Significance of long-term forestry research

Next year will mark the 60th anniversary of the creation of a research section within the forestry division of the then Department of Lands. Field trials and experiments were carried out in forests and establishment sites across the country whose result would form the basis of future forest policy in Ireland.

So what has happened the estimated 1,500 research trials that were established since 1957? Many have produced the required data and have reached the end of their project life, while others have been abandoned and forgotten. The NATFOREX project funded by COFORD – the forestry advisory body in the Forest Service – identified about 100 of the more relevant field trials for retention. However, these trials are no longer managed on a continuous basis, although much of the data is still available but time is running out for many excellent experiments.

This was brought home to me recently when I visited two forest research trials in Banteer Forest, established by Ted Horgan in the early 1990s. A research forester with the Forest Service and subsequently with Coillte, he is now retired but is still actively involved in forestry.

He is the Irish representative in the Future Tree Trust, the organisation dedicated to the improvement of broadleaved trees in Ireland and Britain. He has published a number of research reports and is co-author of A Guide to Forest Tree Species Selection and Silviculture in Ireland, published by COFORD.

The Banteer trials deal with the following two issues:

Species diversity

The species diversity trial is located in Mount Hillary property. In 1993, following the removal of a pioneer crop of lodgepole pine, Ted and his research team established a trial comprising 10 species by three replications on this nutritionally marginal Old Red Sandstone site.

Trialled species, comprised Sitka spruce, Douglas fir, Scots pine, Monterey pine, Japanese and hybrid larch, western red cedar, western hemlock, Spanish (or sweet) chestnut and sessile oak were planted in both pure and in mixed formation.

The performance of most of the species is extremely encouraging. For example, western red cedar and western hemlock have shown themselves to be very much at home on this site type. Most of the larch planted as a nurse species to Sitka spruce has been removed as stake material making way for the spruce to form the final crop.

The pure plots of hybrid larch, have excellent form and yield and will produce a crop in their own right. Monterey pine, which Ted sourced from its native habitat in Guadalupe Island, Mexico, is performing well and has responded well to heavy thinning and pruning to five metres. Having been very impressive in the earlier years, the performance of the Douglas fir is on the wane, except at the lower elevations of the trial.

While the yield of some conifers is exceptional in Mount Hillary, the performance of the oak and chestnut proves that with shelter and the right environment, there is a role for broadleaves even in nutritionally marginal sites. Stumping back (cutting at ground level) of Spanish chestnut was carried out at year six. This encouraged fresh vigorous growth while the oak responded to light when surrounding trees were removed.

So is Ted surprised with the results? “Other research work I carried out over the years has led me to believe that a number of species in Mount Hillary would perform well despite the low nutrient soil,” he said. “Although rarely planted, western red cedar is an ideal species for many old red sandstone sites and the results here are encouraging although not surprising. Oak and chestnut perform well on marginal sites, but need shelter and protection from wind and frost which they receive in Mount Hillery as they are surrounded here with conifers.”

Mixtures in unstable sites

By contrast, the forest property at Cleanrath is a fertile gley site. While capable of producing high-yield classes (24 and over) for Sitka spruce, such crops rarely reach maturity due to windblow.

In 1993, Ted carried out a small experiment aimed at counteracting the threat of windblow to pure Sitka spruce crops. Sitka was mixed (every second tree) with the south coastal provenance of lodgepole pine and a self-thin regime was decided.

There are two obvious results of the trial. First, all the trees are still standing, even after Storm Darwin which caused damage to the surrounding pure Sitka spruce forest in 2014. Second, the Sitka spruce element has out-performed the adjacent pure crops of Sitka spruce in terms of growth rate, form and branching density.

This is a mixture that requires little maintenance and is ideally suited to Sitka spruce on fertile, wind-vulnerable sites, according to Ted. Asked about the risk of low-value lodgepole pine outgrowing and suppressing the Sitka, he said: “The Sitka suffered from frost damage initially but still recovered to outgrow the pine. Lodgepole tends to be a sprinter in the first few years, providing shelter but on fertile sites such as this, the Sitka spruce not only catches up but outgrows and suppresses the lodgepole pine.”

When asked if mixtures were an option for private growers, he said: “If I was a landowner in a windblow prone site, this is the mixture I would consider.” Ted assured me that trials comprising Alaskan provenances of Sitka spruce intermixed with Washington or improved Sitka spruce material also self-thin very effectively.

Long-term research

The two field trials near Banteer demonstrate the worth of research. However, both require continuous monitoring. Otherwise, the information and future benefits are lost forever.

Relevant field trials need to be allowed to run for a crop rotation and beyond before reliable results are obtained. The current short-term nature of research projects and programmes – often no more than three years – fails to acknowledge the forest continuum and the real benefits of research.

“These trials established over the years have provided valuable silvicultural information, which has informed the national afforestation programme but they need to be supplemented by further trials to address new key issues that are facing the forestry sector,” said Pat O’Sullivan, technical director of the Society of Irish Foresters.

The NATFOREX project has the potential to address long-term research needs by evaluating and assessing data for future analysis. However, these trials also require hands on maintenance and silvicultural treatment. This will ensure that sufficient research trials are preserved and managed to benefit Irish forestry well into the future.