This report represented a method which estimated Water Holding Capacities (WHC) of watersheds and made comparison between estimated WHC of two small experimental watersheds. The watersheds were Shozawa No.1 and No.2 experimental watersheds in Takaragawa Forest Watershed Experiment Station of Forestry and Forest Products Research Institute. Soil profiles and soil depths were surveyed at those two experimental watersheds. Soil map and soil depth distribution map were arranged with those surveyed data, and distributing area of soil types and soil depths associates were estimated by overlaying those two types of maps. WHC of soils of two watersheds were calculated using the content rate of soil pores of coarse, medium, and small size classes which were ones of five size classes i.e. fine, coarse, small, and large pore. Calculated WHC of every three pore size classes of No.1 watershed was higher than No.2 watershed and the difference of WHC of small size of pore between two watersheds was most distinguish. Those result was ascribed to deep soil horizon and higher content of small size soil pores of No.1 watershed. On the other hand, difference of water conservation function of the two watersheds was clarified by analysis of accumulated observation data of water discharge at Takaragawa Forest Watershed Experiment Station, and the function of No.1 watershed surpassed that of No.2. The difference is thought to be attributed to the difference of WHC of soils in two watersheds, especially WHC of small size soil pore.

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This study discussed the relationship between snow dynamics and ecological characteristics of trees on the snowy slope of Mt. Yakeishi, central the Oou mountain range, north east Honsyu, Japan. Most of dwarf-type formed deciduous broad leaved trees dominated on the lee ward slope against the winter seasonal wind. The snow folds and snow cracks caused by glide of snow cover extended over a wide area of the lee ward slope and also the debris of full-depth snow avalanches were observed at places. And the scars caused by the snow erosion distributed in the slope. On the other hand, numbers of pit and mound formations caused by uprooting of middle or large size stands were observed on the wind ward slope and the longitudinal shape of the slope showed uneven feature like a staircase. While the dominant tree species on the lee ward slope were Alnus pendula, Weigela hortensis, Fugus crenata and others, those on the wind ward slope were Fugus crenata, Hamamelis japonica var. obutusata, Acer japonicum and others. The stands on the lee ward slope were extremly small in the size and showed the groundlinglike form which had extraordinary large basal bending width in contrast to those on the wind ward slope. The basal bending width varied with each tree species and that of higher ranking dominant tree species was larger on the lee ward slope and smaller on the wind ward slope. It seems advantegeous to the tree species to adapt for the creep and glide pressure of snow on the lee ward slope and to adapt for the settlement force of snow on the wind ward slope for the survival of individuals. Fagus crenata dominated on the both slopes seems to be the species of high snow tolelance capacity adapted to the snow environment which excelled in the settlement force rather than the creep and glide pressur of snow cover. The regeneration style of the stand growing on the snowy slope depend chiefly upon sproutings on the lee ward slope while seedlings on the wind ward slope. The ecological characteristics of trees above mentioned are the reflex of the difference of snow environment, and not only the depth of snow but also the qualitative aspect of snow such as the variety of metamorphic process and the snow dynamics such as glide and avalanches play an important role in the snow environmental factor which affect the distribution of community.

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Changes in weed cover, weed nutrient contents, water chemistry of throughfall and the decomposition process of organic matter after weeding were investigated in stands of young Japanese cedar (Cryptomeria japonica D. Don) and Japanese cypress (Chamaecyparis obtusa Endl.) to study the effects of weeds and weeding on the nutrient dynamics of young stands. Nutrient contents of throughfall in established Japanese cedar and Japanese cypress stands adjacent to the young stands was investigated for comparison with that of young stands. Weed cover amounted to 3〜5t・ha^<-1> in 3〜5-yr-old stands and the nutrient contents of weeds equaled the amount of uptake by established stands. The weeds took more nutrients from the soil than did the young trees. The throughfall in the young stands was approximately 90% of the precipitation and was more than the throughfall of the established stands. The pH values of the weed throughfall (5〜7) were higher than those of the precipitation and the throughfall (4〜5) in the established stands. In the defoliate period, significant increases in the dissolved element concentrations except N were observed in the weed throughfall, because weeds easily leached mineral nutrients. The relationships between the accumulated surface soil temperature after weeding and the residual organic matter satisfied an exponential curve. Great amounts of nutrients were supplied to the soil by the weeding, but most of the nutrients supplied by the decomposition of weeded organic matter could not be used by the young stands, because there was little nutrient uptake by planted trees. Therefore, nonweeding can provide a constant nutrient supply in young stands. The complete weeding is not advantage for maintaining soil productivity and effective biological utilization of nutrient in young stand.

