Beavers in Scotland: consultation on the strategic environmental assessment

4.9 Beavers and standing freshwater habitats and wetland habitats

This section on standing freshwater habitats includes assessment of aquatic vascular macrophytes and wetland habitats, referred to hereafter as 'standing freshwater and wetland habitats'.

4.9.1 How beaver activity affects standing freshwater and wetland habitats

4.9.1.1 Effects of dam-building activities on standing freshwater lochs

The effects of beavers on plants have been linked to changes occurring as a consequence of habitat modification. Numerous studies have looked at the ecological effects of beaver dam-building around pond-wetland complexes and on streams. However, there is less information on the effects of beaver activity on larger, more discrete lake environments. Beavers tend not to dam in water bodies more than 0.85 m deep or more than 6 m wide which means that dam-building does not tend to occur within lakes, but it may occur in outflow and inflow streams.

Pond-wetland complexes inhabited by beavers represent a variety of habitats, which exhibit different stages of colonisation by biota, and therefore support a diversity of species. The diversity of plant species present in beaver ponds has been found to increase with time. Beaver activity also increases the number of invertebrate taxa present in ecosystems. Dam-building in stream systems introduces environments that provide habitat for invertebrates associated with standing waters.

The flooding of terrestrial environments results in the creation of wetland habitats adjacent to fully aquatic environments, increasing the number of niches associated with the standing water. Increased plant and invertebrate species richness supports other components of standing water/wetland systems, for example birds, bats, amphibians and fish. Where ponds are formed as a result of dam-building on stream systems, there may be an overall biodiversity gain, and downstream lotic (i.e. running water) habitats may benefit from better water quality with the dams creating sediment traps, although there may also be localised losses in stream biota.

4.9.1.2 Effects of foraging activities on standing freshwater lochs

Research has been carried out on the terrestrial food preferences of beavers, but also on grazing in aquatic habitats. Aquatic plants have been found to constitute a considerable proportion of beaver diet, though the degree of reliance on such plants varies with time of year and differs between sites.

In North America, beavers have been known to have both positive and negative effects on the abundance of invasive plant species. Although much of the literature relates to terrestrial rather than aquatic plants, parrot's feather Myriophyllum aquaticum and Elodea pondweeds, which are aquatic invasive non-native species present in Scotland, have been found to be highly preferred food species for beavers elsewhere.

Foraging by beavers affects existing habitat not only through the removal of preferred plant species, but also deposition of harvested plant material. Such material includes food for consumption during winter, but also discarded matter. Food caches are stored in slow moving waters and have been linked with positive effects on biodiversity. Compared with existing sand and gravel substrates, a higher abundance of macroinvertebrates, fish and amphibians has been found to be associated with beaver lodges and wood caches in lakes in Ontario and, in general, woody material is considered beneficial for invertebrates and fish in lakes.

4.9.1.3 Effects of damming and foraging activities on wetland habitats

The effects of dam-building activities by beavers on wetlands will vary depending on the local topography and wetland type. Effects are likely to cover the extent of wetland habitats and species, succession processes and the species composition and diversity of wetland communities. The construction of beaver dams can affect the hydrology, water chemistry, sediment transport patterns and nutrient levels in a number of different ways depending on local circumstances. Reduced flow velocity behind dams can lead to increased sediment deposition. Alternatively, the flooding of adjacent land can lead to an increase in the sediment load. The build-up of woody debris can lead to the formation of braided channels, pools and islands.

Dam building and feeding activities can also lead to changes in nutrient levels in the water and, depending on local conditions, beaver ponds can either act as a source of raised nitrogen and phosphorus levels or as nutrient sinks.

In some places raised water levels may lead to the creation of new wetlands or an expansion of the existing wetland habitats. Elsewhere, the maintenance of raised water levels may lead to a reduction in the extent of some wetland habitats, or a change in the vegetation communities present, in response to changes in the hydrological regime, water chemistry, sediment transport patterns and nutrient levels.

A summary of the potential interactions between beavers and standing waters is presented at the end of this section (see Table 4.9.1); where possible these have been attributed to a neutral, positive or negative effect.

Table 4.9.1: Summary of potential interactions between beavers and standing freshwater and wetland habitats

Activity	Mechanism	Positive effects	Negative effects	Notes
Felling	Change in riparian woodland: Opening of woodland canopy and increased patchiness	Increased light levels may increase the maximum depth of colonisation by aquatic plants in lochs Felling/coppicing of trees by beavers could be beneficial to fen flora and fauna by keeping the wetland habitat open
Felling and construction	Changes in amount/diversity of woody material in watercourses	Complexity of habitat is likely to increase with an increase in woody material within standing waters Abundance and diversity of aquatic invertebrates, fish and amphibians may increase as a result of caches, woody debris, etc.	Woody debris may adversely affect plants in shallow water during strong winds, although this is likely to be a localised and minor effect overall
Feeding	Feeding on specific terrestrial herbaceous and aquatic plant species	Selective consumption of edge/emergent plants may lead to colonisation of habitat by submerged species There is a possibility that some invasive non-native species may be consumed Clearance of vegetation that is acting as a barrier to water flow may restore flushing rates in standing waters and prevent backing-up and consequent flooding	Preferential selection of uncommon species, such as saw sedge, may lead to localised losses at individual sites Negative effects on the area covered by aquatic plants may occur in lochs after a number of years of high occupancy by beavers Beavers may spread invasive non-native plant species by increasing fragmentation and incorporating plant material in lodges	Consumption of common species, such as bogbean, white water lily, common club-rush and water horsetail, may have localised effects, but neutral effects overall Incidental uprooting of isoetids when beavers are foraging for other species is not likely to have a considerable effect
Dams/pond creation	Change from lotic to lentic habitat	Creation of pond-wetland systems may improve the quality of water flowing into lochs, thereby improving the water quality of standing waters Numbers of invertebrate and plant species are likely to increase with the presence of both lotic and lentic environments, rather than the presence of running water habitat only	Localised losses of lotic species where lentic habitat is created are likely Considerable change in the balance of lotic and lentic species is possible at the catchment scale, if there are high densities of new ponds
Dams/pond creation	Change in hydrological processes on riparian and downstream habitat and adjacent wetland habitats	Creation of ponds and wetlands in loch catchment areas may protect lochs from the effects of drought Hydrological alternations may restore natural connectivity in wetland-loch systems Creation of ponds and wetlands in loch catchments is likely to increase the number of species present Water level rise in standing waters would be expected to increase the area of standing water habitat Water level rise increases the volumes of standing waters, and greater volume may improve the capacity of a loch for dilution of nutrients and phytoplankton Where the topography is suitable, raised water levels may lead to an expansion of existing wetland habitats or the creation of new ones	Flooding of terrestrial land upstream/adjacent to lochs may result in deterioration of water quality through decay of vegetation and leaching of nutrients from soils Flooding of peaty soils may result in an increase in the concentration of humic substances in the water of lochs, thereby causing a decrease in light penetration With loch water level increases, there is a potential for loss of plant habitat in deeper water because of light limitation With increasing loch volume, water retention time increases, flushing rate decreases and nutrients and phytoplankton are retained for longer within the loch Areas of wetland habitat may be lost where water levels are permanently raised and there is no space for expansion into adjacent areas. Changes in water levels and flooding regimes may lead to change in the wetland type and plant communities present - e.g. leading to transitions from fen vegetation to swamp vegetation. The effects will be dependent on site topography and water levels.	Problems resulting from leaching of nutrients from soils are more likely in catchment areas that are fertilised The significance of increasing levels of humic substances or dissolved organic carbon has not been quantified and would be site specific Areas of wetland habitat lost with increasing water depth may not be replaced if new areas of substrate at suitable depths are smaller or are unsuitable for plant growth Volume and flushing rate are variables that have considerable influence on the effects of nutrient loadings in lochs. Effects of alteration of these factors by beavers are unknown and would be site specific. In effect, reduction in flushing rate may offset increase in volume
Dams/pond creation	Changes in water quality downstream and on adjacent wetlands	Creation of ponds on inflow waters may lead to improvement in the quality of water in the receiving water body through attenuation of flow, sedimentation of solids and assimilation of nutrients within the ponds	Creation of ponds on inflow waters may lead to deterioration of water quality of loch inflows through changes in pH, a decrease in dissolved oxygen levels, a build-up of pollutants and disturbance within the ponds Flooding with impounded river/ loch water onto adjacent wetlands may lead to a loss of those plant communities which are dependent on flushing with base-rich and/or nutrient poor water	Build-up of pollutants within created ponds would be a consequence of upstream land use rather than of beaver activity, so overall the effects of beavers may be neutral/positive
Other
Indirect habitat creation/restoration initiatives as a result of beaver presence	Beavers used to promote opportunities for riparian, freshwater and wetland habitat creation/restoration	Restoration of riparian habitat, for example by extending 'buffer zones' along the edges of watercourses, is likely to result in improvements to water quality of standing waters, and therefore to habitat

