Monitoring Post-Fire Successional Patterns in Interior Alaska
 Biomass burning is one of the most prevalent vehicles of land cover change in the sub-arctic boreal forest, with the frequency of large fire years more than doubling over the past half century across Canada and Alaska. Post-fire succession impacts energy budgets, net ecosystem carbon balance, hydrology, and other ecosystem services, particularly subsistence resources used by Native Peoples in interior Alaska. Successional patterns in burned black spruce forests of interior Alaska are heavily influenced by burn severity, as measured by the burning of deep surface organic layers. Research has shown that more intensely burned black spruce forests are more likely to be colonized by deciduous species such as aspen. If the severity of fires have increased in interior Alaska in recent decades, a feedback mechanism would exist that causes a shift in the species composition of the region to a novel ecosystem: a mix of black spruce and aspen or birch.
 The goal of this research is to determine what factors control shifts in post-fire succession in Alaskan black spruce forests, the dominant species of the Alaskan boreal forest. A combination of remote sensing and in situ data are used to monitor recent variations in the fire regime and altered patterns of post-fire regeneration. Projections of how successional trajectories are likely to unfold in the future will be based on the interactions between fire regime characteristics and mediating environmental conditions. These projections will be incorporated with models of vegetation and biogeochemical cycling to determine impacts on carbon cycling and albedo.
Spatial patterns of burning and variations in severity are determined from Landsat-derived data from the Monitoring Trends in Burn Severity (MTBS) project. Live fire detections from the Moderate Resolution Imaging Spectroradiometer are useful for determining temporal characteristics such as fire frequency and seasonality. Additional sensors such as the Advanced Very High Resolution Radiometer as well as burned area maps from the Alaska Forest Service and the Bureau of Land Management can potentially extend the historical dataset. Because of the difficulty of determining some severity characteristics from spectral data alone, ancillary indicators such as Fire Weather Index can aide in mapping severity in black spruce stands.
 Successional patterns can be observed from remote sensing data, particularly vegetation indices (VIs) such as NDVI or EVI. A map of burn severity in the Alaskan boreal forest will be used to prioritize areas for remote sensing based observation of potential shifts in dominant species. Areas that have regenerated as deciduous dominated stands or a mixed conifer and deciduous stand exhibit a higher VI, seasonal phenology corresponding to green-up and senescence, and higher summer and winter albedo.
In situ observations of pre- and post-burn characteristics such as those collected by the Joint Fire Science Program (JFSP) allow us to determine at a fine scale the mediating environmental conditions in which shifts in succession may occur. Soil properties such as depth of organic layer, soil temperature, texture, and moisture are potential contributing factors to successional trajectory that are difficult if not impossible to determine remotely. The combination of in situ and remote sensing data allow us to observe the mitigating environmental conditions that govern successional shifts and to “scale up” these observations to determine the impact on ecosystem structure and functioning on a landscape scale.
 Finally, it is likely that the shifts that are occurring in species composition will have an impact on future fire regime characteristics. The interactions between vegetation, climate, and fire create the potential for both positive and negative feedbacks with implications for biogeochemical cycles. Patterns of successional growth based on recovery from fire disturbance are a useful input to regional dynamic vegetation models, such as the Alaskan Frame-Based Ecosystem Code (ALFRESCO) and global biogeochemical models such as the Terrestrial Ecosystem Model (TEM). Currently many of these models assume species self-replacement following a fire-related disturbance.
The direct linking of remote sensing and extensive in situ data provides an opportunity to examine the causes of shifts in successional growth, as well as the ability to map such changes at a landscape scale. A spatially explicit model of successional trajectory in the Alaskan boreal forest will likely improve models of vegetation and biogeochemical cycling, providing a more accurate characterization of the interactions between vegetation, climate, and fire.
Principle Investigator: Kirsten Barrett (kbarrett@usgs.gov, 907 786 7419)
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