Species and provenance selection for future resilient forests

Meeting Report: Pro Silva Ireland Spring Field Day 2025

By Sean Hoskins

The sun shone a spotlight on the importance of tree species and genetic selection for CCF forest resilience at Pro Silva Ireland’s Spring Field Day last month.

On a fine County Wexford day, over 60 participants visited the John F. Kennedy Arboretum to tour its forestry plots; national treasure troves which store a wide selection of provenances of commercial conifer species.

Teagasc Senior Forestry Research Officer Dr Niall Farrelly led the day and began by explaining the relevance of genetic adaptation to forest resilience and production in a stand of Douglas Fir.

Douglas fir is a tree that has adapted well to the local conditions, establishes well from seed or planting stock, and has the ability to maximise the growing season and produce quality timber.

"It [Douglas fir] has the ability to establish and successfully produce timber you’d be happy with, as a forester," Dr Farrelly said.

Selection

Maladaptation is when a species or provenance is not suitable for the growing conditions.

Native species are adapted to local conditions but non-native conifer species, important for timber production, have wide genetic variability in their native range, which must be selected from to best match Irish conditions.

Dr Farrelly explained how potential seed provenances were selected for research trials—by identifying areas in original ranges with similar soil conditions, precipitation, length of the day and climate to Ireland and Irish growing scenarios.

Previous work has identified the current common provenances used in Ireland today, but Dr Farrelly explained that ongoing work was helping to identify other provenances that might be similarly or better adapted to Irish conditions, both current conditions and those forecast as a result of climate change.

With regards to Douglas fir, which can produce high quality timber, the identification of the best provenances could lead to more utilisation of the species.

And planting more species in mixed stands, which is a key feature of CCF, increased forest resilience in an era of climate change.

Dr Farrelly said Douglas fir had great potential for wider use in Irish forests on well-drained soils but one challenge was its palatability for deer, so deer control and protection would be a consideration when planting.

“Resilience is the ability of the forest to respond to challenges and maintain a sustainable timber yield; challenges like insects, disease and climate change, “ Dr Farrelly said.

Future climate conditions

Dr Farrelly highlighted the challenge of species selection when there was uncertainty about future climatic conditions.

“What species are best for the future? If they are not establishing then they are not really appropriate but something like say radiata pine, which can establish but isn’t great, if it becomes warmer, might be more suitable, “ Dr Farrelly said.

There was some discussion on this topic over the course of the day, where various contributors highlighted how CCF practice creates resilient forests by inclusion of a variety of species; species that can adapt to new conditions will gradually replace those unable to respond and throughout this evolving process, the forest ecosystem will remain intact.

The speed of climate change was also discussed, along with the challenge for foresters to both select the best-adapted species for the current conditions, while trying to also select species that will be well-adapted to future conditions, which aren’t entirely clear other than being warmer and at times drier.

Dr Farrelly said one rule of thumb was to select species from slightly lower latitudes; they would cope with current conditions and be comfortable with future warmer conditions. With some provenances used in Ireland this is already the case.

Sitka spruce provenances

Dr Richard Walsh, forest sector development with the Forest Service, had also worked in the JFK forestry plots with Dr Farrelly. Part of his work involved identifying species that would compliment Sitka spruce in reforestation and afforestation.

Sites in Ireland had been identified where Sitka spruce exists in a mix with other species, including Norway spruce, Grand fir, Noble fir, Western hemlock and Western red cedar, and Dr Walsh highlighted that the North American species occur naturally together in their home range.

Dr Walsh said mixes might include 30 percent diverse conifer species with 70 percent Sitka spruce, for example, and the study had found that mixes were capable of producing more timber than stands of pure Sitka spruce.

The JFK Arboretum boasts an impressive collection of Sitka spruce provenances, arranged in order of the north-south distribution in their native range, from Alaska to California.

The field day party walked from the northern provenances to the southern, which dramatically highlighted those provenances best adapted to growing conditions at the arboretum.

The Alaskan provenances were smaller and less well-formed. Dr Farrelly explained that these provenances are adapted to the short growing season of their native range and therefore are not able to fully utilise Ireland’s longer growing season.

Meanwhile the Washington provenance, typically planted in Ireland, was much bigger and better formed.

Dr Farrelly said the research he was involved in was identifying other provenances that would also perform well in Ireland, as well as taking into consideration drought tolerance for future climate scenarios.

"Provenances exhibiting drought tolerance were more likely to better withstand secondary stresses such as attacks from insects or diseases during periods of low rainfall," Dr Farrelly said.

Novel conifer species

Other stands of more novel species were also visited.

An impressive stand of coast redwood displayed straight stems and Dr Farrelly said the species’ shade tolerance makes it particularly suitable for CCF applications.

Coast redwood had been found to be more drought tolerant than Sitka spruce. In addition, the bark is fire resistant and it is one of the few conifers with the ability to coppice.

However, young trees require a degree of shelter and are susceptible to frost. This combined with a tolerance for shade suggests this species as suitable for underplanting (enrichment planting) in existing stands, Dr Farrelly said.

Western red cedar is similarly shade tolerant and well-adapted to Irish conditions, Dr Farrelly said. The species grows well with Sitka spruce in its home range where it occupies the damper parts of the site, with the drier occupied by Sitka spruce.

The day concluded in the shade of a stand of Cryptopmeria japonica, Japanese cedar, which exhibited some straight, well-formed stems and is a possible future species to utilise, said Dr. Farrelly. However, it is also palatable to the deer and Pro Silva Ireland committee member Liam Byrne made the point that to diversify Irish forestry, deer numbers would have to be reduced in areas where there was overpopulation.