Thatching, Mulching and Binding

General points

Uses

Thatching, mulching and binding can be used separately or in combination to:

1. Protect exposed or steep dune slopes from wind erosion. Mulches can also be applied to help stabilise path surfaces. Straw bales, which break down to form a mulch, can be used to aid marram planting on steep slopes.
2. Encourage better growth of newly planted or seeded vegetation by providing organic matter and improving the heat- and moisture-retaining capacity of the soil.

Other considerations

1. Thatching, mulching and binding are seldom worth doing except in conjunction with planting or sowing, although thatching can be used alone or with fences to fill in small blowouts and to protect dune cliffs from tidal erosion.
2. Wherever suitable material is available, thatching, mulching and binding are worth including in a planting programme even where the plants may survive without them, because they markedly improve growing conditions. However, thatching does modify the typical marram-dominated open dune habitat by providing suitable conditions for fixed dune species to invade, especially away from the foredune ridge.

Thatching

Thatching is the covering of exposed sand faces with cuttings (brashings, trimmings, lop and top, broust) from scrub thickets or forestry plantations. It is a traditional method of stabilising sand, and was used for example at the end of the 19th century to stabilise large areas of sand blow at Culbin in Moray (CCS, 1981). Thatching should prevent further erosion by the wind, act as a sand trap and discourage people from trampling.

Thatching can be used in combination with planting on difficult sites, to increase the chance of transplant success. Such sites include dune crests, irregular slopes where turbulence is caused, gullies which funnel the wind, and areas likely to be trampled by people or stock. Do not thatch areas of rapid sand build-up, as it may be buried before grasses are established. Where brushwood is in good supply, thatching is quicker than mulching or binding. It is however slower and more expensive if the brushwood has to be gathered and transported some distance. Leafy material can be used on backshore sites, followed by seeding once the thatching is buried. The decaying material improves seeding success.

If you have a choice, use the species recommended for brushwood fencing. Conifer brashings, which are the lower branches trimmed off commercial trees, are better than conifer tops. This is because they are fan shaped, and thus easier to transport and lie flat on the sand, giving good coverage. It is estimated that a 10 tonne open lorry should be able to carry sufficient brushwood to cover 100-150sq m (CCS, 1981). Note that conifer brashings are more combustible than deciduous material, and more likely to be set alight by vandals.

Thatching cannot in itself anchor over-steepened sand slopes, although it helps provide a mat for workers to stand on when planting. Normally it is best to lay thatching before or at the same time as planting a steep face or blowout, unless a thorny species is used when obviously planting should be done first. One problem with thatching after planting is that it tends to damage the newly planted grass.

Procedure

1. Lay the brashings at a density such that about 20-30% of the sand surface is covered (excluding any needles or leaves that will drop off). If the brashings are fan shaped, lay the concave side downwards.
2. Where public pressure is low, you can protect the thatched areas by pushing in brash at a 45 degree angle around the boundaries. Elsewhere, it is usually necessary to fence the path edges to keep people off the thatch unless you have used a thorny species. Where public pressure is intense, it is worth tying the thatch down with old fencing or baling wire (2mm diameter) to keep people from using it for firewood. Run the wire out in parallel lines, about 2m apart, and staple or tie at 3m intervals to short stakes, driven down into the sand to secure. Baler twine can also be used which although not as strong, is less of a hazard when partly buried. This technique is also worth using for sites very exposed to the wind, to stop the brashings being blown about.
3. When thatching a slope, work from the top down. Place the first (topmost) row of branches with their upper twigs just level with or below the top of the dune ridge. If they project higher, wind damage will occur. Turn the branches so that they curve into the slope as shown below.
   
   If turned outwards, the wind is liable to twist them loose. Follow the contours closely.
   