4.9.2 Distribution of suitable standing freshwater and wetland habitats in the beaver policy areas

4.9.2.1 Standing freshwater and wetland habitats of conservation importance

To determine whether the activity of beavers on standing freshwater and wetland habitats is significant in the context of this Strategic Environmental Assessment, the assessment of impacts (positive and negative) has focussed on those freshwater 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. Many such sites have been identified that overlap with potential core beaver woodland, where possible, these have be grouped according to the dominant habitat type.

Table 4.9.2 shows those standing freshwater habitat types and their respective designated sites identified as overlapping with potential core beaver woodland. Maps of these SAC and SSSI sites are detailed in Appendix 1. Those pertaining to aquatic vascular plants (macrophytes) are given in Table 4.9.3 below and those relating to wetland habitats are given in Table 4.9.4.

Table 4.9.2. Summary of sites that overlap with potential core beaver woodland for standing freshwater habitat features of conservation importance, grouped by main loch habitat types.

Standing freshwater habitat	Designated sites
Oligotrophic Lochs
Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea	Cairngorms SAC Dunkeld - Blairgowrie Lochs SAC Glencoe SAC Rannoch Moor SAC River Tay SAC Taynish and Knapdale Woods SAC
Oligotrophic lochs	Cairngorm Lochs Ramsar Cairngorms SSSI Eastern Cairngorms SSSI Geal and Dubh Lochs SSSI Rannoch Moor SSSI
Oligo-mesotrophic and mesotrophic lochs	Lochs of Butterstone, Craiglush and Lowes SSSI Taynish Woods SSSI Lindores Loch SSSI Loch of Lintrathen SSSI Lochmill Loch SSSI Lochs Clunie and Marlee SSSI Long Loch of Lundie SSSI
Loch trophic range	Stronvar Marshes SSSI Knapdale Woods SSSI
Eutrophic Lochs
Eutrophic lochs	Loch Leven Ramsar Loch of Kinnordy Ramsar Dun's Dish SSSI Loch Leven SSSI Loch of Kinnordy SSSI Round Loch of Lundie SSSI

Following the approach taken in the HRA ( Annex 2), dystrophic lochs also referred to as acid peat-stained lakes and ponds have been screened out of this assessment as there is very little core beaver woodland which overlaps with them.

Table 4.9.3. Summary of sites that overlap with potential core beaver woodland with aquatic vascular plant features of conservation importance

Aquatic vascular plant species	Designated site
Slender naiad Najas flexilis	Dunkeld - Blairgowrie Lochs SAC European Protected Species
Pillwort Pilularia globulifera	Dalcroy Promontory SSSI

Table 4.9.4. Summary of sites that overlap with potential core beaver woodland with wetland habitats

Wetland habitats	Designated site
Transition mires and quaking bog	Cairngorms SAC, Dunkeld - Blairgowrie Lochs SAC, Rannoch Moor SAC
Alkaline fens	Beinn a' Ghlo SAC Glen Coe SAC Tulach Hill and Glen Fender Meadows SAC Morrone Birkwoods SAC Tullach Hill SSSI
Basin fen	Ardblair and Myreside Fens SSSI Eslie Moss SSSI Lochs of Butterstone, Craiglush and Lowes SSSI Mill Dam SSSI Rescobie and Balgavies Lochs SSSI Restenneth Moss SSSI
Open water transition fen	Dunalastair Reservoir SSSI Dun's Dish SSSI Hare Myre, Monk Myre and Stormont Loch SSSI Kings Myre SSSI Lindores Loch SSSI Loch Lubnaig Marshes SSSI Loch of Kinnordy SSSI Lochs Clunie and Marlee SSSI Lochs of Butterstone, Craiglush and Lowes SSSI Round Loch of Lundie SSSI Stronvar Marshes SSSI
Transition open fen	Loch Tay Marshes SSSI
Flood Plain Fen	Westerton Water Meadow SSSI
Hydromorphological mire range	Carsebreck and Rhynd Lochs SSSI Geal and Dubh Lochs SSSI Loch Leven SSSI Meikleour Area SSSI
Valley fen	Brig o' Turk Mires SSSI Den of Ogil SSSI Rossie Moor SSSI Tayvallich Juniper and Fen SSSI
Spring fen	Forest Muir SSSI Quoigs Meadow SSSI
Spring and flushes: Springhead rill and flush Springs (including flushes)	Cairngorms SSSI Glen Fender Meadows SSSI Pass of Leny Flushes SSSI Pitarrig Meadow SSSI Schiehallion SSSI

Ben Heasgarnich SAC has been screened out of the SEA as the wetland features are very much confined to the higher steeper slopes, and considered beyond the reach of beavers.

