Effects of understory dwarf bamboo on soil water and the growth of overstory trees in a dense secondary <Emphasis Type="Italic">Betula ermanii</Emphasis> forest,northern Japan

The effects of understory dwarf bamboo (Sasa kurilensis) on soil water and the growth of overstory trees were studied in a dense secondary forest of Betula ermanii in northern Japan. Four plots were established in a Betula ermanii forest with Sasa kurilensis in the understory. The Sasa was removed in two of the plots. The annual increment of the trunk diameter for each tree was measured in the first two years from the commencement of the experiment. Soil water potential was similar in the plots following significant rainfall, but was found to be greater in the plot without Sasa between rainfall events. This suggests that the removal of Sasa slows the reduction of soil water after rainfall. The relative growth rate of the trunk diameter of Betula ermanii increased with tree size in all of the plots because taller trees strongly suppressed smaller ones in the dense forest. The growth rates of Betula ermanii were higher in the plots without Sasa. However, the difference in growth rates between all of the plots tended to be smaller in smaller size classes, possibly because smaller trees were strongly suppressed by larger ones, irrespective of the presence/absence of Sasa. Therefore, the removal of Sasa increased soil water and encouraged the growth of larger Betula ermanii in dense forest during the first two years after the Sasa was removed. The present study suggests that Sasa can reduce the growth of larger Betula ermanii in dense forest by limiting available soil water to these trees.     

Demographic traits of understory trees and population dynamics of aPicea-Abies forest in Taisetsuzan National Park, northern Japan

The size structure transition matrices ofPicea jezoensis, Picea glehnii andAbies sachalinensis of a sub-boreal forest in Hokkaido, northern Japan were constructed based on the demography of each species (Picea jezoensis andPicea glehnii were dealt with together asPicea) during a 4-year period. Two types of matrices, density-independent and density-dependent population dynamics models, were investigated for evaluating the ‘waiting pattern’ betweenPicea spp. andA. sachalinensis. For the density-dependent model, it was assumed that the demographic traits of understory trees, the recruitment rate, the understory mortality rate and the transition probability from the understory to canopy stages, were regulated by the one-sided competitive effect of canopy trees. The observed size structure ofPicea was almost consistent with the stationary size structure obtained in both the density-independent and the density-dependent models, whereas the observed size structure ofA. sachalinensis was not realized in the two models. The effects of both the transition probability from the understory to canopy stages and the recruitment rate on the dynamics of canopy trees were investigated. ForPicea, two parameters—recruitment rate (e _i ) and transition probability from the understory to canopy stages-exponentially affected the dynamics of canopy trees. In contrast, forAbies sachalinensis, the two parameters affected linearly the dynamics of canopy trees. In conclusion, the population dynamics ofPicea andA. sachalinensis was determined by the parameters of the recruitment rate and the transition probability from the understory to canopy stages, relating to waiting patterns of understory trees for future gap formation. InPicea, the demographic parameters of understory trees intensively regulated the dynamics of canopy trees if compared withA. sachalinensis, suggesting that the performance of understory trees plays a key role in the population dynamics ofPicea. This reflects the growth pattern of understory trees in the regeneration of the two species.     

Regeneration and coexistence of two subalpine conifer species in relation to dwarf bamboo in the understorey

Abstract. Microhabitats for seedling establishment and gap regeneration in subalpine forests of northern Japan were studied for two conifers, Abies sachalinensis and Picea glehnii. The abundance of understorey dwarf bamboo (Sasa spp.) was different for the four plots examined. Two types of micro-habitats were recognized for the two conifers: ground and elevated woody substrates (fallen logs and buttresses). Picea regenerated mostly on elevated sites, while Abies regenerated on both ground and elevated sites. The densities of Picea were independent of those of Sasa, but Abies densities decreased with increasing abundance of Sasa because Sasa reduced regeneration on the ground. Density of Abies on elevated sites was higher than that of Picea, irrespective of Sasa and of the density of adult trees. There was no significant difference in growth in sapling trunk height between the two conifers, but Picea grew more slowly under the canopy than Abies and was aggregated into gaps. Thus, in forests with less Sasa, the recruitment capacity of Abies was greater than that of Picea. The long life span of Picea compensated for its low density on elevated sites. Examination of a dynamic system model showed that Picea was excluded by Abies in forests without Sasa because regeneration on the ground is more advantageous than on elevated sites, but the two conifers could coexist in forests with Sasa because of the increased relative success of regeneration on elevated sites by Picea saplings.     

