The potential of Japanese red cedar and western red cedar in Irish Forestry
Dr Niall Farrelly evaluates the potential role of these two red cedars and how these could succeed to assist diversification and fulfil multifunctional objectives of Irish forestry.
Native range and soil preference
Japanese red cedar (Cryptomeria japonica) is native to Japan's central and southern regions and thrives in warm maritime climates with annual rainfall exceeding 1,200 mm per annum. In Ireland, it may be best suited to the east and southeast of the country, where conditions are relatively warmer. The species prefers soils moderate to rich soils in nutrition that are slightly dry to moist. It exhibits moderate shade tolerance and resistance to exposure but is susceptible to late spring frosts and can endure periods of drought.
Western red cedar (Thuja plicata) is a conifer species native to the Pacific Northwest of North America, thriving in coastal and interior regions from Alaska to California. It is a long-lived species, capable of exceeding 1,000 years in age, and is a major component of the forest industry producing high-quality timber which is much in demand. The species is adaptable to various environments, preferring soils that are nutrient-rich and with adequate moisture, it is notable its presence in mixed stands, occurring with hemlock, fir, and spruce and is a shade tolerant species capable of growing well in the forest understory.
Introduction in Ireland
Japanese red cedar was introduced to Britain in 1842, but its use has largely been limited to ornamental plantings. In the Azores, Japanese red cedar has been more widely cultivated, occupies 12,698 ha of plantation forest and is the most commercially important tree species on the islands. The climate of the Azores is classed as Mediterranean to humid subtropical, characterised with warm summer conditions with the absence of winter cold. Western red cedar was introduced to Ireland in 1853, initially as a specimen tree. Formal plantation trials began in the early 20th century, with successful stands recorded at Avondale, Co. Wicklow. However, its adoption in Irish forestry remained limited due to early establishment challenges, particularly susceptibility to cedar leaf blight in nurseries.
Performance in Ireland
Japanese red cedar and western red cedar have comparable yields in Ireland with yield class ranging from 12-22 cubic metres per hectare per year (m3ha-1yr-1) observed. Early demonstration plantings of Japanese red cedar took place at Avondale Forest Park in Co. Wicklow (planted in 1906) and another stand in John F. Kennedy (JFK) Arboretum in Co. Wexford (planted in 1972) are good examples of the species potential in Ireland (picture 1).
Japanese red cedar is prone to establishment issues and frost, so site selection and subsequent maintenance is required to ensure successful establishment. Frost-free sites would be recommended and its use in mixture with other compatible species on free draining soils is possible. Western red cedar plantations in Ireland cover approximately 403 ha in pure stands, with an additional 1,295 ha occurring in mixed stands. Optimal growth is observed on free draining soils (e.g. acid brown earths, grey brown podzolics). However, it has low tolerance to exposure and windthrow, making it unsuitable for highly exposed or very wet soils and is very palatable to deer, so the provision of deer fencing is essential to ensure successful establishment.
Provenance recommendations
Current provenance recommendations for Japanese red cedar suggest the use of material adapted to growing in Irish conditions and seed sourced from established well- developed stands should be preferred. Results from a long‐term provenance trial established in 1979 at Camolin Park, Co. Wexford, suggest provenances sources from southern Japan originating from warmer regions, showed superior performance in terms of stem straightness, height, and diameter (DBH) compared to their northern counterparts.
These findings suggest that southern seed sources, adapted to nearly continuous growth in warmer climates, may confer advantages over their northern counterparts when grown in Ireland. A good example of western red cedar is that from Masset provenance, from the Haida Gwaii Islands (previously Queen Charlotte Islands) which is on display in JFK arboretum in Co. Wexford (picture 2). Data from provenance trials, which have been evaluated across Europe, indicate that seed sources from the Olympic Peninsula, Washington, perform best.
Timber and Economic Value
Japanese red cedar (Cryptomeria japonica) is a widely cultivated softwood species known for its excellent wood properties in its native range. It is lightweight and soft density, typically ranging from 0.30 to 0.45 g/cm³. The timber has a reddish-brown heartwood with a straight grain and a fine, even texture, making it visually attractive for construction and decorative uses. It is easy to machine, plane, and nail, with minimal splitting. However, it can be prone to tearing during sawing due to its soft nature. Japanese red cedar has a distinct aromatic scent due to its natural oils, which also provide antimicrobial properties, making it suitable for health-related applications.
It has moderate natural durability, especially the heartwood, which contains extractives that offer some resistance to decay and insects. However, it is less durable than western red cedar (Thuja plicata). Western red cedar produces high-value timber with natural resistance to decay and insects, making it ideal for cladding, fencing, and outdoor structures (picture 3). The timber is also lightweight, aromatic, and durable, reducing the need for chemical treatments. Western red cedar is a highly valued timber species in North America, contributing significantly to the forest economy. In Ireland, the market remains underdeveloped, but the species' natural durability, attractive appearance, and resistance to decay make it a promising candidate for cladding, fencing, and other outdoor applications.
Conclusion
Both Japanese red cedar and western red cedar have potential to be a valuable addition to Ireland’s forestry portfolio as climate conditions warm. As they both perform well in mixture, they could be considered for deployment for systems such as Forest Type 11 and Forest Type 12, read more about Forest Type 11 grants here. Their notable shade tolerance characteristics offer potential for diversification and use in continuous cover (CCF) systems as an understory species where their presence in the lower canopy would allow structural diversity and multifunctional roles to be fulfilled.
Western red cedar has more potential at this time owing to more widespread evidence of the species performance across more than 1,700 ha of forest already established. Further research, including provenance trials and long-term performance assessments, would be beneficial to fully understand its adaptability, growth rates, and resilience to local pests and diseases. Such studies would provide valuable insights for forest managers and policymakers aiming to enhance species diversity and resilience in Ireland's forests.