4.9.3 Assessment of likely effects on standing freshwater and wetland habitats of conservation importance in the beaver policy area

Each of the species and habitat types identified in Tables 4.9.2, 4.9.3 and 4.9.4 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 habitat or species. Assessment of other habitat or species (i.e. SSSI notified features), has been made in the context of the SNH HRA advice in combination with knowledge of the individual standing water and wetland 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 a riparian woodland restoration programme; by extending 'buffer zones' along the edges of watercourses, for example, improvements to water quality of standing waters, and therefore to habitat is likely to result.

4.9.3.1 Consideration of potential positive effects on standing freshwater and wetland habitats of conservation importance

The impact of beaver activity on standing freshwater and wetland habitats discussed below is considered to have a positive or neutral effect. A more general discussion is provided first, followed by a more species / site-based assessment.

Beavers may have a variety of beneficial effects on standing freshwater and wetland habitats. These are mostly connected with their dam building and foraging habits and the physical, hydrological and chemical changes these can effect.

Dams constructed on influent streams and which lead to the development of ponds may attenuate flows and reduce the pollutant loading of lochs. Ponds and wetland complexes created by beavers may also act as pollutant sinks and buffer against the effects of drought.

Positive effects from dam building activity can lead to, for example, the creation of new habitat, perhaps through changing from running (lotic) to standing (lentic) water systems, or changes to hydrological process downstream of a dam. This can be summarised as:

• Creation of pond-wetland systems may improve the quality of water flowing into lochs, thereby improving the water quality of standing waters
• Numbers of invertebrate and plant species are likely to increase with the presence of both lotic and lentic environments, rather than the presence of running water habitat only
• Creation of ponds and wetlands in loch catchment areas may protect lochs from the effects of drought
• Hydrological alternations may restore natural connectivity in wetland-loch systems
• Creation of ponds and wetlands in loch catchments is likely to increase the number of species present and an expansion of the area of wetland habitat
• Water level rise in standing waters would be expected to increase the area of standing water habitat
• Water level rise increases the volumes of standing waters, and greater volume may improve the capacity of a loch for dilution of nutrients and phytoplankton
• Creation of ponds on inflow waters may lead to improvement in the quality of water in the receiving water body and in connected wetlands through attenuation of flow, sedimentation of solids and assimilation of nutrients within the ponds

Positive effects from foraging activity, either through direct herbivory on aquatic macrophyte or wetland species or indirectly through felling trees can lead to a number of positive effects. These can be summarised as:

• Increased light levels may increase the maximum depth of colonisation by aquatic plants in lochs
• Complexity of habitat is likely to increase with an increase in woody material within standing waters
• Abundance and diversity of aquatic invertebrates, fish and amphibians may increase as a result of caches, woody debris, etc.
• Selective consumption of edge/emergent plants may lead to colonisation of habitat by submerged species
• Clearance of vegetation that is acting as a barrier to water flow may restore flushing rates in standing waters and prevent backing-up and consequent flooding
• Felling/coppicing of trees by beavers may help to keep wetland habitats open and largely free of encroaching scrub.

Individual site/species accounts follow:

Slender Naiad (Najas Flexilis)

Slender naiad Najas flexilis is a submerged rooted macrophyte that occurs in lochs, often strongly associated with the mesotrophic and oligo-mesotrophic lochs priority habitat.

Knapdale

There are no sites identified in the Knapdale beaver policy area that are designated for slender naiad.

Tayside

• Dunkeld - Blairgowrie Lochs SAC

This site contains the most easterly occurrence of slender naiad (Najas flexilis) on the Scottish mainland and is the second-largest known population. The site consists of a cluster of five lochs lying along a river valley - the Lochs of Butterstone, Craiglush and Lowes are about 5 km upstream of Lochs Clunie and Marlee. They are all mesotrophic waterbodies with a diverse macrophyte flora. Slender naiad has been recorded since the 19 ^th century in the lochs.

HRA Advice

Theoretically, should damming raise the water level sufficiently in one of the lochs, or should new habitat at appropriate depth be unsuitable for colonising, it is possible that there could be negative effects on the qualifier. This could also happen if water quality was adversely affected, e.g. by increased water opacity, or additional nutrients were released as an effect of inundation of nutrient rich areas. However, dam building by Eurasian beavers is not considered to be of sufficient scale to deepen the lochs to such an extent that slender naiad might be negatively affected. Neither will their feeding on other water plants have a negative effect on the species.

The SNH HRA advice concluded that that it can be ascertained that there is no adverse effect on site integrity of the Dunkeld - Blairgowrie Lochs SAC through impacts to slender naiad.

European Protected Species

Slendar naiad is classed as European Protected Species, and is fully protected under The Habitats Regulations 1994 (as amended in Scotland).

It is anticipated that the potential impacts from the policy will not be detrimental to the maintenance of the population of the species (slender naiad) concerned at Favourable Conservation Status in their natural range.

Pillwort Pilularia Globulifera

This tiny plant is a type of creeping fern. It is hard to spot because it has thin, grass-like leaves and often grows with water grasses or small rushes. The 'pills' are tiny round spore cases at the bases of the stems.

Knapdale

There are no sites identified in the Knapdale beaver policy area that are designated for pillwort.

Tayside

• Dalcroy Promontory SSSI

SSSI Advice

Beaver dams may stabilize water levels. Whilst this might be expected to provide stable conditions suitable for submerged plants, there are also plants that rely on the exposure of substrate such as pillwort, an aquatic fern which grows on bare mud and is able to tolerate seasonal fluctuations in water levels. However, it has been reported that beavers may not tolerate excessive or unnatural water-level fluctuations. This suggests that they are less likely to inhabit lochs where water levels are significantly affected by activities such as power generation, e.g. Loch Tummel which, at its western end supports pillwort at Dalcroy Promontory SSSI.

Therefore, while there are natural heritage interests of national importance on this site, these are unlikely be affected by the beaver activity.

4.9.3.2 Consideration of potential negative effects on standing freshwater and wetland habitats of conservation importance

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

All Oligotrophic Loch Types

Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea is often referred to as, clear-water lakes or lochs with aquatic vegetation and poor to moderate nutrient levels. The Oligotrophic (and dystrophic) lochs priority habitat occurs throughout Scotland and includes thousands of sparsely-vegetated lochs on acid, generally impermeable geology. It is characterised by water with acid to neutral pH, low levels of alkalinity and low concentrations of easily available nutrients. Oligotrophic lakes have water column total phosphorus ( TP) levels of less than 10 μg P L-1 ( OECD, 1982). Dystrophic standing waters may have higher TP levels, but P is present in a form that is not readily available to plants.

