Biodiversity, Forestry and Wood report criticised for statements about continuous-cover forestry.

A report on biodiversity and forestry published by Confor has been heavily criticised by advocates for continuous-cover forestry (CCF).

The Continuous Cover Forestry Group has described several assertions made in Biodiversity, Forestry and Wood as “inaccurate and wrong”.

The group said it was contacted by several of its members who were concerned with comments made in the report.

Taking the view that some of the concerns were valid and the report is unduly pessimistic about the potential use of CCF in Britain, the group issued a public response, stating: “We feel the sections which discuss potential methods for management of existing forests are inadequate and appear to assume that patch clearfelling systems should be the default silvicultural system used in British forests.

“This is a missed opportunity, since the wider use of silvicultural systems that follow CCF principles can be used to both increase production and enrich nature of existing forests.”

The CCFG said its specific criticisms were as follows:

A. Pages 15–16 – Managing light and shade. There are several places in this section where statements are made about CCF that are either wrong or misunderstand the British and international literature on the use of CCF. These are:

i. “Continuous cover forestry and shade tolerant species.” The suggestion on page 15 is that CCF is reliant on shade-tolerant species and that this will perpetuate heavy shade at ground level to the disadvantage of ground flora and other elements of forest biodiversity. This is wrong on two counts. CCF can be applied with species that are either intermediate in shade tolerance or light demanding, provided that the larger gap sizes found in group selection or irregular shelterwood systems are used to promote regeneration. More importantly, since an adequate light environment is required to promote regeneration, CCF stands have to be thinned, and therefore will cast a lighter shade than found in dense mature even-aged conifer stands close to rotation age.

ii. “CCF shows significantly lower tree growth with (negative) implications for carbon capture and wood production.” This assertion is based on a single paper which used Finnish Norway spruce data to show how tree growth models would need to be adapted to take account of differences in growth rate and habit of individual trees growing in irregular stands. Such adjustments are needed to predict outturn from CCF stands compared to even-aged ones. The authors of the cited paper noted that the lower growth of individual trees in the selection (CCF) stands after thinning reflected the heterogeneity of the canopy structure. They did not extrapolate individual tree growth to whole stand production nor do they mention any implications for carbon capture.

The mistaken inference drawn from this reference oversimplifies the ‘complex problem’ of comparing the relative productivity of multi-aged (i.e. CCF) and even-aged stands. A more evidence-based approach would have noted that there are many empirical studies of this problem in the literature. Some report greater productivity in even-aged stands, others report the reverse, and a fair conclusion is that it is unlikely that there is a universal truth that one management regime is more productive than another.

READ MORE: ICF, Confor, and RFS unite for English Tree Strategy response​

As far as carbon is concerned, if one accepts that there is little practical difference in productivity between CCF and even-aged stands, then it is likely that differences in carbon capture will also be insignificant. However, since CCF makes much less use of intensive site cultivation for establishing young trees, greater use of CCF is likely to be beneficial for maintenance of soil carbon. In addition, a recent American study showed higher primary productivity in forests with the type of complex canopy structures that would be favoured by CCF, with potential beneficial implications for forest carbon.

The BFW report seems to base these rather negative views of CCF upon extrapolation from “places where CCF and rotational forestry are both practised on a large scale”. These “places” are not defined, but the use of the Finnish reference suggests that this is likely to refer to Scandinavia. However, there are recent publications from both Finland and Sweden which compare the impacts of CCF and even-aged management and reach a different conclusion to the BFW report. For example, CCF was better suited than even-aged forestry to delivering multifunctional forest management in Finland; at a landscape level, CCF was better in terms of carbon sequestration and biodiversity and more profitable than even-aged forestry delivered by low thinning. Building on these results, Swedish researchers have concluded that greater use of CCF is desirable to increase the resilience of production forests to climate change and to enhance the range of ecosystem services they provide.

iii. “In many upland forests thinning and CCF is impossible due to windthrow risk.” We agree that wind risk is a major constraint on silvicultural practice in more exposed areas of upland Britain. However, with the advent of more sophisticated wind risk models such as ForestGALES, we can begin to explore how silvicultural practices such as greater use of mixtures and early thinning can increase a stand’s resistance to windthrow, especially if the forests are located on soils that allow adequate rooting. This is exemplified by the successful installation of CCF regimes in Sitka spruce forests on exposed sites such as Bryn Arau Duon and Clocaenog. The greater stability of the dominant trees in irregular stands and the presence of lower canopy layers which reduce wind penetration through a stand explain why irregular stands can be more windfirm than those subject to even-aged management. The point here is that we need to avoid the deterministic expectations of windthrow at given age/tree height as predicted by the old Windthrow Hazard Classification, and recognise that foresters’ actions can significantly affect the occurrence of windthrow. Thus, it is not that thinning and CCF are ‘impossible’ in many upland forests, but that these operations may be ‘risky’, depending on site, soil, and previous stand management.

iv. “It is easy to find the fallen stands of optimistic foresters who tested its [windthrow risk] limits.” The issue with this phrase is that it fails to recognise that abiotic disturbances (wind, snow, ice, fire) are a fact of life in British forestry and will inevitably influence the structure of our forests. We could counter by commenting about the prevalence of windthrow in non-thin stands.

