Takashi Kohyama

Size-structured tree populations in gap-dynamic forest: the forest architecture hypothesis for the stable coexistence of species

The forest architecture hypothesis of tree species coexistence proposed here was developed from a general model of size-structured tree populations in gapdynamic rain forest. The model consists of a submodel describing the dynamics of the age distribution of local stands, which reflects gap-dynamic processes in a whole forest, and another describing the change in size distribution of trees in stands of each age. The model expresses the dynamics of both species-averaged systems and multi-species systems. In the model, the intensity of suppression of tree size growth, survival and seedling recruitment is a function of local crowding. Crowding is measured in each stand in terms of the cumulative basal area of trees of all species that are larger than the subject individual, while the potential rate of seedling recruitment is proportional to the basal area of mother trees in a whole forest (...)

Significance of allometry in tropical saplings.

Differences in allometric relationships of understorey saplings (60-300 cm tall) between nine common shade-tolerant species of subcanopy, canopy and emergent trees were examined in an old-growth foothill rain forest in West Sumatra, Indonesia. Interspecific variation was found in the intercept of the regression line between logarithmic dimensions but not in the slope. Detected interspecific differences could be interpreted as a result of a trade-off between height growth (for future exploitation of better-lit conditions at higher levels in the canopy) and leaf area extension (for current exploitation of poor light nearer the base of the canopy). Saplings of emergent Swintonia schwenkii Teijsm. & Binn. ex Hook. f. favoured height growth rather than expansion of assimilative area. Trends of interspecific differences in sapling allometry in tropical rain forest were similar to those in warm-temperate rain forest. Tropical saplings had more slender trunks and greater total leaf area at a given height than warm-temperate saplings, but dry weight proportions among organs were similar. We hypothesize that the advantage of maintaining assimilative area in present height is diminished in a habitat with higher growth rate and/or steeper vertical light gradient such as in

Size-structured multi-species model of rain forest trees

On the basis of permanent plot research in a warm−temperate rain forest in southern Japan dominated by evergreen broad-leaved trees, a multi-species model of size-structured tree populations is proposed, which takes into account the effect of one-sided competition. The strength of the density effect due to one-sided competition for light on a forest tree of a given size is expressed in terms of the cumulative basal area of trees irrespective of species larger than this tree in the forest stand (...)

Tree species stratification in relation to allometry and demography in a warm-temperate rain forest

1 We studied stratification of tree species by analysing the allometry and demography of 14 abundant species in a warm-temperate rain forest on Yakushima Island, southern Japan. 2 We regressed relationships between trunk diameter at breast height (d.b.h.) and top height of trees using an expanded allometry which incorporates an upper limit to height. As trees grew up towards the canopy, individuals with the same d.b.h. were taller if they came from species with larger maximum height. This appeared to reflect a trade-off between height growth and lateral growth of crowns. Two canopy dominants continued to gain in d.b.h. after they had reached the canopy, while their height remained almost constant. 3 We examined size-specific patterns of relative growth rate of d.b.h. from a decade of field censuses. By fitting a Gompertz-type growth curve to size-specific growth of individual trees, we derived a projected potential maximum size for each species. The projected maximum size (both d.b.h. and height) was similar to the observed value for most species. Three canopy species exhibited larger projected maximum d.b.h. than observed values; the difference seemed to be due to mortality during the long period that each of these species resides in the canopy. 4 Understorey species recruited equally well as larger-growing species amongst the 14 studied species, although their tree mass increments per unit time were smaller. This suggests that understorey species have more effective recruiting capacity relative to vegetative growth.

A functional model describing sapling growth under a tropical forest canopy

The consequence of the trade-off between trunk growth and crown growth in understorey saplings is examined using a simple growth model. The model is based on published findings of interspecific variation in allometric relationships of saplings of shade-tolerant trees, their physiological parameters, and the light environment under forest canopy in south-east Asian tropical rain forests. All interspecific differences in allometries are described to reflect the difference in the allocation of dry weight between trunk stem and branch stem. In the model, branchdeveloping saplings have greater above-ground weight, larger trunk diameter, wider crown area and lower leaf area density at the same height than trunk-developing saplings. The model calculates the architecture-specific sapling growth rate, applying a classic canopy photosynthesis model to express crown photosynthesis, taking into account the self-shading within the sapling crown. Results show that the optimal allocation which maximizes sapling height growth rate for the understorey light environment is within the observed range of allocation in saplings of shade-tolerant tree species. It is proposed that fluctuation of the understorey light condition in time and space brings about the allometric variation among coexisting saplings. Key-words: Allocation, allometry, branching architecture, growth model, light environment, saplings, simulation, tropical rain forest

Regeneration and coexistence of two Abies species dominating subalpine forests in central Japan

