2.1 A comprehensive search of the literature reveals very little on the impact of coastal dune quarrying or restoration. Coastal sand quarrying is covered by a number of authors (e.g. Ritchie and Mather 1984, Doody 1989, Hewett 1989, Sanjaume and Pardo 1992, Hilton 1994), but with most discussion referring to threats posed by beach and offshore mining. Only two references were found which referred to the general effects (as opposed to site specific references) of dune/machair quarrying (Mather and Ritchie 1977 and Ritchie and Mather 1984). These are listed as the creation of deflational surfaces and erosional features which can expand to blowouts, modification of the water table, safety aspects, visual aspects and the use of the disused pits as rubbish tips. Impacts of extraction at particular sites in the west of Scotland is referred to by several papers (Mather and Crofts 1971, Harris and Ritchie 1989a, and 1989b) although widespread erosion as a consequence of quarrying is reported just once (Harris and Ritchie 1989a).
2.2 Similarly, just two rather brief accounts of restoration of coastal sand pits in Britain appear in the literature, covering sites at Hayle in Cornwall (Lewis 1992) and East Lothian in Scotland (BTCV 1986). Most of the literature on sand quarry reinstatement in Europe and North America covers the restoration of water bodies in inland sand quarries to wildlife sites (e.g. Andrew and Kinsman 1990, Potter 1983, Merritt 1994), which is not greatly relevant to the west coast situation. Various aspects of ecological recovery after restoration of sand mines are covered in the Australian and South African literature (e.g. Majer 1985, Majer and Kock 1992, John 1993). However, there is only limited scope for the application of the findings to the situation in the study area.
2.3 In the absence of information on reinstatement of coastal sand pits, the sand dune restoration literature was searched for relevant techniques. This required the characterisation of the sand pits in the study area to avoid covering irrelevant subject areas.
2.4 Field visits and consultations showed that the great majority of sandpits are located in dune and machair grassland, rather than mobile dunes. This means that there is no source of incoming sand, although the pits may suffer wind erosion. They are also not exposed to wave erosion. Hence, measures used on fore and mobile dunes to prevent wind and wave attack, such as beach protection and replenishment, the use of sand fences and dune grass planting, are not relevant to the reinstatement of most pits in the study area. It is recognised that pits are occasionally sited in mobile dunes, as for example at Barvas on Lewis, and that some pits formerly in fixed dune or machair can be breached by blowouts or wave attack in the adjacent mobile zone. Measures to deal with such situations are given brief outline coverage in the relevant part of Chapter Five - "Guidelines for Reinstatement", but are not covered in this chapter.
2.5 The literature review therefore concentrates on dune restoration techniques which do not depend on fresh sand deposition. It will follow the logical order of slope stabilization, infilling, sand fixing and revegetation techniques.
2.6 In situations of very high sand mobility, and minimal surviving vegetation, residual clumps of vegetation promote wind funnelling until they themselves are eroded out. Dune contouring can be undertaken to iron out irregularities, including cutting away residual vegetation, lessening slope angles, smoothing slope profiles and decreasing slope height to reduce wind scour and the risk of blow out. It is largely covered in the literature as a method used in the fore and mobile dunes, but some mention is made of slope grading to restore eroded machair edge. This technique, along with seeding, was proposed as far back as 1799 to repair eroded machair on North Uist (Angus and Elliott 1992). Sand obtained from contouring operations can be used to partially fill in blowouts and erosion holes (Ranwell and Boar 1986, Lewis 1992).
2.7 Steep sand slopes are very prone to undercutting and erosion, while a gentle slope will allow the wind to ride over it with a smooth even air flow. Loose dry sand rests at an angle of about 30 to 35 degrees (Carter, Hesp and Nordstrom 1990, Hesp and Thom 1990, Barrere 1992), but vegetation can allow stable slopes of up to 40 to 43 degrees (Carter, Hesp and Nordstrom 1990). These latter authors maintain that an eroded slope has to have slumped to below the angle of repose before natural stabilization will occur, but there appears to be no real consensus in the literature on the ideal slope gradient for sand slope grading.
