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RESEARCH ARTICLE
Contents Vol 17(4)

Evaluating the ability of the differenced Normalized Burn Ratio (dNBR) to predict ecologically significant burn severity in Alaskan boreal forests

Karen A. Murphy A C , Joel H. Reynolds A and John M. Koltun B
+ Author Affiliations
- Author Affiliations

A US Fish and Wildlife Service, National Wildlife Refuge System, 1011 E Tudor Road MS221, Anchorage, AK 99503, USA.

B Geographic Resource Solutions, Anchorage, AK 99503, USA.

C Corresponding author. Email: Karen_A_Murphy@fws.gov

International Journal of Wildland Fire 17(4) 490-499 https://doi.org/10.1071/WF08050
Submitted: 7 April 2008  Accepted: 6 May 2008   Published: 6 August 2008

Abstract

During the 2004 fire season ~6.6 million acres (~2.7 million ha) burned across Alaska. Nearly 2 million of these were on National Wildlife Refuge System lands inaccessible from the state’s limited road system. Many fires burned through September, driven by unusually warm and dry temperatures throughout the summer. Using several fires from this season, we assessed the national burn severity methodology’s performance on refuge lands. Six fires, spanning 814 489 acres (329 613 ha), were sampled on five boreal forest refuges. In total, 347 sites were sampled for vegetation composition and ground-based burn severity estimates following the national protocols. The relationship between the differenced Normalized Burn Ratio (dNBR) and composite burn index (CBI) was unexpectedly weak (R2adjusted, 0.11–0.64). The weak relationship was not a result of data or image processing errors, nor of any biotic or abiotic confounding variable. The inconsistent results, and dNBR’s limited ability to discern the ecologically significant differences within moderate and high severity burn sites, indicate that the current methodology does not satisfy key Alaskan boreal forest management objectives.

Additional keywords: Alaska, black spruce, composite burn index (CBI), fire effects, NBR, Picea, remote sensing, vegetation succession.


Acknowledgements

This has been a collaborative effort as multiple agencies and groups have worked with us to identify problems and discuss solutions. Some of the key individuals that have provided valuable assistance are Jennifer Allen and Brian Sorbel (National Park Service) who graciously shared data and ideas, Dave Verbyla (University of Alaska – Fairbanks), Eric Kasischke (University of Maryland), Merritt Turetsky (University of Michigan), and Nancy French (Michigan Technological University) who all shared preliminary results from their research. Stephen Howard, Randy McKinley, Zhi-Liang Zhu, and Jeffery Eidenshink of the EROS Data Center as well as Nate Benson (NPS) and Carl Key (Missoula Fire Laboratory) have been patient and helpful as we have encountered problems and looked for solutions. Finally, this project could not have been completed without Lisa Saperstein (Kanuti Refuge), Steve Kovach (Innoko Refuge), Merben Cebrian (Tetlin Refuge) and Michael Stefancic (intern) who were integral in data collection and in supporting this work. The manuscript was greatly improved in response to comments from two anonymous reviewers.


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