Image analysis of charcoal fragments to explore Holocene fire - vegetation dynamics in Northern Europe

Many sedimentary deposits are vital archives of fire-vegetation-climate records. Developing a better understanding of these relationships has relevance to understanding the impact of changes in climatic conditions, such as the increase in summer temperatures that is forecast for the next fifty years and beyond. Charcoal fragments can be used as a proxy for fire events however there is no standard method for their isolation from sediments or standard quantification unit. Many of the fire histories for the U.K. focus on a narrow temporal range and use a variety of quantification units to overcome methodological difficulties in comparing and compiling records. Statistical techniques can be employed to compile records; however, this leads to a reduction in the sensitivity of the data in detecting low impact disturbances such as ground fire and the light impact of early Mesolithic tribes. For this thesis, an image analysis method has been devised and robustly tested through analysis of macrocharcoal fragments. This method is initially used to explore the fire-vegetation-climate history of an upland ombrotrophic bog, Robinsons Moss, Peak District, U.K. in a multiproxy study covering the last 8200 years. The analysis is then extended to determine the local fire history for upland sites in and around the Peak District region using the Landscape Reconstruction Algorithm devised by Sugita (2007 a, b) in an empirical data-driven approach that does not require data transformation of charcoal records and the subsequent loss of sensitivity in the results. Four sites in northern Europe are used to explore the wider spatial fire- vegetation-climate relationships. This is achieved by using the new method for charcoal fragment analysis combined with the quantitative fire – vegetation response technique, redundancy analysis. Results show that the percentage of the variance in the vegetation dynamics explained by fire for sites within the Peak District and also for the sites in Denmark, Germany and Sweden does not exceed 30% for the last 13,500 years. Although fire is not the dominant driver at the sites explored in this thesis, it does have a substantial impact on the vegetation dynamics and soil chemistry. The results from this research implies that climate is more likely to have long-term control over vegetation dynamics at these sites