How Have Wildfires Affected Fall Color?

Thanks to this summer’s wildfires, it’s been hazy for a month here in the Sierra Foothills.

Haze is not unusual to the foothills. Each autumn, Central Valley rice fields and other agricultural croplands are burned to dispose of leftover straw (stubble) and control disease and pest problems. For centuries before, native people burned grasses at summer’s end, to make it easier to collect oak acorns (a principal food source).

So, hazy skies have been part of California’s late summer for thousands of years. Though this summer’s many wildfires added particulates, gasses and ash in abnormally high quantities to our normally clean skies, causing people to ask, “How have the wildfires affected fall color?”

Plant scientists say smoke both benefits and harms plants.

Benefit – Smoke or haze are the product of combustion, which means higher levels of Carbon Dioxide (CO2) can exist, compared to normal. As CO2 increases, plant growth does as well, as long as there is sufficient sunlight. Nutrients in ash from a fire benefit new growth. And, fire opens a forest, eliminating mature trees and making space for young plants.

Harm – Smoke also drops ash and other particulates that reduce photosynthesis; those can clog “stomatal pores, reducing gas exchange in the leaf,” New Mexico University scientists write. Holocaustic wildfire can devastate a forest’s ecosystem, seriously depleting endangered species.

As we reported two years ago (Death of the Sierra), 100 years of fire suppression has created a catastrophe for the forest, air quality, wildlife and humanity. This year, we ate the bitter fruit of those decisions as we watched forests in Mendocino County, Shasta County, Mariposa County and countless other locations go up in smoke.

The most evident effect of a wildfire on fall color is that it will take years for stands of most species of deciduous trees to grow back. Deciduous plants that grow near water (aspen, cottonwood, willows) are the most resilient and first to recover.

It’s been three years since an oft-photographed aspen grove near Big Bear was burned in a major wildfire. At the time, we reported that the aspen would be the first trees to recover (Burnt Aspen to Recover).

Today, we spoke with Teddi Boston at the Barton Flats Visitor Center who said that within three months of that fire, the aspen were three feet tall and they’ve recovered fast since.

However, access to this grove is limited by logging which is occurring on the one-lane road that leads to the grove. So, until the logging ends access to the aspen is blocked.

One way to see aspen in the San Bernardino National Forest is to visit its Barton Flats Visitor Center where many aspen grow near the center. We also plan to send a reporter out to the Aspen Grove at peak to photograph Big Bear’s grove since the fire.

In contrast, deciduous forests in areas overrun by this past summer’s wildfires weren’t fire-resistant aspen, and were incinerated. Most of the deciduous trees lost to this year’s fires were maple, oaks and alder, which will take years to recover.

Fortunately, as expansive as this summer’s fires were, the number of trees destroyed still represent a fraction of the entire forest. Areas that were not burned will continue to display fall color, as they have in past years. For example, Yosemite’s fires occurred mostly outside the National Park. None of the black oak, bigleaf maple, or dogwood in Yosemite Valley were damaged.

Nevertheless, color spotters have been reporting signs that haze and overcast may have reduced photosynthesis, triggering earlier displays of autumn color.

Jeff Luke Titcomb reports from Plumas County that Western Dogwood are showing early rose and Big Leaf Maple are beginning to turn yellow.

Elsewhere in Sierra Foothill suburbs, exotic Chinese Pistache are showing early change of color, becoming splashed with yellow and orange.

Offering an optimistic view is Butte County color spotter Cindy Hoover who reports, “The one thing I have really been watching are the aspen. I think this year may be a phenomenal year since there’s been so much rain. The aspen leaves are darker green this year. I can only imagine the bounty of yellow, deep gold and red they’re going to share.”

Reports like Cindy’s indicate that a normal autumn is more likely than an accellerated one.

So, do not confuse today’s reintroduction of the Pumpkin Spice Latte at Starbucks, the feel of autumn in the air or a scattered number of trees and shrubs turning color early as proof that autumn has arrived.

Autumn has not arrived significantly earlier than in past years. Fall will happen just about as it has in previous years, regardless of the year’s many wildfires.