Much British upland vegetation is considered impoverished owing to sheep-grazing. An attempt to recreate species rich-vegetation considered to have existed in the Pennine Hills of northern England before sheep introduction (a thousand or so years previously), commenced in 1955 in Moor House National Nature Reserve. About 30 species of plants (mostly upland species with restricted ranges) were introduced. Here, results of the first 15 years of trials at four grassland sites are summarised.
Exclosures were erected at four sites in the nature reserve to exclude sheep and other large grazers, two base-rich (Rough Sike and Knock Fell) and two acidic (Hard Hill and Little Dun Fell), extending upwards from about the natural tree-line. Sheep densities (sheep/ha for 7 summer months) were 7.0, 3.1, 1.8 and 3.4 respectfully. The exclosure at Rough Sike was 1,570 m² (no control). At the other sites they were 100 m², each with a 900 m² control area.
Plants (hitherto absent) were introduced via transplanting of turves (from around 10 x 5 cm to 30 x 20 cm in size) in 1955, 1956 and 1957, soon after exclosures had been fenced. The transplants were marked by pegs and examined each year.
By 1960, six transplanted species, dwarf cornel Cornus suecica (syn: Chamaepericlymenum suecicum), mossy cyphel Minuartia sedoides (syn: Cherleria sedoides), dwarf cudweed Gnaphalium supinum, Alpine clubmoss Lycopodium alpinum, glaucous meadow-grass Poa glauca and alpine saxifrage Saxifraga nivalis had died out.
The effect on the floristic richness of removing grazing was not always beneficial; vigorous growth by some grasses suppressed many of the herbaceous plants (e.g. Alpine lady’s mantle Alchemilla alpina. At one site however (Rough Sike) by 1970, introduced dwarf-shrubs (i.e. mountain willow Salix arbuscula and net-leavedwillow S.reticulata) were increasing; also a few heather Calluna vulgaris plants (previously present but scarcely detectable prior to exclosure) flourished. Several naturally but infrequently occurring herbs also did well and spread within the exclosures, including twisted whitlow-grass Draba incana, , viviparous bistort Polygonum viviparum, alpine cinquefoil Potentilla crantzii and alpine meadow-rue Thalictrum alpinum.
Several of the introduced species became well established, including Alchemilla alpina, S. arbuscula, S. reticulata, and alpine saw-wort Saussurea alpina.
The authors suggest that where a whole area was previously grazed, increasing the number of ungrazed sites (e.g. through the provision of exclosures) will enhance overall floristic diversity.
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