Holocene expansion of the Caledonian pinewoods: spatial and temporal patterns at regional and landscape scales

Background To facilitate climatic change adaptation, landscape and conservation managers require understanding of spatio-temporal patterns of expansion of potential dominant species. Studying past expansions of canopy-dominant trees can contribute such understanding. Aims Test hypotheses about expansions of dominants using as a model the mid-Holocene expansion of forests dominated by Pinus sylvestris in the Scottish Highlands. Methods Pollen analysis and radiocarbon dating of Holocene sediments of a larger basin and several small hollows were performed in three landscapes along a north-south transect. A larger basin records expansion timing at landscape scale, whilst small hollows evidence within-landscape spatio-temporal patterns. Results Vegetation existing prior to the expansion of pinewoods influenced landscape-scale spatio-temporal expansion patterns of P. sylvestris. Open vegetation generally was invaded earlier and/or to a greater extent; invasion was often later, or did not occur, where woodland with a substantial temperate broadleaved tree and shrub component (e.g. Corylus avellana, Quercus spp.) was present. Most small hollows, not just those where pinewoods became locally established, recorded vegetation change during the expansion. Some present landscape-scale forest composition patterns were established at that time. Conclusions Studying past expansions of dominants provides evidence relevant to planning conservation and landscape management to facilitate ecological adaptation as species adjust their distributions and abundances in response to climatic change.