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Diversifying structure

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Home Adaptation Measures Diversifying structure

Structural diversification in woodland and forests refers to mixed tree heights in mixed aged stands.

Forests with a diverse structure are more resilient and may be better able to withstand some of the risks from climate change compared to even-aged uniform stands. Structural diversity can be increased both at the stand scale and forest/landscape scale.

Diversifying structure at the stand scale

The structure of the stand is determined by the age and age structure of the trees, the presence of any understorey and the mix (if any) of species or types (broadleaf/conifer, evergreen/deciduous). Management influences all of these, and the key choice for many managers is between even-aged stands and continuous cover forestry (CCF).

Benefits:

  • Likely to recover more quickly from drought than unthinned or dense, even-aged stands, as they generally have a lower density of mature trees than even-aged stands.
  • Young under-planted trees or naturally regenerated seedlings on a site managed using CCF techniques would be at lower risk from drought due to the shade and shelter afforded by the overstorey.
  • Frost risk to seedlings is reduced under a canopy managed using CCF approaches.
  • Can improve soil water quality through reduced nitrate leaching and surface water acidification during heavy winter precipitation events, compared to even-aged stands.

Guidance notes

  • Structural diversity can be increased in different ways, so consideration of management objectives is essential to inform selection. Simple structures have one or two canopy layers; complex structures have three or more canopy layers.
  • Planning future thinning operations should aim to promote structural diversity.
  • Stand restocking can be through underplanting or natural regeneration (where there is a viable seed bank and predation can be managed).
  • Pay particular attention to the light levels in the understorey to ensure that they are adequate for natural regeneration or the growth of underplanted seedlings to succeed.
  • If changing species, it is likely that under-planting will be required. Refer to guidance on species choice and management of underplanting operations.
  • Monitor the transformation of the stand and adapt management accordingly. It is important that comprehensive records and management plans are kept in an accessible format that allows successive managers to understand and follow the long-term plan.

Diversifying structure at forest and landscape scale

Guidance notes

  • An even spread of stand ages across a forest or landscape reduces the overall risk at any one time.
  • There are benefits and risks involved in either shortening or prolonging rotation lengths, which need to be balanced in any decision to change a rotation length.
  • It is important to give careful consideration to tree species, their optimum growth requirements, and the risks posed by wind or other threats (including insect pests) before changing rotation lengths.

For further advice see the UKFS Practice Guide ‘Adapting forest and woodland management to the changing climate’

Download the UKFS Adaptation Practice Guide

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Reducing climate change risks

The following risks may be reduced if the adaptation measure is applied appropriately:

Measure likely to reduce risk if applied appropriately
Measure may reduce risk but about which less is known
Measure unlikely to reduce, and may exacerbate, risk
Lack of information or unknown

Case studies

Low impact silvicultural systems have been adopted in an exposed site to help reduce the risk of storm damage and other climate change impacts.

A range of adaptation measures including thinning were implemented on a public forest estate to help combat the threat of more frequent drought episodes.