Summary0 Acer mono is one of the earliest germinating species in hardwood forests of northern Japan[ To evaluate the advantage of early germination for the seedling establishment\ di}erences in the temporal pattern of leaf development between the seedlings and overstorey trees were investigated\ together with the timing of dry mass gain and allocation\ survival and mortality agents of seedlings[ These traits were contrasted at four sites with di}erent types of foliage phenology in the overstorey trees "FU!0 and FU!1\ forest understorey in which overstorey trees unfolded and shed the leaves as ã ush and succeedingly\ respectively^SG\ small gaps^and FE\ forest edge#[ 1 Seasonal growth patterns of the seedlings were greatly a}ected by the di}erences in the coupling of leaf development between the seedlings and the overstorey trees[ For early germinating cohorts of Acer mono\ 68\ 50\ 49 and 42) of annual dry mass gain occurred within 1 months of germination\ in FU!0\ FU!1\ SG and FE\ respectively[ After this point "canopy closure# mass increment decreased abruptly in both FU sites\ but continued to increase in both SG and FE[ Seedling mass\ however\ increased after September again in FU!1 but not in FU!0\ mainly due to earlier leaf shedding of the canopy trees in FU!1[ 2 After canopy closure\ leaf mass ratio was greatest in FU!0 where light was most limited\ but lowest in FE[ In contrast\ root mass ratio was greatest in FE but lowest in FU!0 where soil moisture was most abundant[ These traits might lead to the optimization of growth by making all resources equally limiting even after canopy closure in forest understorey[ 3 Higher seedling survival resulting from early germination was observed in all four sites\ since predators and pathogens selectively attacked late germinating individuals[ The advantage of early germination was greater in both FU!0 and FU!1 than in FE\ mainly due to large di}erences in available light for early vs[ late germinating indi! viduals in both FU sites compared with the FE site[ 4 These observations suggest that phenological traits of A[ mono such as rapid ger! mination in early spring and earlier deployment of leaves compared with overstorey trees has been selected to maximize annual mass gain and survival in understorey habitats of deciduous broad!leaved forests[ Keywords] causes of mortality\ biomass allocation\ RGR\ light\ shade avoidance Journal of Ecology "0887# 75\ 108Ð117

Effects of seed size and phenology on the establishment of five deciduous broad-leaved tree species were examined in deciduous woodland. Treatments included absence and presence of litter in the forest understory, a small gap, and a large gap. Seedling emergence of large-seeded species Quercus mongolica var. grosseserrata and Acer mono was not reduced by accumulation of litter in the forest understory, but was promoted in the large gap where litter was less. Seedling emergence of small-seeded species, Alnus hirsuta, Cercidiphyllumjaponicum and Betula platyphylla var. japonica, was reduced by the litter in almost all of the sites. Seedlings of large-seeded species avoid shade stress phenologically by unfolding all of their large leaves in a short period before canopy closure in the forest understory. These species had little mortality after seedling emergence. In contrast, small-seeded species have a longer duration of leaf emergence, shorter leaf longevity, and rapid leaf turnover in all the sites. These seedlings attained similar height to those of the large-seeded species at the end of the second year in the large gap, but survival and height growth rate decreased after canopy closure in the forest understory. We suggest that the importance of seed size in determining seedling establishment largely depends on the relationships between seasonal changes of environmental conditions and phenological traits of seedlings, which are related to seed size.

