Effects of climate change on Cupressaceae pollen grains in Japan

In Japan, the number of people with Japanese cedar (JC) pollinosis has increased since the 1970s. We have detected allergenic airborne pollen grains since 1987, when the govern- ment started to investigate JC pollinosis for treatment and prevention. We have studied im- portant allergenic pollen grains, Cupressaceae (JC and the Cypress family), and their cor- relations with climatic factors, for about 30 years at nine locations. Pollen grains are collected by the gravitational method. They are counted, classified, and summarized every year. From 1987 to 2021 (at latest), we have analyzed annual pollen grains counts with ref- erence to the meteorological conditions near the nine monitoring locations. Cupressaceae pollen counts have marked annual fluctuations and increase. They have a significant positive correlation with climatic conditions when the male flower buds are formed, the pollination starting days in the North regions have become earlier, and they have a negative correlation with February mean temperature. Over the 30-year period, pollen grains counts have mostly increased. The pollination season has gradually come to start at the same time throughout Japan because of the earlier start of the season in northern Japan, as a result of climate change, particularly the rise in temperature. We consider that one of reason for the increase of JC pollinosis is that climate change may be affecting Cupressaceae pollen grains counts, with counts increasing in the areas of conifer-forest with trees older than 30 years with an- other reason being the earlier start of the JC pollen season in the north of Japan.