New guidance on Ash dieback in SSSI woodland

Natural England has released new guidance on Ash dieback.  

The guidance is specifically designed for SSSI woodland (Sites of Special Scientific Interest) and focuses on a set of commonly asked questions:

• Will all my ash trees die? 
• Should diseased trees be felled? 
• Should I fell healthy trees now? 
• How can I manage the structure of my wood? 
• Should ash coppice or pollards be cut? 
• How will the designated features be affected? 
• How should replacement trees be established? 
• What replacement species can be used? 
• What should I do about sycamore? 
• Will my wood be classed as “unfavourable”?

Over half of the woodland and wood-pasture SSSIs in England contain significant amounts of ash. As nationally important areas for the conservation of biological diversity, it is vital that the impact of ash dieback disease on the SSSI ‘features of interest’ is managed to reduce negative effects where this is possible. 

Whilst various suggestions are made in the guidance Natural England points out that there is only limited experience of implementing many of these in the UK ash dieback scenario. Therefore there is a need to trial different management strategies, monitor their effectiveness, and continue to share practical experience.

It is also very important that this guidance, and the of the Forestry Commission, is tailored to the specific conditions on each site, including: 

• the current proportion of ash and other trees and shrubs present
• the woodland structure
• existing issues and challenges acting on the wood
• its context in the surrounding landscape
• the SSSI features of interest
• the owner’s objectives
• public access and safety

The advice has been summarised in the table below.  The full document can be downloaded here.

New report assesses alternative tree species to Ash

We have been closely following Ash dieback over the last two years and have spoken to many woodland managers and stakeholders about the impact of the disease.

One of the most frequently asked questions relates to how woodlands will adapt to the disease, and in particular which tree species will make effective replacements.

Until recently our response to this question was fairly limited and was based on a few species such as small leaved lime.

It is therefore very timely that Natural England has released a new report that may help guide practitioners in the selection of alternative tree species that are ecologically similar to Ash.

The report (Assessing and addressing the impacts of ash dieback on UK woodlands and trees of conservation importance) examines the ecological function of 11 tree species considered most likely to replace ash across the UK. 

It also provides a range of case studies showing how existing management plans may be adapted to conserve ash-associated biodiversity should significant ash dieback occur.

In this post we have attempted to summarise the main findings of the report to assist with the dissemination of the findings.  If proactive management action is being considered we recommend reading the report in full.

The eleven tree species looked at were:

• rowan
• birch (silver or downy)
• field maple
• sycamore
• aspen
• oak (pedunculate or sessile)
• beech
• lime
• alder
• walnut (black or common)
• wild cherry

The ecological similarity of these alternative to Ash was assessed by considering three main factors:

• their ecological functioning
• the number of ash-associated species they support
• their traits

Ideally any alternative tree should be similar to ash in all of these characteristics.

Ecological functioning

Ash lies at an extreme of the ecological range of native tree species in the UK. It produces nutrient-rich highly degradable litter that does not form a deep litter layer and which maintains a high soil pH.

For ecological functioning the  11 alternative species were assessed in terms of leaf litter decomposition rates, litter quality (chemical and physical properties), nutrient cycling and succession rates.

A change from ash to a tree species with very different ecosystem functioning (e.g. oak or beech) will result in changes in the characteristics of the woodland: slower nutrient cycling, increased carbon storage and changes in the ground flora species present.

Ash-associated species

Around 1,000 species are known to 'use' Ash trees and tree species native to the UK support more ash-associated species than non-native tree species.

Native oak species were found to support the greatest number of ash-associated birds, invertebrate, lichen and mammal species.  

Elm, hazel, oak, aspen and sycamore were found to support the greatest number of the ash-associated species that are most vulnerable to ash-dieback. However elm remains susceptible to Dutch elm disease and is therefore not widely suitable as an alternative to ash.

Traits of alternative tree species

The traits of trees such as tree height, bark pH and fruit type indicate, in part, the type of habitat created by a tree species and the resources available to species that use the tree. Ideally the traits of any alternative tree should be as similar as possible to ash.

