TEMPORAL AND SPATIAL VARIATION OF AIRBORNE SCOTS PINE (PINUS-SYLVESTRIS) POLLEN

The occurrence of airborne Scots pine pollen was continuously monitore d with Burkard traps at five locations situated along a 1000 kilometre transect in Finland during the ten-year period 1982-1991. The variati on between years in airborne pollen dispersal was significant. The pol len season (defined as 10% of the cumulative pollen count for the year ) began in South Finland, on average, on June 1st, and in North Finlan d 24 days later. The length of the mean local pollen season was 11 day s, increasing towards the north. On average over 21% of the total poll en count of the year was caught on one single day. The temperature sum s (d.d. >+5-degrees-C) required for the start of the pollen season dec reased almost linearly from 193 d.d. in the south to 132 d.d. in the n orth. However, in several years the pollen seasons overlapped between sites at a distance of 500 km or more. The temperature sum on June 1st explained over 80% of the variation in the onset, median and end of t he pollen season in Finland.