A3.6 Holocene vegetation history of SW Connemara, Co. Galway with particular reference to Carna and Roundstone
O'Connell, Michael McDonnell, Karina
O'Connell, Michael
McDonnell, Karina
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2019
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Book chapter
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O'Connell, Michael, & McDonnell, Karina. (2019). A3.6 Holocene vegetation history of SW Connemara, Co. Galway with particular reference to Carna and Roundstone. In Pete Coxon (Ed.), The Quaternary of Western Ireland. INQUA Field Guide Pre:GL-2. Dublin: Irish Quaternary Association.
Abstract
Conclusions A 14C-dated pollen profile from Loch an Chorcail, southern Carna peninsula provides a detailed record of vegetation and land-use change that spans most of the Holocene. Pine (P. sylvestris, i.e. Scots pine), oak (Quercus; most likely Q. petraea which characterises present-day western oak woodlands) and hazel (Corylus) are the dominant woody species for much of the Holocene. Pine declines after a pronounced phase of colonising bog surfaces during the so-called pine flush that lasted from ca. 5000 4750 cal. BP. The final decline in oak took place shortly after 3000 cal. BP. Bog/heath taxa are already locally present and common in the early Holocene (Calluna from ca. 9700 cal. BP; E. tetralix from ca. 8100 cal. BP). The fern, Osmunda regalis, was already frequent by 10 800 cal. BP, and Hymenophyllum wilsonii spores are first recorded at ca. 10 400 cal. BP indicating local presence of this filmy fern since the early Holocene. Eriocaulon pollen is recorded with relatively high consistency from ca. 6730 cal. BP until recent times which suggests continuous presence of E. aquaticum (American pipewort) at Loch an Chorcail over this period. As far as we are aware, this is the longest Holocene record for Ireland and indeed Europe. The micro-charcoal record indicates that fire was important from at least 10 000 cal. BP onwards. Sandy layers are recorded in the centuries around the Elm Decline (dated to 5870 cal. BP) which suggest soil erosion but there is no evidence for a pronounced Neolithic Landnam event as at other sites in Connemara (e.g. Lough Sheeauns; Molloy and O Connell 1991). Major changes in woodland composition and also woodland extent began at ca. 3830 cal. BP, i.e. in the early Bronze Age, and led to lake infilling and shallow lake conditions that favoured aquatic plants. Considerable soil erosion, which manifested itself as sandy layers in the lake sediment, was a feature of the early and mid-Iron Age (ca. 2500 1800 cal. BP). Cereal-type pollen is not recorded and pollen of ruderals are poorly represented so it seems that there was little or no cereal cultivation in the vicinity of the lake due probably to unfavourable edaphic conditions caused by bog/heath development. Pollen profiles from the nearby Roundstone peninsula show similar vegetation history. A key mid-Holocene feature is the widespread but short-lived colonization of peat surfaces by pine (Pinus sylvestris) that was probably mediated by climate change, i.e. drier/warmer followed by wetter/cooler conditions. The data provide evidence for considerable change not only in woodland composition and extent, but also bog/heath development and loss of open water bodies and reedswamps, especially in the later Holocene as sediment-infilling progressed apace, furthered by increased human impact.
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Irish Quaternary Association
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Attribution-NonCommercial-NoDerivs 3.0 Ireland