Roles of dominant understory Sasa bamboo in carbon and nitrogen dynamics following canopy tree removal in a cool‐temperate forest in northern Japan

To clarify the role of dense understory vegetation in the stand structure, and in carbon (C) and nitrogen (N) dynamics of forest ecosystems with various conditions of overstory trees, we: (i) quantified the above‐ and below‐ground biomasses of understory dwarf bamboo (Sasa senanensis) at the old canopy‐gap area and the closed‐canopy area and compared the stand‐level biomasses of S. senanensis with that of overstory trees; (ii) determined the N leaching, soil respiration rates, fine‐root dynamics, plant area index (PAI) of S. senanensis, and soil temperature and moisture at the tree‐cut patches (cut) and the intact closed‐canopy patches (control). The biomass of S. senanensis in the canopy‐gap area was twice that at the closed‐canopy area. It equated to 12% of total biomass above ground but 41% below ground in the stand. The concentrations of NO₃^? and NH₄⁺ in the soil solution and soil respiration rates did not significantly change between cut and control plots, indicating that gap creation did not affect the C or N dynamics in the soil. Root‐length density and PAI of S. senanensis were significantly greater at the cut plots, suggesting the promotion of S. senanensis growth following tree cutting. The levels of soil temperature and soil moisture were not changed following tree cutting. These results show that S. senanensis is a key component species in this cool‐temperate forest ecosystem and plays significant roles in mitigating the loss of N and C from the soil following tree cutting by increasing its leaf and root biomass and stabilizing the soil environment.     

Spatial dynamics of regeneration in a conifer/broad‐leaved forest in northern Japan

Abstract. This study deals with stand dynamics over a 6‐yr period in a conifer/broad‐leaved mixed forest in Hokkaido, northern Japan. The annual rates of gap formation and recovery were 81.3 m²/ha and 66.7 m²/ha, respectively and turnover time of the canopy was 125 yr. The recruitment processes of the component species in this cool‐temperate forest were governed by different canopy types: gap, canopy edge and closed canopy. Magnolia obovata regenerated in canopy edges, and Acer mono and Prunus ssiori regenerated in canopy edges and gaps. The results suggested that the mosaic structure made up of closed canopy, canopy edge and gap was related to various regeneration niches. Abies sachalinensis had high mortality rates, initiating gap expansion. The transition probabilities from closed canopy or canopy edge to gap for deciduous broad‐leaved trees were lower than for A. sachalinensis, which implies that the difference in degeneration patterns of conifer and broad‐leaved canopies contributes to the heterogeneity of spatial structure in the mixed forests. Spatial dynamics were determined by a combination of gap expansion by A. sachalinensis (neighbour‐dependent disturbance) and gap formation by deciduous broad‐leaved trees (random disturbance).     

Stand structure and growth patterns of understorey trees in a coniferous forest,Taisetsuzan National Park,northern Japan

