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Management options

Silviculture of ash in the light of ash dieback

Introduction

Ash dieback, Hymenoscyphus fraxineus, is developing rapidly across the island of Ireland. Ireland’s ash woodlands, particularly first rotation plantations, are quite unique and are at a particular risk of rapid decline.  Urgent action is required in order to minimise the economic, ecological and social impact of the disease.  However, in order for this to happen forest owners require guidance regarding potential positive management interventions. 

This document outlines a suite of potential silvicultural options that were demonstrated at the Teagasc Ash Management event in Ballyhaise College, Co. Cavan on 23 October 2018.

These options are presented as an initial attempt at providing guidance and are derived from international practice and literature. They may develop over time as more information and experimental data becomes available.

Potential management interventions

Selection thinning 

Selection thinning is the standard practice for thinning of ash in Ireland and is the minimum that should be carried out to help maintain the vigour and health of an ash stand, whether there is disease present or not.

Management intervention:

  • Access racks at 14 m spacing
  • Mark 300 Potential Crop Trees (PCTs) per ha
    • Disease free
    • Vigorous
    • Good stem form
    • Good distribution
  • Remove diseased trees
  • Remove competitors to the PCTs
    • 2-3 crown competitors

More information can be found in the Silvicultural Guidelines for the Tending and Thinning of Broadleaves (PDF). 

Free-growth

The objective of the free-growth system is to increase the volume of a limited number of selected trees as quickly as possible. It can be viewed as a more intensive selection thinning. It is a heavier thinning but done to favour fewer selected trees. The selected trees should have the potential to be the final crop.

Management intervention:

  • Access racks at 14 m spacing
  • Mark 100 Final Crop Trees per ha
    • Disease free
    • Vigorous (large crown)
    • Good stem form
    • Good distribution
  • Remove all adjacent crown competitors from the selected trees.
  • Remove diseased trees

It is important to note that the selected trees must have large crowns to enable them to react positively to the decreased competition. An annual stem diameter increment of more than 2 cm can be attainable under this system in favourable conditions.

   

Bands 3-line

Bands can be superimposed on the selection felling system. This system will facilitate the planting of alternative species whilst maintaining a modified micro-climate more conducive to the establishment of young trees.

Management intervention:

  • Mark 4 contiguous lines from 7 for felling
    • 1 line is a rack (14 m spacing)
  • Mark 150 PCTs per ha
    • Disease free
    • Vigorous
    • Good stem form
    • Good distribution
  • Remove 2-3 crown competitors from the selected trees.
  • Remove diseased trees
  • Replant 3 lines from 7

Coupe felling

Coupe felling can be superimposed on the selection felling system. Coupe felling will provide the opportunity to plant, or favour the natural regeneration of, an alternative species to the ash. Carrying out the selection thinning on the remaining trees will help maintain their vigour and health.

Management intervention:

  • Access racks at 14 m spacing
  • 15 coupes per ha of 20 m diameter = approx. 0.5 ha
  • Mark 150 PCTs per ha
    • Disease free
    • Vigorous
    • Good stem form
    • Good distribution
  • Remove all adjacent crown competitors from the selected PCTs
  • Remove diseased trees
  • Replant coupes with mix of alternative species
    • Match species choice with site, light availability and objectives

Please keep in mind that:

  • The presence of deer and/or rabbits/hares will require planted trees and natural regeneration to be protected by either tree shelters or fencing.
  • Future management may include vegetation control in the coupes to remove competition from replanted trees.
  • Management should continue to thin the remaining ash trees and widen the coupes as light availability to the understorey decreases.
  • The location of coupes can be influenced by the availability of existing natural regeneration of alternative species.
  • Their diameter should be influenced by the height of the stand (taller stand → larger coupe) and shade tolerance of the alternative species (greater shade tolerance → smaller coupe).

 

Some positives from ash dieback?

Whilst the occurrence of ash dieback in Ireland will likely have a significant impact on ash, there may be a few positives that we can gain from it if we grasp the opportunities presented to us.

  • We may have the opportunity to ameliorate poor-performing ash stands, particularly those where site:species matching was not ideal.
  • We have the opportunity to use silviculture that is more site-specific, rather than prescriptive.
  • The existence of trees in the stand will have made the soil more suitable for tree growth and will provide the opportunity to plant trees into a more conducive sheltered environment for tree growth, rather than an exposed green-field site.
  • The establishment of mixes of species, and a diversity of stand structure, may lead to greater ecological and economic resilience.

Relevant publications and presentations

Further information

  • Please contact Dr Ian Short, Broadleaf Forestry Research Officer