   On very shallow slopes, angle the branches at about 45 degrees to discourage people from walking on top of or between them.
4. Where both sides of a ridge require treatment, thatch the lee face first and then the windward face, which should overtop the lee thatching to protect it from the wind. When thatching the top of a rounded dune, angle the branches nearly horizontally, with-their tips at an even height and intertwined to protect against variable winds. On sharply peaked dunes, you may have to start thatching a few feet below the summit and allow the top to be eroded to the level of the thatching. per hectare) planting the grass and placing the thatching.
5. Place small branches with their butt ends 225-375mm (9-15″) apart and larger brash 375-760mm (15-30″) apart. Mix any branches over 1.2m (4′) in with smaller branches or save them for use on flat expanses.
   Push all branches well into the sand: at least 75mm (3″) for 600mm (2′) long branches, 150-225mm (6-9″) for 1.2m (4′) long branches and 300mm (1′) or more for longer branches.
6. On gentle slopes not exposed to strong winds, you can limit thatching to a border around the edge of the area, with strips of brushwood placed across the enclosure at right angles to the prevailing winds. Make the border at least one yard wide. If necessary, you can extend the inner strips to form a complete ‘maze’. Mulch open areas between brashings to give some protection against wind while grass becomes established.
7. When thatching a large conical blowout, place cuttings around the periphery and work down in concentric rings, with the brushy ends of the branches sticking outward to discourage people from walking over them. Leave an exit at the front of the blowout while you work. Then block this off with a line of brushwood pointing outward.
   
   It is usually necessary to fence the perimeter of thatched blowouts where the area is subject to access pressure. You may have to extend the fence along the dune crest or around the entire ridge if you find that people concentrate their trampling just to the sides of the fenced blowout and start to create new gulleys.
8. When thatching extensive areas, it may be wise to leave occasional paths through the thatched area, so that people are less tempted to disturb the thatch. Be sure to align and surface the paths as necessary to prevent them eroding (see Chapter 8 – Vegetation Management).

Work rate

Bacon (1975) suggests that thatching at the density suggested above (his ‘open work’ method), plus planting, takes from 139 to 232 man-hours per acre (348-579 hours per hectare). This includes 59 to 112 hours per acre (148-279 hours per hectare) bundling and transporting the cuttings and gathering the grass offsets, and 80 to 120 hours per acre (200-300 hours per hectare) planting the grass and placing the thatching.

Rooting thatching

Some thatching material, such as poplar, may resprout if set in the sand over the winter. This can be an advantage in badly eroded areas around car parks, for example, as it stabilises the surface, gets something growing, and keeps people off. Use only species which are native to the area, and do not try this technique on areas where spread of scrub would be undesirable.

Mulching

Mulching can be used to reduce erosion, keep the ground surface moist and gradually fertilise the soil as the mulch breaks down.

Mulching may be done by hand or machine. The latter is most efficient where a large area is to be covered. Access for machinery is often difficult in soft sand but mulches can be pumped in the form of slurry up to 180m (200 yds) (Kirk, 1970, p43). If this is to be done, seeds can be added to the mulch to combine sowing and seeding in one operation. Where a binder is used, this can be added to the mix if necessary, although it may be more effective to spray on the binder afterwards (see below).

Note that on nature reserves it may not be desirable to use mulches such as straw, topsoil or manure since these contain seeds of plants which may be alien to the reserve.

Mulches which can be used for dune stabilisation work include:

