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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.

Contents
Beavers in Scotland: consultation on the strategic environmental assessment
4.2 Beavers and Woodland

4.2 Beavers and Woodland

4.2.1 How beaver activity affects riparian woodland

The main mechanisms by which beavers affect riparian [1] woodland are tree-felling for food and construction, and flooding. They generally avoid conifers, but will use most native broadleaved tree species that occur in Scotland, and other non-native broadleaved trees.

Where numbers of other herbivores are high, the impacts of beavers may be exacerbated if subsequent browsing of regrowth by other herbivores prevents coppice regrowth and tree regeneration. Hence, careful management of deer and livestock in areas colonised by beavers will maximise the likelihood of an overall positive impact of beavers on woodland ecosystems.

These mechanisms can lead to a range of impacts on woodland, as outlined in section 4.2.1.1 - 4.2.1.3 below. A summary of the potential interactions between beavers and riparian woodlands is presented at the end of this section (see Table 4.2.1); where possible these have been attributed to a neutral, positive or negative effect.

4.2.1.1 Woodland structure

In general, beavers prefer smaller stems, less than 0.1 m in diameter, but will take much larger ones as well. When choosing material for construction, stem size may be more important than species. Most broadleaved trees can regrow from cut stumps, but the vitality of the regrowth varies with species and the age of the tree.

Since beavers select a tree according to its stem size, and as younger trees generally produce more, stronger, regrowth shoots than older trees, a younger age profile is likely to develop over time, with a loss of both older stems and older growth riparian woodland communities. If a large proportion of the woodland is affected then ecological continuity could be interrupted, particularly with impacts on lichens and other species characteristic of older stems.

Most felling is within 10 m of the water's edge and, because beavers are usually considered to be central place foragers, impacts vary along watercourses according to distance from lodges. The impact of beavers may therefore be patchy, leading to greater structural diversity along the length of watercourses.

Felling large trees opens the canopy, allowing more light to reach the ground, and allowing regeneration from seed, which could potentially lead to increased structural diversity in even-aged woodland.

Where browsing from other herbivores is high, regrowth may be prevented, and this could lead to a reduction in structural diversity and ultimately loss of woodland cover.

4.2.1.2 Species Composition

Beaver have a clear preference for some tree species over others, in particular aspen Populus tremula and willow Salix spp. These species generally resprout rapidly, and beavers seem to avoid young aspen regrowth. However, young shoots are very attractive to deer, and the combined impact may lead to the loss of beaver-preferred species.

More generally, although beavers often use species according to their abundance, they may also preferentially select less common species in order to fulfil their need for a diverse diet. This could lead to reduced species diversity, which might be exacerbated by differences in the responses of tree species to beaver browsing and the preference of deer for different species. Willow and ash Fraxinus excelsior produce stronger shoots than alder Alnus glutinosa or birch Betula pubescens, but are also more attractive to deer.

Inundation of woodland will lead to the death of trees of many species, but could promote the growth of others, especially willow, which can grow well even in standing water.

4.2.1.3 Deadwood

Although tree-felling by beavers could lead to increased fallen dead wood in some areas, much of the material is removed for food and construction, some of which falls in, or is placed in, water bodies (see Annex 1, section 3.4.3).

In flooded areas, the death of trees which are unable to cope with increased water levels will lead to an increase in standing dead wood, which is generally present at only low levels in British woods. Such areas may become hotspots for dead wood biodiversity (see, for example, Annex 1, sections 3.4.6 and 3.4.9).

Table 4.2.1: Summary of potential interactions between beavers and woodland.

Activity

Mechanism

Positive effects

Negative effects

Notes

Felling

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

  • Most felling is within 10 m of the water's edge. Beavers are central place foragers, so impacts also vary along watercourses according to distance from lodges. The impact of beavers may therefore be patchy, leading to greater structural diversity along the length of watercourses
  • Felling large trees opens the canopy, allowing more light to reach the ground and allowing regeneration from seed, which could lead to increased structural diversity in even-aged woodland.
  • Where woodland is already very open, the impact of beavers could lead to localised loss of woodland cover, especially where levels of deer browsing are high, and could prevent regeneration from seed

Felling

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

  • Young shoots are very attractive to deer, and the combined impact may lead to loss of preferred species. In some cases, aspen could be lost from parts of the core beaver habitat, where near-permanent beaver presence prevents substantial regrowth
  • Beaver may preferentially select less common species in order to fulfil their need for a diverse diet. This could lead to reduced species diversity, which might be exacerbated by differences in the responses of tree species to beaver browsing

Beavers have a clear preference for some tree species, particularly aspen and willow. These species generally resprout rapidly, and beavers seem to avoid young aspen regrowth

Felling

Change in riparian woodland: Change in age classes of trees

  • Where browsing from other herbivores is high, regrowth may be prevented, and this could lead to a reduction in structural diversity and ultimately loss of woodland cover
  • Since beavers select according to stem size, and as younger trees generally produce more and stronger shoots than older ones, a younger age profile is likely to develop over time, with a loss of older trees and of climax riparian woodland communities. If a large proportion of the woodland is affected then ecological continuity could be interrupted within the riparian zone

Most broadleaved tree species can regrow from cut stumps, but the vitality of the regrowth varies with species and age. In Knapdale, ash and willow were found to produce stronger shoots than birch and alder

Felling

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

  • Tree-felling by beavers could lead to increased fallen dead wood in some areas, although much of the material is removed for food and construction

Dams/pond creation

Change in hydrological processes on riparian and downstream habitat

  • Inundation of woodland could promote the growth of some species, especially willow, which can grow well even in standing water. Bog woodland may be restored or more habitat created
  • If a large proportion of an area of woodland is inundated, and willow is unable to regenerate, loss of woodland cover could be considered a negative impact

