The Ecological Importance of California’s Rim Fire
Large, intense fires have always been a natural part of fire regimes in Sierra Nevada forests
Since the Rim fire began in the central Sierra Nevada on August 17, there has been a steady stream of fearful, hyperbolic, and misinformed reporting in much of the media. The fire, which is currently 188,000 acres in size and covers portions of the Stanislaus National Forest and the northwestern corner of Yosemite National Park, has been consistently described as “catastrophic”, “destructive”, and “devastating.” One story featured a quote from a local man who said he expected “nothing to be left”. However, if we can, for a moment, set aside the fear, the panic, and the decades of misunderstanding about wildland fires in our forests, it turns out that the facts differ dramatically from the popular misconceptions. The Rim fire is a good thing for the health of the forest ecosystem. It is not devastation, or loss. It is ecological restoration.
Photo courtesy USDA
What relatively few people in the general public understand at present is that large, intense fires have always been a natural part of fire regimes in Sierra Nevada forests. Patches of high-intensity fire, wherein most or all trees are killed, creates “snag forest habitat,” which is the rarest, and one of the most ecologically important, forest habitat types in the entire Sierra Nevada. Contrary to common myths, even when forest fires burn hottest, only a tiny proportion of the aboveground biomass is actually consumed (typically less than 3 percent). Habitat is not lost. Far from it. Instead, mature forest is transformed into “snag forest”, which is abundant in standing fire-killed trees, or “snags,” patches of native fire-following shrubs, downed logs, colorful flowers, and dense pockets of natural conifer regeneration.
This forest rejuvenation begins in the first spring after the fire. Native wood-boring beetles rapidly colonize burn areas, detecting the fires from dozens of miles away through infrared receptors that these species have evolved over millennia, in a long relationship with fire. The beetles bore under the bark of standing snags and lay their eggs, and the larvae feed and develop there. Woodpecker species, such as the rare and imperiled black-backed woodpecker (currently proposed for listing under the Endangered Species Act), depend upon snag forest habitat and wood-boring beetles for survival.
One black-backed woodpecker eats about 13,500 beetle larvae every year — and that generally requires at least 100 to 200 standing dead trees per acre. Black-backed woodpeckers, which are naturally camouflaged against the charred bark of a fire-killed tree, are a keystone species, and they excavate a new nest cavity every year, even when they stay in the same territory. This creates homes for numerous secondary cavity-nesting species, like the mountain bluebird (and, occasionally, squirrels and even martens), that cannot excavate their own nest cavities. The native flowering shrubs that germinate after fire attract many species of flying insects, which provide food for flycatchers and bats; and the shrubs, new conifer growth, and downed logs provide excellent habitat for small mammals. This, in turn, attracts raptors, like the California spotted owl and northern goshawk, which nest and roost mainly in the low/moderate-intensity fire areas, or in adjacent unburned forest, but actively forage in the snag forest habitat patches created by high-intensity fire — a sort of “bedroom and kitchen” effect. Deer thrive on the new growth, black bears forage happily on the rich source of berries, grubs, and small mammals in snag forest habitat, and even rare carnivores like the Pacific fisher actively hunt for small mammals in this post-fire habitat.
Photo by Rachel Fazio
In fact, every scientific study that has been conducted in large, intense fires in the Sierra Nevada has found that the big patches of snag forest habitat support levels of native biodiversity and total wildlife abundance that are equal to or (in most cases) higher than old-growth forest. This has been found in the Donner fire of 1960, the Manter and Storrie fires of 2000, the McNally fire of 2002, and the Moonlight fire of 2007, to name a few. Wildlife abundance in snag forest increases up to about 25 or 30 years after fire, and then declines as snag forest is replaced by a new stand of forest (increasing again, several decades later, after the new stand becomes old forest). The woodpeckers, like the black-backed woodpecker, thrive for 7 to 10 years after fire generally, and then must move on to find a new fire, as their beetle larvae prey begins to dwindle. Flycatchers and other birds increase after 10 years post-fire, and continue to increase for another two decades. Thus, snag forest habitat is ephemeral, and native biodiversity in the Sierra Nevada depends upon a constantly replenished supply of new fires.
