Pollen production of Alopecurus pratensis L., Dactylis glomerata L., Elytrigia repens var. aristata and Phalaris arundinacea were investigated in the central part of Sapporo City from Jun. to Sep. in 2016 and 2017. In order to estimate the number of pollen grains produced per flowering head of one square meter, the numbers of florets per flowering head, of anthers per floret and of pollen grains per anther were counted for four grass plants. The numbers of pollen grains per flowering head calculated using these data were 3.3 × 106 grains for A. pratensis, 9.2 × 106 grains for D. glomerata, 0.7 × 106 grains for E. repens var. aristata and 2.7 × 106 grains for P. arundinacea, respectively. Consequently, the numbers of pollen grains produced per square meter [× 106・m2] were estimated at 4.3 for A. pratensis, 2046.2 for D. glomerata, 26.5 for E. repens var. aristata and 0.3 for P. arundinacea. Pollen　production per flowering head or unit area had lower values in this study, compared to the estimates in previously - measured in Morioka City, Iwate Prefecture. In particular, our result were lower numbers of florets and of pollen grains per anther. Further the number of pollen per anther of the native plant’s P. arundinacea were less than 50% to 60%. It’s also suggesting the strength of fertility of the other three grass plants of alien species. Therefore alien species produces a lot of pollen over a wide area　beyond the suitable area and increases the risk of hay fever.

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Progress of the Cryptomeria japonica pollen front in 2018 (Fig. 1) was monitored by tracking the first day of pollen release using a Durham sampler at 83 sites and an IS-Rotary sampler at 8 sites distributed from Hokkaido to Kyushu. Results from the Durham sampler showed that, in early February, the pollen front had reached northwestern Kyushu and southern Kanto and Tokai. In mid-February, the front reached southern and central Kanto, southern Tokai and Kinki, western Chugoku, and almost all of Kyushu and Shikoku. In late February, the front had moved up to northern Kanto, central Chubu, central and northern Kinki, and eastern Chugoku. By early March, the front was observed in central Tohoku, Hokuriku, and unexpectedly, southern Tokai and northern Chugoku. In mid-March it reached northern Tohoku. The front finally arrived in eastern Hokkaido in late March to early April.

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