Spring 2018Continuous Cover Forestry Group

CCFG / BES Seminar at Rushmore, Dorset in April 2017

Biodiversity effects of ‘irregular’ silviculture in native woodland

Continuous Cover Forestry Group 4.1 Spring 2015

Spring 2015

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On 5th and 6th of April a group of about 70 enthused and inquisitive people met for this two day

seminar in the splendid surroundings of the Rushmore estate, straddling the Dorset/Wiltshire

border. The event started with a presentation about the use of CCF at Rushmore followed by a

series of talks describing new and informative research into the effects of different forms of

irregular silviculture upon biodiversity in native woodlands. Copies of all the presentations can be

found on the CCFG website at http://www.ccfg.org.uk/category/events/2017/

Andy Poore, consultant forester for the Rushmore Estate, provided an overview of the history

and management of the woodlands on the estate, based on nearly 30 years of experience with

these woodlands. The 833 hectares of woodland at Rushmore are 69 per cent broadleaved and

26 per cent conifers with avenues and similar making up the remainder. Annual timber

production is about 1900 m3 of softwood and 1100 m3 of hardwood. 434 hectares are designated

as a SSSI, comprised largely of ancient semi-natural broadleaved woodland. He noted that there

had been a long tradition of coppice management in these woodlands, but this had largely

ceased by the 1970s. For management purposes the woods had been divided into a number of

working circles – those which were the focus of the seminar were; semi-natural broadleaved high

forest managed by CCF, closed stands (mostly managed under minimum intervention) and

coppice-with–standards (either hazel or birch dominated). The key message from this session

was the complexity of stand types across the estate. They did not adhere to standard yield

models. Instead, successful management resulted from highly specific silvicultural interventions.

Management has been, first and foremost, economically driven. Any benefits to biodiversity are

a result of forest management that is all the while, profitable. Underpinning this approach was a

stand monitoring system adopted from the AFI (Association Futaie Irregulaire), which provided

detailed real-time data regarding the performance of individual stands.

Participants were then given a couple of presentations outlining interim findings from the

ongoing ‘Rushmore Biodiversity Research Project’, which was a partnership between the Estate,

Dorset County Council, Dorset Environmental Records Centre and Manchester Metropolitan

University. This five year project aims to uncover the relationships between the different forest

structures and biodiversity in these semi-natural woodlands with a particular aim of seeing if a

forest managed using irregular silviculture can provide favourable conditions for general

woodland biodiversity as well as protecting species of particular environmental concern.

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Continuous Cover Forestry Group 4.1 Spring 2015

Continuous Cover Forestry Group Spring 2015

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Danny Alder (Manchester Metropolitan University) presented his findings from research into the

habitat associations of particular woodland birds and their interactions with the matrix of stand

types at different periods in the year. The results showed a strong correlation between stands of

lower stem densities having a greater array of different species and larger populations of these

species. However this was not the case for every species; with a minority displaying a preference

for denser and closed canopy stands, particularly at certain times of year. Notably, greater

spotted woodpeckers would move into higher density stands in summer in response to increased

food availability. A similar effect was also seen in the research into the abundance of bat

populations in different stand types. The irregular high forest stands contained a significantly

higher average abundance of most bat species, although some species showed a marked

preference for both the minimum intervention and coppiced stands. Dr. Phil Sterling (Dorset

County Council) had examined moth populations within the different stand types. The

abundance of rarer woodland moths was higher in the irregular stands than in either the coppice

woodlands or those with minimum intervention. Numbers of leaf mining moths were also higher

in the irregular stands than in the coppice woods. He concluded by saying that these initial

results suggested that irregular forest management was at least as good as coppice or minimum

intervention in conserving moth biodiversity.

The indoor session was closed by Dr. Rob Fuller (BTO and the University of East Anglia) who

reviewed current understanding of the relationship between forest structure and biodiversity,

with particular emphasis upon broadleaved woodland. He outlined how management actions

(such as the choice of silvicultural system) will influence the structure of the woodland habitat

and consequently the functional resources available for woodland biodiversity. There was general

agreement that the two stages of most importance for woodland bird populations were the early

establishment phases and old growth stands with spatially varied structures and substantial

amounts of deadwood. Neither stage tended to be favoured by conventional even-aged

management. Field studies had shown a major decline in vegetation cover over 20 years in

unmanaged broadleaved stands with substantial decreases in some woodland birds, while results

from irregular conifer stands showed higher number of bird species than in regular stands.

Irregular forest management could be valuable in diversifying woodland habitat, particularly if

using group based silvicultural systems, where the groups could provide adequate habitat for bird

species found in the early successional stages. He concluded by stressing the need for using a

range of silvicultural systems to provide habitat diversity at a landscape scale, and noted the

important interaction with the management of deer.

