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William Tweed

Giant sequoia trees are tough, long-lived organisms. Their survival strategy, perfected over millions of years, is to live for dozens of centuries.

Most everyone knows this, but much of what the trees pursue to achieve this goal is missed by many who visit the groves.

No sequoia better demonstrates the longevity strategy than the famous General Sherman Tree in Sequoia National Park's Giant Forest. Long recognized as the largest tree in the world in terms of overall volume, the Sherman Tree appears to be perhaps 1,500 to 2,000 years old.

It's a vigorous, fast-growing tree. But it also has the habit of losing big pieces with some regularity, and therein lies our story.
As befits a very large tree, the General Sherman has really large branches. Because the tree's height equals that of a 25-story building (think of it as being three time as tall as Visalia's Radisson Hotel), even large branches may not look all that big.

Careful measurement has disclosed, however, that several of the tree's branches have diameters of 6 feet or more where they diverge from the tree's primary trunk.

It was one of these very large branches that came crashing to the ground during the powerful storms that swept the Sierra beginning on New Year's Day.

These storms were not only wet but also windy, and strong winds challenge tall trees in just the same way that they used to threaten sailing ships. Too much sail could bring a ship to grief, and trees face the same risk.

This problem is particularly serious for evergreen trees, which retain their foliage during winter, with its heavy snow and strong winds.

What is a tree to do if it has too much "sail" exposed to the wind during a storm? The possible outcomes are clear. A solid, well-designed tree runs the risk of catastrophic failure if the wind exceeds its natural strength.

In this scenario, the tree will fail at its weakest point, which is often at its base, where the unitary trunk divides into multiple roots. In human terms this is a "blow down," and such failures are common among pine and fir trees in the Sierra during major storms.

There is another possible strategy, however, and it is here that the sequoia demonstrates yet again how well it is designed to survive nature's challenges.

To avoid catastrophic failure, sequoias have evolved to lose branches. Even the biggest sequoia branches seem to be relatively weak in relation to the tree's massive trunk. What this means is that during extreme storms, branches will fail but the tree itself is likely to survive.

This is what happened to the General Sherman Tree during the New Year's storm. Powerful winds howled through the tree's exposed crown, threatening the very existence of this ancient organism, but before the tree could be uprooted, one of its huge branches failed and crashed the ground.

With a diameter of over six feet and a length in excess of 100 feet, this branch formed a huge "sail" during the storm, catching the wind like the sails on a square-rigged ship.

Its loss quite possibly saved the Sherman Tree from "capsizing."

Contradictory as it may sound, weak branches can make for long-lived trees when they are attached to a stout central trunk. The sequoia, unlike most of its conifer forest neighbors, also has the ability to grow new branches in its old age.

Together, these design details help the tree pursue its goal of longevity. Some sequoias live more than 3,000 years before the environment's natural stresses finally bring them down.

The last big branch came off the General Sherman in the winter of 1978 during another cycle of extreme storms. Other branches will come off in the future. It's just the way the tree works.

This spring, once the snow melts, Park Service crews will clear the huge broken branch from the trail that circles the tree. This will be done in a way that allows visitors to study the branch's mass and ponder its meaning.

In the cycles of nature, death often leads to life. And so it is with the giant sequoias and their branches. By sacrificing a part, the whole can go on living. It's the way big trees work.Visalia Times Delta