A Quantitative Method for Stratigraphic Analysis of Bryophytes in Holocene Peat

Abstract

(1) A new method of analysing the changes in amounts of bryophytes in autochthonous peats is developed. Bryophyte concentration changes (expressed as number of fragments per 100 ml of peat) and percentages of types are calculated and presented in continuous stratigraphical diagrams. (2) A formula used to calculate Sphagnum concentrations is based on counts of Sphagnum plants, branches, and leaves. This makes it possible to present Sphagnum together with other bryophytes in the same diagrams. (3) As an illustration of the method a 3.8-m deep peat core was analysed from Red Lake Peatland, on the bed of Glacial Lake Agassiz in northern Minnesota. Peat accumulation began at this site about 3500 years ago. (4) Scorpidium scorpioides and Calliergon trifarium are the major peat formers during several recurring episodes of peat accuimulation. Seven other species of the Amblystegiaceae are recorded. One or more of six Sphagnum species dominate other periods of the accumulation. Four additional types belong to the Bryaceae, Meesiaceae, Aulacomniaceae and Polytrichaceae. (5) Five local bryophyte zones are sharply delimited in the late Holocene peat of this Red Lake Peatland site. The four lower zones reflect either changes in the water level in a non-patterned fen system or fluctuations in the size of low hummocks formed by emergent, minerotrophic bryophytes in a patterned fen. The uppermost zone indicates the formation of less minerotrophic vegetation on top of the fen peat and periodic advances of the bog margin over the fen at the coring site. (6) Bryophyte concentration data are useful in interpreting peat ontogeny and the local hydrological environment during peat accumulation. The bryophyte assemblages reflect shifts along a minerotrophic-ombrotrophic gradient of one of the dominant components of the local wetland vegetation.