Askham Bog

Askham Bog
Site of Special Scientific Interest
Location	North Yorkshire
Grid reference	SE 575 481
Area	110.7 acres (44.8 ha)
Notification	1961
Location map	Natural England

Last updated February 21, 2024

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.

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.^[1] Two ridges of terminal moraine had formed on either side of the hollow, trapping the glacial meltwater between and behind them.^[2]

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 , holly-leaved naiad and bogbean.^[2]

When 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.^[2] 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 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.^[2] 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 Anglian fens.^[3]

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.^[4]

Ecology and habitats

Askham Bog is regarded as one of the most ecologically diverse sites in Northern England;^[5] especially regarding plants, invertebrates and birds.^[2] The ecological diversity is due to a wide range of habitats ranging from fen-meadow 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 and soil pH. Askham Bog is one of the few northern examples in England to show such an array of habitat transitions.^[2]

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.^[6]

Askham Bog is a heavily wooded area, with birch being widespread throughout. Willow also grows extensively throughout.^[7] 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,^[8] especially where much of the wood in the north central part has been clear-felled.^[2] 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.^[8] 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.^[8]

Natural history

Herbaceous plants

The diverse flora of Askham Bog is similar to plant communities in southern England.^[2] Notable species include greater spearwort, marsh stitchwort, saw sedge, marsh fern, great water dock, meadow thistle, purple small reed, Carex appropinquata and water violet. Askham Bog also holds the largest and most north-eastern colony in England of the rare gingerbread sedge Carex elongata ,^[9] 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.^[7] Although the drop in pH and elevational increase on the peat domes is attributable to sphagnum growth,^[7] no sphagnum has been found in one vegetation assemblage characterized by honeysuckle and Rubus fruticosus within the acid centre of the bog.^[10] This appears to be inconsistent with the usual course of succession and may be explained by unusually high concentration of inorganic phosphate.^[10] Low water tables in the raised area may promote mineralization of phosphate, with low pH counteracting microbial conversion to organic phosphate, so that the resultant high inorganic phosphate component in the raised peat favours growth of this plant community.^[10]

Birds

Over 90 bird species have been recorded at Askham Bog, attracting both winter and summer visitors. Despite the proximity of potential sources of human disturbance, the bog provides suitable refuge for wildlife within a relatively unfavourable agricultural landscape and offers a rich supply of fruit and seed supply in winter and invertebrates in summer.^[2] Known resident species include marsh tit, willow tit, treecreeper, kingfisher, goldcrest, bullfinch, tawny owl, buzzard, sparrowhawk and sometimes green woodpecker ^[11] Winter visitors include fieldfare, redwing, brambling, siskin, lesser redpoll, goldfinch, snipe, jack snipe, woodcock, coot and sometimes grasshopper warbler.^[11] All migrant warblers have been found at the bog in spring and summer,^[11] with the reed beds in the northeast part in Near Wood comprising an important colony for reed warblers.^[2]

Invertebrates

Askham Bog is nationally recognised for its diverse invertebrate fauna, including a variety of water beetles such as Haliplidae, Noteridae, Dytiscidae and Gyrinidae. The bog is also home to some rare beetle species including Dromius sigma, Agabus undulatus; alongside one record of Pselaphus dresdensis which has been found in moss from pond margins at the bog, the only known location in England.^[2] Beetle abundance and species richness have been decreasing at Askham Bog since the early 20th century.^[2] This coincides with the establishment of a municipal landfill site at the adjacent Challoner's Whin.^[1] Other characteristic insect species include the fen square-spot moth ^[6] and the emperor dragonfly.^[1]

There is a large proportion of wetland indicator spider species given the relatively dry status of the reserve and gradual encroachment by trees. This may be because the present spider community reflects historic moisture levels within the bog and is yet to completely respond to the habitat changes.^[12] A very rare spider species Cornicularia kochi (O.P.-C) in its hundreds was once recorded in piles of cut-down Phragmites during winter.^[3]

Mammals and amphibians

Typical amphibians of Askham Bog include common frog, common toad, and smooth newt. Typical mammals include roe deer and red foxes. The water vole was once common at Askham Bog, but has now been largely displaced by invasive American mink.^[11]

