DEFORESTATION, CANNABIS CULTIVATION AND SCHWINGMOOR FORMATION AT CORS LLYN (LLYN MIRE), CENTRAL WALES

Abstract

SummaryPollen and macrofossil diagrams from the schwingmoor sediments of Llyn Mire are presented. Prior to the formation of the schwingmoor, Cannabis sativa was cultivated around Llyn lake, first to the east and later to the west of the basin. Despite Cannabis cultivation so close to Llyn, there is no evidence to suggest that the lake was used for retting purposes.A period of woodland clearance occurred immediately after the Cannabis cultivation and this process may have been responsible for the changes which led to schwingmoor formation in the basin. It is suggested that increased soil erosion into the lake, together with some eutrophication, encouraged the colonization of the lake surface by a floating mat of vegetation. The schwingmoor was formed in historic times by a floating carpet of such taxa as Carex rostrata, Sphagnum recurvum and Sphagnum section Subsecunda. The mat was initiated in the western part of the basin.The use made of Cannabis/Humulus pollen density as a marker horizon in these studies demanded that these pollen taxa should be adequately separated, and the large numbers of grains of this type present in the sediments permitted the employment of numerical methods based on pore protrusion, which are described here.