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The water holding capacities of the catchments of 107 multipurpose dams were estimated by the runoff analysis. Differences from surface geological, the average water holding capacity of the catchments was 253mm on the metamophic rocks, 252mm on the granites, 213mm on the volcanic rocks, 207mm on thesedimentary rocks of the Palaeozoic or the Mesozoic, and 188mm on the sedimentary rocks of the Tertiary. The average water holding capacity of 107 catchments was 219mm, and was almost same value as the average of the effective water reservior capacity of 107 dams was 233mm. Differences from regional, the average water holding capacity of the catchments in Kinki and Shikoku region were less than 200mm, Tohoku region was the largest value at 247mm. The average water holding capacity of the catchments estimated by the runoff analysis was almost same level as the average rainwater strage capacity of forest soils of the catchments estimated by the pore analysis in some past reports. From these results, it suggested that not only the direct runoff but also the base flow of the forest catchments were closely connected with the properties of soil water retentivity.

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Betula maximowicziana was naturally regenerated by seeding on a regeneration area where Chamaecyparis obtusa was planted after a more than 300-year-old mixed stand of Chamaecyparis obtusa, C. pisifera, and Betula maximowicziana was clearcut and Sasa senanensis and other vegetation were controlled. Weeding was ceased to research the coexistent relationship between C. obtusa and B. maximowicziana. Eight years later, a two-layered forest of B. maximowicziana and C. obtusa was being established, i.e., the upper layer was dominated by B. maximowicziana and the lower layer was dominated by C. obtusa. In the plot where weeding was conducted, the density, height, and dominancy of C. obtusa were lower and the dominancy and height of S. senanensis was higher than those in the controlled plot. This was attributed to the decreased shading effect of the fast growing broad-leaved species on S. senanensis owing to suppression of these fast growing species by weeding. The removal of the fast growing broad-leaved species also created harsh conditions by making C. obtusa prone to damage by frost. The structure of the stand left uncut which was adjacent to the experimental plots was analyzed. The dominancy of the upper layer was high in the order of C. obtusa, C. pisifera, and B. maximowicziana, but young generation of them was very rare in the lower layer.

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Canopy gaps and gap phase replacement in an old-growth beech forest with dwarf bamboo understory, Wakasugi Forest Reserve, southwestern Japan, were surveyed to clarify the regeneration and to predict the future status of the beech forest. Percentage gap area (percentage of total gap area to the area surveyed) was 15.2%. Gap density was 13.7gaps ha^<-1> and mean gap size was 110.6m^2 ranging from 9.1m^2 to 285.0m^2. Gaps smaller than 160m^2 were much more abundant than larger ones (73.7% of total 19gaps). About 68% of all gaps were those formed by single gapmakers and the remainder were by multiple gapmakers. Dominant mode for the death of canopy trees was by broken trunks; 42.9% of canopy trees died by broken trunks. Death of canopy trees by leaving standing-dead was 10.7% and that by uprooting was 7.1% of all gapmakers (28trees). Density and size traits of canopy trees in this forest were not different with those of other old-growth beech forests. Of important canopy tree species, Fagus crenata and Cryptomeria japonica might regenerate in gaps from saplings recruited before gap formation, although Betula grossa and Quercus mongolica had no regenerations. Thirty-nine percent of the area under crowns of canopy trees sampled and 58% of the understory of all gaps surveyed were occupied by a dwarf bamboo, Sasamorpha borealis, and were without regenerations of any tree species. If this situation continues, it seems that density and number of species of canopy trees in this forest will clearly decrease.

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