Just like the undulating terrain of the tussocky tundra we traverse, our days also take unexpected twists and turns. After a beautiful last day of sampling the East Fork fire scar along the Andreafsky River, where three moose visited us and delivered a personal goodbye, we were all excited for our first day of sampling the Apoon Pass fire scar via helicopter. But our spirits were momentarily dampened by news of Savanna, our pilot flying in from Nome, getting stuck in a thunderstorm on her way to our base in St. Mary’s, Alaska. Her arrival, delayed until early afternoon, was just the prelude to a challenge-laden morning.
Further issues emerged with our satellite communications device, requiring transatlantic collaboration with our colleagues in Amsterdam (many thanks to Thomas for his unwavering support!) These obstacles left us momentarily uncertain about the feasibility of flying at all that day. Miraculously, by 2 p.m., the looming cumulus of problems and bad weather began to disperse, and by 2:30 p.m., with a renewed sense of purpose, we embarked on our mission to sample the second fire of our field campaign.
The flight itself proved to be a standout experience, treating us to a breathtaking panorama over the hilly tundra that we had sampled along the Andreafsky River in the preceding days. The Apoon Pass fire scar, though not far from the East Fork fire, is geographically quite different, as it is located in very flat lowland terrain. Flying over the last crests of the hill range provided a captivating sight of the vast lowlands extending in all directions.
To our surprise, we were only able to spot the difference between burned and unburned tundra when descending to a relatively low altitude. This observation, together with the satellite imagery prepared by our campaign lead Lucas, led us to an initial conjecture that fire severity would be lower than what we had previously seen.
To systematically assess fire severity and carbon emissions in our plots, we are following protocols established by Mack et al. (2011) and Moubarak et al. (2023) for tundra fires in Alaska. We use two independent methods to estimate the burn depth based on the height of tussocks and Sphagnum (peat moss) patches in our plots. For the tussock-based method, we compare the height of tussocks that survived the fire with the height of tussocks in unburned locations. This gives us an estimate how much duff and other organic material has been combusted. For the Sphagnum-based method, we connect different moss patches of similar height with a thread and measure the distance from the thread to the surface at 25-centimeter intervals. This will give us an overview of the variability in burn depth within our sampling locations.
These two measurements will allow us to quantify the amount of carbon combusted per plot, which we can relate to the satellite imagery, as well as to the thickness of the active layer we are measuring at each plot to assess how the fire is affecting the permafrost.
In the end, to our surprise, our first helicopter day turned into one of the best sampling days we had during the campaign so far. We were gifted with beautiful, sunny weather until 9 p.m., and sampled even more plots than we had initially expected. We have now become a well-oiled machine, capable of sampling a plot within a mere hour and a half. Having the helicopter with us at all times offered an invaluable advantage—the ability to swiftly transport parts of our team to nearby sampling sites. After having returned to our base, we are excited for another day in the beautiful tussock tundra of southwestern Alaska—keeping our fingers crossed for another couple of days of good weather!