OPP-PRF: Investigating Fire-Biotic Disturbance Interactions and Their Sensitivity to Climate in the North American Boreal Biome

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Boreal forests are important because they store large amounts of carbon. Almost 30% of all forest carbon is stored in this biome. The frequency of disturbances, such as forest fires, pests, herbivores, and diseases, are increasing with climate change. More frequent fires combust carbon on the forest floor of boreal black spruce forests, which can prevent spruce from growing back. When black spruce trees fail to grow back after fire, deciduous species such as birch, aspen or willow grow instead. New insect outbreaks and diseases are showing up in the North American boreal forest, which threaten to kill many of these deciduous trees. However, little is known about the causes and effects of these new outbreaks, and how they may continue to affect carbon storage in boreal forests. This research will use computer simulations to better understand (1) the extent, impact and potential threats of new pests, herbivores, and diseases in Alaskan boreal forests; (2) how new outbreaks of pests, herbivores, and diseases may interact with fire and climate to alter how boreal forests store carbon.The boreal biome is a globally important terrestrial carbon sink: Approximately 30% of all terrestrial carbon is stored within boreal forests and the soils and permafrost (frozen soil) underneath. However, the future fate of boreal carbon depends on the impact of climate change on multiple disturbances and their interactions. Boreal forest fires are sensitive to climate and are increasing in frequency, size, and severity. Increasing short-interval fires combust legacy carbon in surface organic layers of black spruce stands and drive transitions in post-fire species regeneration from spruce to broadleaf dominance. Altered forest regeneration following short-interval fires creates a pulse of emissions, causes shifts in carbon stocks from below to aboveground and alters the vulnerability of subsequent carbon accumulation. New biotic disturbances are concurrently emerging in the North American boreal forest that could cause widespread broadleaf tree mortality and threaten to release the carbon accumulated in broadleaf biomass. However, little is known about the causes and consequences of these emerging biotic disturbances, and how they may further alter boreal carbon storage. This project will use process-based forest modeling (1) to develop a systems-based framework leveraging available and emerging data to model new impacts of biotic disturbances and their interactions, synthesizing current understanding of these emerging threats; and (2) apply that framework to a suite of climatic and biotic agent scenarios, testing the impact of fire-climate-biotic interactions on ecosystem carbon and successional trajectories at landscape scales under current and future conditions.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.