2.8 Reclamationists grading steep sided blowouts at Hayle in Cornwall aimed to achieve convex slopes of 30 to 35 degrees (Lewis 1992). Restoration of dunes after pipeline laying at St Fergus and Cruden Bay on the east coast of Scotland graded back the restored dunes to a seaward slope of 15 to 20 degrees (Ritchie and Gimingham 1989). Nineteenth century French engineers found that an angle of 10 to 11 degrees for the seaward slope was ideal when constructing a 230km long protective artificial dune on the Gascony coast. In all of these cases the slopes were to be planted with marram after grading.
2.9 It is likely that slope gradient will in fact be determined by site conditions and character. A windward slope angle of 3 to 6 degrees (1:20-1:10) in mobile dunes is the ideal recommended by the British Trust for Conservation Volunteers (BTCV 1986) and the Institute for Terrestrial Ecology (ITE) (Ranwell and Boar 1986). However, both recognise that a site may not be wide enough, or there may not be enough sand to attain this ideal, and suggest maximum figures of 1:2 of 1:5 for hand and mechanical planting techniques respectively. They also recommend a figure of 30 to 40 degrees for grading eroded machair edge or cliff. This is greater than that recommended for mobile dunes probably because it is assumed that the machair is more stable.
2.10 Slope profile is also important and cornices are particularly prone to undercutting (Barrere 1992). Cutting off dune crests with spades to remove peaks and overhangs is recommended in a number of papers (Skarregaard 1989, Feilberg and Jensen 1992), and is a similar technique to that recommended for machair cliff grading and re-turfing, using either hand or machine cutting (BTCV 1986). (See Section 2.34-2.36 for a more detailed account of re-turfing). However, in machair restoration operations at Oldshorebeag, Sutherland, it was found that the newly graded upper slope has to be protected, in this case with brashing, to prevent the undercutting process from starting again (A. Scott, pers. comm. 1996). The use of rolled up geotextile, possibly filled with seaweed, pegged in under the undercut area was suggested in the place of grading where brashing is not available, this being a more long term alternative to grading.
2.11 Slope height has little mention apart from a recommendation by Barrere (1992) that dunes should not be permitted to grow to excessive height. He describes how the height of 12 to 15m for the Gascony dune ridge, mentioned above, was thought to be ideal and that later ridges 20 to 25m in height are thought to be too big as they absorb too much wind energy.
2.12 Large scale regrading in mobile dune systems is often done by tracked earth movers, although the Countryside Commission for Scotland (CCS) recommends a standard rear-wheel drive JCB for grading dune pasture and machair "cliff" edge (CCS 1987). This is probably because of the need to use the back-acter for cutting back turf edges on the top of the cliffs to allow slope grading and, also, to cut turves for re-laying once grading had finished. However, in machair restoration operations at Oldshorebeag crawlers were used to dig away undercut faces, working from the top of the slope (A. Scott, pers. comm. 1996).
2.13 Care has to be taken not to cause secondary erosion either through damaging existing vegetation or regrading at windy times of year. Timing of operations at Hayle in Cornwall was found to be critical, with late April to early May proving the safest and most successful time to carry out earth moving (Lewis 1992). This is when the worst of the winter weather is over and a full growing season lies ahead.
2.14 In the Hayle scheme the operator worked by starting at the top and back of the eroded dunes and pushing the remaining peaks into the troughs. This created a broad topped ridge which is then pushed down in oblique sweeps (BTCV 1986). As well as recommending that existing vegetation is saved and replanted, BTCV also suggest that it may sometimes be possible for the bulldozer driver to carefully sweep whole clods of vegetation from one place to another.
2.15 There is very limited coverage of these techniques in the British dune literature, presumably because they are rarely used, apart from infilling erosion holes and blowouts using sand from contouring operations. Angus and Elliott (1992) report that infilling of erosion holes on the dune/beach edge in the Western Isles with builder's rubble and rip-rap boulders has had limited success and in some cases has resulted in re-erosion. They also mention that inland machair blowholes have been "infilled" with organic material and then reseeded under the Environmentally Sensitive Area Scheme. (However, the nature of this "infilling" is not specified and could possibly just refer to the use of surface mulches rather than gross infilling). They recommend that no solid materials, including old vehicles, should be dumped into blowouts, as they merely act to increase wind scour. The use of old cars dumped in blow holes to prevent further erosion of the machair at Luskentyre is reported to have failed (Harris and Ritchie 1989b).
