Ninth International Conference on Permafrost ... - IARC Research

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Simulating the Effects of Wildfire on Permafrost and Soil Carbon Dynamics ofBlack Spruce Over the Yukon River Basin Using a Terrestrial Ecosystem ModelShuhua YiInstitute of Arctic Biology, University of Alaska FairbanksA. David McGuireU.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research UnitIntroductionJennifer HardenU.S. Geological Survey, Menlo Park, CaliforniaWildfire is considered an important disturbance agent inboreal forest ecosystems (Kasischke et al. 2006). It can affecthigh latitude carbon dynamics directly through combustionemissions, and indirectly through vegetation succession andremoval of the surface organic layer, which might acceleratethe degradation of permafrost and, hence, the release of soilcarbon. At the regional scale, the direct effects of fire havereceived a lot of attention, but the evaluation of the indirecteffects has been more limited because the appropriate toolshave not yet been developed for application at the regionalscale.Research objectives and questionsIn this study, we implemented a dynamic soil layermodule in the Terrestrial Ecosystem Model (hereafter DSL-TEM) to answer the following questions: (1) What is thechange of permafrost over the Yukon River Basin for periodsbefore and after year 1976, when there was a shift in thePacific Decadal Oscillation? (2) What is the effect of fireon permafrost? and (3) What is the effect of fire on carbonfluxes between the land surface and the atmosphere?Model DescriptionTEM is a process-based ecosystem model that simulatescarbon and nitrogen dynamics of plants and soils forterrestrial ecosystems. TEM has been widely used toinvestigate the effects of climate, carbon dioxide fertilization,and wildfire disturbances on the carbon dynamics of NorthAmerica. Research has focused on developing TEM forapplications in high latitudes, including incorporation ofthe Goodrich algorithm for calculation of soil temperaturesfor permafrost and seasonal frost regions; and incorporationof the hydrological module for methane production andtransport for high latitude wetlands. In this study, furtherimprovements have been made to account for the indirecteffects of wildfire in developing the DSL-TEM. The DSL-TEM consists of four interaction modules: an environmentalmodule, an ecological module, a fire disturbance module,and a dynamic soil layer module (Fig. 1). The environmentalmodule has been evaluated and presented at previousscientific conferences (Yi et al. 2007).Environmental moduleThe processes considered in the environmental module areFigure 1. Overall structure of DSL-TEM.canopy interception of snow and rain; drip and throughfallof snow and rain; canopy transpiration, evaporation, andsublimation; soil evaporation; snow sublimation; melt andaccumulation; surface runoff; and subsurface baseflow.A Two-Directional Stefan Algorithm was first appliedto simulate the freezing/thawing fronts in soil layers.Temperatures of snow/soil/rock layers were then updated bysolving finite difference equations for layers above the firstfront, layers below the last front, and layers between the firstand last fronts. Soil water contents of the unfrozen soil layerwere updated by solving Richard’s equations.The above processes are simulated at a daily timestep. Themonthly averaged soil temperature and moisture are thenpassed to the ecological module.Ecological moduleIn addition to the carbon and nitrogen dynamics describedin previous studies using TEM, a few new features areincluded in DSL-TEM, including explicit simulation of soilcarbon vertical distribution and change of the thicknesses oforganic layers based on the soil carbon content.Soil carbon content of each layer is determined by the litterfall input and carbon decomposition. The above- and belowgroundlitter fall are assigned to each soil layer according tothe fine root distribution. Carbon decomposition is calculatedusing the soil temperature, moisture, and carbon pool of eachsoil layer.The carbon contents of the organic soil layer, includingshallow organic and deep organic soil layers, are usedto determine the thickness of organic layers, basedon the relationship derived from field and laboratorymeasurements.The simulated leaf area index is passed to the ecologicalmodule; the organic layer thicknesses are passed to thedynamic soil layer module.357
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s tFire disturbance moduleThe fire disturbance module is run at an annual timestep.When a fire happens, it is used to calculate the fire severitybased on the drainage (poorly drained and moderatelydrained), fire season (early season or late season), and firesize (small, large to ultra-large). The severity is used tocalculate the burned organic layer thickness, which is thenpassed to the dynamic soil layer module.The above- and below-ground living vegetation is alsokilled by wildfire. It is assumed that only 1% of abovegroundvegetation remains alive, while the fraction of livingbelow-ground vegetation depends on the burned organiclayer thickness and the fine root distribution.Dynamic soil layer moduleThe dynamic soil layer module is used to manipulatesoil layer structures to maintain stability and efficiencyof the soil temperature and moisture calculations, whenthe thickness of the organic layer is changed by wildfiredisturbance and ecological processes. There are at most 2moss layers, 3 shallow organic layers, and 3 deep organiclayers. The minimum thickness of a soil layer is set to 2 cm.When an organic layer is too thin, it may be either removedor combined to an adjacent soil layer of the same type.When an organic layer is too thick, it will be divided intotwo layers.DatasetsThe input datasets include nonspatial datasets (atmosphericCO 2concentration and fire size), grid-level datasets (0.5°by 0.5°, climate, fire return interval, fire season and soiltexture), and pixel-level datasets (1 km by 1 km vegetationtype, drainage, and fire history).Three different cohort-level datasets have been created,based on grid- and pixel-level information. To initializeDSL-TEM, each cohort is run to an equilibrium state usingthe 1901–1930 mean climate, without disturbances. Theequilibrium cohort is a unique combination of drainage,vegetation, and climate. During the next phase of simulation,the spinup stage, each cohort is run using 1901–1930atmospheric data in a cyclic fashion that considers firedisturbance over the period 1001–1900. Thus the spinupcohort is a unique combination of equilibrium cohort and firehistory during period 1001–1900. To save computing time,the fire history has been reclassified into several categoriesbased on the first recorded fire occurrence after 1900. Thefinal phase of the simulation results in a transient cohort thatis a unique combination of a spinup cohort and both climateand fire history from 1901–2006.Overall, for black spruce in the Yukon River Basin, thereare 