Tanaka Kenzo

Development of allometric relationships for accurate estimation of above- and below-ground biomass in tropical secondary forests in Sarawak, Malaysia.

We developed allometric relationships between tree size parameters (stem diameter at breast height (dbh), at ground surface ( D 0 ) and tree height) and leaf, stem, small-root (diameter

Ecological distribution of homobaric and heterobaric leaves in tree species of Malaysian lowland tropical rainforest

Tree species can generally be classified into two groups, heterobaric and homobaric leafed species, according to whether bundle-sheath extensions (BSEs) are found in the leaf (heterobaric leaf) or not (homobaric leaf). In this study, we study whether the leaf type is related to the growth environment and/or life form type, even in a tropical rain forest, where most trees have evergreen leaves that are generally homobaric. Accordingly, we investigated the distribution of leaf morphological differences across different life forms of 250 tree species in 45 families in a tropical rainforest. In total, 151 species (60%) in 36 families had homobaric leaves, and 99 species (40%) in 21 families had heterobaric leaves. We found that the proportion of heterobaric and homobaric leaf species differed clearly across taxonomic groups and life form types, which were divided into five life form types by their mature tree heights (understory, subcanopy, canopy, and emergent species) and as canopy gap species. Most understory (94%) and subcanopy (83%) species such as Annonaceae had homobaric leaves. In contrast, heterobaric leaf trees appeared more frequently in the canopy species (43%), the emergent species (96%) (such as Dipterocarpaceae), and the canopy gap species (62%). Our results suggest that tree species in the tropical rainforest adapt to spatial differences in the environmental conditions experienced at the mature height of each tree species, such as light intensity and vapor pressure difference, by having differing leaf types (heterobaric or homobaric) because these types potentially have different physiological and/or mechanical functions.

Modeling CO2 exchange over a Bornean tropical rain forest using measured vertical and horizontal variations in leaf‐level physiological parameters and leaf area densities

Southeast Asian tropical rain forests are among the worlds most important biomes in terms of global carbon cycling; nevertheless, the impact of environmental factors on the ecosystem CO 2 flux remains poorly understood. One-dimensional multilayer biosphere-atmosphere models such as soil-vegetation-atmosphere transfer (SVAT) models are promising tools for understanding how interactions between environmental factors and leaf-level physiological parameters might impact canopy-level CO 2 exchange. To examine application of the SVAT model in tropical rain forests, which is expected to be difficult partly because of the complex canopy structure and large number of tree species, we measured vertical and horizontal variations in leaf-level physiological parameters and leaf area densities together with eddy covariance measurements using a canopy crane in a tropical rain forest in Sarawak, Malaysia. Despite differences in species and canopy positions, leaf nitrogen per unit area (N a ) within the canopy could be one-dimensionally described as a linear function of height. N a also clearly explained the other leaf-level physiological parameters across species and canopy positions. Even though the leaf area density profile likely varies in this tropical forest, the SVAT model satisfactorily reproduced the eddy covariance measurements. Furthermore, the CO 2 flux calculated on the assumption that N a measured in the upper canopy was distributed evenly throughout was almost the same as that taking the vertical gradient into consideration. These findings suggest that when reproducing the CO 2 flux in tropical rain forests using the SVAT model, the leaf area density profile obtained from the leaf area index (LAI) measured at one point and leaf-level physiological properties measured across species in the upper canopy are sufficient.

Are stored carbohydrates necessary for seed production in temperate deciduous trees

Summary 1. Many tree species undergo large fluctuations from year to year in seed production, a phenomenon known as masting. The resource budget model, based on the assumption that abundant seeding in a masting year depends on the abundance of resources stored over several years, is a key hypothesis in explaining the mechanism of masting. But do masting species really need such long-term storage to produce a large seed crop? 2. To test this hypothesis, we studied the relationship between the carbon accumulation period for seed production, as estimated by radiocarbon ( 14 C) analyses, and the coefficient of variation of annual seed production in 10 canopy tree species in a temperate deciduous forest. These species differ widely in their reproductive intervals. 3. In all the species studied, the accumulation period was < 1.4 years before seed maturation. Moreover, without taking species or reproductive intervals into account, there was no significant correlation between the carbon accumulation period and the fluctuation of annual seed production; both remained at an even level. 4. Synthesis. Our results suggest that temperate canopy trees used photosynthates produced in the current and/or the previous year for seed production, regardless of reproductive intervals. It might therefore be necessary to reconsider the importance of stored carbohydrate resources for masting.

