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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
4.5 Beavers and Invertebrates

4.5 Beavers and Invertebrates

4.5.1 How beaver activity affects invertebrates

4.5.1.1 Effects from dam building activity

The current literature suggests that the effects of beaver impoundments on aquatic invertebrates are mostly positive. By building dams and digging small canals, beavers create and extend wetland micro-habitats that support many invertebrate taxa. Beaver dams change the predominantly flowing character of aquatic ecosystems to a mixture of flowing and still conditions, which is of particular benefit to predatory invertebrates. The wetland micro-habitat created by beavers attracts water beetle colonists and several species of Odonata (dragonflies and damselflies), which are at the top of the food pyramid.

Studies in Germany have shown that the numbers of Odonata are significantly higher in beaver territories and dammed waters than in areas without beavers. In a river system where beavers had been established since 1981, 29 species of dragonflies were associated with beaver ponds and the surrounding wetland. In comparison, only four species were found in the streams. These figures are not surprising, as the number of dragonfly species that breed in flowing water is far fewer than those breeding in still waters. In North America, dragonflies have long been associated with newly created beaver ponds. In Virginia, 43 dragonfly and 23 damselfly species (a third of them on the state's rare species list) were found in the Laurel Fork recreation area, which consists of a series of river systems with beaver ponds. The majority of species were in beaver ponds and four were known from only beaver ponds or their vicinity. At one specific site of the study, the number of species of dragonflies fell from 61 to four when beavers abandoned it.

In Sweden, Dytiscidae (predatory diving beetles) and Corixidae (aquatic Hemiptera, or true bugs) are abundant and typical beaver pond fauna. Studies in Canada and Finland showed that larval densities of Ephemeroptera (mayflies), Trichoptera (caddisflies) and Plecoptera (stoneflies) decreased in dammed river beds. In the USA, a site immediately downstream of a beaver dam exhibited lower Plecoptera and Trichoptera densities than upstream, but the densities of Diptera (true flies), Ephemeroptera and invertebrate predators in general were higher immediately downstream of the beaver dam.

4.5.1.2 Effects from beaver foraging activity

Beaver herbivory on cottonwood trees in western USA caused an increase in shoot length, which subsequently led to an increase in sawfly (Hymenoptera: Symphyta) abundance. In addition, the open canopy created by beavers allowed the white pine weevil Pissodes strobi to flourish where it had been absent previously even in the presence of its food source, the white pine Pinus strobus.

A summary (see Table 4.5.1) of the potential interactions between beavers and invertebrates is presented below; where possible these have been attributed to a neutral, positive or negative effect.

Table 4.5.1: Summary of potential interactions between beavers and invertebrates.

Activity

Mechanism

Positive effects

Negative effects

Notes

Felling

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

  • If scrub is removed as a result of beaver grazing, clearings will be created, which is favourable to some invertebrates, such as some sun-loving dragonfly and butterfly species
  • Overall positive effects on diversity at landscape scale since beaver activity markedly increases habitat heterogeneity and patchiness through the creation of canopy gaps, etc.
  • Increased light penetration may lead to increased production within streams, ponds and lochs. Increased primary productivity and temperature may increase production of aquatic macroinvertebrates
  • May benefit species which can damage or kill tree species (e.g. white pine weevil in North America can benefit from open canopy created by beavers)

Limited information in the literature so there are many areas of uncertainty

Felling

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

  • Bark-stripping of felled, larger aspen trees destroys the microhabitat required by the rare aspen hoverfly. Felled young aspen also interrupt the succession process and reduce the availability of dead wood. Fourteen moth species and 14 saproxylic flies also depend on aspen

See also Annex 1 Table 3.4 for beaver effects on aspen

Felling

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

  • Increase in the volume of dead and decaying wood will be beneficial to saproxylic species, particularly beetles

Felling and constructions

Changes in amount/diversity of woody material in watercourses

  • Accumulation of woody debris may shelter water beetles from predatory fish and provide protection for water beetle prey species
  • In deeper water, submerged debris may sustain an invertebrate fauna dependent on the algal biofilm that grows on wood

