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  • NWDG/WT workshop to discuss “sycamore: the future for base-rich woods?”, Woodhill Wood, Alva, Clackmannanshire, 1st July 2017

    Attendees: Matt Elliott (WT), Alan Crawford (RDIA/WT), Alasdair Firth (RDIA/WT), Eamon Wall, Simon Stuart, Andy Acton, Brian Coppins, Sandy Coppins, Richard Toleman

    Written by Alasdair Firth, July/August 2017

    Background

    Woodhill wood is a largely broadleaved woodland on south-facing slopes of the Ochil hills on the north side of the lower Forth valley. The base rock is basalt, which overlies sedimentary rock and breaks down to form rich brown earth soils. The woodland canopy is composed mainly of sycamore and ash, along with minority species which include hawthorn, holly, hazel, oak, beech, larch and remnants of wych elm. By far the largest areas of single species domination in the wood is the central area which is composed of high, medium-aged sycamore, with very occasional ash. In areas like this with high forest sycamore canopy there are no young trees but there are many seedlings, almost entirely ash; there are no sycamore seedlings. In other parts of the wood there are some younger trees, including sycamore and hawthorn. The woodland floor has a scattering of species at moderate cover, especially Mercurialis perennis dog’s mercury and the grass Brachypodium sylvaticum wood false-brome along with other species indicative of rich soils and shade like upland enchanters nightshade Circea x intermedia. Roe deer are present in the wood in low densities. There is a network of paths through the wood. The wood (c74 hectares) is owned and managed by the Woodland Trust.

    The site visit and workshop were undertaken to discuss the implications of the potential changes in the woodland canopy from Chalara ash dieback. Chalara is present in the wood and is already killing some trees.
    The visit consisted of a series of stops at relevant points of discussion. The main topics discussed were the historic factors that led to the current woodland composition and structure, the characterisation of trees like sycamore and beech as non-natives and the implications for biodiversity, the impacts of tree diseases and objectives of woodland management at Woodhill wood and other base-rich woods in general.

    Sycamore Acer pseudoplatanus is not usually considered a native species in Scotland. It is thought to be either an archeophyte (introduced by humans before 1500) or a neophyte (introduced by humans after 1500). In some situations (for example Glen Urquart) it has been removed from woods as a non-native invasive species. Acer campestre field maple, the only Acer native to the British Isles, is considered native in England but not in Scotland. Sycamore trees support a large number of invertebrate species and their bark is suitable for colonisation by a wide range of lichen species. Sycamore is suited to similar conditions to ash, but is slightly less tolerant of wet conditions and tends to suffer from butt rot when grown in wet places. Casts heavier shade than ash, the wood is not quite as versatile, but has some specialist uses and is generally a good timber. It generally seeds freely and spreads, especially into enriched or disturbed ground where there are sufficient light levels. There is some evidence of alteration of generations between ash and sycamore. Sycamore is a minor component of many continental beech woods. In Woodhill wood sycamore - and in fact most species other than ash - are not currently regenerating. Much of Woodhill wood already has a dense canopy and there is little ground disturbance in the open areas. Generally in Scotland, sycamore is undergoing range expansion mainly through natural regeneration along with some planting.

    Site visit

    After entering the wood, the group discussions started with thoughts on the general historical and ecological context of this wood. We discussed the background of sycamore in Scotland and whether its spread should be thought of as having a negative or positive impact. Was this spread ‘natural’, ‘an invasion’ or maybe ‘semi-natural’? We moved on to discuss other ‘non-native’ tree species (there was some debate about what native/non-native actually meant), tree diseases, future change in woodlands and silvicultural management. We often returned to discussing the objectives of management.
    In some previous management recommendations (for example for woodlands in the Clyde valley) an upper limit of 40% sycamore in the canopy was proposed. This percentage has also been used to assess designated woodlands (SSSI/SAC) for favourable or unfavourable condition. We discussed why this had been suggested and whether this was appropriate. We also talked about whether such an upper limit should be proposed for other species, for example oak in western woodlands and pine or birch in more eastern and upland woods. The discussion revolved around resilience and whether, as in other parts of the world, forests in Scotland with a greater number of species in them would be more likely to survive in the face of threats from tree disease, climate change and other long-term impacts.

