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Know your Forest

Assessing how your trees are growing is important.

It is the only way to know when to start your timber harvesting operations. While you may have management records from when your forest was originally established, nothing beats getting into your forest to monitor its current development. Having a clear understanding of your objectives is also very important. For example, you may wish to plan for a future clearfell, or to maintain forest cover indefinitely by using a continuous cover forest (CCF) management approach, or prepare for forest certification.

Gathering information

You should keep a Forestry Folder to store all relevant documents and records relating to your forest. One of your most important forestry documents is your Certified Species Map which was produced at the time of establishing your forest. This map contains important information about your forest such as plot boundaries, plot areas, the tree species planted, the planting date(s) and the estimated productivity (Yield Class).

A Biodiversity Map (BIO Map) may also have been prepared at the establishment stage. This map will help highlight environmental or archaeological features within or close to your forest. Important information such as prescribed unplanted setback distances, hazard zones and exclusion zones and other protection areas and measures will be included.

Have a Forest Management Plan

The DAFM (Forestry Division) will require you to prepare and submit a Forest Management Plan, when your conifer forest reaches 10 years of age and is 10 ha or greater in area. This plan must be prepared by a Registered Forester, following a field assessment. This plan is an important document that should be kept in your forestry folder. It will provide updated details on each of your forestry plots, including the tree stocking rate, nutrient status, average heights and Yield Class estimates of the different species. It will also include details on when further management interventions are required, including thinning and clearfell and the projected year for each operation. Recommendations for access and roading requirements to facilitate harvesting operations will also be included.

If your conifer forest is less than 10 hectares, you do not have to prepare and submit a Forest Management Plan. However, this is a very useful exercise, and you should consider engaging a Registered Forester to assess your forest and prepare a plan, irrespective of DAFM requirements. All future applications to the DAFM, including Felling Licence and Forest Road Grant applications should be based on the details contained in the Forest Management Plan and associated Certified Species Map.

Inspection paths

Inspection paths are necessary to allow you access your conifer forest prior to first thinning. They serve three main functions:

  • they allow easy access through the young conifer forest
  • they facilitate monitoring and gathering of crop inventory details
  • they make forests more presentable to foresters, prospective timber buyers and harvesting contractors

They should be installed once canopy closure occurs and are cut about 100 metres apart following the planting lines. The lower branches of trees along the paths are removed (brashed) using a handsaw or chainsaw. It is not an expensive operation and is often carried out by forest owners themselves (taking appropriate safety precautions).

It is a good idea to record the location of your inspection paths on a map and to clearly mark their start and end points at the edge of your forest so that they can be easily located by others.

Measure your forest

Once your inspection paths have been cut, you can begin to carry out an inventory i.e. measure some important parameters such as:

  • Productive Area:
    An estimate of the area of your forest in which trees are actually growing. It excludes unplanted setbacks, ditches, ride lines and roads and also any areas that have not established properly.
  • Stocking:
    The average number of trees growing in a fixed area of your forest.
  • Mean Diameter:
    The average diameter of your trees, measured at 1.3 metres above ground level. It is referred to as Diameter at Breast Height or DBH.
  • Top Height:
    The average height of some of your largest diameter (DBH) trees.
  • Yield Class:
    This is an estimate of the productivity of your forest and is expressed in cubic metres m³/ha/year. For example, a 'Yield Class 20' forest should yield an average of 20 m³/ha/year over its lifetime. Yield Class can be calculated by entering the measured Top Height and age of your forest into a Yield Class lookup table. It can be a useful indicator of when and how to thin and clearfell your forest.

It is not practical to measure each tree in a forest.

However, useful measurements can be collected by taking samples of trees in a number of plots representative of the whole forest. You may want to carry out some measurements yourself, using the useful guides available here:

However, as your forest develops and your timber becomes more valuable, you should engage a Registered Forester to carry out more detailed inventory and site assessment. Important site considerations should be reviewed at this stage including, the drainage status, crop stability, entrance and roading requirements. Information gathered in the inventory will help to determine when best to carry out harvesting operations.

Harvesting objectives

For any forest to achieve its full commercial potential along with achieving other objectives, management is required.

This normally involves carrying out thinning interventions at the appropriate time and at the appropriate intensity. Thinning too late or at the wrong intensity can lead to increased windthrow risk or a reduction in potential growth. Well executed thinning operations will increase the quality and size of your remaining trees, allowing larger, more valuable commercial timber to grow.

First thinning in conifer forests should normally start when your trees are between 10 and 12 metres in height.

The Teagasc Thinning Ready Reckoner is an indicative tool that can help you determine the best time to start your first thinning operations. However, it is important to understand that not all forests may be suitable for thinning due to soil type or their location. These forests if thinned, may become excessively unstable and more liable to wind throw damage.

The Teagasc Thinning Ready Reckoner is a simple aid for working out when your conifer forest is ready for thinning and is available here Thinning Ready Reckoner (with explanatory video).