Abstract
Evidence of increasing fire extent and severity in the western US in recent decades has raised concern over the effects of fire on threatened species such as the spotted owl (Strix occidentalis Xantus de Vesey), which nests in forests with large trees and high canopy cover that are vulnerable to high-severity wildfire. A dichotomy of views exists on the impact of high-severity wildfire on the spotted owl. One view holds that reduction in the extent of forests with large trees and high canopy cover due to high-severity wildfire is a primary threat to spotted owls, and that fuels reduction treatments that successfully reduce the risk of high-severity wildfire can aid in sustaining desired conditions for this owl. A conflicting view maintains that high-severity wildfire was relatively common in many forest types occupied by spotted owls and does not pose an immediate threat to spotted owls, and that fuels reduction treatments are misguided because they degrade owl habitat and do not reduce the extent of high-severity fire. Based on the existing literature, we argue that considerable uncertainty remains regarding the response of spotted owls to high-severity wildfire, especially over longer time frames and across the three subspecies (California [Strix occidentalis occidentalis Xantus de Vesey], Mexican [S. o. lucida Nelson], and northern [S. o. caurina Merriam]) of spotted owls. The considerable extent of high-severity wildfire within the ranges of these subspecies over recent years, coupled with the trend toward increasing extent and severity of megafires, suggests that the cumulative effects of these fires could be significant throughout the range of this owl. Forest restoration or fuels reduction treatments may aid in reducing habitat loss, particularly when strategically located to optimize reduction of fire risk, but also may locally impact spotted owl habitat. We advocate further evaluation of both the impacts of such treatments to spotted owls and the effectiveness of such treatments in mitigating fire behavior. We also advocate wider use of managed fire to reduce risk of high-severity wildfire. Finally, given the paucity of long-term data on this topic, we recommend targeted research aimed at a decade or longer time periods after fires. These studies should include measures of demographic performance, and should be designed to elucidate differences in those metrics related to landscape pattern, forest type, and subspecies ecology. Such information would inform the debate over how to integrate the conservation of spotted owls and their habitat with fuels reduction and forest restoration objectives.
Highlights
Fire historically served as a major disturbance agent structuring forests in the western United States (Agee 1993, Covington et al 1994, Allen et al 2002, Baker 2015a)
Based on the existing literature, we argue that considerable uncertainty remains regarding the response of spotted owls to high-severity wildfire, especially over longer time frames and across the three subspecies (California [Strix occidentalis occidentalis Xantus de Vesey], Mexican [S. o. lucida Nelson], and northern [S. o. caurina Merriam]) of spotted owls
Due to stand density and abundance of dead material, most nesting stands have high fuel loads and are vulnerable to high-severity wildfire. This is true in drier forest types, but even mesic nesting stands can be vulnerable when embedded in landscapes dominated by drier forest types that are susceptible to crown fires following decades of fire suppression
Summary
Fire historically served as a major disturbance agent structuring forests in the western United States (Agee 1993, Covington et al 1994, Allen et al 2002, Baker 2015a). A conflicting viewpoint has emerged, suggesting that fuels-reduction treatments are unnecessary and misguided because they degrade owl habitat, do not reduce the extent of high-severity fire, and may result in greater loss of spotted owl habitat than wildfire alone would cause (Hanson et al 2009a, b; DellaSala et al 2013; Odion et al 2014; Baker 2015b; Hanson and Odion 2016; but see Spies et al 2009). Sub- Parameter Salvage Owls or Fires Years post species evaluated logging territories (n) (n) fire (n) Response
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