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The Cost of Transforming Even-Aged Coniferous Stands to Continuous Cover Forestry

The perception is still doing the rounds, that transformation to continuous cover is costly and hence people will not contemplate it unless grant aid is forthcoming.

What does transformation involve within a young even-aged planted stand, and why is it costly?

As your readers may be aware, it essentially involves undertaking initially, a cycle of thinnings with a grade that is very similar to crown thinning. (F.C. Information Note 2001 and Yorke 2001). The first crown thinning is undertaken (ideally) after the first mechanical thinning is completed, in order to obtain initial access into the unbrashed stand at the earliest age that can be silviculturally justified.

As a result, there is in most, but not all circumstances, a net cost penalty arising out of this first mechanical thin – and the subsequent first crown thinning at the commencement of transformation, due to the small mean tree size produced. This cost penalty also invariably occurs if one is thinning a comparable even-aged stand to the marginal (management table) intensity i.e. a low thinning grade. In fact, the potential cost penalty is increased as a result of a smaller mean tree size being produced from a low thinning compared with that from a crown thinning at a similar age… (See relevant F.C. yield models).

Therefore it is the decision (with associated future benefits) to thin that may require financial assistance to offset this initial cost, and not the decision per se, to transform to continuous cover.

As the cycles of crown thinning progress and the stand structure becomes more diverse, and the age of onset of prolific seed production is reached, ongoing natural regeneration begins to establish within the stand.

The stand is now well on the way to being transformed to the manager’s objectives and becomes self-sustaining. The mean-tree size harvested steadily increases until it reaches a consistent level, with a maximum content of approximately 20 - 30% small round wood depending upon circumstances.

A proportion (or the total) of this may or may not be more cost-effective to leave at stump. Assuming that deer are under control and browsing levels are acceptable and the tree canopy (at a variety of levels from saplings to large trees) is maintained in order to suppress competing ground vegetation and avoid excessive and blanket regeneration of tree species, what excessive net costs are involved that justify additional grant aid ? Management time is surely no greater than that involved primarily with net income generating thinning operations, employed skilled and experienced forest craftsmen. The need for tending operations (respacing, cleaning etc.. of regeneration) is minimal as a result of some harvesting damage combined with natural suppression and self-selection and control of the canopy. The need for a range of other costly operations associated with restocking after clear fell is eliminated.

In conclusion therefore, once the periodic transformation (crown) thinnings reach a mean tree size that generates a net income, thereafter what is the justification for further grant aid in stands on appropriate site types and managed and worked by skilled and accustomed personnel?

References include:
“Transforming Even-aged Conifer Stands to Continuous Cover Management” – Forestry Commission Information Note 2001. “Practical Aspects of Transforming Plantations to Continuous Cover Woodland” – Mark Yorke, Continuous Cover Forestry Group 2001.

The writer intends in due course, to highlight the financial and other potential benefits of adopting the “crown thinning” grade (in preference to current “low thinning” practice) irrespective of whether or not the manager is proposing to transform to continuous cover. Whether these benefits can actually be achieved following training and sustained experience of the thinning machine operator, is questionable.

Mark Yorke

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