PS 34-231 - Understory vegetation response to thinning and prescribed fire in a high elevation mixed-conifer forest, New Mexico USA

Abstract: Quality forest management is integral to maintaining healthy and diverse forests, especially with today’s climate-driven high-severity wildfires. Reducing canopy closure through thinning and prescribed fire can mean the difference between a low-intensity wildfire that is beneficial and high-intensity megafires that decimate natural regeneration. Federal agencies are responsible for millions of acres of land and with the right resources have the opportunity to use adaptive management to quell high severity fires through correctly administered forest restoration practices. At Valles Caldera National Preserve in northern New Mexico, a combination of thinning and prescribed fire was utilized to reduce canopy closure and create healthy open stands. Park scientists aimed to get a better understanding of the herbaceous response to this prescription. During this seven-year study we were able to track successional vegetation changes over time and the plant communities’ response to multi-faceted forest management by measuring vegetation cover and species distribution, forest stand characteristics, and fuel loads using a before-after/control-impact (BACI) experimental design. We found that utilizing thinning followed by prescribed fire creates healthy forest openings that are both beneficial to wildlife and forest structure alike. While graminoid cover saw a rapid response to thinning activities it took two years for this community to come back even stronger from prescribed fire. After three years post-treatment forb species are finally to pre-treatment levels of cover. These results confirm that thinning and prescribed fire used for restoration can successfully create conditions for understory herbaceous species to thrive. Land management agencies can utilize multi-faceted forest restoration practices on the landscape to help ameliorate the threat of severe wildfires by creating beneficial forest gaps.