Dams/pond creation

Change from lotic to lentic habitat

  • Overall positive effects on diversity at landscape scale since beaver activity markedly increases habitat heterogeneity and patchiness, with lentic and associated wetland habitat interspersed with lotic habitat
  • A change to localised lentic conditions is beneficial to some predatory groups such as Dytiscidae (predaceous diving beetles) and Corixidae (aquatic Hemiptera, or true bugs)
  • A reduction in the volume of floating macrophyte detritus may reduce the size of breeding habitat for some dragonflies
  • Reducing the amount of flowing water may be negative for the beautiful demoiselle and other fast water species such as the golden-ringed dragonfly
  • Possible localised reduction in larval densities of Ephemeroptera (mayflies), Trichoptera (caddisflies) and Plecoptera (stoneflies) in ponds
  • A possible reduction in habitat suitability for juvenile freshwater pearl mussel in beaver ponds

.

Dams/pond creation

Change in hydrological processes on riparian and downstream habitat

Likely to be a range of subtle effects, which will affect different species in different ways.

Dams/pond creation

Changes in water quality downstream

  • Reduction in sediment loads resulting from filtering effect of dams, potentially improving downstream habitat quality for species such as freshwater pearl mussel

Dams/pond creation

Change in standing dead wood resulting from inundation of trees

  • Standing dead trees and semi-submerged wood may create suitable breeding sites for several species groups (among them the rare Lipsothrix spp. craneflies)

Dams/pond creation

Impacts on movement of species

  • Possible effect on freshwater pearl mussel if migration of salmonid hosts is affected by the presence of dams (see Annex 1 Table 3.14 for beaver effects on fish)

Other constructions

Creation of lodges, burrows, canals etc.

  • Beaver activity (foraging and excavation of canals) will increase habitat diversity (heterogeneity and patchiness)

Indirect habitat creation/restoration initiatives as result of beaver presence

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

  • Any programme of riparian woodland/wetland restoration and creation is likely to benefit overall invertebrate diversity

4.5.2 Distribution of invertebrates in the beaver policy area

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

4.5.2.1 Invertebrates of conservation importance

To determine whether the activity of beavers on invertebrates is significant in the context of this Strategic Environmental Assessment, 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 4.5.2 below therefore identifies those invertebrates of conservation importance that utilise 'potential beaver core woodland' (as described in section 4.1 of this report) and are found within the beaver policy areas.

The Aspen Hover fly has been screened out due to the limited overlap with the beaver policy area and Aspen dominated woodlands as discussed in the section 4.2 Beavers and Woodland. The Northern emerald dragonfly has been screened out, as it breeds in moorland bogs and pools as well as open areas in pine woods; there is therefore very limited overlap with habitats utilised by beavers. Similarly for Marsh Fritillary butterfly which tends to inhabit short coastal grasslands. Both species of whorl snail (Round-mouthed and Geyer's) found in areas where calcareous ground water percolates to the surface have been screened out as their locations are very unlikely to be significantly affected by beaver activity either through dam building or tree felling.

Table 4.5.2: Summary of invertebrates of conservation importance within the beaver policy area that overlap with potential beaver core woodland

Invertebrate (species or group)

Conservation importance

Beetles

Coille Coire Chuilc SSSI
Gannochy Gorge SSSI
Loch Leven SSSI
Rossie Moor SSSI
Struan Wood SSSI
Taynish Woods SSSI

Moths

Struan Wood SSSI
Taynish Woods SSSI

Fresh water pearl mussel

River Dee SAC
River South Esk SAC
River Spey SAC
River Spey SSSI
Lubnaig Marshes SSSI

Dragonflies and Damselflies

Black Wood of Rannoch SSSI
Ellary Woods SSSI
Knapdale Woods SSSI
Taynish Woods SSSI
Tayvallich Juniper and Fen SSSI

Flies

Cambusurich Wood SSSI
Coille Coire Chuilc SSSI
Pass of Killiecrankie SSSI
Taynish Woods SSSI
Rossie Moor SSSI
Shingle Islands SSSI
Loch Lubnaig Marshes SSSI

Invertebrate assemblage

Black Wood of Rannoch SSSI
Cairngorms SSSI
Crannach Wood SSSI
Den of Airlie SSSI
Eastern Cairngorms SSSI
Glen Lochay Woods SSSI
Methven Woods SSSI

4.5.3 Assessment of likely effects on invertebrates of conservation importance in the beaver policy area

Each of the invertebrate species identified in Table 4.5.2 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 species. Assessment of other species (i.e. SSSI notified features), has been made in the context of the SNH HRA advice in combination with knowledge of the individual 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.

