MONITORED POLLEN DEPOSITION, A TOOL FOR CALIBRATING TREE-LINES AND SUMMER TEMPERATURE

As part of the INQUA Holocene Commission Work Group ‘Pollen Monitoring Programme’ (PMP) pollen deposition has been recorded by ‘Tauber type’ pollen traps in a standardized manner at 15 sites in northernmost Fennoscandia over the past 20 years (1982 – 2001). Results are shown for the three major tree species (Betula, Pinus and Picea) for the last six years. These are visualized from the programme’s database: PMPdata using the tool PMPtracker. Pollen deposition is seen to carry a dual signal, depending upon the temporal scale at which it is analysed. Annual variation is related to climate while long term average values are related to the abundance of each tree in the vicinity of the traps. A clear correlation is seen between Pinus pollen abundance and July temperature of the year prior to pollen emission. On the basis of the long term average values of the three tree species it is possible to delimit a pollen deposition threshold for the presence absence of each tree: 500 grains cm-2 year-1 for Betula, 500 for Pinus and 50 for Picea. This can potentially be used to locate tree-lines in the past on the basis of pollen accumulation rates. A comparison of pollen deposition in openings (mires) as opposed to within the forest (records for the last 5 years at another 4 sites) shows that these threshold values only hold good for openings of a certain size. The relationship between pollen deposition and opening size for a regional pine-dominated vegetation belt is demonstrated by using the Prentice model of pollen dispersal. Pinus deposition values from within the forest are used as input to the model and the output is predicted deposition for different sizes of opening. These predictions match the values monitored in such openings, thus given some validation to the model. Acknowledging these spatial and temporal confinements, modern pollen deposition records provide a good tool for more precise interpretations of fossil pollen assemblages in terms of tree-lines and climate.