Kiyoshi Umeki

Modeling the relationship between the asymmetry in crown display and local environment

Abstract The asymmetry in crown display was modeled with respect to neighbors and microtopography. The direction and magnitude of the asymmetry were expressed by the ‘crown-vector’, the horizontal two-dimensional vector that joins the stem base position of a focal tree with the centroid of its projected crown area. In the model, the crown-vector of a focal tree was a function of the position and size of its neighbors and the direction and inclination of the slope on which it occurred. Using the model, the effect of repelling behavior of crowns on the spatial pattern of crowns was quantified; spatial patterns of crowns were more regular than those of stem bases. The effects of parameters in the model on the spatial pattern of population were also quantified. The model was applied to the data derived from two study plots: one in cool temperate deciduous broad-leaved forest in northern Japan and the other in warm temperate evergreen broad-leaved forest in central Japan. The least-squares fit of the model accounted for 56% and 73% of the total variance in crown-vector for the two study plots, respectively.

Some evidence for an adaptive linkage between leaf phenology and shoot architecture in sapling trees

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.

Long‐term growth dynamics of natural forests in Hokkaido, northern Japan

The long-term growth dynamics of natural forest stands on the island of Hokkaido were described on the basis of an analysis of data from 38 permanent plots spanning 15- 22yr. Stand structure was characterized by basal area, stem density and tree size variability. To detect trends in stand structure, regression models for recruitment rate (per ha per yr), mortality rate and the rate of change in stem density and tree size variability were developed by a stepwise method using initial basal area, stem density, tree size variability, species composition summarized by LNMDS ordination, alti- tude, annual mean temperature, annual precipitation, type of understorey vegetation, topography and slope aspect as candi- dates for predictor variables. The same analyses were con- ducted for basal area increment (net growth) and its compo- nents: survivor growth = basal area gain by growth of surviv- ing individuals and mortality = basal area loss by death of individuals.

Relationship between leaf characteristics, tree sizes and species distribution along a slope in a warm temperate forest

The relationships between some leaf characteristics, tree size and species distribution were investigated for evergreen tree species along a slope in a warm temperate forest in Japan. Tree species were classified into three groups based on their dominance on the slope: ‘ridge species’ that were aggregated in an uppersite, ‘valley species’ that were aggregated in a lowersite, and ‘uniform species’ that were distributed almost uniformly. The ridge species had a more positive leaf carbon isotope ratio than the valley species, which suggests that the ridge species have larger water use efficiency than the valley species. This may give some advantage to the ridge species over the valley species in the uppersite where water availability would be limited. However, the ridge species had smaller leaf nitrogen content on a mass basis and larger leaf mass per area than the valley species, which suggests that the ridge species had a smaller mass-based leaf photosynthetic capacity than the valley species. This may be disadvantageous to ridge species in the lowersite, because smaller leaf photosynthetic capacities cause lower leaf carbon gain and thus lower growth than the valley species. These differences in leaf characteristics between the ridge and the valley species were affected by microenvironments, and were also partly affected by the difference in species specific responses to microenvironments on the slope.

Mean labor time of a leaf

The mean labor time of a leaf (hour/day−1) is defined as the ratio of mean daily photosynthetic rate of a leaf (Da; mol m−2 day−1) to the mean value of potential hourly photosynthetic rate (60 ⋅ 60Amax mol m−2 h−1) of the leaf. A model was proposed to estimate mean labor time of leaves. Mean labor time was obtained as the product of 24 (hours/day−1) and the four effects, each of which reduces production of a leaf: diel change in light (Diel Effect), reduction in light during cloudy and rainy days (Cloudy Effect), shading on the focal leaves (Shading Effect), and midday and afternoon depression in photosynthesis (Depression Effect). These four effects were estimated for open grown saplings of alder (Alnus sieboldiana), by measuring instantaneous photosynthetic rate and photon flux density above each leaf. The potential daily photosynthetic rate calculated from diel light condition in a clear day was 46.5% of hypothetical daily photosynthetic rate where maximum instantaneous photosynthetic rate was assumed to last throughout the life of the leaf (Diel Effect). The average of the daily photosynthetic rate considering clear, cloudy and rainy days was 79.7% of the clear day (Cloudy Effect). The photosynthetic rate estimated from light condition on the leaf was 85.6% of that in the open site (Shading Effect). Midday depression reduced the daily photosynthetic rate to 72.1% of the potential daily photosynthetic rate (Depression Effect). The product of the four effects multiplied by 24 h gave the estimate of mean labor time of leaves to be approximately 5.5 (h/day−1).

