Late Holocene mire development of the lowland raised bogs Cors Caron and Cors Fochno : a palaeoecological approach using high resolution macrofossil analysis

Abstract

The main objective of this project is to examine the direction and rate of change in raised bog vegetation succession over the last 2000 years at the two lowland raised bogs Cors Caron and Cors Fochno as well as the factors which caused these changes.

From Cors Caron a significant deceleration in peat accumulation was reported in all three bogs by previous research (Morris 2001), which appeared to be a rather unusual feature compared with other raised bogs. The vegetation of both study sites has undergone changes of varying degree including the extinction or decrease of S. austinii and the spread or invasion of species which usually do not occur in raised bog vegetation. The pioneering work of Godwin and Conway (1939) enables a study of the vegetation development at the Cors Caron West Bog over the past sixty five years by re-survey. In order to study the history of S. austinii in a wider context, an Irish raised bog (Raheenmore Bog) was selected where the species still occurs.

Macrofossil analyses were completed on multiple cores including the estimation of vegetative plant remains (Quadrat and Leaf Count Macrofossil Analysis) as well as the counting of propagules and animal remains. Horizons with significant changes in the macrofossil assemblages were radiocarbon dated to study the rate in peat accumulation. For the re-survey of the Cors Caron West Bog the vegetation cover of was recorded by establishing quadrats in representative areas and the species abundances estimated as percentage cover.

The comparison of the vegetation in 1936/37 and 2001/02 shows that there was a rapid deterioration in the peat forming vegetation on Cors Caron West Bog, leading to its currently poor condition with the species composition on the West Bog strongly suggesting that the vegetation suffers from drying out. These dry surface conditions are linked to the absence of a properly developed acrotelm over extended parts of the West Bog. An examination of the history of species which do not normally occur in raised bog habitats revealed that on Cors Caron Molinia caerulea and Betula did not appear in the macrofossil record and colonised the bog in very recent times. This could have been caused by higher water level fluctuations and increased atmospheric nitrogen deposition. On Cors Fochno Myrica gale was a component of the vegetation over the investigated time span and its recent increase is likely to be a result of increased water level fluctuations.

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