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Publication - Consultation Paper

Beavers in Scotland: consultation on the strategic environmental assessment

Published: 12 Dec 2017

A consultation on the policy to reintroduce beavers to Scotland and the strategic environmental assessment of this policy.

170 page PDF

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170 page PDF

3.0MB

Contents
Beavers in Scotland: consultation on the strategic environmental assessment
4.3 Beavers and bryophytes, fungi and lichens

170 page PDF

3.0MB

4.3 Beavers and bryophytes, fungi and lichens

4.3.1 How beaver activity affects bryophytes, fungi and lichens

Bryophytes (mosses and liverworts), fungi and lichens are diverse groups of organisms that make up a large proportion of Scotland's biodiversity. Over 1,500 species of lichen occur in Scotland and the Scottish Biodiversity List includes 210 species of bryophyte, 207 fungi and 486 lichens. The majority of these species will never be affected by beavers because their habitat occurs mainly or entirely outside potential beaver habitat. However, Scotland is an internationally recognised hotspot for biodiversity associated with oceanic woodland. In particular, many species of bryophyte and lichen have the majority or all of their European population in Scottish woodlands (example species and maps are presented elsewhere). Since beavers directly affect trees - and therefore woodland structure, continuity and composition - their effect on woodland oceanic bryophytes and lichens is highlighted here. Fungi are less well known in terms of their distribution and conservation status. However, they provide key ecosystem services, so are considered here in terms of the mechanisms by which beavers may affect them.

When considering the overall impact of beavers on bryophytes, lichens and fungi, it is important to consider the scale of assessment. For example, most of these species respond to small-scale habitat variation as much as, if not more than, broad habitat variation. This means it is necessary to consider the impact of beavers not only on broad habitats, but also on the occurrence of small-scale habitats such as dead wood, boulders within woodland and deeply fissured bark on old trees. The biodiversity benefits of beavers should also consider the national and international impact of beavers as well as local impacts. It is important to compare local species losses and gains against each species' wider distribution. For example, negative local impacts on the globally restricted oceanic bryophytes and lichens referred to above should not be compared like-for-like with positive local impacts on species that have much wider global distributions.

The diversity of bryophytes, lichens and fungi makes it difficult to make general statements about the potential impact of beavers. It is possible, however, to identify the main mechanisms by which beavers may affect these species. A summary of the potential interactions between beavers and bryophytes, fungi and lichens is presented below (see Table 4.3.1) where possible these have been attributed to a neutral, positive or negative effect.

4.3.1.1 Loss of old woodland micro-habitats and habitat continuity

Species diversity is positively correlated with micro-habitat diversity. Old woodland supports a wider range of micro- habitats and associated species than young woodland. Beaver activity is likely to result in localised loss of old woodland micro-habitats through medium - to long-term loss of old trees ( section 4.2). This will result in medium - to long-term localised loss of old woodland species.

Species associated with young tree micro-habitats may increase in abundance, but these are much more common and widespread in Scotland.

Many old woodland species are poor recolonisers. Micro-habitats associated with old woodland may also take many years to recover. This may result in local extinction of old woodland species or species associated with old trees, many of which have their core European populations in Scotland, such as Atlantic Hazelwoods as discussed below.

A more detailed description of the importance of micro-habitat diversity and temporal habitat continuity is provided in the SBT monitoring report on lichens.

Atlantic Hazelwoods

Atlantic hazel provides habitat for a diverse assemblage of oceanic lichens. A community of crust-like lichens called the Graphidion grows on young smooth-barked stems while older, rougher stems support a community dominated by larger, leafy lichens called the Lobarion. The coexistence of these two lichen communities, along with the equitable oceanic climate, stand structure and the long temporal continuity of many Atlantic hazelwoods, all contribute to the ability of Atlantic hazel to support a high diversity of lichens.

