Collaborative Research: Fire Influences on Forest Recovery and Associated Ecosystem Feedbacks in Arctic Larch Forests.

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Larch forests overlie extensive areas of Arctic permafrost and contain half the carbon (C) in some boreal forests. Although larch is a fire-dependent tree species, previous research and that of others suggests that increased fire activity may limit larch forest recovery and potentially trigger forest loss and a shift to alternative vegetation dominated by shrubs or grasses. Forest loss could have large consequences for climate because of changes in C storage and reflection of heat and light (albedo). Larch forests occur across much of the Arctic latitudinal treeline, and future larch recruitment dynamics will be a primary determinant of whether boreal forests respond to climate warming via treeline migration. Despite the global importance of these forests and the potential for an altered fire regime to modify recruitment patterns and future forest cover, larch forests remain largely understudied compared to the boreal forests of North America. The many mechanisms governing post-fire larch recruitment and the consequences for system-level feedbacks to regional and global climate remain untested. This research will link constraints on larch forest recruitment after fire to system-wide observations of larch recruitment failure and associated feedbacks to climate.
Boreal forests cover a large portion of the vegetated land area above the Arctic Circle and are a critical component of the Arctic System. In larch forests, increased fire activity associated with climate warming and drying can lead to larch recruitment failure, which in turn can limit forest recovery and trigger forest loss. A transition from forests to successional trajectories dominated by shrubs or grasses could have important consequences for climate feedbacks. The primary objective of this research is to delineate the causes of varying larch recruitment after fire and to quantify the consequences of larch recruitment failure for climate feedbacks via changes in C storage and albedo using a combination of field-based measurements, dendrochronological analysis, remotely-sensed data, and statistical modeling. The project hypothesizes that post-fire larch recruitment will be most constrained by seed sources (i.e., biological legacies) but that environmental conditions (e.g., soil organic layer depth) and biotic interactions (e.g., degree of mycorrhizal colonization and community structure) will impose secondary limitations on recruitment when seed sources are available. Larch recruitment failure will shift successional trajectories to those dominated by shrubs and grasses, resulting in reduced C storage, higher albedo, and cooling of regional climate. We will test hypotheses via field observations and experimental manipulations, combine field- derived data and statistical modeling to determine the factors that most influence larch recruitment, use high-resolution satellite imagery to determine the recent extent of regional larch recruitment failure after fire, and estimate C pools and albedo across gradients of larch recruitment and stand succession to determine the relative system-level consequences of changes in these parameters for regional climate forcing. By focusing on the mechanistic connections between fire and larch recruitment, the research will provide critical information on the net feedback of an intensified fire regime in arctic ecosystems to regional and global climate.
This project will train about 16 undergraduate students, one MS student, three PhD students, and two post-doctoral scholars. It will provide support for four female scientists, two of whom are early-career. It will share results with researchers in Amsterdam for inclusion in a circumpolar map of fire activity and forest recruitment, further improving international collaborations. Research findings will be widely disseminated to the scientific community through publications in scientific journals, presentations at national conference, and professional seminars. PIs will develop and lead a workshop aimed at improving middle school teachers' understanding of climate change science and their ability to effectively teach climate science to students.