Yuichiro Yashiro

Estimation of root biomass based on excavation of individual root systems in a primary dipterocarp forest in Pasoh Forest Reserve, Peninsular Malaysia.

Precise estimation of root biomass is important for understanding carbon stocks and dynamics in tropical rain forests. However, limited information is available on individual root masses, especially large trees. We excavated 121 root systems of various species (78) and sizes (up to 116 cm in dbh), and estimated both above- and below-ground biomass in a lowland primary dipterocarp forest in the Pasoh Forest Reserve, Peninsular Malaysia. A tree census was conducted in four research plots (each 0.2 ha) and stand-level biomass was estimated. We examined relationships between tree size parameters and masses of coarse roots (roots ≥ 5 mm in diameter) and derived a dbh-based allometric equation. The amounts of coarse roots that were lost during excavation were corrected. Coarse-root biomass before and after correction for lost roots was estimated to be 63.8 and 82.7 Mg ha -1 , indicating that significant amounts of roots (23%) were lost during the sampling. We also estimated the biomass of small root (<5 mm) by applying pipe-model theory. The estimate, 13.3 Mg ha -1 , was similar to another estimate of small roots, 16.4 Mg ha -1 , which was obtained directly by the soil-pit sampling method. Total below-ground (BGB) and above-ground biomass (AGB) was estimated to be 95.9 and 536 Mg ha -1 , respectively. The biomass-partitioning ratio (BGB/AGB) was about 0.18. In conclusion, the dbh-based allometric equation for coarse roots developed in this study, which kept good linearity even including the data of larger trees, might be useful for evaluating below-ground carbon stocks in other stands of similar forest (old-growth dipterocarp) in South-East Asia.

Emission of nitrous oxide through a snowpack in ten types of temperate ecosystems in Japan

The release of N2O from the snow surface in winter and the soil in summer was measured in ten types of temperate ecosystems (bare ground, grassland, forest, marsh, and crop field) in Japan. The snow-covered crop field emitted by far the largest amount of N2O during the winter. Among the snow-covered natural ecosystems studied, marshy ecosystems showed the largest effluxes of N2O. Based on results showing that the magnitude of the winter N2O fluxes was not negligible compared with that of the summer N2O fluxes and because the snow period in the areas studied area is sufficiently long, we suggest that the winter N2O fluxes contribute significantly to the annual emission of N2O in the study areas.

The effect of dense understory dwarf bamboo (Sasa senanensis) on soil respiration before and after clearcutting of cool temperate deciduous broad-leaved forest

To evaluate the effect of understory dwarf bamboo (Sasa senanensis) on soil respiration in forest ecosystems, we compared soil respiration rates between four deciduous broad-leaved forest sites representing two levels of understory Sasa (with and without) and two levels of forest stand age (50-year-old stand and 1-year-old stand after clearcut). The understory Sasa enhances the soil respiration rate both before and after the clearcutting of deciduous broad-leaved forest. The Sasa sites had larger total belowground biomass compared with the non-Sasa sites, which could be attributed to Sasa presence. Our results also suggest that clearcutting decreases temperature-normalized soil respiration rates (R15) and temperature sensitivity (Q10) in both Sasa and non-Sasa ecosystems. Clearcutting significantly reduced the fine root biomass of trees and Sasa. The fine roots of trees and Sasa had high specific respiration rates compared with larger roots and rhizomes at Sasa and non-Sasa sites, respectively. Therefore, we hypothesize that the loss of fine roots after clearcutting is responsible for the reduction in soil respiration rate. A comparison with other studies revealed a positive linear relationship between total (tree and Sasa) fine root biomass and R15, suggesting that fine root biomass controls soil respiration at the landscape scale. The Q10 value is also likely to be related to fine root biomass, although the relationship was not significant. We conclude that understory Sasa increases belowground biomass, especially fine roots, and the spatial variation in soil respiration at the landscape scale.