Sugi Pollen Disease from the Forester's Viewpoint with Special Respect to Pollen Production in Some Forests

Abstract

Stands of Sugi, Cryptomeria japonica, and Hinoki, Chamaecyparis obtusa, produce 10¹⁴ pollen grains per ha per yr in a productive year and 10¹¹-10¹² grains in an unproductive one. Little year-toyear fluctuation in pollen production by stands of pioneer and secondary trees is evident, the maximum/minimum ratio within a stand being about 2. In comparison, alder stands produce 2-5×10¹³grains in both productive and unproductive years. Pollen production rates of Sugi stands increase with increasing age of the stand until 50 yr, showing a constant upper limit for several hundred years thereafter. With regard to year-to-year fluctuations in pollen production rates for Sugi stands, annual rates alternate from high to low every year. This rhythm may be interrupted by the accidental effects of unusually hot dry weather in late June and July. The amount of pollen dispersed into the air can be predicted from the number of male flower buds that fall before flowering in autumn and winter. Control of pollen production in forests by silvicultural techniques while paying attention to the environmental conservation of forests is considered extremely difficult.