Palaeo-environmental overview and past climate change

The soils of the region are generally poor at preserving organic remains. The alkaline soils on Magnesian Limestone areas of South Yorkshire allow some preservation, but the better quality palaeo-environmental information has come from low-lying wetland sites. The Coal Measures geology is still largely a blank area, but there is some limited evidence for the Pennine uplands. There remains a problem with resolution – some site-specific palaeo-environmental evidence from South Yorkshire is good, as is some of the wider regional data; but intermediate sequences suitable for describing the entire county are lacking. The information below inevitably draws on additional evidence from further north in West Yorkshire, further west in Derbyshire, and further south in the Trent Valley of Nottinghamshire.

The first extensive woodland clearance in South Yorkshire appears to have taken place during the Bronze Age, with charcoal layers at Thorne Moor indicative of burning and an associated increase in grassland and perhaps pastoralism (Smith 2002: 35-6). There was alder and birch carr on much of north and central Thorne Moor (Chapman and Gearey 2013: 141). Evidence at Leash Fen and Stoke Flat in the Pennines of Derbyshire indicates clearance, grazing and cereal cultivation from the later Bronze Age (Heath 2003: 35; Long, Chambers and Barnatt 1998: 512). To the south-east, peat from River Trent palaeochannels reveals a decline in woodland and a rise in grasses and sedges from 1200–1000 BC, with possible cultivation and pastoralism (Brayshay and Dinnin 1999; Knight and Howard 2004; Smith and Howard 2004). The Rivers Trent, Don, Idle and Torne drained into the Humberhead Levels, which was a shifting mosaic of alder and birch carr, open water and reed swamp, peat bog and raised mires (Van de Noort and Ellis 1997, 1999). These areas may have been seasonally exploited for wildfowl, plant foods, construction materials and bog iron ore; and might also have held significant symbolic meanings.

At Hatfield Moors, there is evidence that small-scale Bronze Age woodland clearance accelerated during the earlier Iron Age (Buckland 1976, 1979; Chapman and Gearey 2013; Dinnin and Whitehouse 1997; Smith 2002). Peat formation in both the Pennine uplands and the raised mires of the Humberhead Levels was probably underway by the late Bronze Age. Pools of standing water and reed swamps in the levels were common, with some heathland on drier areas (Buckland 1976: 208-9; Chapman and Gearey 2013: 138; Smith 2002: 43). There was possibly increased run-off of calcareous water from Magnesian Limestone areas (Buckland 1976: 212; 1979: 63; Smith 2002: 91), perhaps linked to clearance and cultivation.

This increased clearance and peat formation in upland mires, lowland mires and river valleys was possibly exacerbated by a climatic downturn across north-western Europe between c. 1000–800 BC, perhaps indicating a change from a more continental to a more oceanic if warmer climatic regime (P. Buckland pers. comm.). There may have been marine transgression sea levels and thus also rising inland water tables in the East Anglian Fens and Humberhead Levels from around 500 BC onwards (Bell 1996; Dinnin, Ellis and Weir 1997). The exact nature and scale of these large-scale changes continues to be a matter of intense debate. The wetter, colder conditions were once linked to volcanic eruptions or even cometary showers (e.g. Baillie 1991; C. Burgess 1985, 1989), and were regarded as causing the abandonment of upland settlements, famine and population collapse, large-scale population movements to the lowlands, and a concomitant increase in conflict between social groups that lead to the creation of linear earthworks and hillforts.

Such overly environmentally deterministic arguments have been criticised, however (e.g. Buckland, Dugmore and Edwards 1997), and although the nature and scale of human occupation might have changed, there does not seem to have been a wholesale abandonment of upland areas (Cockrell 2016; Tipping 2002; Young and Simmonds 1995). There is evidence of some level of widespread change with colder, wetter conditions; but the mechanisms behind this and the impact upon human communities is still disputed, in some cases by researchers using data from the same regions (e.g. Amesbury et al. 2008; Armit et al. 2014; Turney et al. 2016).

At Thorne Moors there were increases in indicators of grassy environments recorded from c. 870–540 BC, and human activities do not appear to have significantly diminished there or across the Humberhead Levels, with evidence for pastoralism and arable agriculture (Smith 2002: 36, 48-9). Low-lying areas and river valleys in South Yorkshire at sites such as Sutton Common and Balby Carr were probably still dominated by alder carr, with some willow, birch, hazel and oak, and wet grassland (Boardman 1997: 245-247; Gearey 2007: 62-64; Greig 2007: 13; Roper and Whitehouse 1997: 244). Many valley bottoms and low-lying areas had large pools or lakes of shallow standing water called meres during winter and spring, but these formed lush pastures in summer and autumn. Areas such as Potteric Carr and Balby Carr would have had such meres until the later Iron Age and Romano-British periods when areas were reclaimed and drained by ditches to leave wet and dry meadows.

