Vegetation and ombrotrophy on the mires of Abernethy Forest, Scotland

Abstract

Background: Abernethy Forest, an area of native Caledonian Scots pine forest, includes areas of open or sparsely forested peatland, largely ombrotrophic, but locally influenced by water from mineral ground. Aims: To relate vegetation species-composition to the limit of ombrotrophy inferred from water chemistry. Methods: Species composition was listed in 300 sample quadrats; chemical analyses of water samples were available from 200 of these. The vegetation data were classified using TWINSPAN. Relationships between vegetation and chemical results were analysed statistically using contingency tables. Results: Eleven ‘vegetation types’ were recognised, five (189 samples) judged as primarily ombrotrophic-bog vegetation. The others showed evidence of flushing, or transition to forest. A previous analysis of major cations in the 200 water samples indicated that a limiting Ca/Mg ratio of 1.0 divided 61 samples showing telluric influence from 139 essentially ombrotrophic samples. Neither division was sharp. Contingency tables showed that the division based on vegetation types was strongly associated with the division of the water samples based on cation ratios. Conclusions: Large areas of bog south and east of Loch Garten are unequivocally ombrotrophic; the main telluric-influenced sites occupy openings in the forest west of the loch. The limited ‘fen’ flora probably reflects the small size and isolation of the calcium-rich sites and the dominating influence of the ombrotrophic peats.