BAAD: a biomass and allometry database for woody plants

Understanding how plants are constructed—i.e., how key size dimensions and the amount of mass invested in different tissues varies among individuals—is essential for modeling plant growth, carbon stocks, and energy fluxes in the terrestrial biosphere. Allocation patterns can differ through ontogeny, but also among coexisting species and among species adapted to different environments. While a variety of models dealing with biomass allocation exist, we lack a synthetic understanding of the underlying processes. This is partly due to the lack of suitable data sets for validating and parameterizing models. To that end, we present the Biomass And Allometry Database (BAAD) for woody plants. The BAAD contains 259 634 measurements collected in 176 different studies, from 21 084 individuals across 678 species. Most of these data come from existing publications. However, raw data were rarely made public at the time of publication. Thus, the BAAD contains data from different studies, transformed into standard units and variable names. The transformations were achieved using a common workflow for all raw data files. Other features that distinguish the BAAD are: (i) measurements were for individual plants rather than stand averages; (ii) individuals spanning a range of sizes were measured; (iii) plants from 0.01–100 m in height were included; and (iv) biomass was estimated directly, i.e., not indirectly via allometric equations (except in very large trees where biomass was estimated from detailed sub-sampling). We included both wild and artificially grown plants. The data set contains the following size metrics: total leaf area; area of stem cross-section including sapwood, heartwood, and bark; height of plant and crown base, crown area, and surface area; and the dry mass of leaf, stem, branches, sapwood, heartwood, bark, coarse roots, and fine root tissues. We also report other properties of individuals (age, leaf size, leaf mass per area, wood density, nitrogen content of leaves and wood), as well as information about the growing environment (location, light, experimental treatment, vegetation type) where available. It is our hope that making these data available will improve our ability to understand plant growth, ecosystem dynamics, and carbon cycling in the worlds vegetation.

Height-related changes in leaf photosynthetic traits in diverse Bornean tropical rain forest trees

Knowledge of variations in morphophysiological leaf traits with forest height is essential for quantifying carbon and water fluxes from forest ecosystems. Here, we examined changes in leaf traits with forest height in diverse tree species and their role in environmental acclimation in a tropical rain forest in Borneo that does not experience dry spells. Height-related changes in leaf physiological and morphological traits [e.g., maximum photosynthetic rate (Amax), stomatal conductance (gs), dark respiration rate (Rd), carbon isotope ratio (δ13C), nitrogen (N) content, and leaf mass per area (LMA)] from understory to emergent trees were investigated in 104 species in 29 families. We found that many leaf area-based physiological traits (e.g., Amax-area, Rd, gs), N, δ13C, and LMA increased linearly with tree height, while leaf mass-based physiological traits (e.g., Amax-mass) only increased slightly. These patterns differed from other biomes such as temperate and tropical dry forests, where trees usually show decreased photosynthetic capacity (e.g., Amax-area, Amax-mass) with height. Increases in photosynthetic capacity, LMA, and δ13C are favored under bright and dry upper canopy conditions with higher photosynthetic productivity and drought tolerance, whereas lower Rd and LMA may improve shade tolerance in lower canopy trees. Rapid recovery of leaf midday water potential to theoretical gravity potential during the night supports the idea that the majority of trees do not suffer from strong drought stress. Overall, leaf area-based photosynthetic traits were associated with tree height and the degree of leaf drought stress, even in diverse tropical rain forest trees.

Changes in leaf water use after removal of leaf lower surface hairs on Mallotus macrostachyus (Euphorbiaceae) in a tropical secondary forest in Malaysia

