The world’s largest trees have survived for more than 3,000 years, but their futures lie in human hands.
They are the giants of nature; the skyscrapers of Mother Earth. In Sequoia National Park, some 8,000 giant sequoias rise firmly from the forest floor and branch out at a height of up to 80 metres. Only by placing humans next to their roots can one really fathom their size. The species is not the world’s tallest tree type. Nor is it the widest or oldest. But by trunk volume, it is the biggest.
The giant sequoia grows fast and lives long. As they expand, they produce an estimated 40 cubic feet of wood per year. Most are believed to be between 1,800 and 2,700 years old. “The oldest sequoia that we know of was measured by counting the annual rings of a stump – some 3,200 of them,” says Malinee Crapsey, who has worked in the park for 25 years. “We don’t know if any of the standing trees are older than that.”
For a sequoia to fulfil its potential, the environmental factors must be perfect. One crucial element – surprising as it sounds – is fire. Yes, the mosaic of small, frequent and relatively cool fires paves way for young sequoias. “Fire clears the ground of layers of forest litter and duff, leaving bare, ash-fertilised soil,” says Crapsey. “It removes some of the plants that compete with young sequoias for water and nutrients – those thin-barked firs and pines that are less evolved to survive fire – which also allows more sunlight to reach the forest floor. Finally, it opens the cones, which releases sequoia seeds onto the perfect soil bed.”
The quality of the soil is fundamental. In some places where log has been burnt, the soil has become mineral-rich and given birth to a line of thriving sequoias. “They live long because they have evolved to resist insect infestations, most rot, fire, and disease,” says Crapsey. “Not every tree gets large. If the seed lands in a spot with the ideal combination of soil depth and moisture, and experiences the preferred level of fire activity around it, it has a chance to become what we call a ‘monarch’.”
One tree to enjoy such favourable conditions is General Sherman. It is, with its 1,500-cubic-metre trunk, the largest tree in the world. It stretches up to 84 metres and has a diameter of 11 metres. Its name is taken after William Tecumseh Sherman, an American Civil War general.
When the Sequoia National Park was established in 1890, it became the second national park in the United States after Yellowstone. The decision rescued the trees from logging. “From time to time, however, sequoias fall over,” says Crapsey. “The reasons? Some combination of strong wind, uneven snow loads, waterlogged or eroded soil around the roots, root damage, or something else that unbalances them.”
Those factors are difficult to control. But others are in human hands. Crapsey says climate change is the most difficult factor to work with. “If it changes the amount of water available to the trees, the intensity of fire, the timing of precipitation… all these could affect the survivability of sequoias,” she says. The park management is working hard at studying the potential scenarios climate change might provoke. “It is a huge challenge,” she says.
Photos: Jim Lopes, Kara Jade Quan-Montgomery, Pierdelune [all via Shutterstock.com].