Past use and current management

Peat cutting

From the early Roman period until the mid-18th century, Askham Bog and its environsy appeared to have been intensely exploited for peat as fuel.^[2] The earliest evidence of nearby peat cutting from the Roman period was discovered in a Roman well in York in the form of lumps of sphagnum peat.^[13]

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.^[2] Intensive peat cutting had probably caused substantial topographical changes on the bog since its original geographic formation. In turn, a lowering of the acid peat layer through extraction would have allowed base-rich groundwater to inundate the centre, transforming it into an open fen.^[2] Further physical evidence exists in the form of dykes surrounding the current main peat domes. These dykes would have been dug to aid removal of peat by boat.^[7]

The whole bog became vegetated with woody shrubs and trees after cessation of peat cutting around the 1750s.^[2] It was then extensively used as game covert from the late 19th century until the Second World War, which probably explains the extensive felling of Far Wood during this time. The bog was acquired in 1946 by Sir Francis Terry and Joseph Rowntree, who subsequently both of whom gifted it to Yorkshire Naturalists' Trust (now known as Yorkshire Wildlife Trust) in 1946. It is Yorkshire Wildlife Trust's oldest nature reserve.^[12]

Hemp cultivation

Fossil evidence found in distinct horizons between layers of fen peat and Scorpidium-Sphagnum peat at Askham Bog suggests 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)^[14]^[15] 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.^[15]

The cultivation of hemp at Askham was probably intense during the Tudor period, although the exact dates are not known. The crop was extensively cultivated and retted in England by royal decree for hemp rope for the British navy. Askham Bog's Acomb Court Roll of 1594 provides documentary evidence of hemp retting restrictions due to the malodour produced by retted fibres and the potential for retting water to pollute rivers.^[2] However, hemp retting stopped in the 19th century with the increased importation of hemp rope from Europe and Russia and the increasing switch to sisal from America and jute from India..^[14]

Habitat conservation

The Yorkshire Wildlife Trust was originally established to conserve Askham Bog.^[12] The first management plan was designed to maintain habitat diversity throughout the bog. To achieve this, the National Conservation Corps was enlisted to create more open water by digging ponds and blocking dykes, along with scrub clearance in the damp cotton-grass areas. In 1998, Yorkshire Wildlife Trust received a substantial Heritage Lottery Fund for restoration of many of its nature reserves. A large portion of this funding was used to manage Askham Bog and maintain suitable water conditions for the wildlife.^[12]

Most of the species-rich fen areas are grazed by Exmoor ponies to encourage early successional plant species such as marsh orchid and meadow thistle, and to suppress vigorous grasses, reed and saplings.^[16] This is considered a more effective management tool than cutting, though some meadows on the site are still cut for hay..^[1]

Related Research Articles

Peat is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. Sphagnum moss, also called peat moss, is one of the most common components in peat, although many other plants can contribute. The biological features of sphagnum mosses act to create a habitat aiding peat formation, a phenomenon termed 'habitat manipulation'. Soils consisting primarily of peat are known as histosols. Peat forms in wetland conditions, where flooding or stagnant water obstructs the flow of oxygen from the atmosphere, slowing the rate of decomposition. Peat properties such as organic matter content and saturated hydraulic conductivity can exhibit high spatial heterogeneity.

Redgrave and Lopham Fens is a 127 hectare biological Site of Special Scientific Interest between Thelnetham in Suffolk and Diss in Norfolk. It is a national nature reserve, a Ramsar internationally important wetland site, a Nature Conservation Review site, Grade I, and part of the Waveney and Little Ouse Valley Fens Special Area of Conservation. It is managed by the Suffolk Wildlife Trust.

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 wetlands along with marshes, swamps, and bogs. Bogs and fens, both peat-forming ecosystems, are also known as mires. The unique water chemistry of fens is a result of the ground or surface water input. Typically, this input results in higher mineral concentrations and a more basic pH than found in bogs. As peat accumulates in a fen, groundwater input can be reduced or cut off, making the fen ombrotrophic rather than minerotrophic. In this way, fens can become more acidic and transition to bogs over time.