Under natural conditions, hazel is a multi-stemmed shrub. Despite this growth form being similar to hazel that has been coppiced, there is no evidence that species-rich stands of Atlantic hazel were ever coppiced in the past. An individual is referred to as a 'stool', with each stool normally supporting a range of stem ages from thin, young stems (often called 'sun-shoots') to large old rough-barked stems. As the largest and oldest stems die or snap off under their own weight, they create a gap that allows replacement by young hazel stems from the bank of sun-shoots at the stool base. A single naturally self-perpetuating hazel stool can therefore be ancient and, while individual stems have a finite life, they provide long periods of ecological continuity of young, smooth-barked and old rough-barked stems. This temporal microhabitat continuity is an important determinant of lichen diversity. The loss of all, or a particular age-class, of stems from a stool, either through coppicing by humans or felling by beavers, can result in the loss of long-term habitat continuity and thereby loss or deterioration of ancient woodland lichens assemblages.

Atlantic hazel occurs in oceanic areas in western Britain. This climatic association and other attributes associated with hazel as described above result in a high diversity of lichens. While the strength of association between Atlantic hazel and a particular lichen varies, many species are of high conservation value e.g. IUCN near threated or vulnerable, nationally rare or scare and species for which Scotland has International Responsibility. For many Atlantic hazel associates, Scotland is their European headquarters. One endemic species, Graphis alboscripta, occurs nowhere else on earth other than in Scottish Atlantic hazelwoods.

4.3.1.2 Gains and losses in riparian woodland extent and suitability for bryophytes, lichens and fungi

The reintroduction of beavers may be accompanied by incentives to promote riparian woodland restoration and creation. This indirect effect may create future habitat for bryophytes, lichens and fungi. However, there may be localised losses of old woodland supporting bryophytes, lichens and fungi of conservation concern in the long term if beaver-felled trees do not regenerate due to over- browsing by deer. Areas of woodland habitat for these species may also be lost due to flooding, although many species associated with dead wood will benefit in the short to medium term in such circumstances. Beavers are likely to increase the area of wet woodland. Wet woodland supports a different range of species from dry woodland. For example, there will be an increase in mycorrhizal fungi associated with wet woodland trees (e.g. aldercaps) and a decrease in species associated with dry woodland.

Moisture-loving species, such as bog mosses, and scarce species associated with damp, wet wood may increase (Swedish pouchwort Calypogeia suecica and Heller's notchwort Anastrophyllum hellerianum are examples of nationally scarce liverworts associated with damp dead wood - Scotland has an international responsibility for the conservation of such oceanic species). Epiphytic species associated with moisture-intolerant trees may decline if these tree species are lost.

Species vary in their requirements for light and shelter. The more open canopy that would be created by beaver activity will favour species of bryophyte and lichen that require higher light levels but that can withstand exposure. Species that tolerate lower light levels and require shelter to maintain high humidity are likely to be negatively affected. Woodland floor features such as boulders and dead wood are particularly important habitats for mosses and liverworts. An increase in the cover of vascular plants and large, robust bryophyte cover in areas opened up by beavers may have a negative impact on smaller and less competitive woodland floor bryophytes through increased competition.

Many species of bryophyte, lichen and fungus are associated with specific tree species. Medium- to long- term loss of mature trees of species preferred by beaver may result in the loss of a suite of associated species.

4.3.1.3 Deadwood

Beavers may increase the quantity and variety of dead wood, at least in the short to medium term. Many bryophytes, lichens and fungi are associated with dead wood, either as a substrate or, in the case of fungi, as a food source. The long-term impacts of beaver on dead wood habitat are less clear. Depending on beaver colonisation patterns at the landscape scale, there may be fewer large trees in the future to supply large-volume dead wood. Many species of lichen, bryophyte and fungus have strong associations with large-volume dead wood and standing dead wood supports a number of threatened lichens. Standing deadwood supports lichens classed as 'vulnerable' by the IUCN, such as the forked hair-lichen Bryoria furcellata which is on the Scottish Biodiversity List.

4.3.1.4 Historical perspective

The Scottish landscape has changed significantly since the national extinction of beavers several hundred years ago. In this time, habitats have been subject to disturbance through often drastic changes in land use (e.g. conversion to conifer plantations). Hence, many areas, such as Knapdale, have suffered severe habitat reduction, and ancient woodland lichen, bryophyte and fungus populations could be described as remnants, only now beginning to recover. Beavers have the potential to reintroduce a further source of habitat disturbance, albeit one that occurred as a natural component of the landscape in the past. Whether habitats, particularly those that support ancient woodland species, have the resilience to withstand additional disturbance should be a key consideration when interpreting the information available on the effects of beavers.

