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International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire
RESEARCH ARTICLE

Do you CBI what I see? The relationship between the Composite Burn Index and quantitative field measures of burn severity varies across gradients of forest structure

Saba J. Saberi A B , Michelle C. Agne A and Brian J. Harvey A
+ Author Affiliations
- Author Affiliations

A School of Environmental and Forest Sciences, University of Washington, Seattle, WA 98195, USA.

B Corresponding author. Email: sjsaberi@uw.edu

International Journal of Wildland Fire 31(2) 112-123 https://doi.org/10.1071/WF21062
Submitted: 12 May 2021  Accepted: 24 November 2021   Published: 11 January 2022

Abstract

Burn severity in forests is commonly assessed in the field with visual ordinal estimates such as the Composite Burn Index (CBI). However, how CBI (a composite of several individual field measures) relates to independent quantitative measures of burn severity (e.g. fire-caused tree mortality, surface charring) has not been widely tested. Here, we use field data from 315 plots in 14 fires in the north-western USA to ask: (1) how CBI relates to eight independent field measures of burn severity; and (2) how these relationships vary across gradients of pre-fire forest structure. Overall, CBI corresponded well with most independent field measures, but some measures of extreme burn severity (e.g. deep charring on trees and snags) were not captured by CBI. Additionally, some measures of canopy burn severity corresponded to lower CBI values in forests with larger average tree size (diameter and height) – potentially from decoupling of surface and canopy fire effects in stands with larger, fire-resistant trees. Our findings suggest continued broad utility of CBI, while highlighting how the correspondence of aggregate plot-level CBI to different measures of burn severity can vary with forest conditions. We also suggest considerations for broadening CBI to account for more extreme levels of burn severity.

Keywords: Cascade Mountains, conifer forests, deep char, fire ecology, fire effects, north-western USA, Rocky Mountains, tree mortality.


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