2.16 Infilling and soil reinstatement techniques are carried out after coastal dune mining in Australia and South Africa where sand waste, from which economically significant minerals have been extracted, is used as infill to rebuild dunes. This is in contrast to quarrying in the study area where there is no sand waste to reuse. The other difference is that the mined dunes in these two countries are older than machair systems of the study area (very much so in the case of Australia) and exhibit greater soil development, making the conservation and reuse of topsoil easier. In both cases attempts have been made to re-create the indigenous vegetation, which in both countries includes bushes and trees. In Australia, where old podsolic sand dunes are mined, reinstatement of soil horizons has proved difficult, with root impedance (Burrows 1986, Enright and Lamont 1992) and rapid leaching of the reinstated horizons (Prosser and Roseby 1995) occurring. In South Africa where the dunes are younger, re-creation of indigenous secondary forest appears to been easier (Camp 1990).
2.17 In contrast, machair soils are likely to be shallow and difficult to store and reuse, and furthermore the original vegetation and top soil is often lost to erosion or extraction. Turfing, a form of soil reinstatement, is usually only a fairly small scale operation in machair reinstatement, using odd pieces salvaged from grading operations or which have broken away from slumped faces. However, advance turf stripping and storage and later replacement is possible, being reportedly carried out by operators at a coastal sand quarry in East Lothian (BTCV 1986).
2.18 Without an adequate supply of fresh sand, dune grasses, such as marram and lyme grass, cannot be used to stabilize bare sand surfaces, necessitating the sowing of mixed turf grasses instead. However, before seeding can take place the sand surface has to be fixed to prevent loss of sand cover and seed mix, usually by binding or mulching. This is particularly important in the first few weeks after sowing and during the first winter when die-back may leave the surface relatively unprotected.
2.19 Binders are chemical glues sprayed onto the sand to prevent wind erosion of areas which have been planted or seeded. They create a "skin", which helps to hold the sand surface together, particularly on slopes, and reduces surface drying. Binders can be used for reseeding dune pasture or machair where the site is exposed, but may not be necessary where the sand is already rich in organic matter provided that the location is sheltered (CCS 1982).
2.20 Binders come as a range of different chemical products, the main ones being plastics, alginates, bitumen emulsion and oil/latex. In their information sheets CCS review in some detail the efficacy of various makes of binders (CCS 1982). This is summarised in the BTCV manual, which in 1986 listed three products as being suitable for use on dune pastures (as opposed to dunes after planting). These are Huls 801, Curasol AE and Vinamul 3277, which are all plastics binders. These glues were found not to produce too rigid or brittle crusts, which is important as the crust needs to collapse with drying and give continued protection to the sand beneath, otherwise scour can occur at the crust edges (CCS 1982). In the Hayle restoration scheme it was found that a very rigid crust can also be lifted off the surface, air pruning germinating seedlings (Lewis 1992).
2.21 Although binders were originally developed for hydraulic seeding (hydro-seeding), this latter method is reported to be unsatisfactory for sand, as the seed is only sown in the surface layer which does not allow deep enough rooting to withstand surface drought (BTCV 1986). Attempts to hydroseed with a mix of slurry of grass seed, binder, fertilizer and water in the Hayle restoration scheme were relatively unsuccessful because of the air pruning effect described above (Lewis 1992). Furthermore, CCS report that germination is reduced if the waterproof coat comes into contact with the seed. Binders are therefore recommended by BTCV and CCS to be used only after the seed has been raked or harrowed into the sand.
2.22 The effect of a binder on water entry into the sand is fairly complex. Although some binders are promoted on the strength of conserving moisture, it is reported that where there is little water already present in the sand, a negative effect of preventing water entry occurs and seedling establishment is depressed (CCS 1982). This is relevant to sites with dry sand but which are not exposed, where the need to fix the sand surface does not outweigh the disadvantages of drought risk from using a binder.
2.23 Diluted binder can be sprayed using a knapsack sprayer or small crop sprayer. It is applied in parallel strips immediately after sowing, fertilising and covering with sand, starting at the top of a slope and working down (BTCV 1986). When used on dune pastures after seeding, a binder should only be needed for 6-8 weeks while the seedlings establish (CCS 1982 and BTCV 1986). It may also be required in the first winter when dieback may be significant.