Table 4.3.1: Summary of potential interactions between beavers and bryophytes, fungi and lichens.

Activity

Mechanism

Positive effects

Negative effects

Notes

Felling

Change in riparian woodland: Opening of woodland canopy and increased patchiness

  • More open canopy due to beaver activity will favour tree-dwelling species of bryophyte and lichen that require higher levels of light but that can withstand some exposure
  • Some tree-dwelling species that tolerate low levels of light and require shelter to maintain high humidity may be negatively affected as beavers create more open woodland
  • An increase in the cover of vascular plants and large, robust bryophyte cover in areas opened up by beavers may have a negative impact on smaller and less competitive woodland floor bryophytes through increased competition
  • Where browsing from other herbivores is high, tree regrowth may be prevented, and this could lead to a reduction in structural diversity and ultimately localised loss of areas of important lichen, bryophyte and fungus woodland habitat

Felling

Change in riparian woodland: Change in relative abundance of different tree species

  • Medium- to long-term loss of mature trees of species preferred by beaver, such as aspen, may result in loss of a suite of associated species
  • Mature trees on river banks are particularly important for lichens in eastern Scotland and support a number of rare or threatened species

Felling

Change in riparian woodland: Change in age classes of trees

  • Old trees provide habitat for a high diversity of bryophytes, lichens and fungi that do not occur in young woodland. Beavers may prevent trees from becoming old at local levels
  • Breaks in the temporal and spatial continuity of old woodland characteristic will have a negative impact on the many bryophytes, lichens and fungi that are poor dispersers and/or colonisers. There is a risk of local extinction for some species

Ecological, or micro-habitat, diversity and continuity are key requirements for many species for which Scotland holds internationally important populations

Felling

Change in riparian woodland: Amount/diversity of fallen dead wood on woodland floor

  • Many bryophytes, lichens and fungi are associated with dead wood, either as a substrate or, in the case of fungi, as a food source. Beavers may increase the amount of dead wood in some areas
  • Any increase in the diversity of dead wood (e.g. size, moisture content, exposure, tree species, orientation) is likely to increase the diversity of these species
  • Beaver activity may result in fewer large trees in the future to supply large-volume dead wood. Many species of lichen, bryophyte and fungus have strong associations with large-volume dead wood.
  • Large standing dead wood supports a number of threatened lichens and bryophytes, some of which may become locally extinct

Much of the beaver-felled timber is removed for food and construction

Positive impacts are likely to be greater in the short term as large-volume dead wood is created, but this benefit may be lost in the long term

Dams/pond creation

Change in hydrological processes on riparian and downstream habitat

  • Wet woodland supports a different range of species from dry woodland. Some species of bryophyte and fungus will benefit
  • Wet woodland supports a different range of species from dry woodland. Some species of bryophyte, lichen and fungus will decline or become locally extinct as moisture levels increase and woodland composition and structure changes

There is overlap between potential core beaver habitat and watercourses identified as being internationally important for water-loving oceanic bryophytes. The impacts of beaver activity on hydrology with respect to these species is unknown but requires monitoring

Dams/pond creation

Changes in water quality downstream

  • Possible positive impact on aquatic lichens, e.g. the protected river jelly-lichen, due to changes to sediment transport and water chemistry
  • Possible negative impact on aquatic lichens, e.g. the protected river jelly-lichen, due to changes to sediment transport and water chemistry

Many effects are unknown

Dams/pond creation

Change in standing dead wood resulting from inundation of trees

  • Standing dead wood, particularly when it has lost its bark, provides an important habitat for a number of lichen and fungus species. Beaver may locally increase standing dead wood in the short term in inundated areas

There is uncertainty about the long-term availability of standing dead wood once trees have died and decayed in an area. However, volumes may be maintained at the landscape scale as beavers abandon territories and colonise new areas