This might be positive/negative or neutral depending on the area, tree species and regeneration

Dams/pond creation

Change in standing dead wood resulting from inundation of trees

  • Death of trees which are unable to cope with the water levels will lead to an increase in standing dead wood, which is generally present at only low levels in British woods
  • Inundation of woodland will lead to the death of trees of certain species

This might be positive/negative or neutral depending on the area, tree species, regeneration and the pre-existing biodiversity value of the inundated woodland

Dams/pond creation

Longer term successional changes after dam abandonment, e.g. beaver meadows

  • In previously homogeneous woods, this increase in integral open space would add diversity and improve the habitat for some species groups, e.g. the adults of dead wood invertebrates often require nectar sources
  • In fragmented woodland, this loss of woodland cover would be considered a negative impact

This might be positive/negative or neutral depending on the pre-existing woodland structure

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 will aim to increase the abundance of this much reduced habitat, and of particular preferred species, such as aspen

4.2.2 Distribution of suitable riparian woodland habitat in the beaver policy area

As identified in section 4.1, work has been done through the Beaver in Scotland report to further refine the 'potential beaver woodland' dataset to identify 'potential core beaver woodland' which anticipates areas that beavers would be more likely to set up long-term territories in proximity to these areas of woodland (see Map 4 in Appendix 1).

The Tayside beaver policy area is estimated to have around 14,700 ha of potential core beaver woodland. Woodland connectivity is relatively good, and if beavers were to remain on Tayside then it is anticipated that in the long term a significant proportion would eventually be colonised. The potential core beaver woodland is less than 1.3% of the Tayside beaver policy area.

The Knapdale beaver policy area is estimated to have almost 1000 ha of potential core beaver woodland. The beaver population at Knapdale, with additional reinforcement, is expected to expand and use additional areas of riparian woodland, although there may be limited colonisation outside Knapdale Forest over the medium term of 30 years (see Annex 1, section 3.2). The potential core beaver woodland is less than 1.5% of the Knapdale beaver policy area.

4.2.2.1 Riparian woodland habitat of conservation importance

To determine whether the activity of beavers on riparian woodland habitat is significant in the context of this Strategic Environmental Assessment, the assessment of impacts (positive and negative) has focussed on those woodland sites 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. Of these, ninety such sites have been identified that overlap with potential core beaver woodland. These can be grouped according to the dominant tree species.

Table 4.2.2: Summary of riparian woodland types and the sites that overlap with potential core beaver woodland, grouped as per the dominant tree species

Conservation importance

Woodland Type

SAC

SSSI

Dominant Trees Species: Alder and Willow

Alder woodland on floodplains

Shingle Islands SAC

Wet woodland

Bolfracks Wood SSSI
Cambusurich Wood SSSI
Coille Chriche SSSI
Damhead Wood SSSI
Edinchip Wood SSSI
Glen Coe SSSI
Glen Lochay Woods SSSI
Glen Lyon Woods SSSI
Loch Tay Marshes SSSI
Milton Wood SSSI
Pollochro Woods SSSI
Round Loch of Lundie SSSI
Stronvar Marshes SSSI

Scrub

Bog Wood and Meadow SSSI
Den of Ogil SSSI

Dominant Tree Species: Ash

Mixed woodland on base-rich soils associated with rocky slopes

Craighall Gorge SAC
Keltneyburn SAC

Upland mixed ash woodland

Back Burn Wood and Meadows SSSI
Birks of Aberfeldy SSSI
Cambusurich Wood SSSI
Craighall Gorge SSSI
Den of Airlie SSSI
Den of Alyth SSSI
Den of Fowlis SSSI
Den of Riechip SSSI
Devon Gorge SSSI
Dollar Glen SSSI
Finlarig Burn SSSI
Flisk Wood SSSI
Glen Lochay Woods SSSI
Glen Tilt Woods SSSI
Keltneyburn SSSI
Romadie Wood SSSI

Dominant Tree Species: Oak and Birch

Western acidic oak woodland

Moine Mhor SAC
Tarbert Woods SAC
Taynish and Knapdale Woods SAC
Loch Lomond Woods SAC
Upper Strathearn Oakwoods SAC

Upland oak woodland

Artilligan and Abhainn Srathain Burns SSSI
Cambusurich Wood SSSI
Cardney Wood SSSI
Carie and Cragganester Woods SSSI
Comrie Woods SSSI
Edinchip Wood SSSI
Ellary Woods SSSI
Glen Falloch Woods SSSI
Innishewan Wood SSSI
Inverneil Burn SSSI
Knapdale Woods SSSI
Moine Mhor SSSI
Monzie Wood SSSI
Pass of Killiecrankie SSSI
Pass of Leny Flushes SSSI
Taynish Woods SSSI
Tayvallich Juniper and Fen SSSI

Upland birch woodland

Beinn a' Ghlo SSSI
Black Wood of Rannoch SSSI
Glen Lochay Woods SSSI
Leven Valley SSSI
Linn of Tummel SSSI
Struan Wood SSSI

Lowland mixed broadleaved woodland

Drummond Lochs SSSI
Kincardine Castle Wood SSSI
Methven Woods SSSI

Dominant Tree Species: Pine

Bog woodland

Ballochbuie SAC
Cairngorms SAC

Caledonian forest

Ballochbuie SAC
Black Wood of Rannoch SAC
Cairngorms SAC

Native pinewood

Black Wood of Rannoch SSSI
Creag Clunie and the Lion's Face SSSI
Cairngorms SSSI
Easter Cairngorm SSSI
Allt Broighleachan SSSI
Coille Coire Chuilc SSSI
Crannach Wood SSSI
Crossbog Pinewood SSSI
Doire Darach SSSI
Glen Falloch Pinewood SSSI
Meggernie and Croch na Keys Woods SSSI

Dominant Tree Species: Hazel

Atlantic hazelwoods

See Map 11 for distribution below

4.2.3 Assessment of likely effects on woodlands of conservation importance in the beaver policy area

Each of the woodland habitat types identified in Table 4.2.2 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'). For the purpose of this assessment, the concluding points of the SNH HRA advice have been replicated where appropriate for each woodland type. Assessment of other woodland habitat types (i.e. SSSI woodland habitat types), has been made in the context of the SNH HRA advice in combination with knowledge of the individual woodland sites and their 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.

