Analysis of late-glacial and Holocene rates of vegetational change at two sites in the British Isles

Rates of vegetational change are analysed from pollen records of sediment sequences at Loch Lang, Western Isles, Scotland, and Hockham Mere, Norfolk, England. Comparisons are made between rates of change calculated from eight dissimilarity coefficients, with unsmoothed and smoothed data, and with timescales based on radiocarbon and calendar years. The most useful coefficient overall was found to be a χ² - 2 dissimilarity coefficient. The effect of smoothing is variable, depending in part on the dissimilarity coefficient, and so results based on smoothed data need to be compared with results from unsmoothed data. Calibration makes little difference to rates of change from Holocene samples, except during the earliest 500 years of the Holocene. Rates of change at the two sites are compared using a χ² dissimilarity coefficient. A period of rapid change is seen at the end of the last glaciation, and it occurs at a higher rate at Hockham Mere than Loch Lang. At Loch Lang, there is less abrupt, more continuous change throughout the Holocene. No other periods of change are apparently synchronous at the two sites and caused by the same factor.