Building resilience into planted forests: recent ...

XIV WORLD FORESTRY CONGRESS, Durban, South Africa, 7-11 September 2015

G Kerr1, J F Webber2, W L Mason3, R L Jinks2 and T Jennings4 !

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Recent concerns about the effects of newly arrived pests and pathogens and uncertainty about the future effects of climate change, has led to new thinking about planted forests in Great Britain. The policy response has been to build greater resilience into the forest estate by encouraging diversification. On a practical level this has led to the introduction of a wider range of silvicultural systems and an active programme of species diversification. Successful outcomes have only been possible because of a sound evidence base and good communication between scientists and forest managers. However, knowledge and understanding is not yet complete and sustained efforts are required to maintain momentum. Experience from Britain may be of interest to other countries with similar challenges.

The impact of the First World War on many of Britain’s forests was devastating. Timber was a key raw material for the war effort, and the forests of Britain, which had been reduced to just 5% of the land area, could not meet the demand. Following the war a sustained effort was put into expanding the forest area, mainly through planting single species forests in the uplands of northern and western Britain. Early trials showed that Sitka spruce, a non-native species from northwest America, was successful in these exposed, acid and nutrient poor soils and it became the dominant species planted. At the end of the century the area of forest had more than doubled to 12% of the land area and was mainly composed of single species conifer plantations. Recently, trees in Britain have been subjected to an exponential increase in the number of new pests and diseases (Figure 1, Appendix 1) and some of these have had a significant effect on the main forest species. In addition, there are significant concerns about future climate change; projections of anticipated temperature and rainfall using the most recent data suggest that forests in southern Britain could be experiencing climates characteristic of Mediterranean Europe by the 2080s (Broadmeadow et al., 2009). The policy response to this has been to try to build resilience into the forest estate by encouraging diversification (resilience is defined as ‘the ability of a social or ecological system to absorb disturbances while retaining the same basic structure and ways of functioning, the capacity for selforganisation, and the capacity to adapt to stress and change’ (Forestry Commission, 2011)). On a

practical level this has led to the introduction of a wider range of silvicultural systems and an active programme of species diversification (DeRose and Long, 2014). The objective of this paper is to review progress in building resilience into forest stands in Britain, describe a case study from eastern England and offer conclusions, which may be of interest to other countries with similar challenges.

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The main silvicultural system used in planted forests in Britain has been patch clear-felling combined with artificial regeneration (Malcolm, 1997). The need to diversify the range of silvicultural systems has mainly been achieved through increased adoption of Continuous Cover Forestry (CCF). This is an approach to management which seeks to manage the forest ecosystem rather than purely the trees, which uses natural processes as the basis of stand management, works with site limitations and seeks to create diverse stand structures with a range of species (Mason et al., 1999). The following actions have been critical steps in the development of CCF in Britain. Changes in policy The Forestry Policy for Great Britain in 1991 (Forestry Commission, 1991) makes no mention of alternative silvicultural approaches or CCF. However, 20 years later the use of CCF has become enshrined in the UK Forestry Standard (Forestry Commission, 2011), the United Kingdom Government’s approach to sustainable forest management, and in the UK Woodland Assurance Standard (UKWAS, 2012), approved by the Forest Stewardship Council (FSC) and the Programme for the Endorsement of Forest Certification (PEFC). Continuous Cover Forestry Group (http://www.ccfg.org.uk/) This Group was formed in 1991 by a group of professional foresters who believed passionately that forestry in Britain was too reliant on clearfelling and that other approaches to management should be more actively considered. The main role of the group is to promote the transformation of even-aged plantations to structurally, visually and biologically diverse woodlands whilst still aiming to enhance the production of high quality timber according to the principles of CCF. The main activities of the Group are to organize field meetings in Britain and abroad, undertake training courses and contribute to policy