Stand structure was studied with special reference to growth and mortality patterns of sapling and understorey trees in a coniferousPicea jezoensis andAbies sachalinensis forest in Taisetsuzan National Park, Hokkaido, northern Japan.Picea jezoensis was dominant in the basal area, whileA. sachalinensis was abundant in large numbers in the canopy. Estimated mortalities increased significantly with diameter at breast height (DBH) for bothP. jezoensis andA. sachalinensis in the canopy, but the tendency was different between the two species.Picea jezoensis had a lower mortality rate thanA. sachalinensis, especially at small DBH classes. The spatial distribution of understorey individuals ofA. sachalinensis did not show any significant correlation with the spatial distribution of canopy gaps, but that ofP. jezoensis showed a significant correlation.Abies sachalinensis can grow higher thanP. jezoensis under suppressed conditions; whileP. jezoensis requires canopy gaps for steady height growth. This growth pattern leads to a different waiting height in the understorey (≥2 m in height and 10 cm in diameter at breast height).Abies sachalinensis waited for an improvement in light conditions at higher strata (max. 7 m), whileP. jezoensis waited at lower strata (max. 3 m). The estimated mortality of understoreyA. sachalinensis increased with size, while that of understoreyP. jezoensis decreased. Therefore,P. jezoensis gives priority to survival whileA. sachalinensis gives priority to understorey growth. The difference in the ‘waiting pattern’ between the two species in the understorey was considered a significant feature for the canopy recruitment process ofP. jezoensis andA. sachalinensis.     

Short‐term changes affecting regeneration of Fagus crenata after the simultaneous death of Sasa kurilensis

Abstract. Question: The aim of the present study is to determine whether seed/seedling predation will increase and Fagus survival will decline with the recovery of the Sasa cover. Methods: We examined Fagus crenata regeneration for seven years in an old‐growth Fagus‐Sasa forest near Lake Towada, northern Japan, by examining the effects of simultaneous death of Sasa, tree canopy gap formation, mast seeding of Fagus and seed and seedling predation by rodents on the survival of Fagus seeds and current year seedlings. We established four types of sites differing in forest canopy (closed or gap) and Sasa status (dead or alive) following the simultaneous flowering and death of Sasa kurilensis (dwarf bamboo) in 1995. Results: Fallen Fagus seed was abundant in 1997 and 2000 (mast years). In sites with alive Sasa, survival from the first growing season was low due to high seed and seedling predation. In sites with dead Sasa, seed survival under the canopy was high for both mast years, but in gaps it varied between years. Seedling survival was highest in canopy gaps with dead Sasa (gap‐dead) in 1998, because of higher light levels and lower predation by rodents. However, seedling survival in these plots was low in 2001, apparently because rapid Sasa recovery favoured rodent predation. In both mast years, Sasa die‐back had significant positive effects on seed and seedling survival under closed canopies because the seedlings there were more successful in escaping predation. Conclusion: The change in successful sites for the early stage of regeneration of Fagus appears to reflect the combined effects of canopy gap, seed/seedling predation and revegetation of Sasa.     

An interactive effect of simultaneous death of dwarf bamboo, canopy gap, and predatory rodents on beech regeneration

To clarify the interactive effect of the simultaneous death of dwarf bamboo (Sasa kurilensis), forest canopy gap formation, and seed predators on beech (Fagus crenata) regeneration, we analyzed beech demography from seed fall until the end of the first growing season of seedlings in an old-growth forest near Lake Towada, northern Japan. The simultaneous death of S. kurilensis took place in 1995. We established four types of sampling site differing in forest canopy conditions (closed or gap) and Sasa status (dead or alive). Beech seed survival and emergence ratio were both highest in gaps with dead Sasa (gap-dead), because rate of predation was lowest. Seedling survival during the first growing season was also highest in the gap-dead treatment, because of less predation and less damping off. As a result, even though density of seed fall was lowest in the gap-dead treatment, the living seedling density there was highest at the end of the first growing season. Predation, which caused the greatest mortality during the seed and seedling stages, was significantly lower at both sites in gaps and sites with dead Sasa. This was probably due to changes in the behavior of rodents in response to the structure of the forest canopy and undergrowth. Both the death of Sasa and canopy gap formation allowed seedlings to avoid damping off because of the high light availability. The indirect effect of the simultaneous death of Sasa and canopy gap formation in reducing predation contributed more to beech regeneration than their direct effect in increasing light for the seedlings.     

