Climate change and the northern Russian treeline zone

The Russian treeline is a dynamic ecotone typified by steep gradients in summer temperature and regionally variable gradients in albedo and heat flux. The location of the treeline is largely controlled by summer temperatures and growing season length. Temperatures have responded strongly to twentieth-century global warming and will display a magnified response to future warming. Dendroecological studies indicate enhanced conifer recruitment during the twentieth century. However, conifers have not yet recolonized many areas where trees were present during the Medieval Warm period (ca AD 800–1300) or the Holocene Thermal Maximum (HTM; ca 10 000–3000 years ago). Reconstruction of tree distributions during the HTM suggests that the future position of the treeline due to global warming may approximate its former Holocene maximum position. An increased dominance of evergreen tree species in the northern Siberian forests may be an important difference between past and future conditions. Based on the slow rates of treeline expansion observed during the twentieth century, the presence of steep climatic gradients associated with the current Arctic coastline and the prevalence of organic soils, it is possible that rates of treeline expansion will be regionally variable and transient forest communities with species abundances different from today's may develop

Palaeoecology of human impact during the historic period: palynology and geochemistry of a peat deposit at Abbeyknockmoy, Co. Galway, Ireland

Understanding the present condition of the cultural landscape requires a palaeoecological perspective with a particular emphasis on the growing intensity of human impact over the last few centuries. Detailed palynological investigations of the uppermost metre of peat at Abbeyknockmoy Bog were supplemented by silicon and titanium analyses to give additional proxy records for the intensity of human impact on the local landscape. The AMS radiocarbon chronology for this profile is constrained by the presence of the Hekla-1 tephra isochron of AD 1104. The palaeoenvironmental evidence correlates closely to the local historical and archaeological records. The results indicate a late Iron Age lull in human impact in the early centuries AD, which is followed by increasing agricultural activity during the early Christian period. The establishment of the Cistercian monastery of Abbeyknockmoy in the twelfth century AD had a significant impact upon the landscape. A peak in deforestation and farming activity is registered in the seventeenth and eighteenth centuries AD. The silicon and titanium records correlate strongly with the pollen indicators for increased human disturbance