Askham Bog is small area of peat bog and Site of Special Scientific Interest situated within the Vale of York in North Yorkshire, England. It lies to the south-west of York, north of Copmanthorpe and near Askham Richard and Askham Bryan. It is regarded as one of the most ecologically diverse sites in Northern England.
During the 2010s, a development of 500 houses was proposed for the edge of the bog on the outskirts of York city, but this was overturned in 2020.
History and geographical formation
Askham Bog formed in the Vale of York in a hollow which was flooded by meltwater from the last glacial retreat about 15,000 years ago.
The bog's lowest layer is made up of sealed boulder clay, sand, and gravel. Above this is a distinct layer of organic deposits, which collectively reflect a series of biological and geological periods. The basal clay layer is covered by additional lake clay and nutrient-rich nekron mud, which is supplied by the surrounding moraines. Further up, there are layers of fen peat and sphagnum peat. The latter contains traces of Scorpidium and Eriophorum. The Nekron peat layer reflects a permanent shift to a relatively warm post-glacial climate. Formed during this time, this layer contains an abundance of plant remains, indicating a period of rich floral growth. Some of these plants include Potamogeton, holly-leaved naiad and bogbean.
A site on the edge of Askham Bog was earmarked by a developer for a plot of 500 homes. The appeal by the community and Yorkshire Wildlife Trust enlisted the help of Sir David Attenborough, who said that "it is our collective responsibility to save it." The development was denied by planning inspectors in May 2020.
Ecology and habitats
thumb|Habitat in Askham Bog
Askham Bog is regarded as one of the most ecologically diverse sites in Northern England; especially regarding plants, invertebrates and birds.
Askham Bog is a heavily wooded area, with birch being widespread throughout. Willow also grows extensively throughout. Alder and grey sallow are locally dominant on the fen margins, while oak is dominant in the acid centre. Other tree species growing alongside oak in the acid centre include hazel, alder buckthorn and rowan. Birch has declined in favour of oak, alder and ash, especially where much of the wood in the north central part has been clear-felled. and is renowned for the presence of royal fern.
The vegetation of Askham Bog can be divided into two main groups, reflecting the broad underlying dichotomy between basic and acidic soil. One is a species-rich fen community around the margins. This includes characteristic species such as meadowsweet, common meadow rue, stinging nettle, marsh bedstraw, dewberry, bittersweet, skullcap, yellow loosestrife, creeping Jenny and rough meadow grass. The other community is a species-poor acid one towards the centre, including species such as Sphagnum palustre, purple moor grass, Rubus fruticosus and honeysuckle. This appears to be inconsistent with the usual course of succession and may be explained by unusually high concentration of inorganic phosphate. Winter visitors include fieldfare, redwing, brambling, siskin, lesser redpoll, goldfinch, snipe, jack snipe, woodcock, coot and sometimes grasshopper warbler.
Given the relatively dry status of the reserve and gradual encroachment by trees, there is a large proportion of wetland indicator spider species. This may be because the current spider community reflects historic moisture levels within the bog and has not yet fully responded to habitat changes.
In the Middle Ages, peat was cut by the villagers of Dringhouses and Acomb, as evidenced by the written bylaws of the Manor of Drighouses and Acomb Court Rolls, which restricted peat cutting by tenants. The severe penalties imposed by these legal restrictions reflect the attempt by the local authorities back then to counteract the damaging intensity of peat extraction at Askham Bog.
Hemp cultivation
Distinct forms of fossil evidence found between layers of fen peat and Scorpidium-Sphagnum peat at Askham Bog suggest that hemp was once cultivated there. The evidence takes the form of preserved hemp achenes and pollen, which may be relics of retting (steeping in water) Pollen of aquatic plants such water lilies and cattails have also been found in the same peat cores as hemp seeds and pollen. It is therefore suggested that these hemp residues were submerged during this period. This is considered a more effective management tool than cutting, though some meadows on the site are still cut for hay..