A fifty-year record of airborne pollen, collected in Sagamihara, Japan, reveals significant changes in both annual pollen accumulation rate and timing of pollen release of major plant taxa in 1965-2014. Samples have been collected at hospital roof with a Durham sampler. During the period the annual pollen accumulation rate has increased for Cryptomeria japonica, Cupressaceae, Betulaceae, Ulmaceae and Fagaceae; that for Fagaceae has increased dramatically in particular. No specific trend in annual pollen accumulation rate has been found for Pinaceae; annual pollen accumulation rates have had significant positive correlations among tree taxa, except for Pinaceae. Among non-arboreal taxa, annual pollen accumulation rates of Gramineae and Humulus japanicus have not shown any significant trends, except for the Gramineae decline in 1966. However, those for Artemisia have been decreased continuously, and those for Ambrosia increased significantly until 1990s but have decreased gradually since then. For Cryptomeria japonica pollen, the dates of the initial and final pollen observation in a year have become earlier and later, respectively; the total pollen deposition in the fall, which has also a significant correlation to the pollen deposition in the next spring, has been increasing. In recent years, timing of pollen release has become later than before for non-arboreal taxa, such as Artemisia, Ambrosia, and Humulus japonicus. It was suggested that such delays closely linked to global warming. Fifty-year observation made it possible to objectively evaluate a transition of airborne pollen accumulation rate.

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Sydowia japonica is a fungal parasite of the male strobili of Japanese cedar (Cryptomeria japonica). However, knowledge of its impact on the pollen production of C. japonica in natural conditions is limited. We marked 25 branches with dead male strobili by S. japonica. The secondary infection rate was 36% on average of lateral branches that were approximately 40 cm in length. Pollen production was reduced by approximately 50% relative to that of the control.

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The 2016 results from 83 airborne pollen monitoring sites throughout Japan have been compiled and analysed. The data for Cryptomeria japonica, and for Chamaecyparis obtusa, from the 70 sites selected among 83 sites for our study Table 1 include: A) observation date of maximum pollen dispersal, B) the maximum daily pollen count, and C) the total pollen count during the dispersal season. The airborne pollen monitoring data during 2016 are summarized as follows: 1) The western side of Japan, where there are 32 monitoring sites. Here the maximum daily pollen count value (1,520 grains/cm^2) for Cryptomeria japonica was recorded on March 5th in Nagato-City, Yamaguchi Prefecture. While for Chamaecyparis obtusa, 616 grains/cm^2 was recorded on April 6th in Tenri-City, Nara Prefecture. The highest maximum total pollen count value recorded for Cryptomeria japonica was 3,960 grains/cm^2 in ShinguCity, Wakayama Prefecture. While for Chamaecyparis obtusa the highest total pollen count value of 2,171 grains/cm^2 was recorded at Yonago-City, Tottori Prefecture. 2) In the eastern part of Japan, there are 38 monitoring sites. Here the maximum daily pollen count value (1,965 grains/cm^2) for Cryptomeria japonica was recorded on March 8th in Iwaki-City, Fukushima Prefecture. While for Chamaecyparis obtusa, 885 grains/cm^2 was recorded on March 8 at Mibumachi, Tochigi Prefecture. The highest values of the maximum total pollen count for Cryptomeria japonica was recorded as 12,860 grains/cm^2 at Sakado-City, Saitama Prefecture. While for Chamaecyparis obtusa the highest total pollen count value of 5,624 grains/cm^2 was recorded at Ohmeshi, Tokyo.

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