Oligotrophic sites are more variable than dystrophic standing waters. They range in size from 1 ha up to several hundred hectares in size. Some of Scotland's largest lochs are examples of this habitat, for example, Loch Tay. They generally have coarse substrates, but large sites may have sheltered bays with soft substrates, as well as rocky, wave-washed shores. A greater range of species may be found in oligotrophic lochs than in dystrophic sites, but overall biomass remains fairly low. There may be extensive stands of sedges in shallow, sheltered bays (typically bottle sedge Carex rostrata). Small, rosette species are often found along rocky shores, including shoreweed Littorella uniflora and water lobelia Lobelia dortmanna. Water colour may be clear, or peat-stained, though not to the intensity of water colour found in dystrophic water bodies.

Knapdale

• Taynish and Knapdale Woods SAC
• Taynish Woods SSSI
• Knapdale Woods SSSI

Tayside

• Cairngorms SAC
• Cairngorm Lochs Ramsar
• Dunkeld - Blairgowrie Lochs SAC
• Glencoe SAC
• Rannoch Moor SAC
• River Tay SAC
• Cairngorms SSSI
• Eastern Cairngorms SSSI
• Geal and Dubh Lochs SSSI
• Rannoch Moor SSSI
• Lochs of Butterstone, Craiglush and Lowes SSSI
• Lindores Loch SSSI
• Loch of Lintrathen SSSI
• Lochmill Loch SSSI
• Lochs Clunie and Marlee SSSI
• Long Loch of Lundie SSSI
• Stronvar Marshes SSSI

SNH HRA advice

Advice is outlined below with respect to each SAC included reference to appropriate mitigation. 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.

Taynish and Knapdale Lochs SAC

Work already published concludes that there is no AESI on the submerged vegetation community of the standing water habitat from the beavers resident in the SAC area. However, dam management was a condition of the SBT and although dam-building did not have an AESI during the SBT, there may be adverse effects in the future should circumstances change (such as additional water-level increases, higher densities of beavers etc.). Any potential adverse impacts on the site from water level changes must be mitigated.

Grazing by beavers may affect most macrophyte species though it may be limited to effects upon the structure and abundance of rhizomatous edge vegetation. However any negative impacts on the vegetation community that might constitute an AESI should be avoided. Monitoring of beaver grazing activity is required and such mitigation could form part of a management plan to control the potentially damaging effects of beavers on the SAC.

The SNH HRA advice concluded it that it can be ascertained that there is no adverse effect on the site integrity of Taynish and Knapdale Woods SAC provided the ability to implement mitigation is maintained .

Mitigation

Monitoring of dams is required, and water flows that will not have an AESI must be maintained. Mitigation could include a management plan involving measures such as the installation of dam-regulators or the removal of dams.

SSSI Assessment

Impacts within SSSI loch habitats are likely to be similar to those described above for Taynish and Knapdale Lochs SAC. There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance. Mitigation outlined above will be relevant to both Taynish Woods and Knapdale Woods SSSIs.

Cairngorm SAC

Colonisation of the catchment of Loch Einich, and the plateau and corrie lochs over 900m is improbable given the harsher climate and low extent of tree cover. However, beavers are more likely to colonise the areas around the lower lying lochs which are generally found further north in the SAC.

Damming of inflows, if it occurred, may result in reduction of silt and finer sediments flowing into the lochs. This would reduce the nutrient inputs and would be considered positive. The overall phosphorus loading will not be increased by the trapping of silt. Silt from failed or abandoned dams is likely to be remobilised by storm and flooding events when flushing rates will be relatively high. In some circumstances the wetting-up of drier areas and the trapping of organic material may result in more anaerobic conditions resulting in the release of phosphorus. Damming may also affect the timing of the release of sediment. The precise effects on water chemistry and nutrients will vary for each site and may be complex. The effects of these changes on the qualifying interests may also be complex; however, the scale and speed of the impacts means that where they were thought to possibly lead to an adverse effect on site integrity, they would need to be mitigated through appropriate management measures which are able to identify impacts to site integrity before they occur and modify or remove dams as necessary.

The SNH HRA advice concluded if beavers settle in the vicinity of the valley lochs any potential adverse impacts from water level changes could be prevented by having a mitigation plan in place to identify those impacts before they had an adverse effect on site integrity.

Mitigation

Mitigation is likely to include the use of flow control devices to manage dams, the removal of dams, or if necessary beavers. Any adverse impacts on the vegetation community would also be avoided by having a mitigation / management plan in place for beavers.

Ramsar & SSSI Assessment

Impacts within Ramsar and SSSI loch habitats are likely to be similar to those described above for Cairngorms SAC. There is therefore potential for beaver activity to adversely affect the natural heritage interests of national and international importance. Mitigation outlined above will be relevant to Cairngorm Lochs Ramsar, Cairngorm SSSI and Eastern Cairngorms SSSI.

Dunkeld - Blairgowrie Lochs SAC

The impact of damming is generally considered to be beneficial returning catchments to a more natural and diverse condition which would have been in place prior to the removal of beavers. Damming of inflows may result in reduction of silt and finer sediments flowing into the lochs. This would reduce the nutrient inputs and would be considered positive. The overall phosphorus loading will not be increased by the trapping of silt. Silt from failing or abandoned dams is likely to be remobilised by storm or flooding events when flushing rates will be relatively high. In some circumstances the wetting up of drier areas and the trapping of organic material may result in more anaerobic conditions resulting in the release of phosphorus. Damming may also affect the timing of the release of sediment. The effects on water chemistry and nutrients will vary for each site and may be complex. The effects of these changes on the qualifying interests may also be complex.

The SNH HRA advice concluded it can be ascertained that there is no adverse effect on site integrity of Dunkeld - Blairgowrie Lochs SAC through impacts to the loch qualifying interest, provided any potential adverse impacts on integrity from damming are prevented by having a management plan in place to monitor beaver activity and install control devices or remove dams as necessary.

Potential adverse impacts on the vegetation community of the SAC lochs should also be avoided by having a management plan in place to monitor and control beavers where their activities might result in an AESI.

Mitigation

Mitigation is likely to include the use of flow control devices to manage dams, the removal of dams, or if necessary beavers. Any adverse impacts on the vegetation community would also be avoided by having a mitigation / management plan in place for beavers.

SSSI Assessment

Impacts within SSSI loch habitats are likely to be similar to those described above for Dunkeld-Blairgowrie Lochs SAC. There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance. Mitigation outlined above will be relevant to both Lochs Clunie and Marlee SSSI and Lochs of Butterstone, Craiglush and Lowes SSSI.

Glen Coe SAC

Dam-building is unlikely, though possible, given the low level of tree cover near the loch. If the area was colonised, grazing by beavers might have an effect on most macrophyte species though it is likely to be limited to effects upon the structure and abundance of rhizomatous edge-vegetation.