Mitigation

The need for mitigation will depend on site-specific circumstances related to the woodland type, the condition of the woodland and the influence of other pressures. Moreover, it will also depend on the degree and duration of beaver occupancy. Mitigation is therefore discussed more generally below, with further commentary provided in section 5 with reference to exclusion fencing, individual tree protection and management techniques to minimise or avoid unwanted impacts from beavers' activity.

Beaver opportunities

As summarised above, beaver activity has the potential to create positive effects. More than this, the presence of beavers in an area could provide a basis for a riparian woodland restoration programme to help increase the abundance of this much reduced habitat.

4.2.3.1 Consideration of potential positive effects on woodland of conservation importance

All Woodland Types (Excluding Atlantic Hazelwoods)

For all of the aforementioned identified woodland types, spanning some ninety sites, as outlined in Table 4.2.2 above, the precise effects will often be site-specific, wide-ranging and uncertain in their detail. Many of the effects can be positive or neutral in their outcomes, however taking a strategic and precautionary approach the SNH HRA advice considered that there remains the potential for a Likely Significant Effect in some cases - these are dealt with in section 4.2.4.2 below), as is Atlantic Hazelwoods.

As noted in the summary of effects above, due to their activities, beavers have a variety of positive effects on woodland structure, leading to a greater diversity of age classes, particularly in even-aged stands, improving the variety of species present in woodlands and potentially creating hot spots of biodiversity through the creation of increased levels of standing dead wood. Positive gains from beaver activity on woodland habitat can be described in general terms as follows:

  • The impact of beavers may be patchy, leading to greater structural diversity along the length of watercourses.
  • Felling large trees opens the canopy, allowing more light to reach the ground and allowing regeneration from seed, which could lead to increased structural and species diversity in even-aged woodland.
  • In previously homogeneous woods, this increase in integral open space would add diversity and improve the habitat for some species groups, e.g. the adults of dead wood invertebrates often require nectar sources
  • Inundation of woodland could promote the growth of some species, especially willow, which can grow well even in standing water. Bog woodland may be restored or more created.
  • Death of trees which are unable to cope with the water levels will lead to an increase in standing dead wood, which is generally present at only low levels in British woods
  • Tree-felling by beavers could lead to increased fallen dead wood in some areas, although much of the material is removed for food and construction

Short, medium or long-term changes in the vegetation structure, and / or hydrology of localised areas of accessible woodland as a result of beaver activity, is likely to increase the dynamism of woodland processes. Provided regeneration of felled trees and shrubs is able to continue, this is likely to increase the overall conservation value of the these woodland sites (for example, by increasing the amount of standing dead wood resulting from flooding, thereby increasing habitat for dead wood 'typical species', as discussed above).

Many of the ninety sites identified in this analysis are in unfavourable condition and do not meet their site attribute targets for volume of deadwood, level of grazing / browsing, structural diversity (i.e. number of different age classes of target tree species) or evidence of regeneration. As described above, beaver activity has the potential to address some of these failing targets. Monitoring will therefore be required to assess the impact of beaver activity and how any benefit may come about; see section 7 for discussion of Site Condition Monitoring and beavers.

4.2.3.2 Consideration of potential negative effects on woodland of conservation importance

Beaver browsing of trees and other elements of woodlands for food is the main mechanism of change considered; however trees may also be felled for, or flooded by, dam-building. Selective browsing can lead to reduced tree diversity as well as tree and shrub growth and regrowth, particularly within 30m of freshwater where the large majority of beaver browsing activity takes place. The most important factors in determining the degree of impact from beavers will usually be:

  • The total size of woodland area, with a generally diluted impact on larger wooded areas and greater impact on smaller areas.
  • The proportion of preferred tree species (such as aspen, willow, and possibly hazel) within a wooded area.
  • The existing degree of pressure on woodland from browsing by other herbivores, especially deer.

Dam-building can also lead to the inundation of previously less wet areas drowning some trees with resulting impacts on woodland structures.

The main factor causing unfavourable condition across Scottish woodlands is grazing / browsing pressure from herbivores (largely deer and sheep). At present, saplings can be considered 'safe' from further browsing once they get to a certain size (the specific size varies with the species). However, since beavers are able to fell quite large trees, this will no longer be the case in areas colonised by beavers for a reasonable length of time. Continuation of woodland will depend on coppice regrowth from the felled stumps or suckering from roots. Whilst all native Scottish broadleaves are able to coppice or sucker, if the regrowth is subsequently eaten by deer, sheep, or other large herbivores, there could be a simplification in the structure of the woodland, and possibly deterioration or even loss of the woodland habitat.

The impact of beaver activity on the woodlands habitat types discussed below is considered to have a negative or have the potential for a negative effect.