    We also discussed woodland management and silviculture. The detailed history of Woodhill wood was not known to the group, and it was unclear whether the main sycamore areas of the wood were a result purely of planting or of a mixture of planting and natural regeneration. In the main sycamore areas the trees are even-aged (probably around 70 years old) and of low silvicultural value for their timber, having small crown diameters and often warped or crooked main trunks. Some are multi-stemmed. Perhaps sycamore was originally planted as a resource for the silver mines nearby, but as the mine operated nearly 200 years ago this would not explain why there were stands of sycamore of this more recent date. The last felling here was probably around the time of the Second World War. Extraction on the steep slope would be difficult. It seemed unlikely that there would have been an alternation of generations between ash and sycamore on this site.

    A stone dyke at the top edge of the sycamore marked a vague transition to more mixed woodland where ash and silver birch were more dominant as well as some oak, elm and hawthorn along with sycamore. This mixed woodland above appeared to be of similar age to the sycamore, with the exception of some much older open-grown oak. We debated whether Woodhill wood was previously much more open, like many of the small stands of trees on the southern slopes of the Ochils. If so, it probably infilled with trees once grazing was removed.
    Chalara ash dieback is already seriously affecting trees in the wood although it was only confirmed here this year, and we discussed this disease in detail.

    Matt Elliott gave some details of disease pathology. Ash dieback is a fungal infection that disrupts water transport in the tree, causing dieback. It is often visible in the cambium layer of younger shoots. The fungus is a disease of Manchurian ash, but this species of ash is very tolerant of it and it causes only minor symptoms. In European ash, the fungus has much more serious consequences. It causes a cyclical infection, the fungus entering the leaves, replicating on the rachis after the leaves dropped, and spreading through young leaves again in the spring into the wood of the tree itself. Because re-infection occurs annually from leaf litter, places where leaves survive longer, like damp places, will have higher infection rates year-on-year. Ash dieback will have very high costs but it is not clear who will pay these. Many ashes are wayside and hedgerow trees, and tree safety will be an issue in the longer term.

    With the buffer zones proposed when the disease was first found in Great Britain having failed to stop the spread of the disease, it does not seem that is will be possible to slow the rate of spread. The fungal spores are bourn on the wind and can travel at least 10km. Road corridors have become corridors for spore dispersal because vehicles move air along them. With the high spore production rates due to the large amount of infected leaf litter it is unlikely that any ash in Scotland will remain free of ash dieback in the long term. The fungus is also transported by blown leaf litter and probably through the movements of birds and other animals.

    Ash dieback is different from Dutch elm disease because elm can survive, although since older stems are killed, it is suppressed. Chalara ultimately kills ash. Chalara has more unknowns and tolerance may vary over the country, but some places are likely to lose ash sooner than others. There are still uncertainties and it is a case of waiting to see what happens in the long term.

    Other tree diseases are like Dutch elm disease and Xylella are also a threat to base-rich woods. Although there is no potential buffer zone for ash there is potential to develop a buffer zone against Dutch elm disease in wych elm around or north of the Great Glen. Dutch elm disease is moving south-west along Loch Ness side, but there are substantial gaps with little or no elm between there and the west coast where the largest elm populations in Scotland remain. Proactive management for elm has worked in the past, for example Edinburgh still retains elms because the city council actively removes diseased-looking trees.
    The import of plants is a potential source for the spread of tree disease. Xylella is a major disease of olives and has the potential to affect a wide range of plants, including Acers like sycamore. With the dual threats of ash dieback and Dutch elm disease, it seems that base-rich woods in Scotland are already more seriously threatened by disease than most. However, globally, the most threatened forests or stand-types are monocultures. For example Phytopthora lateralis has affected commercial harvests of Lawsons cypressus, which is planted as a single species crop in North America. Where there are more tree species, disease spread is potentially slower and less devastating.

    On the point of whether sycamore is more of a ‘threat’ than beech or western hemlock or rhododendron we came to the conclusion that the effect of the dominance of sycamore in a wood is different than that of these other species, although ideally perhaps no single species should be dominant.

    Non-native species can certainly add something to a wood (and perhaps, as a non-native species ourselves we should be grateful for that). But they can also significantly alter a wood from what was there before. Questions about what is desirable and what is not should revolve around the objectives for the wood rather than the native or non-native status of the species concerned.