Other

Beaver management

  • Fencing to exclude beavers from sensitive habitat could result in deterioration of habitat for bryophytes and lichens due to under-grazing and subsequent shading by dense herbaceous or tree regeneration within exclosures

It should be possible to use fencing that does not exclude other grazers. Fence requirements will be habitat and site specific

Indirect habitat creation/restoration initiatives as a result of beaver presence

Beavers used to promote opportunities for riparian and freshwater habitat creation/restoration

  • Any riparian woodland restoration programme is likely to benefit woodland bryophytes, lichens and fungi in the medium to long term

Rhododendron control and deer management in particular will benefit bryophytes and lichens

These may be compensatory measures outside the range of beavers to improve habitat for species that will be negatively affected within beaver habitat

4.3.2 Distribution of bryophytes, fungi and lichens in the beaver policy area

The following section concentrates on those bryophytes, fungi and lichens of conservation importance that are likely to overlap with core beaver habitat and as such maybe positively or negatively affected by beaver activity.

4.3.2.1 Bryophytes, fungi and lichens of conservation importance

To determine whether the activity of beavers on bryophytes, fungi and lichens is significant in the context of this SEA, the assessment of impacts (positive and negative) has focussed on those species for which beaver activity may affect directly or indirectly (as discussed above), which are considered as having conservation importance and as such are afforded European or national protection wherever they occur.

Table 4.3.2 below therefore identifies those bryophytes and lichens or assemblages of conservation importance that utilise 'potential beaver core habitat' (as described in section 4.1. of this report) and are found within the beaver policy area.

In addition to these designated sites, the Atlantic hazelwood habitat has also been screened into this assessment in light of its international importance as discussed above.

While Cairngorm SAC designated for its green shield-moss bryophyte occurs within the beaver policy area, the known locations of this bryophyte do no overlap with potential core beaver habitat, and a conclusion of No Likely Significant Effect was reached in the SNH HRA advice (see Annex 2). It has therefore been screened out of the SEA. Fungi assemblage has also been screened out as the three sites that overlap with potential core beaver woodland are associated with Scots pine - beavers generally avoid pine and other conifer tree species.

Table 4.3.2: Summary of bryophytes and lichens of conservation importance within the beaver policy area that overlap with potential beaver core habitat

Conservation importance: SSSI

Species or assemblage

Lichen

Den of Airlie SSSI

River jelly lichen

Birks of Aberfeldy SSSI
Black Wood of Rannoch SSSI
Cairngorms SSSI
Craighall Gorge SSSI
Drummond Lochs SSSI
Ellary Woods SSSI
Gannochy Gorge SSSI
Glen Lyon Woods SSSI
Inverneil Burn SSSI
Knapdale Woods SSSI
Milton Wood SSSI
Pollochro Woods SSSI
Taynish Woods SSSI

Lichen assemblage

Bryophyte

Cairngorms SSSI
Den of Airlie SSSI
Ellary Woods SSSI
Gannochy Gorge SSSI
Glen Coe SSSI
Inverneil Burn SSSI
Knapdale Woods SSSI
Pollochro Woods SSSI
Taynish Woods SSSI

Bryophyte assemblage

4.3.3 Assessment of likely effects on bryophytes, fungi and lichens of conservation importance in the beaver policy area

Each of the species or assemblages identified in Table 4.3.2 above are discussed in turn below in the context of those effects (positive or negative) that have been identified as a result of beaver activity. Where this relates to a habitat included in the Habitats Regulation Appraisal of the policy (i.e. in an SAC), a summary of the advice from SNH, provided to inform an appropriate assessment ( AA) of the policy with respect to SAC sites (see Annex 2 for the full advice) has been used (referred to hereafter as ' SNH HRA advice'). Assessment of SSSI features is based on expert judgement together with knowledge of each site and its condition. Where mitigation or monitoring maybe appropriate, this has been identified in the narrative. Further discussion relating to the management of beavers including mitigation and monitoring options is provided in sections 5 and 7 respectively.

