Borth bog, a real hair raiser!

Borth Bog or Cors Fochno in Welsh is one if the most well preserved examples of a raised Bog in Wales!

A view over the central dome of the raised bog in the foreground

Geomorphological origins and coastal protection

Cors Fochno is a raised bog situated within the Dyfi estuarine floodplain complex. The Dyfi is a relatively short river but has a wide funnel floodplain type on an “estuarine” raised bog has developed, a highly threatened ecosystem in Western Europe. The estuary developed in a depression that remained when the Cardigan Bay ice sheet met the Dyfi valley ice sheet during the last age. The estuary was significantly reduced in size during the 1860’s by the construction of the Dyfi junction to Borth rail line embankment. Effectively the saltmarsh, once connected with the Cors Focnho is now isolated by the embankment and sediment accretion has meant the saltmarsh now undercuts the estuarine sands. This leaves the bog, at 5 meter above sea level in the centre, susceptible to extreme flooding events under current sea level rise scenarios. The bog would flood without sufficient time to adjust as it would under normal conditions due to saltmarsh migration, now interrupted by coastal squeeze, and integration with the ombrotrophic influenced bog communities.

The raised bog has lain down peat for 5000 years and has a peat depth of at least 5 meters and it suggested that the bog has changed in time from reed swamp to wet woodland and eventually a raised bog. This is due to findings of oak, pine and birch remains. This is evident as some stumps are visible today on the bog and beach.

The formation of a shingle ridge, the Ynyslas spit, approximately 4500 years ago was the trigger development of waterlogged conditions as the impediment to drainage would have created floating fen conditions and subsequent colonisation by Sphagnum and Cotton-grass species.

Management of the Bog

Peat cutting by local villagers was carried out in the 1700 – 1800’s to one spade depth but   the central 200ha of the bog was left untouched, but lightly grazed. Peat cutting around the fringes of the bog has steepened the gradient and together with extensive radial drainage for access to these cuttings has made run-off very efficient, allowing the bog to lose rainwater quicker leading to peat loss. Peat cutting also affects the hydrology of the bog by acting as drainage ditches themselves. The degraded peat around the bog edges are inhabited by Molinia caerulea (Purple moor grass) and Juncus effusus (Soft rush). Molinia is quite an aggressive graminoid species, tolerant of oxygenated soils and quickly takes over when the water table is too low. It is vitally important to conserve bogs on a global scale they are susceptible to a changing climate as their only water source is from precipitation and they are important storage facilities for carbon.  

A large open pool was the result of damming one of the

old drainage ditches. It is used by eels and stickleback but the water is too acidic for 

most fish species. Birds such as teal and water rail also visit the bog.

Scrub management

It is useful to leave scrub to provides a habitat resource for many species of bird and invertebrate as well as mammals such as the otter (Lutra lutra) who visits the bog to feed on Eels and wash their coat in the freshwater pool after feeding on the nearby coastal saltwater. That said, scrub control is carried out on site to control its' encroachment onto the good quality raised bog habitat. Four species of reptile also occur at the site including common lizard, grass snake, adder and slow worm.

A mammal run created by an otter as it enters the pool.

A management experiment at the fringes of the bog to see the 

effect of restoration on the degraded peat. Dragonfly such as Black and Common darter

breed in the bog pools and Sphagnum mosses are spreading out.

The Bog is currently grazed by Welsh Mountain ponies as well as some 

Highland cattle. They are good at controlling scrub.

Common darter dragonfly on one of the wooden gates at Borth Bog

The current management is focused on raising the water levels of the bog by blocking drainage ditches. The ditches are being blocked with peat dams taken from damaged peat from on-site, these however are unstable was exposed peat eventually oxidizes and is emitted as CO₂. As a result of ditch blocking the site now host 14 species of Spagnum moss which all have slightly different tolerances to hydrology and water chemistry within the bog microtopography. Some species like S. cuspidatum and S. pulcrum prefer being submerged in wet hollows whilst some like S. capillifolium prefer low hummocks just above the water level and some like S. fuscum creates tall hummocks raised above the water level.