2.24 Binders can be used in conjunction with mulches. CCS (1982) report that chopped straw worked into the sand before the binder is sprayed gives significant additional wind protection, although care has to be taken to prevent build up of straw preventing seedling growth. They suggest that other mulch-plus-binder combinations should only be used where the nutrient retaining or providing capabilities of the mulch are sought. Sewage sludge as a thin mulch in combination with binder is not recommended because the thin layers dry out and curl up.
2.25 Mulches cover a wide range of substances which can be spread over the ground as a solid dressing to either assist stabilization, and/or improve moisture retention and provide nutrients, but are not growing mediums. They include digested sewage sludge, peat, wood chippings, wood pulp, shredded paper waste, cotton cellulose, chopped straw, topsoil, reed or other cut grass, seaweed and other storm litter and manure (CCS 1982, BTCV 1986). Most mulches can be spread by muck spreader, while some, such as sewage sludge, granulated peat, chopped straw and wood chips, can be sprayed on. Those materials relevant to the west coast of Scotland are reviewed below.
2.26 CCS report that mulches applied in thin layers are not effective unless applied with binders because of their capacity to be stripped off by the wind, although conversely Band (1979) reports that peat applied as a top dressing could achieve the same affect as a binder. Long fibred mulches, such as straw, are, however, reported to be an exception if both partially dug in and glued in place (CCS 1982). Australian researches found lightly disking straw into the sand to be very effective on hind and inland dunes (Mitchell 1974). A rate of five to six tonnes of straw per hectare is suggested by Adriani and Terwindt (1974), and wheat or oat straw is recommended in preference to barley, which decays more quickly (Bacon 1975).
2.27 Peat, a raw material readily available in the west of Scotland, is particularly useful for machair restoration work, as long as it is not dug up from bogs of special nature conservation value! It is reported to have been used by the CCS to restore machair at Traigh Geiraha on Lewis (Angus and Elliott 1992). BTCV (1986) recommend spreading by hand to an average thickness of about 10mm before raking in the grass seed, rather than hydroseeding with granulated peat and binder, in which it is sprayed to a 1-2mm thickness. CCS (1987) recommend chopping the peat lumps to a 2cm thick layer when spreading by hand. However, hand spreading was found to be impractical in machair stabilization operations at Oldshorebeag in Sutherland, while careful backlaying to 2 to 3cm depth using a bulldozer was more effective (A. Scott, pers. comm. 1996). The use of wet peat was found to be imperative, but a chemical binder used with the peat was found not to be successful, possibly because the weather was very dry when the trial was carried out.
2.28 Seaweed has long been used in the Outer Hebrides, where it is collected in winter, to stabilize blowouts and to top dress farmland (Angus and Elliott 1992). It is applied on the machair surface prior to cultivation and also on pasture. Because of the high water content, large quantities are used; one reported rate of application is six tonnes per hectare (Seaton 1968), however, 40t/hectare is recommended in the ESA scheme (J.Love, pers. comm. 1996). It is best spread wet for maximum nutritional value, but in this case seed has to be sown and raked in prior to spreading to avoid contact with the seaweed and salt water (CCS 1987). A layer of 5cm thickness is recommended (i.e. 1m3 per 20m2), this drying out in a few weeks to about 1cm thickness. However, Ranwell and Boar (1986) state that dry seaweed tends to blow away unless well anchored, although they were probably referring to its use in repairing seaward mobile dunes. That seaweed is an effective stabilizer is supported by comments by local people that cultivated areas at Barvas, Lewis, where large scale erosion of the machair is occurring, had been more stable when seaweed was used as a fertilizer (Harris and Ritchie 1989a).
2.29 Topsoil or leaf litter can be used as a mulch, i.e. as a top dressing a few inches thick, rather than as a complete growing layer. Volunteers are reported to have used leaf litter and humus from nearby woodlands to help fill machair edge erosion on Mull (BTCV 1986). Restoration work on dune grassland and dune slacks after pipeline laying at St Fergus and Cruden Bay in North East Scotland used a top soil cap plus a bitumen stabilizer after sowing to retain moisture.