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 muskeg; alkaline mires are called fens. A bayhead is another type of bog found in the forest of the Gulf Coast states in the United States. They are often covered in heath or heather shrubs rooted in the sphagnum moss and peat. The gradual accumulation of decayed plant material in a bog functions as a carbon sink.

Moorland or moor is a type of habitat found in upland areas in temperate grasslands, savannas, and shrublands and montane grasslands and shrublands biomes, characterised by low-growing vegetation on acidic soils. Moorland, nowadays, generally means uncultivated hill land, but also includes low-lying wetlands. It is closely related to heath, although experts disagree on what precisely distinguishes these types of vegetation. Generally, moor refers to highland and high rainfall zones, whereas heath refers to lowland zones which are more likely to be the result of human activity. Moorland habitats mostly occur in tropical Africa, northern and western Europe, and neotropical South America. Most of the world's moorlands are diverse ecosystems. In the extensive moorlands of the tropics, biodiversity can be extremely high. Moorland also bears a relationship to tundra, appearing as the tundra and the natural tree zone. The boundary between tundra and moorland constantly shifts with climatic change.

<i>Sphagnum</i> Genus of mosses, peat moss

Sphagnum is a genus of approximately 380 accepted species of mosses, commonly known as sphagnum moss, also bog moss and quacker moss. Accumulations of Sphagnum can store water, since both living and dead plants can hold large quantities of water inside their cells; plants may hold 16 to 26 times as much water as their dry weight, depending on the species. The empty cells help retain water in drier conditions.

<span class="mw-page-title-main">Yorkshire Wildlife Trust</span> Charitable organisation focused on environmental conservation in Yorkshire, UK

The Yorkshire Wildlife Trust is a charitable non-governmental organisation, one of the UK's 46 county-based Wildlife Trusts. Its focus is nature conservation and it works to achieve a nature-rich Yorkshire with healthy and resilient ecosystems that support both Yorkshire's wildlife and its people.

The Portlethen Moss is an acidic bog nature reserve located to the west of the town of Portlethen, Aberdeenshire in Scotland. Like other mosses, this wetland area supports a variety of plant and animal species, even though it has been subject to certain development and agricultural degradation pressures. For example, the Great Crested Newt was found here prior to the expansion of the town of Portlethen. Many acid loving vegetative species occur in Portlethen Moss, and the habitat is monitored by the Scottish Wildlife Trust.

Cors Caron is a raised bog in Ceredigion, Wales. Cors is the Welsh word for "bog". Cors Caron covers an area of approximately 349 hectares. Cors Caron represents the most intact surviving example of a raised bog landscape in the United Kingdom. About 44 different species groups inhabit the area including various land and aquatic plants, fish, insects, crustaceans, lichen, fungi, terrestrial mammals and birds.

Minerotrophic refers to environments that receive nutrients primarily through groundwater that flows through mineral-rich soils or rock, or surface water flowing over land. Minerotrophic, “minerogenous”, and “geogenous” are now often used interchangeably, although the latter two terms refer primarily to hydrological systems, while the former refers to nutrient dynamics. The hydrologic process behind minerotrophic wetlands results in water that has acquired dissolved chemicals which raise the nutrient levels and reduce the acidity. This in turn affects vegetation assemblages and diversity in the wetland in question. If dissolved chemicals include chemical bases such as calcium or magnesium ions, the water is referred to as base-rich and is neutral or alkaline. In contrast to minerotrophic environments, ombrotrophic environments get their water mainly from precipitation, and so are very low in nutrients and more acidic. Of the various wetland types, fens and rich fens are often minerotrophic while poor fens and bogs are often ombrotrophic. Marshes and swamps may also be fed through groundwater sources to a degree.

Lowland heath is a Biodiversity Action Plan habitat as it is a type of ancient wild landscape. Natural England's Environmental Stewardship scheme describes lowland heath as containing dry heath, wet heath and valley mire communities, usually below 250 metres (820 ft) in altitude, on acidic soils and shallow peat, typically comprising heathers, gorses, fine grasses, wild flowers and lichens in a complex mosaic. Heathers and other dwarf shrubs usually account for at least 25% of the ground cover. By contrast, upland heath, which is above 300 metres (980 ft) in altitude, is called moorland, Dartmoor being an example.

