Continuous cover silviculture

Research Areas

Managing stands using continuous cover

Objectives

This work area aims to improve understanding of the effects of stand manipulation on factors that influence the successful transformation of stands from a clear fell management regime to continuous cover and their subsequent management.

Background

Manipulation of the stand, through the use of thinning, is one of the main tools available to managers when transforming stands to continuous cover silviculture. Traditional thinning regimes are primarily designed to maintain cumulative volume production and prepare the stand for clearfelling. However, when carrying out continuous cover forestry it is important that management is adaptive. This means basing silvicultural interventions on stand level information, monitoring what happens and learning from the results. It is a simple two-stage process:

1. Collecting useful stand level data
2. Using that information to specify silvicultural interventions.

Overall guidance on continuous cover forestry can be found in the following handbook (Leslie 2026) and prescriptions for creation and management of specific complex stands can be found on the Forest Research Forest Development Types page.

Stand suitability

Adoption of CCF should only be attempted when site and stand conditions are appropriate.  A structured approach to evaluating stands has been developed and is described in Mason and Kerr (2004) and a field sheet for data is also available.  This involves assessing stand stability, , species suitability, level of browsing and other factors influencing regeneration

Regeneration

In many cases when stands are managed under continuous cover, natural regeneration is favoured. Objective information must be collected on species composition, size, distribution and browsing damage on regeneration. This is useful because many forest managers:

• Over-estimate the amount of regeneration in a stand
• Under-estimate the level of browsing (often this will be one of the main reasons why there is little, or no, regeneration)
• Give emphasis to seedling regeneration, especially where there is a lot of it, rather than saplings that are much more likely to become part of the new stand
• Only focus on the preferred target species to regenerate instead of considering the wider species mix that will develop
• Have no way of assessing the distribution of regeneration (this can have important implications for thinning CCF stands). Some users linked their stand level data to a GIS by using a GPS. This has enabled them to examine the data spatially.

The structure of a stand is critically important for thinning.

For managing irregular CCF stands information should be collected on species composition basal area and the diameter distribution of the stems within the stand.  A method for capturing this information is presented in Kerr et. al. 2002.  At present we have some information concerning the correct range of basal areas to use when transforming stands (see Hale 2004) but have little understanding of how this will vary with site and during different stages of transformation.  An established approach is to use a ‘reverse-j distribution’ where the stand contains many small trees and much fewer large trees.  A spreadsheet has been developed to help managers when thinning a stand to this distribution and is available on this web page.

Contacts

Andrew Leslie, Victoria Stokes
 

Regeneration of continuous cover forests

Objectives

• To determine the key factors influencing the success of natural regeneration and underplanting and how they will be affected by climate change
• To specify best practice for underplanting when using continuous cover silviculture.

Background

Transformation of forests to continuous cover management requires successful establishment and growth of seedlings beneath a canopy, and their subsequent recruitment into the overstorey. This can be achieved by natural regeneration or by planting. Previously the focus of work in the project has been on natural regeneration and this has shown that for the best chances of success with natural regeneration you need:

• A good supply of seed
• A receptive seedbed for germination
• Favourable stand conditions (Hale, 2004)
• To control competitive weeds
• Little or no browsing.

Guidance on using natural regeneration in continuous cover forests can be found in  Leslie (2026) and in more detail in Nixon and Worrell (1999) for conifers and in Evans (1988) for broadleaves.

Other work in the project developed a simple method to assess the likelihood of natural regeneration of Sitka spruce, Scots pine, Douglas-fir and larch. Full details of this method and how managers can apply it in the field were reported respectively in the following papers:

• Prediction of conifer natural regeneration in a ‘data-poor’ environment (PDF, 2213K)
  Reproduced with kind permission from the Royal Scottish Forestry Society
• Natural regeneration of conifers – helping forest managers to predict success (PDF, 1651K)
  Reproduced with kind permission from the Royal Forestry Society

More recently work has focused on underplanting, a practice that allows greater control of the species in the stand.  Many tree species benefit from the forest microclimate under a canopy and recent work has shown that underplanting can extend the range of suitable species on hot, dry sites in south east England. The following are recent publications or presentations on the topic:

• Successful underplanting. A Silvicultural Guide.
• Underplanting of conifers in Britain: research experience from Clocaenog Forest
• Underplanting extends the range of coniferous tree species that could potentially be used to diversify future commercial timber production in the United Kingdom

Contact

Victoria Stokes and Ian Willoughby
 

Windthrow risk and CCF

Objective

To produce a wind risk model that can be applied to any stand structure.

Background

Wind is a major constraint to transformation to and management of CCF stands. Existing work on the stability of forests has concentrated on the risk of wind damage to even-aged single-species conifer stands. However, other forms of forest management have increased in prevalence, such as silvicultural systems associated with continuous cover forestry. There is therefore a growing need to understand the stability of forests being transformed and managed under CCF, and of trees growing in mixed-species stands. This involves a change in emphasis from stand-level to tree-level risk.

