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Individual study: Revegetation of a gravel extraction site through transfer of semi-natural grassland and marshland vegetation and soil, Heathrow, Greater London, England

Published source details

Worthington T.R. & Helliwell D.R. (1987) Transference of semi-natural grassland and marshland onto newly created landfill. Biological Conservation, 41, 301-311

Summary

In the UK, mitigation measures may be undertaken in an attempt to compensate for habitat of nature conservation value to be lost to ‘development’. This study describes revegetation of a gravel extraction site (near Heathrow Airport, southern England) through transfer of nearby semi-natural vegetation and soil.

The donor site to be excavated for gravel (4.6 ha) comprised mainly hawthorn Crataegus scrub, grassland and marsh. Vascular plants present were generally common species. Marsh arrowgrass Triglochin palustris, a locally scarce plant, was also present. In September 1980, the gravel company transferred the most floristically diverse areas to the restoration site, a gravel extraction pit (approx. 40 ×110 m; part filled with clay and other materials) 400 m away.

The vegetation/soil was orderly removed in three separate layers; a 6 m grid was marked out (chosen as in reach of the boom on the hydraulic excavator used), the depth of soil layers at the centre of each square established (by hand auger boring) and replaced sequentially on the restoration site.This was done separately for soil/plant material of ‘dry grassland’ (350 m2 moved)’, ‘moist grassland’ (2,500 m2) and ‘marsh’ (1,500 m2). To avoid compaction, machinery was not driven over either site. After transfer, the restoration site had about 30% green vegetation cover and appeared as a ‘badly cultivated grass field’.

Vegetation monitoring: The donor site was surveyed on 1-2 October 1980 prior to transfer in quadrats (1 m²) placed at random in the dry grassland (8), moist grassland (15), and wet area (12); 85 vascular plant species recorded. The receptor site (after soil/vegetation transfer) was likewise surveyed over the following six years.

Vegetation growth was rapid (almost 100% cover by the end of May 1981). Thus, in late summer 1981 the site was cattle grazed for 7-10 days, also rolled in autumn to smooth the substrate and seeding docks Rumex spp. hand-pulled and removed. In 1982, the vegetation was cut (cuttings removed) in autumn. In 1983, cattle were grazed in May and late summer; thistles and rushes were 'topped' with a mower in autumn.

The number of plant species on the restoration area in October 1986 was 89, i.e. after six years floristic diversity had been maintained. Some species increased after transfer (including T.palustris), some decreased (mostly on dry areas), but the appearance of the vegetation was very similar to that of the original site.

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