Conifer pollen abundance provides a proxy for summer temperature: evidence from the latitudinal forest limit in Finland

A 23‐year record of pollen deposition (pollen accumulation rates: PARs) indicates that pollen production of the two most common northern boreal conifers – pine and spruce – varies dramatically from year to year and that high and low pollen years show consistency over the whole of northern Lapland. Testing for a calibration between the annual PARs of these two trees and a whole range of meteorological parameters reveals that the highest correlation is between pollen quantity and summer temperature centred around July of the year before pollen emission. Critical mean July temperature limits for the flowering of Pinus and Picea are 12°C and 13°C, respectively. This strong and region‐wide relationship suggests that fossil Pinus and Picea PARs could be used as a proxy for summer temperature. Results are illustrated as maps showing the relationship between forest limits and July temperature and between PARs and the correlation coefficient with July temperature. It is noticeable, however, that although the climate signal is strong at the forest limit of the taxon in question, it is often weaker in the centre of its ecological range. This has implications when interpreting fossil pollen records. Temperature calibrations will vary spatially as the position of the forest limit changes.