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 any programme of riparian woodland/wetland restoration and creation which is likely to benefit overall invertebrate diversity.

4.5.3.1 Consideration of potential positive effects on invertebrates of conservation importance

The impact of beaver activity on the invertebrate species 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 4.5.3.2. A more general discussion is provided first, followed by a more species / site-based assessment.

The effects of beavers on aquatic invertebrates are considered generally positive because their activity (such as foraging and excavation of canals) markedly increases habitat heterogeneity and patchiness by the creation of canopy gaps, and generates wetland habitats through impoundment. Structures built by beavers, such as dams, lodges and beaver meadows, also create novel colonising opportunities for different species groups. As a consequence, beaver ponds show greater abundance and diversity of aquatic invertebrates in relation to other wetland types.

The positive effect of beaver interaction with woodland habitats for invertebrates can be summarised as:

  • If scrub is removed as a result of beaver grazing, clearings will be created, which is favourable to some invertebrates, such as some sun-loving dragonfly and butterfly species.
  • Overall positive effects on diversity at landscape scale since beaver activity markedly increases habitat heterogeneity and patchiness through the creation of canopy gaps, etc.
  • Increase in the volume of dead and decaying wood will be beneficial to saproxylic species, particularly beetles.
  • Standing dead trees and semi-submerged wood may create suitable breeding sites for several species groups (among them the rare Lipsothrix spp. craneflies)

The positive effect of beaver interaction with freshwater/wetland habitats for invertebrates can be summarised as:

  • Increased light penetration may lead to increased production within streams, ponds and lochs. Increased primary productivity and temperature may increase production of aquatic macroinvertebrates.
  • Accumulation of woody debris may shelter water beetles from predatory fish and provide protection for water beetle prey species. In deeper water, submerged debris may sustain an invertebrate fauna dependent on the algal biofilm that grows on wood.
  • Reduction in sediment loads resulting from filtering effect of dams, potentially improving downstream habitat quality for species such as freshwater pearl mussel
  • A change to localised lentic conditions is beneficial to some predatory groups such as Dytiscidae (predaceous diving beetles) and Corixidae (aquatic Hemiptera, or true bugs)
  • Overall positive effects on diversity at landscape scale since beaver activity markedly increases habitat heterogeneity and patchiness, with lentic and associated wetland habitat interspersed with lotic habitat.

Further narrative is provided below with respect to certain groups of invertebrates: beetles and moths.

Beetles

Beetles belong to the Order Coleoptera, meaning "sheath-winged", a reference to their hardened forewings. They range in size from 0.25 mm to over 17 cm, and occur in almost every habitat.

Beetles are the largest group of insects, with approximately 400,000 species described across the world. There are about 4,000 species from the British Isles of which about two thirds, or between 2,500 and 3,000, occur in Scotland. However, most of Scotland remains poorly surveyed and our knowledge of the beetle fauna as a whole is patchy and incomplete.

Beetles fulfil a range of roles in a healthy ecosystem. Many beetles are important pollinators, while dung beetles (especially (scarabs) remove vast quantities of dung from the environment.

Knapdale

  • Taynish Woods SSSI

Tayside

  • Coille Coire Chuilc SSSI
  • Gannochy Gorge SSSI
  • Loch Leven SSSI
  • Rossie Moor SSSI
  • Struan Wood SSSI

SSSI Assessment

See section 4.5.3.2 below for narrative with respect to the following SSSIs, Coille Coire Chuilc, Gannochy Gorge, Struan Wood and Taynish Woods.

