Abstract
Pollen production rates were investigated in about ten-year-old Alnus firma stands in 1991. The number of pollen grains contained in male catkins was measured using a microscope. The dry weight of pollen grains contained in male catkins was measured by collecting pollen grains with pollination bags. Pollen production rates in stands were estimated from the number of fallen male catkins which were collected by litter-traps. One male catkin contained ten million pollen grains. The percentage of pollen dry weight to the dry weight of male catkins after pollen dispersal was 35.4% on an average. It was estimated that a young A. firma stand produced 126.5kg and 1.66×10^<13> pollen grains/ha・yr. Also it was estimated that individual trees ranging from 2.1cm to 9.5cm in breast height diameter produced 1.02〜39.74×10^9 pollen grains.