    However, a species that is a benefit in one site type might be considered a threat in another. For example, there are differences in nutrient cycling rates in acidic and base-rich woods, so leaf litter like beech litter that decomposes fairly quickly in soils with high nutrient turnovers (base rich woods) may persist for longer in woods with slower turnover rates (acidic woods).
    We briefly compared the characteristics of beech and rhododendron. Both species can fundamentally alter the ground flora, acidify the soil and eliminate other species through preventing their regeneration. The main difference between them is that beech is less insidious. Rhododendron is vigorous in most conditions where it is damp enough. Beech, in woods like Woodhill wood, has very low regeneration rates (evidenced by the lack of seedlings). Beech litter breaks down fairly quickly in soils with high nutrient turn-over, but rhododendron leaves are resistant to decomposition. Beech is probably not a great threat in base-rich woods, because although individual beech trees can grow well, and grow to very large sizes, they tend not to regenerate as freely as in more acidic conditions; here they would add diversity rather than altering the wood completely. There were some differences of opinion in the group over whether movement to beech dominance in the long term would be positive or negative.

    We discussed the relationship between trees and lichens. Woodhill wood has lower lichen numbers and diversity than other comparable woods for example further west. The main cause is historic air pollution and possible discontinuity of habitat. Ash trees are a good habitat for lichens, but as well as the species of host tree, the age, position and the form of the tree are important. Lichens need to find the appropriate niche habitat and isolated older individual trees provide a larger number of niches, especially in terms of light levels, than do most trees in woodland. Patchiness is beneficial for biodiversity. Monitoring of the wood can be very helpful to identify particular areas or patches in woods which have high biodiversity or potential for this to develop. Management might also aim to create suitable host trees for lichens by allowing open-grown structures to develop.
    We stopped at an open area dominated by bracken. There was a little regeneration of ash around the edges of the bracken, but nothing else. Near to this the woodland was more diverse with ash and silver birch and some very old oaks. We discussed whether bracken glades like this were beneficial for biodiversity or whether bracken should also be considered an invasive species, albeit native. Would planting be appropriate here and might a tree canopy naturally suppress the spread of bracken? It might be appropriate, if possible, to manage woods at a scale that takes things like this into consideration, for example, opening up the canopy in areas away from bracken colonies where regeneration may occur without the threat of bracken invasion.

    The final area we looked at was an area near the bottom of the wood where the canopy had previously been opened up by the removal of a coup of moderate size, possibly around twenty years ago. Regeneration had been abundant, mostly of ash, with sycamore, hawthorn, cherry and regrowth of sycamore from cut stumps. The ground disturbance at time of felling may have aided sycamore regeneration since we had seen no seedlings in the rest of the wood.

    Summary

    The Woodland Trust’s general objectives for the woods they manage relate mainly to improving woodland biodiversity and increasing peoples’ understanding and enjoyment of woodland. Although the most of the trees in Woodhill wood are non-native sycamore, the management objectives for the wood mainly relate to recreation within a woodland setting and the differences between ash and sycamore are not likely to affect this much. Woodland Trust management guidelines refer to a long term vision of restoring or transitioning non-native plantations and secondary woods to woods of predominantly native species composition and semi-natural structure. It is not clear how this could be implemented at Woodhill wood where native species are a minority and the structure will continue to be affected by impacts of tree disease. The complexities of this relatively small woodland indicate that increasing a woodland’s long-term resilience to changes imposed by tree disease and climate may be at least as important as specific objectives or targets for native species and biodiversity in determining future composition and structure in base-rich Scottish woods.

    References:

    How to Replicate the Functions and Biodiversity of a Threatened Tree Species? The Case of Fraxinus excelsior in Britain. Mitchell et al. Ecosystems. 2016
    Sycamore. Townsend. Woodland Trust position statement. 2008
    Urquhart Bay. Management Plan 2013-2018. Woodland Trust. 2013
    Wood Hill Wood – Management Plan 2016-2021. Woodland Trust Scotland. 2016
    A history of the Native Woodlands of Scotland, 1500-1920. T.C.Smout, Alan R MacDonald & Fiona Watson. Edinburgh university Press 2005
    Stand dynamics in Tilio-Acerion woodlands of the Clyde Valley. Thompson & Peace. Highland Birchwoods. 2005

  • Dodgson Wood from HDDN on Vimeo.