For species and habitats of conservation interest in the wider countryside there will be an ongoing need to assess data derived from general surveillance and monitoring activities that are already in place, and intervene with management if and when necessary. This will be informed by a more strategic approach to management being developed in due course.

Monitoring

There are no significant studies from other countries on the specific impact of beavers on bryophytes, lichens or fungi. It is possible to interpret studies on habitat structure and diversity which would affect these species, but this does not add significantly to the evidence acquired from the SBT. So far it is possible to predict the impact of beavers based only on information from the SBT at Knapdale.

SBT monitoring focused on the impact on lichens because of the relatively large overlap of important lichen habitat (Atlantic hazel woodland) with potential beaver habitat. To the best of our knowledge, this is the first specific monitoring to assess the impact of beavers on lichens. Although the Tayside beaver population is much larger than the Knapdale population, its impact on lichens, bryophytes and fungi has not yet been assessed. Further details outlining the key conclusion from this monitoring on lichens can be found in Annex 1, section 3.4.4.

Monitoring the effect of beavers on bryophytes, lichens and fungi will therefore be required going forward. A number of principal policy, monitoring and analysis recommendations, as well as actions, can be summarised as follows:

  • Promote the proactive expansion of aspen woodland, ensuring temporal continuity of young and old trees
  • Promote the proactive expansion of Atlantic hazelwood lichen habitat in western Scotland
  • Address existing pressures on priority bryophyte, lichen and fungus woodland habitat, e.g. rhododendron, under- or over-grazing
  • Assess the relative impact on restricted compared with widespread species
  • Assess the overlap between lichens, bryophytes and fungi of conservation concern, particularly those that depend on old trees, and potential beaver habitat prior to local reintroductions, and monitor and manage where appropriate
  • Assess the overlap between potential beaver habitat and nationally/internationally important wooded oceanic ravine bryophyte habitat, and monitor and manage where appropriate
  • Monitor impact on species of European importance (see below) and manage as required
  • Research the impact of beaver control fencing on woodland lichen and bryophyte habitat quality, and produce guidance
  • Research the long-term impact of beavers on large- volume dead-wood habitat

Where it has been possible to provide more site-specific commentary on monitoring requirement this has been outlined below. Further narrative is detailed in section 5.

Beaver opportunities

Any riparian woodland restoration programme, as highlighted in section 4.2, is also likely to benefit woodland bryophytes, lichens and fungi in the medium to long term. In addition, there may also be positive long-term benefits to international restricted old woodland species, for example:

  • Expansion of fluvial woodland to improve beaver habitat could result in an overall increase in old woodland habitat if beavers move about within the landscape and allow old-growth woodland to develop
  • Management of deer to prevent over-grazing within beaver habitat will benefit the long-term continuity of bryophyte, lichen and fungal habitat by promoting woodland regeneration
  • An increase in dead wood (but note that there is some uncertainty as to the impact beavers will have on important large-diameter dead wood, see Annex 1 section 3.4.1)

4.3.3.1 Consideration of potential positive effects on bryophytes and lichens conservation importance

The impact of beaver activity on bryophytes and lichens discussed below is considered to be either positive or neutral. Where there is considered to be a negative effect or the potential for a negative effect, these are discussed in the following section, see 4.3.3.2.

River Jelly Lichen

The river jelly lichen Collema dichotomum, an aquatic species which is nationally rare, is found on flat sandstone rocks in the River Isla within Den of Airlie SSSI. The population here is thoughts to be the largest in the Britain.

Knapdale

There are no SSSIs within the Knapdale beaver policy area designated for river jelly lichen.

Tayside

  • Den of Airlie SSSI

SSSI Assessment

This lichen is sensitive to changes in water depth and sediment deposition, both of which could be affected by beavers, in positive way depending on where dams are created.

Monitoring

Monitoring will therefore be required to detect whether beavers establish within this site, and if they do the potential for positive effects should be assessed and any appropriate management put in place. See section 7 for further details on the approach to Site Condition Monitoring ( SCM) and beavers.

