12 June 2025

Leaf it to science

As climate change reshapes growing conditions, Irish forests must adapt. New research explores how species choice, genetic diversity, and forest management can help build resilience from the roots up.

Continuous cover forestry systems are close to nature forests and allow newly regenerated seedlings to prosper under the cover of older trees to create the new forest of the future. Credit: Teagasc

Climate change has the potential to pose specific challenges to Irish forests. Projected increases in seasonal temperature and rainfall will affect the growth and productivity of forests, resulting – in some cases – in reduced tree growth with the potential to affect species suitability.

Some tree species will be able to adapt and thrive, especially those already suited to warmer climates. Others may struggle and become less viable in the long term. One of the key steps in building climate resilience is assessing the performance of different planting materials and exploring new forest management practices that can help deal with the uncertainty climate change brings.

Figure 1: A key component of adaption is frost tolerance related to latitude of seed origin (Latitude °N), choosing the varieties which are adapted to Irish climates is critical part of adaption.

Adapting for the long haul

Because trees evolve over millennia, their ability to adapt in place over just a few decades is limited. Niall Farrelly, Research Officer at Teagasc Athenry, explains: “Their short-term survival depends largely on phenotypic plasticity, their ability to adjust to environmental changes within a single lifetime. For example, the oak trees planted today may still be standing well into the 22nd century, by which time the Irish climate could be very different from what we know now.”

In some cases, importing tree seed from warmer regions may be a viable adaptation strategy, but only with proper testing to assess performance. Certain species and provenances can thrive in Ireland if the climate of their origin matches ours. However, bringing in seed from climates that are too warm can backfire. For instance, selecting seed from south of the 46th parallel can significantly reduce frost hardiness (see Figure 1).

Table 1: Examples of species where provenance experiments have been used to identify the best source material for planting.

Learning from living data

Historical data and long-term evidence play a key role in understanding how well tree species can adapt. This includes research plots in arboreta, dedicated tree research gardens where a wide variety of species are planted and monitored over time, as well as in formal experimental trials, such as those at Avondale Forest Park, John F. Kennedy Arboretum and other test sites. These plantings provide valuable insights into the adaptive potential of different species (see Table 1). In some cases, certain trees have even shown higher productivity in Ireland than in their native environments.

“Many native tree species are naturally well suited to Irish conditions,” Niall explains. “However, some non-native species have also become naturalised, meaning they now grow successfully in the wild. One example is beech, which can produce high-quality timber, is visually appealing and is commonly used for ornamental planting, shelterbelts and hedging.”

As Ireland’s climate changes, we may need to look further afield for suitable species. Trees currently growing in warmer parts of Europe and the United States, such as walnut, hickory, red oak, and wingnut, could offer potential. Test plantings at sites like John F. Kennedy Arboretum give us valuable insights into how these species might perform under Irish conditions in the future.

More species, more strength

Trees with high genetic diversity are more likely to possess adaptive traits, such as tolerance to drought, pests, or diseases, that help them cope with changing conditions. Assessing this diversity can be a useful strategy for selecting species that are better equipped for the future.

Niall says: “Among Ireland’s timber species, increasing resilience is becoming more important than ever. That means selecting trees that can withstand new pests, changing rainfall patterns and drier soils.”

Diversifying the range of tree species is one way to build this resilience. Species like Douglas fir, western red cedar, and coast redwood offer promising options to complement Sitka spruce, which currently dominates Irish forestry. These alternative species can help increase structural diversity and support continuous cover forestry systems, where forests are managed without large-scale clearfelling, a practice in which most or all trees in an area are uniformly cut down. Douglas fir, in particular, shows strong potential. It performs well on sheltered sites and is well suited to drier soils, making it a good choice for planting in the east of the country. 

Designing forests for resilience

The term resilience is a measure of how a forest responds to perturbation and how quickly it can recover to its ideal state. Identifying vulnerabilities in Irish forests and increasing resilience will ensure the vitality and sustainability of our forest resource into the future. To offset the threats of biotic and abiotic threats, new diverse species options may need to be considered.  This can help create resilient forests of the future.

Niall highlights: “Planting the ‘best tree in the best place’ is crucial to the creation and sustainability of the forests of the future.”

The impact of diverse and adaptive forest management options is very important to avoid the large-scale impact of disturbance events on our forest resource. Devastating events such as windblow may require a redesign of our forests to minimise risks, these may include creating forests of uneven-aged structure, increasing wind firm edges, and limiting soils disturbance in reforestation. The use of natural regeneration using seed from the surrounding forests can afford the new generation of forests without the disturbing impact of a clearfell operation. 

Funding

This research was funded under the FitForests project by a grant from the Department of Agriculture, Food and the Marine, Republic of Ireland, under the (2019R511) project. 

Contributors 

Niall Farrelly, Research Officer, Teagasc Athenry niall.farrelly@teagasc.ie