The largest tree in the world wears a peculiar apron made of aluminum foil these days. California firefighters have put the lower two meters of the thick trunk of the sequoia, named after the American Civil War General William Sherman, in the silver cover in Sequoia National Park to protect it from an approaching forest fire. Not only the Sherman tree, but almost all of the huge, ancient conifers in the park, often more than ten meters in diameter, are now wrapped in the heat-repellent film. "We want to avoid a disaster like last year," says the superintendent of the national park, Clayton Jordan.
At that time, more than 10,000 sequoias burned in the so-called Castle Fire. This corresponds to about ten percent of all this giant tree species, which only occurs in California's Sierra Nevada. Nobody knows exactly how many trees of the species Sequoiadendron giganteum there are in the granite mountains. However, experts had estimated that there could be a total of up to 120,000 copies. Only trees with a trunk diameter of more than 1.20 meters are counted. Younger and thinner trees are not included in the statistics. These sequoias occur only on the western slopes of the mountains between Lake Tahoe in the north and the county town of Visalia in the south in a narrowly limited altitude range between 1400 and 2400 meters. In total there are about 80 stalls of Sequoias in this area,whose thick bark appears wonderfully red in favorable light - hence the American name Mountain Redwoods.
Forest fires are important for reproduction
The tree can live up to 3,000 years old, and fire plays an important role in the life cycle of the species. Despite its enormous size - the Sherman Tree, for example, is nearly 90 meters high - its cones are barely larger than a plum tree.
However, the seeds stuck in it can only sprout if they are brought to life by flames.
Forest fires are therefore important for the reproduction of this unique tree species.
In addition, the bark of these trees is so thick that light fires do not cause any major damage.
However, the flames are only life-giving for the sequoias if they are not too hot. Before the California Sierra Nevada was largely settled about 170 years ago because of the gold rush, most of the forest fires there were quite tame. Frequent fires, kindled by lightning, prevented large amounts of dry undergrowth and dead branches from building up on the forest floor. The Native Americans did the rest with self-set fires to keep the forests largely free of easily combustible deadwood.
For more than a century, the strategy of the white settlers to fight fires stood in the way of this natural fire cycle.
Forest fires had to be fought intensively immediately.
As a result, more and more old combustible material accumulated in the forests.
There is now so much “fuel” along the western slopes of the Sierras Nevada that almost any forest fire can turn into a catastrophe.
Little chance of survival as soon as they burn
One of the dramatic examples of such extremely hot fire behavior was last year in Tulare County, which includes large parts of the Sequoia National Park and the national forest of the same name.
The Castle Fire, ignited by lightning, burned for four and a half months, eating its way through 700 square kilometers of wooded area.
It also recorded 20 of the approximately 80 stands of sequoias in the Sierra Nevada.
The flames were sometimes so hot and blazed so high that they reached the tops of even large sequoias.
As soon as they burn, the trees have little chance of survival, because once all the branches are burned, the delicate needles cannot regenerate and the tree dies.
After the Castle Fire only finally went out this January, biologists Nathan Stephenson of the United States Geological Survey and Christy Brigham of Sequoia Park spent weeks in the devastated wooded area.
On foot and from the helicopter, they counted all the burnt sequoia trees in the 20 stalls that were hit by the fire.
The resulting number was as shocking to biologists as it was to the California public.
Around 10,000 sequoias, a good tenth of the total population of these iconic plants, fell victim to the fire.
Protect aprons made of aluminum foil
To prevent a similar fire disaster this summer, the fire fighters who specialize in forest fires developed protective measures for the sequoia trees. This includes setting fire to scrub and dead wood in the Sequoia stands under controlled conditions - and protecting the largest trees with aluminum foil from the flames from spreading.
The next few days will show how effective these measures are. At the moment, two fires that were ignited by lightning almost two weeks ago are burning again in Sequoia National Park. It is expected that the two fires will unite in the coming days, which will then threaten what is probably the most famous sequoia tree. In this so-called Giant Forest there are not only the General Sherman Tree, but dozens of other similarly huge sequoias.
Usually several hundred thousand people visit the stand every year - but at the moment the whole area is completely closed. Even the employees of the park administration and the rangers had to leave the forest. Apart from the rustling of the aluminum foil in the wind, it is therefore unusually quiet in the park - only occasionally you can hear the roar of a tanker, spraying water and fire extinguishers on the active fires.