Aulacomnium palustre, the bog groove-moss or ribbed bog moss, is a moss that is nearly cosmopolitan in distribution. It occurs in North America, Hispaniola, Venezuela, Eurasia, and New Zealand. In North America, it occurs across southern arctic, subboreal, and boreal regions from Alaska and British Columbia to Greenland and Quebec. Documentation of ribbed bog moss's distribution in the contiguous United States is probably incomplete. It is reported sporadically south to Washington, Wyoming, Georgia, and Virginia.

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 (ombrotrophy) and from mineral salts introduced from the air. They thus represent a special type of bog, hydrologically, ecologically and in terms of their development history, in which the growth of peat mosses over centuries or millennia plays a decisive role. They also differ in character from blanket bogs which are much thinner and occur in wetter, cloudier climatic zones.

Purple moor grass and rush pastures is a type of Biodiversity Action Plan habitat in the UK. It occurs on poorly drained neutral and acidic soils of the lowlands and upland fringe. It is found in the South West of England, especially in Devon.

Blo' Norton and Thelnetham Fens are a 21.3-hectare (53-acre) biological Site of Special Scientific Interest (SSSI) on the Norfolk/Suffolk border. Blo' Norton Fen is in the parish of Blo' Norton in Norfolk and Thelnetham Fen is in Thelnetham parish in Suffolk. It is a Nature Conservation Review site, Grade 2, and part of the Waveney and Little Ouse Valley Fens Special Area of Conservation, Thelnetham Fen is managed by the Suffolk Wildlife Trust and Blo' Norton Fen by the Little Ouse Headwaters Project (LOHP).

Foulshaw Moss is a raised bog in Cumbria, England. In 1998 it was bought by Cumbria Wildlife Trust, which has worked to reverse damage caused to the bog by drainage and afforestation. It is protected as a Site of Special Scientific Interest and as part of the Witherslack Mosses Special Area of Conservation along with two smaller bogs Meathop Moss and Nichols Moss.

Forsinard Flows is a national nature reserve (NNR) covering much of the area surrounding Forsinard in the Highland council area of Scotland. It lies at the heart of the Flow Country, a large, rolling expanse of peatland and wetland area of Caithness and Sutherland that makes up almost 5% of the world's blanket bog. The reserve is managed by the Royal Society for the Protection of Birds (RSPB), and is designated a Category II protected area by the International Union for Conservation of Nature. Much of the NNR overlaps with the designated area of the Caithness and Sutherland Peatlands Special Protection Area and Special Area of Conservation.

Mar Field Fen is a Site of Special Scientific Interest, or SSSI, north of Masham, North Yorkshire, England, in a rural area known as Marfield. It is situated on land containing woodland carr, fen, spring-fed marshy grassland and drier calcareous grassland, between the River Ure to the east and Marfield Wetland nature reserve to the west. As "one of the best examples of fen habitat in the Vale of York," it is a protected habitat for a variety of plants, including the common butterwort, a carnivorous plant. There is no public access to this site.

Sturgeon Bay Provincial Park is a provincial park on the western shore of Lake Winnipeg in Manitoba, Canada. The park is considered to be a Class Ib protected area under the IUCN protected area management categories. It is 144.9 km² (55.9 sq mi) in size.