Microsite variation in light availability and photosynthesis in a cool-temperate deciduous broadleaf forest in central Japan

An empirical light simulation model was applied to estimate stand scale photosynthesis in a deciduous broadleaved forest in central Japan. Based on diurnal courses of photosynthetically active photon flux density (PPFD), we characterized the components of incoming light within the forest canopy, and found that the instantaneous relative PPFD (PPFD under the canopy relative to that above the canopy) under diffuse light condition was a reliable estimator of the intensity and duration of PPFD. We calculated the daily photosynthesis (A_day) for each PPFD class using photosynthesis–light response curves. Model simulated A_day were corroborated with the estimates obtained from the nearby CO₂ flux tower. The result demonstrated the potential of the light simulation model. The light use efficiency of two dominant species, Betula ermanii as overstory and Sasa senanensis as understory species, were then evaluated. At the forest understory, PPFD under 50 mol m^–2 s^–1 contributed to 77% of the sunshine duration on a completely clear day. Therefore, a higher apparent quantum yield for S. senanensis enhanced the utilization of low PPFD for photosynthesis. On the other hand, at the upper forest canopies, B. ermanii with a higher light-saturated photosynthetic rate used high PPFD efficiently. Consequently, potential of daily net photosynthesis for both B. ermanii and S. senanensis was high under each light condition. Such interspecific difference in the patterns of light utilization was suggested as one of factors allowing coexistence of the two species in the study forest.     

Gap characteristics and gap regeneration in a subalpine coniferous forest on Mt Ontake,central Honshu,Japan

Gap characteristics and gap regeneration were studied in three mature stands belonging to different community types in a subalpine coniferous forest on Mt Ontake, central Honshu, Japan. Gap disturbance regimes were remarkably similar among stands studied; percentage gap area to surveyed area, gap density and mean gap size were 7.3–8.5%, 17.8–20.0 ha⁻¹ and 40.8–42.5 m², respectively. The gap size class distributions were also similar and showed a strong positive skewness with a few large and many small gaps; gaps <40m² were most frequent and gaps >200m² were rare. Forty-five to 66% of gaps were due to the death of single canopy trees. Canopy trees more often died leaving standing dead wood (40–5.7%) or broken trunks (43–49%). Shade tolerantAbies mariesii andAbies veitchii, frequently, andTsuga diversifolia, less frequently, regenerated in gaps, from advance regenerations recruited before gap formation.Picea jezoensis var.hondoensis may regenerate in gaps, from new individuals recruited after gap formation. The breakage of denseSasa coverage and the mineral soils exposed by the uprooted plants that form gaps might provide regeneration opportunities for shade intolerantBetula. Of the important species limited to the ridge site,Chamaecyparis obtusa, frequently, andThuja standishii, infrequently, regenerated from plants alreadyin situ. Regeneration ofPinus parviflora was not seen. Based on the gap characteristics and gap regeneration behaviour of each species described, stand dynamics in each stand are discussed.     

Size-structure dynamics of two conifers in relation to understorey dwarf bamboo: A simulation study

Abstract. Size-structure dynamics and co-existence of the conifers Abies sachalinensis and Picea glehnii in subalpine forests in Japan, in relation to the understorey dwarf bamboo Sasa, were examined using a simulation model. This model explicitly incorporated recruitment rate, size growth rate and mortality. Recruitment and growth rates were assumed to be suppressed by the cumulative basal area of taller trees and the density of Sasa. As for the one-sided crowding effect, two types of model were examined. The total basal area of the two species suppresses the growth and recruitment rates in an additive model, while the basal area of each species has a separate effect included in a specific model. Two types of recruitment process were examined, i.e. open and closed systems; recruitment rates of open and closed systems are independent of, and proportional to, the basal area of the same species within the plot, respectively. Parameters were estimated from data of plot censuses for four years. The parameters of the specific model showed that recruitment and size growth rates were more suppressed by the same species than the other species. Recruitment of A. sachalinensis was more sensitive to suppression by Sasa compared with P. glehnii. The stationary size structure of the two species, generated from both the models with the open system, fitted well to the observed size structures across various Sasa densities. A. sachalinensis and P. glehnii dominated at lower and higher densities of Sasa, respectively. However, the closed-system simulation showed that the stable co-existence of the two species with a good fit to the observed size structure occurred only in the specific model. These results suggest that within-species interference, which is more severe than between-species interference, is important for the co-existence of the two species and that the relative dominance of the two species readily explained the differential responses to Sasa abundance.     

