The recent timber mobilisation report claimed that a large number of plantations in Ireland are either not thinned or not thinned on time. Long-term timber volume forecasts are based on production from regular thinnings, which is important for timber processors who need a continuous supply of logs for Irish and international markets.

We stressed the importance of first thinning on time (27 June), which represents the first source of income from the crop, usually after State funding has ceased, which is now at year 15.

To maximise income, the aim should be to thin early and often, providing the crop has a good stocking of trees evenly distributed and is located on a wind-firm site. By thinning early, the owner increases the number of potential thinnings before final harvest or clearfell.

This week we discuss the importance of subsequent thinnings. There are two main objectives: thinning provides a regular income with major value and economic benefits at the clearfell stage. The final harvest is the big payday for owners.

Thinning requires the removal of smaller and poorly formed trees while better-formed, quality trees are retained. These should be identified and marked after first thinning when the crop is more accessible. We also advised in last week’s article that these should be high pruned to provide knot-free timber up to a height of six metres.

The number of years between thinning, or thinning cycle, varies from three to five years depending on crop yield or yield class (YC) – cubic metres (m3)/ha/annum. The higher the YC, the more frequent the number of thinnings.

For example, a Sitka spruce crop with an estimated 26YC will provide five thinnings from years 15 to 27, yielding 45-50m3/ha per thinning (Table 1). This represents a cumulative volume of between 225m3 and 250m3/ha before final harvest. Depending on prices, thinning at this intensity could yield a cumulative income of between €4,500 and €6,000/ha over a 12-year period.

On low YC sites (10 and less) the thinning cycle may be six years and more for conifers such as Scots pine, while the interval years may be 10 years and more for slow-growing hardwoods such as beech (see panel).

While the volume of timber removed remains more or less the same with each thinning, the value of the timber increases as the crop matures. The number of trees decreases per hectare with each thinning but the volume remains constant as the average tree size increases.

While first and second thinnings contain a high percentage of pulpwood and medium-sized sawlog (timber for pallet and some fencing), later thinnings contain a much higher percentage of large sawlog material. This results in an increase in the value of timber removed per hectare. It is advisable therefore to make sure you receive the best price for your timber as well as securing your timber against theft when it is being harvested and removed.

Sale agreements

It is vital to have a clearly defined comprehensive sale agreement in place with the purchaser as well as having timber security measures to safeguard your investment. All timber sale agreements should include a comprehensive contract and an adequate deposit should be in place before commencement along with subsequent pre-agreed instalment payments at various stages during the sale.

In order to assist timber growers in the thinning, felling and timber sale process, the Irish Timber Growers Association (ITGA) has a Template Master Tree Sales Agreement which covers a range of potential sale situations and forest types, including warranties, payment terms, right of access, and harvesting, as well as insurance and health and safety isues.

In relation to timber security, the ITGA has also developed a Model Timber Sales Dispatch System, designed to minimise the risk of theft. This is available on the Table 2). This crop will already have received a tending or light thinning when its top height is 6-8m, as outlined on 20 June.

Again, the main objective is to benefit the final crop by removing badly formed or diseased trees. In addition to producing well-formed final-crop trees, thinning should also aim to produce well-balanced uniform crowns on final crop trees.

Final crop trees, numbering 200-350/ha depending on species (Table 2), should be identified and marked at the tending stage. These may need pruning to form clean stems up to 6m heights if the intention is to eventually sell timber to furniture, panelling, flooring, joinery and other high-added-value end markets.

Correction: in Table 1 featured in Irish Farmers Journal (27 June), I provided incorrect data for first thinnings for yield class (YC) 14 to 28 – ranging from 45 to 80m3. Yields from first thinnings will not vary as dramatically, regardless of YC, providing the thinning operation is carried out on time. So Sitka spruce will produce on average 45-55m3/ha from first thinnings between YC14 and 28, the difference being that YC28 will produce this volume at year 14 while YC14 won’t produce this volume until year 22, the recommended time for first thinning. Yields supplied were for delayed thinning. A more accurate estimate on average volumes produced from first and subsequent thinnings is provided in Table 1 this week.