Montane Forests

Ponderosa pine forest in Cedar Grove, Kings Canyon National Park, after a fire
Ponderosa pine forest after a fire in the Cedar Grove area of Kings Canyon National Park. Fire is an important natural process in Sierra Nevada forests, reducing surface fuels, creating favorable conditions for young trees to establish, and maintaining the open structure of these forests.

Photo by Anthony Caprio

Unlike many of the cone-bearing, evergreen forests of the world, which are dominated by a single species of tree, the mixed-conifer montane forests that cloak the lower and middle slopes of the Sierra Nevada are remarkably diverse. Here ponderosa pine, incense-cedar, white fir, sugar pine, and scattered groves of giant sequoia intermix and coexist. These trees, many of which reach tremendous heights, form some of the most extensive stands of old-growth coniferous forest that remain in the world.

 
Giant sequoias displaying bark charring at base from fire
The charring on the bark of these giant sequoias is from both recent prescribed burning and older fires. The thick bark of giant sequoias protects them from the heat of fires, and although some of the bark is burned, most of it typically remains intact.

Photo by Linda Mutch

The iconic giant sequoias grow interspersed with other trees in a mixed-conifer forest. These include white fir, sugar pine, incense-cedar, red fir, and ponderosa pine. While giant sequoias dominate in terms of size and volume, they are outnumbered by other types of trees. Giant sequoias are the world's largest trees when measured by volume, and can live to be over 3,200 years old. They have a limited distribution, reflecting climatic patterns of the past several thousand years. Once more widespread, today they occur naturally only in the Sierra Nevada. In their current range, cold temperatures may have limited their expansion into higher elevations while drought has limited grove boundaries at low elevations. Soil characteristics also are important: Giant sequoias prefer deep, sandy loam soils that are wetter, less acidic, higher in calcium, and lower in nitrogen than soils associated with neighboring conifer forests.

Periodic fire plays an important role in giant sequoia reproduction. It stimulates seed release from cones, exposes mineral soil where the seeds can germinate, sterilizes the soil (killing seedling pathogens), and opens up the forest canopy to allow in enough sunlight for sequoia seedlings to establish and grow.

To learn more about these magnificent trees, visit the Giant Sequoias page. Learn more about the effects of fire and changing climate on giant sequoias at these pages: Giant Sequoias and Fire or Giant Sequoias and Climate. If you would like to visit a sequoia grove, go to the Discovering Sequoia Groves page to get introduced to a few of the parks' groves.

 
Red fir forest in Sequoia National Park
Red fir forests are typically shady, cool forests without many plants growing beneath them. While red fir can be interspersed with giant sequoias and white fir, they typically grow at higher elevations in stands where they are the dominant species.
In the upper montane, the mixed coniferous forest is replaced by nearly pure stands of red fir and lodgepole pine. Characterized by deep snow accumulation during the winter months and a dense canopy that limits the amount of sunlight that reaches the forest floor, the red fir forests lack a diverse herbaceous component. Only the most shade tolerant herbs thrive beneath the towering trees. Lodgepole pines have an unusual distribution, growing in both moist lowlands and in drier sites on benches and ridges. In wetter sites, these forests can support a rich assortment of herbs and wildflowers in their understory.

 
Low intensity fire burns on forest floor under giant sequoias and other conifers
View of prescribed burn through the trunks of two giant sequoias, Giant Forest, 2014.

NPS / Tony Caprio

Role of Fire

From fire history studies using tree-ring records, we know that mixed-conifer forests prior to 1860 burned at the following fire return intervals (time between fires):

  • Ponderosa pine-mixed conifer forests (lowest elevation) - average of 4-6 years
  • White fir/giant sequoia-mixed conifer forests (medium elevation) - average of 10-16 years
  • Red fir forests - average of 30-50 years

From the late 1860s to the early 1900s, grazing and decline of Native American use of fire reduced fire frequency, followed by fire suppression that excluded fire from most of these forests. Starting in 1968, these parks began prescribed burning and allowing some lightning-caused fires to burn in remote areas.While some areas have had recent fire, many forests have not burned in decades. In the past decade, high-severity wildfires have caused extensive tree mortality in Sierran mixed-conifer forests, including killing an estimated 13-19 percent of all large giant sequoias. See the Giant Sequoias and Fire page for more information.

 

Impacts of Climate Change on Mixed Conifer Forests

Visit the photo links below to learn more about climate change impacts on giant sequoias and other types of conifer forests.

 

Climate Change Impacts on Forests

Last updated: October 17, 2022

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