A Decade of Fire Mimicry

Dead an dying coast live oak trees in Big Sur, CA

The past decade has been a tough one on California oaks. Tens of thousands of oaks have died and many more are in distress, simply because they are no longer being tended. For millennia the Indigenous People of California used, and still use, fire to improve the health of the native trees and forests.

Also over the past decade I and others have been tasked with restoring to health many of these oaks. During this time we have tended well over 1,000 oaks and other trees, with mostly positive, if not remarkable, results. Due to the severely overgrown nature of fire-suppressed forests, applying fire is not an immediate option. Therefore, we have been developing tending practices that mimic fire in ways that benefit the oaks.

Below are a selection of oaks, one per year of this past decade, that have inspired me to stay committed to tending our oaks. Many of these are legacies of the indigenous past and will, with our help, continue to be legacies in our future.

A decade of healing oaks . . .

Hearst Castle oak – 2010

Fairfax oak – 2011

Advertisement

Recovery of oaks following the 2017 Sonoma fires

Yesterday I inspected a grove of oaks that had burned during the 2017 Sonoma fires.  Previous to the fire these oaks had been treated with fire mimicry, which included pruning the lower branches (ladder fuel), clearing away underbrush, removing mosses and lichens from the trunks, fertilizing the soils with compost tea and soil minerals, and applying a limewash to the trunks. During the fires all of the ground vegetation burned, but none of the flames spread into the upper canopies. Thus, all of the oaks survived (as did several nearby homes), and, as the photos show, are doing well after 1.5 years. A caveat – these results are influenced by the spring flush of new leaves, and a better comparison can be made when I visit the site again this October.

These findings represent the combined effects of a ground fire AND fire mimicry treatments on improving the health of California oaks.

Fire mimicry treatments likely saved homes and oak groves from Sonoma wildfires

Compare untreated oaks in the background (right) with oaks in the foreground (left) treated with fire mimicry.

In 2009 I was contacted by a property owner who had just purchased a home and several acres of oak forest near the town of Sonoma, CA. The forest had been neglected for many years and was in poor health. There was also a dense growth of underbrush around the trees and many dead limbs on the oaks. I provided him a fire mimicry treatment plan that involved clearing of the underbrush and pruning the oaks, focusing on removing the ladder fuels near the ground. I also proposed to fertilize the oaks with alkaline-rich soil minerals, removed mosses and lichens from the trunks, and applied limewash.

The owner agreed to this plan and during the next couple years I and several colleagues spent many weeks clearing brush, pruning limbs, burning brush piles, and fertilizing a large grove of more than 50 valley oak, blue oak, and coast live oak trees.

Afterwards, in 2015, another property owner in Glen Ellen, CA contracted with me to care for her oaks with fire mimicry. This grove of about 30 oaks was treated in the same manner as described above.

Both of these properties were impacted by the recent wildfires in Sonoma.  Yesterday I visited these properties and I’m pleased to report that they sustained very little permanent damage. No structures were lost and nearly all of the oak trees appear to have survived. I estimate that the survival rate of trees on both properties is about 98%, although it will be another year or so before we know the exact percentage.

With regards to the first property, the photos here show that the fire burned the adjacent forest severely, with a complete loss of the forest canopy in places. However, once the fires reached the areas treated with fire mimicry, the severity lessened and fire stayed on the ground. None of the trees in the treated areas experienced a canopy fire. The boundary between the treated and untreated trees, showing this difference in fire severity, can be seen in the above and below photos.

I should add that while this home did not burn, four nearby homes were completely destroyed.

The second property also had no loss of structures and only minor damage to the oaks (see last photo below). The fire did not spread into the canopies and all of the affected oaks will likely recover.

With regards to the “cause” of these severe wildfires, some focus on the source of the initial spark, such as a downed power line or arson. Others point the finger at climate change affecting the health of the forests.

My take, based on the results shown here and elsewhere in the scientific literature, is that the cause of the severe wildfires is due to the suppression of fires and lack of management of the forests. Historically, oak forests were regularly burned by the California native people to enhance the health of the oak savanna ecosystem. Under a frequent burning regime the fires tended to be ground fires, which rejuvenate the soils but do not damage the tree canopies. Without these traditional management practices, our oak forests have become overgrown and stressed. Now-a-days, when fires do burn, they tend to be destructive canopy fires, rather than rejuvenating ground fires.

The oak forests and homes on these properties were saved in spite of adjacent ignition sources from raging fires. Nor did we change the climate. We simply went in ahead of time and mimicked wildfire in these areas. It is clear to me from this and other studies that proper forest management is fundamental in solving the wildfire problem in California.

Fence line of property separating burned/untreated oak forests (right) and unburned/treated oak forests (left).

Black oaks and coast live oaks in Glen Ellen, CA respond to fire mimicry

A grove of black oaks and coast live oaks in Glen Ellen, CA treated last year with fire mimicry are showing a nice positive response in canopy health, except for one black oak (see photo below) that has lost it’s leaves early and appears distressed. All of these trees survived the recent fires that burned through the area.

Oaks in Glen Ellen, CA responding to fire mimicry

Seven years ago I began treating a group of coast live oaks with fire mimicry. Several of the oaks are infected with bleeding stem cankers, probably Sudden Oak Death. Despite being diseased, the oaks have shown a steady recovery over the years as can be seen in these photos from 2013, and 2015. On Tuesday I checked on these oaks again and as the photos here show their health, for the most part, continues to improve.

For all the fear-filled hype about diseases and insect pests ravaging our forests, I find very little news about the fact that, whether or not the trees are infected with this disease or infested with that pest or stressed by climate change, sick trees can be brought back to health. I know this from doing the work, treating sick trees, and seeing the results such as these.