At Balby Carr there was evidence for wetter environments with carr woodland of alder and willow, water-filled ditches, open wet ground of swamp/fen and some standing water with sedges, rushes and bur-reed. There were drier areas of waste ground, hedgerow, heath and grassland with hazel and hawthorn, sloe, bramble and wild rose, and heather and bracken. There were wet meadows with sweet-grass and buttercup, and drier pasture, with a low-level of arable cultivation of barley (Hordeum), and emmer and spelt wheat (Triticum dicoccum/spelta) on higher, drier ground (Greig 2007: 34-6; Smith and Tetlow 2007: 44-5; Wyles 2016: 14-16).

During the Iron Age and Roman periods, much of the eastern lowland part of South Yorkshire would have consisted of open landscapes with pasture and arable fields interspersed with small copses of managed woodland (Buckland 1986: 4; Greig 2007: 36). Plants associated with hedges may have helped define some ditched boundaries. The introduction of hay cropping may have taken place after the Roman occupation, with no firm evidence of it beforehand (Greig 1984; M. Jones 1996; Lambrick 1992). Stands of wildwood might have remained on steeper hillsides and upland areas, but most tree cover had probably disappeared by the earlier Iron Age. Woodland management was probably undertaken through plot-felling, with managed stands coppiced in identifiable cycles (Buckland 1986: 4). Rod fragments of ash, and worked round wood or boards of oak, alder, beech and willow were found at Balby Carr (Allen 2005; Gale 2007; Hall et al. 2005). Mather (1991) recorded evidence of widespread woodland clearance during the Romano-British period near Rossington Bridge, with an expansion of grassland accompanied by the presence of barley, oats or wheat and possibly hemp. Much of this may have been driven by the demands of the military for timber, but also the pottery industries for fuel.

This evidence broadly corresponds with that derived from more recent investigations at Potteric Carr as part of the FARRRS and i-Port developments (e.g. Daniel 2017: 34, 37, 38-9; Daniel, Harrison and Powell 2014a: 18-20, 2014b: 18-19). In addition to cereal remains (see below), hazelnut, apple, and sloe fragments and an almost complete tuber of pignut were recovered from the waterholes of later Iron Age and Romano-British date. The weed assemblage was indicative of grassland, field margins and arable environments (Daniel 2017: 33-5). Wood charcoal included oak, alder, hazel, willow or poplar, wild cherry, hawthorn and ash. Much of this, from branches or coppiced stems, was probably remains of fuel waste from domestic hearths. Charred stems of grasses, sedges and occasionally heather found in some of the waterholes probably relate to the burning of turves (Daniel, Harrison and Powell 2014b: 18). Waterlogged remains of alder and willow were found in waterholes and boundary ditches. Damp and waterlogged conditions suggested by the alder, willow and poplar were further indicated by crowfoot, water pepper and marsh pennywort that grow in shallow margins of ponds, ditches and slow-flowing streams; along with evidence for blinks, spikerush, rushes and sedges, caddisfly larvae case fragments, and a single egg case of water flea.

Remains of thistle, creeping buttercup, and grasses indicated grazed grassland in the vicinity. Knotgrass, chickweed, nettles, nightshade and other indicators of disturbed or nitrogen-rich soils were also in evidence, along with bracken. Remains of beetles and mites were also found (Daniel 2017: 41) but have not yet been fully analysed. Pollen assemblages of the waterholes were dominated by oak, hazel, alder and birch, elm, lime and holly; either from residual primary woodland or more likely secondary woodland/scrub growth after a phase of clearance. Pollen from a ditch at FARRRS indicated a more open landscape with wet pasture and cultivation, but at a very local level a change from wet, grass-sedge vegetation to alder carr woodland. The ditches, well and waterholes at Finningley Quarry produced oak, alder and hazel charcoal, waterlogged remains of elder and bramble, and beetle remains that are also not fully analysed or published (Alldritt 2006a: 123).

This all indicates a mosaic of vegetation in an essentially open landscape with grazing on low-lying areas of wet grassland and cultivation on slightly higher, drier ground, as well as for the presence of heathland. Samples taken from the Scaftworth Roman fortlet also indicated that away from the alder and willow carr woodland on the River Idle floodplain, the landscape was essentially open and farmed during the Romano-British period (Gilbertson and Blackham 1985) with a mixed arable and pastoral regime. For Britain as a whole, the climate became warmer and drier from the later Iron Age onwards (Lamb 1981: 62-63; Simmons 2001: 53). Even on higher ground, however, water tables have probably been lowered in the past few hundred years due to post-medieval and early modern drainage, and there would have been more springs and minor becks (Berg 2001: 4), especially on hillsides.

On the eastern limestone areas of West Yorkshire there were probably extensive open grasslands, with evidence for ploughing and arable cropping (Long and Tipping 2001: 225; Richardson 2001: 248). The South Yorkshire evidence is less clear as there has been a general lack of published data from the smaller number of excavations on Magnesian Limestone areas, and several excavated sites unfortunately remain unpublished, such as the investigations around Brodsworth by the Universities of Sheffield and Hull. The plant remains recorded at Barnburgh Hall suggested cultivation and weeds of disturbed and open cultivated land, but only indications of cereal consumption rather than processing (Young and Alldritt 2005). Few plant and snail remains were recovered from Redhouse Farm, Adwick-le-Street, with little potential for palaeo-environmental information (Deighton 2004: 25).

