Mitsunori Yoshimura

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.

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.

Measurement of tropical rainforest three-dimensional light environment and its diurnal change

A key link to understand the relationship between tropical forest canopy physiology and remote-sensing technology is forest light distribution. Accordingly, we conducted three-dimensional light environment measurements to acquire a quantitative and qualitative understanding of tropical rainforests at Lambir Hills National Park, Sarawak, Borneo, Malaysia, as a typical tropical rainforest region. The aim of this study was to elucidate links between canopy physiological studies and remote-sensing technology, and to investigate the up-scaling capability of canopy processes and mechanisms. Measurements were conducted using a ground-based laser profiler system and terrestrial survey instrument. For understanding qualitative forest characteristics, both reflective and transmissive light measurements were conducted, using photon and quantum sensors and a spectroradiometer. Our results suggest there is no great difference in canopy height, when all trees are mature, are interdependent and are employing the same growth strategies. Photosynthetic active radiation attenuation showed no changes over time.

Vegetation Map Generation by Image Interpretation Using Multi-temporal Satellite Imageries

This paper describes on a study for ganerating a vegetation map using an image interpretation of multi temporal Landsat TM imageries. The TM data obtained in spring and autumn seasons were used for this interpretation. The discrimination of vegetation types was achieved by the interpretation of the differences of color tone due to the differences of vegetation types which were introduced by the results of ground investigations. The vegetation map was generated through two kinds of interpretation steps.As the preliminary step, two major types of ever green vegetation and deciduous vegetation were identified using the TM imageries obtained in the autumn season.Next, more detailed vegetation types were discriminated using the color tone differences in the multi-seasonal TM imageries and the results of preliminary interpretation.Through this study, the image interpetation of satellite imageries was verified to be a practical and effective method for making a reasonal vegetation map, which may be expected to be used as one of the environmental information in some local regions.