Thursday, 23 March 2017

Blysmus intervention

Blysmus compressus grows in only one place in Oxfordshire (V.C. 23), in Old Marston within the complex of meadows and floodplain grassland along the River Cherwell designated as the Almonds Farm and Burnt Mill Meadows Local Wildlife Site. The population of Blysmus is quite healthy, extending over about 30m of the bank and with  thousands of inflorescences produced last summer. However, its future has been uncertain for several years with the cessation of grazing following the lapse of the previous tenancy and there has been no management for the last six years.

Not any more! This last weekend volunteers mowed the bank on which Blysmus grows in order to set back the coarse sedges and grasses beginning to overwhelm the smaller plants requiring shorter, finer vegetation, Blysmus included. Without this cutting Blysmus will eventually disappear under a thatch of coarse grasses and sedges, joining the list of Oxfordshire's extinct plants. Repeated again toward the end of summer and again in future seasons this management should result in a diverse sward of herbs and short sedges, just as it ought to look!

Many thanks to the volunteers who helped with this conservation intervention, to the owners Oxford City Council for their permission and assistance, and to the tenant farmer for his permission and sympathy for the cause of this threatened plant. Judy Webb who helped to organise the day has put some excellent photos and videos of scything in action on her website — except for the clothes and the kind of scythes used, the scene could be medieval.

Vegetation supporting Blysmus at Marston, dominated by grasses and with abundant Equisetum arvense and Potentilla anserina. According to results of the Threatened Plants Project the latter is a common associate of Blysmus compressus.

The flattened inflorescence from which Blysmus compressus derives its name. J.A. Webb
A rhizomatous species of alkaline or brackish springs and seepages, Blysmus compressus has been lost from many sites across lowland England, Oxon included, due to drainage, agricultural improvement and cessation of grazing. It is assessed as Vulnerable in England and is a species of principle importance (former BAP). At Marston it grows on the bank of the terrace above the river where there is lateral seepage of groundwater from the terrace deposits. The fenny vegetation also supports Succisa pratensis and Valeriana dioica, both threatened species, and around a spring the uncommon liverwort Riccia subbifurca.

The coarse, un-managed vegetation of the bank dominated by lesser pond sedge (Carex acutiformis) and tussocky grasses (above left); the author's weapon against vegetation succession, an Austrian style scythe (left); volunteers hard at work cutting and raking the bank (middle); and the finished job, neatly mown for the coming season (right).

As the meadow looked in summer 2010 when it was grazed by horses (below left), with Valeriana dioica in flower, and the bank in flower summer 2014 (below right). J.A. Webb

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