Erosion control and vegetation restoration

Erosion is a serious problem on many popular paths and areas where the public have unrestricted access. Excessive trampling destroys the vegetation, so exposing the soil to rain splash and overland flow, and causing a great increase in the rate of erosion. The steeper the slope, the greater is the problem. Damaged landscapes range from mountain tops to peat moorlands, chalk downs, lowland heaths and coastlands.

There are various ways of tackling the problem:

1. Reducing the total volume of use. This can only be done indirectly, by restricting the availability of car parking at road access points, or by reducing publicity for certain routes. In the past, serious damage has been caused by mass walks, particularly on upland areas of peat bog. The effects can be especially long-lasting if a sponsored walk, training exercise or other event coincides with a period of wet weather. The damage caused by a single event may be seen for many years. These events are now actively discouraged in most vulnerable areas. Some types of use, particularly by off-road vehicles and mountain bikes, are very damaging. Where the legal situation is clear, barriers can be erected to illegal use, although this may be physically difficult and almost impossible to enforce in some areas. On other routes, the legal status is still being clarified.
2. Reducing grazing. Grazing by sheep, deer, goats and rabbits on upland and moorland areas can have a very great effect on the species content and vigour of the vegetation cover. The reduction or exclusion of grazing may be the most important single factor in vegetation restoration. During the 1980s, dramatic changes were made to the flanks of Kinder Scout in the Peak District, by banning all sheep from the moor, and rounding up all trespassing sheep (over 25,000 sheep removed in 10 years). There has been a great reduction in the amount of bare ground, and an increase in the amount of heather, bilberry and other desirable species (The National Trust, 1993). Once such areas have regenerated and stabilised, grazing may be allowed again at the rate of about one sheep to 1.5 ha, in order to help maintain the moorland vegetation.
3. Spreading use over a wider area to lessen the impact on one particular path or location. On the large scale, this may be part of a management scheme for an extensive area of countryside, such as a National Park. On the small scale, this may require simply the removal of fences enclosing a path to allow use to spread. On chalk downland and ancient monuments particularly, the aim is often to encourage an even use all over the site by removing ‘targets’ and desire lines, or in other words, allowing access without the development of paths. See also Chapter 3 – Path design and Chapter 4 – Safety, equipment and organisation.
4. Draining and improving the path, or altering its line, to allow natural regeneration of the hillside. See Chapter 6 – Path clearance, Chapter 7 – Drainage, Chapter 8 – Surfacing, Chapter 9 – Boardwalks and bridges and Chapter 10 – Steps.
5. Restoring damaged areas by constructing revetments and erosion barriers, filling, grading, reseeding and transplanting. These techniques are considered below. Successful restoration requires keeping people off the area being restored, and is a complementary process to improving the path. Techniques to encourage users to keep to the path are discussed in Chapter 4 – Path design.

Over the years, many techniques have been tried, mainly on an experimental basis, to re-establish vegetation. The overall picture that emerges is that where trampling is confined to the path, and grazing is excluded, vegetation has a great capacity to recover, either from the seed bank contained in the substrate, or by the artificial spreading of seed. On eroding slopes, the most important procedures are to create drains, improve the path to confine trampling and remove grazing if possible. Then vegetation can recover. Within this general picture, there are of course great variations, according to the site, location, local climate, use and so on. Amongst the most difficult areas are acid peat, where the seed bank is low, and acidity, worsened by acid rain, and low nutrient levels, resulting in little or no vegetation growth. The situation can be improved by the spreading of lime and fertiliser.

The other general point that emerges is that although products such as geotextiles and gabions may help in certain situations, there is no ‘quick fix’. The simplest techniques are often the best. Careful use of natural materials on site, together with long term management planning for the whole area gives the best results.

The moment to act

In many places the moment for a ‘stitch in time’ passed by many years ago, and damage is extensive. However, most areas have developed the techniques and the expertise to deal with nearly all situations, and given time and resources managers are confident that they have the problem solved. Hopefully, many areas will never again suffer the extent of damage that was occurring in the 1970s and 80s. However, there is still much work to be done.

Studies have shown that soil structure is damaged by trampling while vegetation is still maintaining itself, and by the time there is visual evidence of declining plant cover, the critical period in which erosion is initiated is already past. This presents a dilemma to anyone responsible for deciding when action should be taken, as it suggests that to prevent erosion one should surface or strengthen an apparently resistant grass path, assuming that levels of use are to remain constant. This would obviously be an unpopular decision. In practice, most areas have a backlog of paths which are already eroded and in urgent need of treatment. In National Parks and other areas, path networks have been carefully surveyed to prioritise work, and management and maintenance plans for years ahead are being drawn up.