References

1 2 3 4 "Askham Bog Nature Reserve". Yorkshire Wildlife Trust. Retrieved 15 April 2018.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fitter A. H., Smith C. J. 1979. A Wood in Ascam, a Study in Wetland Conservation. Ebor Press, York.
1 2 Smith C. J. 1962. The Linyphiid spiders of Askham Bog. The Naturalist: 121–124.
↑ "Inspectors reject Attenborough-opposed homes plan". BBC News. 13 May 2020. Retrieved 14 May 2020.
↑ Usher M. B. 1979. Changes in the species-area relations of higher plants on nature reserves. Journal of Applied Ecology16:213–215.
1 2 LP Authority. 1984. Askham Bog Status – Natural England’s SSSI information. https://designatedsites.naturalengland.org.uk/PDFsForWeb/Citation/1000196.pdf
1 2 3 4 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.
1 2 3 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.
↑ David R. W. 1978. The distribution of Carex elongata in Britain. Watsonia12: 158–60.
1 2 3 Wilson K. A., Fitter A. H. 1984. The role of phosphorus in vegetational differentiation in a small valley mire. Journal of Ecology 72: 463–473.
1 2 3 4 "Askham Bog YWT". York Ornithological Club. Retrieved 14 May 2020.
1 2 3 4 Oxford G. S., Scott A. G. 2003. The spider fauna of Askham Bog, York, and the assessment of conservation value. Naturalist128: 157–170.
↑ Hall A., Hood J. R. S., Kenworthy H., Williams D. 1979. Biological evidence from Roman deposits at Skledergate. The Archaeology of York14 3.
1 2 Bradshaw R. H. W., Coxon P. 1981. New fossil evidence for the past cultivation and processing of hemp (Cannabis sativa L.) in eastern England. New Phytologist 89: 503–510.
1 2 Gearey B. R., Hall A. R., Bunting M. J. et al. 2005. Recent palaeoenvironmental evidence for the processing of hemp (Cannabis sativa L.) in eastern England during the medieval period. Medieval Archaeology. pp 317–322. ISSN 0076-6097.
↑ "HLS funds grazing management improvement at Askham Bog". 27 February 2012. Archived from the original on 19 April 2018. Retrieved 15 April 2018.

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[ywtreserves-1] 1 2 3 4 "Askham Bog Nature Reserve". Yorkshire Wildlife Trust. Retrieved 15 April 2018.

[FitterSmith-2] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 Fitter A. H., Smith C. J. 1979. A Wood in Ascam, a Study in Wetland Conservation. Ebor Press, York.

[Smith-3] 1 2 Smith C. J. 1962. The Linyphiid spiders of Askham Bog. The Naturalist: 121–124.

[4] "Inspectors reject Attenborough-opposed homes plan". BBC News. 13 May 2020. Retrieved 14 May 2020.

[5] Usher M. B. 1979. Changes in the species-area relations of higher plants on nature reserves. Journal of Applied Ecology16:213–215.

[LP-6] 1 2 LP Authority. 1984. Askham Bog Status – Natural England’s SSSI information. https://designatedsites.naturalengland.org.uk/PDFsForWeb/Citation/1000196.pdf

[Fitter1980-7] 1 2 3 4 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.

[Pogg-8] 1 2 3 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.

[9] David R. W. 1978. The distribution of Carex elongata in Britain. Watsonia12: 158–60.

[Wilson-10] 1 2 3 Wilson K. A., Fitter A. H. 1984. The role of phosphorus in vegetational differentiation in a small valley mire. Journal of Ecology 72: 463–473.

[yorkbirding-11] 1 2 3 4 "Askham Bog YWT". York Ornithological Club. Retrieved 14 May 2020.

[Oxford-12] 1 2 3 4 Oxford G. S., Scott A. G. 2003. The spider fauna of Askham Bog, York, and the assessment of conservation value. Naturalist128: 157–170.

[13] Hall A., Hood J. R. S., Kenworthy H., Williams D. 1979. Biological evidence from Roman deposits at Skledergate. The Archaeology of York14 3.

[Bradshaw-14] 1 2 Bradshaw R. H. W., Coxon P. 1981. New fossil evidence for the past cultivation and processing of hemp (Cannabis sativa L.) in eastern England. New Phytologist 89: 503–510.

[Gearey-15] 1 2 Gearey B. R., Hall A. R., Bunting M. J. et al. 2005. Recent palaeoenvironmental evidence for the processing of hemp (Cannabis sativa L.) in eastern England during the medieval period. Medieval Archaeology. pp 317–322. ISSN 0076-6097.

[ywtgrazing-16] "HLS funds grazing management improvement at Askham Bog". 27 February 2012. Archived from the original on 19 April 2018. Retrieved 15 April 2018.

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