Farm Ireland

Tuesday 20 February 2018

It works elsewhere so could continuous cover forestry help us here?

Over the last century, a combination of the State and thousands of private landowners has succeeded in establishing an almost entirely new forest estate that covers about 10pc of the country.

This is a remarkable achievement by any standards, and one that could not have been possible without the introduction of foreign species of tree, principally Sitka Spruce and Lodgepole Pine, with to a lesser extent species such as Norway Spruce, Douglas Fir and Larch.

It was impossible to achieve this level of forest cover without the introduction of these 'alien' or 'exotic' species because, due entirely to a geological accident, Ireland has a very limited range of native species with which to work.

The silvicultural practices we have adopted and developed with these plantation forests are essentially not dissimilar to food production -- the land is prepared, the crop planted and tended, and finally harvested.

The difference, of course, is in the length of time between sowing and harvesting the crop, but in many respects our conventional forest management can equally well be described as 'tree farming'.

The clearfell system of silviculture that we practise has a number of attractions. It is straightforward to plan and execute, it is relatively easy to predict how a plantation is going to behave, and the final harvest is simple -- just remove every tree from the site before replanting and starting the cycle again. In fact, after 100 years and with our favourable conditions which result in such high growth rates, in some areas we are now already well into our third such cycle.

However, despite all these attractions, there are a number of distinct disadvantages. Is our current system in fact the best approach to adopt for even the medium-term, let alone long-term, management of our forests? Increasingly such questions are being asked, and many experts believe that planting, clear-felling and replanting on a 35-40 year rotation is not the best way forward.

Because of their permanence, forests are fundamentally different to other forms of agricultural land use. Over time, flora and fauna colonise them in a way that is impossible in annual crops; they form permanent landscape features. It is now universally accepted that for a forest to be managed in a truly sustainable manner, economic, environmental and social criteria must all be served equally.

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The conventional approach regards our plantations as commercial ventures where the felling and replanting will be repeated in perpetuity. A different approach is to view them as pioneer forests, albeit ones that have been pioneered by man rather than becoming established through natural processes. While Sitka Spruce is not normally a pioneer species, it has nevertheless served this function extremely well.

This alternative view is the one taken by the proponents of an entirely different form of silviculture, known as continuous cover forestry (CCF), or sometimes 'close to nature' forest management. This is a management system that works closely with natural processes to ensure the forest cover is maintained indefinitely, and ultimately benefits the forest owner, the environment and society in general.

CCF is far from a new concept and has been practiced widely throughout Europe for generations. In some countries, for example Slovenia where, with Switzerland, the 'modern' concept of CCF was pioneered in the late 19th century, clearfell is illegal. A number of other countries with very similar afforestation histories to our own are now implementing it as policy. In Denmark it is now national forest policy that all forests are managed using a close to nature system, and in Wales the policy is that 50pc of all forests are to be similarly managed.

The ultimate goal of CCF is to achieve a mixed-age, mixed-species woodland, where conditions conducive to natural regeneration are fostered, obviating the need to replant manually, and where individual trees are micro-managed to maturity.

The end result leads to greater bio-diversity, a healthier woodland, and one to which people, as well as plants and animals, undoubtedly respond more positively. Is it possible, though, to change course mid-rotation and convert a typical plantation of a few hectares of Sitka Spruce, originally planned with three or four thinnings in mind before clear-felling, to a continuous cover system of management? The answer to this question is yes, it is, on many sites, and provided an informed decision to do so is taken early enough.

The first thing to accept is that nothing in forestry happens overnight, with the exception of catastrophic events such as fire and windblow. Conversion to CCF will take many years, but it is achieved through the thinning process so income from those thinnings during the conversion period will still be realised. A series of 'transformation' thinnings must be undertaken, however. These entail a different approach to that taken in conventional thinning. A few tips on how to go about transformation thinning can be summarised as follows:

- Thin early, and often. This will have the added effect that individual trees will develop a lower centre of gravity and therefore become more resistant to wind.

- In these early thinnings, selectively thin the poorest quality trees, regardless of size. The intention is to gradually improve the overall quality of the growing stock, which will vary in size.

- Don't be overly concerned about spacing -- resulting gaps will create opportunities for the manual introduction of other species and natural regeneration.

- Once a stand of consistent quality has been achieved, change the thinning regime to remove the largest trees. As these are the most valuable in the stand, thinning will quickly become more profitable. This is perhaps the hardest aspect for foresters used to the conventional system to embrace as we are all programmed to select the largest stems as our final crop trees and to thin to these.

- Never thin more than the increment -- the aim, after all, is sustainable forest management.

Over time, this regime should produce the conditions where regeneration will naturally follow. However, there are certain conditions that will prevent this if allowed to persist. These include browsing mammals, which must be controlled; an unreceptive seed bed (scarification may sometimes be necessary); and competition from weeds, as there is always a delicate balance between allowing sufficient light for seedlings to thrive and not so much that invasive weeds suppress them. On occasion chemical control is necessary.

While natural regeneration is the goal, sometimes it's slow at first, in which case some planting after the first and second transformation thinnings may be required. Experience has shown that natural regeneration usually follows quite quickly after such planting.

In Ireland, interest in CCF has been growing since the Irish branch of Pro Silva had its inaugural meeting in 2000. A number of forest owners, including Coillte, have started the transformation process in some of their woodlands. Pro Silva is a European federation of foresters and forest owners committed to CCF.

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

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