The Klamath-Siskiyou Mountains support a Mediterranean climate with relatively wet winters and long, dry summers. During these dry summer months the region frequently experiences widespread lightning storms. The receptive fuels respond with wildfire ignitions, often in remote and rugged terrain. These fires can burn for months during a variety of weather conditions and in a wide variety of habitat types and plant communities, creating diverse mixed-severity fire effects.
Fire is an important natural process influencing vegetation in the Klamath-Siskiyou Mountains. The forests of the Klamath-Siskiyou Mountains are fire adapted and particularly diverse. Each forest, in fact each stand, has its own personal relationship with fire, making fire ecology an extremely complex science. Burn patterns are also influenced by weather, terrain, aspect, slope position, fire history, vegetation patterns and the region’s complex geology.
The Klamath-Siskiyou Mountains contain a diversity of habitats and microclimates, including vast mixed conifer forests adapted to a mixed-severity fire regime. These forests support dense forests on north- and east-facing slopes and in the deep canyon bottoms. These locations are often adapted to low- and moderate-severity fire effects with the occasional high-severity run. They are often colonized by closed canopy stands of Douglas fir, sugar pine, white fir and a variety of hardwood species.
On south and west facing slopes, as well as high on the ridges, stringers of pine and fir, mixed with groves of hardwood trees grow among rocky areas and chaparral patches. These areas tend to burn more frequently and with mixed-severity effects. High-severity fire rejuvenates our chaparral, mixed hardwood stands and serotinous coned conifer species, such as knobcone pine, lodgepole pine and Baker’s cypress. High-severity fire clears away competition, triggers regeneration and vigorous young growth with enhanced levels of biodiversity.
Significant fire refugia also occurs on the rocky headwalls, barren areas and cool, moist high elevation habitats. Fire sensitive Brewer’s spruce, Alaska yellow cedar, pacific silver fir, Engelmann’s spruce, mountain hemlock and subalpine fir are found in protected, often rocky, high-elevation habitats that tend not to burn or burns at very low severity.
Fire severity in the Klamath-Siskiyou is largely influenced by local weather conditions and the region’s steep dissected terrain. When weather and terrain come into alignment fire behavior can become extreme, creating high-severity, stand-replacing fire effects. Hot, dry slopes and upper slope positions tend to burn at higher severity and with higher levels of mortality.
Heavy natural smoke inversions and terrain-moderated, backing fires also influence fire severity in our region. Smoke inversions often cap the region during wildfire events, trapping moisture, reducing ambient air temperatures and limiting air movement. These factors tend to create vast low severity, understory fire effects and largely maintaining forest canopies. These low-severity fires burn in the understory beneath closed canopy forest habitats. They also maintain the staggered canopy conditions of fire-adapted ponderosa pine and sugar pine, allowing for vigorous growth and providing opportunities for regeneration.
The world-class diversity of the Klamath-Siskiyou Mountains has been shaped by fire. For millennia wildfires have burned across the region, responding to weather conditions, terrain and vegetation. The mixed-severity fire regime is variable in its frequency and its fire effects. Today, contemporary wildfires demonstrate similar patterns of frequency and fire severity, creating diverse fire footprints, vegetative mosaics and restorative fire effects. Although fire suppression and commercial logging have influenced the structure of these forests, the basic natural process of fire has returned and our intact forest legacies continue to demonstrate resilience.