Lichen Assemblage

Scotland has an amazing diversity of lichens, with just over 1500 species. Clean air, diverse habitats, relatively cool summers and mild winters all contribute to this diversity and abundance. Scotland is important for lichens on a European and even global scale. Each type of lichen is a successful partnership between two species, a fungus and an alga (or blue-green alga). The fungus provides a protective home for the alga and in return, the alga produces food for the fungus from sunshine, water and air.

The lichen assemblages referred to below are mostly associated with Native pinewoods, Upland oak woodland, Upland mixed ash woodland, Lowland mixed broadleaved woodland and Wet woodland habitats, see section 4.2 Beavers and woodlands.

Knapdale

  • Ellary Woods SSSI
  • Inverneil Burn SSSI
  • Knapdale Woods SSSI
  • Taynish Woods SSSI

Tayside

  • Birks of Aberfeldy SSSI
  • Black Wood of Rannoch SSSI
  • Cairngorms SSSI
  • Craighall Gorge SSSI
  • Drummond Lochs SSSI
  • Gannochy Gorge SSSI
  • Glen Lyon Woods SSSI
  • Milton Wood SSSI
  • Pollochro Woods SSSI

SSSI Assessment

As mentioned above , there are no significant studies from other countries on the specific impact of beavers on lichens, with the only monitoring carried out occurring at the SBT. Therefore, it is possible, so far, to predict the impact of beavers based only on information from the SBT at Knapdale. Potential positive effects are anticipated to include:

  • A more open canopy due to beaver activity will favour tree-dwelling species of lichen that require higher levels of light but that can withstand some exposure.
  • Many lichens are associated with dead wood utilising it as a substrate. Beavers may increase the amount of dead wood in some areas. Any increase in the diversity of dead wood (e.g. size, moisture content, exposure, tree species, orientation) is likely to increase the diversity of lichen species. Standing dead wood, particularly when it has lost its bark, provides an important habitat for a number of lichen species. Beaver may locally increase standing dead wood in the short term in inundated areas

However uncertainty does remain as to the precise effect beaver activity will have on lichens. Therefore, further site-specific monitoring tailored to each site will be required going forward.

Monitoring

See section 7 for further details on the approach to Site Condition Monitoring ( SCM) and beavers.

Bryophyte Assemblage

Mosses and liverworts are tiny plants that produce spores instead of flowers and seeds. There are differences between mosses and liverworts, but they share many important characteristics and are collectively called bryophytes. Despite their small size, they play a hugely important role in health and function of our environment. Present on land since before the dinosaurs, Scotland's 977 mosses and liverworts represent a diverse and unique part of our biodiversity at a European and global scale. This is due to Scotland's diverse landscape and a climate influenced strongly by the Atlantic Ocean. Relatively warm winters and cool, wet summers, especially on the west coast, provide perfect conditions for these little plants.

The bryophyte assemblages referred to below are mostly associated with Native pinewoods, Upland oak woodland, Upland mixed ash woodland, and Wet woodland habitats, see section 4.2 Beavers and woodlands.

Knapdale

  • Ellary Woods SSSI
  • Inverneil Burn SSSI
  • Knapdale Woods SSSI
  • Taynish Woods SSSI

Tayside

  • Cairngorms SSSI
  • Den of Airlie SSSI
  • Gannochy Gorge SSSI
  • Glen Coe SSSI
  • Pollochro Woods SSSI

SSSI Assessment

As mentioned above, there are no significant studies from other countries on the specific impact of beavers on bryophytes. Potential positive effects are anticipated to include:

  • A more open canopy due to beaver activity will favour tree-dwelling species of bryophyte that require higher levels of light but that can withstand some exposure
  • Many bryophytes are associated with dead wood, utilising it as a substrate. Beavers may increase the amount of dead wood in some areas. Any increase in the diversity of dead wood (e.g. size, moisture content, exposure, tree species, orientation) is likely to increase the diversity of bryophyte species.

The Beaver in Scotland report (2015) assessed the likely impact to these sites from beaver activity and concluded they were unlikely to be affected (see Annex 1, section 3.4.4) and as such no adverse effects to natural heritage interests of national importance are expected within these sites.

