Recoupling fire and grazing reduces wildland fuel loads on rangelands

Heath D Starns,R Dwayne Elmore,Dirac Twidwell,Eric T Thacker,Torre J Hovick,Barney Luttbeg,Samuel D Fuhlendorf

doi:10.1002/ecs2.2578

Abstract

AbstractFire suppression and exclusion, the historically dominant paradigm of fire management, has resulted in major modifications of fire‐dependent ecosystems worldwide. These changes are partially credited with a recent increase in wildfire number and extent, as well as more extreme fire behavior. Fire and herbivory historically interacted, and research has shown that the interaction creates a unique mosaic of vegetation heterogeneity that each disturbance alone does not create. Because fire and grazing have largely been decoupled in modern times, the degree to which the interaction affects fuels and fire regimes has not yet been quantified. We evaluated effects of fire‐only and pyric herbivory on rangeland fuels and fire behavior simulated using BehavePlus at four sites across the southern Great Plains. We predicted patches managed via pyric herbivory would maintain lower fuel loads, and less intense simulated fire behavior than fire alone. We found that time since fire was a significant predictor of fuel loads and simulated fire behavior characteristics at all sites. Fuel loads and simulated fire behavior characteristics (flame length and rate of spread) increased with increasing time since fire in all simulated weather scenarios. Pyric herbivory mediated fuel accumulation at all sites. Mean fuel loads in fire‐only treatments exceeded 5000 kg/ha within 24 months, but pyric herbivory treatments remained below 5000 kg/ha for approximately 36 months. Simulated flame lengths in fire‐only treatments were consistently higher (up to 3 × ) than in pyric herbivory treatments. Similarly, fire spread rates were higher in fire‐only than in pyric herbivory treatments in all simulated weather conditions. Although all sites had potential to burn in the most extreme weather conditions, pyric herbivory reduced fuel accumulations, flame lengths, and rates of spread across all weather patterns simulated. These reductions extended the amount of time standard wildland firefighting techniques remain effective. Therefore, incorporating pyric herbivory into fuel management practices, in areas of high herbaceous productivity, increases the effectiveness of fuel treatments.

Highlights

Fire and grazing have occurred on every vegetated continent for millions of years and are two of the primary factors that influence most aspects of the dominant ecosystems of the world (Bond and Keeley 2005, Bowman 2005, Archibald et al 2013)
Time since fire was a significant predictor of biomass and 1-h fuel loads across study sites, and when grazing interacted with fires, the fuel management lasted longer than when grazing was excluded
Months since fire was a significant predictor of biomass, which increased with months since fire (MSF) (b = 2.19, r = 0.088, P < 0.001)

Summary

Introduction

Fire and grazing have occurred on every vegetated continent for millions of years and are two of the primary factors that influence most aspects of the dominant ecosystems of the world (Bond and Keeley 2005, Bowman 2005, Archibald et al 2013). Subsequent decades of fire exclusion, coupled with heavy uniform grazing by domestic livestock, in addition to a host of other environmental and anthropogenic factors, contributed to extensive transformation of grasslands into shrublands and woodlands (Archer et al 2017). This transition, primarily caused by the decoupling of fire and grazing (Fuhlendorf et al 2009), shifted fuel structure allowing large, catastrophic wildfires

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