Last week, we looked at the new National Forest Inventory (NFI) findings on tree and plant species diversity, ownership, timber production and forest cover.

This week, we explore two major findings in the NFI – forest health and forest carbon. Both are interlinked because without a healthy resource, the forest cannot maximise its sustainable benefits, including yield and carbon stock.

Forest health and vitality dictate the future wood and non-wood value of forests. Forest health is categorised into areas of serious concern (“high” and “critical” damage) and minimal damage (“low” and “moderate”).

The NFI author’s summary is positive: “Overall, the forest estate appears healthy,” they claim. While “63.2% of stocked forest areas display some signs of damage”, the severity of this damage is “low”.

The NFI divides forest health and vitality into biotic and abiotic factors.

Biotic factors

Biotic factors refer to disease, insect and animal damage, along with vegetation competition and tree harvesting, and tree injury.

There are 18 biotic agents that cause damage but most are negligible. We assess four: ash dieback, Phytophtora ramorum (the fungus-like pathogen that threatens a number of species, especially larch), animals, and harvesting damage (Table 1).

The most common biotic damage is “caused by animals (eg browsing by deer)”, followed by “harvesting operations and ash dieback,” according to the NFI.

Ash growers would place these in reverse order because damage by harvesting is minimal, while deer damage is still low nationally (Table 1).

The areas of most concern are ash dieback and P. ramorum in larch. Ash in particular faces extinction while both species are no longer grant-aided for afforestation.

The NFI estimates that ash cover is at 24,350ha, down from 25,280ha in 2017, but it is also present as a minor species in a further 10,045ha of woodland.

The report states: “Ash dieback is now widespread and was noted to be present at 34,395ha of forests visited.”

The fact that 14,400ha of ash could be classed in the “low” or “moderate” damage categories is incomprehensible, as it is now accepted that all infected ash plantations are either dead or dying. It’s therefore surprising that ash still accounts for a presumably healthy 24,350ha of the forest estate – public and private – according to the NFI.

There is little evidence of serious P. ramorum, but this is a disease that can be difficult to assess, as larch is one of the few conifers that sheds its needles in the dormant season.

Also, the “systematic nature of the NFI sampling grid is not conducive to accurately report on small area statistics [such as P. ramorum]”, the authors explain.

Detected in 2003, already 1,300ha of infected larch have been removed, according to Teagasc, and the species is no longer grant-aided in Ireland. However, only 400ha was detected with the disease in the NFI, which is minimal considering there are 23,820ha of larch in Irish forests, comprising Japanese (21,400ha), European (1,990ha) and hybrid (430ha).

It may be time to reappraise this species, especially hybrid larch.

A more targeted survey is planned and if the damage is not widespread, larch could possibly be reintroduced as a grant-aided species in regions where the disease is not present.

Abiotic factors

Abiotic damage can result from climate change, nutrient deficiency and human activity.

“In terms of abiotic damage, climatic factors (eg windthrow) were the most common type of damage, followed by nutrient deficiency and anthropogenic [human] factors,” the NFI states.

Forests rated as having “high” and “critical” damage amounted to less than 13% of the area in three of the four key categories examined here (Table 2).

These comprise frost (8.8%), exposure (2.3%) and endemic windblow (12.9%), while forests showing nitrogen or phosphorus deficiency (30%) were well above the average recorded.

Carbon

The NFI results indicate that the national forest estate continues as an expanding sink for carbon, currently estimated at 323.5 metric tons (mt) (Table 3).

New carbon accounting has been introduced over the years and while soil carbon (252.1mt) is up on the 2017 inventory, it is down on 2012 at 323.7mt. The carbon stock in wood biomass – above and below ground – has increased from 65.1mt in 2017 to 71.4mt in 2022.

The NFI places strong emphasis on non-commercial wood aspects of forestry, including vegetation and lichens, deadwood, non-commercial native species and carbon.

This is in line with the EU forestry strategy, which also emphasises non-wood forestry but acknowledges the need to provide financial incentives for the provision of ecosystem services, including carbon sequestration.

With 10 years of NFI carbon accounting now available, a Forest Carbon Code for Ireland in line with the EU forestry strategy is long overdue.