Vegetation Trends and Cycles in the Fire-Prone Landscapes of Lake, Napa, and Sonoma Counties
Developed under CAL FIRE grant 19-FH-LNU-086 by Baseline Consulting, Pepperwood Preserve, Tukman Geospatial and James Thorne, PhD.
This project examines the relationship between fire and vegetation across a region which has suffered some of California’s most devastating recent wildfires. Integrating historical and recent data (1870-2020), we are developing a detailed understanding of fire and vegetation cycles across a diverse landscape with wide variations in fire history (return intervals < 10 to >100 yrs).
This effort combines a wide range of sources, including newspaper reports prior to the mid-20th century; CAL FIRE’s database of mapped perimeters; late 19th-century General Land Office survey vegetation data; UC Berkeley’s Vegetation Type Mapping from the 1930s; 1960s Soil Vegetation Maps; 1990s Wildlife-Habitat Relationship maps compiled by the Department of Fish and Wildlife; and recent vegetation mapping efforts (e.g. Sonoma Veg Map, 2014).
Long-term fire data can identify patterns that are not apparent within shorter time periods. For example, on the eve of the 2017 Nunns Fire, CAL FIRE records, covering about 70 years, showed only one large fire within its perimeter (1964). Research since 2017 has revealed that large fires also burned there in 1880, 1923 and 1936; in fact, one 4000-acre zone has burned in every major fire in the last 140 years. Research also identified 1000 acres nearby that had no recorded burn prior to 2017.
Long-term vegetation data allows us to explore how a landscape’s fire history is reflected in its vegetation. Data for a portion of the Sonoma/Napa study area suggests a dynamic cycle of: Fire; Shrub Growth; Replacement by Trees; and a return of Fire within 40-60 years. The project’s broad scope—200 square miles in four study areas in Lake, Napa and Sonoma Counties—will allow us to evaluate how widespread such a cycle is and how parameters such as slope aspect, elevation, wind patterns and proximity to the coast affect the relationship between fire and vegetation. In addition, the Sonoma West study area, immediately northeast of Guerneville, offers the opportunity to compare forest regrowth after timber harvest to post-fire vegetation recovery.
We are also investigating the most effective point in the fire and revegetation cycle for fuel reduction efforts which minimize wildfire emissions and threats to communities and ecosystem services, while also maximizing carbon sequestration. The results of this work will inform site-specific actions and build public understanding of fire risk and support for vegetation management in their community.