1. Chopped straw, forked into the sand prior to planting or seeding or spread on afterwards. This provides a very small amount of surface roughness and is useful where it is important to reduce sand blow from the treated surface (as at Camber, East Sussex). Adriani and Terwindt (1974, pp45-55) suggest mulching with straw at a rate of 5-6 tonnes per hectare (2-2.5 tons per acre). Bacon (1975, p6) recommends wheat or oat straw in preference to barley, which decays more quickly. Wheat and oat straw remain effective for two or three months before rotting, when spread at a density of one bale per 33-50 sq m (40- 60 sq yds). You may be able to get old straw bales free from farmers in March and April.
2. Peat. This is particularly useful for machair restoration work, when peat may be dug from inland bogs, broken up on site and spread by hand to an average thickness of about 10mm before raking in grass seed. Despite the tendency of the wet, cohesive peat to dry into uneven, patchy lumps, germination is faster and more consistent than in the alternative method of hydraumatic seeding. In the hydraumatic method, granulated peat is mixed with seed and binder and sprayed over the surface to an overall thickness of about 1-2mm (1/16″). Both methods achieve a much higher germination rate than if the seeds are raked into pure sand (Countryside Commission for Scotland, 1978, p10).
3. ‘Horizons’ of topsoil or leaf litter, dumped and spread on dune faces to provide a stable sill 50-100 mm (2-4″) thick. In pipeline restoration work in Aberdeenshire, overburden from a nearly access road was used for this purpose (Ritchie, 1975). At Calgary Bay on the Island of Mull, volunteers have used leaf litter and humus from nearby woodlands to help fill machair-edge erosion.
4. Reed, cut grass or other coarse herbaceous vegetation, which combines the features of thatching and mulching. If possible, harvest the material when seeds are nearly ripe and take it to the restoration site as soon as possible to avoid loss of seed. Germinating plants help bind the sand and form a turf under the planted dune-building grasses.
5. Seaweed and other storm litter. This can be used to repair minor dunedamage and to promote the growth of embryo dunes if it is collected and spread above high water mark. It is especially useful for treating heavily trampled beaches and foredunes.
   On parts of the Sefton coast, the local council clear the beach each winter of rubbish and rotting seaweed. To encourage foredune formation, the Sefton Coast Management Scheme asked them to dump the material at the back of the beach, where it was then graded with a bulldozer. By early April a mass of seedling plants had emerged from the seed contained within the debris. The dilemma is that councils are expected to keep recreational beaches tidy and odour-free, but the rubbish in fact helps prevent sand blow. The most visually unattractive beaches are often the most ecologically sound. In the Outer Hebrides, seaweed is collected on a large scale in the winter to spread on machairblowouts and to top-dress farmland. It is applied at a rate of 6 tonnes per hectare (15 tons per acre) (Seaton, 1968).
   At Ynyslas National Nature Reserve, Dyfed, volunteers have collected dead Sparfina from the strandline and used it to form a layer about 150mm (6″) deep between concrete blocks placed as foundations for new dunes (the concrete is from old road and military works on site). The Spartina is gathered with garden forks and loaded into a trailer for transport. Pebbles, collected from below high water mark, are then scattered on the mulch to hold it down.
6. Wood pulp. At Northam Burrows, Devon, wood pulp has been applied to about 4 hectares (10 acres). It successfully promotes vegetation and lasts about as long as straw mulch, but less long than bitumen binders in extreme maritime conditions (Hewett and Lamerton, 1970, p29). Pulp, chipped bark or peelings from fence posts may be cheaply available from sawmills. Peelings are unpleasant to walk on, which can be advantageous, and free of weed seeds.
   Sawdust is not recommended, because it is unpleasant to handle, tends to blow away and may actually reduce soil nutrient levels as it rots.
7. Farmyard manure. This has been used, at 6 tonnes per hectare (15 tons per acre), to maintain machair surfaces. It can also be spread on dunefaces. Unless well rotted, it supplies weed seeds to help colonise the dune.
8. Sewage sludge. This is recommended for use on dunes by Paul Johnson and Professor A D Bradshaw of the University of Liverpool, who have conducted trials including a major erosion control programme near Prestatyn, Clwyd. Merseyside County Council have used sewage sludge on a large dune protection scheme at Formby.
   Sludge can be obtained very cheaply, often for nothing, from local sewage works – but avoid works which receive industrial effluent because sludge from these sources may contain heavy metals and other toxic substances. The sludge can be poured over the sand to coat eroding hollows or spread in two or three thin coats to adhere to gentle slopes. The total thickness should be about 25mm (1″). It dries to a stiff crust which stabilises the surface, acts as a slow-release fertiliser of comparable value to artificial fertilisers and catches blown plant seeds so that the surface is quickly colonised by native plants. Sewage sludge also has self-fencing qualities: most people avoid walking on it!

Matting

A new matting material has been used experimentally at Ainsdale NNR, Merseyside, to stabilise an eroding foredune on its windward face. The material is made of a straw filling sandwiched between two layers of netting. It is laid direct onto the sand surface and pegged down with metal pegs. Holes are then made in it, using a crowbar, and marram transplants set in. It is important that corners are well anchored, so that the wind cannot lift it. The surface can be disguised with sand to discourage pyromaniacs. Trials so far have been promising. A similar material called Geojute 500 is now being marketed by Ardon International Ltd, PO Box 111, Tunbridge Wells, Kent TN4 9NW.

Binders

The following information is based on the laboratory and field tests carried out by the Countryside Commission for Scotland, the results of which are detailed in the leaflet ‘Sand Stabilisation by Spraying’ (CCS, 1982).

Binders are chemical glues which are used 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. The improved vegetation growth which it provides more than makes up for the loss of sand-trapping capacity of the dune itself, which is made rather smoother by the use of the binder. Where the sand slips, it moves under the skin which should remain intact.