2.30 Farmyard manure is reported to have been used, at a rate of 6 tonnes per hectare, to maintain machair surfaces and can also be spread on dune surfaces (BTCV 1986). Cattle dung has been used for stabilising bare areas, particularly in the Uists, (Angus and Elliot 1992). Sewage sludge is commonly used in many types of land restoration schemes and has been used on several dune restoration schemes (BTCV 1986), the success of which is not reported. A layer of about 25mm thickness is applied in two or three coats, drying to form a stiff crust which as well as stabilizing the surface, acts as a slow release fertilizer and catches wind blown seeds. It can often be obtained cheaply or for nothing from local sewage works, although works receiving industrial effluent should be avoided.
2.31 Wood pulp has been found to successfully promote vegetation and lasts about the same time as straw mulch. Pulp, chipped bark or peelings from fence posts may be cheaply available from sawmills.
2.32 Use of materials such as top soil, straw and manure have been pointed out to be possibly undesirable in areas of special nature conservation value because of the "weed" species they could contain (BTCV 1986). However, it is possible that the harsh conditions experienced in dune and machair systems prevent such species from permanently establishing. For example, "alien" species were accidentally imported with the topsoil used at the St Fergus and Cruden Bay schemes mentioned above, but all significantly decreased or disappeared after a few years (Ritchie and Gimingham 1989). Likewise, a similar effect is also reported to have occurred after fertilizer applications on foredunes (van Boheman & Meesters 1992). In some cases a rich seed source, as found in dung from cattle grazed on machair, can be a useful aid to natural colonisation (Angus and Elliott 1992).
2.33 Fixed dune and machair grassland comprises perennial turf grasses and mosses together with a wide variety of herb species where sand accretion is minimal. The grasses are characterised by short wiry leaves, and the capacity to tiller freely under grazing, and they form a tight turf which is very effective in protecting underlying sand from erosion. The annual death and regeneration of new shoots help to build up a moisture-retentive humus layer near the surface. One of the biggest problems in trying to regenerate dune turf is building up the soil humus which supports it. This section covers re-establishment of the turf, which can comprise either turfing or seeding, or a combination of both, and in some situations, planting of marram plants.
2.34 Work at Achmelvich, Sutherland, and at other sites has involved covering areas of eroded machair edge with turfs to mark out areas for sowing and to encourage spread of vegetation (BTCV 1986). At the former site, turfs about 200mm thick and 600m wide were cut from the edge of the machair "cliff" and allowed to slide down the face on to the beach. These were then stacked while re-contouring took place. The "cliff" was re-graded by cutting back at the top and shifting sand to the bottom, producing a final slope of between 30 to 45 degrees with a rolling profile (`s' shaped). CCS recommend a final profile of no more than 1 in 5 if a standard JCB is used for the task (CCS 1987).
2.35 A line of turfs were then dug in at the base of the graded slope and, where the slope was more than a few feet high, half way up the slope. Occasional rows were also placed running up and down to divide the slope into a series of rectangles. The horizontal rows reduce sand slip and provide the basis for vegetation to spread, while the vertical rows mark the slope into convenient areas for sowing. It is suggested by BTCV that if there is not enough turf to create such rows, it might be possible to use turves from areas where they would be removed anyway, e.g. new car parks etc. The unturfed areas can then be seeded.
2.36 CCS (1987) recommend that a JCB can be used for the task of cutting turfs and slope grading, but suggest that turves should be buried if not used elsewhere on site to prevent them from impeding operations.
2.37 There is no information in the sand dune restoration literature on depth of cut or storage methods for turves. However, the general rule for turf transplantation in grassland and heathland translocation is that as much of the rooting system should be removed as possible to prevent disintegration, drying of the turf and loss of deep rooted species (English Nature 1990). Depths of 50cm, 35cm, 20cm and 15cm have been used for inland grassland translocation (e.g. Landscape News 1990, English Nature 1990 and Park 1989), while turves of semi-improved machair pasture cut to 10-15cm were successfully transplanted in pipeline restoration at Brighouse Bay in Aberdeensire (I. Taylor, pers. comm. 1996).
