Decomposition processes of leaf litter were observed during one year with same kinds of substrates at a warm-temperate evergreen oak forest in Japan and a tropical rain forest in Sumatra simultaneously. A warm-temperate forest showed high rates of carbon-weight loss in summer. A tropical rain forest had high rates at the initial stages in particular and apparently low rates during the severe dry weather in early 1997. When time trends of carbon-weight loss could be approximated by a single exponential curve for each leaf litter, the average values of decomposition factor of five Japanese fagaceous leaf litter were 0.70±0.13 y^-1 at a warm-temperate forest and 1.62±0.24 y^-1 at a tropical rain forest, respectively. The C/N ratios of litter gradually decreased with the progress of decomposition at the initial stages, then tended to be constant at about C/N =20 at the last stages irrespective of kinds of leaf litter and study sites. Basing on these results we discussed characteristics of decomposition at these two forest ecosystems.

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A tidal flood forest (várzea) and an interior upland forest (terra firme) from the Urubueua Island in the Amazon estuary were compared according to the number of trees and species, above-ground biomass, human impact and vessel parameters in stem cross sections between rainy (high water) and dry (low water) seasons. Both the number of individuals and species were larger in the terra firme (individuals: 85/400 m², species: 22/400 m²), but in the vilrzeathe number of individuals showed major variations among quadiats (individuals:62.0 ± 19.5) due to the selective removal of competing trees for the management of açai palm (Euterpe oleracea Mart.), an income source in the estuary. The human impact was found in the tree height class as well. The average of above-ground biomass per quadrat showed a similar value (vázea: 12.4 t, terra firme: 11.6 t). However, the difference among quadrats was quite large in várzea (S.D.: ± 6.02 t), and this fact suggests that the growth rate occurs independent from human impact. From the comparisons of vessel area, vessel number, diameter and circumference between rainy and dry seasons, it was found that the growth of trees on the terra firme is rainy season-dependent, while the várzea counterpart subjecting to periodic flooding grows mainly in the dry season with low water depth.

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The characteristics of tree species in a riverside forest were investigated from forest inventory and tree ring analysis of stem transection in three quadrats (100 m² each) along the Duda River in Macarena National Park, Colombia. As the distance from the river channel became longer, the number of individual trees decreased from 103 to 45 (/100 m²), while the canopy height increased from 10 m to 20 m, the diameter at breast height DBH) increased from 10 cm to 25 cm, and the summation of (DBH)²H also increased from 1.39 m³ to 11.62 m³. Cecropia membranacea was widespread in all the quadrats. This species has the characteristic of fast thickening growth in the early stages but the cycle between establishment and death is shorter than 10 years even in a landside quadrat. Because the vessel diameter is larger than 250 μm, however, it is estimated to be one of the first tree species to be established in a riverbank. Ficus insipida and Piptadenia flava are believed to be canopy species because they have a large vessel diameter and their growth rate is steady. On the other hand, species with a small vessel diameter such as Guarea guidonia and Inga bomplandiana mainly have thickening growth rather than extension growth and remain as the medium and shrub species.

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Vertical and horizontal profiles of redox potential were studied in two wetland forest ecosystems in Lahei, Central Kalimantan, Indonesia. Eh of the soil surface showed a clear correspondence to the surface micro-topography of a 40 cm difference in relative elevation. The lower inundated soil showed the low values of Eh (0-300 mV) and the higher emerged area showed the high values of Eh (>500 mV). The values of Eh changed clearly at the boundary between inundated and emerged soil. A vertical profile of Eh showed the difference between the plot in a peat swamp forest on well-developed peat, accumulated up to 7.5 m and the plot in a temporal wetland shrub community on 15-30 cm of peat layer, The Eh in the shrub community decreased from the top to a depth of 45 cm. However, the Eh in the peat swamp forest showed constant values from the top to a depth of 50 cm, and the values were > 400 mV. Constantly high values of Eh in the peat swamp forest would be due to aeration by aerenchyma of plants and to the low activity of microorganisms in the peat.

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We evaluated proton budget and soil acidification rate in a forested watershed in Jiulianshan, southern China. In this watershed, atmospheric deposition of H⁺ , NH₄⁺ , Ca²⁺, SO₄^2- (400, 351, 299 and 876 eq/ha/yr, respectively) were higher than those of other solutes (< 200 eq/ha/yr), and origin of these substances may be southwestern or northem China. Soil acidification rate was 2562 mol/ha/yr, and was not high. The most important process for the soil acidification was the base cation export from the watershed by “ion exchange and weathering” in the soil, mainly owing to the net loss of Mg²⁺ (830 eq/ha/y). However, the high retention of H⁺ , NH₄⁺ and SO₄^2- in this watershed also acidified the watershed soil (399,321 and 723 eq/ha/yr, respectively), and the SO₄^2- retention had a major influence on soil acidification. When the proton budget was evaluated for the soil compartment, the importance of anion retention was suggested. Although the watershed soil is becoming more acidic, the stream water was not acidic. However, continuous atmospheric deposition of acidifying substances and further acidification of the soil may lower pH in this stream.

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As for the origin of Asian cultivated rice (Oryza sativa L.), many questions and problems still remained unknown. The origin of waxy (glutinous) rice is one of these questions. For more than 30 years after Watabe’s pioneer work, we have no information about “Glutinous Rice Zone” at which rice cultivars grown are waxy (glutinous) one, because the political situation of the zone had been unstable until 1990s. For the purpose to investigate the genetic diversity among waxy rice cultivars in Glutinous Rice Zone and estimate origin of waxy rice, scientific trips in Laos from 1991 to 1999 and evaluation for genetic features of waxy rice cultivars were carried out. Judging from results of the intensive observations in ’95 and ’96, traditional cultivars have been replaced to improved ones due to promotion of the Government. It was considered that the social, economical and environmental situations during this 30 years altered rice cultivation in this area. In whole Laos, we found that these waxy cultivars possess high phenotypic diversity such as frequency of glabrous phenotype, but show monomorphism in waxy locus. It was concluded that the waxy mutation of cultivars in Laos had originated from japonica lines, independently apparent indica-japonica differentiation.

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