Rossie Moor SSSI is designated for its aquatic beetle assemblage. Recent studies in Swedish wetlands have found that the diversity of aquatic plants and water beetles was higher at the patch, site and landscape scale than in other non-beaver-related wetland types within the same area. This was also reflected through monitoring at Knapdale ( SBT) which recorded an increase in water beetle diversity when compared to baseline surveys without beaver occupancy. The creation of woody debris in particular, through feeding and creation of food caches may be an important component of habitat complexity in beaver occupied ponds/lochs. It provides many beetle species with direct shelter and refugia from fish, as well as concealment from other predatory species of beetles. Therefore, while there are natural heritage interests of national importance on this site, they are unlikely be adversely affected by beaver activity.

Loch Leven SSSI has an extremely rare carrion beetle associated with its wetland habitat. The adult beetle feeds on any type of carrion on the water's edge and the larvae feeds on aquatic snails. The presence of beaver will not affect these food sources. Therefore, while there are natural heritage interests of national importance on this site, they are unlikely be adversely affected by beaver activity.

Mitigation

No mitigation has been identified.

Moths

Moths are less known compared with butterflies mainly because they generally fly by night. They are, however, also much more diverse and include some species that are even more striking than our butterflies. There are about 34 species of butterfly seen regularly in Scotland but about 1,300 species of moth. Some moths do fly by day such as the red and black burnet moths in grassland that still has a good range of flowers, especially by the sea.

Knapdale

  • Taynish Woods SSSI

Tayside

  • Struan Wood SSSI

SSSI Assessment

Taynish Woods SSSI is designated for its micro moth Clepsis rurinana and other moths associated with semi natural woodland. Struan Wood SSSI is designated for its Rannoch roller moth Ancylis tineana.

Woodlands that benefit moth species are generally diverse and uneven in structure. They are likely to have a mixture of mature and tall trees, patches of open areas as well as patches of dense regeneration and tree canopy. All of which provide different micro habitats for moth species to carry out various parts of their life cycle such as areas where eggs can be laid, where pupae can develop undisturbed and where caterpillars can feed; for example the Rannoch roller utilises birch, blackthorn and hawthorn, whereas Clepsis rurunana larve mainly feed on honeysuckle, oak and dog rose species.

As noted in section 4.2 (Beavers and Woodland), beaver felling activity can lead to changes in the structural diversity or patchiness of the riparian woodland zone all of which could contribute to many of the ecological requirements of moth species including those identified above, noting however that beaver activity is mostly found within 10m of the water's edge and as such, depending on the individual moth species requirement, there may be very little overlap with beavers. Therefore, while there are natural heritage interests of national importance on these sites, they are unlikely be adversely affected by beaver activity.

4.5.3.2 Consideration of potential negative effects on invertebrates of conservation importance

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

Freshwater Pearl Mussel

The freshwater pearl mussel is an important part of our biodiversity and has an important place in our cultural heritage. Moreover, the species is one of the most critically endangered molluscs in the world. Part of the reason pearl mussels are rare in Scotland is due to ongoing, illegal pearl fishing. Scotland contains many of the world's most important remaining populations.

Freshwater pearl mussels are similar in shape to common marine mussels but grow much larger and live far longer than their marine relatives. Incredibly, they can live for more than 100 years, making them one of the longest-lived invertebrates. They can grow to as large as your hand and are dark brown to black in colour. They live at the bottom of clean, fast-flowing rivers, where they can be completely or partly buried in course sand or fine gravel. They feed by drawing in river water and filtering out fine particles. Each day an adult is able to filter more water than we use in an average shower. They have a complex lifecycle and, in their first year, they harmlessly live on the gills of young salmon or trout.

Knapdale

There are no sites identified at Knapdale beaver policy area for fresh water pearl mussel.

Tayside

  • River Dee SAC
  • River South Esk SAC
  • River Spey SAC
  • River Spey SSSI
  • Lubnaig Marshes SSSI

HRA advice

The principle means by which beavers could affect pearl mussels in any SAC, is through the construction of dams. This could have a detrimental effect if pearl mussels are immediately upstream, potentially causing disturbance of the species and changing the habitat that can support pearl mussels. However, it is worth noting that in all SACs more than 99.9% of pearl mussels are in the main stems of the rivers which are too large for beavers to dam.