2.38 General recommendations on the timing of cutting that are applicable to the machiar situation is to avoid transplanting in summer, to minimise disturbance to invertebrates, and in very dry weather, when the turves could break up (English Nature 1990). The turf removal operation at Brighouse Bay took place in December, with turves stored through to Easter on wooden pallets. However, turf cutting as part of the sand pit reinstatement operation will usually be determined by the timing of the grading operations, which have to avoid the windiest times of year.
2.39 There is also nothing in the sand dune restoration literature on turf storage, possibly because it is assumed that turves will be relaid very soon after cutting and grading. Turves survived three to four months in the Brighouse bay operation discussed above, partly because storage took place out of the growing season and partly becasue they were kept moist by a sprinkler system (I.Taylor, pers. comm. 1996). However, there is a general presumption against turf storage in grassland translocation operations because of disintegration and drying (English Nature 1990).
2.40 Seeding can be carried out on areas that do not receive more than 2-3cm of blown sand per year. Even in the absence of fresh sand input, care has to be taken that newly seeded areas are not inundated by sand blown from adjacent bare areas within the same site (CCS 1987). This can be avoided by seeding a whole site at the same time. However, where this is not possible, for example, if a site is too large, or where phased working and restoration is planned, planting marram on the first areas to be treated would at least stabilize the sand, allowing seeding at a later date once the rest of the site had been stabilized. Sites directly facing wind borne salt spray may not be suitable for seeding as germinating seedlings are likely to perish (CCS 1987).
2.41 As discussed above, dune and machair grassland show some degree of soil development, including an organic upper layer. Seeding onto bare sand cannot therefore easily reproduce the species composition of established machair. In most cases the objective will be rather to produce a rapid ground cover using a simple seed mix, relying on natural processes over the years to enable the local vegetation to re-establish at the expense of the sown species (CCS 1987). Ranwell and Boar (1986), however, suggest that seeding may result in only a temporary closed sward, which is liable to degenerate into very sparse cover within a few years as a result of drought and rabbit damage. They maintain that the success of seeding schemes partly depends on freedom from excessive wind disturbance.
2.42 Under the Environmentally Sensitive Areas Scheme for the machairs of Uists, grants are provided for restoration of dune and machair blowouts. In this scheme, reseeding is undertaken using grass mixes specifically formulated for the Uists machair (Angus and Elliott 1992). However, these have been criticised for including too high a proportion of agricultural pasture species.
2.43 A basic seed mix recommended by CCS (1987) is 60% Slender Creeping Red Fescue, 30% Perennial Ryegrass, 5% Smooth-Stalked Meadow-Grass and 5% White Clover. The Slender Creeping Fescue is salt tolerant, spreads by running roots and can be heavily grazed or trampled. The rye-grass gives a rapid initial cover, dying out as the drought resistant and slower growing fescues take over (BTCV 1986). It is possible to use either a slow maturing and winter perennial hardy ryegrass, or a short-lived Italian Ryegrass as a nurse crop to provide wind shelter for the first growing season only. Only a small amount of Smooth-Stalked Meadow-Grass is included because although it is common in dune and machair grassland, it is slow to establish. The CCS Information Sheet, 5.2.2 Reseeding of Dune Pastures, gives full details of suitable cultivars of all the species listed in the mix above.
2.44 The CCS maintain, however, that their recommended seed mix, and other commercially available mixes, may not be suitable for sites of high botanical value because of the risk of some of the sown grasses invading surrounding areas. They recommend two options for such sites: the first to collect seed locally, which is extremely time consuming, and the second to sow only a short-lived nurse species only, like Westerwold Ryegrass, that will die out after one or two years in the absence of fertilizer. A more practical alternative to collecting local seed, and one that has been successful, is the use of a green hay crop (A.Booth, pers. comm. 1996). The latter option of a nurse crop relies on natural invasion of other species to provide a vegetation cover when the nurse thins out after one to two years and is reported to have been tried successfully on the east coast of Scotland. However, it may not be a suitable technique on instable or exposed areas because of the risk that natural colonisation might not proceed fast enough to achieve a relatively complete ground cover before the nurse species dies out. This problem could be overcome by seaweed applications in subsequent years to promote good soil structure which will encourage natural colonisation.
