The general picture is of a loss of these species-rich grasslands, due to the invasion of scrub from lack of rabbit and stock grazing, the spread of introduced scrub species, and the loss of vegetation cover from trampling, erosion and over-grazing. Much area has also been permanently lost to urban development, agricultural improvement and military and recreational use (see Chapter 2 – Management Planning). Where intervention is decided to be appropriate, it may take one of the following forms:
- Except in areas of mobile dune, follow-up management of the vegetation resulting from scrub clearance will be needed. As well as spraying or cutting of regrowth, as described above, grazing or mowing will be needed to encourage the return of short-sward species.
- At the stage before dune grassland succeeds to scrub, grazing, mowing or burning can be used to reduce the amount of coarse grasses and prevent scrub encroachment.
- Restoration may be needed where over-grazing, trampling or erosion has caused loss of turf. The first stage is to tackle the problem at source, by reducing grazing levels or fencing to keep stock and rabbits out, and by taking measures to control access. Measures to hasten recovery of vegetation cover, by seeding, fertilising and mulching are described in Chapter 7 – Vegetation Establishment.
Restoration after clearance
Few records have been made of the recolonisation of dune vegetation following scrub removal; a gap now being tackled by analysis of the recovery of dune vegetation at Murlough NNR, following sea buckthorn clearance (Ellis, edit. 1983).
Any after-treatment is made very much easier if stumps are removed, both so nutrient enrichment does not occur, and so that mowing or cutting machines have easy access.
Burning does not necessarily enrich the soil. Allen (1964) showed loss of nitrogen up to 45kg/ha, and losses of other nutrients which form volatile compounds when heather is burnt. However, input from rainfall can more than make up for the losses. At bonfire sites on sandy soils the nutrients remaining in the ash are likely to be quickly leached, therefore removal of ash is not necessary. At Whitford Burrows, bonfire sites do not show enrichment, but are recolonised first by mosses. Burning of vegetation is an important way of reducing fertility on a site.
Grazing is likely to be needed at quite high levels initially, to knock back the flush of growth after clearance. Cattle or horses are more useful than sheep in grazing rough and lush vegetation.
If cutting or mowing is used, this needs to be done two or three times in the first season, with all cuttings removed to reduce nutrient enrichment, and to prevent the material suppressing the germination and growth of more desirable species. Any management by grazing or mowing must be maintained, or coarser vegetation will rapidly spread back.
Grazing and mowing
Experimental work with mowing and grazing by sheep is being carried out at Newborough Warren NNR, and the results of many years work in the Netherlands are reviewed by Oosterveld (in Doody, 1985).
In general, cutting results in a short vegetation sward, tending towards uniformity. Conversely, grazing introduces diversification, due to uneven trampling, dunging and grazing, with palatable species being selected preferentially.
According to Oosterveld, the most important factor in grazing is that no improvement should be made by way of fertilising, draining or levelling of the land. Slight overgrazing seems to do little harm, so long as it is not to the level that can only be supported by supplementary feeding of hay or silage. Damage of this type has occurred at South Walney, Cumbria, where the Cumbria Trust for Nature Conservation who manage the site have no control over the numbers of cattle being grazed, and in winter silage is fed to support a high stocking level. It is feared that permanent damage will occur, as in places the vegetation is being completely destroyed, with subsequent erosion. Some of the most vulnerable areas, and those used for shade and shelter and thus most heavily trampled, are being protected by fencing.
Oosterveld has demonstrated a non-random use of grazing areas by stock, due to such factors as shade and water. He has shown that cattle and horses prefer to graze facing away from the sun, which in large grazing areas results in a daily clockwise pattern of herd movement. During the middle part of the day, most animals will be in the northern part of the area, moving towards the south eastern part to sleep. Where grazirig plots are being established, it can be arranged that the most vulnerable vegetation types are not situated at the border of the area, especially in the northern and south-eastern parts.
Overgrazing of dune-heathland can cause conversion to grassland, which is usually less desirable. Stocking levels will vary greatly with the area, but an example is given below of levels suggested by the NCC for the management of dune-heath at Earlshall Muir SSSI, Fife (Doody. 1985).
The recommendation is that there should be no grazing on the frontal dunes, due to vulnerability to erosion. The main area of dune-heath, which had been lightly grazed in the previous 20 years, should also be mainly not grazed, apart from some winter/spring grazing at the rate of 0.5 ewes per hectare in years when the rabbit population is low. Cattle should not be grazed, because of the damage done by heavy trampling to lichen-rich heath. On the areas which are mainly grassland, grazing should be continued at 0.15 beef cattle per hectare, or sheep equivalent.
