Holocene stand-scale vegetation dynamics and fire history of an old-growth spruce forest in southern Finland

Abstract

Forest vegetation composition, including dominant keystone species and floristic diversity, is driven by natural and anthropogenic disturbances. Disentangling these complex interactions to identify the role of species competition, climate and disturbances in boreal forest dynamics is challenging. Here, pollen and charcoal data are used to reconstruct Holocene vegetation and fire history at the local stand-scale within an old-growth Picea abies (Norway spruce) forest hollow in southern Finland. The aim is to reconstruct vegetation history with specific emphasis on the mid-Holocene expansion of Picea and the decline in deciduous species in relation to fire history. Early-Holocene forest development and vegetation dynamics are primarily driven by climatic variations. The spread of Picea at approximately 5,200 cal bp does not coincide with local natural or anthropogenic disturbance or a decline in deciduous species and is consistent with its regional expansion, suggesting climate as the most likely control over the late establishment of this taxon. The mid-Holocene decline in deciduous species corresponds to an increased fire frequency suggesting a higher anthropogenic disturbance (also considered as the primary reason for the loss of floristic diversity in southern Finland). The ‘natural’ fire frequency in this local stand-scale boreal forest is lower than that observed in the recent past (i.e. the time of significant anthropogenic impact), yet the present-day absence or low frequency of fire remains within the range of natural variability observed during the early- and mid-Holocene.