Pollen analyses from the deposits of six upland tarns in the Lake District

Abstract

The first part of an investigation designed to cover most of the tarns of the English Lake District is described. This investigation was planned as an application of the techniques of Quaternary research to a detailed analysis of the late-Quaternary history of a single limited area which forms a clearly defined geographical region. The primary concern of the investigation is the relationship between stratigraphy and pollen content of the lake deposits, in an attempt to reconstruct the history of deposition in each tarn in relation to late- and post-Glacial changes in climate, and consequent changes in soil and vegetation in the drainage basins. In the account of pollen analysis of the sediments of six tarns at various altitudes in the south-western quadrant of the Lake District, comparisons between these various pollen diagrams from a fairly small area serve to emphasize the contrast between those widespread regional changes due to climatic change on which the pollen zonation is based, which are common to all the diagrams, and local changes due to local topography and human history, which differ in a consistent way from one tarn to another. The differences between the late-Glacial deposits of the six tarns are related to topography, and the probable limits of the last corrie glaciation of the Lake District. Evidence from pollen analysis suggests very strongly that in the early post-Glacial period forest extended over the Lake District hillsides up to the altitude of the highest tarn investigated (1800 ft.). The first indication of disturbance of the primary forest occurs at the zone boundary VIIa/bthe elm decline (which, as Godwin showed in his Croonian lecture of 1960, has been established to be broadly synchronous in north-west Europe atca. 3000 B.C.). Evidence is put forward suggesting that destruction of the elm in the Lake District during the early Neolithic period was particularly pronounced round tarns near to the sites of the stone-axe factories. The next phases of forest clearance are shown to be most clearly demonstrated in those tarns around which are abundant remains of upland settlement of Bronze Age type. The relation between the successive phases of forest clearance, post-Glacial soil degradation, peat formation and soil erosion is discussed, in relation to chemical investigations by F. J. H. Mackereth (at the Windermere laboratory of the Freshwater Biological Association) which suggest that the lake deposits are derived mainly from soils in the drainage basins.