Ninth International Conference on Permafrost ... - IARC Research

Effect of Fire on Pond Dynamics in Regions of Discontinuous Permafrost: A State ofChange Following the Fires of 2004 and 2005?Garrett AltmannSchool of Natural Resources and Agricultural Sciences, University of Alaska FairbanksDave VerbylaSchool of Natural Resources and Agricultural Sciences, University of Alaska FairbanksKenji YoshikawaWater and Environmental Research Center, Institute of Northern Engineering, University of Alaska FairbanksJohn FoxSchool of Natural Resources and Agricultural Sciences, University of Alaska FairbanksIntroductionClimate change at high latitudes affects both thedisturbance and hydrologic regimes of boreal forests.Throughout Interior Alaska, wildfire is the dominantdisturbance regime regulating boreal forests associatedwith discontinuous permafrost. In recent years, fire activityhas signaled a potential shift in this disturbance regime, assignificant increases in total burned area and burn severityhave occurred. The effects of a potential regime shift mayhave profound impacts on the permafrost and hydrologicfeatures associated with it.Previous studies have examined the effects of fire onpermafrost and have attributed a deepening of the activelayer, as well as increased soil moisture resulting from theremoval of insulating vegetation during fire (Yoshikawa etal. 2002, Liljedahl et al. 2007, Burn 1998). Ishikawa et al.(2008) has further implicated fire severity as a significantsource of variability among these effects. To examine therelationship between fire, burn severity, and pond dynamics,this study uses remote sensing and GIS to compare pondsaffected by fire, to ponds not affected by fire.Data and MethodsWe use remote sensing and geographic informationsystems (GIS) to examine the effect of fire on pond sizesthroughout four Interior Alaska basins: Tanana Valley, YukonFlats, Innoko Flats, and Minchumina Basin (Fig. 1). UsingLandsat TM/ETM+ imagery and historic fire parametersattained from the Alaska Fire Service, a multi-temporalanalysis from 1980 to present is used to observe surface areachanges in ponds following fires. To observe pond dynamicsin fire-affected areas, historic burn parameters are overlaidon pre-fire and post-fire georeferenced Landsat scenes. AllGIS layers are analyzed using the Alaska Alber’s Equal Areaprojection to provide accurate representations of surfacearea. Pond dynamics within burn areas are then compared toponds outside burn parameters. Ponds displaying variabilityare tagged and compared at varying time periods. To evaluatethe influence of fire severity, we examine thermal IR (band6) data within the burn area from imagery attained one yearpost-burn. As a test of our methodology, a pilot study wasapplied to the Yukon Flats portion of our study area. DespiteFigure 1. Study area locations.the inability to assess pond depth from a remote sensingperspective, we feel confident our methodology will allow usto observe pond dynamics in relation to fire in the remainingstudy areas.ResultsInitial results reveal a static state of pond sizes followingfires prior to 2004. During the larger, more severe firesoccurring in 2004 and 2005, ponds located in burn areasshow greater variability in surface area than ponds locatedoutside the burn area. Increased shrinkage was observedwithin burn areas during the years immediately followingthe fire. Short-term observations (1–3 years) in burn areasprior to 2004 do not reveal this effect. Periods 5–15 yearsfollowing a fire show little/no variability in surface area,and fluctuations tend to be dominated by the regional watertable. Long-term (15–25 years) reveal similar trends to thoseexperienced during short-term observations associated withhigh fire severity.DiscussionIn our initial hypothesis, we expected pond sizes withinburn parameters to increase as a result of the removal ofa transpiring vegetation layer. Contrary to this hypothesis,we observe a decrease in surface area of ponds in areas3