Oosterveld, writing about the Netherlands, gives figures of 1 horse or cow per hectare or 3 sheep per hectare for seasonal grazing. For year round grazing without additional winter feed, onlv very low rates are possible, at 1 horse or cow per 10 hectares or 1 sheep per 5 hectares. Horses are more suitable for year round grazing as they can compensate for low quality fodder by eating greater quantities.
The grazing experiments at Newborough Warren use the equivalent of 1 or 2 sheep per 0.3 hectare, grazed for either one third, two-thirds or the whole year. For management reasons, flocks of 4 and 8 sheep are used. The mean number of plant species recorded as a result of grazing were highest for plots grazed for 2/3 of the year by 2 sheep. The highest grazing level, of 2 sheep per 0.3 hectare all year was too high for optimum numbers of species (Hewett, 1985).
Experience at Braunton Burrows has indicated that it is not worth burning areas unless follow-up management by grazing can be done. Without it, areas quickly return to their previous condition. Here, as in other areas, the topography and wartime hazards make mowing a difficult job, although small areas have been cut with hand machines, on an experimental basis.
Since the introduction of myxomatosis in the 1950s, and the great reduction in the rabbit population during that and the following decade, numbers have been building back up again in some parts of the country. Fluctuations of population occur due to further local outbreaks of the disease. The problem with this is that during times of low rabbit numbers, the vegetation grows taller, with coarser grasses becoming dominant, that are less palatable to rabbits. Under a sustained moderate level of grazing, the more interesting, attractive and palatable species are retained. In the past, this moderate level was probably sustained by cropping.
Work at Holy Island (Garson, in Doody, 1985) suggests that forage is in short supply from November/ December to April/May. During the summer, some of the slacks are heavily grazed, reducing flowering and seeding in years when the population is high. The summer grazing period is important in determining the success of that year’s juveniles. It was found that by fencing a slack against rabbits, flowering and seeding was improved. However, it is also suggested that such exclosure reduces the numbers of juveniles surviving in that year, due to forage shortage, so such exclosures may provide a way of keeping populations at a moderate level. If this forage shortage is allowed to develop naturally through high population increase, it is likely that grazing would be at too high a level to maintain an interesting sward. Following further experiments at Holy Island, Garson recommends using temporary electric netting (see ‘Fencing’, Agate, 1986) as a cheap and effective alternative to permanent galvanised netting. This need not be formed into an exclosure, but can simply be run out along a line barring the routes from burrows to slack.
Practicalities
The following section is contributed by David Hewett.
The preceding paragraphs give an indication of the grazing regimes that can be applied to dune grassland. However, there are considerations concerning grazing which do not apply to the management of vegetation by machines. .A tractor or mower can be stored in a shed, and requires limited maintenance, whereas responsibility for animals is a 24 hour/day, all year job. This will fall largely on the owner of the animals, but the land manager has a certain responsibility. If grazing is let, then the manager specifies the conditions, such as the number of animals and the time of year during which the land is grazed. It will be essential to ensure that conditions are followed, and careful records kept.
As a general rule, land cannot be grazed without fencing to contain the stock. The type and height of fencing will vary with the stock (see ‘Fencing’, Agate, 1986). It may even be possible to maintain a population of rabbits, but they must be kept out of neighbouring farmland.
For the health and well-being of the animals, an annual programme of care must be followed. This is likely to include dosing, vaccination, care of hooves, as well as statutory requirements such as dipping of sheep and treatment for warble fly in cattle. An example routine for sheep management is given in the MAFF leaflet ‘The Lowland Ewe – Shepherd’s Calendar’. Management of flock or herd numbers by breeding, buying, selling and slaughtering must also be considered. The whole exercise needs to be thought through carefully before any animals are brought onto the site.
In addition to fixed equipment such as fences, pens and dips, a truck or trailer for transporting animals may also be needed. It may be necessary to move animals elsewhere for certain periods, for example to allow summer flowering plants to seed, or when food is short. Supplementary feeding of hay and concentrates is not usually desirable where land management is primarily for conservation, as alien seed can be introduced. When fodder is in such short supply, damage to the vegetation and soil surface is also likely to occur.
