Peter Cowan - POST
By ,
Director of Conservation Science

It felt eerily like the Michigan winters I grew up with — the ground was covered in white and the tree branches above were bare and dark. But the cloud of ash my steps made quickly dispelled that thought. It’s been nearly three months since the CZU Lightening Complex began, proceeding to burn through nearly all of the nearly 9,000-acre San Vicente Redwoods property near Davenport that POST helped protect in 2011. I had come to assess the fire’s impact in the Santa Cruz Mountains and to begin what will be years of learning about how the forest transforms through fire.

Redwoods Program POST
San Vicente Redwoods is marked here in red. Click to zoom in.

San Vicente Redwoods is especially close to our hearts at POST. With a long and complex history that includes damaging clearcutting in the early 20th century, we have been working hard to restore the forest’s health for years — all while taking additional steps that we hoped would increase wildfire resilience. However, we could not anticipate the extreme scope of this year’s historic fire. And as one of the largest continuous areas of protected redwood forest in Santa Cruz Mountains, the state of this property impacts the ecological health of our entire region.

 

 

Lightning in mid-August 2020 ignited fires across the Bay Area. The CZU Lightning Complex spread through the heart of our local redwoods, burning through almost all of the 9,000-acre San Vicente Redwoods (pictured here). 

The Fire’s Effects

One thing that’s clear is that historically, fire was a regular part of the landscape, so much so that many plants such as Arctostaphylos andersonii, the Santa Cruz manzanita, can’t reproduce without it. Other plants like coast redwoods are fantastically adapted to survive fires, with thick insulating bark and the ability to sprout from their trunks, branches and roots.

However, even species adapted to wildfire can be killed if it burns too hot or for too long. Assessing how intensely the CZU fire burned at San Vicente Redwoods was my first order of business. I discovered that the property contains a mosaic of burn severity, ranging from low to high. In this way, it can serve as a microcosm of the over 86,000-acre footprint of the fire and provide valuable insights.

Map of Bay Area fire severity from the 2020 season
Using near-infrared and shortwave-infrared data, researchers at Nasa’s Ames Research Center were able to provide an initial measure of the severity from the SCU and CZU Lightning Complex fires.

How a fire burns is as (or more) important as how much it burns. Weather — like wind speed and humidity — and how steep the hillsides are have a big impact on the intensity of the fire. And, just like a campfire, the more wood the fire has as fuel, the longer and hotter it burns.

When a fire burns slowly on the ground, primarily consuming leaves and wood on the forest floor, it tends to kill fewer trees. It also provides important benefits such as stimulating seedbanks and releasing nutrients into the soil. As intensity increases, so too does the damage. The leaves of living trees are scorched, and for more sensitive species like Douglas Fir this can be fatal. In extreme cases, fires may burn so hot or long that underground parts of resprouting plants and seedbanks are killed. Fortunately, on my visit to San Vicente Redwoods, we didn’t see that level of burn severity — though there are still areas to be assessed.

The CZU Lightning Complex fire burned at a much higher intensity through large parts of Big Basin State Park (pictured here), consuming the forest’s canopy as well as scouring its vital soils. 

Looking Ahead

Already, there are signs of how resilient our California species — plants as well as animals — are to wildfire. Though many madrones stand leafless, with their red trunks scarred, almost every single one has a green tuft of leaves at its base; the same is true for tan oaks, redwoods and others.

It will take decades for this forest to resemble what it looked like just a few months ago — in the meantime, we’ll likely see new species like fire ephemerals. Elsewhere, new fern fiddleheads are unfurling, causing me to marvel at plants’ ability to gather water, even during a drought after a fire.

Tree sprouts race toward the sky within San Vicente Redwoods, signaling this forest’s resilience to moderate intensity fire. Photos: Teddy Miller

And, while water is scarce now, we are busily trying to prepare San Vicente Redwoods for the coming winter, repairing damaged roads and culverts that burned to protect the streams from their sediment as best we can. We are also making plans for how we can use this property as a “living laboratory:” revisiting research plots established before the fire to measure changes in the forest; replacing scientific equipment to monitor impacts on wildlife populations; and looking closely at the measures we took such as forest thinning, shaded fuel breaks and prescribed burns to understand their effectiveness in reducing fire intensity.

More observation is needed in the months and years ahead, but there are promising signs that our actions prior to the CZU fire significantly reduced the fire’s severity. This gives me hope that we have been on the right path — we will continue adapting our management practices as we learn more so that we can be better prepared as the heat and droughts intensified by climate change continue to increase fire risk throughout the West.

                                   

About the author:

Dr. Peter Cowan is an ecologist fascinated by how species interactions, climate and humans shape nature. A Stanford and Berkeley graduate, he has concentrated on conservation throughout California for the past three years. After completing his dissertation on the evolution of chaparral and other fire-prone plant communities, he worked on science policy in Sacramento and Washington DC before returning to the Peninsula. He joined POST as Director of Conservation Science in early 2018.

 

About Post

Peninsula Open Space Trust (POST) protects open space on the Peninsula and in the South Bay for the benefit of all. Since its founding in 1977, POST has been responsible for saving more than 80,000 acres as permanently protected land in San Mateo, Santa Clara and Santa Cruz counties. Learn more

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