The most important publication in Irish forestry is the National Forest Inventory (NFI) as it provides accurate, up-to-date information about the extent and changing nature of Ireland’s forests. The NFI, undertaken by the forestry inspectorate in the Forest Service, involves a comprehensive nationwide field survey of Ireland’s forests using a set of 1,923 permanent sample plots compared with 1,827 in previous surveys.

The inventory provides detailed information encompassing “the traditional parameters such as area, growing stock and species composition in the national forest estate as well as information with regard to biodiversity, health and vitality, carbon content and soil type”.

The current inventory provides key information on changing patterns in Irish forestry as comparisons can be drawn with two of the previous NFI cycles, completed in 2006 and 2012. Comparisons with previous inventories need to take account of the increased number of permanent plots and changes in estimation methodology as well as “the identification of pre-existing forests for the first time during the third NFI cycle”.

This probably explains why the forest estate increased by 38,368ha (0.5%) since the 2012 NFI, even though afforestation (new planting) accounted for 30,725ha during this period. The national forest estate, now at 770,020ha, comprises 50.8% public forests and 49.2% private forests. The private forest estate may now exceed Coillte’s forests when National Parks and Wildlife Service and local authority woodlands are deducted from the public forest estate.

Species

Conifers represent 71.2% of the stocked forest area, while the share of broadleaf species continues to rise from 24.3% in 2007, 25.8% in 2012 and 28.7% in 2017. This is not surprising as annual afforestation of broadleaves increased to an average of 30% of total planting over the past 15 years compared with little over 5% for much of the last century.

In addition, many of the pre-existing forests identified in the current inventory “are predominantly semi-natural broadleaf forests, which were not apparent during previous NFI aerial photo interpretation exercises, due to the lower-resolution aerial photos available at that time”, according to the inventory authors.

While the increase in broadleaves illustrates a more diverse forest estate, it means that the production capacity is reducing as the share of high-yielding conifers in the species mix continues to decrease. This trend is likely to be maintained as ash – a high-yielding broadleaf – will no longer feature in broadleaf afforestation and existing ash woodlands will decline due to the presence of ash dieback.

When the more detailed NFI is made available, it will be interesting to analyse the current broadleaf mix. For example, the area under birch has increased by 59% since the 2007 NFI. This dramatic increase in birch from 29,700ha to 47,100ha has biodiversity benefits if planned but presents long-term silvicultural, production and stocking problems if it represents natural regeneration by default, especially in reforestation sites.

Wood mobilisation

Mean annual volumes of timber harvested by Coillte and private forest owners has increased from 3,616,000m3 during the period 2006-2012 to 4.896,000m3 up to 2017. Coillte forest production increased by 20% while annual volumes harvested in private forests increased by a massive 140% which is a major finding in the NFI. This average annual felling amounts to 1,116,100m3, which is more than double the average annual harvesting data produced by COFORD during the period 2013-2016 and much higher than the most optimistic forecasts produced over the past 10 years. The NFI authors make no reference to the inexplicable increase in volumes felled in private forests, although they acknowledge that the overall increase – Coillte and private – needs further analyses “to get a full understanding of the reasons for the differential between the NFI and COFORD estimates”.

Growing stock

The total growing stock in Irish forests is estimated at 116 million m³, an increase of over 19 million m³ over 2012. Gross mean annual volume increment between 2013 and 2017 was 8.4 million m3, while the mean annual standing volume felled within this period was 4.9 million m3.

However, the annul growing stock, which increased by 36% during the period 2006 to 2012, reduced to 19% during the period 2013-2017. Species shift from more productive conifers to lower-yielding broadleaves along with greater harvesting intensity may be contributing factors.

It is difficult to assess forest harvesting activity as the bulk of the estate is under 20 years so 46% is too young to thin, while 13% of forests are deemed not suitable for thinning. Some 16% of forests have been thinned and 25% of forests are categorised “no thin”, some of which could – or should – have been thinned in theory but may have passed the thinning stage so are left unthinned. This means that many forest owners will have missed out on revenue from first and subsequent thinnings.

Climate change

The NFI results indicate that the national forest estate is an important and expanding sink for carbon, currently estimated at 312m tonnes (Mt). Based on the NFI data, Ireland’s forests have removed an average of 3.8Mt of carbon dioxide equivalents per year from the atmosphere over the period 2007 to 2016. From a global climate change perspective, the NFI states: “This [forest] carbon resource has proven to be of pivotal significance in Ireland achieving its Kyoto target under the first commitment period of 2008-2012.”

While the survey outlines how forests can play a key role in mitigating climate change by sequestering and storing carbon CO2 from the atmosphere, it doesn’t address forestry as a carbon sink in the context of its implications for agriculture.

As reported by Thomas Hubert in last week’s Irish Farmers Journal, the removal 3.8Mt of carbon dioxide equivalents represents half the equivalent emissions from Irish milk production in 2017.

The authors may argue that commenting on the implications of forest expansion in reducing greenhouse gas (GHG) emissions and facilitating expansion in Irish agriculture production is outside the remit of the NFI. However, forestry as a carbon sink has to feature in the debate on sustainable land use in Ireland.

The Irish Farmers Journal will carry out a more detailed assessment of the NFI when the more comprehensive publication Ireland’s National Forest Inventory 2017 – Results is made available. This will provide detailed information on species, stocking, forest type and forest ownership on a county-by-county basis.

All NFI publications, including the main findings booklet, are available on the Department’s website at www.agriculture.gov.ie/nfi. Further information on the NFI and hard copies may be obtained from the Department of Agriculture, Food and the Marine, Johnstown Castle Estate, Co Wexford; Tel 053-916 3400 or email: nfi@agriculture.gov.ie