Alder and Willow Dominated Woodland Sites

Woodland Type: Alder Woodland on Floodplains

Alder woodland on floodplains is also referred to as, Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Padion, Alnion incanae, Salicion albae). The woodland canopy is varied but dominated by alder Alnus glutinosa, with frequent willows Salix spp., ash Fraxinus excelsior, downy birch Betula pubescens and occasional wych elm Ulmus glabra. Hawthorn Crataegus monogyna, rowan Sorbus aucuparia, bird cherry Prunus padus and hazel Corylus avellana all occur in the understorey. The ground flora is also very diverse with many fen species in the wetter areas and more typical woodland herbs elsewhere. Small areas of drier woodland, dominated by ash Fraxinus excelsior with occasional pedunculate oak Quercus robur, and transitions to other shingle, scrub and grassland communities, further enhance the site's diversity.

Knapdale

There are no sites identified in Knapdale that are designated for alder woodland on floodplains habitat.

Tayside

  • Shingle Islands SAC

SNH HRA advice

Beaver activity in combination with browsing pressure from other herbivores could lead to a loss of habitat, if regeneration is prevented. This qualifying interest is, by its nature, wholly within the core beaver woodland. There is no reason to suppose that impact will vary across the site and, provided regeneration is able to continue, there should be no change in the distribution of the habitat. Change in structure is likely, but difficult to predict. Possible impacts include changes in the volume of deadwood, increases in dense young growth or in open space. Provided regeneration is able to continue, these changes are most likely to be beneficial, contributing to the dynamism which is an important feature of this habitat. Short, medium or long-term changes in the vegetative structure, and/or hydrology of localised areas of alder woodland, as a result of beaver activity, are likely to increase the dynamism of woodland processes. Provided regeneration is able to continue, this is likely to increase the overall conservation value of the site (for example, by increasing the amount of standing dead wood resulting from flooding, thereby increasing habitat for dead wood 'typical species'). Such changes would be compatible with this conservation objective and do not undermine it. The Eurasian beaver is a natural component of this habitat type across Europe.

The SNH HRA advice concluded that it cannot be ascertained that there is no adverse effect on site integrity as a result of the potential combined grazing and browsing impacts of beaver and other herbivores on the alder woodland on floodplains qualifier without mitigation.

Mitigation

Any potential adverse impacts on the integrity of the SAC should be mitigated through increased herbivore management measures (upon deer, goats, sheep, or beavers as appropriate) before they occur. Signs of over-grazing can be detected before any adverse impacts result. As beavers are now present at this site, impacts should be monitored using the Woodland Grazing Toolbox methodology. If the necessary mitigation measures, including monitoring are carried out then SNH advise that it can be ascertained that there is no adverse effect on site integrity.

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Wet Woodland

Wet woodland occurs on poorly drained or seasonally wet soils, usually with alder, birch and willows as the predominant tree species, but sometimes including ash, oak, pine and beech on the drier riparian areas. It is found on floodplains, as successional habitat on fens, mires and bogs, along streams and hill-side flushes, and in peaty hollows.

Many alder woods are ancient and have a long history of coppice management which has determined their structure, and in some situations it appears that this practice has maintained alder as the dominant species and impeded succession to drier woodland communities. Other wet woodland may have developed through natural succession on open wetlands (sometimes following cessation of active management) and structurally are little influenced by direct forestry treatments.

A review of the above identified wet woodland SSSI indicates that many are in unfavourable condition, failing to meet their site attribute targets for volume of deadwood, level of grazing / browsing, structural diversity (i.e. number of different age classes of target tree species) or evidence of regeneration

Knapdale

There are no sites identified in Knapdale that are designated for wet woodland habitat.

Tayside

  • Bolfracks Wood SSSI
  • Cambusurich Wood SSSI
  • Coille Chriche SSSI
  • Damhead Wood SSSI
  • Edinchip Wood SSSI
  • Glen Coe SSSI
  • Glen Lochay Woods SSSI
  • Glen Lyon Woods SSSI
  • Loch Tay Marshes SSSI
  • Milton Wood SSSI
  • Pollochro Woods SSSI
  • Round Loch of Lundie SSSI
  • Stronvar Marshes SSSI

SSSI Assessment

Impacts within wet woodland SSSI habitat are likely to be similar to those described above for alder woodland on floodplains habitat. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance.

Mitigation

As beavers continue to naturally colonise 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. These impacts should then be mitigated by using all necessary herbivore management measures (of deer or beavers, or both).

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Scrub

Knapdale

There are no sites identified in Knapdale that are designated for scrub dominated woodland habitats.

Tayside

  • Bog Wood and Meadow SSSI
  • Den of Ogil SSSI

Bog Wood and Meadow SSSI

Below the fen meadow in Bog Wood and Meadow SSSI is a small area of fen interspersed with tussocks of greater tussock sedge, which grades into willow scrub which contains bay willow Salix pentandra. This type of scrub woodland is nationally scarce.

A review of SCM site attribute targets highlights little evidence of regeneration but noted prolific regeneration from cut stump on the wayleave intersecting the site indicating the potential for regeneration exits. As such, all target were deemed to have been met and the site is in favourable condition.

SSSI Assessment

Beavers show a clear preference for some trees species such as willow and that more generally they often use a species according to its abundance. At Knapdale ( SBT) beavers showed a strong preference for willow (as well as ash, rowan and hazel) but avoided alder. Willow and ash show a higher propensity for coppice regrowth than alder or birch. While the inundation of woodland can lead to the death of trees of many species, it can promote the growth of others, especially willow, which can grow well even in standing water.

On balance while beavers show a strong preference for willow, its regeneration and water tolerate characteristics suggest it's unlikely that beaver activity at this SSSI would detrimentally impact the overall condition of the area.

Monitoring

Beavers are now present on this site and so, impacts should be monitored using the Woodland Grazing Toolbox methodology and an assessment made of the extent to which they utilise the willow scrub. See section 7 for details on the approach to SCM and beavers.

