|Sequoiadendron giganteum subsp. var.||Big tree, Giant sequoia, Sierra redwood|
Sequoiadendron giganteum (giant sequoia, Sierra redwood, Sierran redwood, or Wellingtonia) is the sole living species in the genus Sequoiadendron, and one of three species of coniferous trees known as redwoods, classified in the family Cupressaceae in the subfamily Sequoioideae, together with Sequoia sempervirens (Coast Redwood) and Metasequoia glyptostroboides (Dawn Redwood). The common use of the name "sequoia" generally refers to Sequoiadendron, which occurs naturally only in the various groves that exist on the western slopes of the Sierra Nevada Mountains of California.
Giant Sequoias are the world's largest trees in terms of total volume (technically, only 7 living Giant Sequoia exceed the 42500 cuft m3 of the Lost Monarch Coast Redwood tree; see Largest trees). They grow to an average height of 50–85 m (165–280 ft) and 6–8 m (18–24 ft) in diameter. Record trees have been measured to be 94.8 m (311 ft) in height and 17 m (57 ft) in diameter. The oldest known Giant Sequoia based on ring count is 3,500 years old. Sequoia bark is fibrous, furrowed, and may be 90 cm (3 ft) thick at the base of the columnar trunk. It provides significant fire protection for the trees. The leaves are evergreen, awl-shaped, 3–6 mm long, and arranged spirally on the shoots. The seed cones are 4–7 cm long and mature in 18–20 months, though they typically remain green and closed for up to 20 years; each cone has 30-50 spirally arranged scales, with several seeds on each scale giving an average of 230 seeds per cone. The seed is dark brown, 4–5 mm long and 1 mm broad, with a 1 mm wide yellow-brown wing along each side. Some seed is shed when the cone scales shrink during hot weather in late summer, but most seeds are liberated when the cone dries from fire heat or is damaged by insects (see Ecology, below).
Giant sequoia regenerates by seed. Trees up to about 20 years old may produce stump sprouts subsequent to injury. Giant sequoia of all ages may sprout from the bole when old branches are lost to fire or breakage, but (unlike coast redwood) mature trees do not sprout from cut stumps. Young trees start to bear cones at the age of 12 years.
At any given time, a large tree may be expected to have approximately 11,000 cones. The upper part of the crown of any mature Giant Sequoia invariably produces a greater abundance of cones than its lower portions. A mature giant sequoia has been estimated to disperse from 300,000-400,000 seeds per year. The winged seeds may be carried up to 180 m (600 ft) from the parent tree.
Lower branches die fairly readily from shading, but trees less than 100 years old retain most of their dead branches. Trunks of mature trees in groves are generally free of branches to a height of 20–50 m, but solitary trees will retain low branches.
Giant Sequoia is a very popular ornamental tree in many areas. Sequoiadendron has been successfully planted in the British Isles, parts of continental Europe, as well as in much of the western, southern, and eastern USA. Trees can withstand temperatures of −31 °C (−25 °F) or colder, for short periods of time providing the ground around the roots is insulated with either heavy snow or mulch. Outside its natural range, sequoia's foliage suffers from damaging windburn.
The giant sequoias are having difficulty reproducing in their original habitat (and very rarely reproduce in cultivation) due to the seeds only being able to grow successfully in mineral soils in full sunlight, free from competing vegetation.
Pests and diseases
- ↑ Template:Harvnb
- ↑ Overview of the horticultural varieties (cultivars) of the giant sequoia, telenet.be