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9 Dec 2022

Plant of the month: Sequoiadendron giganteum

Written by Fran Culverhouse, PLANTS Project Inventory Officer
A view looking up the very tall trunk of a giant redwood tree from the ground.
The giant redwood at Holmwood
Although Holmwood is best known for its fine house designed by Alexander ‘Greek’ Thomson, its grounds are home to many notable trees. While inventorying the plant collection this summer, the PLANTS team were particularly struck by one: the giant redwood.

Sequoiadendron giganteum are remarkable trees that are native to a small region in central California, where they can grow to over 80m tall with a girth of over 8m. Although not the tallest trees on earth, they are the largest by mass and are among the oldest, as they can live for over 3,000 years. They typically grow at altitudes between 1,000m and 2,000m, where summers are warm and dry, and winters have reliable snowfall.

Many very tall giant redwood trees grow in a forest. The sky is slightly hazy due to a recent forest fire.
Enormous giant redwoods (Sequoiadendron giganteum) in Yosemite National Park, California, USA | Image: Sundry Photography, Shutterstock

The giant redwood is now a familiar tree in cultivation. However, back in the 19th century, when news of the giant redwood groves in California was spreading, the race was on to become the first to grow them outside of the US and introduce them into cultivation. An estate in Perthshire, owned by the father of a gold prospector, was in fact where the first seeds of a giant redwood were sent in August 1853 to be successfully propagated. In December of the same year, a nursery in England was wrongly credited with this achievement; it has since been recognised that the Scottish introduction occurred four months earlier.

“The genus Sequoiadendron is believed to be named after Sequoyah, the man who created a writing system for the Cherokee language; dendron means tree in Greek.”

Despite the difference in growing conditions from their native range, the giant redwoods seem to be enjoying the Scottish climate. Many of the biggest specimens in the UK are found in Scotland, with fine examples growing in other National Trust for Scotland gardens, such as Geilston and Craigievar, as well as Holmwood. Because giant redwoods have grown in the UK for less than 200 years, it’s not yet known what size they will ultimately reach here.

Common names for these trees include giant tree, giant sequoia, Sierra redwood, mammoth tree and Wellingtonia, although giant redwood is perhaps the best known. It can sometimes cause confusion when the same common name is given to different plants, and this is the case with ‘redwood’. The name is shared with two closely related tree species: the coastal redwood (Sequoia sempervirens) and the dawn redwood (Metasequoia glyptostroboides). All three sit within the cypress family (Cupressaceae) and each is a monotypic genus (the only living species within the genus). They may look similar initially but they are quite different on closer inspection.

One of the most recognisable features of the giant redwood is its thick, fibrous, reddish-brown bark, which is spongy to the touch. The insulating properties of the bark have evolved to protect giant redwoods from forest fires in their native habitat.

The base of a giant redwood trunk is flared, and its branches often sweep down and then curve upwards at the ends. The small leaves are evergreen and scaly, with stomata (pores) dotted across the leaf, unlike many conifers which have stomata arranged in bands.

Female seed cones have a distinctive diamond pattern, which someone once said to me resembled wrinkly lips – that’s an image that has stuck with me! The cones can remain green on the tree for many years before opening to release the tiny seeds. Forest fires can trigger huge amounts of seeds to be released as the heat rises into the canopy drying the cones. Each seed has two small wings to aid dispersal by wind.

Due to their height, giant redwoods are prone to lightning strikes. Should this occur, they respond by sending up new trunks. A good example of this can be seen in a specimen just 3 miles south of Holmwood, in the paddock in front of Greenbank House.

Giant redwoods have faced numerous threats over the years in their native habitat, from mass felling in the 19th century to the jeopardy of climate change today. Although most of these majestic trees are now in protected areas, they face increasingly frequent forest fires and decreasing rainfall. They are classified by the IUCN as endangered in the wild.

The history of Holmwood has been well recorded over the years, yet little is known about the history of its tree collection. We think the Holmwood giant redwoods are approximately 100 years old, making them still saplings compared with their Californian relatives! They are a fine sight to behold, standing tall in this quiet corner of Glasgow. The PLANTS project team look forward to finding more of these giants as they continue with their surveys next summer.

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