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Enduring effects of megafires on spotted owls

Date: August 31, 2021

The negative effects of megafires on spotted owls are not ephemeral, but instead are likely to be enduring.

A map of the 2014 King Fire area, with spotted owl nesting sites shown by dots and the study area outlined. The fire burned a portion of the study area.
Study area map showing the distribution of spotted owl sites in relation to the King Fire. The Before–After Control-Impact natural experiment was made possible because some sites were unburned while other sites experienced a gradient of burn severity.
The combination of historical fire suppression and ongoing climate change is a recipe for megafires in the seasonally dry forests of western North America. Reducing the risk of large, stand-replacing fires can be partly achieved through fuels reduction and forest restoration activities, but these actions can alter the habitat of wildlife species. Understanding the short- and longer-term impacts of megafires on sensitive old forest-dependent wildlife like the spotted owl (Strix occidentalis) is a key element to understanding forest restoration trade-offs. For example, if megafires are detrimental to the spotted owl, fuels reduction and forest restoration that reduce the likelihood that such fires occur are likely to provide benefits to this and other old-forest species.

We have studied a population of spotted owls in the central Sierra Nevada, CA since the 1980s – tracking owl survival, reproduction, and territory occupancy on an annual basis. Then, 25 years after we began the study, a large, severe fire (the King Fire) burned through approximately half of our long-term study area in 2014, creating a rare and powerful opportunity to study the effects of fire on spotted owls via a natural experiment (i.e., a ‘before-after control-impact’ study design). In other words, with half of our study area having burned and the other half remaining unburned, along with a quarter-century of pre-fire data, we could directly evaluate the effects of the fire on our population of owls by comparing the status of owls in burned and unburned areas. We tracked the trajectory of owl populations and drivers of territory occupancy for 6-years post-fire.

A graph showing spotted owl occupancy grouped by fire severity pre- and post-fire. Occupancy in sites with >50% severe fire drops sharply post-fire.
Derived annual occupancy from 1989 to 2020 for spotted owl sites grouped by the percentage of the home range (1500 m) that experienced severe fire. The grey vertical line indicates the timing of the 2014 King Fire.

Key Findings

  • Extensive severe fire within spotted owl territories resulted in both immediate territory abandonment and prolonged lack of re-colonization by owls six years post-fire.
  • Each additional 10 hectares of severe fire decreased the likelihood that owls would persist in a territory by 7.8% and decreased the likelihood a territory would be recolonized post-fire by 8.3%.
  • Owl territories that experienced a greater mix of burn intensities (or high “pyrodiversity”) tended to persist after the fire.
  • Salvage logging did not explain variation in post-fire persistence or recolonization; effects to owls could only be attributed to severe fire extent and pyrodiversity.
  • Given the severe and persistent impacts of the King Fire on spotted owls, our work suggests that fuels reduction that limits megafires could benefit this species.

Featured Publications

Jones, Gavin ; Kramer, H. A. ; Berigan, W. J. ; Whitmore, S. A. ; Gutierrez, R. J. ; Peery, M. Z. , 2021

Principal Investigators: 
Principal Investigators - External: 
M. Zach Peery - University of Wisconsin