COS 218-5 - Quaking aspen (Populus tremuloides) controls on satellite-derived fire radiative power (FRP) during recent wildfires in the Western U.S.

Abstract: Quaking aspen (Populus tremuloides) is the most widely distributed tree species in North America. In many regions of the western United States, it serves as the dominant deciduous tree species, providing numerous ecosystem service benefits ranging from biodiversity and wildlife habitat to economic and recreational value. Aspen forests have been associated with wildfire adaptation and expansion of such forest types has been proposed as a method for managing community risk to wildfire. While it is broadly understood that aspen stands are typically less flammable than conifer stands and that this may moderate fire behavior, we lack a quantitative understanding of the relative influence on wildfire spread, severity, and intensity in current wildfires. Recent advances in remote sensing and the increasing trend of open access data allow for novel analyses to determine whether aspen stands may reduce fire behavior, and under what conditions.

In this study, we relate fire radiative power (FRP), a proxy for fire intensity, from VIIRS (Visible Infrared Imaging Radiometer Suite, 375-m resolution) active fire detections to aspen presence and landscape configuration (patch dynamics) along with ancillary variables related to topography, weather, and fuels. We demonstrate the use of sequential autoregression (SAR) to construct multivariate models across a subset of wildfire events that burned in landscapes composed of at least five percent aspen cover in the western US (2019-2022). Given the effects of aspen stands on fire behavior may depend on fire weather conditions, we test for interactions with fire weather variables including daily maximum temperature, wind speed, 100-hr and 1000-hr fuel moisture. Finally, we compare SAR model coefficients across individual wildfire events. We show that the proportion of aspen forest cover influences satellite-derived FRP measurements, but this effect varies under different burning conditions. The results of this work help inform forest managers about the potential for aspen stands to act as natural fire breaks in current wildfires.