Search

1. We test an expectation regarding the phenology of leafing in sapling trees: that the inclination of the terminal shoot from the vertical in species with a flushing type leaf emergence will be greater than that of species with successive leafing. 2. A large inclination of the terminal shoot will minimize self-shading among leaves that emerge simultaneously; this may be an advantage in maximizing carbon gain. A small inclination leads to more self-shading but allows a sapling to attain a greater height within a shorter period; this may be an advantage in situations where shading by adjacent plants is a greater potential problem than self-shading. 3. We observed that the shoot inclination in Tilia japonica and Quercus crispula, which have a flushing type leaf emergence, was more than 30 ° in open, sunlit habitat. In contrast, the shoot inclinations of Betula platyphilla var japonica and Alnus hirsuta, which have successive type leaf emergence, were less than 10°. These observations suggest a functional linkage between leaf-emergence pattern and shoot inclination that can be considered adaptive if selection is maximizing carbon gain by the whole shoot over the growing season.

Leaf longevities of three woody dwarf-shrub species were investigated in relation to the length of the snow-free period in a mountain area in Hokkaido, northern Japan. Leaf longevity of a deciduous species, Sieversia pentapetala, slightly increased with increasing length of the snow free period. In contrast, the leaf life-span of two evergreen species, Phyllodoce aleutica and Rhododendron aureum, decreased with increasing snow-free period. These trends are consistent with a cost-benefit model for leaf longevity as a function of the changing length of the yearly period favorable for photosynthesis. Hence the plastic changes in leaf longevity with varying snow-free periods were concluded to be adaptive traits for maximizing photosynthetic gain for the plants

SUMMARY (1) The growth patterns of tree height and stem diameter in crowded Abies veitchii, A. mariesii and Betula ermanii populations were investigated based on the diffusion model for growth dynamics in size-structured populations. (2) Size-dependent growth was found in each species, but the pattern was different between the species. Small, suppressed individuals of Abies spp. showed little growth in tree height but grew in stem diameter. In small, suppressed individuals of B. ermanii, the converse was found. (3) The diffusion model revealed that stem diameter growth of Abies spp. and tree height growth of B. ermanii are affected only a little by competition between individuals even under crowded conditions, and thus that growth in these dimensions is determined in a genetically strict manner for each species. These growth patterns correspond to the life-history traits and the successional status of Abies spp. (shade-tolerant late-successional species) and B. ermanii (a shade-intolerant early-successional species). (4) This study indicates the quantitative differences of assimilate partitioning between tree height growth and stem diameter growth in size-structured plant populations in relation to the characteristics and successional status of species.

Number of flowers was monitored until fruit maturation of Daphne kamtchatica var. jezoensis, a gynodioecious shrub species in a deciduous broad-leaved forest in Hokkaido, northern Japan, during three seasons from 1986 to 1988. No pollen grains were found in the anthers of female flowers. Pollen grain numbers in the anthers of hermaphrodite flowers ranged from 1000 to 7000 per anther. Fruit sets or ratios of number of ovaries in June to number of flowers in May were significantly higher in females than hermaphrodites. Results of experimental manipulation and hand pollination showed that emasculation with hand pollination as well as emasculation alone raised significantly the fruit set of hermaphrodite flowers. Bagged hermaphrodite flowers produced no fruit, implying self incompatibility. Hand pollination significantly increased the fruit set of female flowers. This indicates that pollination is the limiting factor in fruit set. Only three pollen grains per stigma on an average were found on the stigma of female flowers. More than 200 pollen grains, almost all of which are assumed to be shed by the anthers of own flower, covered the stigma surface of the hermaphroditic flowers. The phenomenon, or clogging by pollen grains of own flower is assumed to be a main factor driving the evolution towards gynodioecy in this species. A model is proposed in which fitness of the female organ inversely decreases while that of the male organ asymptotically increases with the increase of pollen grains, resulting in a bimodal pattern of total fitness explaining evolution of gynodioecism.

(1) Leaf-litter production was investigated from 1973 to 1982 in a plantation of Alnus inokumae. (2) The annual total leaf-fall was relatively constant with a mean of 340 g m-2 year-l except for 2 years when leaf-fall was about 100 g m-2 year-' less due to outbreaks of winter-moth larvae. (3) The seasonal pattern of leaf-fall was bimodal with peaks in summer and autumn in most years. Of the total leaf-fall, 20-35% had occurred by the end of July and 30-60% by the end of August. This summer leaf-fall consisted mainly of the three basal leaves on each shoot. (4) The large summer leaf-fall together with the long period of leaf-emergence are considered to be adaptive to open, mesic sites.