Collaborative Research: Regional impacts of increasing fire frequency on carbon dynamics and species composition in the boreal forest

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The Arctic is warming faster than any other area of the world and its boreal forests have experienced dramatic increases in the size and frequency of fires. The fast pace of these changes has prompted concern because boreal forests make up about a third of all forests worldwide, contain almost half of the world's stored carbon, and have been historically stable with black spruce dominating this landscape for the past 6,000 years. Warming of 2-8 °C is projected by the end of the century and the emergence of a new fire regime threatens to disrupt this forest ecosystem. For example, in some regions of interior Alaska, the fire return interval has decreased to 10-50 years, causing shifts from black spruce to deciduous trees and grasses. Changes in the climate and fire regime are also expected to affect global carbon cycling since fires and thawing of frozen soils (permafrost) may release large amounts of carbon into the atmosphere. This research will incorporate field studies and computer simulations to determine how fire frequency and climate change affect shifts between vegetation types (e.g. switch from conifer to grasses) and long term carbon storage in this vast and under-studied region. The study will train graduate students and involve Native American high school students from the Rural Alaska Honors Institute (RAHI) in field work. The investigators will collaborate with Your World Rocks (YWR), a nonprofit organization of female scientists and engineers dedicated to promoting science education in elementary schools. They will develop hands-on activities focusing on climate change, forests, and fire and conduct free hands-on activities in elementary schools in the greater Portland/Vancouver metro area, with a particular focus on underserved Title 1 schools. The fast pace of climate warming and an increase in fire frequency over the past few decades in northern latitudes has raised concerns about major shifts in vegetation and the long-term ability of ecosystems to capture and store carbon. Boreal forest ecosystems account for about 33% of all forests worldwide and contain about 45% of the world's carbon stocks, with the majority (~85%) stored belowground. For the past 6,000 years, black spruce (Picea mariana (Mill.) B.S.P.) has been the dominant species over a large proportion of this landscape, exhibiting substantial resilience to changes in climate. However, unprecedented warming (causing earlier snowmelt, permafrost thawing, and longer growing seasons) and the emergence of a new fire regime over the past 60 years threatens to disrupt the existing dominance by black spruce and release globally significant amounts of carbon into the atmosphere. The goal of this research is to quantify the potential for large-scale changes in carbon (C) sink strength, C stocks, and vegetation in boreal forests due to climate change and repeated wildfires by integrating mechanistic field and lab work with dynamic, spatially explicit landscape modeling. Working in central Alaska, the investigators will: 1) determine how fire frequency and climate change affect successional trajectories and above- and belowground C cycling, and 2) assess how the mechanisms that cause tipping points between vegetation types (i.e. conifer, hardwood, graminoid) and C sequestration (i.e. sink, source) vary spatially and temporally. To achieve these objectives, the investiagors will empirically measure above- and belowground C stocks, productivity, heterotrophic respiration, soil temperature and moisture content, and active layer thickness in the field and quantify C mineralization using laboratory soil incubations. They will also develop and validate a physically based permafrost/hydrology module for a widely-used, high resolution landscape simulation model (LANDIS-II) to forecast long-term dynamics of species composition and C source/sink status given projected changes in climate (including thawing permafrost) and fire. The work will improve our understanding of how C cycling and species composition in boreal forests will respond to climate change and disturbances at the fine spatial scales critical to accurately project the future of the boreal forest.