Sequoia sempervirens, also known as coast redwood, coastal redwood, Californian redwood, is a species which is increasingly mentioned when considering alternative tree species to cope with a changing climate in Wales. This may come as a surprise to some given that the deep leaf litter it produces decays slowly and deters ground flora causing a lack of biodiversity. In recent years, this has often been used as evidence against its wider planting benefits. At the same time coast redwood is delivering landscape and societal benefits by storing carbon in the leaf litter substrate and standing timber. As Forest Research say “This is a species that could be grown more widely in Britain with climate warming, not least because it produces a high quality timber.”
In early February 2020, Woodknowledge Wales staff Dainis Dauksta and Ceri Loxton visited the Royal Forestry Society’s Redwood Grove at Leighton, near Welshpool, with Dominic Driver of Natural Resources Wales and Anna Dauksta of Tir Coed to see the coast redwood grove and discuss the potential for Sequoia sempervirens and other softwood species in Wales.
In its natural range, Sequoia sempervirens is confined to a narrow coastal belt, mainly in central and northern California. In the UK, coast redwood was introduced in the 1850s and has been planted on a small scale, often for silvicultural demonstration, landscape and amenity purposes by the Forestry Commission and private estates. The redwood grove at Leighton is impressive – tall straight stems, large diameter trunks covered in thick fibrous bark, towering canopies and dappled light throwing patterns on the deep leaf litter.
New Zealand is one of the countries starting to look at the species more closely and to encourage its planting and establishment. Should Wales follow this example?
Mitigating climate risks
Sequoia sempervirens has some natural advantages to reduce risks associated with climate change in our regions:
● Wind: Its root system can reduce the effects of severe wind. Trees join roots with neighbouring trees and form a strong underground link. The bonding with nearby trees enables them to withstand major weather events.
● Fire: It has the unique ability amongst conifers to re-sprout branches after a fire. Tough fibrous bark insulates the trunk from much of the heat of a fire. While existing branches may be burned the trunk remains alive and sprouts new branches. If a forest has been planted for carbon offsetting, this means that the forest will continue to grow and reduce the potential for future liabilities.
● Insects: In its native range in California there are lots of insects. No insect is known to cause economic damage and none is capable of killing a mature tree.
● Vegetative reproduction: It will sprout from old cut stumps and fallen logs. Because the stumps and roots remain alive and because the heartwood is naturally durable coastal redwood carries more carbon forward into the next rotation.
Adaptability and Carbon Storage Potential
The most interesting characteristics of coast redwood reside in its genetic makeup. Its genetic diversity is very high and the highest of all North American conifer species. Sequoia sempervirens is the only hexaploid conifer with a genome size three times that of its near relative, the giant sequoia. This polyploidy (having more than two paired sets of chromosomes) may explain its extreme survival capability and longevity. The species can clone itself from roots, burls and cuttings. The phenotypic plasticity (how of its leaves allow them to adapt to a wide range of light conditions.
New Zealand foresters are confident that they will be able to breed coast redwoods with more desirable traits than their Californian peers, so that the species can be optimised as industrial roundwood. Attractive compact groves could realise an extremely high carbon storage potential which would justify their new role within Welsh mosaic landscapes.
Suitability for Welsh geography
Forest Research (2016) advise that coast redwood is most suitable for mild, moist climates with more than 1250mm of rainfall, such as those found in Argyll, Wales and southwest England. Favourable locations in terms of climate and site quality will be lower slope and valley bottom sites.
Coast redwood is likely to be a high yielding species. Data from the limited trial sites in the UK indicate high productivity with general yield classes of between 24 and 30 being achieved in England and Wales.
Coast redwood is a species to consider where larch crops are being diversified due to Phytophthora ramorum infection and where site conditions are suitable.
Timber quality – suitable for construction and joinery?
At the site in Leighton a small cabin has been built using local timbers including coast redwood cut from the site. In its native range coast redwood is reported to be used as “veneer, construction lumber, beams, posts, decking external furniture and trim (https://www.wood-database.com/redwood/). However, there is a lack of information about wood properties grown under British conditions.
“My own experience as a sawmiller is that coast redwood cuts and dries really nicely. The heartwood is reasonably durable although there’s a lower proportion compared with western red cedar or larch. The thick fibrous bark may offer potential as an insulating material.” Dainis Dauksta.
Future uses: explore and experiment!
There is more to learn about this species, and while there is a lack of information about wood properties, we also do not know precisely what our wood requirements will be in the future and what processing advancements will have been made. Given the diverse and evolving nature of the timber processing sector it is likely that there will be many future uses.
Because of its high productivity and unusual growth characteristics this species will be of increasing interest in British forestry under predicted climate change. If the carbon sequestration potential of different species is to be considered alongside other properties and multiple landscape requirements, then surely it won’t be long before we start to see increasing groves of coast redwood planted here in Wales?