Environmental evidence for the Mesolithic-Neolithic transition

The environmental context for the transition from the Mesolithic to the Neolithic has not received sufficient attention. Abrupt climatic fluctuations appear broadly coincident with the transition, from c. 6350 BP until c. 5750 BP (Bonsall et al. 2002; Tipping 2010 but see Schulting 2012), although whether these had any causal influence on human activities – that is the eventual decision to abandon a lifestyle based purely on exploiting wild resources – remains unknown.

Increased storminess may have been a significant environmental characteristic during the period of the transition. This is evident from patterns of sand dune accumulation that are interpreted as a consequence of abrupt climate change and storminess in Sweden (Bjorck and Clemmensen 2004; De Jong et al. 2006), Portugal (Clarke and Rendell 2006) and Wales (Orme, Davies and Duller 2015). Dunes on the Outer Isles (Gilbertson et al. 1999; Dawson et al. 2004), in Wester Ross (Wilson 2002) and along the north Irish coast (Wilson, McGourty and Bateman 2004) suggest periodicity rather than continuity in dune and machair accumulation, this appearing to start towards the end of the Mesolithic and during the early Neolithic c. 6300-5200 BP. Again, whether increased storminess had a causal influence on the process of transition from the Mesolithic to the Neolithic, remains to be explored.

Whilst the dating of the archaeological record of the Late Mesolithic and the Early Neolithic remains poorly resolved, and the economic activities of these communities remains ill-defined by archaeological evidence, the environmental record might provide insights into the economies of these periods and the chronology for the development of farming as the predominant way of life. The possibility that Mesolithic people might have planted cereal crops was once an intriguing idea (Edwards 1989; Edwards and Hirons 1984). Macklin et al. (2000) report cereal-type pollen as early as c. 11,200 BP at Gallanach Beg but interprets this as deriving from wild grasses. Cereal-type pollen was found in pre-elm decline sediments at Rhoin Farm (Edwards and Mackintosh 1988) but could not be shown to be unambiguously from cereal grasses: almost all the pollen grains were of Hordeum type (barley type), which includes many wild grasses known to produce cereal-size pollen in habitats such as the sand dunes that surround Rhoin Farm today, and probably did so in prehistory.

Around Coire Clachach in central Mull (Walker and Lowe 1985), Plantago lanceolata appears in the early Neolithic at c. 5800 BP, and some dryland trees such as hazel and oak decline. This pattern is also described from Loch a’Bhogaidh on Islay from a similar date (Edwards and Berridge 1994) and from the Sorn Valley (Andrews in McCullagh 1989) from c. 5700 BP, though at the latter site by a single pollen grain only. At Gribun on the exposed west coast of Mull, a plant community with wild grasses was established before the elm decline, further increasing from c. 4800 BP as the birch population fell (Walker and Lowe 1987). A decline in hazel and an expansion of grassland with P. lanceolata occurred prior to the elm decline around Iona Loch, and cereal type pollen is recorded from the elm decline (Scaife and Dimbleby 1990). Bohncke (in Barber 1981) suggested that Neolithic farming on Iona had included cereal crops. Near Kilmartin, valley-floor woods at Torbhlaren were partly cleared from as early as c. 6300 BP (Tipping et al. 2011), with cereal cultivation introduced at c. 5300 cal BP, and arboreal regeneration between c. 5200 and c. 4900 BP. Tipping et al. (2011) suggested that at c. 4900 BP oak woodland began to be conserved, or perhaps planted, and grown on for some 800 years until the woodland was abruptly felled at c. 4100 BP. This activity may have coincided with the creation of rock art on the valley floor. At Lochan Taynish, Rymer (1974) reported only limited woodland disturbance in the Neolithic, after c. 5400 BP. Close by at Loch Cill an Aonghais (Peglar 1980), whilst P. lanceolata appeared at the elm decline, grassland expanded only from c. 5400 BP. In the Sorn Valley, grassland with P. lanceolata was established around 5100 BP (Andrews in McCullagh 1991).

Another environmental signal that might reflect Late Mesolithic and Early Neolithic economic activity is changing sedimentation patterns in terrestrial locations, both colluviation (slope and soil erosion and subsequent re-deposition) and alluviation (fluvial erosion and deposition). Again, the available evidence is sparse.

Tipping et al. (2011) obtained a securely dated record of slope and soil erosion in Scotland at Torbhlaren in the lower Add valley. Peat forming on the valley-side above the floodplain received varying amounts of soil eroded from sandy glacio-marine terraces above. An alluvial fan on the slope began to form from c. 9500 BP and in one colluvial record, colluviation also commenced within the Mesolithic period, at c. 7060 BP. Despite being only a couple of hundred metres apart, three dated sediment cores suggest diachronous phases of the most intense soil erosion. Sediment delivered at high energies to one borehole between c. 6800 and c. 6200 BP has no counterpart in an adjacent borehole, though comparable high-energy events might be recorded in both at c. 5800-c. 5200 cal BC and c. 5550 and c. 5400 BP.

In the Oban region, Rhodes, Rumsby and Macklin (1992) and Macklin et al. (2000) analysed soil erosion from geochemical signals. Rhodes et al. (1992) investigated a range of elements at Gallanech Beg but with no discussion of the data while Macklin et al. (2000) report only potassium (K) in three additional peat sequences at Lon Mor, Bhuilgh bhith and Cnoc Philip. They argue that soil erosion was greatest between c. 5500 and c. 4000 BP, when they claim the first evidence for farming appears in the sequences, although in the same paragraph they also argue for soil stability between c. 5600 and c. 4000 BP.

With regard to fluvial activity, Carter and Tipping (1991-2; Tipping, Carter and Haggart (1994) mapped the terrace surfaces along the lower Carra Water on Kintyre. Most are related to glacial or relative sea level stages but the extensive Rhonadale Wood Terrace is fluvial. It began to accumulate between 6500 and 5500 BP when sufficient sediment from earlier-formed terrace fills or soils on slopes filled the river enough to promote frequent flooding and the creation of a floodplain.

While these isolated reports are insufficient to provide an informed history of landscape, they suggest that colluviation and alluviation were significant in the Early Neolithic, implying significant landscape change. But whether this should be attributed to economic activity of climate changes remains unclear. It is likely that geomorphic changes in the highlands and on steep slopes were climatic in origin (Ballantyne 2004) because pastoralism is likely to have made few impacts, but colluviation in lowland valleys as at Torbhlaren need not have been. Yet here Mesolithic and Neolithic colluviation occurred in the absence of evidence for major human activities in the pollen record (Tipping et al. 2011). As such, a climatic causation for Holocene alluviation remains plausible, as it do so elsewhere in Britain (Macklin, Johnstone and Lewin 2005).