The other relevant potential impact is the effects on the salmonid host(s). Dam building in the tributaries of the SACs could impede the migration of local Atlantic salmon and trout populations upon which the mussels depend to complete their life cycle, although nearly all of the mussels in all three SACs live further downstream in the mainstems of the SAC rivers where damming will not affect the pearl mussels. The appraisal for the Atlantic salmon qualifying interest of each of the three riverine SACs in section 4.11 Beavers and Fish, which concludes that an adverse effect on Atlantic salmon cannot be ruled out without mitigation.

The SNH HRA concluded given that freshwater pearl mussels (within only limited exceptions on the River Spey) are located far downstream of locations where beavers may be able to build dams, then an indirect impact on pearl mussels is improbable. However, an adverse effect cannot be ruled out with certainty for the three SACs without the implementation of the mitigation required for Atlantic salmon.

SSSI Assessment

Impacts to freshwater pearl mussel for River Spey SSSI and Lubnaig Marshes SSSI are likely to be similar to those described above for the aforementioned SACs. There is therefore potential for beaver activity to adversely affect the natural heritage interest of national importance.

Mitigation

The relevant text from Section 4.11 Beavers and Fish, has been replicated here to aid the reader.

Mitigation to ensure passage may be achieved through the easement or removal of barriers at certain times of year important for salmon (i.e. during spawning and smolt emigration) or through the installation of flow control devices. However; it is unclear at this time whether flow control devices could be used to assist the upstream migration of large Atlantic salmon (which is typical of 'Spring' fish). If a beaver dam might cause an adverse effect on the integrity of the SAC and a flow control device might not allow passage upstream, then alternative mitigation measures which will allow passage must be put in place. These mitigation measures should be included in a Beaver Management Plan for the individual SACs, which should also set out in what circumstances there could be an adverse effect on site integrity, and a framework through which to implement any mitigation measures should they become necessary.

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.

Beetles

Beetles belong to the Order Coleoptera, meaning "sheath-winged", a reference to their hardened forewings. They range in size from 0.25 mm to over 17 cm, and occur in almost every habitat.

Beetles are the largest group of insects, with approximately 400,000 species described across the world. There are about 4,000 species from the British Isles of which about two thirds, or between 2,500 and 3,000, occur in Scotland. However, most of Scotland remains poorly surveyed and our knowledge of the beetle fauna as a whole is patchy and incomplete.

Beetles fulfil a range of roles in a healthy ecosystem. Many beetles are important pollinators, while dung beetles (especially (scarabs) remove vast quantities of dung from the environment.

Knapdale

  • Taynish Woods SSSI

Tayside

  • Coille Coire Chuilc SSSI
  • Gannochy Gorge SSSI
  • Loch Leven SSSI
  • Rossie Moor SSSI
  • Struan Wood SSSI

SSSI Assessment

The following SSSIs, Coille Coire Chuilc, Gannochy Gorge, Struan Wood and Taynish Woods, all have beetle assemblage comprising of saproxylic beetles i.e. beetles dependant on dead or decaying wood. They may not be dependent on dead wood for their entire life cycle, for example for some species it's the larvae that feed on decaying wood whereas the adults may feed on other things such as nectar.

Rossie Moor SSSI is designated for its aquatic beetle assemblage; and Loch Leven for it's rare beetle species; assessment of impacts to these sites have been dealt with above in section 4.5.3.1. and are expected to be positive or neutral.

Coille Coire Chuilc, Gannochy Gorge, Struan Wood and Taynish Woods SSSIs

As noted in section 4.2 (Beavers and Woodland), beaver felling of trees could lead to increased fallen dead wood in some areas, although much of the material is removed for food and construction. Beaver damming activity and pond creation can lead to the 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. Therefore while beaver activity is expected to increase the volume of deadwood within woodlands, and noting that most beaver felling occurs with 10m of the water's edge in the riparian zone, monitoring would be required to assess the scale of effect of removing the wood for consumption i.e. it could be eaten immediately or placed underwater by a beaver in a food cache, both of which would make it unavailable to saproxylic beetles. This demonstrates that there is some potential for beaver activity to adversely affect the natural heritage interests of national importance but the extent to which will be dependent on site-specific circumstances, including the size of the riparian woodland zone compared with the distribution of suitable woodland across the designated site, the volume and location of the existing deadwood resource and the nature of the beaver occupancy.