4.3.3.2 Consideration of potential negative effects on bryophytes and lichens of conservation importance

The impact of beaver activity on the bryophytes and lichens discussed below is considered to have a negative effect or have to the potential for a negative effect.

River Jelly Lichen

The river jelly lichen Collema dichotomum, an aquatic species which is nationally rare, is found on flat sandstone rocks in the River Isla within Den of Airlie SSSI. Although found elsewhere, the population here is thought to be the largest in the Britain,

Knapdale

There are no SSSIs within the Knapdale beaver policy area designated for river jelly lichen.

Tayside

  • Den of Airlie SSSI

SSSI Assessment

This lichen is sensitive to changes in water depth and sediment deposition, both of which could be affected by beavers, in negative way (acknowledging in 4.3.3.1 above that these could be positive) depending on where or if dams are created. There is therefore potential for beaver activity to adversely affect natural heritage interests of national importance. Monitoring will be required to detect whether beavers establish within this site, and if they do their impact should be assessed and appropriate management put in place.

Mitigation

See section 7 for further details on the approach to Site Condition Monitoring ( SCM) and beavers. See section 5 for beaver management techniques used to mitigate the impact of damming beaver activity; those techniques outlined include measures that would avoid or reduce any impact considered to be adverse to the River jelly lichen at the Den of Airlie SSSI.

Lichen Assemblage

Scotland has an amazing diversity of lichens, with just over 1500 species. Clean air, diverse habitats, relatively cool summers and mild winters all contribute to this diversity and abundance. Scotland is important for lichens on a European and even global scale. Each type of lichen is a successful partnership between two species, a fungus and an alga (or blue-green alga). The fungus provides a protective home for the alga and in return, the alga produces food for the fungus from sunshine, water and air.

The lichen assemblages referred to below are mostly associated with Native pinewoods, Upland oak woodland, Upland mixed ash woodland, Lowland mixed broadleaved woodland and Wet woodland habitats, see section 4.2 Beavers and woodlands.

Knapdale

  • Ellary Woods SSSI
  • Inverneil Burn SSSI
  • Knapdale Woods SSSI
  • Taynish Woods SSSI

Tayside

  • Birks of Aberfeldy SSSI
  • Black Wood of Rannoch SSSI
  • Cairngorms SSSI
  • Craighall Gorge SSSI
  • Drummond Lochs SSSI
  • Gannochy Gorge SSSI
  • Glen Lyon Woods SSSI
  • Milton Wood SSSI
  • Pollochro Woods SSSI

As mentioned above , there are no significant studies from other countries on the specific impact of beavers on lichens, with the only monitoring carried out occurring at the SBT. Therefore, it is possible, so far, to predict the impact of beavers based only on information from the SBT at Knapdale. Potential negative effects are anticipated to include:

  • Some tree-dwelling species that tolerate low levels of light and require shelter to maintain high humidity may be negatively affected as beavers create more open woodland.
  • Where browsing from other herbivores is high, tree regrowth may be prevented, and this could lead to a reduction in structural diversity and ultimately localised loss of areas of important lichen habitat.
  • Old trees provide habitat for a high diversity of lichens that do not occur in young woodland. Beavers may prevent trees from becoming old at local levels. Breaks in the temporal and spatial continuity of old woodland characteristic will have a negative impact on the many lichens that are poor dispersers and/or colonisers. There is a risk of local extinction for some species.
  • Beaver activity may result in fewer large trees in the future to supply large-volume dead wood. Many species of lichen have strong associations with large-volume dead wood. Large standing dead wood supports a number of threatened lichens some of which may become locally extinct

There is therefore potential for beaver activity to adversely affect natural heritage interests of national importance. Monitoring will be required to detect whether beavers establish within these sites, and if they do their impact should be assessed and appropriate management put in place.

Mitigation

See section 7 for further details on the approach to Site Condition Monitoring ( SCM) and beavers. See section 5 for beaver management techniques used to mitigate the impact of beaver activity; those techniques outlined include measures that would avoid or reduce any impact considered to be adverse to the SSSIs identified in the list above.