Den of Ogil SSSI

The Den of Ogil SSSI is important because of its species-rich plant communities, particularly the fens associated with upwelling springs which drain into the Burn of Ogil, and also for its wet willow (Salix sp.) and alder (Alnus glutinosa) carr scrub woodland. A large proportion of the site is covered with alder and willow carr, much of which was originally planted in an attempt to dry out the area. A review of SCM site attribute targets indicated that all targets have been met. Consequently, this site is in favourable condition.

SSSI Assessment

Beavers show a clear preference for some trees species such as willow and that more generally they often use a species according to it abundance. At Knapdale beavers showed a strong preference for willow (as well as ash, rowan and hazel) but avoided alder. Willow and ash show a higher propensity for coppice regrowth than alder or birch. While the inundation of woodland can lead to the death of trees of many species, it can promote the growth of others, especially willow, which can grow well even in standing water.

On balance while beavers show a strong preference for willow, its regeneration and water tolerate characteristics suggest it's unlikely that beaver activity at this SSSI would harm the overall condition of the area.

Monitoring

As beavers naturally colonise this site, impacts should be monitored using the Woodland Grazing Toolbox methodology and an assessment made of the extent to which they utilise the alder carr. See section 7 for details on the approach to SCM and beavers.

Pine Dominated Woodland Sites

Consideration of Aspen

Most of the aspen rich woodlands found in Scotland occur in the Strathspey area, beyond the SEA policy boundary. This is reflected in the GIS analysis undertaken, reporting a total area of 1.46ha of aspen (area with 80% or more in the tree canopy) present in the Tayside beaver policy area. The commentary below with respect to Cairngorms SAC includes reference to aspen because the SAC boundary, while only partially overlapping the Tayside beaver policy area, reaches north towards Strathspey and so has a greater proportion of aspen within the broadleaf woodland component. The HRA process takes a site wide precautionary view, hence its inclusion. Cairngorms and Eastern Cairngorms SSSI underpins Cairngorms SAC in extent and so reference is also made in the assessment to aspen, see below. SSSIs overlapping further south, well within the SEA policy boundary do not have much aspen within their pinewoods. Aspen is not present in Knapdale other in a few odd groups of trees.

SEA name Area of aspen >= 50% canopy (ha) Area of aspen >= 80% canopy (ha)
Knapdale 0 0
Tayside 2.30 1.46
Total 2.30 1.46

Woodland Type: Caledonian Forest

Caledonian forest comprises relict, indigenous pine forests of Scots pine Pinus sylvestris var. scotica, and associated birch Betula spp. and juniper Juniperus communis woodlands of northern character. Self-sown stands naturally regenerated from stock of genuinely native local origin recorded in the Caledonian Pinewood Inventory are included in the Annex I type. It is usually found on strongly-leached, acidic podzols, and these soil conditions are reflected in the ground flora, which typically includes the dwarf shrubs heather Calluna vulgaris, bilberry Vaccinium myrtillus and cowberry V. vitis-idaea, wavy hair-grass Deschampsia flexuosa, and the bryophytes Dicranum scoparium, Hylocomium splendens, Pleurozium schreberi and Rhytidiadelphus loreus.

Knapdale

There are no sites identified in Knapdale that are designated for Caledonian Forest habitat.

Tayside

  • Ballochbuie SAC
  • Black Wood of Rannoch SAC
  • Cairngorms SAC

SNH HRA advice

Beaver generally avoid pine and other conifers however broadleaved species are an important component of Caledonian forest and beavers will utilise these. Changes in structure of the broadleaved component in the immediate vicinity of rivers is possible due to beaver foraging and dam building, although any potential impacts would only be considered adverse if their regeneration is impeded or restricted, e.g. due to excessive pressure from other herbivores. Short, medium or long-term changes in the vegetative structure, and/or hydrology of areas in the immediate vicinity of rivers, is likely to increase the dynamism of woodland processes. Provided regeneration is able to continue, this is likely to increase the overall conservation value of the site (for example, by increasing the amount of standing dead wood resulting from flooding, thereby increasing habitat for dead wood 'typical species'). Such changes would be compatible with this conservation objective and do not undermine it.

The SNH HRA advice concluded that it is not possible to ascertain no adverse effect on site integrity of Ballochbuie SAC and Black Wood of Rannoch SAC from impacts to Caledonian Forest without mitigation. Impacts could result from the cumulative effects of beavers and other herbivores on the broadleaved component of these sites: where beavers might fell some trees and / or shrubs, and other herbivores then prevent the natural regeneration of those trees through browsing.

In addition, an adverse effect on site integrity is possible in the Cairngorms SAC via the actions of beavers alone. In this SAC beavers could reduce the amount of aspen due to their preference for it as food, including mature and over-mature specimens which are especially important for maintaining biodiversity.

Mitigation

Adverse impacts on these SACs can be mitigated through any necessary herbivore management measures (of deer or beavers, or both). Monitoring for signs of over-grazing should be carried out using the Woodland Grazing Toolbox methodology to ensure any impacts can be avoided before they have an adverse effect on site integrity.

With respect to aspen and Cairngorms SAC, impacts on this SAC can be mitigated by protecting important areas of aspen, to prevent access by beavers. Monitoring for signs of over-grazing should be carried out using the Woodland Grazing Toolbox methodology to ensure any impacts can be avoided before they have an adverse effect on site integrity.