Dragonflies

The order Odonata comprises dragonflies (wings outstretched at rest) and damselflies (wings folded at rest). They are an ancient group, having arisen in the Carboniferous Period (300 million years ago). This is 150 million years before the first birds, and 295 million years before man appeared on Earth.

They are mainly tropical insects with over 5,000 species worldwide. Europe has about 114 breeding species, the British Isles 38 and Scotland 21. In Scotland, the commonest species breed in ponds and lochans.

The adults feed on live insects which they catch while in flight, particularly midges and mosquitoes. They also will take butterflies, moths and smaller dragonflies. The adults frequent sheltered, sunny glades where prey is plentiful. Eggs are deposited in, or near, fresh water or into aquatic vegetation. The larvae prey on a variety of aquatic organisms and moult several times over a period of months, or years depending on species.

Knapdale

  • Ellary Woods SSSI
  • Knapdale Woods SSSI
  • Taynish Woods SSSI
  • Tayvallich Juniper and Fen SSSI

Tayside

  • Black Wood of Rannoch SSSI

SSSI Assessment

Each of the sites identified above have a variety of different damsel and dragonfly species that contribute to its assemblage feature. Evidence from Europe suggests that numbers of Odonata species are higher in areas occupied by beavers where they make use of beaver pond and surrounding wetlands. In North America, dragonflies have long been associated with newly created beaver ponds. In Virginia, 43 dragonfly and 23 damselfly species were found in the Laurel Fork recreation area, which consists of a series of river systems with beaver ponds. At one specific site of the study, the number of species of dragonflies fell from 61 to four when beavers abandoned it.

Beavers can feed directly on many of the aquatic and emergent plant species that some dragonflies rely upon to complete certain stages in their life history. This was noted in Knapdale ( SBT) in relation to the hairy dragonfly Brachytron pratense where the loss of cover of key emergent vegetation through beaver grazing or water level rise, resulted in a loss of trapped floating macrophyte detritus habitat and so a loss of suitable breeding habitat . Conversely, glades created in the willow and birch scrub around many of the beaver lochs, created sheltered feeding areas for adults including other species such as the beautiful demoiselle Calopteryx virgo which was similarly monitored at Knapdale. The beautiful demoiselle is adapted to flowing water conditions and the impact of damming on the habitat requirements of this species may be affected by reducing the amount of flowing water downstream of any dam.

Experience from Scotland and elsewhere suggests that while there are positive benefits to many odonata species (see section 4.5.3.1 above), that the interaction between beavers and individual species is complex and while there may be positive gain overall all, some species may lose out. Therefore, there may be some potential for beaver activity to adversely affect the natural heritage interests of national importance with respect to the above mentioned SSSIs but the extent to which will be dependent on the site-specific circumstances.

Mitigation

If beaver colonise these sites, impacts should be monitored through SCM and appropriate mitigation put in place if required. 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.

Flies

Although beetles are the dominant insect group worldwide, flies (Order Diptera, meaning "two wings") are more abundant in temperate regions. In the British Isles, there are about 7,000 species.

The young stages of flies - the larvae - are commonly found in the soil, water, plants, carrion, dung, dead wood - mostly places with high levels of moisture. Many are nectar feeders and play an important role as pollinators. That's the case of hoverflies; they are familiar garden visitors. Others feed on decaying matter and are important for recycling dung and dead animals.

Scotland is home of two hoverflies of special interest because of their rarity and the conservation efforts put together to protect them; they are the aspen hoverfly and the pine hoverfly.

Other important species in Scotland are the craneflies, Scottish yellow splinter and the Northern yellow Splinter, and the stiletto fly Spiriverpa lunulata.