The SNH HRA advice concluded that it can be ascertained that there is no adverse effect on site integrity Glen Coe SAC provided suitable mitigation is identified, and will be implemented if it proves necessary.

Mitigation

In such a situation any potential adverse impacts on the vegetation community should be avoided by having a suitable management plan with mitigation, in place to manage beavers.

Rannoch Moor SAC

The SAC is sufficiently unattractive to beavers due to: the low percentage of woodland cover in the catchment of the Rannoch Moor lochs (c. 2%), the harsh climate, and exposed nature of Rannoch Moor, meaning they are not expected to colonise the area.

The SNH HRA advice concluded that it can be ascertained that there is no adverse effect on site integrity.

SSSI Assessment

Impacts within SSSI loch habitats are likely to be similar to those described above for Rannoch Moor SAC.

River Tay SAC

Colonisation of the catchments of the lochs is possible given the level of tree cover and the existing areas of the Tay catchment already colonised. Should beavers settle near the smaller lochs and build dams at their outflows, any potential adverse impacts on these smaller lochs from water level changes should be prevented by having suitable mitigation in place that can identify potential adverse effects and install control devices, or remove dams or beavers where necessary.

The SNH HRA advice concluded that it can be ascertained that there is no adverse effect on site integrity of the River Tay SAC, provided suitable mitigation is identified and can be implemented if it proves necessary.

Mitigation

Grazing by beavers might have an effect on macrophyte species though it is likely to be limited to effects upon the structure and abundance of rhizomatous edge-vegetation. Where it is identified that this might happen any potential adverse impacts on the vegetation community should be avoided by having a suitable management plan with mitigation in place to manage the impacts of beavers.

• Geal and Dubh Lochs SSSI
• Lindores Loch SSSI
• Loch Lintrathen SSSI
• Lochmill Loch SSSI
• Long Loch of Lundie SSSI
• Stronavar Marshes SSSI

SSSI Assessment

Impacts to these lochs are likely to be similar to those described above and so may include effects of beaver grazing on macrophyte species or the effects on water chemistry and nutrients from damming activity which are likely to vary for each site and may be complex. There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance.

Mitigation

Mitigation is likely to include the use of flow control devices to manage dams, the removal of dams, or if necessary beavers. Any adverse impacts on the vegetation community would also be avoided by having a mitigation / management plan in place for beavers.

Eutrophic Lochs

Eutrophic standing waters have high productivity as a result of presence of high alkalinity and nutrient levels; the water column typically contains at least 35 μg P L-1 of total phosphorus ( TP) ( OECD, 1982) and 500 μg N L-1 or more total inorganic nitrogen (mainly in the form of dissolved nitrate).

Unpolluted examples of this habitat are often characterised by deep fringes of emergent vegetation comprising common reed Phragmites australis or bulrush Typha spp., and beds of floating-leaved species such as yellow water lily Nuphar lutea. Submerged species associated with this type of water body include fennel-leaved pondweed Potamogeton pectinatus and spiked water-milfoil Myriophyllum spicatum. The open water of richer sites may be dominated by algae, which gives the water a green colour.

This habitat supports abundant populations of planktonic algae and zooplankton. Snails, dragonflies and water beetles dominate the benthic fauna. In sites that have suffered from artificial enrichment, the variety of species may be reduced to one or two pollution-tolerant species of leech and chironomid larvae, although the numbers of each species may be high. The abundance of food resulting from the artificial enrichment may support internationally important numbers of birds. For example, Loch Leven supports over 20,000 waterfowl including nationally important numbers of wigeon Anas penelope, gadwall Anas strepera, Shoveler Anas clypeata and large numbers of wintering whooper swan Cygnus cygnus. The fish fauna is usually dominated by coarse fish, such as pike Esox lucius. Eutrophic standing waters are generally shallow, and have bays or shores that are sheltered from wave action. Dark anaerobic muds, rich in organic matter may be the dominant substrates.

Knapdale

There are no sites identified in the Knapdale beaver policy area designated for eutrophic lochs.

Tayside

• Loch Leven Ramsar
• Loch of Kinnordy Ramsar
• Dun's Dish SSSI
• Loch Leven SSSI
• Loch of Kinnordy SSSI
• Round Loch of Lundie SSSI

Ramsar and SSSI Assessment

Although eutrophic lochs differ in their environmental characteristic from the range of oligotrophic lochs described above, mainly through their much higher nutrient loading and resulting suite of aquatic macrophytes adapted to such conditions, the likely impact from beaver activity will be broadly similar.

Grazing by beavers may affect macrophyte species though it may be limited to effects upon the structure and abundance of rhizomatous edge vegetation. Monitoring of beaver grazing activity is therefore required and such mitigation could form part of a management plan to control any potentially damaging effects of beavers on these sites.

Damming of any inflows may result in reduction of silt and finer sediments flowing into these lochs. Silt from failed or abandoned dams is likely to be remobilised by storm and flooding events when flushing rates will be relatively high. In some circumstances the wetting-up of drier areas and the trapping of organic material may result in more anaerobic conditions resulting in the release of phosphorus. Damming may also affect the timing of the release of sediment. The precise effects on water chemistry and nutrients will vary for each site and may be complex.

Any damming on outflow burns may reduce the existing water level fluctuation or slow down certain nutrient processes. The resulting impacts on water chemistry will vary for each site and may be complex.

There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance.

Mitigation

Potential adverse impacts on the vegetation community of these lochs should be avoided by having a management plan in place to monitor and control beavers where their activities might result in an adverse effect.

Any potential adverse impacts from damming should be avoided by having a management plan in place to monitor beaver activity and install control devices or remove dams as necessary.

Many of the lochs (e.g. Loch of Kinnordy and Loch Leven) do have existing management or catchment plans in place; any mitigation would seek to align with these.

Transition Mires and Quaking Bog

Transition mires and quaking bogs occur in waterlogged situations where they receive water from rainfall, as well as water and nutrients from the surrounding catchment. The vegetation is typically dominated by sedges and rushes over a ground layer of semi-aquatic bog-moss Sphagnum species or feather-mosses such as Calliergon species. The term transition mire refers to the fact that the vegetation and ecological/hydrochemical characteristics are transitional between acidic bog and alkaline fen conditions. This transitional state can arise either by being in an intermediate position between bog and fen or by being a successional stage in which, after accumulating in fen or over open water, rainwater-fed (ombrogenous) peat, which is wholly or partly isolated from groundwater influence, accumulates.

Many of these systems are very unstable underfoot and are also described as 'quaking bogs'. Examples include the transitions between bog and fen vegetation associated with valley mires or basin mires, or the marginal lagg areas of raised bogs.