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Native Pinewood

Native pinewoods occur on infertile, strongly leached, podsolic soils. They do not support a large diversity of plants and animals compared with some more fertile habitats. However, there is a characteristic plant and animal community which includes many rare and uncommon species. The main tree species is Scots pine although birches Betula spp., rowan Sorbus aucuparia, alder Alnus glutinosa, willows Salix spp., bird cherry Prunus padus are also found. Sessile oak Quercus petracea also occurs infrequently, mainly in the northeast of Scotland. A shrub understorey, where browsing levels are low, includes common juniper Juniperus communis, aspen Populus tremula, holly Ilex aquifolium and hazel Corylus avellana. Old or dead trees and rotting wood supports significant beetle and bryophyte communities. The field layer is characterised by acid-tolerant plants like bell heather Erica cinerea, billberry Vaccinium myrtillus and crowberry Empetrum nigrum.

A review of SCM site attribute targets highlights that only two of the sites are in favourable condition, the rest are unfavourable mostly due to negative levels of browsing, poor structural diversity assessed through the number of age classes of trees present, a lack of regeneration and in a few sites, insufficient volume of deadwood.

Knapdale

There are no sites identified in Knapdale that are designated for Native pinewood habitat.

Tayside

  • Black Wood of Rannoch SSSI
  • Creag Clunie and the Lion's Face SSSI
  • Cairngorms SSSI
  • Easter Cairngorm SSSI
  • Allt Broighleachan SSSI
  • Coille Coire Chuilc SSSI
  • Crannach Wood SSSI
  • Crossbog Pinewood SSSI
  • Doire Darach SSSI
  • Glen Falloch Pinewood SSSI
  • Meggernie and Croch na Keys Woods SSSI

SSSI Assessment

Impacts within Native pinewood SSSI habitat are undistinguishable from those described above for Caledonian Forest habitat. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance.

Moreover, the action of beavers alone may also adversely affect the natural heritage interests of national importance for some of the more northern SSSIs (egg Cairngorm and Eastern Cairngorm SSSIs) where aspen contribute to the broadleaf component of the native pinewoods. In these SSSI beavers could reduce the amount of aspen due to their preference for it as food, including mature and over-mature specimens which are especially important for maintaining biodiversity.

Mitigation

Adverse impacts on these SSSIs can be mitigated through any necessary herbivore management measures (on either deer or beavers or both). Monitoring for signs of over-grazing should be carried out using the Woodland Grazing Toolbox methodology to ensure any impacts can be avoided before they have an adverse effect on site integrity.

With respect to aspen, impacts within northern SSSIs can be mitigated by protecting important areas of aspen to prevent access by beavers. Monitoring for signs of over-grazing should be carried out using the Woodland Grazing Toolbox methodology to ensure any impacts can be avoided before they have an adverse effect on site integrity.

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Bog Woodland

A few examples of this unusual habitat type are found in areas of Scotland where summer drying may permit the establishment and growth of tree roots in the upper peat layers. The structure and function of this habitat type is finely balanced between tree growth and bog development. Tree growth, however, is always slow (or the trees would take over the bog); the trees are likely to be widely-spaced (because much of the surface area is too wet for them to establish), and dead trees may be common even among the fairly small individuals (because their weight depresses the peat locally leading to waterlogging and death). Although stunted in form these trees may be of considerable age, with the oldest individuals in bog woodland in Scotland estimated at 350 years old.

The principal tree species in this form of Bog woodland is Scots pine Pinus sylvestris. Pine bog woodland types are likely to be intermediate in character between NVC type W18 Pinus sylvestris - Hylocomium splendens woodland and more open mire types such as M18 Erica tetralix - Sphagnum papillosum mire or M19 Calluna vulgaris - Eriophorum vaginatum blanket mire.

Knapdale

There are no sites identified in Knapdale that are designated for bog woodland habitat.

Tayside

  • Ballochbuie SAC
  • Cairngorms SAC

HRA advice

Beaver generally avoid felling pine trees, and other tree species form only a tiny component of bog woodland. Therefore there is an extremely limited ability for beavers to impact on the bog woodland qualifier for these two SACs in any way that might undermine the conservation objectives.

The SNH HRA advice concluded that it can be ascertained that there is no adverse effect on site integrity through impacts to bog woodland at Ballochbuie SAC and Cairngorms SAC.

Oak and Birch Dominated Woodland Sites

Woodland Type: Western Acidic Oak Woodland

Old sessile oak woods with Ilex and Blechnum in the British Isles, often referred to as western acidic oak woodland, are a widespread woodland type found across much of the upland landscape of the UK. The habitat type comprises a range of woodland types dominated by mixtures of oak ( Quercus robur and/or Quercus petraea) and birch ( Betula pendula and/or Betula pubescens). The more frequently encountered associated trees and shrubs are holly Ilex aquifolium and rowan Sorbus aucuparia. It is characteristic of acidic, base-poor soils in upland areas with at least moderately high rainfall. It shows considerable variation across its range, in terms of the associated ground flora and the richness of bryophyte communities. There is also a continuous spectrum of variation between oak-dominated and birch-dominated stands. Often these local variations reflect factors such as rainfall, slope, aspect, soil depth, and past and present woodland management (e.g. coppicing, planting, grazing).

Knapdale

  • Moine Mhor SAC
  • Tarbert Woods SAC
  • Taynish and Knapdale Woods SAC

Tayside

  • Loch Lomond Woods SAC
  • Upper Strathearn Oakwoods SAC

HRA advice

Beaver foraging activity in combination with grazing and browsing pressure from other herbivores could lead to a loss of qualifying habitat.

The Knapdale Beaver Trial monitoring suggested that beavers rarely moved more than 30m from waterbodies, so any loss of habitat is likely to be confined to a small proportion of the site. Therefore some loss or deterioration of qualifying woodland near waterbodies is possible due to the combined impacts of beaver and other herbivores, leading to a change in the distribution of the habitat.

