Giant Sequoias

 

A forest with giant sequoias, the largest trees in the world, is a feast for the senses. The giant sequoias’ red/orange bark is distinct among the grey and brown bark of other trees. And if you stand beneath one of these giants, you can gaze all the way up its tall trunk and through its high branches to see sky above. The treetop is often hidden above the highest branches. If you are quiet and listen, you may hear a breeze rustling the foliage of smaller trees – the sugar pines, white and red firs, or incense-cedar. Or perhaps you’ll hear a woodpecker calling and tapping against a tree, seeking insects. If you have time to take a walk, you may see a giant sequoia along the trail – try to press your fingers against its spongy, thick bark. Take the time to experience the beauty of these trees and the other plants and animals that live in these forests.

Giant sequoias grow at middle elevations along the west slope of the Sierra Nevada. While not the world’s oldest trees, they are known to reach ages of up to 3,400 years. Tree ring studies of giant sequoias provide a long record of climate and fire history, helping park managers and scientists better understand relationships of climate, fire, and the giant sequoia life cycle.

 
Scientist at the top of a giant sequoia tree, roped in and wearing a helmet, collects foliage sample.
Scientist Anthony Ambrose from the University of California, Berkeley collects foliage samples near the top of a giant sequoia to learn more about tree responses to drought.

Photo courtesy of Wendy Baxter, University of California, Berkeley

Sequoias and Climate

Giant sequoias have survived a varied climate over the past two to three thousand years. For many years, we believed that giant sequoias died by falling over, or having extensive crown scorch from a fire. Standing death from disease or insects (unrelated to crown scorch) was rarely observed by scientists and managers who have worked for decades in the Sierra Nevada.

A hotter drought occurred in 2012-2016. Higher temperatures intensified the effects of low precipitation, causing greater water loss and low moisture availability for trees. Although non-sequoia conifers suffered extensive mortality, sequoias mostly did not. However, during 2014, scientists observed extensive sequoia foliage dieback. During and after this drought, they documented nearly 40 giant sequoias that died standing, associated with native bark beetle activity and fire-caused damage around the base of the tree. Scientists and managers are gathering information to better understand the responses of giant sequoia to drought and to characterize landscape-scale patterns of vulnerability to hotter drought.
 
Two giant sequoias (one with fire scar) and nearby shrubs with golden/red autumn color
Giant sequoias in Redwood Mountain Grove, Kings Canyon National Park. Sequoia on right side has a large fire-scarred black surface from a lifetime of periodic fires.

NPS / Anthony Caprio

Sequoias and Fire

Fire plays a crucial role in the giant sequoia ecosystem. Toward summer's end in the dry season forest conditions favor fire, and lightning storms are not uncommon in the mountains. Fire scars in tree rings dating back 2,000 years show that fires have occurred naturally at varying intervals, generally between 3 and 35 years, in these forests.

Giant sequoias are adapted to periodic fire. Sequoia bark typically protects the trees against significant damage. At up to 18 inches (46 cm) thick and extremely fibrous, sequoia bark not only resists burning but also insulates the tree against fire's heat. Should fire penetrate the bark and scar the living tissue, new growth may heal the scar. However, giant sequoias experience many fires over their long lives, and may not keep up with healing over decades to centuries of fire scars. Thus, you will see blackened areas that extend from 1 to many feet up the height of older sequoias where fires scarred the tree many times.

Fire also prepares the bare, mineral soil required by sequoia seeds for germination. It burns off undergrowth and trees that compete for the abundant sunlight young sequoias require. The reproductive success of giant sequoias demands only that each tree produce one maturing offspring over its lifespan of several thousand years.
 
Two giant sequoia cones lying on burned area with small oatmeal flake-sized seeds around them.
Giant sequoia cones and seeds after a fire. The scattered seeds resemble small flakes of oatmeal.

NPS / Anthony Caprio

Sequoia Cones, Seeds, and Fire

The sequoia's cone-and-seed strategy evolved with fire. Sequoia cones retain their seeds – unlike other trees in their forest environs – in closed cones for perhaps 20 years. When fire burns through the forest the hot air dries out older cones. They open up and, within one to two weeks, begin to rain down their seeds loads onto fire-swept, bare soil.

The life story of the giant sequoia begins with a very small seed, the size of a grain of oatmeal 91,000 sequoia seeds weigh just 1 pound! To germinate and survive, sequoia seeds must fall on the mineral soil left bare by fire without it, seeds will not successfully grow into new sequoia seedlings. Both Douglas squirrels and cone-boring beetles can also release seeds, but if they don’t fall on bare soil cleared by fire, they cannot germinate.

Last updated: June 22, 2020

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