formulation and wider debates about sustainable forestry in Britain. The Group is a member of ProSilva Europe, a federation of forestry organisations committed to advancing ‘close to nature’ silvicultural systems. Review of past practice This review was carried out by Cyril Hart (Hart, 1995) who was a well respected professional forester. He visited sites where existing attempts to use silvicultural systems other than clearfelling were in progress. The sites covered the full range of site conditions in Britain including native broadleaved woodland, conifer plantations, lowland and upland forests. The main conclusions of the review were that: a. The use of irregular silvicultural systems is possible on a wide range of sites in upland and lowland Britain. b. The key to success is continuity of management. c. The costs of management can be high when compared with patch clear-felling and hence is not favoured by economic analysis based on financial yield. d. The potential of irregular forestry to produce non-market benefits can be high compared with forests managed by patch clear-felling. Provision of guidance based on incomplete knowledge To meet the demand for information and guidance from professional foresters a number of technical publications were produced. The most significant were: Mason et al. (1999), Mason and Kerr (2004) and Kerr (2008); these were free publications produced by the Forestry Commission. The defining characteristic of this guidance was that it tried to demystify the subject of silvicultural systems and offer guidance based on incomplete knowledge. Mason and Kerr (2004) was notable in this respect and outlined an approach to the transformation of even-aged conifer stands to CCF in Britain as a three stage process. Firstly, the potential of a stand for CCF is ranked using a scoring system for windthrow risk, soil fertility and species suitability. Secondly, the manager makes a decision on whether objectives can be achieved with a simple (1 or 2 canopy strata) or complex (3 or more canopy strata) stand structure. Thirdly, four easy to follow options are outlined for transforming even-aged stands based upon the structure desired and the age of a given stand. The key decision was to try to avoid the complex jargon often associated with discussions of ‘silvicultural systems’ and to encourage forest managers to consider the final structure required by the objectives and how this could be achieved. A measure of the success of this approach is that the terms ‘simple’ and ‘complex’ are now in common usage in forestry in Britain. A programme of systematic research The guidance described above was based on incomplete knowledge but an important point is that there has been a programme of systematic research to support and refine the guidance, which has been reviewed by Mason (2015). The conclusion of Mason’s review is that the introduction of alternative silvicultural approaches may take decades and must overcome technical challenges and cultural resistance. The establishment of working demonstrations There have been a number of initiatives to establish working demonstrations in state and privately owned woodlands. Kerr (2008) describes the Forestry Commission initiative and many of these are now flourishing. However, it is perhaps a measure of how continuous cover has become part of mainstream forestry thinking in Britain that the influence of these centres of excellence is now diminishing.

Progress in implementation Malcolm et al. (2001) estimated that up to half the area of conifer planted forest in Britain could be suitable for transformation to continuous cover based on knowledge of soils and wind climate; however, they believed that only 5 per cent was being managed using this approach. Despite policy support precise figures on the areas that have been placed under this type of management are difficult to obtain. A recent review of the adoption of continuous cover identified some 60K ha of forests actively managed under this approach (around 3 per cent of forest cover) (Wilson, 2013) but did not include large areas of public forests where there were aspirations to use continuous cover. A safe estimate of the extent to which continuous cover is being used in planted forests in Britain is therefore 10-20% and rising. !

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After the last ice age, only 37 major tree species recolonised the British Isles, yet the climate and soils are conducive for growing hundreds of species not only from regions with a similar climate but also from cooler and warmer regions of the world. There are about 500 major tree species introduced from across the temperate forest regions that have been successfully grown in arboreta or small experimental plots. Nearly half of all introduced tree species have been trialled to differing degrees for forest use, mainly during the first half of the 20th century. The main focus of such trialling was on conifer species with comparatively few introduced broadleaved species receiving detailed examination. A comprehensive summary of these trials can be found in MacDonald et al. (1957), which gives a detailed account of the performance in Britain of 160 non-native species, the majority of which are conifers (110). Despite this effort, species use has concentrated on a few major conifers; Table 1 shows that the twelve main species in Britain account for 85% of forests. The present position with regard to the twelve most common tree species and significant pest and disease problems, particularly those that have been introduced in recent decades, is summarized in Table 1. As can be seen there are significant problems for both the conifer resource and for woodlands composed of native species. Table 1: Main forest species, new pests (P) and diseases (D) and possible future threats ! #

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For more information see http://www.forestry.gov.uk/pestsanddiseases and the UK Plant Health Risk Register (https://secure.fera.defra.gov.uk/phiw/riskRegister/index.cfm; both accessed 2 April 2015).

