This study assessed the effect of the change in forest structure including understory vegetation of Sasa nipponica on soil C and N accumulation from 0 to 40-yr Japanese oak ( Quercus crispula ) plantation chronosequence. The peak of understory biomass was at 7 years after afforestation. Biomass of the overstory species linearly increased, and the biomass of overstory species was more than that of understory species after 8-yr. According to leaf mass index change along with stand age, canopy closure was occurred about 12 years after afforestation. The ranges of temporal changes in both soil C and N accumulations increased from surface to deep soil layers. The changes in C and N accumulation of O layer were large during early stage of stand development, and C and N accumulations increased until 10 years and 20 years after afforestation, respectively. Overstory leaf mass positively correlated with C and N accumulations in O layer. Understory biomass negatively correlated with N accumulation in O layer and positively correlated with C/N ratio. The N accumulations both in mineral soil 0-4 and 4-8cm in depth were negatively correlated with fine root mass of S. nipponica . The results suggested that change in vegetation structure such as canopy closure by overstory and dynamics of understory biomass affected soil C and N accumulations.
We investigated the green moisture content and basic density of 95 woody species growing in Kyushu University Forests. In softwood species, the green moisture content of heartwood ranged from 28% in Cryptomeria japonica to 67% in Abies firma, and in sapwood, from 75% in Tsuga sieboldii to 160% in Cryptomeria japonica. The green moisture content of softwood trees was greater in sapwood than heartwood. The green moisture content in the heartwood of hardwood species ranged from 34% in Euonymus alatus f. striatus to 83% in Kalopanax pictus, and in sapwood, from 45% in Fraxinus sieboldiana to 153% in Actinidia polygama. We found three radial variation pattern types in stems of hardwood species. The green moisture content was higher in heartwood than sapwood, in the first type, whereas in the second, it was higher in sapwood than heartwood. In a third type, differences between heartwood and sapwood were relatively small. The basic density of softwood species ranged from 378 kg/m3 in Cryptomeria japonica to 524 kg/m3 in Tsuga sieboldii. Most trees tended to decrease in basic density from corewood to outerwood. Basic density in hardwood species ranged from 266 kg/m3 in Paulownia tomentosa to 751 kg/m3 in Rhaphiolepis indica var. umbellata. We identified three types of radial variation pattern in stems of hardwood species. In the first type, basic density was higher in corewood than outerwood, whereas in second, it was higher in outerwood. In the third type, differences between corewood and outerwood were small. We also provided the information on the age and size of heartwood formation. Keyword:green moisture content; basic density; Kyushu University Forests; Japan
