The state of Sonoma County’s forests

Editor's Note: This is part two of a series about the indigenous forests that blanket Sonoma County - their past, present and threats to their future.

Our forests “are undergoing a sea change,” observes Mark Tukman, founder of Tukman Geospatial, who is spearheading the Sonoma County Agricultural Preservation and Open Space District's development of a fine-scale vegetation map.

“I've spent over a year looking at aerial photos and coordinating field teams. Many of our oak woodlands are disappearing rapidly, transitioning to Douglas fir and California bay,” he said.

In many places this is visible at ground level - dead manzanitas scattered beneath oaks dying in the shade of Douglas firs - a century of change visible in a glance. Of course, oaks and firs represent just a few of our native trees. Sonoma County's wide range of geology, soils, landforms and climate has been described as “where Alaska meets Mexico.” With 10 species of oaks and 19 conifers, our forests reflect this diversity.

Close up, they can seem infinitely complex. But if you pull back, larger patterns emerge. Moving west to east, conifers grow in parallel bands - Bishop pine along the cool coast, then redwoods, and finally Douglas fir reaching warmer areas far inland. Interspersed are woodlands of oak, bay, madrone and other hardwoods. There are no hard boundaries between any of these types - in fact mixed conifer-hardwood forests are more common than either alone.

By the early 20th century, forested lands had seen severe impacts. Logged-off tracts of redwood and Douglas fir were now brushy and crowded with young trees. Oak and madrone woodlands, leveled for firewood, had become grassland. Settlements replaced oak savannahs. By all indications, there were far less trees 100 years ago than today.

Even so, in some areas, a mix of surviving forest, brushy areas recovering from timber harvest, and chaparral stands created conditions ripe for catastrophe. One of the county's first large-scale wildfires occurred in September 1923. Pushed by strong winds, it burned 10,000 acres, destroying many homes and structures in Sonoma Valley. Afterward, citizens formed several rural fire departments. Rather than treating it as a tool, as Native Americans had with intentional, frequent burning, fire became the enemy. Suppression was the goal.

In the short run this was fairly successful, but there were long-term consequences. Without regular fire, more seedlings became full-size trees. Meanwhile, increasing fossil fuel use led to cutting fewer trees for firewood and charcoal. Even where woodlands had been cleared, trees often re-sprouted from their stumps. Over decades, forests returned and the land healed.

But today's regenerated forests are different from the ones that were cut. Without harvesting and burning, trees grew more densely. Douglas fir and bay became more common and widespread, expanding into areas that had been oak woodland, grassland and chaparral for hundreds or thousands of years.

Crowded forests are less healthy than more open ones, as trees compete for limited sunlight, water and nutrients. Just as human sicknesses spread quickly under crowded conditions, so do plant diseases. Bay trees carry the sudden oak death pathogen but rarely succumb to it. In dense conditions, the disease spreads easily to coast live and tan oaks, which are now dying off in large numbers.

Without fire, dead wood and leaf litter accumulate, providing an ever-increasing amount of fuel. This is one reason why horrific events like the 2015 Lake County fires have become more common. Frequent, low-intensity fires reduce this risk and improve ecological health; this approach is being tested at several preserves in the county.

Another wave of logging, mostly in second growth redwood and Douglas fir stands, ran from the 1950s into the '70s. After that, merchantable timber grew much more limited. Mills shut as demand and prices for wood declined. Traditional corporate logging basically cut itself out of business. Simultaneously, public opposition to logging was growing with actions like the 1990 Redwood Summer organized by Earth First.

The value we place on trees depends on our needs and wants.

“Before 1990,” says forester and Climate Action Reserve's Vice President John Nickerson, “nobody rewarded forest landowners for anything but timber.”

Today, “aspects like biodiversity, watershed protection and carbon sequestration are coming into play,” he said. Trees also benefit our physical and emotional well-being, even in urban environments. The trick is to bring these values into the economic system.

As professional forester and Santa Rosa Junior College instructor Fred Euphrat says, “forestry is a multigenerational project. You have to plant climate-ready trees for harvest 50 years from now. It's the only form of agriculture where you harvest things you didn't plant and plant things you'll never harvest.”

Starting in the early 1990s, policy has shifted toward sustainable management and now requires submitting 100-year forest plans on commercial timber lands. By the late '90s, the first non-timber monetary value was being placed on forests as they were recognized for their ability to buffer climate change through capturing carbon.

Two centuries ago, our forests were “patchier,” part of a mosaic of grasslands and chaparral. Such conditions support healthier individual trees and more biodiverse wildlife. Moderate disturbances, particularly low-intensity burns, helped maintain this pattern. Such fires, which recycle soil nutrients and keep the forest open, are far different than the high-intensity wildfires of today. Likewise, selective cutting for firewood and timber, when carefully done, is a moderate disturbance that results in healthier, more biodiverse forests. Misti Arias, acquisition program manager at the open space district, remembers the agency's old attitude as: “Don't allow any tree cutting!” But a growing understanding of forest dynamics and climate change has led to a shift in thinking.

“Carbon funding,” she reflects, “increases the scale of what's possible on forest land.”

The 18,000-acre Buckeye Forest in the northwest county, one of the largest nonprofit-owned working forests in the West, is an example. Mostly second-growth redwoods, its purchase by the Conservation Fund in 2013 was supported by funding from the open space district, the Sonoma Land Trust, the Coastal Conservancy and other partners.

Ultimately, what made the purchase possible were credits for the 40,000 tons of carbon Buckeye Forest captures annually (equivalent to 2,500 fossil-fueled cars). As a source of income worth many millions of dollars, these credits are being sold to industries needing emissions offsets under California's Cap and Trade program. Use of Buckeye Forest is restricted to sustainable forestry, restoration, grazing and public recreation under a perpetual easement.

Carbon credits are also beginning to benefit smaller landowners. Most county forest land is in parcels of 40 acres or less. California's Greenhouse Gas Reduction Fund provides resources for small landowner groups to both improve forest health and sequester carbon.

There's no such thing as untouched forest in Sonoma County; influenced by humans for millennia, they are part of our cultural landscape. But the relationship goes both ways and forests shape us as well. After all, there are far more trees here than people and they are still the oldest settlers around. We live in their world as much as they live in ours.

Arthur Dawson is a Glen Ellen-based historical ecologist. Contact him at baseline@vom.com.