Icelandic volcanic ash and the mid- Holocene Scots pine (Pinus sylvestris) pollen decline in northern Scotland

Abstract

A volcanic ash-layer in peat from northern Scotland has been identified and coincides exactly with an abrupt decline in Pinus sylvestris L. (Scots pine) pollen frequencies. This provides an isochrone (time-equivalent marker horizon) with which to investigate the timing of the Holocene 'pine-decline'. Furthermore, two possible causes of the southward shift of the range of Pinus in Scotland c. 4000 BP are suggested; a direct effect of acid pollution by chemicals produced by the eruption of Hekla (H-4), or a volcanically-induced climatic perturbation. These possibilities have wider implications for the influence of volcanism on postglacial environmental change.

Volcanic impacts on the Holocene vegetation history of Britain and Ireland? A review and meta-analysis of the pollen evidence

“…There is no significant relationship in all the other records, including some such as Strath of Kildonan-K1 (Charman et al 1995) and Loch Lèir (Blackford et al 1992) which have been suggested to show pollen changes at the time of tephra deposition. In Strath of Kildonan-K1, the tephra profile is rather diffuse, with the most distinct changes (replacement of Coryloid by Cyperaceae pollen) occurring below the tephra peak and therefore not identified as being related to tephra deposition in our analyses.…”

“…Volcanic impact models explain a significant proportion of variance in four profiles (Table 2): the Croaghaun East site of Dwyer and Mitchell (1997), the Portmagee site of Hall (2003b), the Dallican Water site of Bennett et al (1992) and the Altnabreac site of Blackford et al (1992).…”

“…Birks 1975;Bridge et al 1990;Charman 1994;Pilcher et al 1995b;Anderson et al 1998;Lageard et al 1999;Tipping et al 2008). At Loch Lèir the data of Blackford et al (1992) show a two-stage decline in Pinus with the larger changes above the tephra peak. Only in the Altnabreac profile is the Pinus decline almost exactly synchronous with the peak concentration of Hekla-4 tephra and there is a clear decline in Pinus percentage in the sample(s) above the tephra peak.…”

“…The original discussion of putative volcanic impacts by Blackford et al (1992), and subsequent publications, centred on the possibility of a causal relationship between the decline in Pinus pollen and the Hekla-4 eruption. A mid-Holocene Pinus decline has been widely reported from pollen and macrofossil studies in Britain and Ireland.…”

“…The term tephropalynology has been coined for such studies (Edwards 1996;Lowe and Hunt 2001;Edwards et al 2004). Blackford et al (1992) were the first to investigate the palynological record across a volcanic ash layer at high resolution (Table 1). At two peatland sites in Scotland, these authors showed coincidence between the ca.…”