Allochthonous and autochthonous mire deposits, slope instability and palaeoenvironmental investigations in the Borve Valley, Barra, Outer Hebrides, Scotland

This paper suggests that sediment depth-age anomalies, and the lithological and palaeoecological properties of a peat core from Borve mire on the Outer Hebridean island of Barra, reflect the episodic impacts of rapid mass-movement of superficial pears and mineral soils from the adjacent hillslopes in the period 3000 to 1750 C-14 years BP. Alternative explanations such as mismeasurement of radiocarbon or contamination by floods, are thought less likely. The research implies that there is a general need for caution in the interpretation of mire deposits from sites which are adjacent to sleep peat-covered hillslopes and which have not been investigated with the support of substantial radiocarbon and lithological studies programmes. The environmental and vegetational history of this exposed and isolated Atlantic island is shown to have not been one of treeless homogeneity. A variety of deciduous and coniferous tree species colonized early in the Holocene, with distinctive birch-hazel woodland developing at one point in time. The landscape became increasingly treeless in the Bronze Age, with most but not all trees having been lost by the Medieval period. Valley side peats provide palynological evidence of pastoral and arable farming on poor soils in the Dark Age-Early Medieval period, at sites beyond the present limits of cultivation.