Knapdale

  • Taynish Woods SSSI

Tayside

  • Cambusurich Wood SSSI
  • Coille Coire Chuilc SSSI
  • Pass of Killiecrankie SSSI
  • Rossie Moor SSSI
  • Shingle Islands SSSI
  • Loch Lubnaig Marshes SSSI

SSSI Assessment

The aforementioned SSSIs are all notified for their fly species or assemblage features. Some are associated with specific habitats such as semi-natural woodland at Cambusurich Wood and Pass of Killiecrankie SSSIs, or more moist areas such as mire, fen and flush habitats at Coille Coire Chuilc, Taynish Woods and Rossie Moor SSSIs. Some sites, such as Loch Lubnaig Marshes SSSI are important for specific species such as the hoverfly Chamaesyrphus scavoides and the cranefly Tipula limbata or the stiletto fly Spiriverpa lunulata at Shingle Islands SSSI.

The limited current knowledge of the habitat requirements of many of these fly species for which these sites have been designated, combined with their often complex life history characteristics, makes understanding how and when beaver activity could affect them, either positively or negatively, particularly difficult. And while we have a growing evidence base demonstrating how beaver activity affects certain habitats types, some of which has been described in other sections e.g. 4.2 Beavers and Woodlands as well as 4.9 Beavers and standing freshwater habitats, the scale of effects at an individual site or species level is not always possible in the context of currently available science.

Therefore, there may be some potential for beaver activity to adversely affect the natural heritage interests of national importance with respect to the above mentioned SSSIs but the extent to which will be dependent on the site-specific circumstances.

Mitigation

If beaver colonise these sites, impacts should be monitored through SCM and appropriate mitigation put in place if required. 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.

Invertebrate Assemblage

Most invertebrates have annual life cycles and, unlike plants, which can have dormant seed or resistant vegetative rootstocks, they cannot survive adverse conditions or periods when their habitat is unsuitable. This position is further complicated by the fact that many invertebrates, particularly insects, have complex life histories in which the early growing stages (e.g. larvae) typically have different needs from the more mobile, reproductive adult stage. A familiar example is the plant-feeding larva of a butterfly in contrast to the flower-visiting adult.

Invertebrates are small, and their body temperature - and hence their activity - is greatly influenced by the micro-climate where they live. Consequently, vegetation structure, as well as species composition, has a profound effect upon the distribution and numbers of many species.

Although many invertebrates are highly mobile and can rapidly colonise newly available habitats (for instance some butterflies and moths, dragonflies and caddis flies), others are sedentary and typically move only short distances. Another characteristic of many invertebrates is their great specialisation: they are able to occupy narrow niches and exploit tiny micro-habitats within, for example, plant seeds or sap runs on mature trees, or they are the internal parasitoids of the eggs or later stages of other invertebrates. This specialisation enables many species to coexist within a habitat, but it can also mean that the rarest species, which tend to display the greatest specialisation, are vulnerable to local extinction if their precise habitat requirements and life cycle needs disappear.

Knapdale

There are no sites identified with the Knapdale beaver policy area with an Invertebrate assemblage feature.

Tayside

  • Black Wood of Rannoch SSSI
  • Cairngorms SSSI
  • Crannach Wood SSSI
  • Den of Airlie SSSI
  • Eastern Cairngorms SSSI
  • Glen Lochay Woods SSSI
  • Methven Woods SSSI

SSSI Assessment

The aforementioned SSSIs all have notified invertebrate assemblage features. Each site has a variety of the different invertebrate groups including, spiders, wood ants, flies, beetles as well as dragonflies, butterflies and moths. Some of these will be associated with the woodland habitats distributed on the site and others may be associated with lochs and wetlands. As indicated above (4.5.1) there are many example of beaver foraging and damming activity that provides positive benefits to a wide range of invertebrate species, however the interaction between beavers and invertebrates at an individual species level is complex and while there may be positive gain overall all, some species may lose out.

Therefore, there may be some potential for beaver activity to adversely affect the natural heritage interests of national importance with respect to the above mentioned SSSIs but the extent to which will be dependent on the site-specific circumstances.

Mitigation

If beaver colonise these sites, impacts should be monitored through SCM and appropriate mitigation put in place if required. 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.


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