Change in the northward movement of the pollen front of Cryptomeria japonica in Japan, during 1986-1991.

A map of pollen fronts of Cryptomeria japonica was compiled from pollen counts taken at 28 airborne sampling sites in Japan in 1986. Thereafter, the number of sites was increased, reaching 80 in 1991. In this way an accurate and complete map of the C. japonica pollen fronts was compiled annually. We used the results obtained from mapping the pollen fronts to draw up a map of the average locations of the front, from which the beginning of the pollen season can be predicted. A close correlation was found between the latitude of the airborne sampling sites and the mean interval between January 1 and the day pollen release began during these 6 years.