Abstract
The production rates of pollen, male catkins, female strobili and seed cones in a 26-year-old Alnus sieboldiana stand, planted on the site of an old landslide in a Sugi and Hinoki plantation, were studied in 1987 and 1988. These rates, in terms of number and dry weight on an area basis, were measured using litter traps. Male catkins from four trees in the study stand were sampled on suitable dates before pollen release. Number of bracts per catkin, number of stamens per bract, and number and dry weight of pollen grains per stamen were measured, and pollen yields per catkin were estimated by multiplying the mean values for the trees. Mean pollen quantities per catkin were 22.34×10^6 grains and 227.3mg in 1987, and 19.47×10^6 grains and 180.9mg in 1988. The dry weight of a single pollen grain, obtained by dividing the weight by the number of pollen grains per stamen, was 10.29×10^<-6>mg in 1987 and 9.41×10^<-6>mg in 1988. Pollen production rates, obtained by multiplying the pollen yield (by number and dry weight) per catkin by the number of open male catkins per ha, were estimated to be 40.5×10^<12> grains/ha and 412kg/ha in 1987, and 35.1×10^<12> grains/ha and 326kg/ha in 1988. The mean numerical ratio of pollen grains to ovules (P/Ov ratio) for the two study years was 120×10^3. The dry-matter production rates of male components were 829.5kg/ha in 1987 and 755.6kg/ha in 1988, and pollen allocations reached 49.7% and 43.2%, respectively. The investment of photosynthates in reproduction or the mean dry-matter production rate for male plus female components was 1,035.9kg/ha, among which pollen allocation reached 35.7%.
