Assessing the Relationship between Forest Structure and Fire Severity on the North Rim of the Grand Canyon

Valentijn Hoff,Casey Teske,Tim Wallace,Lloyd Queen,Eric Rowell

doi:10.3390/fire2010010

Valentijn Hoff, Casey Teske + Show 3 more

Open Access

https://doi.org/10.3390/fire2010010

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Abstract

While operational fire severity products inform fire management decisions in Grand Canyon National Park (GRCA), managers have expressed the need for better quantification of the consequences of severity, specifically forest structure. In this study we computed metrics related to the forest structure from airborne laser scanning (ALS) data and investigated the influence that fires that burned in the decade previous had on forest structure on the North Rim of the Grand Canyon in Arizona. We found that fire severity best explains the occurrence of structure classes that include canopy cover, vertical fuel distribution, and surface roughness. In general we found that high fire severity resulted in structure types that exhibit lower canopy cover and higher surface roughness. Areas that burned more frequently with lower fire severity in general had a more closed canopy and a lower surface roughness, with less brush and less conifer regeneration. In a random forests modeling exercise to examine the relationship between severity and structure we found mean canopy height to be a powerful explanatory variable, but still proved less informative than the three-component structure classification. We show that fire severity not only impacts forest structure but also brings heterogeneity to vegetation types along the elevation gradient on the Kaibab plateau. This work provides managers with a unique dataset, usable in conjunction with vegetation, fuels and fire history data, to support management decisions at GRCA.

Highlights

Fire, as a disturbance, is a key driver in the diversification of forested ecosystems in terms of forest structure and species response [1]
The structure classification we use which includes a horizontal canopy component, a vertical canopy component and a surface fuel component is sensitive to previous fire severity
Mean canopy height was a good explanatory variable, especially in areas that burned with a high severity, where the canopy height was severely reduced

Summary

Introduction

As a disturbance, is a key driver in the diversification of forested ecosystems in terms of forest structure and species response [1]. Fire is a fundamental disturbance process globally; spatio-temporal expressions of fire events equate to the fire regime of a specific landscape, which are net effects on the landscape based on the type, intensity, size, and frequency of fire [2,3]. The mosaic of fire severity types within the landscape can be considered the driving force behind forest structure, as absence of disturbance would end in the expected result of a steady-state condition [4]. Embedded within fire regimes is the expectation that most forested lands in the western U.S. are composed of mixed-severity burns [5], where a single fire event will exhibit a range of patterns, intensity, severity, and disturbance interactions that affect how fire propagates across a landscape [6]. We posit that the expected severity of fire should result in predictable patterns of forest structure across a landscape

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