Regeneration in subalpine coniferous forests

The regeneration process of a subalpine coniferous forest, a mixed forest ofTsuga diversifolia (dominant species),Abies veitchii, Abies mariessi, andPicea jezoensis var.hondoensis, was studied on the basis of annual ring data. The age class distribution was discontinuous and four age groups occurred in the study plot (30m×30m). The canopy layer was a mosaic of patches (83.8–133.7 m² patch area), which had different mean ages. The recruitment of canopy trees was carried out only by advance regeneration in the plot. The diameter growth ofAbies andPicea exceeded diameter growth ofTsuga in the gap.Abies lived for 200–300 years and their trunks were susceptible to heart rot.Picea lived for 300–400 years andTsuga for more than 400 years. The regeneration process derived from the analysis of the plot consisted of three phases leading to the development of a even-aged patch; (1) the establishment of saplings before a gap opening, (2) the opening of a gap in the canopy and repair of the canopy by advance regenerated saplings dominated by rapid growth species,Abies andPicea, and (3) the dying off of canopy trees as each species reached the end of its life-span, resulting in pure patches of long-livedTsuga.     

Stand development and regeneration during a 33-year period in a seral Picea glehnii forest, northern Japan

Stand development and regeneration were studied during a 33-year period (1965-1998) in a 1-ha plot in a seral Picea glehnii forest in northern Japan. P. glehnii was mono-dominant in the upper canopy layer, but its understory trees were rarely found in 1965. Other species were scarcely observed in 1965. Many recruited saplings of Abies sachalinensis which had grown to > 5 cm diameter at breast height (DBH) by 1998 had become dominant in the understory layer. Mortality of P. glehnii canopy trees was low. Therefore, the stand basal area increased during the census period due to the growth of surviving canopy trees. Stand development brought about intense competition among trees by increasing local crowding for each tree, and promoted dominance of larger trees and suppression of smaller trees. Although growth rates of understory trees of the two conifers decreased with the increase in local crowding, the growth rate of A. sachalinensis was consistently higher than that of P. glehnii at all extents of local crowding. The recruitment rate (growing to 5 cm DBH) of the two conifers was less affected by local crowding. However, the number of recruits of P. glehnii was only about a quarter of that of A. sachalinensis during the census period because the regeneration of P. glehnii was largely restricted to fallen logs and within 1 m of the base of any live tree > 20 cm DBH. Therefore, our long-term study suggests that A. sachalinensis will dominate over P. glehnii in the seral forest because of higher recruitment and growth rates of the former than the latter in the understory.An erratum to this article can be found at     

A forest-structure-based analysis of rain flow into soil in a dense deciduous Betula ermanii forest with understory dwarf bamboo

The relationship between rain flow into the soil and forest structure was investigated in a dense deciduous Betula ermanii forest in northern Japan. The forest floor was covered with dwarf bamboo Sasa kurilensis. Observation was conducted from mid-July to late October in 1998. Leaf fall of Betula started in early September and ended in late October. Stemflow was proportional to rainfall and tree size [diameter at breast height (DBH)], and for the same rainfall, stemflow increased with leaf fall. On the contrary, throughfall decreased with leaf fall. Throughfall was intercepted also by Sasa in proportion to its leaf area. Multiple linear regression analysis revealed that stemflow and throughfall of Betula and Sasa were predictable as functions of rainfall and forest structural characteristics, such as DBH, tree density, and stand leaf mass. The rain interception by plants tended to decrease from summer to autumn, but the difference in the interception was about 2% between July (fully expanded leaves) and late October (lack of leaves). About 96 and 87% of rainfall reached the above- and below-Sasa layers, respectively. Thus, this study showed that understory Sasa is a major component of rain interception within the stand and that rain flow into the soil can be estimated by using rainfall and the forest structural parameters, such as DBH, tree density and stand leaf mass.     

