Askham Bog is small area of

peat bog A bog or bogland is a wetland that accumulates peat as a deposit of dead plant materials often mosses, typically sphagnum moss. It is one of the four main types of wetlands. Other names for bogs include mire, mosses, quagmire, and muske ...

and

Site of Special Scientific Interest A Site of Special Scientific Interest (SSSI) in Great Britain, or an Area of Special Scientific Interest (ASSI) in the Isle of Man and Northern Ireland, is a conservation designation denoting a protected area in the United Kingdom and Isle ...

situated within the

Vale of York The Vale of York is an area of flat land in the northeast of England. The vale is a major agricultural area and serves as the main north–south transport corridor for Northern England. The Vale of York is a broad area of flat land in northe ...

North Yorkshire North Yorkshire is a Ceremonial counties of England, ceremonial county in Northern England.The Unitary authorities of England, unitary authority areas of City of York, York and North Yorkshire (district), North Yorkshire are in Yorkshire and t ...

, England. It lies to the south-west of

York York is a cathedral city in North Yorkshire, England, with Roman Britain, Roman origins, sited at the confluence of the rivers River Ouse, Yorkshire, Ouse and River Foss, Foss. It has many historic buildings and other structures, such as a Yor ...

, north of

Copmanthorpe Copmanthorpe () is a village and civil parishes in England, civil parish in the City of York in the English county of North Yorkshire, south-west of York, west of Bishopthorpe and close to Acaster Malbis, Askham Bryan and Askham Richard. Accord ...

and near

Askham Richard Askham Richard is a village and civil parish in the unitary authority of City of York in the north of England, south-west of York, close to Copmanthorpe, Bilbrough and Askham Bryan. The population of the civil parish at the 2011 census was 351 ...

and

Askham Bryan Askham Bryan is a village and civil parishes in England, civil parish in the Unitary authorities of England, unitary authority area of City of York in the north of England, south-west of York, west of Bishopthorpe, and close to Askham Richard a ...

. 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. Two ridges of terminal

moraine A moraine is any accumulation of unconsolidated debris (regolith and Rock (geology), rock), sometimes referred to as glacial till, that occurs in both currently and formerly glaciated regions, and that has been previously carried along by a gla ...

had formed on either side of the hollow, trapping the glacial meltwater between and behind them.Fitter A. H., Smith C. J. 1979. ''A Wood in Ascam, a Study in Wetland Conservation''. Ebor Press, York. The bog has a lowermost layer of

boulder clay Boulder clay is an unsorted agglomeration of clastic sediment that is unstratified and structureless and contains gravel of various sizes, shapes, and compositions distributed at random in a fine-grained matrix. The fine-grained matrix consists o ...

, 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 A fen is a type of peat-accumulating wetland fed by mineral-rich ground or surface water. It is one of the main types of wetland along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires ...

peat Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...

and

sphagnum ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store water, since ...

peat, of which the latter also contains traces of ''

Scorpidium ''Scorpidium'' is a genus of mosses belonging to the family Amblystegiaceae. The genus has an almost cosmopolitan distribution In biogeography, a cosmopolitan distribution is the range of a taxon that extends across most or all of the surf ...

'' and ''

Eriophorum ''Eriophorum'' (cottongrass, cotton-grass or cottonsedge) is a genus of flowering plants in the family Cyperaceae, the sedge family. They are found in the cool temperate, alpine, and Arctic regions of the Northern Hemisphere, primarily in the mi ...

''. 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 ''Potamogeton'' is a genus of aquatic, mostly freshwater, plants of the family Potamogetonaceae. Most are known by the common name pondweed, although many unrelated plants may be called pondweed, such as Canadian pondweed (''Elodea canadensis' ...

'',

holly-leaved naiad ''Najas marina'' is a species of aquatic plant known by the common names spiny water nymph, spiny naiad and holly-leaved naiad. It is an extremely widespread species, reported across Europe, Asia, Africa, Australia, the Americas and many oceanic ...

and

bogbean ''Menyanthes'' is a monotypic genus of flowering plants in the family Menyanthaceae containing the single species ''Menyanthes trifoliata''. The North American form is often referred to as ''M. trifoliata'' var. ''minor'' Michx. It is known ...

. When

common reed ''Phragmites australis'', known as the common reed, is a species of flowering plant in the grass family Poaceae. It is a wetland grass that can grow up to tall and has a cosmopolitan distribution worldwide. Description ''Phragmites australis' ...

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. Consequently, a layer of fen peat gradually built up above the bog mud in the centre of the bog, forming a

raised bog Raised bogs, also called ombrotrophic bogs, are acidic, wet habitats that are poor in mineral salts and are home to flora and fauna that can cope with such extreme conditions. Raised bogs, unlike fens, are exclusively fed by precipitation (ombro ...

. The increased elevation in the centre cut the bog off from the direct influx of base-rich water from the surrounding land. Rainfall 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 Acidophiles or acidophilic organisms are those that thrive under highly acidic conditions (usually at pH 5.0 or below). These organisms can be found in different branches of the tree of life, including Archaea, Bacteria,Becker, A.Types of Bacteri ...

sphagnum mosses ''Sphagnum'' is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss (although that term is also sometimes used for peat). Accumulations of ''Sphagnum'' can store water, since ...

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 Ombrotrophic ("cloud-fed"), from Ancient Greek ὄμβρος (''ómvros'') meaning "rain" and τροφή (''trofí'') meaning "food"), refers to Soil, soils or vegetation which receive all of their water and nutrients from precipitation, rather ...

