My first encounter with this tree was during childhood. A fine specimen grew in my village, in the grounds of the rectory. We were choirboys and we took delight in punching the soft bark of the tree every time we passed by. It was a game all village boys and girls knew. We would take visitors to another conifer species (with hard bark) and invite them to punch. No-one was hospitalised.
The tree has a reddish and soft bark, and sheds its lower branches (in its native range this means the active canopy is above any wildfire). This specimen is at the Dawyck Botanic Garden near Peebles. Image: Chris Jeffree.
The natural range of the tree is a small region of California, a narrow band on the western slopes of the Sierra Nevada mountains. Many of the trees are huge and very old, a few over 3,000 years. Some have celebrity status and are named after national heroes: eg General Grant, General Sherman, Washington.
The largest individuals may have 1400 m3 of wood, 6700 m2 of leaf area (equivalent to one football pitch), and a height approaching 100 metres. They are the largest trees on the planet, but not the tallest: that prize goes to another Californian species, the Coast Redwood Sequoia sempervirens which has attained 116 metres. Australia’s Eucalyptus regnans can exceed 100 metres and even Sitka Spruce in its native land can be 100 metres tall.
The canopy is not dense, but the total leaf area can be very large (measurements on older trees in California suggest 6700 m2 of leaf area, equivalent to one football pitch). Image: Chris Jeffree.
From Cretaceous deposits we believe the species was formerly widespread, not just in North America but also in Europe and Asia, and even in New Zealand and Australia. It was wiped out from most areas during the last glaciation. Now it exists in the wild as a rather small population of perhaps 80,000 trees in California. The International Union for Conservation of Nature (IUCN) has listed the Giant Sequoa as a Threatened Species.
It is a fire-resistant tree, but some wildfires are simply too much for it. As in many other parts of the world, well-meaning foresters suppressed fire for many decades with the result that combustible material accumulated. However, when fires do occur under such a regime they are more intense owing to the accumulated fuel load. Some trees have therefore been lost because of severe wildfire. The solution is to carry out ‘prescribed burning’ whereby frequent small fires are made to prevent the accumulation of too much organic debris.
Sequoiadendron giganteum at Cluny, Aberfeldy, Perthshire, May 2022. It is one of the largest in Scotland and may have grown from the original 1853 seed collection. Photo: John Grace.
Like some other woody species it has specific adaptations to withstand fire, and even needs fire to make the cones open and distribute the seeds. The thick layer of soft bark insulates the living tissues inside and therefore protects the tree from all but the most severe wildfires. However, drought increases flammability, and Californian droughts from 2012 onwards culminating in the record-breaking heat waves of 2020 and 2021 produced the largest wildfires ever seen in California. Fanned by strong winds, many trees died, perhaps over 10 % of the giant trees. Many scientists have considered the long drought to be one of the early symptoms of climate change.
Leaves are awl-shaped, spirally-arranged and long-lived. This shoot is being colonised by a foliaceous lichen (Parmelia?). Image: Chris Jeffree.
Another factor contributing to the decline of the species in California is thought to be the compaction of soil caused by too many visitors. Compacted soil restricts gas diffusion and surface roots can suffocate from a lack of oxygen. In an effort to reduce footfall and motor vehicles, a booking is required to drive into or through Yosemite National Park from April to October this year.
The tree is monoecious (male and female cones on the same tree). Left: immature male cones. Right: nearly-mature female cones. Attribution: Thereidshome, Public domain, via Wikimedia Commons
In Britain the growth rate is rapid, and many of those trees planted in the 19th Century are now fine specimens. All kinds of people take an interest in measuring the height of tall trees and records of ‘monumental trees’ are published online. The tallest Giant Redwood trees in Scotland include those at North Kessock (near Inverness) and Cluny (near Aberfeldy).
One of the keenest record-keepers was Alan Mitchell (1922 – 1995), author of the book The Field Guide to the Trees of Britain and Northern Europe. He founded the Tree Register, and his ashes were scattered in 1995 in Diana’s Grove at the Atholl estate (Perthshire), famed for its tall redwood trees and said to be one of Alan’s favourite places.
