Flora Locale - Restoration Areas

flora

LOCALE

Twyford Down Project

Downland Restoration Areas

The timing of the main construction contract dictated when the areas destined for downland restoration would become available. Therefore it was necessary to divide the restoration work into three phases:


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Arethusa A

Both hand cutting and macroturfing methods were used to remove turf to the site, with the most species-rich turf being placed in the optimum positions and the less rich in less favourable areas. The areas not turfed were harrowed to form a seedbed and in March sown in three sections with three distinct seed mixes. A short turf mix for the area surrounding the species-rich turf, a mix for longer turf, and a mix of seed collected from local sites using suction equipment. After sowing the area was lightly rolled. Over the next 18 months some 31 000 pot plants of seven species of downland plants - Kidney Vetch, Horseshoe Vetch, Rockrose, Thyme, Clustered Bellflower, Cowslip and Hairy Violet - all except the last having been grown from local seed or cuttings, were planted into this area.

Some 200 Juniper plants were also planted in five rabbit- and stock-proof exclosures in order to add further diversity. Juniper is a typical downland plant which is declining in southern England.

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Arethusa B

The topsoil was stripped and removed as in the previous site. No turf was available, so the entire area was sown with a single mixture of seed. The bulk of this mix, 59 species in all, was seed of commercial origin, mixed with hand-collected seed of species otherwise unobtainable. To supplement to seeding 22 000 plug plants of six species of downland plants - Devil's-bit Scabious, Horseshoe Vetch, Cowslip, Hairy Violet, Clustered Bellflower and Rockrose - were planted. These were all grown from local source material.

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The Restored A33

The road was broken up and the old, overgrown cutting faces and backs were cleared of scrub. Chalk from the excavation of the northbound carriageway of the new cutting was used to fill and landscape the site. Care was taken to give a natural effect and recreate as closely as possible the original shape of the hill. The landscaping of the site was carried out from the bottom upward in order to preserve areas of potentially useful turf which lay at the top of one of the old cuttings. Topsoil was spread over the chalk, thinly in areas which were to become downland, but much more thickly where shrubs and trees were to be planted. All shrub and tree planting was protected by stock-proof exclosures. The slopes were seeded with a downland mix of 51 species prepared as before. However, an area at the foot of St Catherine's Hill and Plague Pit Valley which, due to its south-facing aspect, was potentially of special interest was sown with a richer, shorter turf mix of 37 species. In early May, some 44 500 plug plants were planted in appropriate areas, the same species used as on Arethusa A with the addition of Devil's-bit Scabious.

All the downland restoration areas were surrounded by rabbit- and stock-proof fencing. This was to protect not only the developing turf and invertebrate populations in the early stages of colonisation, but also grazing stock from the public and their dogs. As soon as the turf develops sufficiently, rabbits are allowed controlled access as they are seen as an important element in the management of downlands. The fences also give close control of the grazing animals, the most successful of which was a small flock of Shetland sheep. As soon as the turf on the restoration areas is considered to be robust enough, the dividing fences will be removed and the areas managed as an integral part of Hampshire Wildlife Trust's St Catherine's Hill reserve.

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Habitat Management

Nearly all herb-rich calcareous grassland requires management if it is not to be taken over by coarser vegetation, scrub, and eventually by woodland. The nature and speed of this process - and hence the intensity and frequency of management required to counter it - vary greatly with the depth and fertility of the soil, and with topography and local climate.

Of the downland created following the construction of the M3, only the steep embankments of the new motorway are unlikely to need frequent management if they are to develop a wildlife interest. All the other grasslands will require annual management. To begin with, the restoration areas are considered individually while they are in a very early stage of development and require special treatment. However, as soon as is practical, the management of the reconstructed downlands will become an integral part of the management regime of the St Catherine's Hill SSSI.

Grazing is the traditional form of management on most chalk grassland and is the preferred method for St Catherine's Hill. Grazed swards usually support a greater diversity and abundance of invertebrates than mown hay meadows, and a different, though not necessarily richer, flora.

Mowing, however, is sometimes the only practical way of managing small isolated sites, or those where livestock are unsuitable, and it is far better to mow grasslands than to abandon them. On chalk, an annual cut in late summer is usually adequate to maintain the flora in the short term, but it is important that the cuttings are removed. In the longer term, rotational mowing will produce a more diverse grassland, supporting a wider range of invertebrates. Mowing is also the most satisfactory way of managing new grassland created from seed, for the first year or two after it is sown, as grazing by heavy livestock can damage the seedbed.

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Monitoring

It has been a major criticism of most previous attempts at habitat translocation and restoration that there has been little or no follow up, to ascertain the "success" of the work. This means that little has been learnt about the processes involved or what can be done to improve methods for use in the future. However, at Twyford Down the Highways Agency is funding botanical and invertebrate monitoring for a period of ten years. The progress of all the reconstructed downland areas and the translocated flood meadows is being monitored both to assess the success of the work and to give feedback to "fine-tune" the management works.

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Habitat Management Restored A33 - Late '94 Restoration Methods Arethusa B - Winter '93 Arethusa A - October '92 Introduction Progress to Date Monitoring