In order to clarify the vegetation and soil characteristics in the dry dipterocarp forest (DDF) and mixed deciduous forest (MDF) at Mae Chaem district, Chiang Mai, Thailand, fifteen quadrats (40×40m) were set up in each forest type. In DDF, 30 families, 56 tree species were identified, and the relative dominance of DIPTEROCARPACEAE was 75%. In MDF, 28 families, 77 tree species were identified and the relative dominance of LEGMINOSAE was 41%, VERVENACEAE was 18%. Though absence in DDF, bamboos was 26m^2 per hectare for stem basal area in MDF. The value of tree density in DDF was higher than that in MDF, however, the value of total basal area in DDF was lower than that in MDF. DDF was more simple stand structure as compared with MDF. Nutrient contents significantly differed in the upper soil layer among the soil profiles. DDF had lower contents of soil nutrients than MDF. In DDF, there were no differences in soil chemical properties among the three sites as upper, middle and lower on the slope. On the other hand, the pH, available P, total C content, total N content and exchangeable Ca content of the lower site at MDF was significantly higher than those of the other two sites.

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Monitoring survey for acid precipitation, forest soil, and also forest decline has been carried out for five years since 1990 all over Japan. A monitoring survey site was placed at each 20km×20km. The rain water was collected for 10 days in June (rainy season). Survey of forest decline degree and soil profile were also carried out. Chemical property of rain water and soil was analyzed. In this report, the characteristics of rain water, forest soil and forest decline in Kyushu area in this period were summarized. As for pH value of rainwater, at over 80% of sampling sites the pH value showed below pH5.6. In Kyushu area the ion concentrations of Cl^-, NO_3^-, SO_4^<2-> and K^+ in rain water were lower than the average of all over Japan. The average values of soil pH in Kyushu was 5.1 and was mostly the same with the other area of Japan. The soil pH was lower in northern Kyushu than in southern Kyushu. The average concentration of exchangeable base cation (K+Ca+Mg) of soil in Kyushu was lower than that in the other area. In the case that the soil pH value was lower than pH 5.2, the concentration of exchangeable Al in soils increased with the decrease of soil pH. The decline of forest was very few in Kyushu area.

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The ion flux of rainfall, throughfall, stemflow and percolate from A_0 horizon were investigated for three years at a Castanopsis cuspidata stand and a Cryptomeria japonica stand in the Miyazaki University Forests. Neutralization capacities of hydrogen ion throgh the Castanopsis cuspidata stand were not distinctly different from that of the Cryptomeria japonica stand. The annual average of hydrogen ion flux of the percolate from A_0 horizon in both stands were equal. However, the process that hydrogen ion was neutralized was different between the stands. In the Castanopsis cuspidata stand, canopy and stem were the main sink of hydrogen ion. In contrast, in the Cryptomeria japonica stand, A_0 horizon neutralized hydrogen ion in rainfall and that produced on canopy and stem. Exchange reactions with magnesium ion and calcium ion was the major hydrogen ion sink of the A_0 horizon of both stands. In the Cryptomeria japonica stand, most of the hydrogen ion would be exchanged for calcium ion leached from litter.

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The vegetation of the Nobeyamahara area at the foot of Mt. Yatsugatake, the location of the University of Tsukuba experimental forest, is characterized by a secondary natural forest, primarily composed of the cool-temperate zone species Quercus mongolica var. grosseserrata. Betula spp. is another important component of this mixed forest, but Fagus crenata is distinctive by its absence. To elucidate the reason for the lack of Fagus crenata, the correlation between late frost and the time of budding was investigated in the 6-year period from 1993 to 1998. The budding of F. crenata varied over a period of 22 days during the 6 years, from May 2 to May 24. The budding of Q. mongolica var. grosseserrata varied over a period of 20 days, from May 11 to May 31, or 9 days later than F. crenata on average (range, 7-14 days). The mean daily temperature on the day of budding was 10-13℃ for F. crenata and 11-12℃ for Q. mongolica var. grosseserrata. The cumulative temperature on the day of budding (mean value for 6 years) was alos calculated for both species. During the period under investigation, late frosts occurred from May 9 to 29. Since these developed after the budding and flushing of F. crenata, the leaves or entire plants died from damage caused by the late frost. Q. mongolica var. grosseserrata, on the other hand, either failed to encounter late frosts in certain years, or suffered almost no visible damage immediately after budding or flushing when late frosts did occur. It can therefore be conjectured that such differences between these two tree species may have determined their respective courses of distribution.

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