In order to re-examine species and provenance choices for British forestry an evaluation strategy was developed by Hubert et al. (2009). The first part of this strategy was to conduct a thorough review of all known information on species performance in Britain. This mainly included published information on species performance in forests, knowledge in the ‘grey literature’ and other sources of data from arboreta, forest gardens and the Tree Register Handbook (Johnson, 2011). This information was used to develop a shortlist of species that were felt to have potential for further consideration in British forestry. Species in the list were then divided into two categories: Category 2: mainly introduced species that have either had limited use in the past (‘minor species’) or that have been tested (plot-stage testing) for forestry to varying extents but were never widely planted even though they have many suitable attributes. Category 3: potential species (‘lesser-known species’) that have not been tested in plots, but are productive species in their native ranges and, based on performance in specimen collections, appear to be adapted to our climate. It should be noted that according to this classification Category 1 are those introduced and native species that are currently widely planted and whose silvicultural characteristics are well understood. The traditional way of evaluating potential new species begins with the initial planting (i.e. screening) in arboreta and/or plots in forest gardens, followed several decades later by more systematic and replicated comparative experiments on a range of site types containing the most promising species. This approach has continued to be used and the intention is that in general the priority for Category 3 species is screening to identify candidates for testing in experimental and operational trials. For Category 2 species the aim is to identify and recommend suitable provenances for the current and future climate. One important point is that this work is expensive as it involves the establishment of a network of field trials with a wide range of species covering a broad geographical range. A number of different approaches have been used to reduce and offset costs and each of these has associated benefits and risks. Since Hubert’s review work has involved: 1. Publishing known information on silviculture, provenance and timber quality on over 50 species on the Forest Research website (http://www.forestry.gov.uk/fr/treespecies). 2. Recalibrating our Ecological Site Classification decision support system to include 60 Category 2 species in addition to the existing Category 1 species. This is a spatial system that can give guidance on species choice for any site in Britain and consider how performance may change under different climate change scenarios (http://www.forestry.gov.uk/fr/infd-7nkfmq).

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3. Working in partnership with others to increase knowledge. This has involved an on-going relationship with the Futures Trees Trust (http://www.futuretrees.org); Botanic Gardens at Kew and Edinburgh; supporting initiatives such as Silvifuture (http://www.silvifuture.org.uk) and joining the REINFFORCE project that has established a series of experiments along the western coast of Europe (Orazio et al. 2013). 4. Revisiting species experiments to re-evaluate the future role of particular species in British forestry. A good example of this is Kerr et al. (2015) who re-evaluated European silver fir based on a series of provenance experiments. 5. Seeking funding to establish new species trials. $

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Created in 1922 by the Forestry Commission as a commercial forest, the 19,210 hectare Thetford Forest is the largest lowland pine forest in England. Managed for the multiple benefits of timber, wildlife, recreation and archaeology, designations include a Site of Special Scientific Interest (several rare species) and a Special Protection Area (17,653 hectares) for ground nesting birds (nightjar and woodlark). Thetford is located in eastern England and receives low rainfall (600mm per annum), a moderate amount of sunshine, and the soils are generally sandy and/or calcareous. Soils range from a pH of 4.5 through to a pH of 7.5 but are all freely draining. Corsican pine forms 53% of the total forest area with a further 14% of Scots and other pines. The main silvicultural system is clearfell-replant and each year 62,000 tonnes of timber are produced from 200 hectares of felling and a further 155,000 tonnes are produced from thinning. Dothistroma needle blight (DNB) caused by the fungal pathogen Dothistroma septosporum, was first recognised in the forest in 1997 and manifested itself as a few discoloured needles on occasional trees. However, in 2006 surveys revealed that many stands aged 8–35 years had poor needle retention and did not look healthy. Within a very short time the situation went from innocuous to devastating and DNB seemed to affect Corsican pine throughout the forest. It quickly became apparent that significant changes to silvicultural practice were required and had to be based on the best available scientific advice from Forest Research as described by Locher and Jennings (2015). The following points are a summary of the main changes that have taken place: 1. There was a moratorium on planting Corsican pine in 2006. 2. Species choice for restocking had to be revised and resulted in the use of more Scots pine, larch and Douglas-fir. 3. Thinning practice has changed from first thinning at 25-30 years to much heavier and earlier interventions to promote airflow in the canopy, which is thought to reduce the likelihood of infection and sporulation by the DNB pathogen. 4. In the most heavily affected stands there is little chance of recovery of the Corsican pine. To ensure future timber production an active programme of underplanting has commenced in such stands at first thinning (below 20 years) with a range of shade tolerant species including Douglas-fir, Grand fir, European silver fir, Serbian spruce, Western red cedar, Atlas cedar, Japanese red cedar, Macedonian pine, Weymouth pine and coast redwood (Figure 2, Appendix 2).

