ARCUS | Arctic Research Consortium of the United States

6th Annual ARCUS Award for Arctic Research Excellence

Submitted by		Qianlai Zhuang
Authors		Qianlai Zhuang, A.D. McGuire, K.P. O'Neill, J.W. Harden, V.E. Romanovsky, and J. Yarie
Category		Interdisciplinary Research
Title		Modeling Soil Thermal and Carbon Dynamics of a Fire Chronosequence in Interior Alaska
Affiliation		Biology and Wildlife, University of Alaska - Fairbanks, Fairbanks, AK, USA

Abstract

In this study, the dynamics of soil thermal, hydrologic and ecosystem processes were coupled to provide the capability to project how the carbon budgets of boreal forests will respond to changes in atmospheric CO₂, climate, and fire, which is a major disturbance in the boreal region. The ability of the model to simulate seasonal patterns of gross primary production and ecosystem respiration was verified for a mature black spruce ecosystem in Canada, and the age-dependent pattern of vegetation carbon simulated by the model was verified with inventory data on aboveground growth of black spruce in interior Alaska. The model was applied to a post-fire chronosequence in interior Alaska and simulated soil temperature, soil respiration, and soil carbon storage were compared with measurements of these variables made in 1997. Comparisons between simulated and field-based estimates revealed that the model was able to accurately simulate monthly temperatures at 10 cm (R > 0.93) during the growing season for control and burned stands in the chronosequence. Similarly, the simulated and field-based estimates of soil respiration during the growing season for control and burned stands in the chronosequence were correlated (R = 0.84 and 0.74 for control and burned stands, respectively). The simulated and observed decadal to century-scale dynamics of soil temperature, which are represented by mean monthly temperatures during the growing season (May - September) were correlated among stands of the fire chronosequence (R = 0.93 and 0.71 for soil temperature at 20 cm and 10 cm depths, respectively). Similarly, among stands of the chronosequence the simulated and observed decadal to century-scale carbon dynamics were also highly correlated for soil respiration during the growing season (R = 0.95) and for soil carbon (R = 0.91). Analyses also suggested that along with differences in fire history, that the climate experienced by stands after fire and nitrogen fixation are important factors to consider in simulating the long-term dynamics of soil carbon. Sensitivity analyses were conducted with the model to identify the importance of moss growth after fire, soil moisture levels that might be associated with differences in drainage, and fire severity on soil thermal and carbon dynamics after fire. Taken together, the sensitivity analyses indicate that the growth of moss, changes in the depth of the organic layer, and nitrogen fixation should be represented in models that simulate the effects of fire disturbance in boreal forests. The sensitivity analyses also revealed that soil drainage and fire severity should be considered in spatial application of these models to simulate carbon dynamics at landscape to regional scales.