Giant sequoias need fire, and a small beetle, to release their seeds
A giant sequoia can hold 11,000 cones that stay green and shut for up to 20 years. Most seeds escape only when fire's rising heat dries the cones, or when longhorn beetle larvae bore in and cut off their water. Without flames clearing the ground, the planet's most massive trees struggle to raise any young.
Sequoiadendron giganteum grows wild only in 81 scattered groves on the western slopes of California's Sierra Nevada, covering just 35,620 acres in total. Adults usually stand 50 to 85 metres tall with trunks 6 to 8 metres wide, and the record height is 94.8 metres. Dendrochronology puts the oldest known tree at 3,200 to 3,266 years, a lifespan exceeded only by bristlecone pine and alerce. The IUCN lists the species as endangered, with fewer than 80,000 left in its native range.
Its whole life cycle is tuned to fire. Bark up to 90 centimetres thick at the base, and sap laced with tannic acid, shield the trunk. Seedlings survive only in full sun on bare mineral soil, so they depend on periodic burns to strip away competing plants and needle litter; in damp humus they sprout in spring then die when summer dries it out. Convection from a blaze carries hot air into the crown to open cones just as the ground is freshly cleared, and loose ash may even shade fallen seeds from ultraviolet light. Early twentieth-century fire suppression let white fir crowd in and fuel pile up, so in 1970 the National Park Service began controlled burns.
The name has a myth attached. Josiah Whitney wrote in 1868 that the genus honoured Sequoyah, creator of the Cherokee syllabary, and the story stuck. A 2012 study concluded instead that the Austrian botanist Stephan Endlicher built it from the Latin sequi, to follow, because seed counts per cone fitted a numerical sequence with related genera.
The timber is brittle and shatters when felled, fit mostly for fence posts and matches, yet it resists decay so well that a log near Nelder Grove radiocarbon-dated to 10,000 years. Planted abroad since the nineteenth century, the tree thrives in Britain, where a laser-scanning study estimated open-grown specimens lock away about 85 kilograms of carbon a year.
Source: Sequoiadendron giganteum