Of the native tree species assessed elm had the most traits the same as ash followed by silver birch and rowan.

Results

The study found that the alternative tree species that support the greatest number of ash-associated species are very dissimilar to ash when assessed by traits and ecological function. 

• Oak supports 640 of the 955 ash-associated species and beech supports 505 ash associated species.
• However, in terms of ecological function, oak and beech have much slower rates of leaf litter decomposition and nutrient cycling than ash and their canopies cast a much darker shade which will influence the ground flora species.
• Alder is similar to ash with respect to ecological function (leaf decomposition rates, litter quality and nutrient cycling) but supports fewer ash-associated species (389 out of 955)

As such the method that is most suitable to assess how similar the alternative tree species are to ash will depend on the objectives at the site, for example maintaining ash associated species or maintaining the woodland character and ecological function.

Management scenarios

Six management scenarios that could be applied to woods infected with ash-dieback were considered over two time periods (1-10 years and 50-100 years). The scenarios were:

1. Non-intervention – stands are allowed to develop naturally with no interventions.
2. No felling with natural regeneration promoted – no felling but otherwise stands initially managed for natural regeneration.
3. Felling – all ash trees and coppice removed in one operation with, if necessary, additional trees of other species cut to make the operation more viable.
4. Felling and replanting – all ash trees and coppice removed in one operation with, if necessary, additional trees of other species cut to make the operation more viable. Then active management to replant with alternative tree and shrub species.
5. Thinning – regular operations to thin stands by removing diseased and dead trees or coppicing ash, with, if necessary, additional trees of other species cut to make the operation more viable.
6. Felling with natural regeneration promoted – all ash trees and coppice removed in one operation with, if necessary, additional trees of other species cut to make the operation more viable. Then active management initially to achieve natural regeneration in the stand, with subsequent management to develop overstorey species.

In the short term (1-10 years) more ash-associated species were supported under scenario (5) ‘thinning’ than scenario (6) ‘felling with natural regeneration promoted’.

In the long-term (50-100 years) there was little difference between scenarios (5) and (6) in their impact on obligate and highly associated ash species with of these species predicted to decline in abundance or be at risk of extinction. 

However, the confidence level of these assessments is only low to medium suggesting that the actual impact on ash-associated species is currently only partially understood.

For species 'partially associated' the assessment is somewhat brighter:

• Species partially associated with ash are generally predicted to decline initially following the onset of ash dieback but after 50-100 years the majority of partially associated species are predicted to be unchanged in abundance compared to current population levels due to an increase in the abundance of other tree species which they utilise.

Overall there is a clear difference in the response of highly associated species, which are predicted to either decline or go extinct and the majority of partially associated species which are predicted to remain unchanged in abundance after 50-100 years.

Conclusion

When woodland managers are considering which alternative tree/shrub species to regenerate or plant in order to mitigate the impacts of ash-dieback on biodiversity, the number of ash-associated species supported is only one factor to consider. 

Woodland managers should also think about other information provided in this report such as the impact alternative trees might have on ecosystem function and factors which will influence the occurrence of ash-associated species in the woodland, such as: woodland structure, food availability, the size, shape and number of holes in trees for roosting bats and hole nesting birds, interactions between species, and changes in woodland ground flora composition.

Ash dieback is just one of several diseases and other potential drivers of change within woodlands within the UK. Other tree diseases and drivers such as grazing, pollution and climate change will also need to be taken into account. 

Management for biodiversity will usually be considered together with the other objectives of woodland management including timber production, amenity, flood prevention and carbon sequestration.

Ecosystem services from Environmental Stewardship that benefit agricultural production

Natural England has released a new report entitled "Ecosystem services from Environmental Stewardship that benefit agricultural production".  Given that trees and woodland form a key part of the agricultural landscape we've taken a quick look at the report to see what it says about them.

We've borrowed heavily from the report for this article - for the complete document click here.

