Long-Term Impacts of Fuel Treatment Placement with Respect to Forest Cover Type on Potential Fire Behavior across a Mountainous Landscape

Seth A Ex,Chad M Hoffman,Justin P Ziegler,Wade T Tinkham

doi:10.3390/f10050438

Abstract

Research Highlights: The impact of variation in fuels and fuel dynamics among forest cover types on the outcome of fuel treatments is poorly understood. This study investigated the potential effects of treatment placement with respect to cover type on the development of potential fire behavior over time for 48 km2 of forest in Colorado, USA. Our findings can inform the placement of fuel treatments in similar forests to maximize their effectiveness and longevity. Background and Objectives: Efficient placement of fuel treatments is essential to maximize the impact of limited resources for fuels management. We investigated how the placement of treatments with respect to forest cover type affected the rate of spread, size, and prevalence of different fire types for simulated wildfires for 50 years after treatment. Materials and Methods: We generated an analysis landscape consisting of two cover types: stands on southerly aspects had low rates of tree growth and regeneration compared to stands on northerly aspects. We then simulated 1) thinning treatments across 20% of the landscape, with treatments exclusively located on either southerly (‘south treatment’) or northerly (‘north treatment’) aspects; 2) subsequent tree growth and regeneration; and 3) wildfires at 10-year intervals. Finally, we used metrics of fuel hazard and potential fire behavior to understand the interplay between stand-level fuel dynamics and related impacts to potential fire behavior across the broader landscape. Results: Although post-treatment metrics of stand-level fuel hazard were similar among treatment scenarios, only the south treatment reduced rates of fire spread and fire size relative to no treatment. Most differences in modeled fire behavior between treatment scenarios disappeared after two decades, despite persistently greater rates of stand-level fuel hazard development post-treatment for the north treatment. For all scenarios, the overall trajectory was of shrinking fires and less crown fire behavior over time, owing to crown recession in untreated stands. Conclusions: Systematic differences among cover types, such as those in our study area, have the potential to influence fuel treatment outcomes. However, complex interactions between treatment effects, topography, and vegetation structure and dynamics warrant additional study.

Highlights

Over a century of past land management practices including fire exclusion, timber harvesting and grazing have contributed to greater structural homogeneity in many dry, western USA conifer forests at stand and landscape scales [1,2,3,4,5]
Results: post-treatment metrics of stand-level fuel hazard were similar among treatment scenarios, only the south treatment reduced rates of fire spread and fire size relative to no treatment
Pre- to post-treatment changes in stand structure metrics were relatively greater for stands on northerly aspects compared to stands on southerly aspects apart from QMD, which increased by 2% and 6%, respectively

Summary

Introduction

Over a century of past land management practices including fire exclusion, timber harvesting and grazing have contributed to greater structural homogeneity in many dry, western USA conifer forests at stand and landscape scales [1,2,3,4,5] These changes in forest structure, alongside increasing drought. In response to these changes, forest managers often design and implement treatments to moderate fire behavior by manipulating the amount and arrangement of fuels in forest stands This generally consists of fuel reduction through treatments that often involve thinning and / or prescribed fire to achieve a combination of objectives that typically include reduced canopy fuel connectivity, removal of ladder fuel, and reduced surface fuel load [13,14]. Many of these treatments occur in dry, mixed-conifer forests which are characterized by spatial patterns in forest cover types that are related to topography

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