One of the most troublesome species on sand dunes is sea buckthorn (Hippophae rhamnoides), especially where it is introduced into west coast dune systems. Sea buckthorn is considered separately below. Other introduced species which may spread include turkey oak and rhododendron, with native birch, privet, sallow, gorse and creeping willow also becoming a nuisance in some areas.
Scrub has benefits to offer, and the need to control has to be assessed by careful study of each site. Such advantages include:
- Stabilisation of the dunes. This can be useful in areas of public: pressure and erosion damage.
- Control of access by keeping people to paths and excluding them from certain areas.
- Shelter and nesting sites for birds, shelter for invertebrates and mammals.
Young seedlings of many species can be pulled by hand, but older plants will need cutting, and any regrowth spraying. The herbicide currently favoured for use on woody growth is Garlon 2. To aid thorough treatment, a red dye can be mixed with the herbicide to colour areas which have been sprayed. The dye is supplied in powder form, and is simply sprinkled in to give the required colour. It is available from Hortichem, 14 Edison Road, Churchfields Industrial Estate, Salisbury, Wiltshire SP2 7NU.
At Braunton Burrows, clearance is carried out of areas of sallow carr, hawthorn and privet. The method used is to first fell trees and larger shrubs using a chain saw, followed by a clearing saw to take the tops off the remaining growth. Volunteers then come in to clear and burn the debris. This procedure avoids volunteers having to work with the noise and danger of machinery. All clearance is done in December and January to minimise the disturbance to birds. A tractor can be used to grub up hawthorn growing in the drier part of the reserve, but sallow indicates wetter areas where a tractor is liable to get stuck. Any regrowth is sprayed with glyphosate in late May, with a re-spray in July if necessary. The aim is to spray when regrowth is about 500mm high, as any higher than this requires excessive expense on herbicide. After-treatment can be a problem, as the rotting stumps add nutrient to the soil, and it is reckoned to take at least 10 years for nutrients to leach out. The stumps also make it difficult to bring in machines to mow the resulting vegetation. On this site, wartime rubbish, ant-hills and other hazards make machinery use awkward.
Where gorse occurs on dune heathland, some clearance may be needed to reduce fire risk. At Studland NNR, firebreaks have been cut through large stands of gorse. Once cut to ground level, rabbits nibble the soft young growth, so further cutting is not needed, provided rabbits are present in sufficient numbers.
Creeping willow supports a large number of invertebrates but, due to myxomatosis reducing rabbit grazing, has become invasive of some wet areas. Experimental cutting with an Allenscythe seems to give promising results, provided the clippings are removed to prevent them resprouting. Grazing by cattle over a period of 10 years or more has also been successful in maintaining an excellent species mix in an area which would otherwise be entirely comprised of creeping willow.
In general, grazing is not effective as a method of reducing scrub growth, as animals merely move away from those areas to more palatable vegetation. Grazing is better used as a method of management following mechanical clearance. This is clearly shown by photos of Braunton Burrows in ‘Sand Dunes and their Management’ (Hope-Simpson, J, in Doody, 1985). These show how the rabbit-free years from 1954 to the early 70s allowed shrubs to invade. When rabbit population picked up again in the 70s, these individual plants were above rabbit-damage height, and have since increased greatly in area. However, no new individual plants have appeared, due to the rabbits destroying the seedlings.
According to Oosterveld (in Doody. 1985), increased stocking rates in autumn can retard shrub development, when other fodder is becoming short in supply. Browsing and bark damage by sheep can destroy young trees. At Newborough Warren, hawthorn and birch up to 2m high were killed by sheep damaging the bark, but blackthorn were only browsed, and were thus not destroyed. Creeping willow was also only browsed, which encouraged shooting from ground level, so overall cover was not reduced (Hewett, 1985). Blackthorn can be as invasive as sea buckthorn, spreading in similar fashion from underground shoots, and similar control measures may be necessary.
