The progression of the pollen fronts of Cryptomeria japonica and Chamaecyparis obtusa in 2025 was monitored by tracking the first day of pollen release from these species using a Durham sampler at 78 sites between Kyushu and Hokkaido.

The C. japonica pollen front was first observed parts of northern Kyushu, western Chugoku and southern Kanto from early to late January. By mid-February, it had reached Kyushu, southern Kinki, and most of Tokai and Kanto. By late February, it had extended to most of Chugoku and Shikoku, western Kinki, most of Hokuriku and Tohoku. By early March, it had reached northeastern Shikoku, central Kinki, and parts of Hokuriku and Tokai. By mid-March, it had advanced to the northernmost area in Tohoku and, unexpectedly, parts of northern Chugoku. It ultimately reached Sapporo in Hokkaido between late March and early April.

The C. obtusa pollen front was first detected parts of southern Kanto and Tokai in early March. By mid-March, it had spread to most of Kyushu, western Chugoku, Hokuriku, Kanto and parts of northern Tohoku. By late March, it had reached most of Shikoku, Chugoku, Kinki, Hokuriku, and additional areas of Tokai and Kanto, and northern Tohoku. By early April, it had arrived at the northernmost area of Tohoku, and the western region of Hokkaido. Finally, in mid-April, the front reached a limited area along the coast of Mutu Bay in northern Tohoku.

Background: In the 1970s, Japan saw a sharp rise in people suffering from Japanese cedar pollen allergies. Since then, the Japanese government has been monitoring pollen levels nationwide using a device called the Durham Sampler to help prevent and treat these allergies.

Method of study: We wanted to see how well the Durham Sampler works compared to another pollen-measuring device called the Burkard Sampler (also known as the Seven-Day Recording Volumetric Spore Trap). We collected pollen data using both methods in Fukuoka City from 2012 to 2016, focusing mainly on tree pollen with some grass and weed pollen.

Results: We found that both methods showed similar patterns when measuring pollen levels week by week and day by day and thus both are effective in guiding patient care. However, the Burkard Sampler consistently detected more pollen grains than the Durham Sampler. The difference between the two methods varied depending on the size of grain. The biggest differences occurred with pollen grain that was about 20 micrometres across.

Conclusion: Both the Durham Sampler and Burkard Sampler are useful for monitoring pollen levels. However, as Japan's climate continues to change, use of the Burkard Sampler will be desirable for tracking important allergenic pollen that affects people internationally.

In this study, we verified the predictive accuracy of a new regression model for estimating total Cryptomeria japonica (Japanese cedar) and Chamaecyparis obtusa (Japanese cypress) pollen dispersal by incorporating not only conventional summer meteorological factors but also sunshine duration in June and July, which comprise the floral bud differentiation period. With the old method, the correlation between precipitation and pollen dispersal was almost absent for cedar (r = 0.21) and moderately negative for cypress (r = -0.64). In contrast, with the new method, the correlation between mean monthly sunshine duration in June and July of the previous year and pollen dispersal was strong for cedar (r = 0.83) and moderate for cypress (r = 0.62). The predictive accuracy (coefficient of determination, R2) improved to 0.72 for cedar and 0.56 for cypress. The amount of male cedar inflorescences in Aichi Prefecture also showed a moderate correlation (r = 0.50) with pollen dispersal, suggesting that this factor also contributed. Further improvements in accuracy are expected through approaches that integrate meteorological factors and biological indicators.