Less fuel for the fire: How will drought amplify effects of short-interval fire?

1. PROBLEM STATEMENT. Area burned is increasing across western United States forests, and the synergistic effects of warming, drying climate and increasing area burned on future forested landscapes are not well understood. Forests may be vulnerable to transitioning to shrublands or grasslands when fires reburn young forests at short fire return intervals (FRI) relative to rates of forest recovery, and post-fire drought can amplify the likelihood of post-fire regeneration failure. This is of particular concern in subalpine, lodgepole pine-dominated forests of the US Northern Rocky Mountains. These forests recover rapidly from infrequent (100-300 year FRI), high-severity fire but have recently experienced many severe reburns less than 30 years after previous fire. Forest fuels differ in young versus mature subalpine forests, potentially leading to qualitative differences in fire behavior when forests reburn. I propose to address key gaps in understanding how simultaneous, interacting changes in climate and fire frequency affect trajectories of post-fire forest and fuels recovery, while also developing methods for monitoring forest change at management-relevant scales using unpersonned aerial systems (UAS).

2. OBJECTIVES. I will undertake a field data campaign in 13 reburns where recent fire burned subalpine, lodgepole pine forests at short (< 30 year) FRI in the Greater Yellowstone Ecosystem (GYE). In a subset of post-fire plots, I will fly a low-cost UAS and develop methods for using UAS to measure forest and fuels recovery. In a minimum of 30 paired short- and long-interval post-fire plots (n = 60 total plots), I will measure tree regeneration, stem ages, plant biomass, and canopy and surface fuels to address two unresolved questions: (1) How do interactions between fire return interval and post-fire drought affect forest recovery? (2) How do forest fuels vary with time since fire following short- versus long-interval fires? I expect a synergistic interaction between short FRI and post-fire drought to amplify reductions in post-fire tree regeneration and delay recovery of forest fuels. I will use statistical analyses to disentangle the relative importance of each driver and develop models to predict fuel loads with time since fire. I will also test multiple methods for deriving forest characteristics from UAS data.

3. BENEFITS. My results will assist forest managers in predicting and monitoring forest recovery and fuel accumulation following both short- and long-interval fires, which is critical for anticipating future fire behavior and planning appropriate management activities. I will disseminate research results via a peer-reviewed publication, presentation at a professional fire conference, and YouTube video featuring UAS footage. Specifically targeting forest and fire managers, I will also lead a webinar and create a resource guide on GitHub detailing final methods for using UAS to measure and monitor forest and fuels recovery.