The Sequoiadendron Giganteum (giant sequoia) was once a dominant tree in North America and Europe, along with its cousin, Sequoiadendron sempervirens (coastal redwood). During the Jurassic Period, 180-135 million-years-ago, the planet was warm and moist, holding higher temperatures that were more accommodating to the large trees.
Guide to Sequoia
Ancient Climate Change
Some time near the end of the Cretaceous Period, 35-70 million-years-ago, the dinosaurs enjoyed their final days, and the Earth’s climate began to change, cooling and drying.
These conditions were not favorable to the large trees, and their species began a retreat that continues to this day. Around 20 million years ago, the Sequoiadendron became extinct in Europe, and continued a westward movement in North America.
68 Groves of Sequoia
A mere 68 groves exist naturally today in the Sierra Nevada between 5,000 and 7,000 feet, although they appear to be healthy. Around 40 separate groves containing an estimated 16,000 of the rare trees are found within the boundaries of Sequoia and Kings Canyon National Parks.
Sequoia trees are the largest living organisms on Earth. The General Sherman Tree is the largest, measured by volume. It stands 275 feet (83m) tall and holds a diameter of 36 feet (11m) at its base. The trees maintain great width with height, as Sherman retains a diameter of 17.5 feet (5.3) at sixty feet above ground level and its first branch does not spring from its trunk until 130 feet (40m) above the ground. So much for climbing this one…
Tiny Seeds – Giant Trees
The great trees can only grow by seed, unlike their coastal redwood cousins who can send sprouts from roots or from damaged stumps at any time in their lives. Their seeds are unbelievably small, as 91,000 seeds weigh only one pound. A single mature Sequoia may hold up to 11,000 cones in its upper canopy and yield an estimated 300-400 thousand seeds annually.
They are as John Muir noted, seemingly immortal, largely unfazed by disease, drought and fire. They often live more than 2,000 years and some have passed the 3,000 year mark, according to studies based on dendrochronology.
Their bark can be up to 3 feet (1m) thick and contains tannins that deter insects from boring into their trunks, which could open them to potential infections.
Fire… What Fire?
Fire has no real negative effect with bark this thick, and surprisingly, the trees are greatly aided by fire. The Sequoia depend on fire not only to clear the surrounding ground of competing plant growth in crowded forests, but also to produce extreme temperatures, which facilitate the release of seeds from cones.
The tree depends partly on its small tenants for dispersal of its seed, as the Douglas squirrel gnaws on younger cones, releasing seeds as the cone is eaten. Likewise, the longhorn beetle provides a service to the tree, laying eggs on the tree’s cones, into which the larvae bore holes. This damages the cone’s internal water supply, in turn causing it to dry and open, allowing its seeds to release and fall to the ground far below.
Healthy Sequoia
Although small in number compared to previous times and facing an uncertain future in the long-term, these trees are relatively healthy today, protected by natural evolution from ailments that destroy their less hearty limbed brethren.
With any luck at all, these trees should continue to thrive and our ancestors should be able to witness the splendor of walking in their midst a few thousand years from now.
I’m sure glad we didn’t cut them all down…
Guide to Sequoia
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