South Somerset SSSIs a study of successive MG5 grassland (ENRR266)

Details studies of fields of known ages and past treatment within a narrow compass of countryside in Somerset, near the border with Dorset. The ancient grasslands studied were previously identified as among the richest MG5 communities known, supporting up to 47 species in a square metre. This diversity was in part attained through a mixture of species characteristic of all MG5 subcommunities growing together. Analysis revealed predictable effects of past ploughing and disturbances such as reseeding with ryegrass and cropping. Sowing with hay-seed however has produced a very rich grassland within only a few decades. Younger grasslands can be very rich in species, including those regarded as indicators of unimproved grassland. However, the full mixture of subcommunity preferentials, most notably the full range of MG5s species present, continues to develop for well over a century. The mixture of calcareous and acidophilous species found in these grasslands may be the result of natural soil processes causing micro-spatial variation in the mottled and partly gleyed heavy soils where they are found. These studies suggest that the time taken for species-rich mesotrophic grassland communities to develop is a similar order of magnitude to that reported for species-rich calcareous grasslands, i.e. well over a century. These findings must be treated with caution because they are effectively based on a single site in unusually favourable circumstances for the late 20th century.

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