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Independent.ie

Friday 20 October 2017

Facing the challenges of replanting

Minimise risk: greater emphasis must be on species mixtures
Minimise risk: greater emphasis must be on species mixtures

William Merivale

For the majority of private forest owners the main concerns have been focused on how best to establish their new forests and manage them to produce a quality crop. However, an increasing number of timber growers are now facing a new challenge - reforestation following clear-fell of the first rotation.

Some of these owners are in the fortunate position where their forests had reached the age when the harvest could be planned and executed in the normal way, but many others had a rude awakening just over a year ago when part or all of their forests were 'felled' prematurely by Hurricane Darwin in February 2014.

While presenting certain challenges, establishing the second rotation brings many opportunities for improvement. Earlier mistakes can be analysed and care taken to avoid repeating them, owners' objectives can be revised, and alternative silvicultural systems considered. Access can be enhanced and integrated with improved drainage plans.

Species selection

Bearing in mind that such a significant area of forestry has been established within a generation, there are numerous examples around the country of poor species selection, admittedly many of them are only apparent with the benefit of hindsight.

But that hindsight can now be put to good effect, and factors such as the health and growth rate of the first rotation, and the performance of different species in adjoining and nearby forests should be considered before final selection.

The potential consequences of relying too much on a single species should not be ignored, as evidenced by the outbreak of diseases such as Chalara fraxinea (Ash dieback) and Phytophthera ramorum.

While the latter has mostly affected Japanese larch, there have been isolated instances of the disease in Sitka spruce, and the same pathogen has killed a lot of oak in parts of North America. A greater emphasis on mixtures really has to be considered.

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This is also an opportune time to consider genetically improved planting stock, which is likely to increase yields and quality.

Studies into improved trees usually show the additional cost is well worth the investment as it pays off in higher yields, better stem form and wood quality.

Establishment

The site is likely to be covered in a brash mat following the previous harvest, designed to minimise soil disturbance and compaction. This should be left in situ long enough for the needles to fall to return nutrients to the soil before the brash is windrowed usually by excavator. Any additional drainage or drain repair can be carried out at the same time.

If the site is deemed suitable it may be possible to bundle the brash and remove it altogether. Factors allowing this include fertility levels, drainage and other environmental factors, but where it is an option the resultant clean and tidy site should mean lower establishment costs, not least windrowing may not be required. Costs of brash bundling will vary from site to site but as a general rule it is likely to result in a break-even situation as the sale of the biomass should negate the charges for baling and transport.

Pine weevil

The large pine weevil, Hylobius abietis, is the most important pest of replanted conifer sites in Ireland. It is widespread in mature forests but there they feed in the canopy without causing any significant damage.

The problems occur following replanting of a clearfelled site. Here, the adults are attracted to the site by the smell of freshly cut timber where the females lay their eggs in the stumps of the recently cut trees and the immature weevils develop under the bark.

Stumps should be inspected regularly for evidence of larvae, which are creamy-white with brown 'heads' and look like legless caterpillars. The damage occurs when the emerging adults feed on the bark of the young forest transplants. While pine is the preferred food source, weevils feed on a wide variety of both conifers and broadleaves, and Sitka spruce is far from immune.

Young transplants can withstand a small amount of damage but extensive feeding can ultimately cause needle loss, impaired growth and death where the young tree is ring-barked. In the absence of control there have been recorded instances of 100pc failure.

Adult weevils have two peak periods of feeding, between April and June, and again between July and October. These peak periods should be considered when implementing control treatments.

Currently the standard method of control is to dip the transplants in a solution containing the pesticide cypermethrin prior to planting (normally carried out by the nursery).

This provides protection for a period of four to six months, therefore it may be necessary to apply further applications by knapsack sprayer until the young trees are robust enough to withstand any ongoing attack.

Early management

Reforestation sites tend to be more fertile so the second rotation will often fare better than the first, frequently without the need for fertiliser, but this will also result in additional competing vegetation. Weeds such as briar, furze and willow can establish themselves very quickly so early control is very important to prevent them gaining a foothold and smothering the young trees.

In the interests of sustainable forest management, the less one relies on the knapsack sprayer the better. Provided the intervention is carried out early enough, manual cutting of briar and woody weeds, and sometimes just trampling the softer vegetation, is sufficient. A second cutting a year later may be all that's required for the next rotation to take hold.

Finally, it is as important in reforestation areas to ensure the stocking density is maintained at as high a percentage as possible, and certainly at a minimum of 90pc, as it is for afforestation. The site should be checked regularly during the first two to three years and failures replaced.

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

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