In summary, silvicultural practice in Thetford has changed in just 10 years from being dependent on a small number of species, one silvicultural system and forest operations being timed due to economic criteria to one with a much greater diversity of species, innovative approaches to silviculture and the timing of operations governed mainly by the long-term health of the forest ecosystem.

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$ The main lessons from experience of building resilience into planted forests in Britain are: 1. It is important to review past experience of applying a wider range of silvicultural systems and tree species as an essential first step. 2. As far as possible the knowledge base and associated guidance should be based on robust science. 3. To offer forestry professionals guidance it has been necessary to offer the best advice possible based on the evidence, even if this is incomplete. 4. Excellent communication is required between scientists and professionals. Professionals have required written guidance that is accessible and enriched by open dialogue with experts; scientists have required feedback on ideas and advice on the practicality of any guidance proposed. The role of discussion groups and site visits has been an important complement to written guidance. 5. Knowledge is not yet complete and a sustained effort is now required to maintain momentum.

The authors are grateful to the many people who have been involved in the work described in this paper.

, Broadmeadow, M.S.J.; Webber, J.F.; Ray, D.; Berry, P.M. 2009 An assessment of the likely future impacts of climate change on UK forests. In: Combating climate change - A role for UK forests. An assessment of the potential of the UK’s trees and woodlands to mitigate and adapt to climate change; Read, D.J.; Freer-Smith, P.H.; Morison, J.I.L.; Hanley, N.; West, C.C.; Snowdon, P. Eds.. The Stationery Office, Edinburgh, UK DeRose, R.J.; Long, J.N. 2014 Resistance and resilience: a conceptual framework for silviculture. Forest Science, 60(6): 1205-1212 (

Forestry Commission 1991 Forestry Policy for Great Britain. Forestry Commission, Edinburgh Forestry Commission 2011 The UK Forestry Standard. Third edition. Forestry Commission, Edinburgh Hart, C. 1995 Alternative silvicultural systems to clear cutting in Britain: a review. Forestry Commission Bulletin 115. HMSO, London, UK Hubert, J.; Jinks, R.; Lee, S; Mason, B. 2009 Re-examining species and provenance choice in response to a changing climate. Forest Research, Northern Research Station, Edinburgh. (unpublished) Johnson, O. 2011 Champion Trees of Britain and Ireland. Royal Botanic Garden, Kew, London. Kerr, G. 2008 Managing Continuous Cover forests. Forestry Commission Operational Guidance Booklet 7. Forestry Commission, Edinburgh Kerr, G.; Stokes, V.; Peace, A.; Jinks, R. 2015 Effects of provenance on the survival, growth and stem form of European silver fir (Abies alba Mill.) in Britain. European Journal of Forest Research, 134(2):349-363 Locher, C.; Jennings, T.J. 2015 Thetford’s trials and the ecological benefits of clearfelling. Forestry Journal 3/15, 25-27 MacDonald, J.; Wood, R.F.; Edwards, M.V.; Aldhous, J.R. 1957 Exotic forest trees in Great Britain. Forestry Commission Bulletin 30, HMSO, London Malcolm, D.C. 1997 The silviculture of conifers in Great Britain. Forestry, 70: 293-307 Malcolm, D.C.; Mason, W.L.; Clarke, G.C. 2001 The transformation of conifer forests in Great Britain – regeneration, gap size, and silvicultural systems. Forest Ecology and Management, 151: 723 Mason, W.L.; Kerr, G.; Simpson, J.M. 1999 What is Continuous Cover Forestry? Forestry Commission Information Note 29, Forestry Commission, Edinburgh Mason, B.; Kerr, G. (2004) Transforming even-aged conifer stands to continuous cover management. Forestry Commission Information Note 40 (Revised). Forestry Commission, Edinburgh Mason, W.L. 2015 Implementing Continuous Cover Forestry in planted forests: experience with Sitka spruce (Picea sitchensis) in the British Isles. Forests, 6: 879-902 Mitchell, A. (1974). Field guide to the trees of Britain and Northern Europe. Collins, London Orazio, C., Debets, R.C., Lucchio, L. D., Cantero, A., Casero, J.D., Recio, C.P. Bravo, F., Bengoetxea, N.G., Gonzalez, A.A., Jinks, R., Paillassa, E., Lorenzo, M.J.R., Pando, F.J.S., Traver, M.C., Zabalza, S., Nobrega, C., Ferreira, M.G.C., Almeida, M.H. and Correia, A. 2013 Resource INFrastructure for monitoring, adapting and protecting European Atlantic FORest under Changing Climate: Arboretum and Demonstrations Sites. EFI Atlantic, Bordeaux, France UKWAS 2012 United Kingdom Woodland Assurance Standard (UKWAS). Third edition, version 3.1. UKWAS, Edinburgh Wilson, S.McG. 2013 Adoption of alternative silvicultural systems in Great Britain: a review. Quarterly Journal of Forestry, 107:279-293