There are limited results even from more intensive sampling of sites on Coal Measures geology and soils. At Pastures Road, Mexborough, analyses suggested some cultivation and access to woodland, peat, and heathland resources (Alldritt 2008: 27). At Roebuck Hill, Jump, there was also evidence for cultivation and weeds of an arable, relatively open landscape with some woodland, scrub or hedgerows featuring blackberries, hazelnuts and sloes (Schmidl, Jacques and Gardner 2007: 56-8). Some pine charcoal present might also be indicative of sandier heathland. Only a few charred grains of barley and spelt wheat were found at Whirlow Hall Farm, which might indicate only limited crop processing; whilst remains of weeds such as buttercup and burnet suggested open meadow or pasture environments (McLellan 2017: 114). Large charcoal concentrations consisted principally of mature oak wood and hazel branch wood, probably linked to industrial activities such as the metalworking evidenced at the site. The hazel branches may have been used for kindling and the mature oak for stoking fires to high and consistent temperatures.

Across Britain, the generally warmer and drier climatic conditions of the later Iron Age and earlier Roman period may have begun to deteriorate again during the 3rd to 4th centuries AD (Knight and Howard 2004: 116; Lamb 1981: 62-63; Simmons 2001: 53). Along the Rivers Trent, Don and Idle and within the Humberhead Levels there were episodes of flooding and alluviation, perhaps caused by loss of vegetation cover and/or more intensive agriculture with deeper ploughing and additional winter cropping, leading to higher surface run-off and soil loss (Buckland and Sadler 1985; Dinnin 1997; Knight and Howard 2004; Macklin 1999). There may also have been marine transgression in the Humberhead Levels (Dinnin 1997: 32; Van de Noort and Davies 1993: 18). By the late 3rd and 4th centuries AD, this was leading to increased flooding and alluviation. The anthropogenic processes causing or at least contributing to these regional trends are likely to have included further woodland clearance and increased cultivation, perhaps exacerbated by deep-ploughing techniques capable of severing root mats, and the sowing of winter as well as summer crops (Knight, Howard and Leary 2004: 120). Some areas of previous field system and settlement in low-lying areas such as Potteric Car may have been abandoned (Daniel 2017: 52). Field system ditches silted up and these areas abandoned once again, until drainage and reclamation schemes during the recent historic period.

Research questions

  • What was the impact of climate change upon farming practices, especially in lowland and upland areas? How did human communities in South Yorkshire respond to the possible amelioration of climate during the later Iron Age, and the potential deterioration in the later Roman period?
  • Can we chart more closely the processes of woodland clearance and agricultural intensification, their impact upon alluviation and colluviation, and variations between different areas?
  • Large-scale developer-funded work has increased palaeo-environmental evidence for South Yorkshire, but there is still a marked lack of information for the Iron Age and Romano-British periods, especially on Magnesian Limestone and Coal Measures areas. How might this be improved?
  • What was the impact of Roman-period industries such as pottery and metalwork production on the environment?

Priorities and implementation

  • There needs to be a widespread and much more systematic research programme of palaeo-environmental sampling and analysis across South Yorkshire, focused particularly on alluvial deposits along the Rivers Don, Idle, Torne, Went and Rother, and the Idle-Don confluence at Sandtoft;
  • Palaeochannels and alluvial deposits associated with these may be locations where targeted palaeo-environmental sampling through targeted trenching, coring and test pitting might prove particularly productive. This could be undertaken by or in association with a university archaeology department;
  • Palaeo-environmental sampling on archaeological sites is often still too small-scale and/or ad hoc in nature, and resources for analyses may be limited. Specifications for developer-funded projects should stipulate that palaeo-environmental sampling on-site needs to be much more extensive and systematic, and supported by rigorous scientific dating strategies. Sampling for pollen analyses and soil micromorphology studies should be also be more routine, even if soil conditions are not optimal;
  • Deep pits, waterholes, wells and other waterlogged features must be targeted on-site for sampling, as here pollen, snail and insect remains might survive;
  • On developer-funded projects, multiple samples for absolute dating including AMS 14C dating and (where the geology permits) OSL dating, should become routine and along with Bayesian modelling used more extensively to support palaeo-environmental sampling and analyses where possible;
  • On larger research and commercial archaeological projects, palaeo-environmental specialists should be present on-site at times to supervise sampling. Large developer-funded projects must consider the need for the systematic sampling, storage, processing, analysis and publication of palaeo-environmental material;
  • The results of unpublished excavations and palaeo-environmental sampling, especially on Magnesian Limestone and Coal Measures areas, need to be fully analysed, dated and published as a matter of urgency.