Small quaking bogs can occur in a wide variety of landscape situations, including small basins in post-glacial landscapes, the margins of lochs and lochans in blanket bog, and the edges of coastal machair lochs. Larger examples are found in floodplain mires. They are usually found within other, larger, wetlands such as valley mires and blanket bogs.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for transition mires and quaking bog.

Tayside

• Cairngorms SAC
• Dunkeld - Blairgowrie Lochs SAC
• Rannoch Moor SAC

SNH HRA Advice

Cairngorms SAC and Dunkeld - Blairgowrie Lochs SAC

Very wet mires (quaking bogs) would generally not be disadvantaged by the presence of beavers as the habitat tends to form a floating raft of vegetation which can rise and fall in response to the water levels and can effectively become isolated from the underlying water. However, the 'tethered' quaking mire at the edges of the habitat is not able to move freely and could be affected by a change in water levels and water chemistry arising from beaver impoundments. Increased mineral and nutrient levels in the water could result in a shift in the species composition towards more typical fen communities. Precise changes cannot yet be predicted, and will depend upon the nature, scale, duration of the changes and the location of beavers and their activities

Beavers are also selective feeders and may graze on some of the vegetation that contributes to the qualifying habitat.

SNH advice is that it cannot be ascertained that there is no adverse effect on the site integrity of Cairngorms SAC, and Dunkeld - Blairgowrie Lochs SAC without monitoring, and management of beaver dams.

Mitigation

Mitigation in the form of monitoring and management of beaver dams is required to avoid the adverse effect where dams might cause individual stands of transition mires or quaking bogs to be flooded.

Rannoch Moor SAC

Due to the low percentage of woodland cover in the catchment of the Rannoch Moor lochs (c. 2%), the harsh climate, and exposed nature of Rannoch Moor, beavers are not expected to colonise the area.

SNH advice is that it can be ascertained that there is no adverse effect on site integrity.

Alkaline Fens

Alkaline fens consist of a complex assemblage of vegetation types characteristic on sites where there is a high water table, a calcareous base-rich water supply and tufa and/or peat formation. The characteristic vegetation is short sedge communities.

At many sites there are well-marked transitions to a range of other fen vegetation and alkaline fens may occur in association with tall-herb fen, swamp, wet grasslands, rush species, as well as fen carr and, especially in the uplands, wet heath and acid bogs.

There is considerable variation between sites in the associated communities and transitions present, depending on the geomorphological situation in which the fen occurs (e.g. flood plain mire, valley mire, basin mire, hydroseral fen) and the altitude.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for alkaline fens.

Tayside

• Beinn a' Ghlo SAC
• Glen Coe SAC
• Tulach Hill and Glen Fender Meadows SAC
• Morrone Birkwoods SAC
• Tullach Hill SSSI

SNH HRA Advice

Where the topography is shallow, beaver dams constructed close to base-rich fen communities could lead to an expansion of the habitat by increasing the area with suitably high water levels to support wetland habitats. However, if raised water levels are maintained in alkaline fens over long periods this could lead to a transition from fen to swamp, reed-bed or open water.

If damming activity leads to a change in the water quality or water chemistry within the fens, e.g. by flooding the fens with surface waters and effectively reducing the influence of the base-rich, low fertility flushes, this could result in a change in the vegetation communities present and a reduction of the extent of the feature on the site. Changes in the nutrient and base status of the water may lead to a change in the extent, diversity and succession processes of wetland communities.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the qualifying habitat.

SNH advice is that that it can be ascertained that there is no adverse effect on the site integrity of these SACs provided there is monitoring of the location of beaver dams within and upstream of the SACs, in order to manage water flows, and managing or removing any beaver dams which could cause alkaline fens to be flooded with impounded water.

SSSI Assessment

The impacts within the alkaline fen SSSI habitat are likely to be similar to those described above for the SAC alkaline fen habitat. There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance at Tullach Hill SSSI.

Mitigation

Mitigation in the form of monitoring and management of beaver dams is required to avoid adverse effects where dams might cause individual stands of alkaline fens to be flooded.

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.

Basin Fen

As the name suggests basin fens occur in waterlogged depressions or hollows in the landscape, for example those associated with glacial or peri-glacial processes such as kettle holes, or in solution hollows on limestone. Their main water supply source is from overland flow (topogenous) or sometimes from a river or lake. Surface run-off from surrounding slopes can be an important source of water, depending on the surrounding topography, and this may include small flushes along the sides of the basin. These sites may have no surface water flow outlet. Basin and open water transition fens are very similar in characteristics but differ in the proportion of fen area to that of open water.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for basin fens.

Tayside

• Ardblair and Myreside Fens SSSI
• Eslie Moss SSSI
• Lochs of Butterstone, Craiglush and Lowes SSSI
• Mill Dam SSSI
• Rescobie and Balgavies Lochs SSSI
• Restenneth Moss SSSI

SSSI Assessment

Impoundment resulting from beaver activity could lead to raised water levels in basin fens. Prolonged raised water levels could lead to a loss of fen habitat and a transition to swamp communities or open water. Flooding the fens with surface waters could alter the nutrient status and hydrochemistry of the water supply to the fens - thereby reducing the influence of inflow from any base-rich, low fertility springs and flushes. This could result in a change in the vegetation communities present and a reduction of the extent of the feature on the site.

In some situations, where the topography is shallow, impoundment could lead to an expansion of fen habitat but basin fens are often located in confined basins with little scope for this type of expansion.

In some cases an increase in water volume in the fen may dilute the effects of pollutants and this would be beneficial. The felling or coppicing of trees on basin fens by beavers would be beneficial by keeping the fen vegetation open and reducing encroachment by scrub.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the basin fen feature.

There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of basin fen features in order to assess the impacts and manage water flows where necessary.

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on basin mires.

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.

Open Water Transition Fen

Open water transition fens are associated with significant areas of open water, where the water table in the fen is determined by vertical fluctuations of the open water body. They are essentially similar to basin fens but the proportion of open water is greater than that of fen. Extensive areas of transition from swamp to fen vegetation may occur around the open water with further transitions to tall herb fen vegetation and fen woodland reflecting transitions to drier conditions. In the fen the summer water table would generally be at or below ground level while in the swamp the summer water table will be at or above the surface. The particular fen and swamp communities present will be influenced by the trophic status and fluctuations in the levels of the water body. Springs may occur within the feature

Some swamp and tall-herb fen vegetation types are ubiqitous, some are associated with nutrient or base-poor conditions and others with nutrient or base-rich conditions.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for the open water transition fen feature.