Summary1 Sasa spp., dwarf bamboo which dominate the undergrowth of temperate forests in Japan occur as clonal fragments in which ramets in light gaps to are connected to those in shaded understoreys by long rhizomes. We test whether persistence under shaded conditions is supported by translocation of assimilates from illuminated ramets. A dense population of Sasa palmata growing at an open site, was exposed to two light conditions (homogeneous: open-open and heterogeneous: open-shaded) and two rhizome connection treatments (intact and severed) in a full factorial design. 2 Ramet mass, and the mass of many parts of the clonal fragments, was much lower in the shade than in the open, but this effect was less marked when the rhizome connection was intact than when it was severed. Clone parts in shade may therefore be supported by translocation from connected clone parts in the open, with such physiological integration enhancing persistence where light supply is heterogeneous as in the gap -understorey continuum. 3 Above-ground biomass was reduced sooner than that below ground. Clonal fragments of S. palmata recover via dormant buds on rhizomes, whose longer persistence would therefore enhance performance of the clonal fragment. 4 Specific leaf area (SLA) was greater in shade than in the open, irrespective of rhizome connection, suggesting that individual leaves show morphological plasticity independently of only physiological integration.

To evaluate the importance of developmental constraints in the determination of the relative importance of seed size and emergence time, early seedling performance of two woody species with contrasting growth phenology were observed under competitive conditions with tall herbs in an early successional habitat. The oak, Quercus mongolica var. grosseserrata, with determinate shoot development (a single leaf flush), showed a marked influence of seed size on subsequent seedling height growth and survival. Because of determinate growth, emergence time had negligible effects. The walnut, Juglans ailanthifolia, which continued to produce new leaves throughout the growing season (indeterminate development), showed a marked influence of time of emergence on seedling performance, because it affected the amount of growth that could be achieved; seed size, however, had negligible effects as the seedlings grew. These results suggest that relative importance of seed size and emergence time for early seedling performance is closely associated with developmental constraints (growth phenology).

We evaluated the degree of selfing and inbreeding depression at the seed and seedling stages of a threatened tropical canopy tree, Neobalanocarpus heimii, using microsatellite markers. Selection resulted in an overall decrease in the level of surviving selfed progeny from seeds to established seedlings, indicating inbreeding depression during seedling establishment. Mean seed mass of selfed progeny was lower than that of outcrossed progeny. Since the smaller seeds suffered a fitness disadvantage at germination in N. heimii, the reduced seed mass of selfed progeny would be one of the determinants of the observed inbreeding depression during seedling establishment. High selfing rates in some mother trees could be attributed to low local densities of reproductive individuals, thus maintenance of a sufficiently high density of mature N. heimii should facilitate regeneration and conservation of the species.

No abstract

Summary1. The female-biased sex ratio in the genus Salix is widely documented, but little is known about the ecological mechanisms causing this bias. We investigated the flowering sex ratio, population dynamics, clonality and spatial segregation of the sexes in three Salix sachalinensis populations of different ages (young, intermediate and old) for a total of 2922 trees over 3 years. 2. Spatial segregation of the sexes did not occur in any of the populations. 3. Flowering sex ratios were female biased (2 : 1) in both the intermediate and old populations, but were slightly male biased in the young population. The female-biased sex ratios in the mature populations were due to the increasing number of flowering females with increasing plant size, but not to differences in demographic parameters; neither mortality nor growth rate differed between the sexes in any population. 4. Amplified fragment length polymorphism analysis revealed that there were very few clonal individuals in any population, suggesting little effect of clonality on the biased sex ratios. 5. These results suggest an initially and inherently determined female-biased sex ratio in mature S. sachalinensis populations.

To examine whether the Janzen-Connell mechanism applies to temperate forests, seedling survival and causes of mortality were investigated at two distances (beneath, far) from conspecific adults and at two densities (high, low) at each distance for seedlings (n = 7935) of eight tree species co-occurring in a hardwood forest. Six of the eight species showed distance-and/or density-dependent seedling mortality mainly caused by diseases and rodents. In four of the five species primarily killed by disease (i.e. damping-off, blight, rot, powdery mildew), the infectivity (probability of infection by the disease) and/or the virulence (proportion of seedlings killed to those infected by the disease) were higher beneath than far from conspecific adults. These findings suggest that host specificity and/or spatially heterogeneous activity of natural enemies play an important role in the reciprocal replacement of tree species, maintaining species diversity in temperate forests.