What is ‘special’ about Cors Bodeilio SSSI?


Cors Bodeilio has 4 special features.


  • Lime-rich fen, characterised by tall sedges such as great fen sedge and bottle brush sedge.
  • Lime-rich fen fed by springs and flushes with characteristic plants such as black bog rush, sweet gale and small flowered rush.
  • Uncommon plants including fen pondweed, many species of stonewort including the rare dwarf stonewort, the olive earthtongue (a fungus) and a good range of orchids including the narrow-leaved marsh orchid and fly orchid.
  • Populations of uncommon invertebrates including two rare fly species, the medicinal leech and the variable damselfly. 


As well as the features listed above, Cors Bodeilio has other habitat features that contribute to the special interest. These include hedges and areas of scrub along with grassland, pools and ditches and a derelict barn. This mixture of habitats is important for much of the wildlife including grassland fungi, lapwing, barn owl, hen harrier and marsh harrier and these too are key components of the special interest of the site.  Unless specified below, management of this site should aim to look after these habitats as well as the listed features of interest.


What do we want Cors Bodeilio to look like?


The site will continue to have at least 47 ha of tall sedge and spring flushed fen (largely without scrub or tree cover), characterised in part by great fen sedge and elsewhere by mixtures of black bog-rush and blunt-flowered rush, or swamps of bottle sedge and brown mosses. Small patches of open water within the fen will be encouraged for the benefit of medicinal leeches and stoneworts. Patches of willow and birch scrub will be tolerated but should not exceed 10% of the fen area. The fields at Ynys in the centre of the site should develop an increasing proportion of semi-natural grassland species such as crested dogs-tail and knapweed. The stream running through the centre of the site should retain its native plant communities and present channel and flow character. It should be unpolluted. The site should support a rich variety of invertebrates including variable damselflies and medicinal leech. Lapwing, snipe, curlew, barn owl and skylark should nest here with short-eared owl, hen and marsh harrier overwintering and the latter possibly breeding.


What management is needed on Cors Bodeilio SSSI and why?


Although Cors Bodeilio is an excellent place for wildlife it will only remain so if the necessary management continues. CCW’s aim is to work with you to ensure that this management is carried out.


What does this mean in practice?


There are many factors that could damage the special features at Cors Bodeilio if they are not properly managed. These are the ones we regard as most important:


Water level

A high water table level is essential for the survival of wetland plants and animals. It is therefore important that no work is carried out which would lower or change in any other way water levels on the site – for example by widening or deepening ditches. However, some wetland plants and animals require very shallow surface water or moving groundwater, so deep or prolonged flooding can destroy these. Raising water levels should not be undertaken without careful assessment. Equally important is the need to maintain the water supply to the site through springs, groundwater seepage, ditches and surface run off. Any actions that would reduce the amount of water entering Cors Bodeilio would be damaging to the site.


Water quality

Good water quality (particularly the concentration of calcium and magnesium and low levels of nitrogen and phosphorus) is essential for maintenance of the characteristic assemblage of wetland plants and animals at Cors Bodeilio. Measures to enhance soil fertility within the catchment of the site are likely to prove harmful to the special interest features of Cors Bodeilio Nutrients such as nitrogen and phosphorous encourage the spread of strong growing plants such as floating sweet-grass and common reed which can out-compete the less common (and more desirable) species of Cors Bodeilio. This in turn would have a negative effect upon the animals which depend on these plants. Herbicides and pesticides could also damage the site’s wildlife, particularly in the aquatic environment. 


Water movement

Gradual movement of water from springs through the site is essential for the survival of the spring-water flushed wetland. In order to maintain this important passage of water through the site, great care in the management of water supply and levels is needed.



Light grazing removes excess plant material and can be beneficial over much of the site. The most appropriate grazers are cattle or ponies as they can maintain open areas by limiting scrub development and by light poaching of the ground. Animal dung provides an important food resource for some invertebrates and the animals provide occasional blood meals to leeches without serious harm. There should be no supplementary feeding with silage as this raises nutrient levels.


Scrub control

Scrub provides nesting places for birds and shelter for other animals. However too much scrub can alter the special qualities of the wetland site, smothering the valuable flora and increasing evaporation of water. Grazing alone may not be enough to prevent scrub expansion and it may sometimes be necessary to carry out control manually.



Fire was used in the past to clear the land and promote new growth. However uncontrolled fires can damage some plant and animal communities, particularly mosses and invertebrates. Small, controlled fires in winter may be used to rejuvenate patches of fen by removing accumulated plant litter and enabling grazing. Firebreaks may be needed to enable control and to prevent the spread of wildfires.


Invasive aquatic plants

A number of invasive non-native aquatic plants such as water fern are now present on Anglesey. Should any of them be detected within the SSSI steps should be taken immediately to eradicate them.




Our knowledge of wildlife is continually improving.  It is possible that new features of value may appear and new management issues may arise in the future, whilst other issues may disappear.  This statement is written with the best information we have now, but may have to change in the future as our understanding improves. Any information you can provide on the wildlife of your site, its management and its conservation would be much appreciated.


If you would like to discuss any aspect of your SSSI, or have any concerns about your SSSI, please contact your local CCW office.


Your local office is;

Cyngor Cefn Gwlad Cymru/Countryside Council for Wales

North Region

Llys y Bont,

Ffordd y Parc,

Parc Menai,


Gwynedd, LL57 4BN,


Telephone:    01248 672500

Fax:   01248 679259