A related species from the fossil record. Sequoia affinis is a long-extinct species, pictured here at the Florissant fossil beds in Colorado. It has been suggested that Sequoia affinis may be ancestral to both Sequoia sempervirens and Sequoiadendron giganteum. Image: Chris Jeffree.
Sequoiadendron giganteum was introduced to Britain in 1853 by a Perthshire botanist John Matthew, who sent seeds from California home to his father. However, in England it is said that another person, William Lobb, also in 1853, was the one who came with seeds. Probably they both did.
Similar plantings were made in several other European countries as well as Australia and New Zealand. There are large trees in France (58 metres) and Italy (48 metres), but tolerance of extremely low temperatures limits survival in continental climates. One tree in Poland is nevertheless said to have survived -37 degrees Celsius.
A scene from the 19th Century. When giant redwoods were first ‘discovered’ they were the subject of great curiosity. This lithograph shows the aftermath of the felling of a giant tree. 32 invited guests are pictured dancing on the stump in Calaveras County, California. This is the Discovery Tree, said to be the first recorded observation of the species by a non-native American (Augustus Dowd) at the Calaveras Grove in 1852. It was felled in 1853. Source of the image: wikipedia, scanned from Hewes, J.J. 1984. Redwoods: The World’s Largest Trees. Gallery Books.
The wood of the giant trees is brittle, and not suitable for construction. It does however resist decay and has therefore been used to made shingles and fence posts. However, the wood is stronger in young trees, and the UK’s forest research agency Forest Research suggests commercial use of the species in the western and southern areas of England, as part of a ‘diverse mix’. I think it would do well in Scotland too.
Distribution of Giant Redwood in Britain and the world, from BSBI (left) and GBIF (right).
An important research question has been: how tall can trees possibly become? The limiting factor appears to be the tensile strength of water. Trees (and other plants) essentially ‘suck’ water from the soil by regulation of the osmotic properties of the cells in the leaves. The water is sucked up against gravity through the narrow tubes formed by the dead cells that make up the sapwood. Water molecules cling to each other because of the opposite charges on the hydrogen and oxygen atoms. Pure water has a very high tensile strength due to the attraction between molecules of H2O, but water can easily break (the process of ’cavitation’) if there are dissolved gases or other impurities.
To investigate these matters, a group of researchers from the University of California bravely climbed to the tops of 12 Giant Redwood trees (Williams et al 2017). They found the leaves at the top of the tree were small and severely water-stressed, showing all the symptoms of drought. It seems that under normal conditions, a tree cannot raise water to much more than 100 metres.
A ranked list of large Sequoiadendron giganteum trees in Scotland, from Monumentaltrees.com. For other species, see https://www.monumentaltrees.com/en/heightrecords/gbr/scotland/.
When first discovered, the tree was named Wellingtonia gigantea. But shortly after this it was realised that an unrelated species was already called Wellingtonia. So then it was called Sequoia gigantea until it was noted that Coast Redwood already had that name. Then it was called Washingtonia californica but, alas, a palm already had the name Washingtonia. These errors (and more) were corrected in 1939 by John Theodore Buchholz, an American botanist who became President of Botanical Society of America in 1941. The old names are sometimes still used.
Reference
Williams CB et al (2017) Coping with gravity: the foliar water relations of giant sequoia. Tree Physiology 37, 1312–1326.
Web sites consulted
https://www.woodlandtrust.org.uk/visiting-woods/woods/atholl-estate-dianas-grove/
https://www.redwoodworld.co.uk/picturepages/grange.htm
https://www.clunyhousegardens.com/plant_collectors.html
https://www.nps.gov/yose/learn/nature/sequoia-research.htm
https://www.forestryengland.uk/news/over-half-million-natures-giants-the-nations-forests
https://www.monumentaltrees.com/en/gbr/scotland/perthandkinross/4190_blaircastle/21080
©John Grace
Botany in Scotland 