Growth characteristics of six tree species on Hokkaido Island, northern Japan

Based on growth data obtained from 13 804 individual trees in 110 permanent plots, diameter at breast height (d.b.h.) growth was modeled for six major tree species growing in Hokkaido Island, northern Japan. For each species, d.b.h. growth was regressed on independent variables, indicating the effects of initial size, competition, climate and topography. In developing the d.b.h. growth models, independent variables were selected using the stepwise method. For all species analyzed, the final models accounted for significant amounts of the variation (r2 = 5.65−20.99%; P < 5%) in d.b.h. growth. Significant (P < 5%) effects of competition, climate and topography on d.b.h. growth were detected. The model obtained can be used in simulations of forest dynamics. Some ecological questions were examined using the d.b.h. growth models obtained. For hardwoods, the d.b.h. growth rate did not correlate with the published grouping of species in terms of shade-tolerance; however, the plasticity in d.b.h. growth in the presence of competition seemed to be correlated with the shade-tolerance of species. The degree of asymmetry in competition evaluated for each species was not correlated with the availability of underground resources, which was expressed by surrogate variables (mean values of climatic and topographic variables for species). The degree of asymmetry in competition was not different between conifers and hardwoods.

Tree mortality of five major species on Hokkaido Island, northern Japan

The mortality rates of five major tree species (Abies sachalinensis, Acer mono, Magnolia obovata, Quercus crispula, Tilia japonica) on Hokkaido Island, northern Japan were modeled using logistic regressions based on the long-term observation of 8929 individuals in 65 permanent plots. Individual size, recent growth, one-sided and two-sided interactions with neighbors, climatic and topographic factors were used as independent variables in the logistic regressions, and relevant variables were selected using the stepwise method. For all species analyzed, the final models significantly explained tree mortality rates. The regression analyses indicated that individual size and/or recent growth had effects on tree mortality. A significant effect of one-sided interaction on tree mortality was detected for three species, and a significant effect of two-sided interaction was detected for two species. The interactions with neighbors were not necessarily competitive. For all species analyzed, climatic and topographic factors affected tree mortality. The mortality models obtained can be used for forest dynamics simulations. One ecological question was examined using these models. Species that can grow fast in forest stands with smaller basal areas tended to have high mortality rates in forest stands with larger basal areas. Some ecological characteristics of the analyzed species are described based on the results of the regressions.

Evolutionarily stable resource allocation for production of wind-dispersed seeds

We developed a game-theoretic model for wind-dispersed seed production to examine the seed mass–dispersal ability relationship and the evolutionarily stable distance of seed dispersal in terms of exploitation of safe sites. We assumed trade-offs between masses of the embryo (including albumen) and the wind-dispersal structures per seed, and also between seed mass and number of seeds per parent. We showed that ESS wing-loading is independent of embryo mass; that is, heavy seeds are not poor dispersers if the cost of producing wind-dispersal structures per unit area is constant. The ESS embryo mass per seed depends only on the factors which determine the probability of a seedling being established from a seed. However, wing-loading was found to increase with embryo mass when the change in length was isometric and there was a negative correlation between seed mass and dispersal ability. Thus, the area–mass relationship in wind-dispersal structures may have large effects on the ESS production of wind-dispersed seeds. On the other hand, given that only a limited number of adults can be established at a safe site, the ESS seed dispersal distance depends on the relative degree of sib to non-sib competition. A parent disperses its seeds over a wide area to exploit many safe sites if sib competition is strong. However, it disperses its seeds within a narrow area if the mean number of parents per unit area is large, or if non-sib competition is strong. Thus, in addition to an upper limit on the number of adults per safe site, the degree of sib and non-sib competition may be important for the ESS dispersal distance in wind-dispersed seeds.