     

    This is the first in a series of videos produced by Cumbria Woodlands as part of our Heritage Lottery Funded ash heritage project: ASH ECOLOGY AND CULTURAL LANDSCAPE OF CUMBRIA - A RESPONSE TO ASH DIEBACK.

     

    Five questions with project manager Clare de Villanueva:

     

    How does what you’re doing at Dodgson Wood fit into the larger ash project as a whole?

    Dodgson Wood represents a fairly typical lakes woodland, with ash as a part of a species mix. This trial site is looking at ash in a protected woodland setting (it’s a SSSI). Our other trial sites incorporate ash in a productive woodland, as pollards or coppice. There is a long history of management in the Dodgson Wood area, as evidenced by the archaeology, and this has heavily influenced the species mix present there now.

    What is the purpose of the exclosures?

    Historical management plus grazing, has resulted in a woodland that is not particularly diverse and has many trees of a similar age. When combined with thinning of the canopy by felling several oak trees, the exclosures provide opportunity for natural regeneration. This thinning increases the amount of sunlight reaching the forest floor, which lets other plants and trees grow, as long as you keep the deer and sheep out!

    What are your hopes for the Dodgson Wood trial?

    We'd like ash seedlings to regenerate naturally, and they’ll be protected from grazing animals by the fence. We anticipate that a small proportion of this natural regeneration will show some form of tolerance to ash dieback. Natural regeneration is ideal, because it results in genetic variety from the different seeds, so it is more likely that some saplings will show tolerance to the disease. If a woodland has a high diversity of species and ages, then it's more robust to future challenges such as pests, disease and climate change.

    Which other organisations have you worked with on this part of the project?

    We have worked closely with the National Trust – their knowledge and expertise is invaluable and they were happy to get involved with the project, letting us use their land and donating their time. We worked with Rusland Horizons’ apprentices for a few fun and productive days in March. They provided the skills and labour to successfully erect the deer exclosures. Natural England were also helpful with advice and support, especially with the site being a SSSI.

    What's next for the ash project?

    We have a number of other trial sites running which aim to represent different environments where ash grow in Cumbria. There will be a series of videos one for each trial site to cover coppice, productive woodland and pollards. Watch this space!

  • We're really pleased to announce the line-up for our PAWS Certification day:

    • Louise Hackett from the Woodland Trust: Why we care about PAWS, why are they important; a view from the Woodland Trust.
    • Owen Davies from FSC UK: Overview of certification requirements and what is in the UKWAS standard, including an update on its latest review.
    • Heather Swift of the Woodland Trust will illustrate how they go about putting this into practice on their own sites, focusing on planning and audit trails.
    • Vicky Bowman of United Utilities will then give the view from a private company to illustrate how they are putting it into practice.
    • Angela Douglas FICFor BSc(For) from A Douglas Consultancy: An auditor’s role - what is and is not done!

    Full information is here: PAWS Certification Day

  • Come along to Rusland Horizons Woodland Crafts and Tales Weekend at Stott Park Bobbin Mill on the 24 & 25 June. It’s a free event and they are hoping it will be packed out with folk who are keen to enjoy the friendly atmosphere and fascinating demonstrations, walks, talks and lots more.

    At the event there will be a greenwood workshop, hazel hurdle making, swill baskets, bobbin mill tours, walks, talks, storytelling with Taffy Thomas, the annual Coppice Association North West charcoal earthburn, food and music.

    More info on their Facebook page www.facebook.com/RuslandHorizons/ and website www.ruslandhorizons.org/whats-on/2017/april/12/woodland-crafts-and-tales.aspx

  • 09 May 2017

    Working on PAWS sites

    Caption: The Woodland Trust explain the importance of working to improve the long-term survival of PAWS sites

    Cumbria Woodlands and the Woodland Trust are working together to bring important ecological woodlands back into healthier condition.

    We do this with a range of free advice and by helping owners access grants to undertake work on their woodlands.

    If you think you have a Plantation on Ancient Woodland (PAWS) site please contact Jamie (jamie@cumbriawoodlands.co.uk).

    This excellent short film gives a great overview of how to work on PAWS sites.

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