Depth of burning of the soil organic layer, SOL, and resultant carbon, c, emissions from wildfire is an important component of net ecosystem c balance in the above domain. The SOL sequesters the…

This is a $890,482.84 cooperative agreement awarded by NASA to Northern Arizona University (NAU) to conduct research on the impacts of increasing fire severity on the combustion of legacy carbon in forest and tundra ecosystems across the northern regions of North America. The research aims to develop a mechanistic understanding of the ecosystem, landscape, and fire characteristics that control the loss of this long-stored carbon, and to examine the consequences for post-fire permafrost and vegetation dynamics. The work will involve field studies in Alaska and Northwest Territories, Canada, and integrate the results with geospatial data products. This project aligns with NASA's focus on understanding disturbance regime changes and their impacts on ecosystem carbon cycling and physical/biological controls. The award does not have a set-aside designation, reflecting NAU's broad research capabilities across disciplines relevant to federal agencies.

Depth of burning of the soil organic layer, SOL, and resultant carbon, c, emissions from wildfire is an important component of net ecosystem c balance in the above domain. The SOL sequesters the majority of ecosystem c in layers that can be hundreds to thousands of years old. Deeper burning could rapidly shift ecosystems across a c cycle threshold, from net accumulation of c from the atmosphere over multiple fire cycles, to net loss. Yet deeper burning must release c that escaped one or more previous fires which we term legacy c to shift ecosystems into the domain of accelerating feedback between warming climate and fire. The proposed research will combine widely used and scalable SOL consumption metrics with radiocarbon techniques for aging soil c to address the first key question, what are the ecosystem, landscape and regional controls over the combustion of legacy c in forest and tundra regions of the above domain combustion of legacy c indicates that a larger proportion of the SOL was combusted in the current fire than in the previous fire, providing historic context for the current fires severity. New fires that are greater in severity than past fires are expected to be to push ecosystems across thresholds in permafrost and plant composition, rendering c cycling vulnerable to state change after fire. The proposed research will combine a mechanistic understanding of legacy c loss with observations of ecosystem response to address our second key question, what are the consequences of legacy c loss for post fire permafrost and vegetation dynamics? Proposed research for the field campaign will address these key questions by linking field-based, process level studies of legacy c combustion and post fire responses with geospatial data products in two regions, moist acidic tundra near treeline on the north slope of the alaska range, alaska, and boreal conifer forest in the taiga plains and shield ecoregions of northwest territories, canada. These regions provide stark contrast in vegetation structure, yet both occur on warm permafrost soils that could be vulnerable to rapid change following fire. Recent extreme fire activity in both regions provides natural gradients in depth of burning across multiple, spatially independent burn scars, making them ideal for addressing these questions. Specific research objectives are to: 1. Develop a mechanistic understanding of the ecosystem, landscape and fire characteristics that control legacy c loss from tundra and boreal forest wildfires in the above domain; 2. Examine the generality of the mechanistic understanding by synthesizing results with combustion and radiocarbon data collected in other regions; 3. Estimate the magnitude of legacy c loss across landscapes within fire scars by linking the mechanistic understanding with geospatial data products; 4. Determine ecosystem response to legacy c loss and fire severity, focusing on ecosystem vulnerability to state change in permafrost and vegetation; and 5. Project ecosystem response to legacy c loss and fire severity across fire scars and identify the ecosystems, landscape positions, and regions at the greatest risk of state change under an intensifying fire regime. The proposed research fits within the overarching focus of the field campaign because IT focuses on the impacts of an environmental change, intensifying fire regime on ecosystem function in the above domain. The aim to define a novel dimension of fire disturbance, the combustion of legacy c, directly addresses tier 2 science question 3.2 regarding processes contributing to changes in disturbance regimes. Focus on the ecosystem consequences of this loss contribute to other questions, including the direct contribution of emissions to long-term ecosystem c balance, q 3.6, and how losses may indirectly alter physical and biological controls over c cycling, q 3.6, permafrost state, q 3.3, soil drainage, q 3.4, and vegetation composition, q 3.5.