This is a shortened version of the damage report, a copy of which has been deposited with Surrey Archaeological Society at Castle Arch.
Summary
Felling of a number of trees after vegetation clearance in 2006 and the concomitant damage caused by the uplift of their root plates high-lighted the need for an assessment of the condition of the Scheduled Ancient Monument, Holmbury Hillfort. This report details damage by this and other agencies and also recognises that some information about the construction of the eastern ramparts has been gained through exposure of intact archaeology.
Background
Holmbury Hillfort is set on a south-facing spur atop the scarp slope of the greensand ridge which runs west/east through central Surrey. Although harder bands of chert run north/south across the ridge the soils are in general dry, acid, infertile podzols vulnerable to erosion by both natural and human agency. Cartographic evidence from the 19th and early 20th centuries shows the hillfort covered with heathland vegetation, but by the 1960s the interior had become infested with Rhododendron ponticum. Some of the tree growth is likely to have resulted from reduced use of the heathland for grazing, but deliberate planting is also recorded. However, none of the trees in the immediate vicinity of the hillfort appear to be over 100-150 years old.
By 2000 it was recognised that roots from the vegetation within the interior of the hillfort and over the ramparts presented a threat to the underground archaeology which, since only a small proportion has been excavated, should be intact. In 2005 most of the vegetation was removed but a number of trees remained. It may be that removal of the surrounding vegetation left these trees particularly vulnerable - certainly high winds during winters 2006/7 and 2007/8 resulted in at least 11 being toppled, giving rise to concern that pulling up the root plates may have damaged underlying, intact archaeological remains.
This report details any such damage and also comments on damage caused by other agencies.
Damage to southern slope
Damage report
DAMAGE BY TREE FALL BETWEEN 2006 AND 2008
The holes caused by pulling up of the root plates were cleared of loose material but no consolidated material was removed even where it had clearly been deposited either when the tree fell or during the intervening period. It should be noted that damage will have taken place at lower levels than those exposed especially where the tree involved was of a species which could be expected to have had a long tap root.
Of the 11 trees considered sufficiently mature for their roots to have intruded to archaeological levels 9 had been growing on or between the ramparts on the eastern side of the monument, one in the same area but probably below any manmade structures and the remaining example had been on the inner bank on the western side.
Intact archaeology was clearly exposed by one tree. This was a manmade vertical cut into the greensand which had not been visibly penetrated by the roots so no damage appears to have been done but it should be noted that without remedial action this face will now degrade through freeze/thaw and other erosive agencies.
Damage has probably been caused by the withdrawal of the root plates of other trees; in all cases blocks of greensand were observed which would have been part either of the matrix of the ramparts or of any revetment cladding them. One tree had been growing in a position where its roots would have penetrated silts in any ditch constructed between the inner and outer ramparts on the eastern side or, in the absence of a ditch, in tumble from the inner rampart.
DAMAGE BY CYCLISTS, RIDERS AND PEDESTRIANS
Damage, particularly by mountain bikers is an ongoing concern which is being address by the creation of alternative tracks. It is most unfortunate that, despite extensive efforts by the Ranger for Hurtwood Control Trust and members of cycling clubs considerable damage to the Scheduled Monument is still occurring. In some cases large sections of tree trunks placed to block tracks that are causing particular damage have been pushed aside and close to the south-western (modern) entrance ‘alternative' cycle tracks are cutting into intact archaeology.
Barriers removed from track
Only one point has been noted where horse riders may be causing damage, a bridleway which descends steeply over the southern ramparts at their eastern end. Here what appears to be in situ revetment is being kicked out; this is creating bare areas which are being further damaged by water erosion. It should however be noted that only cyclists have been observed using this path.
In general terms very little damage is being caused by pedestrians despite the summit being a popular and accessible location.
DAMAGE BY VEGETATION REGROWTH
The removal of a dense cover of rhododendron has allowed regeneration of opportunistic vegetation. It is assumed that a programme of maintenance is in place and this will be essential if growth of birch is not to damage sensitive areas in the interior of the hillfort.
DAMAGE BY WIND AND WATER EROSION
The degraded soils of the greensand ridge are, in the main, loose, dry, acid sands and whilst they can support heathland species removal of this vegetation leaves them exceptionally vulnerable to erosion. There are a number of points around the ramparts where human agency has worn away the protective cover leaving steep slopes of sand and greensand blocks, often the revetment of the ramparts or their core material exposed. Wind, and more seriously, water, then further cause erosion and deep gullies may result. The bridleway at the eastern end of the southern rampart and deep cut tracks south of the south-western entrance provide cause for concern.
Archaeological information gained during this exercise
Previous archaeological interventions have concentrated on the clearly constructed banks and ditches bounding the gentle approaches to the hillfort from north and west whilst structure of earthworks topping the steep eastern and southern slopes have not been investigated. Intact archaeology exposed under the root plate of one of the trees which had been growing on the outer slope of the inner rampart on the eastern side allows some comment to be made on the nature of the ramparts on that side.
Analytical survey shows the remains of a spread bank with an apparent berm between it and a steep drop to a broad terrace. Although there are signs of a ditch at the bottom of this drop at the northern end of the eastern rampart complex it is not certain that this ditch was present along the length of this side. The terrace, which carries the present path, has a further slight bank on its outer, eastern side, and below that it is not clear whether or not the natural slope of the hill has been enhanced in any way.
Management suggestions
The scarp edge of the greensand ridge between Guildford and Dorking provides a large area of open space the quality of which was recognised in 1958 when it became part of the first area in England to be designated an AONB. Whilst much of the area remains relatively underused certain places have become ‘hot spots' and, with its ease of access and superlative vistas, Holmbury Hill is one of these. Despite the vulnerability of the ‘soft' geology the potentially competing requirements of public access, nature conservation and preservation of historic monuments and landscapes are, in general, well managed but two items give rise to some concern - the risk to intact, underground archaeology posed by uplifting of the root plates of mature trees and the depredations of mountain bikers. The following suggestions are made in light of those concerns:
Some at least of the remaining trees within the scheduled area should be felled
- The excellent work in diverting cycle tracks off sensitive areas of the hillfort should be continued.
- It is assumed that a management plan is in place to prevent further excessive vegetation growth within the cleared area.
- Consideration should be given to closure of the bridle path leaving the hillfort at the eastern end of the southern face.