The effect of dense understory dwarf bamboo (Sasa senanensis) on soil respiration before and after clearcutting of cool temperate deciduous broad-leaved forest

To evaluate the effect of understory dwarf bamboo (Sasa senanensis) on soil respiration in forest ecosystems, we compared soil respiration rates between four deciduous broad-leaved forest sites representing two levels of understory Sasa (with and without) and two levels of forest stand age (50-year-old stand and 1-year-old stand after clearcut). The understory Sasa enhances the soil respiration rate both before and after the clearcutting of deciduous broad-leaved forest. The Sasa sites had larger total belowground biomass compared with the non-Sasa sites, which could be attributed to Sasa presence. Our results also suggest that clearcutting decreases temperature-normalized soil respiration rates (R ₁₅) and temperature sensitivity (Q ₁₀) in both Sasa and non-Sasa ecosystems. Clearcutting significantly reduced the fine root biomass of trees and Sasa. The fine roots of trees and Sasa had high specific respiration rates compared with larger roots and rhizomes at Sasa and non-Sasa sites, respectively. Therefore, we hypothesize that the loss of fine roots after clearcutting is responsible for the reduction in soil respiration rate. A comparison with other studies revealed a positive linear relationship between total (tree and Sasa) fine root biomass and R ₁₅, suggesting that fine root biomass controls soil respiration at the landscape scale. The Q ₁₀ value is also likely to be related to fine root biomass, although the relationship was not significant. We conclude that understory Sasa increases belowground biomass, especially fine roots, and the spatial variation in soil respiration at the landscape scale.     

Regeneration of beech (Fagus crenata) after the simultaneous death of undergrowing dwarf bamboo (Sasa kurilensis)

Seedling recruitment and survivorship of beech (Fagus crenata) were studied with special reference to the simultaneous death of undergrowing bamboo (Sasa kurilensis). The survival rate of beech seedlings on the floor whereSasa had withered was much higher than that on the floor whereSasa survived. Damping off caused the largest mortality among beech seedlings. However, the allocation pattern of matter to different parts of the seedlings indicated that their survival was greatly affected by production economy. The dense cover of dwarf bamboo prevented the establishment of beech seedling banks on the forest floor. The interval between the times when simultaneous death ofSasa occur and the length of its recovery period are thus important factors controlling the dynamics of beech forests in Japan.     

Comparative studies on acorn and seedling dynamics of fourQuercus species in an evergreen broad-leaved forest

The dynamics and regeneration probabilities ofQuercus acuta, Q. gilva, Q. salicina, andQ. sessilifolia were studied in a 0.48 ha plot in an old-growth evergreen broad-leaved forest, Kagoshima prefecture, southwestern Japan. The canopy was well closed and had only one small gap. Seventeen tree species occurred in the canopy. The fourQuercus species ranked second to fifth in basal area. Excluding the trees originated from sprouts,Q. acuta and Q. gilva lacked trees at the subcanopy layer, andQ. salicina andQ. sessilifolia had some trees at the same layer. For eachQuercus species, the amount of fallen acorns fluctuated from year to year. The number of current year seedlings was positively correlated with the number of fallen acorns in the previous year. A disproportion between the spatial distribution of fallen acorns and that of established seedlings has been shown. The establishment of seedlings was frequently observed where no acorns had fallen in the previous year. Saplings of four species survived for several years and formed sapling banks under the closed canopy. During the three years of the study, the mortality ofQ. salicina andQ. sessilifolia saplings was lower than that ofQ. acuta andQ. gilva. However, the differences in the average annual height growth of saplings between four species were not significant, and the most of them did not grow much. These results suggest that the saplings of the fourQuercus, especiallyQ. gilva andQ. acuta, have no chance to recruit to the canopy or subcanopy layer within a closed stand, and that some changes in the environment caused by gap formation are required for their recruitment.     