Appendix 1 New tree disease and pest outbreaks in Britain First Report

Pathogen outbreaks & hosts

First Report

Pest outbreaks & hosts

2012

Hymenoscyphus (Chalara) fraxineus – ash

2012

Asian longhorn beetle – mixed broadleaf species

2011

Phytophthora austrocedri – juniper

2008

Douglas-fir seed bug - conifers

2011

Cryphonectria parasitica – sweet chestnut

2007

Pine-tree lappet moth – various pine species

2010

Phytophthora lateralis – Lawson cypress

2006

Oak Processionary moth - oaks

2009

Phytophthora ramorum - larch

2002

Horse chestnut leaf miner –horse chestnuts

2009

Acute oak decline (combination of pests and pathogens) - oak

19942005

Gypsy moth – various broadleaf species

2007

Phytophthora pseudosyringae beech, hornbeam, Nothofagus

1982

Great spruce bark beetle – spruce

2004

Pseudomonas syringae pv aesculi – horse chestnuts

1972

Larch saw fly

2003

Phytophthora kernoviae – rhododendron and beech

2002

Phytophthora ramorum – non-native oak & rhododendron

1997

Dothistroma needle blight - pines

1993

Phytophthora alni - alders

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Appendix 2 Species mentioned in text Sitka spruce

Picea sitchensis (Bong.) Carr.),

Scots pine

Pinus sylvestris L.

Oak

Quercus robur L.; Q. petraea (Matt.) Lieb.

Birch

Betula pendula Roth; B. pubescens Ehrh.

Lodgepole pine

Pinus contorta Dougl. var. latifolia

Ash

Fraxinus excelsior L.

Larch

Larix kaempferi (Lamb.) Carr.; L. decidua Mill.

Beech

Fagus sylvatica L.

Norway spruce

Picea abies L.

Sycamore

Acer pseudoplatanus L.

Corsican pine

Pinus nigra var. maritima (Ait.) Mel.

Douglas-fir

Pseudotsuga menziesii (Mirb.) Franco

European silver fir

Abies alba Mill.

Grand fir

Abies grandis Lindl.

Serbian spruce

Picea omorika (Pan.) Purk.

Western red cedar

Thuja plicata D. Don

Atlas cedar

Cedrus atlantica (Endl.) Carr.

Japanese red cedar

Cryptomeria japonica (L.f.) Don

Macedonian pine

Pinus peuce Griseb.

Coast redwood

Sequoia sempervirens (D. Don) End.

Authorities according to Mitchell (1974)

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