah Sachs, Mark Schulze

Wildfire reorganizes forests by altering canopy structure, surface energy balance, vegetation activity, and microclimate. However, these effects remain difficult to quantify across seasons, times of day, burn severities, and complex terrain. We used the 2023 Lookout Fire at the H.J. Andrews Experimental Forest, Oregon, to test how fire severity altered coupling between surface temperature and vegetation phenology. We integrated ECOSTRESS land surface temperature (LST), HLS-2 near-infrared reflectance of vegetation (NIRv), RAVG burn severity, Daymet climate, airborne LiDAR, and phenology observations. ECOSTRESS observations were standardized by harmonic regression for seasonal and diurnal acquisition timing. Post-fire warming was strongest in summer and increased with burn severity (1.5 °C increase for severe). High-severity areas warmed more than unburned areas, especially under high shortwave radiation, low rainfall, and high vapor pressure. Open vegetation cover was associated with warmer LST, whereas higher elevations were cooler. At phenology plots, ECOSTRESS LST generally exceeded instantaneous air temperature (ΔT = 0.55), and burn severity steepened this relationship after fire (1 to 1.15 slope). HLS NIRv captured seasonal and disturbance-driven vegetation activity and was associated with Douglas-fir budbreak and summer temperature. Across the landscape, post-fire declines in NIRv were associated with warmer noon-standardized LST, and structural equation modeling indicated that reduced evapotranspiration largely mediated this relationship. Among the first to use ECOSTRESS observations, our study resolved seasonal and diurnal post-fire warming while linking thermal responses to satellite vegetation activity, LiDAR-derived structure, and field phenology. Together, these results show that wildfire severity reorganized thermal regimes across seasons and times of day, while vegetation phenology provided biological context for post-fire climate change.