Skip to main content

Culm Grassland

There are a variety of different grassland types within the Northern Devon NIA project area, from improved rye-grass pastures to species-rich hay meadows, but perhaps the most characteristic and important in ecological terms is what is known as Culm grassland.

Culm grassland is the name given to damp unimproved grasslands that have developed above a geological formation known as the Culm Measures laid down in the Carboniferous period (about 300 million years ago) in north-west Devon and north-east Cornwall. The name comes from the occasional presence of a soft, sooty coal, known in Devon as culm. The majority of the formation consists of shales and thin sandstones although there are also areas of slate, limestone and chert.

The geology of the Culm Measures has given rise to acidic, clay soils that are poorly drained. In addition, the relatively high rainfall experienced in south-west England makes the soil very damp, circumstances that persist even through the driest of summers. The only similar areas elsewhere in the UK are in south Wales, where the term Rhôs pasture is used — Welsh for wet pasture — and in south-west Scotland.

Some 92% of Culm grassland has been lost in the past 100 years, with 48% disappearing between 1984 and 1991 alone. The chief causes have been agricultural improvement of land by drainage, ploughing, reseeding and fertiliser application; afforestation; abandonment and neglect; management inappropriate for conservation purposes (e.g. over-grazing); and habitat fragmentation. Several attempts have been implemented to halt the decline including those by DWT (Culm Natural Networks and more recently the Working Wetlands and Northern Devon NIA projects), Butterfly Conservation (Reconnecting The Culm), and Natural England (through the Higher Level Stewardship Scheme).The Northern Devon NIA contains approximately 35% of the remaining Culm grassland resource in the UK.

 

Key habitats and species

Culm grassland comprises a variety of different plant communities, including purple moor-grass dominated mires, rush-pastures, wet heaths and tall herb-fens. These habitats are noted for their biodiversity, and the unimproved nature of the land allows several rare species to thrive: heath-spotted, lesser butterfly and southern marsh orchids may all be found, in addition to several other plants of conservation interest such as whorled caraway, wavy St John’s-wort and marsh cinquefoil.

 

 

 

 

 

 

 

 

 

 

 

Wetter areas support sharp-flowered rush, ragged robin, marsh bedstraw, meadowsweet and wild angelica, while the drier areas hold such species as meadow thistle, tormentil, devil’s-bit scabious, saw-wort and heathers (ling and cross-leaved heath). Where the soil is waterlogged, bog vegetation comprising Sphagnum mosses, bog pondweed and sedges may develop.

The diverse flora supports several scarce butterflies including marsh fritillary (one of the most threatened butterfly species in Europe), small pearl-bordered fritillary, wood white, marbled white, dingy skipper and small heath. Other insects found on the Culm include the nationally scarce narrow-bordered bee hawkmoth, double line moth and keeled skimmer dragonfly.

There is a wide range of bird species including barn owl, curlew, snipe, woodcock, willow tit, reed bunting and grasshopper warbler, and reptiles and amphibians are well represented with common frog, toad, viviparous lizard, adder and grass snake all found across the region. Mammals that occur include dormouse, harvest mouse, fox, roe and red deer, otter and several species of bat.  

 

Socio-economic value of the Culm

Devon Wildlife Trust, the University of Exeter and the Environment Agency have now published the results of a two year study to understand the hydrological characteristics and potential role of semi-natural Culm grassland in future strategies to protect against flooding, provide safe and secure water supplies, and lock up carbon in the landscape.

The work was primarily funded by the Open Innovation Fund, Exeter University, Environment Agency and DWT.  The Northern Devon NIA also provided funding which allowed investigations to include wet woodland and scrub habitats.

Further details of this research and the published results can be found at http://www.devonwildlifetrust.org/socio-economic-value-of-the-culm/