Tayside

• Dunalastair Reservoir SSSI
• Dun's Dish SSSI
• Hare Myre, Monk Myre and Stormont Loch SSSI
• Kings Myre SSSI,
• Lindores Loch SSSI
• Loch Lubnaig Marshes SSSI
• Loch of Kinnordy SSSI
• Lochs Clunie and Marlee SSSI
• Lochs of Butterstone, Craiglush and Lowes SSSI
• Round Loch of Lundie SSSI
• Stronvar Marshes SSSI

SSSI Assessment

Some of the impacts within open water transition fen SSSI habitat are likely to be similar to those described above for basin fens. In some cases impoundment could lead to an expansion of the overall area of swamp and fen habitat and this would be beneficial but the degree to which this will be possible will depend on local topography and on land management practices.

A lowering of the water table could lead to a marked expansion of tall-herb fen communities at the expense of swamp communities. Conversely, a landward expansion of swamp communities may be caused by raised water levels. These changes may or may not be beneficial to the site. On sites where springs contribute to the water supply of the fen vegetation, an increase in water levels may lead to the dilution of the impacts of any spring water and a change in the nutrient and base-status of the water. Changes in the nutrient and base status of the water may lead to a change in the extent, diversity and succession processes of wetland communities

In some cases an increase in water volume in the fen may dilute the effects of pollutants and this would be beneficial. The felling or coppicing of trees within the fen vegetation by beavers would be beneficial by keeping the fen vegetation open and reducing encroachment by scrub.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the basin fen feature.

There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of open water transition fen features in order to assess impacts and manage water flows where necessary.

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on open water transition fens.

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.

Transition Open Fen

The only site in the beaver policy area which is notified for this feature is Loch Tay Marshes SSSI. This site, on the shores of Loch Tay, has extensive areas of poor fen with transitions to submerged and emergent plant communities, fen meadow, carr woodland and heathland.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for the transition open fen feature.

Tayside

• Loch Tay Marshes SSSI

SSSI Assessment

Impacts within transition open fen SSSI habitat are likely to be similar to those described above for the open water transition fen feature habitat. Increased water levels could lead to an increase in the extent of fen vegetation on the site. Poor fen vegetation is generally fed water low in nutrients. Changes in the nutrient and base status of the water may lead to a change in the extent, diversity and succession processes of wetland communities

A lowering of the water table could lead to an expansion of tall-herb fen communities at the expense of swamp communities. Conversely, raised water levels may lead to an expansion of swamp communities.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the transition open fen feature. The felling or coppicing of trees and scrub in the fen feature by beavers would be beneficial to the condition of the fen communities.

There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of transition fen features in order to assess impacts and manage water flows where necessary

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on the transition fens.

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.

Flood Plain Fen

Floodplain fen develops on a waterlogged, periodically inundated floodplain adjacent to a river or stream. In addition to large rivers this includes sites on flat valley bottoms where the watercourse is small and does not provide significant amounts of water through overbank flooding.

Although the primary water supply mechanism for flood plain fens is topogenous, percolating (soligenous) water sources can be important in some sites and groundwater discharge can also be an important water supply mechanism where the wetland is underlain by an aquifer and not separated by impermeable strata. Topographic variations can result in areas of ponding or soakways and the differences in water levels across a site give rise to zonation within the vegetation. The vegetation of flood-plain fen is varied including, for example, tall eutrophic fen, single species swamps or in some cases poor fen. Reedbed is common, as are other tall fen plant communities in which reed is a major component. The fens may be nutrient-enriched, nutrient-poor, base-rich or base-poor, and these factors are reflected within the vegetation present on each site.

Flood-plain fens are very vulnerable to drainage and interruption of their flooding regime, especially when fragmented by agricultural practices or affected by river engineering. There is commonly a transition from flood-plain fen to wet grassland.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for the flood plain fen feature.

Tayside

• Westerton Water Meadow SSSI

SSSI Assessment

Some of the impacts within flood plain fen SSSI habitat are likely to be similar to those described above for open water transition fen habitat.

Given their flood plain location, the extent of the feature is less likely to be constrained by topography than, for example, basin fen. Raised water levels resulting from beaver activities could therefore lead to an increase in the extent of flood plain fen, though this would also be dependent on land management practices.

The vegetation present in flood plain fens shows a large amount of variation both in the communities present and in transitions between vegetation types. A lowering of the water table could lead to an expansion of tall-herb fen communities at the expense of swamp communities. Conversely, raised water levels may lead to an expansion of swamp communities. Changes in the nutrient and base status of the water may also lead to a change in the extent, diversity and succession processes of some wetland communities.

In some cases an increase in water volume in the fen may dilute the effects of pollutants and this would be beneficial. The felling or coppicing of trees within the fen vegetation by beavers would be beneficial by keeping the fen vegetation open and reducing encroachment by scrub.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the flood plain fen feature.

There is therefore potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of open water flood plain fen features in order to assess impacts and manage water flows where necessary.

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on flood plain fens.

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.

Hydromorphological Mire Range

Many wetland sites contain a wide range of habitats and plant communities and on some designated wetland the importance of this diversity is acknowledged by the designation of the hydromorphological mire range feature. This feature can contain several different wetland habitats on each site, with a wide range of requirements in terms of the supporting hydrological regime and water chemistry.

Within the Tayside beaver policy area, the wetland habitats for this feature are as follows:

Geal and Dubh Lochs SSSI: fen meadows, springs and flushes, open water transition fen

Carsebreck and Rhynd Lochs SSSI: acid wet heaths and flushes, nutrient-rich flushes, rich fen

Loch Leven SSSI: fen and mire communities

Meikleour Area SSSI: fen, willow scrub, swamp, basin mire, lowland raised mire, wet woodland

On most sites there will be a range of wetland plant habitats present including areas of vegetation that represents a transition between different plant community types. There will also be variations over time in the relative proportions of each habitat as a result of natural succession processes. In some cases the succession processes may be further influenced my current or historic land management practices.

Knapdale

• There are no sites identified in the Knapdale beaver area which are designated for this feature.

Tayside

• Carsebreck and Rhynd Lochs SSSI
• Geal and Dubh Lochs SSSI
• Loch Leven SSSI
• Meikleour Area SSSI

SSSI Assessment

This feature is represented by a wide range of wetland communities, each with different requirement in terms of the optimum water levels, the flooding regime and the water chemistry. Water impoundment activity by beavers clearly has the potential to affect some or all of the component wetland communities by altering the maximum water levels in the habitats and the length and timing of the periods when water levels are raised. In some cases, where the topography allows, raised water levels may lead to an increase in the extent of some wetland communities or of the overall extent of wetland habitat. In other cases raised water levels may lead to a reduction the extent of some wetland types and an increase in others e.g. a transition from fen to swamp communities.

In addition some of the wetland communities are dependent on a water supply with specific hydrochemical characteristics e.g. acidic, base-rich or nutrient-poor water. Where beaver dams raise water levels they may thereby reduce the influence of inflow from any acid, base-rich or low fertility springs and flushes. This could result in a change in the vegetation communities present and a reduction of the extent of the specific features on the site.

