Holocene fire and vegetation dynamics in the northern European forests

• Main Author: Clear, Jennifer
• Other Authors: Bradshaw, Richard, Marrs, Rob
• Format: Text
• Language: English
• Subjects: Norway; Fennoscandia
• Online Access: http://livrepository.liverpool.ac.uk/16593/; http://livrepository.liverpool.ac.uk/16593/1/Clear_J_THESIS_FINAL.pdf; http://livrepository.liverpool.ac.uk/16593/4/ClearJen_Nov2013_16593f.pdf

Fire has not always been so elusive in the northern European forest yet forest management and active fire suppression has created an ecosystem almost free of fire. This absence of fire is thought to have contributed to the widespread dominance of Picea abies as well as the decline in deciduous species and subsequent loss of floristic diversity. Forest fires in general are driven by a complex interplay between natural (climate, vegetation and topography) and anthropogenic disturbance and through palaeoecology we are able to explore spatio-temporal variability in the drivers of fire and changing fire dynamics. This thesis explores spatial and temporal variability in Holocene vegetation and disturbance dynamics through stand-scale palynology. Pollen and macroscopic charcoal are used to reconstruct past vegetation and fire dynamics with local- and regional-scale pollen-derived quantitative vegetation reconstructions able to identify both large-scale ecosystem response and local-scale disturbance. Spatio-temporal heterogeneity and variability in biomass burning is explored to identify the drivers of fire and palaeo-vegetation reconstruction is compared to process-based, climate-driven dynamic vegetation model output to test the effect of fire frequency as a driver of vegetation composition and dynamics. Early-Holocene fire was driven by natural climate variations and fuel availability. The establishment and spread of Picea abies (Norway spruce) appears to be driven by an increase in continentality although local disturbance cannot be ruled out. The expansion of Picea led to a step-wise reduction in regional biomass burning and the now widespread dominance of Picea abies is responsible for the low fire frequency observed through Fennoscandia. The mid-Holocene decline in deciduous species was primarily driven by localised anthropogenic disturbance and may have been assisted by the shift to cooler, wetter climate conditions. There is an underlying natural fire frequency of approximately 400 years observed in southern Finland and without intensive anthropogenic disturbance floristic diversity may have remained locally, to the present day. Stand-scale palynology is able to record past local disturbance at a high spatial precision however more than one site is required to understand regional disturbance and the variable controls of fire dynamics.