Vegetation is the perfect control agent against erosion. It works in three ways; breaking the impact of raindrops, trapping sediment and stabilising the upper layers of soil or substrate.
There are three basic methods of vegetation restoration, as listed below. Often a mixture of these methods will be used on any one site, either at the same time, or according to season. The most noticeable attribute of natural vegetation is its lack of uniformity. Avariety of methods, and ‘patchy’ results, will give the most natural effect.
- Allowing vegetation to return naturally, by seed spread or vegetative spread from surrounding vegetation. In grazed areas, the removal of grazing will allow plants to flower and set seed, thus greatly increasing the rate of natural seed spread. The reduction or removal of grazing and trampling will also greatly increase the rate of seedling success, and is nearly always the most important factor in vegetation recovery. Recovery can also be aided by boosting any remnant vegetation with fertiliser, and lime on acid sites.
- Sowing seed, either purchased or collected locally, of grasses and other plants.
- Transplanting turves or clumps of vegetation dug from elsewhere. This may include nursery-grown trees and shrubs.
The success of any of these techniques depends on reducing or removing grazing or trampling pressure. Success will also vary considerably with the soil, altitude, aspect, prevailing weather and other natural factors. Results on apparently similar sites only a short distance apart may vary considerably due to differences in soil, water availability or micro-climate.
Geotextiles can be used in addition to any of the methods listed above, and soil stabilisers can be sprayed onto slopes to assist seeding.
Natural recolonisation
In all but the most extreme locations of high salinity, toxicity, acidity or on moving scree, vegetation should eventually return if trampling is removed or lessened. The plants will only be those occurring locally, and so a ‘natural’ plant community should result. However, in areas where erosion is severe, this natural recolonisation may be too slow to prevent further erosion, and where topsoils are gone, nutrient levels are too low to support much growth. In lowland areas recovery may be rapid, but it can take some years to achieve a balance, as in the first few years the plant community will be dominated by pioneer or weedy (aggressive) species, usually those which are fast growing and can survive in extreme situations. For example, it is likely that thistles, docks and willow herb will arrive before the more desirable slower growing grasses and herbs. After a few years, if the recovering patch is managed in the same way as the rest of the area, the weedy species will decline until the patch blends in unnoticed.
This natural pattern of recovery may be unsuitable for the following reasons:
- The rapid or even instant restoration of a scar or closed- off path may be a vital part of the scheme to persuade walkers to keep to the newly designated path. Walkers are more likely to respect the scheme if they can see that positive measures are being made to restore the eroded area.
- Growth may not be quick or thick enough to prevent renewed erosion of the area, particularly on steep slopes.
- The appearance of the pioneer plant community.
The addition of fertiliser and other treatments such as lime has been tried on several sites, to boost the surviving vegetation. Trials done on trampled areas during the Three Peaks Project in the Yorkshire Dales were inconclusive, but seemed to suggest that the removal or lessening of trampling was a much more important factor than fertiliser treatment.
On the large scale, where trampling is not the only factor in vegetation loss, fertiliser and lime treatments have been very successful on acid peat. In the Kinder Scout area of the Peak District, the National Trust have applied fertiliser and lime by helicopter to stimulate natural regeneration and self-seeding of remnant moorland vegetation (The National Trust, 1993). The lime temporarily reduces the acidity of the peat, and the fertiliser provides the extra nutrients to boost growth. A light application, of about 1 tonne of lime dust and 0.3-0.5 tonnes of fertiliser per hectare, is enough to have a significant effect on plant growth, flowering and seed-set of the remnant sward.
Seeding
Seeding requires careful analysis and preparation if it is to be a success. This will include surveying the local flora, and analysing the soil or substrate to determine if any chemical treatments are necessary. Care must be taken that invasive species are not introduced which may upset the balance of species in surrounding plant communities. Seek advice if necessary from the local office of English Nature, or equivalent nature conservation agency for Wales, Scotland or N. Ireland.
The seed mix should usually be of native species and should include a fast growing ‘nurse’ species, and slow growing long lived species for permanent cover. As well as grasses, seeds of other herbaceous perennials, shrubs and trees can be sown. After seeding the area must be fenced to exclude walkers, preferably for at least a year.
Turfing and transplanting
Like seeding, turfing will only be successful if the original reason for vegetation loss has been removed; usually by the provision of a more resistant path. Turfing has the obvious advantage that its effect is immediate, and it can transform the edges and surrounds to a new path so there is no question in the walker’s mind of following any route other than the path. If turfing is done with care, and the site is meticulously cleared up afterwards, it should be almost impossible to detect any signs of the work that has been done. This cosmetic effect can be vital in successfully altering visitors’ patterns of use. Turfing is slow and sometimes heavy work, and the source of turves may be a limiting factor. Permission to cut turves must always be obtained from the landowner. Under the Conservation of Wild Creatures and Wild Plants Act 1975 it is illegal to dig up any wild plant without the landowner’s permission.