The impact of beaver management options on lichens will require careful consideration. For example, fencing may not be an appropriate method to protect trees or shrubs that provide important lichen habitat. The long-term absence of grazing can be as damaging as over-grazing due to thicket regeneration and shading of light-demanding lichens.

Atlantic Hazelwood Lichens

As discussed in section 4.3.1.1 above, Atlantic Hazelwoods host many lichen species of high conservation importance including internationally. However, there are no designated sites specifically for Atlantic hazelwoods. Instead, their value is recognised as component habitat features of some woodland SACs such as Taynish and Knapdale Woods SAC.

Knapdale

Atlantic hazel woodland is a particularly important habitat for lichens at Knapdale because it supports a wide range of species, many of which have their main European populations in western Scotland. The distribution of Atlantic hazelwoods with 80% or more hazel in the canopy that occur in the Knapdale beaver policy area, that overlap with beaver core habitat are illustrated in Map 11 below .

Map 11: Distribution of Atlantic hazel woods that overlap with core beaver woodland in the Knapdale beaver policy area

Map 11: Distribution of Atlantic hazel woods that overlap with core beaver woodland in the Knapdale beaver policy area

Tayside

Atlantic hazelwoods primarily rely on oceanic climatic conditions experienced by western Scotland. While there are hazel woods within the Tayside beaver policy area (0.72 ha with 80% canopy), they are less likely to host the internationally important licence species referred to above. However, hazel along watercourses can provide habitat for the eastern European extent of otherwise oceanic lichens (Figure 4.3.1) and as such their importance should not be ignored.

Figure 4.3.1: The distribution of notable lichens associated with Atlantic hazelwoods.

Figure 4.3.1: The distribution of notable lichens associated with Atlantic hazelwoods.

Assessment

Particular attention should be given to impacts on the internationally restricted Graphidion and Lobarion lichen communities found within Atlantic hazelwood as there is a moderate risk that hazel stems supporting such species of conservation concern will be felled by beavers and that this could result in local extinctions.

Old trees provide habitat for a high diversity of lichens that do not occur in young woodland and beavers may prevent trees from becoming old at local levels. Breaks in the temporal and spatial continuity of old woodland characteristic will have a negative impact on the many lichens that are poor dispersers and/or colonisers. There is a risk of local extinction for some species

Detailed monitoring of Atlantic hazel habitat within the Knapdale SBT area has demonstrated relatively high impacts that may eventually result in the permanent or temporary localised loss of a globally restricted lichen habitat. The impact was restricted to a maximum of about 60 m from a loch and within woodland on gentler, less bouldery slopes. Within this utilised zone, 24.4% of stems had been felled, affecting just over half of the stools. There was no observable impact on lichens beyond areas where felling had occurred. Within the SBT five-year monitoring period, only 8% of Taynish and Knapdale Woods SAC's area of Atlantic hazel had been affected. Most felled stems supported oceanic lichen communities, including a number of species that are of national and/or international conservation concern. These impacts have to be considered against the fact that the majority of Atlantic hazel habitat within Taynish and Knapdale Woods SAC is unlikely ever to be affected by beavers.

There is therefore potential for beaver activity to adversely affect natural heritage interests of international importance. Monitoring will be required to detect whether beavers establish within these Atlantic hazelwood areas, and if they do their impact should be assessed and appropriate management put in place.

Mitigation

Further monitoring is therefore required over a longer period of time to clarify uncertainties as to the long-term impact on Atlantic hazel habitat, with a particular emphasis on the temporal continuity of young and old stems and interaction with deer browsing. As beavers reach some of these sites, impacts should be monitored using the Woodland Grazing Toolbox methodology. Signs of over-grazing can be detected before any adverse impacts result. Consideration should also be given to the potential to strategically site future plantings of hazel stands in areas out of the reach of beavers which could provide mitigation against any future impacts on existing stands. There may also be merit in additional new planting within existing stands to improve their condition and minimise the impact of any losses attributed to beavers.

See section 7 for further details on the approach to monitoring and beavers. See section 5 for beaver management techniques used to mitigate the impact of beaver activity; those techniques outlined include measures that would avoid or reduce any impact considered to be detrimental to the lichen species within Atlantic hazelwoods.


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