Effects of disturbance and size structure on the regeneration process in a sub-boreal coniferous forest,northern Japan

The stand structure and disturbance history in a sub-boreal coniferous forest dominated byPicea jezoensis, Picea glehnii andAbies sachalinensis were investigated in four study plots set up in Taisetsuzan National Park, Japan. The effect of stand characteristics on the growth and mortality rates of understory trees was examined. Although all the stands showed inverse J-shape d.b.h. (diameter at breast height) distributions, the age structure and disturbance history differed amongst the stands. The stands with wide d.b.h. distribution (i.e. large CV and skewness) were more uneven-aged than those with narrow d.b.h. distribution (i.e. small CV and skewness). The disturbance-return interval based on the model of Hett and Loucks was 31 to 65 years. The gap ratio in the canopy was also different among the stands. These suggest that the variations in stand structure represent different occurrences of natural disturbances. Furthermore, the structural features such as size structure, canopy gap ratio and density of canopy trees also affected the growth dynamics of understory trees (≥2 m in height and <10 cm in diameter at breast height). The growth and mortality rates of understory trees changed with the canopy gap ratio and canopy tree density. The understory trees of stands with wide canopy d.b.h. distribution had higher growth and canopy recruitment rates than those of stands with narrow canopy d.b.h. distribution, contributing to the maintenance of continuous stand stratification. The understory trees of stands with narrow canopy d.b.h. distribution showed lower growth and higher mortality rates than those of stands with narrow canopy d.b.h. distribution, leading to the formation of a single-canopy structure. It is suggested that natural disturbance governs the regeneration process in the future by affecting the growth and mortality patterns of understory trees through the stand structure (size and age structure, canopy tree density, canopy gap ratio).     

Revegetation process on a subalpine mudflow

The process of revegetation on a subalpine mudflow was analyzed on the basis of the vegetation-soil relationship of the revegetated stands, and of the age structure and height growth process of the trees. Based on evidence derived from five independent sources, it was concluded that this mudflow was caused by a typhoon in 1959. The revegetated stands were classified into three vegetation types. AnAlnus maximowiczii stand was established where the surface soil was unstable; aBetula ermanii stand was established where the degree of disturbance by the mudflow was small; anAlnus-Betula stand was the intermediate type and occupied most of the area on the mudflow.Alnus had colonized concentrically 4–6 yr after the mudflow, andBetula and conifers had followed 1–2 yr later. As revegetation proceeded, the trees became differentiated into two populations, a canopy population and a suppressed one. The former was dominated mainly byAlnus and the latter byBetula and conifers. This differentiation was caused by the faster growth ofAlnus during the initial years of colonization. SomeBetula trees have recently grown faster thanAlnus, suggesting future replacement in dominance. Conifers have grown slowly even during recent years; the highly oligotrophic condition of the soil appears to have been responsible for this delayed growth.     

Early post-fire vegetation regeneration in <Emphasis Type="Italic">Larix kaempferi</Emphasis> artificial forests with an undergrowth of <Emphasis Type="Italic">Sasa senanensis</Emphasis>

Post-fire vegetation regeneration was studied for a 6-year period in a 13-year-old-artificial forest consisting of Larix kaempferi with a dense undergrowth of Sasa senanensis. The study site was classified into three fire severity categories according to the degree of Sasa senanensis scorching, that is, a high-severity category, a mid-severity category, and a low-severity category. Study plots were established in areas which fitted the criteria for each category, and in nearby unburned sites. A total of 41 woody species were newly emerged during the 6-year study period in the burned and unburned plots. Only a few seedlings and resprouts emerged in the unburned plots, while many seedlings emerged in the high-severity plots from the first year after fire onward. A high-severity fire that burns the rhizomes of Sasa is necessary for the vegetation recovery by germination of seed. Whereas the establishment of seedlings was restricted to a few years after fire, the regeneration through resprouting continued into the last year of observation. The survival time of resprouts was longer than that of seedlings, and the survival time of shade-tolerant species was longer than that of shade-intolerant species. In contrast, shade-intolerant species grew more rapidly than shade-tolerant species. The plants ability to exceed the maximum height of the Sasa before the bamboo recovers can be critical to the survival of shade-intolerant species. Because resprouts have a stronger resistance to the shade of Sasa than seedlings, the resprouts of shade-tolerant species play a major role in the re-establishment of woody species after fire in sites with considerable Sasa ground-cover.