Fire regimes and effects
Pre-suppression fire regimes in the Lassen area were classified as mixed severity, with fires occurring on average every 5–15 years. The introduction of forest fire suppression activities in 1904 resulted in significant changes to fire regimes in the park and region. These changes in fire regimes have resulted in much longer fire cycles, increased forest density, and changes in tree types.
Prior to 1904, lower elevation forests naturally had more frequent fires than higher elevation forests because they are hotter and drier and generally contain more flammable fuels. The fires generally had effects of varying severity on the vegetation. This creates a mosaic, or quilt-like pattern, of unaffected low, moderate, and high severity patches. These diverse plots help make a landscape more resilient to drought and future forest fires.
Fire suppression activities initiated in 1904 led to a dramatic drop in fire frequency. Meanwhile, land managers actively suppressed most lightning-ignited fires. Over time, this resulted in denser forests with greater numbers of younger trees (which were previously killed by fire) and changing proportions of each species type.
In the 1980s, Lassen Volcanic began to limit its lightning-triggered fire suppression efforts in its new wilderness area. In the decades that followed, Lassen Fire Management used minimal intervention to allow natural fire regimes to return to the Lassen Volcanic Wilderness. These lightning-ignited and directed fires ranged in size from 18 to 3,500 acres and resulted in effects of varying severity.
Over the past decade, the park and Lassen area has seen a dramatic increase in the size and severity of wildfires. The cumulative effects of fire suppression and climate change are now fueling larger, hotter wildfires. The Reading Fire of 2012 (16,098 acres of parkland) and the Dixie Fire of 2021 (73,240 acres of parkland) each far exceeded the size of previous wildfires. More than half of Dixie Fire’s footprint in the park has experienced low to moderate severity effects, in part due to fire management in previous decades. However, one-third of the park area affected experienced high-severity effects concentrated in the southeast area. Since historical fire regimes have not reached this magnitude or severity, Lassen Volcanic and its partners in the Lassen region are using scenario planning to consider implications for the future.