Know when your forest is ready for its first thinning

Wiliam Merivale

May 08 2012 04:48 AM

Proper and timely action can have a huge impact on the overall profitability of your plantation

Many farm forests are at, or rapidly approaching, the stage of first thinning and it is necessary to plan for this important operation in a methodical way. In most situations, proper and timely thinning results in a significant increase in the value to be realised from a timber crop later in the rotation, both from subsequent thinnings and final harvest.

The first thing to appreciate is that a forest cannot be accurately assessed from the boundary, so once the canopy has closed and the trees are 7m to 8m in height inspection paths must be created to allow access. Paths should be brashed to about 2m in height, ideally about 100m apart and interconnected.

This operation is frequently overlooked, but it is essential as it is the only way to 'see the wood from the trees' from within and thus enable planning and timing of operations. It allows purchasers to assess the crop and formulate a fair offer that reflects the value of the timber to be harvested. Once this is done, the owner can establish whether his forest is suitable for thinning and whether it is ready.

In some circumstances where the risks outweigh the advantages, thinning is inadvisable.

This is particularly the case on sites where there is a high risk of windthrow, poor drainage or persistent water logging, or where thinning has been delayed and the stand has grown beyond "critical height".

If in doubt, seek professional advice. Assuming none of these apply, the three most important factors which indicate whether a stand is ready to thin are stocking density, diameter at breast height (dbh), and top height.

An Irish thinning protocol is available as a free download from the Irish Timber Growers Association website. This provides a step-by-step guide to thinning systems in Ireland, and should be considered essential reading for any owner contemplating it.

It gives full details of how to assess stocking density, average dbh and top height. Some of this is quite technical, and again where necessary professional advice should be sought.

Teagasc has also produced a very handy colour-coded chart correlating stems/hectare and dbh, to give a ready reckoner of whether a stand is ready to thin or not. As a very simple guide, if the stocking density is 2,000 stems/ha or greater, and the average dbh at least 16cm, the forest is likely to be ready.

LICENCE

Assuming the plantation meets the criteria for thinning, a general felling licence must be applied for and access provided.

If a road is required, the grant scheme has been amended with effect from January 1 and is now operated on a "just in time, just enough" basis. The grant rate has been reduced to €35 per linear metre and is only available where thinning is imminent and to be done within two years.

In addition, the roading density will be limited to the minimum amount required and remains subject to the maximum of 20m/ha. The grant amounts to 80pc of the eligible costs and is payable in two instalments: the first tranche is paid on completion of the road, and the balance once thinning of half the area served is completed.

As soon as the road is complete, ensure a secure barrier is erected at the entrance. Nothing seems to attract joy-riders more than a recently completed forest road, and the damage can be alarming.

William Merivale is national secretary of PEFC Ireland and a forestry consultant based in Cork. Email: william@cjandco.net