Change in the structure of accessible woodland areas is likely, but difficult to predict with any accuracy at present. Possible impacts include changes in the volume of deadwood, increases in dense young growth or in open space. Provided regeneration of felled trees and shrubs is able to continue, these changes are most likely to be beneficial, contributing to the dynamism which is an important feature of this habitat.

SNH HRA advice is that it is not possible to ascertain no adverse effect on site integrity without mitigation. Impacts are possible in areas of qualifying habitat likely to be used by beavers (i.e. within c.30m of water-bodies), as a result of the cumulative impacts of beaver and other herbivores.

Mitigation

If beaver colonise these sites, impacts should be monitored using the Woodland Grazing Toolbox methodology. Signs of over-grazing can be detected before any adverse impacts result. These impacts should then be mitigated by using all necessary herbivore management measures (of deer or beavers, or both).

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Upland Oak Woodland

This is woodland type is found on well-drained to rather poorly drained, acidic to neutral soils in the upland parts of Britain, where either pedunculate or sessile oak forms at least 30% of the canopy cover. Other tree and shrub species occur commonly, especially downy birch, silver birch, rowan, hazel and holly. Like upland birchwoods (see below), the field layer is often grass or heath dominated, but when very heavily grazed can be dominated by large bryophytes. Small herbs, bryophytes and ferns, including bracken, can be very common, and on rocks, banks, trees and shrubs in the west there can be a rich flora of oceanic bryophytes including some uncommon species.

A review of the above identified upland oak woodland SSSIs indicates that many are in unfavourable condition and are failing to meet their site attribute targets for volume of deadwood, level of grazing / browsing, structural diversity or evidence of regeneration.

Knapdale

  • Artilligan and Abhainn Srathain Burns SSSI
  • Ellary Woods SSSI
  • Inverneil Burn SSSI
  • Knapdale woods SSSI
  • Moine Mhor SSSI
  • Taynish Woods SSSI
  • Tayvallich Juniper and Fen SSSI

Tayside

  • Cambusurich Wood SSSI
  • Cardney Wood SSSI
  • Carie and Cragganester Woods SSSI
  • Comrie Woods SSSI
  • Edinchip Wood SSSI
  • Glen Falloch Woods SSSI
  • Innishewan Wood SSSI
  • Monzie Wood SSSI
  • Pass of Killiecrankie SSSI
  • Pass of Leny Flushes SSSI

SSSI Assessment

Impacts within upland oak woodland SSSI habitat are likely to be similar to those described above for western acidic oak woodland. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance.

Mitigation

As beavers naturally colonise 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. These impacts should then be mitigated by using all necessary herbivore management measures (of deer or beavers, or both).

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Upland Birch Woodland

Upland Birchwoods in Scotland are dominated by a series of stands of downy and/or silver birch with constituents such as rowan, willow, juniper and aspen. Boundaries are often diffuse and liable to change as woodlands expand and contract in response to fires and changes in grazing pressure. Refuges, such as those occurring on cliffs or rocky patches, may develop permanent tree cover that can contain richer, less mobile species. On more acidic soils, rowan is a prominent component, and juniper can form the underwood in the eastern highlands.

A review of the above identified upland birch woodland SSSIs indicates that many are in unfavourable condition and are failing to meet their site attribute targets for volume of deadwood, level of grazing / browsing, structural diversity or evidence of regeneration.

Knapdale

There are no sites identified in Knapdale that are designated for upland birch woodland habitat.

Tayside

  • Beinn a' Ghlo SSSI
  • Black Wood of Rannoch SSSI
  • Glen Lochay Woods SSSI
  • Leven Valley SSSI
  • Linn of Tummel SSSI
  • Struan Wood SSSI

SSSI Assessment

Impacts within upland birch woodland SSSI habitat are likely to be similar to those described above for western acidic oak woodland. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance.

Mitigation

As beavers naturally colonise 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. These impacts should then be mitigated by using all necessary herbivore management measures (of deer or beavers, or both).

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Woodland Type: Lowland Mixed Broadleaved Woodland

Lowland mixed deciduous woodland includes woodland growing on the full range of soil conditions, from very acidic to base-rich, and takes in most semi-natural woodland in southern and eastern England, and in parts of lowland Wales and Scotland. It thus complements the ranges of upland oak and upland ash types. It occurs largely within enclosed landscapes, usually on sites with well-defined boundaries, at relatively low altitudes, although altitude is not a defining feature. Many are ancient woods. The woods tend to be small, less than 20ha. Often there is evidence of past coppicing, particularly on moderately acid to base-rich soils.

A review of the above identified lowland mixed broad leaved SSSIs indicates that many are in unfavourable condition and are failing to meet their site attribute targets for volume of deadwood, level of grazing / browsing, structural diversity or evidence of regeneration.

Knapdale

There are no sites identified in Knapdale that are designated for lowland mixed broad leaved woodland habitat.

Tayside

  • Drummond Lochs SSSI
  • Kincardine Castle Wood SSSI
  • Methven Woods SSSI

SSSI Assessment

Impacts within lowland mixed broadleaved woodland SSSI habitat are likely to be similar to those described above for western acidic oak woodland. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance.

Mitigation

As beaver naturally colonise 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. These impacts should then be mitigated by using all necessary herbivore management measures (of deer or beavers, or both).