SummaryThe mechanism of coexistence of the dominant firs Abies veitchii and A. mariesii is described in relation to regeneration patterns for climax subalpine forests of the northern Yatsugatake Mountains, central Honshu, Japan. Two mature stand types, pure conifer stands of Abies spp., and mixed stands of Abies spp. and hardwoods (mainly the birch Betula ermanii), are distinguished. Pure stands are likely to show simultaneous decay, followed by evenaged regeneration of stand-floor seedlings (<20 cm tall), Rapidly growing A. veitchii dominates over A. mariesii in this type of regeneration, which is occasionally invaded by light-demanding Betula. In constrast, mixed stands degenerate rather slowly, followed by the regeneration of Abies from the bank of suppressed saplings (>20 cm tall), which persist only in mixed stands. The more shade-tolerant A. mariesii is supeior in this type of regeneration, while Betula does not succeed, and mixed stands change to pure stands with time. The fact that two patterns of Abies regeneration occur in a certain ratio in the forest is what enables the two Abies species to coexist. A simple dynamical system model supports this conclusion.

The effects of a typhoon on Japanese warm temperate rainforests

A powerful typhoon (Typhoon No. 13) affected stands of primary warm temperate rainforest in Yakushima, southern Japan, in 1993. Censuses in three sites 1–5 months after the typhoon showed low levels of mortality resulting from the typhoon (0.4–3.0% of stems). Stems killed by the typhoon were generally larger than surviving stems. Among surviving stems there were generally low levels of damage (e.g. 0.5–1.3% of surviving stems lost crowns) and not all damage was widespread (e.g. defoliation was apparent only in one of three sites). The sizes of uprooted stems, stems that lost crowns and relatively undamaged stems were not different. Different species appeared to be damaged in different ways at different sites. Damage was most evident in higher altitude seaward sites but gap formation was more frequent in lower altitude sites near valley floors. After the typhoon the resultant gap area occupied 9.4% of one site and 8.6% of another, which is greater than that before the typhoon. Fresh sprouts were found on 17.35% of 2161 stems after the typhoon, including many apparently undamaged stems as well as those that were damaged. Species which sprouted most frequently were those that regenerate by seed least frequently in these forests; these species may maintain their relative abundance in part by sprouting. Most tree species in these forests may be relatively resistant to typhoons and there may be more opportunities for their regeneration following gap formation caused by the typhoon.

Below- and above-ground allometries of shade-tolerant seedlings in a Japanese warm-temperate rain forest

A comparative study has been made of the allometric relationships among below-ground and above-ground dimensions of seedlings (6.5-27 cm tall) of 14 abundant shade-tolerant species taken from the forest floor in a warm-temperate rain forest on Yakushima Island, southern Japan. The allometric lines between below-ground dimensions are significantly different between species, which reflects the differentiation between the species developing tap-roots and those developing horizontal fine roots in the same forest. The difference correlates with a difference in seed size, but not with height at maturity or habitat (ridge vs slope or gully). It is hypothesized that the differences in root architecture are related to «choices» in microsite for establishment, the large-seeded tap-rooted species being better suited to soft soil and deep litter, and the small-seeded lateral rooters to rocky soil and a lack of litter (...)

Studies on theAbies population of Mt. Shimagare

The survivorship curve is estimated for theAbies population of the subalpine wave-regenerated forest on Mt. Shimagare in the northern Yatsugatake Mountains, Central Japan. The repetition of decay and regeneration of nearly even-aged stands is the nature of this forest in a steady-state, so that the survivorship curve is given as the decrease of density with stand age. Four distinct stages are recognized on the curve. The mortality is high in the first 10 years (stage i). Though germination is observed from the floor under dense canopy to the forest edge, only a portion of the seedlings can survive and form a nearly even-aged young regeneration. The established regeneration enjoys a low mortality before it attains a full density state (stage ii, until 32 years). When full density is reached, as indicated by the −3/2 power law, the mortality increases again due to an intensive self-thinning (stage iii). However, mortality rate declines with age. This decline is thought to occur because canopy trees become uniform in size and spatial distribution. In the last stage the aggregative dying-off of trees takes place (stage iv, about 90 years). The uniformity among trees is believed to promote the collapse of the stand.

Habitat differentiation among tree species with small-scale variation of humus depth and topography in a tropical heath forest of Central Kalimantan, Indonesia

Small-scale spatial association of the distribution for 55 abundant tree species with two environmental factors (humus depth and surface microtopography) was examined in two 1-ha plots of a heath (kerangas) forest in Central Kalimantan, Indonesia. More than 80% of the 55 species showed a significant habitat preference in humus depth and/ or relative elevation in at least one plot. In particular, ten species occurring in both plots showed a consistent significant preference for humus depth or relative elevation in the two plots. Using randomization tests, however, only five species significantly associated with humus depth and no species with relative elevation. These results suggest that edaphic and topographic factors, especially humus depth, contribute to determining local spatial distribution and floristic composition of abundant tree species in the forest.