by Robert Onstott
In 2002 the McNally Fire burned through Sequoia National Forest in the southern part of the Sierra Nevada mountains in California. Like most forest fires, the effects of the burn were not evenly distributed, instead creating a mosaic pattern with patches ranging in severity from undisturbed (no fire at all) to high severity areas where the canopy had been entirely killed, and everything in between. Four years after the McNally Fire, researchers wanted to get an idea of how one of the area’s local inhabitants, the California spotted owl, was getting on (Bond, Lee, et al; 2009). Specifically, they wanted to know if the spotted owls were spending any time in the areas that had been burned.
They found a total of 7 different spotted owls, captured them, and put little radio transceiver “backpacks” onto them. This allowed them to track the owls’ locations, from their daytime roosting to their nighttime foraging missions. Overlay the owls’ coordinates with Forest Service maps of burn severity, and you get a really clear picture of how much or how little the spotted owls are hanging out in post-burn zones.
The movement to save the last remaining old-growth forests has become synonymous with conserving the spotted owl species—the Northern spotted owl in Oregon, Washington, & northern California, and the California spotted owl further south. This is because they have evolved to be specialists within old-growth forests of the west, of which there are scarce remnants due to a century of heavy logging. With the marked increase of large-scale forest fires in the West, the question arises: do the owls use the burned landscape, and if they do, do burned forests need to be a priority for conservation?
Back to those 7 owls and their radio “backpacks”—what did the researchers find? Most strikingly, when it came to foraging, the owls didn’t just use the post-burn areas, they seemed to prefer them. Spotted owls are very particular about where they nest during their breeding season, settling in cavities high up in the canopy of mature, large-diameter trees, so it was no surprise to find that, when it came to nesting and roosting, the owls chose either undisturbed or low-intensity burn areas. But when it came to foraging for prey, the owls spent more time in high-severity burn areas than any other designation. The researchers who published this study (Bond, Lee, et al; 2009) interpreted this as a function of increased prey abundance due to proliferation of post-fire plant cover:
Spotted owl prey species, including dusky-footed woodrats, are more abundant in plant communities with greater understory hardwood, shrub, and herbaceous cover. Understory plants, particularly shrubs and forbs, provide food for woodrats and dense shrubs provide excellent cover. Both of these factors may contribute to greater abundance of this key prey species and stimulate attraction by spotted owls to high-severity burned sites after postfire vegetation regrowth has produced a modest understory.
Later on, the same researchers used Forest Service data to compare the occupancy of spotted owls both before and after the Rim Fire in California, showing that owls re-occupy old nesting sites at a rate of 90% even in the most extreme burn scenarios—where there is no living canopy anywhere within the spotted owls’ 300 acre Protected Activity Center (Lee, Bond; 2015).
Just imagine that! You are out hiking through a burned forest, which was spared from salvage logging by virtue of sitting inside the boundaries of a wilderness area. You see an owl fly into the cavity of a scorched and limbless trunk. Any direction you turn, you’d have to walk a ways to get to the next living tree—few green boughs, little to no canopy or shade, just legions of what look like to you like charcoal telephone poles. You wonder how that owl could survive in this landscape, much less the delicate babies tucked inside of that trunk. In your eyes, this might as well be the surface of the moon. It is beautiful in its own way, but you can’t separate yourself from that feeling of loss. Just a year ago you would have been standing under a canopy so thick that you could barely see the sky, and now you can’t find anywhere to escape it. But life is more dogged and resourceful than you can even imagine. You have been misled by your casual aesthetic intuition of what it means to be full of life; because even here, where the change is so dramatic, the spotted owls come back to reuse their old nests at a rate of 90%.
Most of us agree that when it comes to conservation, there’s no native species too humble to deserve protection. This is inherent to the whole concept of biodiversity, by which we understand that complex life (including human life, for that matter) is only possible because of the high density of inter-species interaction. Nonetheless, certain species seem to get picked as ambassadors for all the rest. They tend to be things we can see without a microscope, maybe a little bit more charismatic than the (equally important) insects and microbes, and they tend to be keystone species whose existence is wholly dependent on the health of the ecosystem that supports them. This makes them valuable indicators—if they are hurting, that’s a good sign that the vitality of the whole ecological scaffolding under them is also in a depleted state. When it comes to old growth forests in the Cascades and Sierras, this species is the spotted owl.
Ever since we realized that these owls had evolved as specialists in mature forests, characterized by high canopies and a diverse composition, we also recognized that they might be driven to extinction if we did not do something to protect the last remnants of their old-growth habitat. But now we understand that whatever the quality is that makes old-growth forests suitable to spotted owls, this quality does not go away after a burn.
Humans may have exacerbated the causes of forest fires, but we did not invent them. Throughout the spotted owl’s evolution, forests periodically burned, and the spotted owl figured out how to deal with it. The post-burn forest is a natural part of the spotted owl’s habitat—one that, weirdly, is kind of endangered. For decades now, we have done everything possible to suppress forest fires, and when they have happened, we have written it off as a loss and sent in logging trucks to haul off the ‘debris.’ So, as far as the spotted owl is concerned, our reaction to forest fire needs to be more nuanced than just: ”cut and replant.” Burns, it turns out, are also an opportunity—an opportunity to regenerate a missing component of the spotted owl’s ancestral habitat.
To see a presentation by Monica Bond related to this research, check out this webinar from Great Old Broads for Wilderness.