Vegetation Trends and Cycles in Fire-Prone Landscapes of Lake, Napa and Sonoma Counties

Principal Investigator: Arthur Dawson, Baseline Consulting

If fire can be considered a member of the community, as Indigenous biocultural heritage conservancy organization, Heron Shadow’s CEO Sara Moncada puts it, “then recent catastrophic fires highlight the consequences of ignoring that community member, or thinking we can banish them entirely.” In order to improve fire readiness and resilience throughout our region, we need to understand the patterns that have led to this moment. To that purpose and as a foundation for responsible stewardship, with funding from the CAL FIRE Forest Health Research Program and in partnership with Baseline Consulting, Tukman Geospatial, and UC Davis, we undertook a years-long study to strengthen our long-term understanding of this landscape’s historical relationship to fire.

The project study area included five areas marked on this map.

Within the last ten years, some of the most destructive and deadly wildfires in California history occurred in Lake, Napa, and Sonoma Counties. Dozens of people died in these fires, hundreds of thousands were evacuated, and nearly 10,000 homes and structures were destroyed. In order to improve fire readiness and resilience throughout our region, we need to understand the patterns that have led to this moment. To that purpose, the goal of this project was to better characterize long-term fire and vegetation patterns to inform hazard reduction and forest resilience strategies, and to advance public awareness. 

In facing the current situation, firefighters, land stewards, and the public are realizing that our long-established practices no longer serve us well. There is a general recognition that fundamental changes are needed. Many of us are relative newcomers to this land, with roots going back only a few generations at most. To thrive here in the long run, or even just survive, we need a deeper understanding of this place. 

Part of that understanding will be built from scientific studies of vegetation, fire, climate and related disciplines. Such knowledge is valuable and useful, but it can perpetuate the illusion that with enough data control is possible, and that fire is an adversary to be fought. But to effectively reimagine our role as human beings in this landscape and change our relationships with fire and vegetation is going to require a much broader vision. As part of that reimagining, this study took an interdisciplinary approach. We incorporated an array of historical and scientific sources and gave equal weight to the perspectives and traditional wisdom of our local Indigenous community. Several people with first-hand experience of cultural burning, as well as knowledge passed down from past generations, shared their knowledge with us. For this gift we are extremely grateful. 

Indigenous wisdom (aka Traditional Ecological Knowledge or TEK) is a slender thread going from the present all the way back to the beginnings of human time in our region. Clint McKay (Dry Creek Pomo, Wappo, Wintun), Chair of the Native Advisory Council at Pepperwood, shared that he can’t identify his earliest memories of cultural burning—it’s part of a cultural tradition extending back to before he was born. Personal memories are less important than the combined memories and experiences of those who came before. 

As a foundation for responsible stewardship, that type of knowledge is a form of generational wealth. Another holder of Indigenous wisdom contacted during this study was Redbird (Pomo, Paiute, Wintu, and Wailaki), Stewardship Coordinator at Heron Shadow, a ‘Biocultural Oasis’ in Graton, owned and stewarded by the Cultural Conservancy. On seeing vegetation maps created for this project, he observed that they show ‘what happens when the land is not being tended properly.’ Considering how long his people and their neighbors have cared for this place, that idea makes an appropriate framework for reflecting on the 150 years of vegetation and fire history collected here. 

If fire can be considered a member of the community, as Heron Shadow’s CEO Sara Moncada puts it, “then the recent catastrophic fires highlight the consequences of ignoring that community member, or thinking we can banish them entirely.” The bulk of this report covers what has happened over the 150-plus years since Indigenous stewardship has been excluded from the landscape. 

Historical data, which included both fire and vegetation maps, was collected and created within areas defined as ‘high fire risk’ by CAL FIRE. As a set of ‘natural experiments’ over a long period of time, it evaluates the influence of various factors on local fire history including vegetation changes over that period. No modeling was done for this study, though several landscape and ecological parameters, such as slope aspect and vegetation type, used in fire modeling, were analyzed. 

Within the four study areas in Lake, Napa, and Sonoma Counties, modern fire suppression began in the 1930s or 1940s. Thus, about half the record documented in this report occurred prior to suppression and half later, giving something of a ‘before and after’ picture of conditions. The earliest ‘mappable’ data used in this study was collected by surveyors working for the General Land Office, primarily in the 1860s and ‘70s. These 19th-century surveys can be challenging to interpret. Nevertheless, they offer an extremely fine-grained picture of the land and the vegetation on it as it existed just a few years after Indigenous stewardship had ended or gone into steep decline.