1,167 equilibrium cohorts, 6,858 spinup cohorts, and40,738 transient cohorts. The total black spruce area in theYukon River Basin is 213,513 km 2 .Model ExperimentThe DSL-TEM was first run to equilibrium state in year1000 and then through the spinup phase over the period from1001–1900. A factorial experiment of 8 simulations was thenperformed over the period from 1901–2006, consideringthe effects of CO 2fertilization (constant vs. transient CO 2),climate (constant vs. transient climate), and fire disturbance(with and without fire disturbance).Results and Discussion1. The mean annual air temperature increased 0.39 to1.14°C over the Yukon River Basin (YRB) between 1950–1975 and 1976–2000. Winter precipitation (DJF) increased4–20 mm at the eastern and western ends of the YRB, anddecreased by 7–14 mm in the Tanana River, Eastern CentralYukon, and Koyukuk River sub-basins between the same timeperiods. The unfrozen column, which is defined as the meanthickness of unfrozen soil layer over a year, increased at boththe eastern and westerns ends of the YRB, but decreased inthe central YRB. This suggests that winter snowfall playsa more important role than air temperature in affectingpermafrost dynamics between the two time periods.2. For the whole YRB, climate plays a dominant rolein determining the thermal state of soil. The effects of fireon soil thermal state are relatively small, in part due to thesmall fraction of burn area, and in part due to the decrease ofwinter snowfall in areas with high fire return interval.3. Fire plays a dominant role in determining the netcarbon flux between the land surface and the atmosphere,especially after 1985. The difference between simulationswith and without fire can be 140 gC m -2 . However, theindirect effect of fire through increasing soil temperature onsoil decomposition is relatively small, usually less than 10gC m -2 .AcknowledgmentsWe would like to thank other coauthors, including EricKasischke, Kristen Manies, Larry Hinzman, Anna Liljedahl,Jim Raderson, Heping Liu, Vladimir Romanovsky, SergeyMarchenko, and Kim Yongwon.ReferencesKasischke, E.S. & Turetsky, M.R. 2006. Recent changesin the fire regime across the North American borealregion – Spatial and temporal patterns of burningacross Canada and Alaska. Geophysical ResearchLetters 33: doi:10.1029/2006GL025677.Yi, S., McGuire, A.D., Harden, J., Kasischke, E., Manies,K., Hinzman, L., Liljedahl, A., Randerson, J., Liu, H.,Romanovsky, V. & Marchenko, S. 2007. A dynamicsoil layer model for assessing the effects of wildfireon high latitude terrestrial ecosystem dynamics. The2007 Fall Meeting of American Geophysical Union,December 10–14, 2007, San Francisco, CA.358
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NICOP 2008 Ninth <
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ContentsPreface ...................
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Mapping and Modeling the Distributi
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Satellite Observations of Frozen Gr
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xiiIce Wedge Thermal Regime in Nort
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xivPermafrost Response to Dynamics
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NICOP SponsorsUniversitiesUniversit
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Deep Permafrost Studies at the Lupi
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Effect of Fire on Pond Dynamics in
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Cryological Status of Russian Soils
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Acoustical Surveys of Methane Plume
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Permafrost Delineation Near Fairban
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Preparatory Work for a Permanent Ge
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A Provisional Soil Map of the Trans
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Martian Permafrost Depths from Orbi
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Time Series Analyses of Active Micr
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Impact of Permafrost Degradation on
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DC Resistivity Soundings Across a P
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Modeling Thermal and Moisture Regim
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A Provisional Permafrost Map of the
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Alpine Permafrost Distribution at M
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Cryogenic Formations of the Caucasu
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Modeling Potential Climatic Change
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A Hypothesis: A Condition of Growth
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Modeled Continual Surface Water Sto
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Freeze/Thaw Properties of Tundra So
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Discontinuous Permafrost Distributi
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Thermal Regime Within an Arctic Was
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Seasonal and Interannual Variabilit
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Twelve-Year Thaw Progression Data f
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Continued Permafrost Warming in Nor
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Landsliding Following Forest Fire o
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A Permafrost Model Incorporating Dy
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Seasonal Sources of Soil Respiratio
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Greenland Permafrost Temperature Si
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The Importance of Snow Cover Evolut
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The Account of Long-Term Air Temper
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The Combined Isotopic Analysis of L
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Adaptating and Managing Nunavik’s
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Human Experience of Cryospheric Cha
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HiRISE Observations of Fractured Mo
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A Soil Freeze-Thaw Model Through th
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Mapping and Modeling the Distributi
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First Results of Ground Surface Tem
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Historical Changes in the Seasonall
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Rock Glaciers in the Kåfjord Area,
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Snowpack Evolution on Permafrost, N
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Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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