The reconstruction of past forest dynamics over the last 13,500 years in SW Sweden

Abstract

Evidence for unbroken continuity of tree taxa over the last c. 13,500 years is presented from a biodiversity ‘hotspot’ nature reserve in south-west Sweden. Forest composition, continuity, fire and disturbance events are reconstructed using palaeoecological methods. A lake record reveals that Pinus sylvestris, Betula spp., Salix spp., Populus tremula and Hippophae rhamnoides were the initial trees scattered in a semi-open, steppe environment. This developed into forest with Pinus, Betula, Corylus, Alnus, Ulmus and Populus with evidence for frequent fires. Deciduous trees became more significant as fires became less frequent and Quercus, Fraxinus and Tilia expanded. Fire frequencies increased again in the Bronze Age probably associated with anthropogenic use of the forest, and the first Fagus sylvatica pollen was recorded. Burning continued through the Iron Age, but charcoal is briefly absent for a period often referred to as the ‘Late Iron Age Lull’. The forest re-expanded with successions involving Juniperus, but with an altered composition from the earlier mixed deciduous community, to one dominated by Fagus. This is coincident with the first pollen records for Picea abies. The early Holocene mixed forest with frequent low-intensity fires is potentially associated with the greatest diversity of red-listed insect species. Forest continuity and the fragmented reservoir populations of old deciduous trees in the Fagus-dominated forest today are likely to have been critical in preserving the present-day, species-rich, rare epiphytic flora, wood-inhabiting fungi and invertebrate communities. As many of these forest fragments may become more vulnerable with future climate change, tree diversity with some disturbance may become essential for survival of the endangered saproxylic species.