Oak trees feed more than 950 kinds of caterpillar
Oaks are keystone trees, hosting over 950 caterpillar species, swarms of gall wasps and partnerships with fungi including truffles. One Bulgarian oak is estimated at 1,637 years old. Yet almost a third of the roughly 500 oak species now face extinction from climate change, invasive pests and lost habitat.
Oaks make up the genus Quercus in the beech family, trees and shrubs spread widely across the Northern Hemisphere, some deciduous, some evergreen. They have spirally arranged leaves, often lobed, and bear acorns sitting in little cups. Many deciduous species cling to their dead leaves until spring. Gardeners split them into red oaks, whose leaf lobes carry soft bristles, and white oaks, which lack them. A single tree produces male catkins and small female flowers each spring.
They can be giants. The white oak, Q. alba, may live 600 years and reach 44 metres tall and 4 metres across. Bulgaria's Granit oak is thought to be Europe's oldest, and the Wi'aaSal live oak on the Pechanga reservation in California is at least 1,000 years old and possibly twice that. At the other extreme, the Japanese evergreen oak tops out around 9 metres. Unequivocal fossil pollen from Austria dates to about 55 million years ago, and North American records from Oregon go back some 44 million years. Free hybridisation between species makes the genus's history hard to untangle.
People have exploited oaks thoroughly. The hard timber goes into buildings and furniture, bark once tanned leather, and oak barrels age sherry and whisky, adding flavour and colour. Cork comes from the spongy bark of the cork oak, and the word cork itself derives from Quercus. Tannin in leaves and acorns deters fungi and insects and can poison cattle, although pigs digest acorns safely.
The tree carries heavy symbolism, standing for strength, serving as a national tree in many countries and linked to thunder gods in Indo-European religions. Celebrated individual trees range from Britain's Royal Oak and America's Charter Oak to the Guernica Oak of the Basques. The English word descends from Old English ac, which survives in place names such as Acton, meaning oak town.
Source: Oak