It would surprise most people to learn that snag forest habitat is far rarer in the Sierra Nevada than old-growth forest. There are about 1.2 million acres of old-growth forest in the Sierra, but less than 400,000 acres of snag forest habitat, even after including the Rim fire to date. This is due to fire suppression, which has, over decades, substantially reduced the average annual amount of high-intensity fire relative to historic levels, according to multiple studies. Because of this, and the combined impact of extensive post-fire commercial logging on national forest lands and private lands, we have far less snag forest habitat now than we had in the early twentieth century, and before. This has put numerous wildlife species at risk. These are species that have evolved to depend upon the many habitat features in snag forest — habitat that cannot be created by any other means. Further, high-intensity fire is not increasing currently, according to most studies (and contrary to widespread assumptions), and our forests are getting wetter, not drier (according to every study that has empirically investigated this question), so we cannot afford to be cavalier and assume that there will be more fire in the future, despite fire suppression efforts. We will need to purposefully allow more fires to burn, especially in the more remote forests.
The black-backed woodpecker, for example, has been reduced to a mere several hundred pairs in the Sierra Nevada due to fire suppression, post-fire logging, and commercial thinning of forests, creating a significant risk of future extinction unless forest management policies change, and unless forest plans on our national forests include protections (which they currently do not). This species is a “management indicator species”, or bellwether, for the entire group of species associated with snag forest habitat. As the black-backed woodpecker goes, so too do many other species, including some that we probably don’t yet know are in trouble. The Rim fire has created valuable snag forest habitat in the area in which it was needed most in the Sierra Nevada: the western slope of the central portion of the range. Even the Forest Service’s own scientists have acknowledged that the levels of high-intensity fire in this area are unnaturally low, and need to be increased. In fact, the last moderately significant fires in this area occurred about a decade ago, and there was a substantial risk that a 200-mile gap in black-backed woodpeckers populations was about to develop, which is not a good sign from a conservation biology standpoint. The Rim fire has helped this situation, but we still have far too little snag forest habitat in the Sierra Nevada, and no protections from the ecological devastation of post-fire logging.
Photo by Doug Bevington
Recent scientific studies have caused scientists to substantially revise previous assumptions about historic fire regimes and forest structure. We now know that Sierra Nevada forests, including ponderosa pine and mixed-conifer forests, were not homogenously “open and parklike” with only low-intensity fire. Instead, many lines of evidence, and many published studies, show that these areas were often very dense, and were dominated by mixed-intensity fire, with high-intensity fire proportions ranging generally from 15 percent to more than 50 percent, depending upon the fire and area. Numerous historic sources, and reconstructions, document that large high-intensity fire patches did in fact occur prior to fire suppression and logging. Often these patches were hundreds of acres in size, and occasionally they were thousands — even tens of thousands — of acres. So, there is no ecological reason to fear or lament fires like the Rim fire, especially in an era of ongoing fire deficit.
Most fires, of course, are much smaller, and less intense than the Rim fire, including the other fires occurring this year. Over the past quarter-century fires in the Sierra Nevada have been dominated on average by low/moderate-intensity effects, including in the areas that have not burned in several decades. But, after decades of fear-inducing, taxpayer-subsidized, anti-fire propaganda from the US Forest Service, it is relatively easier for many to accept smaller, less intense fires, and more challenging to appreciate big fires like the Rim fire. However, if we are to manage forests for ecological integrity, and maintain the full range of native wildlife species on the landscape, it is a challenge that we must embrace.
Encouragingly, the previous assumption about a tension between the restoration of more fire in our forests and home protection has proven to be false. Every study that has investigated this issue has found that the only way to effectively protect homes is to reduce combustible brush in “defensible space” within 100 to 200 feet of individual homes. Current forest management policy on national forest lands, unfortunately, remains heavily focused not only on suppressing fires in remote wildlands far from homes, but also on intensive mechanical “thinning” projects — which typically involve the commercial removal of upwards of 80 percent of the trees, including mature trees and often old-growth trees —that are mostly a long distance from homes. This not only diverts scarce resources away from home protection, but also gives homeowners a false sense of security because a federal agency has implied, incorrectly, that they are now protected from fire — a context that puts homes further at risk.
The new scientific data is telling us that we need not fear fire in our forests. Fire is doing important and beneficial ecological work, and we need more of it, including the occasional large, intense fires. Nor do we need to balance home protection with the restoration of fire’s role in our forests. The two are not in conflict. We do, however, need to muster the courage to transcend our fears and outdated assumptions about fire. Our forest ecosystems will be better for it.