Canopy ergodicity: can a single leaf represent an entire plant canopy?

While leaves typically emerge near shoot apices around the outer surface of a plant canopy, their relative position “moves” deeper into the canopy as additional leaves emerge. The photosynthetic capacity (Amax) of a given leaf can be expected to decline over time as its relative position (Pr) in the canopy becomes progressively deeper; this can be observed as a spatial gradient with the Amax of leaves declining distally from the shoot apex. As a consequence, we propose that the photosynthetic capacity averaged over a single leaf’s lifespan is equivalent to the average photosynthetic capacity of the entire plant canopy at a given time; in other words, there is an ergodic time to space averaging in the organization and development of plant canopies. We tested this “canopy ergodic hypothesis” in two woody (Alnus sieboldiana and Mallotus japonica) and two herbaceous (Polygonum sachalinensis and Helianthus tuberosus) species by following the photosynthetic capacity in 100 individual leaves from the time of their emergence until their death. We compared the average photosynthetic capacity of individual leaves through time (time-average) to the average photosynthetic capacity of all the leaves along a shoot at the time of emergence of the focal leaf (space-average). We found that Amax and Pr were positively correlated and that the time-averages of three plant species (Alnus, Mallotus, and Helianthus) were not significantly different from the corresponding space-averages, although the averages differed among individual plants. Polygonum, however, did show significant differences between time and space averages. Ergodicity appears to apply to the leaf–canopy relationship, at least approximately—the average photosynthetic capacity of a single leaf through time (time-average) can represent the average photosynthetic capacity of the entire canopy.

A GIS-based simulation program to predict multi-species size-structure dynamics for natural forests in Hokkaido, northern Japan

Abstract A simulation program that runs on a geographic information system (GIS) was developed to predict the multi-species size-structure dynamics of forest stands. Because important characteristics of a forest stand, including woody biomass accumulation, carbon storage, commercial value of timber, and functions for environmental conservation, can be inferred from the size structures of the component populations, management plans can be made from the predictions of the size-structure dynamics. For example, the simulation can incorporate various forms of thinning; forest managers can then try several thinning plans in simulated forest stands and choose the appropriate plan that achieves the best results. Using GIS to predict the size-structure dynamics of forest stands is of practical importance, because GIS has been used widely in forest management and can easily handle spatial distributions of environmental information (e.g., climate, geology, soils) that may influence tree performance. To predict size-structure dynamics, the program numerically solves a continuum equation that describes size-structure dynamics based on growth and mortality rates of individual trees. When predicting size-structure dynamics of a forest stand, the program obtains the environmental information of the stand from a database stored in the GIS and calculates environmental factors such as warmth index and potential evapotranspiration/precipitation ratio that influence growth and mortality rates. The simulation program calculates growth and mortality rates using published growth and mortality models that incorporate the effects of size of the individual, competition between trees, and abiotic environmental factors. To demonstrate the effects of abiotic environmental factors on the multi-species size-structure dynamics, sensitivity analyses were conducted. The size-structure dynamics varied in a way that was predictable from the responses of the growth and mortality rates to variations in the abiotic environmental factors. To demonstrate the size-structure dynamics in different locations, five test runs of the simulation program were also performed using the same initial size-structure and five different sets of abiotic environmental conditions from five locations. At the end of the simulation, the predicted size structures differed because the growth and mortality rates differed among the five locations. Finally, the response of the size structure to thinning was clarified. The result showed how the size structure of a component species in a forest stand is dependent on the presence of other species.