Sexual reproduction in a Castanopsis cuspidata stand in relation to annual yield of reproductive organs

In a mature stand of Shii chinkapin (Castanopsis cuspidata Schottky) at Matsuotaisya shirine, Arashiyama, Kyoto, annual production rates of reproductive organs were studied using 20 litter traps (each 50 cm * 50 cm in mouth area) in 1986-1989, and those of pollen were estimated by multiplying the number of fallen male catkins per ha per year by the mean amount of pollen per catkin before anthesis. The main results were as follows. The pollen production rate of 218-359 kg d.w. ha(-1) yr(-1) was one of the highest among other species, and that of 64.2-103-10(12) ha(-1) yr(-1) was by far the largest number; moreover, these showed small year-to-year fluctuations. Such a huge number of pollen grains, however, was balanced by the number of ovules in a stand (numerical ratio of pollen grains to ovules: 4.1-8.3 * 10(5)). The light pollen grains (1.94-4.30 * 10(-6) mg d.w.) save the assimilation products invested in pollen formation. Dry matter of reproductive organs by the year of anthesis was within the range 1609-1803 kg d.w. ha(-1), and those of male and female parts were inversely proportional to each other. Annual production rates were within the range 1237-2204 kg d.w.ha(-1) yr(-1), equivalent to values in years of average to poor seed crop. There was no relationship between the annual production rates (by weight) of male and female parts, because fruit maturation requires two growing seasons. In three years among four, the 0- and 1-yr-old parts showed equal dry weight allocation. Seed-maturing ratios or numerical ratios of mature nuts to total female flowers were small (5.5% -10.6%), being approximately equal to those of other species. The year-to-year trend in nut production (by number) prarallelled those of seed-maturing ratio and the number of female flowers. Mean nut weight vs. assimilation products necessary for producing a single nut, calculated by dividing the dry-matter production rate of overall parts by the number of nuts, was 1:3 in a year with an average seed crop, and 1:6 in a year with a poor crop. This seed production efforts was similar to those of five other barachorous species