Continuous Cover Forestry

“Continuous cover forestry (CCF) has the potential to deliver economic, environmental and social benefits like no other form of sustainable forestry. The science of CCF is rapidly developing to provide foresters and woodland owners with the information required for best practice. As a management approach CCF is very hands-on and tangible, and there is great personal fulfilment from working in harmony with nature.”

Edward Wilson, Silviculturist, 2018

What is Continuous Cover Forestry?

Close to nature management of forests that promotes resilience and sustainability

Continuous Cover Forestry (CCF) is an approach to the sustainable management of forests whereby forest stands are maintained in a permanently irregular structure. This structure is created and sustained through the selection and harvesting of individual or small groups of trees, from one stand intervention to the next. The term “continuous cover forestry” does not equate exactly with any one particular silvicultural system. However, it is generally considered to include irregular shelterwood, group selection and single-tree selection silvicultural systems. Existing forest stands may require the application of one or more of these silvicultural systems to achieve and maintain the desired productivity and irregular structure.

There is significant and growing interest in Continuous Cover Forestry at the present time. This is especially true in Europe where socio-economic and ecological factors now favour the development of more diverse, multi-purpose forests, and where traditional clear-felling of even-aged plantations is less desirable. As such, CCF is seen as one of the most effective ways to manage forests for an array of timber and non-timber values (i.e., ecosytem services). In addition, there is evidence that CCF is an important strategy for enhancing forest resilience in the face of climate change and other threats to forest health.

A mature stand of Douglas fir managed on CCF principles with a developing understorey of mixed conifers, including Douglas fir, western hemlock, western red cedar and grand fir | Coombs Wood, Cumbria, UK | Photo:© 2018 E. R. Wilson.

Principles of CCF

The general approach to CCF can be outlined in terms of the following underlying principles, as defined by the Continuous Cover Forestry Group (CCFG):

  • Adapt the forest to the site – The forest manager works with the site and respects inherent variation, rather than imposing artificial uniformity.
  • Adopt a holistic approach – The whole ecosystem is regarded as the production capital of the forest, including soil, carbon, water, fungi, flora, fauna, as well as the trees themselves.
  • Maintain forest habitats – Maintenance of the forest habitat is essential (which requires that clear-felling is avoided).
  • Develop the forest structure – Stand improvement is concentrated upon the development of preferred individual trees rather than the creation of a uniform block of stems. A characteristic of permanently irregular stands is that yield control is based upon measurement of stem diameter and increment rather than age and area.

The principles of managing irregularly-structured woodlands and forests are linked to a developing evidence-base from the UK, Ireland, continental Europe and elsewhere.

An advanced stage of stand structural development in Douglas fir managed on CCF principles | Dodd Wood, Cumbria, UK | Photo: © 2019 E. R. Wilson.

Silvicultural Transformation

The vast majority of productive woodlands in Ireland, Britain and western Europe are derived from plantations. These are usually composed of one or very few tree species. To achieve an irregular structure, these stands must be transformed through a series of planned interventions. These interventions must consider current and future stand stability, the development of irregularity, promotion of natural regeneration and sustained timber production.

In many cases, the most effective strategy for early-stage stand transformation (i.e., in younger stands) is a crown thinning regime. This involves the selection of high value individual trees that are provided with space and freedom from competition so that they can increase in size more rapidly than trees in the matrix of the stand. Ideally, the crown thinning regime will commence from the second stand intervention, onwards. This concentrates stand increment on the best quality trees, which in time form a conveyor belt of value-added stems available for harvest when they achieve their target size. It also drives the irregular structure of the stand by creating variable conditions and gaps for natural regeneration. As the number of stems in the original stand is reduced, seedlings will occupy the canopy gaps and create a permanent, irregular structure. This process of transformation will likely facilitate the influx of a larger number of tree species and provide a more diverse range of habitat features for woodland wildlife, compared with conventional even-aged (planted) forest stands.

For more mature stands, where natural regeneration is already starting to be expressed, the more normal pathway for transformation is to adopt a silvicultural system such as irregular shelterwood, group selection or single-tree selection. Whichever approach is applied, it is important to focus on promoting the best quality stems, while opening the stand canopy in a way that encourages the irregular structure to develop.

A patch of Norway spruce natural regeneration in a stand under transformation to CCF | Ardennes, Belgium | January 2020 | Photo: © 2020 E. R. Wilson.

Transformation is currently an important research theme in forest science. The TranSSFor project (Teagasc/University College Dublin, 2017-2022) is focused on stand transformation to CCF in planted woodlands of Sitka spruce (Picea sitchensis). This is significant because Sitka spruce accounts for approximately 1,000,000 ha of forest area in Ireland and Britain, which represents >50% and >20% of the productive forest area, respectively. The vast majority of Sitka spruce forests are managed on a crop rotation model, with clear-felling normally between stand ages 30-50 years, depending on site productivity and management objectives. The TranSSFor project aims to strengthen the emerging evidence-base for the wider adoption of CCF in Sitka spruce production forests.

TranSSFor Project | Transformation of Sitka spruce stands to continuous cover forestry | 2017-2022

Currently, the TranSSFor project is the most detailed research study addressing the early-stage transformation of Sitka spruce production forests.

There are two strands to the TranSSFor project: 1. comparison of thinning regimes that promote early-stage transformation of Sitka spruce plantations; 2. training in early-stage transformation of Sitka spruce plantations. In both elements of the project the focus is to compare crown and graduated density thinning regimes with the standard (low) thinning regime most commonly applied in plantation forests. The major difference in the thinning regimes is that crown and graduated density thinning promotes greater structural diversity and facilitates natural regeneration; low thinning promotes greater uniformity in the crop trees. A feature of the crown and graduated density thinning regimes is the selection of future crop trees (Q-trees), that have good stem form, light branching and healthy crowns. These trees are given more space to grow than matrix trees as part of the thinning pattern (see below). The study was initiated in 2010 and has completed three thinning interventions. The fourth thinning interventions are planned for 2021-2022.

Results from this research study will be published in peer-review journals, with the first papers due to appear in 2020.

Q-tree (marked with white band) in a graduated density thinning plot | TranSSFor Project | Ballycullen Forest, County Wicklow, Ireland | Photo: © 2019 E. R. Wilson.

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