The nature of the effects, positive or negative, will vary between sites and between different habitats within sites, depending on the plant communities present and the site specific topography and hydrology.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the wetland types that make up the hydromorphological mire range. In addition they may fell or coppice trees in fen, mire or wet woodland communities. In some cases this may be beneficial in helping to keep the wetland communities open.

There is therefore potential for beaver activity in combination with other herbivores to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of the hydromorphological mire range features in order to assess impacts and manage water flows where necessary.

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on hydromorphological mire range features.

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.

Valley Fen

Valley fens are usually described as soligenous mires although differing porosity and mineralogy of the underlying rocks can give rise to several different patterns of water supply. Springs and seepages from the valley sides provide the main source of water but they can also receive inputs from surface water and from groundwater seepage.

This type of fen develops along the lower slopes and floors of small valleys where there is some water movement. They are often drained by an axial stream. The topography of the valley often also helps to maintain a high water table.

Each valley mire may contain a range of wetland types, from base-rich to base-poor, and from oligotrophic to eutrophic, with other variations arising from patterns of land use such as grazing and mowing. There may be a band of scrub or woodland with taller, more eutrophic fen around the axial stream, and poor fen or bog between this and the soligenous margins.

Knapdale

• Tayvallich Juniper and Fen SSSI

Tayside

• Brig o' Turk Mires SSSI
• Den of Ogil SSSI
• Rossie Moor SSSI

SSSI Assessment

Impacts within valley fen SSSI habitat are likely to be similar to those described above for other fen habitats.

Where the topography is shallow, beaver dams constructed close to valley fen communities could lead to an expansion of the habitat by increasing the area with suitably high water levels to support wetland habitats. However, if raised water levels are maintained over long periods this could lead to a transition from fen to swamp, reed-bed or open water.

The construction of dams in the small axial streams could potentially lead to a change in the water quality or water chemistry within the fens, e.g. by flooding the fens with surface waters and effectively reducing the influence of the original water supply from the springs and flushes. Where this leads to a change from base-rich, low fertility water to more nutrient rich water this could result in a change in the type of vegetation communities present, their diversity and succession processes, and a reduction of the extent of the feature on the site.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the qualifying habitat.

Therefore there is potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of the valley fen features in order to assess impacts and manage water flows where necessary.

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on valley fens.

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.

Spring Fen

This type of fen is often found on sloping land beneath a spring or a line of water seepage, or on flatter land at the base of a slope where they are irrigated by groundwater discharge from water reaching the surface under artesian pressure, giving rise to a small dome of mire, usually on flat ground. These fens are frequently small and discrete and not part of an elongated mire along a valley. They are soligenous - water comes out of the saturated soils or rock at one point (spring) or in a discrete zone (seepage). The springs will show a discrete difference in vegetation type from the surrounding fen vegetation as a result of the temperature and nutrient influences from the different water sources.

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for Spring fen.

Tayside

• Forest Muir SSSI
• Quoigs Meadow SSSI

SSSI Assessment

The main route for any effects on spring fen habitats would be if impoundment arising from a beaver dam caused flooding of the spring fed fens with a resulting change in the hydrological regime and water chemistry. In these cases there could be a loss of the characteristic plant communities, e.g. those that are dependent base-rich, acidic or nutrient-poor water, and a transition to other types of wetland communities. The likelihood of any adverse effects on particular fens or sites will depend on their location in the landscape and the surrounding topography. Those located high on steep slopes in the uplands are unlikely to be affected by beaver activity. Those located on flatter ground at the base of slopes may be affected if there is a nearby beaver dam.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the qualifying habitat.

Therefore there is potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of the spring fen features in order to assess impacts and manage water flows

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on spring fens.

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.

Springs and Flushes

Springs and flushes are generally small features. They are often dominated by bryophytes but low-growing sedges and dicotyledonous plants also play an important role in these habitats. There are several different types, depending on the nature of the underlying bedrock. These include base-rich petrifying springs with tufa formation, neutral flushes and acid flushes. Most base-rich wetlands on slopes are spring-fed.

Springs and their associated flushes occur when water wells up to the surface from underground aquifers or reaches the surface at seepage slopes. Where the spring emerges onto a sloping terrestrial surface and the drainage is impeded but not pooled on the surface, the water then feeds flush communities. Spring fens are usually very small, but may form an important part of otherwise extensive wetland complexes.

Hillslope wetlands are found where low-permeability bedrock coupled with high precipitation permits the development of sometimes extensive wetlands fed primarily by surface run-off and rainfall.

Springs and flushes in the lowlands are usually associated with soligenous fens, and often with peat-accumulating systems. Lowland springs often also contain a considerable calcareous input which may support a mosaic of acid and basic mire plant types. Peat deposits associated with calcareous springs are often mixed with tufa.

Springs that flow into water bodies can provide an important water source to swamps, where they contribute to the water quality of the wider wetland. The flow pattern of spring water into standing water is determined by the nature of each water body. Density and temperature differences may constrain the movement of water, resulting in discrete bodies of water, characterised by specific swamp communities. These may be different from the surrounding swamp vegetation, as they are affected by temperature and nutrient influences from the different water sources.

Spring features (including flushes)

• Glen Fender Meadows SSSI
• Pass of Leny Flushes SSSI
• Pitarrig Meadow SSSI
• Schiehallion SSSI

Springhead rill and flush

• Cairngorms SSSI (assemblage feature component)

Knapdale

There are no sites identified in the Knapdale beaver policy area which are designated for either of the spring and flushes feature.

SSSI Assessment

As for spring fen habitats, the main route for any effects on spring features would be if impoundment arising from a beaver dam caused flooding of the spring fed fens with a resulting change in the hydrological regime and water chemistry. In these cases there could be a loss of the characteristic plant communities, e.g. those that are dependent base-rich, acidic or nutrient-poor water, and a transition to other types of wetland communities. The likelihood of any adverse effects on particular fens or sites will depend on their location in the landscape and the surrounding topography. Most spring and flush features are located on steep slopes in the uplands are unlikely to be affected by beaver activity. Those that are located on lower ground and on flatter ground at the base of slopes may be affected if there is a nearby beaver dam.

Beavers are selective feeders and may graze on some of the vegetation that contributes to the qualifying habitat.

Therefore there is potential for beaver activity to adversely affect the natural heritage interests of national importance. This could be avoided provided there is monitoring of the location of beaver dams within and in the vicinity of the spring features in order to assess impacts and manage water flows.

Mitigation

Mitigation is required in the form of monitoring to assess the effects of beaver dams and, where necessary, management to avoid adverse effects on spring features.

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.