JAPANESE JOURNAL OF ECOLOGY

We clarified that the grain-size distribution of the surface sediments influenced the vegetation cover and species composition in different sampling areas where sand and gravel were found. We studied wind-beaten bare ground, river beds, and beaches. We analyzed the relationships of vegetation cover, species composition, and life forms with the soil grain-size distribution of the surface sediments and the interstitial particles in gravel. On wind-beaten bare ground, the vegetation cover increased where the soil grain size was larger. On beaches, the vegetation cover tended to be high where the grain size was larger. On the upper floodplain, more herbaceous vegetation developed where the interstitial soil was finer. On the wind-beaten bare ground and beach, vegetation developed well on coarse gravel, since the larger gravel was relatively stable. The species composition on the wind-beaten bare ground and river channels differed significantly depending on the surface sediments. The life forms of plants differed, depending on the grain size of the mineral soil. The species composition also differed with the soil grain size.

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Aboveground net primary production (ANPP) was estimated using a harvest technique and an allometric technique using the diameter at breast height (DBH) at an early stage after clear-cutting a deciduous broad-leaved forest. The number of stems per hectare increased from 40,700 in May 2005 to 53,300 in November 2009. During the same period, basal area increased from 3.4 to 12.0 m^2ha^<-1>. The study stand consisted of shrubs, sub-canopy trees and canopy trees. Although these tree types had similar relative basal areas in May 2005, canopy trees increased during the study period. The mortality and recruitment of shrubs was more than twice that for the other types. We were not able to use the harvest technique to accurately estimate the interannual variation in ANPP due to the high variation in stand biomass. The allometric technique underestimated the stand biomass and growth because it omitted trees smaller than breast height. However, the allometric technique was able to evaluate the mortality and growth of recruits. When estimating ANPP, it is important to evaluate the mortality and growth of recruits in shrub-rich stands due to the production of shrubs. Therefore, the allometric technique is effective for evaluating the interannual variation in the ANPP in shrub-rich stands.

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The flux in CO₂ has been measured in Takayama Forest, a secondary deciduous broad-leaved forest in the Asia FLUXNET, using the eddy covariance method since 1993. To study biometric-based net ecosystem production (NEP) beneath the flux tower, we set up a permanent 1-ha plot in 1998, and have been measuring ground-based biometric parameters, such as net primary production (NPP) and soil respiration. These intensive, long-term studies of carbon cycling have helped demonstrate the temporal variation in NEP and where and how the forest stores carbon. The biometric-based NEP, which is the balance between NPP and heterotrophic respiration, was 2.1 tC ha^-1yr^-1 for the 5-year period, in good agreement with the eddy covariance-based NEP (2.8 tC ha^-1yr^-1). The NEP was partitioned into 0.3 tC to the biomass pool, 1.0 tC to the coarse woody debris (CWD) pool, and 0.8 tC to the soil organic matter (SOM) pool. The woody tissue NPP varied markedly from 0.88 to 1.96 tC ha^-1yr^-1 during the 11-year period from 1999 through 2009, and was positively correlated with the eddy covariance-based NEP. These data suggest that the interannual variability in ecosystem carbon exchange is directly responsible for much of the interannual variation in autotrophic production, and that there is constant net accumulation of carbon in the nonliving detritus (CWD and SUM) pools in the Takayama Forest. Estimations of the carbon sequestration rate and carbon accumulation processes in the detritus pools are not well represented in current studies. Comparable studies in ecosystems from each vegetation zone need to be conducted in the next decade to determine 1) how much accumulation there is, 2) how long carbon resides, especially in detritus pools, and 3) how successional dynamics affect carbon cycling.

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