Editing Askham Bog (section)

==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.<ref name="ywtreserves"/> Two ridges of terminal [[moraine]] had formed on either side of the hollow, trapping the glacial meltwater between and behind them.<ref name = "FitterSmith">Fitter A.&nbsp;H., Smith C.&nbsp;J. 1979. ''A Wood in Ascam, a Study in Wetland Conservation''. Ebor Press, York.</ref>

The bog has a lowermost layer of [[boulder clay]], sand, and gravel, which is sealed. Above this lies a distinct stratum of organic deposits, which collectively reflect a series of biological and geological periods. The basal clay layer is overlain by more lake clay and nutrient-rich [[nekron mud]] supplied by surrounding moraines. Higher up there are layers of [[fen]] [[peat]] and [[sphagnum]] peat, of which the latter also contains traces of ''[[Scorpidium]]'' and ''[[Eriophorum]]''. The Nekron peat layer reflects a permanent change to a relatively warm post-glacial climate. This layer formed during that time and contains an abundance of plant remains, indicating a period of rich floral growth. Some of these plants include ''[[Potamogeton]]'', [[Najas marina|holly-leaved naiad]] and [[Menyanthes|bogbean]].<ref name = "FitterSmith"/>

When [[Phragmites australis|common reed]] colonised the bog, as evidenced by the presence of fossilised root fragments immediately above the Nekron bog layer, this led to a reduction in the extent of open water.<ref name = "FitterSmith"/> Consequently, a layer of fen peat gradually built up above the bog mud in the centre of the bog, forming a [[raised bog]]. The increased elevation in the centre cut the bog off from the direct influx of base-rich water from the surrounding land. Rainfall [[leaching (pedology)|leached]] out existing bases in the raised peat, leading to a net loss of bases from the peat in the centre of the bog. This gradual loss of bases increased the soil's acidity and caused the loss of the original rich bog community that previously covered the whole area.

The nutrient-poor, acidic environment created by the bog's gradual isolation from minerotrophic water sources allowed [[acidophilic]] [[sphagnum mosses]] to thrive on the raised bog and contribute significantly to the bulk of the peat formed above the fen margins. The continued net accumulation of peat led to a further increase in the elevation of the central peat dome, eventually completely cutting off the supply of base-rich groundwater and rendering the peat centre [[ombrotrophic]].<ref name = "FitterSmith"/> Conversely, the rich fen community at the margins, which receives an influx of base-rich groundwater from the surrounding moraines, creates ecological conditions like those of the [[East Anglia]]n fens.<ref name="Smith">Smith C.&nbsp;J. 1962. The Linyphiid spiders of Askham Bog. The Naturalist: 121–124.</ref>

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.<ref>{{cite news |title=Inspectors reject Attenborough-opposed homes plan |url=https://www.bbc.co.uk/news/uk-england-york-north-yorkshire-52649291 |accessdate=14 May 2020 |work=BBC News |date=13 May 2020}}</ref>