Fire regimes in California are highly variable. To be effective, vegetation and land stewardship must account for this variability (Stephens et al 2014). In contrast to southern California (Syphard et al 2019), this study demonstrates that post-fire vegetation recovery in more northern counties can be rapid and dynamic. In many of the most fire-prone areas covered in this study, shrublands (mapped at 100%) converted to woodlands (65% or more) in just three decades. A decade or two later, after the next wildfire comes through, shrublands return and the cycle begins again. Forest recovery after timber harvest occurs almost as quickly—with ‘barren’ land returning to 59% forest in about four decades. Within these landscapes are places where no fires or major disturbance have been recorded in the last 150 years.

The Napa East study area illustrates this landscape variability well, with vegetation patterns in sharp contrast to the other study areas. Though it is the most fire-prone study area, it does not follow the pattern mentioned above—vegetation changes in the wake of fire proceed so slowly as to be nearly undetectable. Whether this is due to a difference in soils, precipitation or some other factor is unknown at this point.

Mapping and describing the changes in vegetation patterns and fire over the last 150 years is inherently challenging. It requires distilling vegetation data down to its ‘least common denominator.’ What this approach lacks in precision it makes up for in a longer time scale and expanse of landscapes. This lens makes visible the broad outlines of vegetation change over a century and a half, and allows us to put present conditions in context. Some line descriptions in the 19th-century surveys are challenging to interpret. Others, like “mostly only chaparral,” provide a sharp and undeniable contrast in places now heavily forested.

Landscapes reflect the practices and preferences of the people living in them, according to the amount of care and attention they receive, or the lack of it. The only known factor that can account for the prevalence of chaparral in the 19th-century surveys is a widespread tradition of cultural burning. As a way of ‘proper tending,’ cultural burning was done in many kinds of habitats. The incidence of chaparral in the surveys is just the most visible marker in the historical record.

It is well known that human actions can harm the natural world. But things are also thrown out of balance by a lack of engagement and stewardship. Recent catastrophic wildfires indicate that this lack of human involvement not only threatens natural systems but puts us in danger as well. It’s impossible to say what our landscapes, with proper tending, could look like in another 150 years. By looking back a century and a half, this report offers a foundation for such long-term thinking through the following lines of inquiry:

1. How has the relationship between vegetation, fire, and people changed over time?

2. What is the relationship between fire frequency, vegetation trends and cycles, landscape variables, and post-disturbance regeneration?

3. Do vegetation patterns, or other landscape factors suggest a tipping point for large or catastrophic fires? How do these compare with other possible tipping points such as temperature, humidity and wind speed?

4. What is the most effective point in the fire/revegetation cycle for fuel reduction efforts to minimize wildfire emissions and threats to communities and ecosystem services, while also maximizing carbon sequestration for a given location?

5. How might we use fire as a stewardship tool to improve the ecological health of the land?

Learn more about this project via the webinar

https://www.youtube.com/watch?v=FQ4Lr2thEvM

Acknowledgements

The assistance and support of many people was essential to completing this project. We are especially grateful to: Amber Manfree; Ben Nichols, CAL FIRE; Carolyn Ruttan, Clear Lake Environmental Center; Chris Carlson, Sonoma Land Trust; Christopher Kam; David Ackerly, UC Berkeley; David Conklin, Bureau of Land Management; Jill Dawson; Kim Batchelder, Sonoma County Agricultural and Open Space District (Ag & Open Space); Lakeport Library staff; Michelle Halbur, Pepperwood; Monica Delmartini, Ag & Open Space; Morgan Gray, Pepperwood; Penny Sirota; Ryan Ferrell, Pepperwood; Michael Gillogly, Pepperwood; and the members of the Sonoma County Forest Conservation Working Group. 

This study builds on research conducted in the region over the last two decades, funded by a number of agencies and non-profits, including Audubon Canyon Ranch, Pepperwood, Sonoma County Agricultural and Open Space District, Sonoma Land Trust, Golden Gate National Parks Conservancy, Sonoma Land Trust, and Sonoma Ecology Center. 

Funding

Funding for this project was provided by the CAL FIRE Forest Health Research Program, Grant 8GG19813. The Forest Health Research Program is part of California Climate Investments, a statewide initiative that puts billions of Cap-and-Trade dollars to work reducing greenhouse gas emissions, strengthening the economy, and improving public health and the environment—particularly in disadvantaged communities.