"Boreal forests contain large amounts of soil carbon and are susceptible to periodic wildfires. Predicting the response of soil carbon dynamics to fire disturbance requires understanding: (1) the environmental factors governing CO2 efflux; (2) the extent to which fire alters these factors; and, (3) the length of time over which these perturbations persist. In interior Alaska seasonal patterns of CO2 efflux, soil temperature. and soil moisture potential were measured in burned and control pairs of aspen, white spruce, and black spruce stands. Averaged over the growing season, mean CO2 efflux from burned stands (0.51 ± 0.26 g CO2 m−2 hr−1) was two-thirds that of control stands (0.77 ± 0.44 g CO2 M−2 hr1). Soil temperature explained 85 to 90% of the seasonal variability in the control, whereas moisture was a more important determinant in burned stands. Laboratory incubations of recently burned and control humic material indicate that changes in substrate chemistry and increased temperature may enhance rates of decomposition by a factor of 2.2 to 2.8 in the first decade after fire, resulting in a release of 6.3 to 13.4 Mg C ha−1 to the atmosphere. Under saturated moisture conditions, respiration from mosses may contribute 16 to 50% of total soil CO2 emissions. In a 140-year age-sequence of burned black spruce stands, CO2 efflux increased at an average rate of 8.3 kg C ha−1 yr1 up to a maximum of 1.83 Mg C ha−1 yr1. During this same time, accumulation of carbon in organic horizons ranges from 0.34 to 0.50 Mg C ha−1 yr1 and the ratio of microbial to root respiration decreased from 76:24 to 13:87. Numerical modeling of carbon accumulation suggests that these soils functioned as a net source of carbon for the first 7 to 15 years after fire and released 1.8 to 11.0 Mg C ha−1 to the atmosphere. Although conservative, these estimates of post-fire biogenic emissions are on the same order of magnitude as carbon losses during combustion itself, suggesting that current models may underestimate the impact of fire in northern latitudes by as much as a factor of two"--Leaves iv-v.

The boreal forest is the northern-most woodland biome, whose natural history is rooted in the influence of low temperature and high-latitude. Alaska's boreal forest is now warming as rapidly as the rest of Earth, providing an unprecedented look at how this cold-adapted, fire-prone forest adjusts to change. This volume synthesizes current understanding of the ecology of Alaska's boreal forests and describes their unique features in the context of circumpolar and global patterns. It tells how fire and climate contributed to the biome's current dynamics. As climate warms and permafrost (permanently frozen ground) thaws, the boreal forest may be on the cusp of a major change in state. The editors have gathered a remarkable set of contributors to discuss this swift environmental and biotic transformation. Their chapters cover the properties of the forest, the changes it is undergoing, and the challenges these alterations present to boreal forest managers. In the first section, the reader can absorb the geographic and historical context for understanding the boreal forest. The book then delves into the dynamics of plant and animal communities inhabiting this forest, and the biogeochemical processes that link these organisms. In the last section the authors explore landscape phenomena that operate at larger temporal and spatial scales and integrates the processes described in earlier sections. Much of the research on which this book is based results from the Bonanza Creek Long-Term Ecological Research Program. Here is a synthesis of the substantial literature on Alaska's boreal forest that should be accessible to professional ecologists, students, and the interested public.

