The biggest threats to your forest – and the deadly new ones coming down the line

Deadly: Ash dieback will have serious implications not only for timber production but also for biodiversity, carbon sequestration, landscape and culture. Photo: Teagasc

Attend a timber measurement course giving you control over what trees need to be removed. Photo: Teagasc.

Deadly: Ash dieback will have serious implications not only for timber production but also for biodiversity, carbon sequestration, landscape and culture. Photo: Teagasc

Attend a timber measurement course giving you control over what trees need to be removed. Photo: Teagasc.

Deadly: Ash dieback will have serious implications not only for timber production but also for biodiversity, carbon sequestration, landscape and culture. Photo: Teagasc

Steven Meyen

March 06 2023 05:00 AM

I want to look at the more recent threats forests are facing in Ireland. The two most prominent arrivals over the last 20 years are ash dieback and Phytophthora ramorum.

Ash dieback

This very serious fungal disease was brought from Asia to Europe in the early ’90s and is now rampant throughout Ireland.

Most ash trees are likely to succumb to it. This will have serious implications not only for timber production but also for biodiversity, carbon sequestration, landscape and culture.

We also need to be aware of the increasing risk of accidents occurring due to branches dropping or trees falling.

Phytophthora ramorum

A close cousin of potato blight, this is a serious fungal pathogen. It was first detected in Ireland in 2002 on imported rhododendron and viburnum at garden centres.

In 2010 it was observed on Japanese larch in Ireland. As a result, more than 1,300ha of larch forests on the island of Ireland have been removed.

In such cases, infected trees as well as susceptible hosts within a 250-metre radius are removed.

The harvested wood also requires a special phytosanitary permit before it can be moved and processed.

Symptoms of infection on Japanese larch include crown dieback, resinous cankers, excess cone production and the retention of needles.

In North America, P. ramorum is nicknamed ‘Sudden Oak Death’ as it has killed millions of oaks there. Oaks in Europe appear to be more resilient.

Dothistroma needle blight

This fungal disease is widespread in Europe. It was found in Northern Ireland in 2011 on Corsican pine. In 2016, DNB was found on Scots pines in Limerick and Cork.

Infected needles display red and colourful bands. Severely infected trees will appear with mostly just the current year’s foliage intact, creating a ‘bottle brush’ appearance. The lower branches are often more affected.

Oak processionary moth

In July 2020, a nest of the OPM was found in a park in Dublin, on an imported, recently planted amenity tree.

That was the first finding of this pest in Ireland, although OPM is present in all other EU Member States.

The DAFM carried out a wider intensive survey but no further additional findings have been reported to date.

The caterpillars of this moth will very efficiently defoliate and weaken oak trees.

It is also a major hazard to humans and animals as the hairs of the caterpillars can cause severe allergic reactions. Forests with recreational access in continental Europe need to be closed regularly because of the presence of OPM.

There are also some potentially serious threats coming our way:

Ips typographus

The eight-toothed spruce bark beetle is widespread across Europe. This serious forest pest has not been found in Ireland – yet.

Ips typographus tends to attack weak or damaged trees. However, populations can grow rapidly within areas of felled or windblown trees and then attack healthy trees, causing widespread damage.

The needles of attacked trees turn reddish-brown, and drop off within a few weeks.

The likely pathway for Ips typographus to arrive here is through the importation of untreated wood with bark (for instance wood packaging materials such as pallets).

The DAFM carries out checks at ports and other locations to prevent this.

Ips cembrae

The large larch bark beetle attacks mainly larch trees. It tends to breed in logs, windblown stems and dying trees.

Ips cembrae has been introduced into areas where larch trees are planted including Scotland, England, Netherlands and Sweden but has not been detected in Irish forests (or at Irish ports).

Prevention

For more detail, see www.teagasc.ie/forestry > Advice > Forest Protection.

Forest owners should be vigilant for unusual ill-health in trees and report any concerns to forestprotection@agriculture.gov.ie or via www.treecheck.net

The consensus is that the threat from tree pests and diseases will continue to grow as the effects of climate change intensify.

Continuous cover forests consisting of a mix of tree species of varying ages are likely to be more resilient to current and emerging threats. Don’t put all your eggs in the one basket.

Learn how to measure your (conifer) timber

Teagasc has organised five practical timber measurement workshops running from March 15-28.

Teagasc advisors will discuss and demonstrate a range of measuring techniques. Participants will be able to carry out practical tree-marking exercises.