From 2003 to 2012, bark beetles accounted for 32% of observed tree mortality in the western United States forests. Subsequent fires in previously beetle-affected forests are typically characterized by a highly heterogeneous distribution of burn severity. In 2018, a wildfire burned more than 21,000 acres of previously beetle-affected lodgepole pine forest at the AmeriFlux Chimney Park (US-CPk) site in southeastern Wyoming; a site that provided pre- and post-beetle ecosystem flux and vegetation data since 2008. The resulting mosaic comprised of patches that exhibited no fire (NF), understory-only fire (UF), or high-severity, stand-replacing fire (SF). By immediately re-instrumenting the site with sap flow sensors, time-lapse electrical resistivity tomography, and five eddy covariance stations, we were able to quantify and partition carbon, nitrogen, and water fluxes in relation to post-beetle fire intensity and understory vegetation recovery in the first year following sequential and interacting disturbances.
Results/Conclusions
During the first full summer after the fire, volumetric water content was 5-10% lower in NF compared to the other stands in the upper 30 cm of soil, whereas at 50 cm depth all stands were similar. The time-lapse electrical resistivity shows more rapid and deeper infiltration below NF, and more heterogeneous infiltration below UF and SF. Later in the season, the subsurface of NF appears to dry more pervasively and to deeper depths than the soils below UF and SF. Eddy-covariance measurements of evapotranspiration (ET) were similar between SF and above the canopy in NF from July to September, while below canopy ET was greater in NF than UF for early and late summer. Soil temperature and heat flux were consistently higher in SF and snow melt started three weeks earlier in SF compared to NF and UF. Foliar C content in first-year lodgepole pine seedlings was significantly higher in SF compared to those growing in UF whereas foliar N content was significantly lower in SF compared to UF. Our results allow for partitioning of fluxes between abiotic and biotic drivers for improving the predictability of carbon and water dynamics of ecosystems characterized by increasingly overlapping and interacting disturbance regimes.