Motomu Toda

Single level turbulence measurements to determine roughness parameters of complex terrain

An attempt was made to determine roughness length z 0 and zero-plane displacement height do from single level turbulence measurements over a complex area in tropical monsoon environment where standard procedures to derive those parameters were found difficult to apply. The value of do was derived from the nondimensional standard deviation of temperature Φ θ and of vertical wind speed Φ w by making use of the fact that Φ θ and Φ w versus atmospheric stability relationship is sensitive to the do value, by following and by extending the proposal of Rotach [1994]. This method was applied to the two turbulence data sets obtained at 30 and 60 m above a complex terrain in central part of Thailand, and they produced do = 15.7 m. However, investigations into the accuracy of the do value obtainable by this method have revealed that it is probably of the order of meters and thus a simultaneous application of the method to both vertical wind speed and temperature data are recommended to allow an intercomparison of the derived do values to enhance the reliability of the result. The z 0 value was also determined from the single level turbulence data by a method in which the z 0 value that produced the best agreement of the friction velocity values obtained from the eddy correlation method and those from a wind profile equation with the derived do value, the given value of z 0 and single level wind speed data, was selected. This method is not very sensitive to the exact value of do and z 0 = 0.31 m was obtained. Overall, single level turbulence data were found useful to evaluate roughness parameters of a complex area.

Simulating the carbon balance of a temperate larch forest under various meteorological conditions.

BackgroundChanges in the timing of phenological events may cause the annual carbon budget of deciduous forests to change. Therefore, one should take such events into account when evaluating the effects of global warming on deciduous forests. In this article, we report on the results of numerical experiments done with a model that includes a phenological module simulating the timing of bud burst and other phenological events and estimating maximum leaf area index.ResultsThis study suggests that the negative effects of warming on tree productivity (net primary production) outweigh the positive effects of a prolonged growing season. An increase in air temperature by 3°C (5°C) reduces cumulative net primary production by 21.3% (34.2%). Similarly, cumulative net ecosystem production (the difference between cumulative net primary production and heterotrophic respiration) decreases by 43.5% (64.5%) when temperatures are increased by 3°C (5°C). However, the positive effects of CO2 enrichment (2 × CO2) outweigh the negative effects of warming (<5°C).ConclusionAlthough the model was calibrated and validated for a specific forest ecosystem, the implications of the study may be extrapolated to deciduous forests in cool-temperate zones. These forests share common features, and it can be conjectured that carbon stocks would increase in such forests in the face of doubled CO2 and increased temperatures as long as the increase in temperature does not exceed 5°C.

Changes in soil microbial community and activity in warm temperate forests invaded by moso bamboo (Phyllostachys pubescens)

In the past few decades, moso bamboo (Phyllostachys pubescens) forests in Japan have rapidly expanded, and moso bamboo is now invading nearby native forests. In this study, we assessed the effects of moso bamboo invasion on the soil microbial community and activity in warm temperate forests in western Japan. We sampled soil, measured soil microbial respiration, and used phospholipid fatty acid (PLFA) analysis to examine changes in microbial community composition. We found that the invasion of bamboo into the native secondary forest of Japan can cause changes to some soil properties. We also observed a significant difference in soil microbial community composition between the bamboo and native forests. The ratio of bacterial PLFA to fungal PLFA was significantly higher after bamboo invasion, while bacterial PLFA contents were significantly lower in the organic layer. Soil microbial respiration rates significantly decreased in the organic layer, and significantly increased in the mineral layer. Microbial respiration activity, as indicated by soil microbial respiration rates per total PLFA content, decreased in the organic layer but increased in the mineral layer after bamboo invasion. These results indicate that bamboo invasion significantly affects associated soil microbial communities and decomposition patterns of soil organic matter.