Overview

This report reviews the ecosystem services provided by Environmental Stewardship (ES), the main agri-environmental scheme in England. It is concerned with those that are of benefit to agricultural (especially crop) production.

• Ecosystem services can be described as the full range of benefits that people and societies obtain from biological systems, including provisioning, regulating, cultural and supporting services.
• Key ecosystem services considered include soil formation, nutrient cycling, carbon sequestration, water regulation and purification, genetic resources, pest regulation and pollination.

Role of Environmental Stewardship in providing ecosystem services

Environmental Stewardship has the potential to enhance a range of ecosystem services of benefit to agricultural production, though relatively few options have been designed specifically with this purpose in mind. 

Farm woodland in the Sevenoaks area

ES options generally involve either taking land out of production or modifying the production system to enhance environmental benefits, thus reducing production. Indeed, payments to farmers for their participation in the scheme are calculated on the basis of 'profit foregone' as a result of taking up the options concerned. 

Although ES options may enhance overall primary production in some cases (e.g. of woodland or hedgerows), they do not generally increase agricultural production. However, they may help to reduce costs of production by reducing use of inputs such as diesel or fertiliser on less productive areas of land.

ES options involving trees, hedges, woodland, scrub and orchards

What do the results show?

The following sections summarise the role played by trees and woodland in providing ecosystem services in the context of ES and agriculture.

In-field trees

Hedgerow planting on farmland near Ightham

• In-field trees can substantially contribute to carbon sequestration and soil formation by providing organic matter for decomposition.
• The overall impact is likely to be small, although there should be some benefit overall at the national scale.
• Ancient trees will not sequester carbon to the same extent as younger trees. However, this option will prevent the destruction of older trees and so limit the release of stored CO2 into the atmosphere.
• For ancient trees on cultivated land, the 15m radius grass area around the base of the tree will provide some of the benefits of an in-field buffer.

Woodland edges

• Woodland edges will provide a year-round cover of vegetation that can sequester carbon, contribute to soil organic matter accumulation and reduce water erosion.
• Any reductions in wind erosion due to the woodland edge option are likely to be negligible compared to the protection afforded by the woodland itself.

Wood pasture and parkland

• Wood pasture and parkland puts relatively little pressure on the land and so it is sustainable, assuming that it is managed appropriately.
• There is a year-round cover of vegetation and the trees can sequester and store relatively large amounts of carbon.
• Whilst there is no direct evidence from wood pastures, their potential for sequestration and/or contributions to soil fertility can be inferred from data relating to woodland.
• Poulton et al (2003) quantified C and N content of soil in land that was arable for centuries until the late 1800‘s and has since reverted to woodland. The acidic site (mainly oak) gained 2.00 t C/ha/yr over the 118-year period (0.38 t in litter and soil to a depth of 69 cm, plus an estimated 1.62 t in trees and their roots); there were also gains of nitrogen.
• Hughes-Clarke & Mason (1992) examined 35 field corner plantations adjacent to arable fields and noted a significant increase in total N and total C under the plantations compared to the arable land.

High forest near Sevenoaks

Trees can increase the rate of infiltration (Broadmead & Nisbet, 2004) which will assist in water regulation. Work in the Pontbren region in Wales has demonstrated that areas of sheep pasture planted with trees can increase the infiltration rate by up to 60 times after 6 years, although significant increases were observed after only two years (Carroll et al., 2004). 

Creation of wood pasture (HLS option HC14) will have the greatest benefit, but restoration and maintenance options (HC12 and 13) will also have benefits in terms of maintaining the ecosystem services provided by these habitats.

Woodland

• The role of woodlands in regulating water quantity will be the primary benefit to agricultural production, although the beneficiary may not be the farm implementing the option, but a farm downstream.
• Managed woodland can be used for the production of wood as well as livestock.
• Carbon sequestration in conifer and broadleaf woodland is estimated to be in the order of 11 t/ha/year.

