Canopy gaps and tree replacement pattern in the gaps were investigated in the secondary evergreen broad-leaved forest dominated by Castanopsis cuspidata of JIBP Special Research Area at Minamata, southwestern Japan, which had been affected by a powerful typhoon, Typhoon No. 19, 1991. The typhoon produced more (6.7gaps ha^<-1>) and much larger gaps (mean gap size was 230m^2) than those produced before the typhoon disturbance (3.3gaps ha^<-1> and mean gap size was 31.2m^2). Multiple treefalls were occurred by the typhoon, while all gapmakers were single death of canopy trees before the typhoon disturbance. Dominant mode of gapmakers was dead standing before the typhoon disturbance, but the typhoon produced numerous gapmakers with trunk-breakage and did not produce standing-dead gapmakers. Numerous canopy trees of Castanopsis cuspidata were killed or injured by the typhoon, but only a few gap successors of this species could be found. Distylium racemosum, which is a dominant species in old-growth evergreen broad-leaved forests in this region, and Quercus salicina occurred frequently as a gap successor, though there were no or a few canopy trees of these species. Thus, the typhoon disturbance may accelerate the change of dominance from C. cuspidata to Q. salicina and D. recemosum in the canopy layer of the forest.

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The structure of a Beech-Magnolia stand and survival of Magnolia obovata were investigated in a 1.2 ha plot in the Wakasugi Forest Reserve, southwestern Japan, to elucidate the establishing process of the stand. Magnolia obovata occupied about 30% of total basal area as well as of the total number of canopy trees. Magnolia obovata may have appeared almost all at once about 100 years ago. The time of its appearance is similar to that of a pioneer species, Betula grossa. Magnolia obovata may have coexisted with Betula grossa in the canopy layer and formed "Canopy patch of Magnolia obovata and Betula grossa" with 250-2,000m^2 patches. A few seedlings of Magnolia obovata germinated at the middle of July 1994. However, more than 35% of them died from November 1994 to May 1995. All of them beneath the canopy died 2 years after germination. Such low survival rate and poor germination of Magnolia obovata beneath the canopy may be attributed to the lack of suppressed Magnolia obovata saplings with less than 4cm Dbh and over 20cm height in the plot. From these results, it is suggested that disturbances of 250-2,000m^2 size occurred at the same time within the plot and then Magnolia obovata and Betula grossa appeared simultaneously, forming patches in the stand.

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Acid neutralization processes in Hinoki (Chamecyparis obtusa) plantation without understory vegetation were studied through a large scale sprinkling experiment with high pH and low pH artificial rain applied in summer and winter seasons. Throughfall, stem flow and soil water were sampled at the experiment and their chemical compositions were analyzed. The results show that acid neutralization mechanism acts not in canopy nor stem but only in soils. This suggests that soil acidification should become a serious problem in Hinoki plantation without understory vegetation. The pH values of stem flow take a fairly constant values regardless of the varying rain pH value without additional inorganic acid from the stem surface. This findingstrongly suggests that the acidity of stem flow is buffered by organic acid. Ion-exchange and acid adsorption in the soils are found to be the primarily mechanisms on acid neutralization, but the mechanism for the seasonal difference still remain unveiled. Further experiment and analysis should be followed to identify the seasonal difference of adsorption process of various ions to soils.

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The effect of disturbed incubation on the mineralization of soil carbon (C) in a forest soil was investigated. Soil samples from different plot (a lower slope cedar (Cryptomeria japonica D. DON) plot, a lower slope mixed cedar and cypress (Chamaecyparis obtusa ENDL) plot, a mid-slope cypress plot, an upper slope cypress plot and an upper slope deciduous broad-leaved plot) and soil depths were investigated to clarify the characteristics of C mineralization. The C mineralization process in the soils was modelled mathematically using a simple kinetic model, and three parameters (C mineralization potential (C_0), Rate constant of mineralization (k(25℃)) and Apparent activation energy (Ea)) were examined in relation to temperatures and soil properties. Disturbed incubation of soil from the middle and upper slope positions decreased the C_0 by 15-34% at 0-10cm depth and by 15-65% at 10-20cm depth. There were many fine roots in the plots where C_0 was decreased by disturbed incubation. This suggests that the amount of C and the microbial activity in the rhizosphere were reduced by removing the fine roots. However, disturbed incubation had no great effect on the relationships between C_0 and slope positions or depth. k(25℃) was higher in disturbed incubation in most soil samples because microbial activity and CO_2 diffusion were greater in disturbed soils. It was assumed that the removal of fine roots (C source) would increase Ea. However, except for the cedar plot, Ea was lower or similar level in disturbed than in undisturbed incubations. It was concluded that this was because the fine roots and other large organic matter had a lot of material that difficult to mineralize (e.g. Lignin) or which inhibits mineralization (e.g. Terpenoids and Polyphenols).

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Hyogo ken nanbu earthquake, which hit Hanshin Awaji area on the early morning of January 17, 1995, caused soil liquefaction in coastal reclaimed lands, Port Island etc, and it spouted groundwater and reclaimed sand. It was worried that planted trees would be on the decline or dying, since spouted groundwater and reclaimed sand included much amount of sea salt. Therefore we performed to investigate and analyze sand which spouted and deposited on surface soil (deposited sand) and buried surface soil, and observe growth activities of 6 species (Ulmus parvifolia, Myrica rubra, Quercus phillyraeoides, Camellia japonica, Rhaphiolepis indica var. integerrima, Eurya emarginata) planted trees. Those investigation found results following: 1) Deposited sand had a electric conductivity (EC) of 0.7 mS・cm^<-1> and buried surface soil had a EC of 0.3 mS・cm^<-1> on March 14. Afterwards EC had become less than 0.2 mS・cm^<-1> in May when it rained approximately twice as much as average year. 2) Deposited sand intercepted and retained rainfall in which it covered surface soil thickly, therefore buried surface soil had been too dry for plant to grow smoothly. 3) Current year leaves of 5 planted tree species, except Myrica rubra, were smaller in deposited sand covered area than those in no covered area. 4) Carbon and nitrogen content of leaves of 6 species had no remarkable change during March 14 through October 17. 5) Forest floor vegetation was very poor and sexual reproduction species was also poor in deposited sand covered area. 6) Leaf water potential of 6 species indicated -2.0MPa〜-4.5MPa on August 23. Those meant that every species was under the severe by water stressed. Rhaphiolepis indica var. integerrima, Quercus phillyraeoides, and Myrica rubra in deposited sand covered area were under higher stress than in no covered area. 7) Soil liquefaction occurred in dormancy season for trees. Since there is twice rainfall amount in May 1995 compared with an average year, sea salt in deposited sand and surface soil had runoff smoothly by summer season. These were reason why most of trees had kept to live and had not been declining.

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