ForestGALES is a PC-based wind risk decision support tool, developed by FR for use in even-aged conifer monocultures. Recent experimental work and analysis of historic data have enabled us to develop the underlying science to calculate risk to individual trees in stand with an irregular structure, and to add several broadleaf species into ForestGALES. For further information see “Tree stability and wind risk to forests” page.

Contact

Tom Locatelli and Bruce Nicoll
 

Understanding the relationship between stand structure and resilience to damaging agents

Objective

To understand the influence of stand structure on resilience to drought, practitioner acceptability and wood properties.

Background

There is evidence that changes to stand structure can develop resilience to damaging agents such as drought, without compromising productivity.  However, the mechanisms conferring resilience have not been investigated and in 2025 a Centre for Forest Protection funded project was launched to address this.

The project has three work areas.  The first uses LiDAR data from three key forest sites in England (Thetford), Wales (Clocaenog) and Scotland (Aberfoyle) have been combined with additional remote sensing and tree ring data to provide a foundation for examining the relationships between key structural variables and drought resilience.  The second work area applies social research techniques to investigate acceptability of different stand structures to forestry practitioners.  The third area of investigation involves rapid measurements of outerwood stiffness (acoustic methods) and density (resistograph) across trees of different sizes at the three key forestry sites.

Contact

Tom Ovenden
 

Operational aspects – Practical implementation of silvicultural prescriptions.

Photo: Duncan Ireland

Objective

Provide forest managers with useful and relevant guidance on operational aspects of continuous cover silviculture.

Background

This work area is historic, with the work having been completed in the early 2000s.  Projects within the programme were directed at producing guidance for forest mangers on how these recommendations can be put into practice using modern methods and equipment, within the current regulatory framework for forestry in Britain.

This work area used the 12 long-term, large scale CCF (Continuous Cover Forestry) demonstration woodlands established by the Forestry Commission since 2000). At one of these demonstration woodlands, Trallwm in Wales, a joint Forest Research/University of Wales study was carried out with Professor Colin Price and Martin Price (Price and Price, 2006).

In addition, there are many forest managers in the non-state sector who have valuable operation experience of managing forests in transformation or as CCF and it was important for the project to make the best use of this valuable expertise.

The following outputs were generated by this work area:

Ireland, D. (2009). Final Overstorey Removal in Uniform Shelterwood (PDF, 1265K). Forestry Commission Technical Development Internal Project Information Note 45/08. Technical Development, Ae Village.

Ireland, D. and Kerr, G. (2008). CCF Harvesting Method Development: Harvester Head Visibility (PDF, 474K). Forestry Commission Technical Development Internal Project Information Note 10/08. Technical Development, Ae Village.

Ireland, D. (2007). Transformation Thinning in CCF with Advanced Natural Regeneration, Case Study: Clocaenog, North Wales. Forestry Commission Technical Development Internal Project Information Note 21/07. Technical Development, Ae Village.

Ireland, D. (2006). Operational Experience of Continuous Cover Forestry: UK Case Studies (PDF, 5381K). Forestry Commission Technical Development Internal Project Information Note 13/06. Technical Development, Ae Village.

Price, M. and Price, C. (2006). Creaming the best, or creatively transforming? Might felling the biggest trees first be a win-win strategy? Forest Ecology and Management 24(3): 252-257.

McIntosh, B. (2000). Role of continuous cover silvicultural systems in the management of the Forestry Commission estate. CCFG Newsletter 16: 5-9. Continuous Cover Forestry Group, Tyddyn Bach, Llanegryn, Tywyn, Gwynedd, LL36 9UF.
 

Costs and revenues of transformation to continuous cover forestry: Modelling silvicultural options with Sitka spruce

Objective

To determine the financial attractiveness of CCF, through developing a model of costs and revenues.

Background

A study by Forest Research in 2014 has shown that transformation to continuous cover forestry (CCF) can be a desirable economic option compared with clearfelling and replanting (C&R): see theStudy report (PDF, 691K). It is hoped the findings of the work will alleviate concerns that transformation to CCF is always a costly option.

The study examined the costs and revenues associated with three transformation scenarios for a stand of Sitka spruce (GYC14) and compared them with conventional C&R. A flexible yield model was used to predict the growing stock and harvesting yields for programmes of thinnings which follow current guidance. Detailed information on the costs of operations was obtained from work study reports, England Woodland Grant Scheme standard costs and the experience of Forestry Commission staff in CCF Trial Areas.

Transformation scenarios were less costly than C&R over a 20-year period because of high initial thinning returns. In the longer term, transformation to a simple CCF structure was similar to or better than C&R if successful natural regeneration could be obtained. The results were tested for their sensitivity to changes in the level of management overheads (assumed to be higher for transformation), product prices and discount rate. The changes investigated had relatively little effect on the ranking of scenarios.

The report is accompanied by an Analysis spreadsheet (XLS, 3813K) that enables practitioners and policymakers to change input costs, product specifications, roadside prices and the discount rate to suit their local conditions.