Scrub

• The presence of a vegetative cover can assist in preventing soil erosion and creating a reservoir for beneficial soil biota.
• Where it is used as a buffer, there will be some benefit to agricultural production due to reduced losses of soil and associated soil organic matter, and a reduced potential for runoff.

Orchards

No Mans Orchard near Canterbury

• These systems, like woodlands and wood pastures, put little pressure on soil resources and can contribute to soil formation and water regulation.
• ES option HC21, creation of traditional orchards, will have major ecosystem services benefits if created from more intensively managed land, whilst options HC18, HC18 and HC20, will benefit agricultural production as the orchard will be maintained or restored so that fruit production continues, whilst also providing other ecosystem services.

Survey of woodland owners – your views please!

The BritishWoodlands2012 survey is run by the Sylva Foundation and supported by Natural England. We'd also like to hear from farmers and other land managers who are considering creating woodland on their land.

The survey asks about motivations for woodland management, planting and support.

The survey builds on work that has been carried out by Cambridge University‟s Department of Land Economy on five occasions over the last 50 years. Their most recent survey report from 2005 provides some context for a current project entitled "Private Woods in Crisis?"

We hope the survey will help us to:

• gauge the current level of sustainable forest management in British privately-owned woodlands
• assess the potential for woodland creation
• assemble evidence of the level of public benefits that are delivered from private woodlands
• find out why some woods remain unmanaged
• provide ideas to contribute to improvements in grants and to grow the domestic timber markets

The survey should take about 20-30 minutes to complete. All data will be treated with the utmost confidentiality. Results will be presented in an amalgamated version only and will be used to help inform us about how we can best support the woodland and forestry community.

People who take the survey will be invited to a woodland conference at Oxford University to be held in December 2012 at which the results of the survey will be discussed. 

The survey is supported by Royal Institute of Chartered Surveyors, Forestry Commission, Woodland Trust, Natural England and the Institute for Chartered Foresters.

For further information contact Chris.Reid@naturalengland.org.uk

We are encouraging woodland owners, managers and agents to complete the new online questionnaire survey by 30 September 2012.

Sustainable forestry strong in England

Latest figures published by Forestry Commission England show our woodlands are incredibly well protected and sustainable forestry remains strong.

According to records, just 0.4 per cent of trees felled in England were done illegally without a felling licence. Conservation habitats, such as heathland, have been restored from commercial plantations whilst keeping a slowly expanding wooded area overall. A thriving timber industry has increased domestic supply as imports have fallen.

Simon Hodgson, Forestry Commission England Chief Executive said:

“For the first time we have been able to publish a suite of new statistics to show what is happening to woods and forests in England and how Forestry Commission England is performing.

“The overall picture is great news for us. Protection of our woods and forests is strong with miniscule amounts of illegal felling. The general public are very much our eyes and ears on the ground and we are always heartened at the public’s willingness to report suspected illegal activity and we are developing an online system to make this quicker, easier and more accurate.

“We see domestic timber supplies increasing while imports shrink and a growing woodfuel network all of which boosts the local green economy. Commitments to restore and recreate conservation habitats from private and public plantations are being met while we see the overall area of woodland expanding."

The Forestry Commission remains a leader as a significant land manager in the care of the Engalnd’s best wildlife conservation sites - Sites of Special Scientific Interest (SSSIs) – with 99.6% in target condition.

“All that said significant challenges remain. Everyone agrees we need much greater growth in creating new woodlands and we are working to significantly increase long term investment from the private sector. We are working to mitigate the threats from a changing climate to trees in the future from new pests and diseases and poor growing conditions. Last, but most certainly not least, is the appalling record of Health and Safety in the forestry sector: skills and training are high but the number of fatalities in a small industry must be tackled."

Castle Head FSC - Tree Planting - Feb 2009

“We are already working with the sector to implement recommendations from the Forestry Regulation Task Force and look forward to receiving the Independent Forestry Panel’s final report to Government.”

27 June 2012

Forestry Commission News release 15523