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The decline of S. austinii Sull. Ex Aust. (formerly S. imbricatum Hornsch. Ex Russ. ssp. austinii Sull. Ex Aust.), in most cases to local extinction, represents one of the most striking vegetation changes on the raised bogs of Britain and Northwest Europe during the last 2000 years. This study uses plant macrofossil, pollen and geochemical analyses to explore the record of human impact and land-use intensification at the S. austinii decline. There is a clear temporal association between anthropogenic woodland clearance, cereal cultivation, soil erosion and contemporary climatic change, with the decline of S. austinii. These findings suggest that S. austinii is sensitive not only to rapid climate changes but also to the aerial deposition of soil dust and/or accompanying pollutants. A modern comparison of atmospherically derived nitrogen (N) loadings with the present presence/absence of S. austinii on 16 raised bogs shows that the species is only present where the loading lies below a critical threshold for N of 10 kg/ha per yr. The palaeoecological record also shows that S. austinii has re-established itself during phases of reduced human activity but in contemporary Europe it is difficult to see this happening in the near future. [ABSTRACT FROM AUTHOR]

The plant macrofossil records from three raised bogs from western and central Ireland and from Cumbria were compared to investigate variations in the character and timing of the fen-bog transition (FBT). Two modes of raised or ombrotrophic peat formation were recognized. In the first mode the transition develops through a sedge-fen stage directly to raised-bog lawn, maintaining a near surface water table throughout the FBT (Abbeyknockmoy Bog). The second mode is characterized by a switch from fen or reedswamp to a dry Eriophorum-dominated mire type, suggestive of low or unstable water tables (Mongan Bog and Bolton Fell Moss). Comparisons with the Holocene effective precipitation record suggest that the type of transition and its timing may be affected by the prevailing climate regime. All that is required for ombrotrophy is a separation of the growing peat surface from the influence of ground and surface waters. This separation may be achieved by rapid peat accumulation in a moist climate, the accumulation of decay-resistant Eriophorum. vaginatum hummocks or by a lowering of the water table, leading to a 'perched peat bed'. In the latter two cases, a 'pseudo-raised bog' community often persists, laying down highly humified peat, until increased oceanicity enables Sphagnum. to dominate. [ABSTRACT FROM AUTHOR]

Mid-Holocene tephra layers have been located and geochemically analysed from seven ombrotrophic bogs in Scotland. The tephras found in these Scottish peats occur as stratigraphically discrete horizons, not visible to the naked eye, and originate from volcanic activity in Iceland. Identifying and geochemically typing the tephra layers can enable precise correlations between sites on regional scales, depending on the spatial extent of the airfall events. Dispersal of both the Glen Garry and Hekla-4 tephras is excellent over Scotland, enabling snapshot views of the past at the time of these tephra depositions. Palaeoecological analyses have also been undertaken on these bogs, providing detailed reconstructions of past changes in bog vegetation and surface wetness, a proxy for past climates. Correlations between the ombrotrophic bogs at the time of the Glen Garry tephra revealed significant differences between the proxy climate records in the north and the south of Scotland, suggesting asynchronous changes between northern Scotland and the rest of Great Britain. [ABSTRACT FROM AUTHOR]

The decline of Sphagnum imbricatum from the peat stratigraphy of six ombrotrophic mires (Bolton Fell Moss and Walton Moss, Raeburn Flow and Bell’s Flow, and Coom Rigg Moss and Felecia Moss), has been investigated using colorimetric humification, quantitative plant macrofossil, and testate amoebae analyses. The chronology of each peat profile was determined by radiocarbon assay and pollen/land-use correlations. Palaeoclimate reconstructions have been made by linking known documentary/historical changes in climate, and other proxy-climate records, to those inferred from the sites investigated in the study region. In two of the ombrotrophic mires examined, there are wet shifts associated with the decline and local extinction of S. imbricatum, which are dated to cal. ad 1160–1400 (Raeburn Flow and Bell’s Flow). In Coom Rigg Moss and Felecia Moss, wet shifts are also associated with the decline and local extinction of S. imbricatum between cal. ad 1395–1485. The decline of S. imbricatum from two other ombrotrophic mires (Bolton Fell Moss Core L and Walton Moss Core 11) is dated to cal. ad 1030–1400, and may have been due to interspecific competition between Sphagnum species during the ‘Early Medieval Warm Period’ and the ‘Little Ice Age’. [ABSTRACT FROM AUTHOR]