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Ash Dominated Woodland Sites

Woodland Type: Mixed Woodland on Base-Rich Soils Associated With Rocky Slopes

Tilio-Acerion forests of slopes, screes and ravines (also referred to as mixed woodland on base-rich soils associated with rocky slopes) are woods of ash Fraxinus excelsior, wych elm Ulmus glabra and lime (mainly small-leaved lime Tilia cordata but more rarely large-leaved lime T. platyphyllos). Introduced sycamore Acer pseudoplatanus is often present and is a common part of the community in mainland Europe, where it is native. The habitat type typically occurs on nutrient-rich soils that often accumulate in the shady micro-climates towards the bases of slopes and ravines. Therefore it is found on calcareous substrates associated with coarse scree, cliffs, steep rocky slopes and ravines, where inaccessibility has reduced human impact. It often occurs as a series of scattered patches grading into other types of woodland on level valley floors and on slopes above, or as narrow strips along stream-sides. More extensive stands occur on limestone and other base-rich rocks.

Knapdale

There are no sites identified in Knapdale that are designated for mixed woodland on base-rich soils associated with rocky slopes habitat.

Tayside

  • Craighall Gorge SAC
  • Keltneyburn SAC

HRA Advice

Beaver activity in combination with pressure from other herbivores could lead to a loss of qualifying habitat, but this is only possible on flatter ground at these SACs. The steeper slopes which are typical of this habitat are largely avoided by herbivores therefore the exact extent of possible impacts would be limited by the topography of the SACs (if beavers remain in the area).

SNH HRA advice is; as a result of the potential combined grazing and browsing impacts of beaver and other herbivores on this qualifying interest, that without mitigation, it cannot be ascertained that there is no adverse effect on site integrity.

Mitigation

Any potential adverse impacts on the integrity of the SAC should be mitigated through herbivore management measures (upon either deer or beavers or both) before they occur. Signs of over-grazing can be detected before any adverse impacts result. As beavers naturally colonise these sites, impacts should be monitored using the Woodland Grazing Toolbox methodology. If the necessary mitigation measures, including monitoring are carried out then SNH advise that it can be ascertained that there is no adverse effect on site integrity.

Woodland Type: Upland Mixed Ash Woodland

This is woodland on base-rich soils, in upland parts of the UK. The tree canopy typically includes ash Fraxinus excelsior, wych elm Ulmus glabra or sycamore Acer pseudoplatanus. Downy birch Betula pubescens, rowan Sorbus aucuparia, hazel, Corylus avellana goat willow Salix caprea, grey willow Salix cinerea, eared willow Salix aurita, bird cherry Prunus padus and alder Alnus glutinosa can occur too. Some examples, particularly in the extreme west, are dominated by hazel. The field layer is typically herb-rich. Bryophytes are generally common and epiphytic floras can be rich and include mosses, liverworts, large foliose lichens and many smaller crustose lichens.

A review of the below identified upland mixed ash woodland SSSIs indicates that many are in unfavourable condition and are failing to meet their site attribute targets for volume of deadwood, level of grazing / browsing, structural diversity or evidence of regeneration.

Knapdale

There are no sites identified in Knapdale that are designated for upland mixed woodland habitat.

Tayside

  • Back Burn Wood and Meadows SSSI
  • Birks of Aberfeldy SSSI
  • Cambusurich Wood SSSI
  • Craighall Gorge SSSI
  • Den of Airlie SSSI
  • Den of Alyth SSSI
  • Den of Fowlis SSSI
  • Den of Riechip SSSI
  • Devon Gorge SSSI
  • Dollar Glen SSSI
  • Finlarig Burn SSSI
  • Flisk Wood SSSI
  • Glen Lochay Woods SSSI
  • Glen Tilt Woods SSSI
  • Keltneyburn SSSI
  • Romadie Wood SSSI

SSSI Assessment

Impacts within upland mixed ash woodland SSSI habitat are undistinguishable from those described above for mixed ash woodland. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance.

Mitigation

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. These impacts should then be mitigated by using all necessary herbivore management measures (of deer or beavers, or both).

See section 5 for beaver management techniques used to mitigate the impact of beaver foraging and damming activity. See section 7 for details on the approach to SCM and beavers.

Hazel Dominated Woodland

Woodland Type: Atlantic Hazelwoods

Atlantic hazel occurs in the oceanic climatic areas of the Western British Isles, but only in a very few places does it achieve particular characteristics that mark it out as a distinctive habitat of high biodiversity, particularly as it supports a diverse assemblage of oceanic lichens (see section 4.3). Hazel is a multi-stemmed pioneering and light-demanding shrub. A key requirement for its successful germination and establishment is that there is no closed canopy above to shade out the emerging seedling. When cut it coppices readily from its rootstock.

Knapdale

The distribution of Atlantic hazelwoods (with 80% or more hazel in the canopy) that occur within the Knapdale beaver policy area and overlap with beaver core woodland is illustrated in Map 11 below. NB Atlantic hazelwoods are not a qualifying feature of SAC or SSSI but are of conservation importance; they are rich in biodiversity, uncommon habitats, often hosting internationally important lichen populations.

Map 11: Distribution of Atlantic hazel woods that overlap with core beaver woodland in the Knapdale beaver policy area - also included in Appendix 1 for ease of reference.

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 condition experienced by western Scotland. While there are hazelwoods within the Tayside policy area (0.72 ha with 80% canopy), they are less likely to host the internationally important lichen species referred to above. However, hazel along watercourses can provide habitat for the eastern European extent of otherwise oceanic lichens (see section 4.3, Map 11) and as such their importance should not be ignored.

Assessment

Beavers at Knapdale ( SBT) showed strong preferences for willow, ash, rowan and hazel, but avoided alder. They displayed a greater use of hazel Corylus avellana in the two latter years of this study suggesting that this species may ultimately become less abundant, depending on the impact of deer on the regrowth. Alternatively, smaller younger shoots may predominate, with a loss of older stems.

There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of conservation 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. If beavers reach 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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