Abstract
Changes in the pollen accumulation rate (PAR) of Cryptomeria japonica during the last 100 years were reconstructed based on pollen analysis of a sediment core from Lake Biwa dated by Pb-210 and Cs-137 methods. A comparison of the increases in the Lake Biwa PAR data with pollen data from afforested areas of C. japonica, planted during the 1950s, showed notable correlation. Before 1900, the PAR for C. japonica in the Lake Biwa sediment showed relatively low amounts of pollen, 900-1400 grains・cm^<-2>・year^<-1>. After 1900, the PAR increased slightly and, from 1920 to 1970, increased to between 2800-3700 grains・cm^<-2>・year^<-1>. From 1970 until the late 1970's the PAR increase continued, reaching 4200-4400 grains・cm^<-2>・year^<-1>, and further increasing by the early 1980's to 6300-7100 grains・cm^<-2>・year^<-1>. From the late 1980's and into the 1990's, the PAR showed a rapid increase from 8300 to 13400 grains・cm^<-2>・year^<-1>. Comparison of the results of the PAR data from Lake Biwa with estimated data for the mature afforested area of C. japonica suggests that recent increases of airborne pollen of C. japonica have, since the 1950's, been strongly influenced by cultivated forests of C. japonica. The PAR for the Lake Biwa sediment was also consistent with airborne pollen records of years with abundant C. japonica pollen dispersal. Notably, a comparison of the recent PAR data with a pollen analysis of sediment cores from Lake Biwa during the Quaternary period shows the quantities of C. japonica pollen during 3000-2000 cal yr BP, and during the second half of the last interglacial period, to be similar to those of PAR data after the early 1980's.
