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 Oute r Hebridean island of Barra, reflect the episodic impacts of rapid mass-mov ement of superficial pears and mineral soils from the adjacent hillslopes i n the period 3000 to 1750 C-14 years BP. Alternative explanations such as m ismeasurement of radiocarbon or contamination by floods, are thought less l ikely. The research implies that there is a general need for caution in the interpretation of mire deposits from sites which are adjacent to sleep pea t-covered hillslopes and which have not been investigated with the support of substantial radiocarbon and lithological studies programmes. The environ mental and vegetational history of this exposed and isolated Atlantic islan d is shown to have not been one of treeless homogeneity. A variety of decid uous and coniferous tree species colonized early in the Holocene, with dist inctive birch-hazel woodland developing at one point in time. The landscape became increasingly treeless in the Bronze Age, with most but not all tree s having been lost by the Medieval period. Valley side peats provide palyno logical evidence of pastoral and arable farming on poor soils in the Dark A ge-Early Medieval period, at sites beyond the present limits of cultivation .