By Will Richardson
By now, you’re likely sick of these statistics: The 15 largest wildfires in California history (since 1932) have all occurred in the past 20 years, with over half of those taking place in the past 14 months.
Over the past two summers, the Tahoe/Truckee region has experienced unprecedented smoke from several of these record-breaking fires, as well as from a smattering of smaller fires across the broader region. The Caldor Fire was unprecedented as both a threat to the communities of South Lake Tahoe and in terms of sheer scope and scale for Tahoe. In recent months, we at the Tahoe Institute for Natural Science have received countless questions regarding the impacts of both the smoke and fires on our local flora and fauna.
Most Moonshine Ink readers will know that fire is a natural part of the Tahoe ecosystem. In that sense, all of our local species are adapted to fire, at least within the historical context in which they evolved. That means that they should be able to cope with regularly occurring, low-intensity, small fires, ideally within an intact, undeveloped landscape.
Before the Comstock Era (roughly from 1860 to 1900, when much of Tahoe’s old-growth forest was logged for square-set timber bracing in mines of the Virginia Range), approximately half of the Tahoe Basin’s landscape burned at least every 15 years. In an average year, 3,000 to 4,000 acres of forest experienced fire, generally spread over many small fires. For context on some larger fires in recent history, the Angora Fire burned a little over 3,000 acres in 2007. This was a large, relatively destructive fire for Tahoe. The next-largest fires were much smaller: Gondola (272 acres, 2002), Emerald (200 acres, 2016), Showers (119 acres, 2002), and Royal (109 acres, 2003). In comparison, the Caldor Fire burned over 220,000 acres, an estimated 10,000 acres of which was in the Lake Tahoe Basin itself.
Small wildfires can create habitat heterogeneity, resulting in unique assemblages and high species diversity, and benefitting the many species that thrive in post-fire habitats — and there are many! Even larger fires, if they are patchy enough in terms of fire movement and intensity, can produce highly beneficial habitat outcomes for our diverse flora and fauna.
How do our fire-adapted plants and animals cope with these fires? It depends. How individual species and organisms are affected by fire itself depends on many factors, largely related to fire behavior when and where the organisms encounter them. Larger or more mobile animals simply flee the oncoming flames, often taking visual or olfactory cues from thickening smoke. Thankfully, most birds had already fledged their young by the time the Caldor reached Tahoe. Smaller animals attempt to seek shelter, often underground, with many going into a temporary dormancy.
Plants, fungus, and animals of all sizes typically recolonize burned areas from adjacent habitat patches or even unburned patches within the larger burn footprint. While all our species are adapted for a landscape that sees small fires periodically, none have evolved to handle the novel environmental stressors and outright dangers that come with the modern “mega-fires” we have seen in recent years. These fires present unprecedented challenges for our flora and fauna due to their size, intensity, and duration.
Smoke effects on wildlife is a relatively unstudied area, but a recently published overview of known research suggests that as climate change intensifies smoke pollution, more animals are at risk of acute and chronic health outcomes associated with smoke inhalation. This could lower survival and reproductive success. Potentially significant impacts have been demonstrated for birds, reptiles, mammals, invertebrates, and even fish.
During large-scale smoke events, as we’ve seen these last two seasons, even species well-adapted to avoiding smoke cannot find refuge. Animals might respond to smoke from massive fires even when those fires are far away, which could have significant, cascading impacts on wildlife communities.
For example, many species that rely on smoke as a cue to navigate toward burned areas may become disoriented during large-scale smoke events occurring hundreds of miles from the fires, leading to reduced fitness and increased vulnerability to predation. Other species that use visual and olfactory cues from smoke to initiate fire-avoidance behaviors (seeking shelter, finding temporary dormancy, or actively fleeing) may do so at great expense when a fire is not an immediate threat. And regardless of whether an animal wants to move away from, or toward, the fire, when smoke plumes stretch from California to Missouri, it’s near impossible to know how to orient and where to go.
A 2020 study of five GPS-tagged greater white-fronted geese found that these migrating birds strayed significantly from their traditional routes to avoid smoke from the fires in California and Oregon still burning in September of last year. These detours led to a migration period that averaged twice as long as its normal timespan, covering an average of an additional 470 miles, exposing the birds to multiple unfamiliar and often unsuitable stopover sites, and adding considerable effort and stress to what is already an extremely trying and hazardous process.
Smoke has also been implicated in the massive die-offs of migratory birds seen in the southern Rocky Mountains last fall. Though these birds faced a one-two punch of smoke and an early-season snowstorm, severe weather events are not atypical during the migration season.
We biologists do not yet know precisely how the Caldor Fire burned through its footprint in the South Tahoe Basin. Parts of the fire ran into areas of aggressive fuels-thinning treatments, which not only helped save South Lake Tahoe residential communities, but also helped reduce fire intensity in those forest patches wherever those treatments had been completed in recent years.
From satellite images and reporting, it appears that portions of the fire moved swiftly and erratically, leaving a mosaic of unburned patches, lightly burned forest with moderate tree mortality but an intact soil biota and seed bank, and high-intensity patches where all trees were completely killed, and the soil likely sterilized. This latter condition is an important habitat type for a great number of species that favor recently burned forests, from fungus to wood-boring beetles and other invertebrates, nearly all of our woodpecker species, and both of Tahoe’s bluebird species.
Individual organisms surely had a rough time of it during Caldor, and many smaller animals, and possibly large animals, too, succumbed to the heat and smoke. But so long as the acreage ratio is not too heavily skewed toward the high-intensity burn type, and as long as those patches aren’t so large that recolonization from adjacent patches would take decades, we should see a very diverse, heterogeneous, and vigorous rebound from the Caldor Fire.