2.45 A mix recommended by SNH and successfully used on sea-side verges in the Lochaber area comprises Creeping Red Fescue, Smooth Meadow-Grass, Brown Top, Wild White Clover and Bird's-foot Trefoil - proportions and details of suppliers are given in Appendix Two.
2.46 It is possible that the spread of sown species may not be a problem. Ritchie and Gimingham (1989) report that sown grasses in dune grassland reinstated after pipeline laying decreased markedly, to be replaced by dune species of the surrounding habitat. The seed mix in this case was 5 parts perennial ryegrass, 2 parts Smooth-Stalked Meadow Grass, 4 parts Creeping Red Fescue and 2 parts Brown Bent. It is also reported that agricultural reseeds in the Western Isles revert very quickly to the original grassland (N.Buxton pers. comm. 1996).
2.47 CCS identify two seeding windows; early May and late July/early August. Earlier than May there may be a risk to young seedlings from salt borne spray, whilst there is the greatest risk of drought in the early and mid summer period (CCS 1987). Sowing should be no later than early August to allow sufficient development by autumn and survival through the winter. These constraints decrease as the site is more sheltered.
2.48 CCS (1987) recommend that areas up to one hectare in size should be hand seeded. This is because of the potential damage mechanical seeding can cause to the fragile habitat, not only the bare sand, but also the dune pasture and machair grassland which may have to be crossed to get to the area to be seeded. CCS reported that there was little experience of using mechanical equipment for seeding on sand. On larger areas where the ground is sufficiently level for tracked or four wheel drive vehicles, either cross-sowing in drills using a Cambridge roller, or harrowing in, or ideally, direct drilling, are all thought to be possible. Drilling rather than a broadcast method of sowing was found to more successful for restoration of dune grassland at St Fergus after pipeline laying (Ritchie and Gimingham 1989), but there is no mention of how the seed was incorporated, if at all, into the sand, with the broadcast method.
2.49 Hydroseeding is another technique that could be used. Its advantages are that large areas can be treated uniformly with a minimum of labour and that embankments can be seeded without the need to disturb the sand. It is also speedy, with a rate of about a hectare per hour being possible (CCS 1987). In the operation, seed, fertilizer, mulch and stabilizer are sprayed in one single operation from a lorry mounted tank. The mulch material has to be finely divided, and wood chips, fibreglass, chopped straw, granulated peat, chicken manure sewage sludge are all reported to have been used. The mulch layer is generally only 1-3mm deep, and a binder must be incorporated to protect against wind blow (CCS 1982).
2.50 However, hydroseeding is not recommended by CCS except on large sites or on steep slopes where machinery or trampling during hand seeding would create too much instability. The problem of surface sowing in hydroseeding has already been reported in Section 2.21. CCS (1987) also report that the thinness of the mulch layer in hydroseeding results in limited moisture retention and nutrient supply, so that the need for regular fertilization is almost as great as for seeding on sand alone. Finally, the combination of mulch and binder is no more resistant, sometimes less so, to wind blow than the same binder used on its own.
2.51 Turf seeds can germinate in bare sand, but establishment is very slow and may be prevented altogether on an exposed site if the seed mix is removed by the wind. However, if seeding on to bare sand is carried out, the seed is sown at a high rate of 30g/m2 to allow for losses. It is then raked into a depth of 3-4cm if using the CCS recommended seed mix (other smaller seeded species may not survive at this depth) to overcome the drought conditions (CCS 1987). A stabilizer should be applied to the sand surface to prevent wind blow.
2.52 Moisture retention around the seed is improved using a mulch as a surface dressing, through which the seeds grow downwards into the sand. Many mulches also provide added nutrients. The use of seaweed and peat, the two most readily available mulches in the study area, is discussed above. If either is used, seed is sown at 25g/m2 and raked in to the sand, or the peat/sand surface respectively. CCS recommend that a binder, which can be sprayed by vehicle-mounted crop sprayer, should also be applied if the site is exposed (CCS 1987). However, in trials carried out at Oldshorebeag, the use of a chemical binder with a peat mulch was unsuccessful, but possibly because of the very hot weather. Clearly more work needs to be carried out to establish the efficacy of the binder-mulch combination.
