Net production rates and fruiting strategies of Alnus pendula and A. sieboldiana stands with special reference of pollen production

Net production rates and number sequences of each component of the reproductive organ in stepsflower bud differentiation and seed dispersal were studied in two young stands of Alnussieboldiana (S stand) and A. pendula （P stand）pioneer in xeric succession and with capability of nitrogen fixation. Above-ground net productionrates were 2,100 g/M^2 . yr in 1987 and 1988 for the S stand，and 1200 g/M^2. yr in average between both the years for the P. Leaf biomass of the S was arrivedat the peak after canopy closing，网络production. Both the production rates in the S and P on a detrius lack inorganic soils are considerably greater than that of deciduous forests on organic soils，and equal to that of Sugi and evergreen broadleaf ones. The production rates of The reproductiveparts including pollen were 50 - 130g /M^2 . yr，in which seeds occupied only 10% . The low distribution of seeds among dry-matter production of Therepoductive components is profitable for the repoductive strategy of pioneer. No remarkable yearlychanges during 1986 - 1988 were recognized in the number sequences in the S and P，它可以affected by small yearly ones of seeds production. The number of pollen grainsneccessary for the formation of a seed was 500,000 in the S，and 200,000 in the P. in the young S stand，total female strobiles of 70 - 80% were fallen before ripe. In the mature P stand，fruit abscission percentages in 1986 and 1988 were 10%，while in 1987, was as high as 45% due to the spell of rainy weather in flowering period。

Net production rates and number sequences of each component of the reproductive organ in steps between flower bud differentiation and seed dispersal were studied in two young stands of Alnus sieboldiana (S stand) and A. pendula (P stand), pioneer in xeric succession and with capability of nitrogen fixation. Above-ground net production rates were 2,100 g/M^2・yr in 1987 and 1988 for the S stand, and 1,200 g/M^2. yr in average between both the years for the P. Leaf biomass of the S was arrived at the peak after canopy closing, which raised the net production. Both the production rates in the S and P on a detrius lack in organic soils are considerably greater than that of deciduous forests on organic soils, and equal to that of Sugi and evergreen broadleaf ones. The production rates of the reproductive parts including pollen were 50 - 130 g/M^2・yr, in which seeds occupied only 10 %. The low distribution of seeds among dry-matter production of the repoductive components is profitable for the repoductive strategy of pioneer. No remarkable yearly changes during 1986 - 1988 were recognized in the number sequences in the S and P, which can be affected by small yearly ones of seeds production. The number of pollen grains neccessary for the formation of a seed was 500,000 in the S, and 200,000 in the P. In the young S stand, total female strobiles of 70 - 80% were fallen before ripe. In the mature P stand, fruit abscission percentages in 1986 and 1988 were 10%, while in 1987 that was as high as 45% due to the spell of rainy weather in flowering period.