Studying the Structure of Giant Sequoias to Keep Us Safer

Candice Gaukel Andrews August 25, 2020 0

Yosemite National Park is famed for its many natural wonders, including the towering Bridalveil Fall; the granite cliffs of El Capitan and Half Dome; and giant, ancient sequoia trees. ©Candice Gaukel Andrews

Yosemite National Park’s massive mountains—such as El Capitan, one of the world’s tallest monoliths—and its many waterfalls—such as Yosemite Falls, which drops 2,425 feet and is the highest falls in North America—provide some of the most picturesque and unique views of natural wonders anywhere on the planet. And if those marvels aren’t enough to make you feel awestruck and small, the park holds three groves of giant sequoias, a species that includes some of the largest trees on Earth.

Giant sequoias are able to grow big and old—sometimes surviving for thousands of years—because they are generally able to protect themselves against their natural threats. They are too massive to be blown over in the wind; and their up-to-two-feet-thick, tannin-rich bark protects them against fungal rot, insect damage, rock falls and wildfires.

Recently, however, researchers examined the structural properties of the giant sequoia’s bark in detail for the first time and published their results in the International Journal of Molecular Sciences. Surprisingly, what they found could help us construct safer buildings in the future.

The giant sequoia tree’s girth is what truly makes it a colossus. ©John T. Andrews

Old, big and hardy

Giant sequoias are the planet’s largest single trees by volume. They reach an average height of 160 to 279 feet and an average diameter of 20 to 26 feet. Record trees have been identified at 311 feet tall and 56 feet in diameter. The oldest known giant sequoia is estimated to be 3,500 years old. The biggest of these behemoths is the 2,100-year-old General Sherman tree in Sequoia National Park. General Sherman stands 275 feet tall, has a 102-foot circumference and weighs an incredible 2.7 million pounds.

Originally, giant sequoias could be found throughout the Northern Hemisphere. Today, however, they reside in only about 77 scattered groves spread along the western slopes of the Sierra Nevada mountain range, far inland and between 5,000 and 7,000 feet above sea level. That elevation provides the trees with the dry mountain air that is necessary for their cones to open and release seeds. Giant sequoias also require well-drained soil for their shallow roots. Luckily, the snowpack from the Sierra Nevada mountains supplies them with thousands of gallons of water every day.

The oldest known giant sequoia was a 3,266-year-old tree in the Converse Basin Grove in Giant Sequoia National Monument in California. Giant sequoias are outlived only by bristlecone pines—the oldest aged at 4,844 years in Nevada’s Great Basin National Park—and by alerce (or Patagonian cypress) trees—one of which was estimated to be 3,639 years old in Chile. When giant sequoias do die, it is often because of root rot or another weakening of the base. Dry spells, fire and root rot do not typically affect the whole tree; but if they destabilize the base, gravity can eventually fell it, according to Scientific American magazine.

Fire helps release seeds from giant sequoia tree cones; recycle nutrients in the soil; reduce competition from other trees; and open holes in the forest canopy, letting in sunlight for seedlings. ©John T. Andrews

In Yosemite National Park, giant sequoias live in three groves: Mariposa, Merced and Tuolumne. Mariposa Grove, located near the South Entrance of Yosemite, is the largest grove in the park and is home to more than 500 mature giant sequoias. This is where the famous, 209-foot Grizzly Giant lives, a giant sequoia that is about 3,000 years old. Such trees often owe their size to rapid growth rather than to age, so an old giant sequoia will not necessarily be the largest tree.

Located on Tioga Road just east of Crane Flat, the Tuolumne Grove has about two dozen mature giant sequoias; and the Merced Grove, situated about six miles west of Crane Flat, also contains about 24 older giant sequoias.

Fire is an important element of the giant sequoia forest. In order to thrive, seedlings need nutrient-rich soil, lots of sunlight and an area free of competition from other plants. Periodic wildfires help to produce all of these conditions and are, therefore, very beneficial to the reproduction of giant sequoia trees.

During the 2015–2018 Mariposa Grove restoration project, some pavement was removed to improve the natural flow of water and help regenerate giant sequoia habitat. ©John T. Andrews

Unfortunately, fire suppression policies in recent years have increased the growth of brushy, dense undergrowth and reduced the likelihood of giant sequoia regeneration. And climate change continues to affect giant sequoias. The California droughts of the 2010s left many of the trees stressed from lack of water. Some trees are now exhibiting symptoms of dehydration, including brown foliage at their tops. Though giant sequoias usually die after falling, recently scientists have seen some die while still standing.

Ecologists have long been worried about visitor impacts on giant sequoias, particularly compaction and erosion of soils near the base of the trees due to trampling. In 1962, a University of Michigan academic assessed how humans are influencing Yosemite National Park’s Mariposa Grove. More than 50 years later, in spring 2015, Mariposa Grove was closed in order to conduct the largest restoration project in the park’s history. Buildings, roads and trails that were encroaching on the roots of the ancient trees and hydrology issues were addressed. A more giant-sequoia-friendly Mariposa Grove reopened on June 15, 2018.

New, textured and strong

In a study published in the May 9, 2020, issue of the International Journal of Molecular Sciences, researchers examined in detail the structural properties of giant sequoia bark for the first time ever. They discovered that the outer bark of the tree contains many fibers organized into bundles. These cross over each other and are also layered on top of one another, creating a three-dimensional, netted framework.

Giant sequoia tree bark contains fibers that form a 3D network with air pockets, functioning like foam when compressed. ©John T. Andrews

In between the fiber bundles are air-filled cavities. When something hard, such as a rock, strikes the bark, these cavities are compressed. Compressing the hollow spaces and stretching the fiber network has the effect of distributing the energy evenly over the bark, protecting the inside of the tree where its sensitive cambium (which forms the bark and the wood) lies. The bark later returns almost completely to its original state. The cavities also insulate the tree so that it is resistant to the heat generated during wildfires.

Due to this structure, the bark of the giant sequoia tree behaves like an open-pored foam, similar to that used in the construction of cars and houses. And much like what we’ve learned about how to design quieter aircraft by studying owl’s wings or invent Velcro from the workings of cockleburs, scientists are hoping that by studying giant sequoia tree bark they can develop a new type of lightweight concrete with bundles of hollow fibers, which could be used to better insulate and safeguard buildings against destructive forces, such as earthquakes.

The natural vistas to be found in Yosemite National Park are jaw-dropping, to be sure. But nature isn’t only valuable for its intrinsic and soul-stirring qualities. Sometimes, what we work to protect and conserve, in the end, guards and redeems us.

Here’s to finding your true places and natural habitats,

Candy

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