2.53 It is possible to use topsoil as a growing medium, i.e. as a complete cover rather than just a mulch or cap. CCS recommend this for areas that are likely to be heavily trampled, using a layer at least 10cm thick to accommodate the rooting system (CCS 1987). A stabilizer is unnecessary unless the soil is light and there is less need for intensive aftercare. However, CCS also list the disadvantages of using topsoil. Apart from being costly, there is the possibility of it containing a high proportion of stone which is unsightly (a problem also encountered when it is used as a surface dressing) and it may contain weed seeds which may take a hold. Furthermore, machinery is required to spread the soil which would not be suitable for unstable sites. In the St Fergus and Cruden Bay pipeline schemes, the best results in terms of vegetation cover were obtained with imported topsoil, rather than the local sandy topsoil of poorer quality. (Ritchie and Gimingham 1989). However, the criteria for success were based on cover rather than species composition. The relative naturalness of the respective communities of the two soils was not commented on, but it was reported that a high number of non dune species did initially appear in the imported soil.
2.54 CCS (1987) recommend chemical fertilizer application immediately before seeding and at bi-monthly intervals over the first growing season. Application rates and fertilizer types are given in their Information Sheet 5.2.2. Fertilization in the ensuing years is recommended by CCS if reseeding was on to sand rather than topsoil, even if a mulch was used. The policy here is one of building up a good organic layer through productive growth.
2.55 The following fertilizer composition has been successfully used for seeding onto bare sand on seaside verges in Lochaber - 4g nitrogen : 10g phosphate : 10g potash per square metre, applied at the same time as the seed mixture (pers. comm. M. Elliott 1996) - see Appendix Two for further details.
2.56 BTCV note that straight agricultural fertilizers are likely to be as effective as slow-release formulations on machair which are not subject to very rapid leaching and rates and times of application are given (BTCV 1986). They also report that fertilizing machair does not always do much good as plant growth may be limited by trace element deficiency as well as, or rather than, lack of major nutrients.
2.57 BTCV also recommend that chemical fertilizer applications should be restricted to a minimum necessary to maintain the typical flora for the site. This is because fertilization increases the density and luxuriance of grasses at the expense of herbs and bryophytes, which may not be desirable on botanically important sites. In contrast to CCS, they also note that chemical fertilizer use might not be necessary with the use of some organic mulches. This is supported by the long time practice of machair cultivation using only seaweed as an organic fertilizer. (It is reported that whereas the use of artificial fertilizer in blowout and machair restoration schemes is still used, the Islands Development Programme (IDP) and ESA schemes have encouraged a return to seaweed application in some areas (Angus and Elliott 1992)). Again, it is not clear what the definitive method should be regarding fertiliser and mulch applications.
2.58 The literature is very patchy on the need to fence off reseeded areas, although the impacts of overgrazing and trampling on established machair and the need for fencing to allow recovery are well documented (e.g. Doody 1989). It is to be assumed therefore that some form of initial protection will also be needed at reseeded sites. CCS recommends that areas treated with either binders or mulches should be effectively fenced if the site is likely to be used either by people or large grazing animals as the stabilized layer is only a few millimetres in thickness and easily damaged (CCS 1982). Ranwell and Boar (1986) mention the adverse effects of both rabbit damage and trampling by people in preventing establishment of dune grassland, and they recommend fencing to keep people out for 2-3 years at least. Rabbit grazing and, particularly, burrowing activities prevented successful dune turf establishment after reseeding at Oldshorebeag in Sutherland (A.Scott, pers. comm. 1996). Here, scrapes opened up by rabbits were further enlarged by rubbing sheep.
2.59 However, fences can themselves cause problems, attracting rubbing animals and causing sand build up. Avoiding long straight stretches of fenceline was found to reduce these problems at Oldshorebeag. In many cases, some additional form of rabbit control may be needed at large sites. At Oldshorebeag, trapping, gassing and shooting had to be employed (A.Scott, pers. comm. 1996).
2.60 Constant monitoring to identify and remedy post treatment problems whilst still in their early stages was found to be crucial at Oldshorebeag (A.Scott, pers. comm. 1996). This is particularly necessary in the early spring after seeding, when regrowth should be checked, and any necessary remedial reseeding carried out (M. Elliott, pers. comm. 1996 - see Appendix Two).