Leaf hairs may assist in maintaining high leaf water use efficiency in tropical secondary forest tree species. We compared leaf temperature, transpiration, photosynthesis and water use efficiency between hairy and depilated leaves in Mallotus macrostachyus (Euphorbiaceae), to determine the role of leaf hair in leaf water use efficiency (WUE) in tropical degraded secondary forest in Malaysia. Measurements were made on five mature individuals growing in sun-exposed conditions and five in shaded conditions. The hair dry weight per unit leaf area was significantly greater in sun leaves than in shade leaves. The transpiration rate (Trmax) of depilated leaves in sun-exposed conditions was slightly higher than in hairy leaves in both morning and afternoon measurements. In contrast, Trmax in the shade leaves was almost identical in hairy and depilated leaves. Leaf stomatal conductance (gs) in the morning showed almost the same value among leaf types and light conditions. In the afternoon, gs slightly decreased from the morning values in both sun and shade conditions. In the morning, the leaf water use efficiency (Amax/Trmax) in both conditions did not differ significantly between hairy and depilated leaves. However, in the afternoon, WUE in the depilated leaves was significantly lower than in hairy leaves in sun-exposed conditions. These observations suggest that leaf hairs in M. macrostachyus contribute to the high leaf water use efficiency in drought conditions, such as high vapor pressure deficit experienced at midday in degraded tropical secondary forests.

Leaf water use in heterobaric and homobaric leafed canopy tree species in a Malaysian tropical rain forest

Tropical canopy tree species can be classified into two types by their heterobaric and homobaric leaves. We studied the relation between both leaf types and their water use, together with the morphological characteristics of leaves and xylem, in 23 canopy species in a tropical rain forest. The maximum rates of photosynthesis and transpiration were significantly higher in heterobaric leaf species, which also underwent larger diurnal variations of leaf water potential compared to homobaric leaf species. The vessel diameter was significantly larger and the stomatal pore index (SPI) was significantly higher in heterobaric than that in homobaric leaf species. There was a significant positive correlation between the vessel diameter, SPI, and maximum transpiration rates in all the studied species of both leaf types. However, there was no significant difference in other properties, such as leaf water-use efficiency, leaf mass per area, leaf nitrogen content, and leaf δ13C between heterobaric and homobaric leaf species. Our results indicate that leaf and xylem morphological differences between heterobaric and homobaric leaf species are closely related to leaf water-use characteristics, even in the same habitat: heterobaric leaf species achieved a high carbon gain with large water use under strong light conditions, whereas homobaric leaf species can maintain a high leaf water potential even at midday as a result of low water use in the canopy environment.

Photosynthetic water use efficiency in tree crowns of Shorea beccariana and Dryobalanops aromatica in a tropical rain forest in Sarawak, East Malaysia

Photosynthetic water use efficiency (PWUE), stomatal conductance (g s), and water potential were measured at two different positions in the tree crown of two emergent tropical tree species (Shorea beccariana Burck, Dryobalanops aromatica Gaertn. f.). The trees were about 50 m high, in a tropical rain forest in Sarawak, East Malaysia. In both species, g s at the upper crown position at midday was lower than at the lower crown position, even though both positions were exposed to full sunlight; the difference was greater in S. beccariana. Hydraulic limitation occurs in the upper crown position in both species. A midday depression was observed in the photon saturated photosynthetic rate in both species, especially at the upper crown. However, PWUE was markedly higher in the upper crown than the lower crown at midday, even though no morphological adjustment was observed in the leaves; this difference was greater in S. beccariana.

Interspecific variation in leaf water use associated with drought tolerance in four emergent dipterocarp species of a tropical rain forest in Borneo

By use of tree-tower and canopy-crane systems we studied variations in the water use, including transpiration, stomatal conductance, and leaf water potential, of the uppermost sun-exposed canopy leaves of four emergent dipterocarp species in an aseasonal tropical rain forest in Sarawak, Malaysia. Midday depression in stomatal conductance and leaf water potential was observed in all the species studied. Interspecific differences were clearly observed in the maxima of transpiration rates and stomatal conductance and the minima of leaf water potential among the four dipterocarp species. These interspecific variations were closely related to wood density and to factors affecting ecological patterns of distribution. Specifically, Shorea parvifolia and S. smithiana, both of which have a relatively low wood density for Dipterocarpaceae and are found on clay-rich soil, had a high transpiration rate in the daytime but had a large midday depression and a low leaf water potential. In contrast, Dryobalanops aromatica, which has a high wood density and is found in sandy soil areas, consumed less water even during the daytime. Dipterocarpus pachyphyllus, which has a high wood density and is found on clay-rich soil, stood intermediate between Shorea and D. aromatica in leaf water use. The two Shorea species had higher mortality than the others during the severe drought associated with El Niño in 1998, so daily pattern of leaf water use in each dipterocarp species might be correlated with its susceptibility to unusual drought events.