General points
Uses
Shrubs may be used on dunes to:
- Protect eroding windward sand faces in areas where the sand is too steep and mobile for grass to take. In these situations the shrubs tend to be undermined, but even if they die and topple over they trap some sand.
- Check sand drift and slow the rate of accretion on the lee slopes of dunes
- Supply cuttings for use in thatching and brushwood fences
- Form barriers, shelterbelts etc for amenity use and access control
Other considerations
- Shrubs change the dune ecosystem more radically than do grasses and should only be used on sites where they already occur or where the need to retain open dune habitats is less important than the need to fix shifting sand.
- Most sand-trapping shrubs spread horizontally by suckers, but the rate of spread is much slower than their upward or oblique growth through moderate sand burial. For this reason, shrubs maintain a fairly tight form which creates rather steep-sided hummocky dunes which are less erosion resistant in exposed conditions than dunes built by grasses.
- Shrubs should be planted in the period September to April, with February and March being best (Adriani and Terwindt, 1974, p56). This gives the plants time to root before the onset of summer droughts.
- Plant shrubs in groups rather than individually, to give them mutual support and increased overall wind resistance. Where the aim is not to create dense thickets but to provide stability for a variety of herbaceous plants, plant them at about 10m (30′) intervals to allow room for other plants in between (Adriani and Terwindt, 1974, p48).
Species
Sea buckthorn
Sea buckthorn (Hippophae rhamnoides) is rampant on many sites where it occurs naturally or has been introduced, and it is controlled more often than it is fostered where the aim is to promote diverse plant communities. Introduction in such areas is obviously counterproductive. There may be other species native to the site which may be substituted, although with care an all-male colony can be established which is easier to manage than a mixed one since it spreads only by suckering. See here for more on the ecology and management of this species.
Sea buckthorn survives both in dry and damp locations, although growth is poor in soils deficient in lime. On the East Lothian coast older specimens continue to grow even when successively buried by 4.5m (15′) of sand with only about 600mm (2′) of the shoots remaining exposed (Ranwell, 1972a, p18). As with many shrubs, the buried portion dies but the shoots which remain above the sand root again to form new plants at a higher level.
Adriani and Terwindt (1974, p49) recommend planting sea buckthorn suckers or seedlings only where a good cover of grass has already been established. Suckers should have a good root system and should be dug up and planted out on the same day. The roots should be placed 250-400mm (10-16″) deep according to the dampness of the soil.
Sow sea buckthorn in sheltered places having little if any sand disturbance, where it germinates readily, and in areas with too much sand for transplanting. Soil salinity must be below 0.05% (Adriani and Terwindt, 1974, p48). One trouble with sowing is that you can’t ensure an all-male population which will not spread further by self-seeding.
Creeping willow
Creeping willow (Salix repens) is a widespread shrub of moist duneslacks. In areas which are drying out, it often persists and becomes deep rooted.
This is a dwarf species which grows up to 1m (3′) high. Like sea buckthorn, creeping willow has spread rapidly on many sites since the 1950s when myxomatosis reduced the rabbit population and grazing restraints lessened. As yet, control does not seem to have been required. Where it becomes firmly established it acts as a good sand stabiliser, provided accretion is not over about 400mm (16″) per year (Ranwell, 1958, p96). Creeping willow should be established by transplanting seedlings on suckers in the same way as sea buckthorn.
Other species
A few other shrub species may be of use in restricted situations:
- Elder (Sambucus nigra) often invades the landward side of shifting dunes, inland fixed dunes and the borderline between dunes and woodlands. It prefers a relatively rich soil, eg where fresh organic material such as bird droppings decompose rapidly. In such places it often invades and shades out stands of sea buckthorn. It is normally 2-4.5m (6′-15′) high, but under conditions of wind pruning and sand burial it suckers from buried shoots to form low thickets of upright shoots which trap sand efficiently. At Ynyslas Dunes (Dyfi NNR), Dyfed, it has survived well where this has occurred to plants growing on the edges of blowouts.
To propagate elder, take cuttings about 1m (3′) long and force them well down into moist sand with 300-450mm (12-18″) of stem projecting. - Tamarisk (Tamarix spp) is an introduced evergreen shrub from southern Europe which survives along the south coast of England and in places as far north as Lincolnshire. It withstands sea wind and occasional flooding bv salt water and makes a useful coastal hedging plant. Tamarisk spreads by suckering and grows 2-3m (6′-10′) high. As a non-native it should not be planted on nature reserves and other sites of scientific interest.
- Tree lupin (Lupinus arboreus) is an evergreen shrub which grows to 3m (10′) high. It is an exotic species (from California) which has been successfully interplanted with marram at Dawlish Warren, South Devon and has been used to screen car parks on the Suffolk Heritage Coast. It does best where there is not much sand accretion. It is much favoured by rabbits and may require fencing to survive.
- Common, field or English elm (Ulmus procera) has formed dense thickets of suckers in part of the dunes at Holkham, Norfolk, where it is very effective in blocking access and stabilising sand through its mat of surface roots. [t is, however, very subject to rabbit attack when young. [t may be propagated by transplanting suckers.
- Privet (Ligustrum vulgare), a plant which is widespread but most common in the South, is a useful sand stabiliser on calcareous dunes where its thickets form an effective barrier and its dense, fibrous root system holds the sand. It can be propagated from seeds, cuttings or suckers.
- Shrubby seablite (Suaeda fruticosa) has been used in attempts to stabilise mobile shingle (not sand) at Blakeney, Norfolk, around 1953 (Jane and White, 1971, p29).
According to Frank Metson, who has had many years of experience with the Anglian Water Authority, the plants were only able to survive in sheltered places. He concludes that similar plantings along stone revetments in Essex have been worse than useless from a stabilisation viewpoint, since storm waves have tended to pull loose any plants which have rooted, along with a large amount of shingle or stonework.
On more stable shingle this plant can be valuable as a shelter for wildlife and for scenic amenity. It can be transplanted by uprooting existing plants and laying them in at a 45° angle, with the roots well buried.