"The likely direction of change in soil organic carbon (SOC) in the boreal forest biome, which harbors roughly 22% of the global soil carbon pool, is of marked concern because climate warming is projected to be greatest in high latitudes and temperature is the cardinal determinant of soil C mineralization. Moreover, the majority of boreal forest SOC is harbored in surficial organic horizons which are the most susceptible to consumption in wildfire. This research focuses on mechanisms of soil C accumulation in recently burned (2004) and unburned (~1850-1950) black spruce (Picea mariana [Mill.] BSP) forests along gradients in stand productivity and soil temperature. The primary research questions in these three chapters address: 1) how the interaction between stand production and temperature effect the stabilization of C throughout the soil profile, 2) the quantity and composition of water soluble organic carbon (WSOC) as it is leached from the soil across gradients in productivity and climate, and 3) physiographic controls on organic matter consumption in wildfire and the legacy of wildfire in stable C formation (pyrogenic C, or black carbon). Soil WSOC concentrations increased while SOC stocks decreased with increasing soil temperature and stand production along the gradients studied. Stocks of BC were miniscule in comparison to organic horizon SOC stocks, and therefore the C stabilizing effect of wildfire was small in comparison to SOC accumulation through arrested decomposition. We conclude that C stocks are likely to be more vulnerable to burning as soil C stocks decline relative to C sequestered in aboveground woody tissues in a warmer climate. These findings contribute to refining estimates of potential changes in boreal soil C stocks in the context of a changing climate"--Leaf iii.

Much attention has been given to above ground biomass and its potential as a carbon sink, but in a mature forest ecosystem 40 to 60 percent of the stored carbon is below ground. As increasing numbers of forests are managed in a wide diversity of climates and soils, the importance of forest soils as a potential carbon sink grows. The Potenti

"The objective of this study was to assess the effect of throughfall exclusion (1989-2005) on forest vegetation and soil in upland and floodplain landscape positions. In uplands, imposed drought reduced soil moisture at 5, 10, and 20 cm depths and increased soil C storage by slowing decomposer activity at the surface. In the drought plots, aboveground tree growth was reduced and root biomass in mineral soil was increased. In floodplains, imposed drought did not reduce soil moisture as strongly as it did in uplands, though near-surface soil C storage was still increased as a result of reduced decomposer activity. Floodplain vegetation response to imposed drought differed from that of uplands; imposed drought did not reduce aboveground tree growth but instead reduced root biomass in mineral soil. At both landscape positions, imposed drought accelerated the loss of understory vegetation. Overall, the results of the throughfall exclusion indicated that chronic soil drying is likely to increase forest C storage only in floodplains. In uplands, where soil moisture is more limited, forest C storage is not as likely to change because an increase in soil C may be offset by reduced tree growth"--Leaf iii.

The boreal region of Alaska has vast forests spanning hundreds of thousands of square kilometers in the central portion of the state that is prone to large stand replacing summer wildfires. The region stores considerable quantities of terrestrial carbon sequestered in soil horizons down to 1 meter in depth that are strongly influenced by a combination of climate change, permafrost dynamics, vegetative composition, and fire regimes. Data and literature establish that the boreal region of Alaska (and the rest of the Arctic) has been steadily warming at a rate nearly double that of lower latitudes. This warming has resulted in larger fires defined by shorter return intervals. This altered fire regime places the vast stocks of organic soil carbon at risk to greater degrees of combustion, potentially contributing millions more tons of CO2 to the atmosphere in the Arctic region. Between 2000-2015 roughly 5% (~28,000 km2) of the over 560,000 km2 of the boreal region burned, raising CO2 levels and supporting a positive feedback loop between climate and fires; when considering that this region of Alaska is larger than the state of California (~420,000 km2) these emissions are significant. Mean summer temperatures have risen by 1.4° C over the last 100 years, resulting in shorter fire return intervals characterized by more severe and intense, longer fire seasons. This warming is driving more pronounced permafrost degradation that is altering both the extent and depth of regional permafrost layers, increasing labile carbon stocks that serve as additional fuel pools for fires. While permafrost layers are fluctuating more frequently, the warmer temperatures are supporting increased vegetation growth with expansion of the boreal forest into landscapes that were previously hostile, increasing novelty in these area's fire regimes and subsequent emissions. As fire activity increases in the region, forest composition is being altered toward a greater dominance by deciduous rather than coniferous trees, a development that is increasing soil carbon levels as these stands mature. Human suppression policies, despite being well intentioned, are driving more frequent and severe fires due to an unnatural buildup of fuels, especially around regional population centers. Because of these findings, I recommend closing critical data gaps with further data additions, changing timber harvesting and forest management policies, and reexamining fire suppression policies.