LTREB: Following the reorganization and resynchronization of biogeochemical cycles after an unprecedented tundra fire

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The arctic tundra north of the tree line in Alaska is responding to the most rapid rates of warming on the globe. The responses include increased plant growth, thaw of the underlying permafrost, loss of soil carbon through increased microbial activity, and increased frequency and severity of wildfires. Historically, low temperatures have kept tundra fires as relatively infrequent events. But warming is anticipated to impact the fire regime by doubling fire size and frequency in the arctic by the year 2100. Fires impact ecosystem services provided by the tundra for decades to centuries by burning the vegetation and the layer of dead organic matter on top of the soil. As vegetation rapidly recolonizes the landscape after a fire through a process known as succession, its composition changes, as do the cycles of carbon and associated nutrients, like nitrogen and phosphorus. In fact, fires remove a large portion of nutrients needed to fuel the regrowth and recovery of vegetation, while at the same time, increase soil temperatures because the insulating organic layer has also been removed. Warmer soils may increase soil nutrient availability and lead a shift from grasses to shrubs over time. But it is unclear whether these changes are large enough to offset the initial carbon and nutrient losses during the fires, which is the main question this project seeks to answer. Besides the scientific results, an online documentary series will be produced that explains the effects of climate change and fire on arctic ecosystems. Formal outreach programs developed in prior projects that specifically address indigenous and minority populations living on the North Slope in Alaska and in Indiana will also be enhanced.This project will develop a multi-decadal record and mathematical model of post-fire carbon and nutrient cycling across three sites along a disturbance severity gradient within the largest recorded arctic tundra fire, the Anaktuvuk River fire from 2007. An existing eddy covariance system will be used to continue measurements of carbon and energy fluxes begun in 2008, along with soil chambers. A quantitative soil and biomass harvest was conducted in 2011 across a burn severity gradient. Post-fire trajectories from grass to shrub-dominated tundra should create a positive climatic feedback and produce a warming effect through decreased albedo. This project will be used to create a multi-decadal record of carbon, nitrogen and phosphorus fluxes and stocks to parameterize, validate, and test the Multiple Element Limitation (MEL) model as applied to the biogeochemistry of arctic tundra.