The distribution of Tilia cordata and variations in the composition of the forests in upper Swaledale and Wensleydale during the Atlantic period

Abstract

The thermal maximum of the Flandrian period was reached between 7500 B.P. and 5500 B.P. when the broad-leaved thermo- philous forests reached the furthest northern limit of their range in Britain. Tilia cordata is regarded as the most thermophilous of the North European deciduous trees. The distribution of T.cordata at 5000 B.P. (3000 B.C.) has been documented for North England although data has not been available for parts of the Central Pennines in Yorkshire, north of Settle. Pollen analysis of peat deposits in Swaledale and Wensleydale at altitudes from 480m to 590m O.D. shows that T.cordata was present at a frequency of 1% in this area during this period. The Atlantic period forests were composed mainly of Ulmus, Quercus and Alnus, with Betula, Pinus, Tilia and Fraxinus and the shrubs Corylus and Salix. The relative abundance of these genera varied at any one place and from place to place during the 2000 years. Pollen diagrams have been prepared for nine sites for the Atlantic period, pollen assemblage Zone VIIa in the terminology used by Godwin. The pollen diagrams include tree and shrub pollen only. Fagus was represented by scattered grains and has not been included. Multivariate analysis of the tree and shrub pollen data has been made. The variance between the nine sites is greater than the variance within one site. The major source of the variation does not appear to be linked with the lithology of the sites.