. 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 East Anglia is an area of the East of England, often defined as including the counties of Norfolk, Suffolk and Cambridgeshire, with parts of Essex sometimes also included. The name derives from the Anglo-Saxon kingdom of the East Angles, ...

n fens.Smith C. J. 1962. The Linyphiid spiders of Askham Bog. The Naturalist: 121–124. 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 Sir David Frederick Attenborough (; born 8 May 1926) is an English broadcaster, biologist, natural historian and writer. He is best known for writing and presenting, in conjunction with the BBC Studios Natural History Unit, the nine nature d ...

, who said that "it is our collective responsibility to save it." The development was denied by planning inspectors in May 2020.

Ecology and habitats

Askham Bog is regarded as one of the most ecologically diverse sites in Northern England; especially regarding plants, invertebrates and birds. The ecological diversity is due to a wide range of habitats ranging from

fen-meadow A fen-meadow is a type of peatland, common in North America and Europe, that receives water from precipitation and groundwater. Habitat The continuous flow of mineral-rich and nutrient-poor acidic groundwater through fen-meadow topsoil foster ...

with base-rich soils on the periphery to carr woodland and raised bog with acid soil in the centre, interspersed with dykes and stands of open water. The large habitat diversity may be partly explained by the many successional stages present which generally become more advanced towards the centre, in turn related to spatial differences in

topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the landforms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...

and

soil pH Soil pH is a measure of the acidity or basicity (alkalinity) of a soil. Soil pH is a key characteristic that can be used to make informative analysis both qualitative and quantitatively regarding soil characteristics. pH is defined as the neg ...

. Askham Bog is one of the few northern examples in England to show such an array of habitat transitions. Although the raised bog originally largely replaced the original fen, medieval peat cutting brought the vegetation back under the influence of base-rich groundwater. This extensive peat cutting, in turn, led to a return to fen conditions around some of the previously acid soils.LP Authority. 1984. Askham Bog Status – Natural England’s SSSI information. https://designatedsites.naturalengland.org.uk/PDFsForWeb/Citation/1000196.pdf Askham Bog is a heavily wooded area, with

birch A birch is a thin-leaved deciduous hardwood tree of the genus ''Betula'' (), in the family Betulaceae, which also includes alders, hazels, and hornbeams. It is closely related to the beech- oak family Fagaceae. The genus ''Betula'' contains 3 ...

being widespread throughout.

Willow Willows, also called sallows and osiers, of the genus ''Salix'', comprise around 350 species (plus numerous hybrids) of typically deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions. Most species are known ...

also grows extensively throughout.Fitter A. H., Browne J., Dixon T., Tucker J. J. 1980. Ecological studies at Askham Bog Nature Reserve 1. Interrelations of vegetation and environment. ''Naturalist''.

Alder Alders are trees of the genus ''Alnus'' in the birch family Betulaceae. The genus includes about 35 species of monoecious trees and shrubs, a few reaching a large size, distributed throughout the north temperate zone with a few species ex ...

and grey sallow are locally dominant on the fen margins, while

oak An oak is a hardwood tree or shrub in the genus ''Quercus'' of the beech family. They have spirally arranged leaves, often with lobed edges, and a nut called an acorn, borne within a cup. The genus is widely distributed in the Northern Hemisp ...

is dominant in the acid centre. Other tree species growing alongside oak in the acid centre include

hazel Hazels are plants of the genus ''Corylus'' of deciduous trees and large shrubs native to the temperate Northern Hemisphere. The genus is usually placed in the birch family, Betulaceae,Germplasmgobills Information Network''Corylus''Rushforth, K ...

alder buckthorn ''Frangula alnus'', commonly known as alder buckthorn, glossy buckthorn, or breaking buckthorn, is a tall deciduous shrub in the family Rhamnaceae. Unlike other "buckthorns", alder buckthorn does not have thorns. It is native to Europe, northern ...

and

rowan The rowans ( or ) or mountain-ashes are shrubs or trees in the genus ''Sorbus'' of the rose family, Rosaceae. They are native throughout the cool temperate regions of the Northern Hemisphere, with the highest species diversity in the Himalaya ...

. Birch has declined in favour of oak, alder and ash,Pogg P., Squires P., Fitter A. H. 1995. Acidification, nitrogen deposition and rapid vegetational change in a small valley mire in Yorkshire. Biological Conservation 71: 143–153. especially where much of the wood in the north central part has been clear-felled. The reduction in canopy cover in the centre of the bog appears to have had a negative effect on peat growth here, probably through reduced shading and hence increased desiccation of the peat and easier influx of atmospheric

pollutants A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...

. In recent decades, sulphur deposition on the bog has increased due to polluted air moving downwind from a large industrial area with coal-fired power stations.

Natural history

Herbaceous plants

The diverse flora of Askham Bog is similar to plant communities in southern England. Notable species include greater spearwort, marsh stitchwort, saw sedge,

marsh fern ''Thelypteris palustris'', the marsh fern, or eastern marsh fern, is a species of fern native to eastern North America and across Eurasia. It prefers to grow in swamps, bogs, wet fields or thickets, fresh tidal and nontidal marshes, or wooded str ...

great water dock ''Rumex hydrolapathum'', the great water dock, water dock, or giant water dock, is a species of perennial herbaceous plants in the genus ''Rumex'' native to fens and freshwater banks of Europe and Western Asia. It is the tallest species in the g ...

meadow thistle Meadow thistle is a common name for several thistles and may refer to: *''Cirsium dissectum'', native to Europe *''Cirsium scariosum'', native to North America {{Short pages monitor