Binders can be used in the following situations:

1. in combination with marram planting on active dunes. Normally the foliage of the transplants is sufficient to reduce wind erosion during the establishment phase but on exposed locations, such as dune crests and gullies, a binder will help stabilise the surface. A binder with a life of one to three years should be used.
2. for reseeding of dune pastures or machair, where the site is exposed and organic matter is absent from the surface. The binder should be needed for only six to eight weeks, while the seedlings establish.

The binders described below were developed for use in hydraulic seeding, in which seed, fertiliser and binder are applied in one operation. This method is not satisfactory on sand, as the seed is only sown in the surface layer and does not then root deeply enough to withstand surface drought. The binder should therefore be used after the seed has been raked or harrowed into the sand.

Binders form a layer only a few millimetres thick, which can be damaged by trampling. Sprayed areas must therefore be fenced. It is important that the type of binder used forms a flexible layer, so that changes in level as sand settles can be accommodated, without the layer fracturing. Binders can be used in combination with some of the mulches described on page 00, but in most cases are more effective on their own. The Countryside Commission for Scotland have found the following products to be satisfactory.

The first two are recommended for use on dunes after planting with grasses. Both should last one to three years.

‘Dunebond’

Supplier:
Dunlop Irrigation Services Ltd, Box 1, Thame Park Road, Thame, Oxon OX9 3RQ Tel: (084421) 5411
This has good flexibility with reasonable strength. The cost per square metre for materials and labour is about 17p (1982 price), making it the most expensive of the products listed.

‘Bitumuls Stable’

Supplier:
Colas (Scotland) Ltd, Imperial Works, Douglas Park Road, Hamilton ML3 ODF Tel: (0698) 282522
This has good strength and flexibility, but is less permeable to water than ‘Dunebond’. This may cause run-off and gullying at the base of slopes where it is applied. The cost per square metre of materials and labour is about 15p (1982 price).

The following three products are recommended for use on dune pastures after seeding. All have a life of three to twelve months.

‘Huls 801’

Supplier:
Huls UK Ltd, Byrom House, Quay Street, Manchester M3 3HQ Tel: (061) 832 7715
This is strong and permeable, but is rather brittle and should not be used on areas which are liable to settle. The cost per square metre of materials and labour is about 10p (1982 price).

‘Curasol AE’

Supplier:
Hoechst UK Ltd, Salisbury Road, Hounslow, Middlesex TW6 3JM Tel: (01) 570 7712
This has good flexibility with fair strength and water permeability. It can adversely affect seed germination if the seed comes into contact with it. The cost per square metre of materials and labour is about 6p (1982 price).

‘Vinamul 3277’

Supplier:
Vinyl Products, Mill Lane, Carshalton, Surrey SM5 2JU Tel: (01) 669 4422
This has good strength and permeability with fair flexibility. At about 5p per square metre (1982 price), it is the cheapest of the products listed.

Procedural points

1. Depending on the area to be treated, you can spray diluted binders using a watering can, knapsack sprayer or – most practical for many stabilisation programmes, although beyond the scope of most volunteer projects – a small motorised crop sprayer equipped with a hand lance and having a high volume output. For more on knapsack sprayers, see here.
   If you use a motorised sprayer, wear a protective face mask to prevent irritation from fine droplets of oil and resins. Whatever the method used, stand upwind of the area which you are treating when possible. When treating small areas with a watering can, you may have to enlarge the holes of a metal rose to reduce clogging. Plastic roses are less likely to clog.
2. Apply the binder immediately after sowing, fertilising and covering with sand.
3. Binders come in drums which are too big to pour out of easily. It is worth buying and fitting a reusable tap (cheap plastic; taps are readily available). Follow manufacturers’ mixing instructions. When mixing directly in the sprayer reservoir, it is important to put in the water first and the chemical second to get a good mix and avoid clogging.
4. Spray the sand in parallel strips, 600mm-1.2m (2-4′) wide depending on the spray apparatus. Start at the top of a slope and move down. The spray should sink into the top layer of sand. If it remains on the surface you may be spraying too heavily or using too concentrated a mix. But if the spray fails to bind with the surface sand, the mix may be too dilute. Experiment on trial plots first before mixing a large quantity of spray solution.
   Use marker poles or some other means of identifying areas sprayed with light-coloured binders such as latex, otherwise you may have trouble telling sprayed from unsprayed sand until the binder hardens and darkens.
5. Refill sprayers before they are completely empty, and clean them out immediately if you are finished for the day. If you let them sit around they get gummed up.
6. Avoid working in strong winds, which will make even application difficult.