The first afternoon and the second day saw the delegates make the most of the marvelous spring

weather, with numerous stops around the estate to illustrate the relationship between

management practices and their impact upon biodiversity. One stop at Farnham Woods showed,

in particular, the benefit of regular monitoring, such as that provided by the AFI’s stand

monitoring system. This provided a detailed summary of the stand’s composition, structure and

capital value, thus enabling management to make precise and timely harvesting interventions

specific to that stand. The next intervention in two years’ time would focus on removing mostly

mid-diameter ash trees, with the aim of encouraging more oak regeneration. This intervention

would also see the installation of permanent extraction racks; essential for harvesting in irregular

stands, but also a consequential benefit to biodiversity.

Continuous Cover Forestry Group 4.1 Spring 2015

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Fig 1: An ash dominated stand undergoing

transformation to full irregularity. The understorey

has been recently removed and extraction racks have

already been marked in blue

Fig 2: Andy Poore explaining the virtues of the AFI

stand monitoring system

The topic of incorporating a means of measuring biodiversity into the stand monitoring

procedure was also discussed. This might be accomplished by monitoring key indicator species

such as leaf miner moths. Although not currently feasible, it is hoped that this may become a

possibility following the completion of the Rushmore biodiversity project. If successful, this could

provide an effective abbreviated measurement of biodiversity within stands, helping to inform

the type of management intervention that might be taken.

Other stops illustrated issues relating to the practicalities of coppice management when markets

for hazel products are limited and those for birch (e.g. hurdles for horse jumps) may be close to

saturation. One aspiration for the Estate is to reduce management dependence upon uncertain

grant support, so the lack of viable coppice markets is a major reason for the interest in greater

use of irregular forest management. In the last two decades, the woodland account has made a

profit every year, and Andy Poore estimated that the rate of return on the irregularly managed

stands was about 1-2 per cent.

Continuous Cover Forestry Group 4.1 Spring 2015

Continuous Cover Forestry Group Spring 2015

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Fig 3: Rushmore, South Chase, coppice

Fig 4: Rushmore - Irregular high forest

with some mature trees retained to

conserve rare lichen species

The stands in the Continuous Cover working circle have fairly open stand structures with basal

areas generally between 10 and 20 m2 ha-1. In places this open structure has resulted in

appreciable bramble colonization which may limit natural regeneration potential although it will

be beneficial for biodiversity.

One possible problem is that a good proportion of the mature oak trees have very low increment

and are not appreciating in value, so that in strict economic terms they should be felled in the

near future. However, this could risk losing the regeneration niche to competitive vegetation, so

integration of management of the understorey (e.g. hazel) with that of the overstorey would be

critical to successful implementation of irregular forestry. The relatively long thinning cycle

(interventions every 10-15 years) should help to allow the understorey to regrow and dominate

the ground vegetation. Careful deer management would obviously be critical in achieving

successful regeneration and areas of cut hazel coppice are fenced to limit browsing impacts.

Fallow, roe and muntjac are all present, and measures have been taken to reduce deer numbers

and results from deer impact transects suggests that browsing pressure is declining.

Ash dieback may have considerable implications because this species has been a substantial

component of the natural regeneration. Some preemptive felling has been undertaken to remove

susceptible trees and other species are being favoured in thinnings or enrichment planting to

reduce the extent of the risk from this disease. Research is also being carried out by scientists at

York University to see if there is any effect of the more open environment found within the stands in

the Continuous Cover working circle that might limit the impact of this fungal pathogen and how

this might be influenced by tree genotype.

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Continuous Cover Forestry Group June 2015

Spring 20182.1

Some key points from the two days included:

• Variety is crucial. In terms of stand size, density, composition and structure. Although the

irregular high forest working circle demonstrated higher levels of biodiversity (for the species

sampled), the continuing presence of managed coppice stands and areas of minimum

intervention would be crucial for some species.

• Stand monitoring is essential in forming educated decisions when attempting to alter the density,

structure or composition of the stand for both economic and environmental objectives.

• It is important to understand how management actions impact the attributes of the stand and in

turn, the functional resources for biodiversity e.g. thinning intensity/frequency affects the height,

volume and density of the canopy which in turn affects the insect biomass and availability of

nesting sites for birds.

• Profitable forestry does not have to result in poor levels of biodiversity, the two can be

complementary.

It was inspiring to see such a variety of delegates attending the seminar- with foresters, ecologists

and conservationists all sharing ideas and opinions on the topics presented. The seminar was highly

informative and reaffirmed my belief that the benefits of CCF are diverse and far reaching. The

delegates were very grateful to the Trustees of the Rushmore Estate for allowing the meeting to

take place, to the British Ecological Society for helping to sponsor the event, to the various speakers,

and particularly to Andy Poore for organizing the event and for leading the field excursion.

Tom Haynes, University of Cumbria

Modifed by Bill Mason of CCFG

Supplemented with additional information provided by Keith Kirby, University of Oxford

Photographs courtesy of Tom Haynes and Bill Mason