B. Page 11 – Species Mixtures. The opening sentence of this paragraph stating that “no more than 75 per cent of a forest area may be planted with a single species” gives the impression that species mixtures occur widely in British forests. This is far from the case since published statistics suggest less than 50 per cent of British forests are composed of single-species stands. Planting pure blocks of different species is not the same as creating a mixed stand, since in the former the only interaction between species is at the edges of the blocks. In mixtures, two or more tree species interact at various developmental stages and share and/or compete for common resources (e.g. light, water, soil nutrients) and these interactions may change over time. We agree with the statements in the rest of the paragraph that greater use of mixtures in British forestry is very desirable for enhancing biodiversity and increasing resilience. Greater use of CCF would be a very effective means of promoting more mixtures in British forests.

Forestry Journal: W.L. Mason, chair of the CCFG.W.L. Mason, chair of the CCFG.

W.L. Mason, chair of the CCFG committee, said: “We feel the report gives a misleading impression of the options available for the management of British conifer forests and is uncritical about the prevalence of clearfelling and replanting as the default silvicultural system.

“It may take time to transform simple forests into more diverse structures but the long-term gains through enhanced resilience to climate change and pests and diseases will be substantial. Greater use of CCF techniques will be essential for integrating ecology and profitability in British forests as desired by the BFW report.

“We should recognise that there is increasing evidence in Britain and elsewhere that CCF techniques are preferred methods of developing varied and attractive forests that are both socially acceptable and environmentally desirable.”

Responding to the Continuous Cover Forestry Group comments on Biodiversity, Forestry and Wood, the report’s author, Eleanor Harris, said:

Confor produced this report in response to assumptions in some quarters that the wood-producing forests of the last century have little or no biodiversity value, that forestry’s environmental practices have not delivered improvements in recent decades, and that wood production in general is incompatible with promoting biodiversity.

If we are to tackle the twin challenges of a climate emergency and biodiversity decline then it is important that actions are based on evidence. This report argues that the assumptions above are not based on evidence. There is always plenty of room for better evidence and further improvement, which is why ongoing research and continuous improvement are so deeply embedded in UK forestry practice through Forest Research and UKFS. However, there is also widespread evidence that our existing productive forests are delivering biodiversity benefit, and are improving in this regard.

Forestry Journal: Eleanor Harris, policy researcher at Confor.Eleanor Harris, policy researcher at Confor.

We welcome the discussion initiated by the report, but it is important that comment is based on an understanding of what the report is, and what it is not. The CCFG criticises the report for “assuming that patch clearfelling systems should be the default silvicultural system”. In fact, the report does not seek to establish what should be a theoretical ideal silvicultural system – it notes that forestry systems at all points on the clearfell–continuous spectrum have their own biodiversity advantages. Rather, it seeks to identify the biodiversity value of the forests we have inherited from past management choices, and their likely evolution as habitats in the future.

It is disappointing that the CCFG critique focuses intently on improving the management of conifer crops, and apparently dismisses as irrelevant the continuous improvement achieved through 40 years of regulation and certification through UKFS and UKWAS. The critique also ignores the second half of the report which looks at bringing native woodland into continuous-cover management for biodiversity and wood production. This section highlights the big biodiversity opportunity in the other half of our forest resource. As the recently published British Woodlands Survey reveals, most of our native woodlands still lack resilient management plans and their owners lack awareness of UKFS. While most owners cite biodiversity as their chief management aim, few have the knowledge or financial resources to improve their often even-aged and herbivore-damaged native woodlands. The survey found that the minority of native woodlands which are also managed for wood production were in better condition for biodiversity.

Many of our native woodlands are still relatively young (planted within the past 150 years), even-aged, and often neglected. The report argues that sensitive harvesting from these woodlands would let in light, encourage natural regeneration, facilitate stronger tree growth, and create an income stream while supplying low-carbon wood products.

The section on silvicultural systems was necessarily brief, like the sections on open ground habitats, deer and squirrel control, natural regeneration, and native woodland expansion, all of which have received criticism from advocates who would like to have seen them covered in more depth. However, focusing on these factors, which are already extensively covered elsewhere in the literature, would have unbalanced a report which sought to provide an overview of the biodiversity benefit of the whole UK wood supply chain in a global context.

The Confor Biodiversity, Forestry and Wood report seeks to bring balance to the debate around forestry and biodiversity by arguing, first, that the UK’s wood-producing productive forests, managed under UKFS and UKWAS, are delivering significant benefits for biodiversity which deserve recognition in land management discussions. Second, it argues that the chronic neglect of the native broadleaf half of the UK woodland resource is a huge missed opportunity for biodiversity, and this is an area where policy needs to focus more on practical solutions. The knowledge and expertise within the CCFG is clearly important in delivering a transformation in our native woodlands. Persuading policymakers to support us in delivering more extensive, more biodiverse and more productive woodlands in the UK will require foresters to focus on the policies on which we agree.

To read Confor’s Biodiversity, Forestry and Wood report, click here.

For the CCFG’s full statement (with supporting references), click here.

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