Masahiko Ohsawa

Differentiation of vegetation zones and species strategies in the subalpine region of Mt. Fuji

The floristic and structural differentiation of vegetation along the altitudinal gradient in four subalpine forests of different developmental stages on Mt. Fuji has been studied. Near the forest limit a micropattern of vegetation corresponding to the altitudinal zonation has been observed which elucidated the mechanisms of development of the vegetation zonation. As to early stages of vegetation development only two types can be distinguished: the volcanic desert above 1500 m and the pioneer forests below. As to later stages a differentiation of subzones includes from higher to lower altitudes: the Alnus maximowiczii, Betula ermanii, Abies veitchii and Tsuga diversifolia forests. Larix leptolepis and Sorbus americana ssp. japonica, appear as co-dominants in ecotonal communities between the principal subzones and are also important pioneers in early stages. Similarity analyses reveal that the upper subalpine Alnus-Betula forests can be regarded as early successional phases of the climax Abies-Tsuga forests of the lower subalpine zone. The regular arrangement of A. maximowiczii-B. ermanii-A. veitchii is studied along the gradient from the margin to the interior of the forest growing near the forest limit where locally favourable conditions prevail. Growth form, height growth, photosynthetic activity, seed supply, and seedling distribution of the three principal species have been compared, as well as biomass and production relations in contiguous forests of these species. The marginal Alnus type community is productive and disturbance-tolerant, and has a wide ecological and sociological amplitude along the gradient, while the central Abies community is accumulative and disturbance-intolerant, and has a narrower tolerance range, but is superior in competition under stable habitat conditions. A vegetation organization, ‘temporal multi-storeyed structure’, is suggested which means that a zonal pattern of vegetation within a climax region develops by successive replacement of successional species along an environmental gradient.

Adaptive significance of sprouting ofEuptelea polyandra, a deciduous tree growing on steep slopes with shallow soil

We investigated growth characteristics ofEuptelea polyandra Sieb. et Zucc. (Eupteleaceae), a Japanese endemic deciduous tree species growing on unstable ground such as that of very steep slopes with thin soil.Euptelea polyandra began to sprout at the juvenile stage and had a multiple-stemmed tree form. There was a positive correlation between diameter of the maximumsized stem within a stool (DMS) and the number of stems within the stool. Many stools had suffered from disturbances as shown by the fact that uprooting scars were found on 31.4% and 42.4%, respectively, of the stools of the two populations studied. Sprouting played a significance role in repairing damaged stems and stools, and at least 15.5% and 18.2% of the stools of the two populations, respectively, had apparently avoided death by sprouting. Sprouted stems gradually inclined with the increase in their relative sizes within each stool, and this seemed to facilitate the establishment of younger sprouted stems. The small younger sprouted stems had their own roots. There were dormant buds on stems which originated from axillary buds, and secondary dormant buds occurred by branching. The total number of dormant buds in a stool increased with DMS. It is concluded thatE. polyandra accumulates dormant buds for sprouting in order to respond to disturbances quickly.

Topographical pattern of the forest vegetation on a river basin in a warm-temperate hilly region, central Japan

The relationship between tree distribution and topography was examined in a small river basin (3.4 ha) comprising a complex mosaic of topographical units at 102 to 103 m2 order, each of which had a shallow valley bordered by small ridges or breaks of slopes. Twenty-five major woody species were divided into two groups (groups A and B) based on a cluster analysis using the distribution data in the basin. Group A, which mainly consisted of early-successional species, was distributed around the valley sites of the topographical units, while group B, which mainly consisted of late-successional species, was distributed around the ridge sites of the topographical units. This vegetation pattern coincided with erosional condition in the basin. That is, the valley sites were eroded more actively than the ridge sites, as soil depth tended to be thin in the valley sites and thick in the ridge sites, and because large (canopy) trees were restricted in the ridge sites. There was no tendency that group B was replacing group A, and hence it was suggested that repeated disturbance by slope failures or small-scale shallow landslides have prevented compositional change from the early-successional (group A) to the late-successional (group B) species by preventing the invasion of the latter into valley sites.

Soil nitrogen mineralization rates of rainforests in a matrix of elevations and geological substrates on Mount Kinabalu, Borneo

Mt Kinabalu, Borneo, is characterized by a deep elevational gradient and mosaics of geological substrates. We chose a pair of two geological substrates (sedimentary vs ultrabasic) at five altitudes (800, 1400, 2100, 2700 and 3100 m a.s.l.). We investigated soil nitrogen (N) mineralization and nitrification rates using an incubation technique to assay the pattern and control of soil N status in this environmental matrix. In situ net mineralization rates decreased with elevation on both substrates. The decreasing pattern was linear across altitudes on ultrabasic rock, whereas on sedimentary rock it was depressed in the middle slope wet cloud zone. Sedimentary sites in this zone had low soil redox potential values and this anoxic soil condition might be related to slow N mineralization. The in situ rates were significantly greater (P < 0.05, anova) on sedimentary than on ultrabasic rock at the same altitudes except in the cloud zone. Net mineralization rates of the soils that were collected from different elevations and incubated in the same conditions were statistically invariable (P > 0.05) among the original elevations for sedimentary rock, but were variable (P < 0.05) for ultrabasic rock. Those of the soils that were collected from the same elevation and incubated at different elevations decreased significantly across altitudes (P < 0.05) for sedimentary rock, while they were invariable (P > 0.05) for ultrabasic rock. Thus, temperature had stronger effects on net N mineralization on sedimentary rock, whereas inherent soil quality had stronger effects on ultrabasic rock. Controls of soil N mineralization might be different between the two substrates, leading to diverse biogeochemical site conditions on Kinabalu.

Structural comparison of tropical montane rain forests along latitudinal and altitudinal gradients in south and east Asia

Geographical patterns of altitudinal zonation, floristic composition, and structural features of tropical montane rain forests were examined along latitudinal gradients in south and east Asia. On equatorial mountains, the tropical montane rain forests occur above 1000 m. Toward middle latitudes, they come farther down and reach sea level at c. 35° N. Thus, the forests are equivalent to the subtropical rain forests of the latitudinal, horizontal zonation series. They exhibit gradual changes in floristic composition and structure along both altitudinal and latitudinal gradients. On equatorial mountains, they are divided into three types, i.e. tropical lower montane, upper montane, and subalpine forests. The three tree regeneration types, having emergent, sporadic and inverse-J type stem-diameter class frequency distributions, coexist in the lower montane forests, but the upper and subalpine forests display only the inverse-J type species with a few species of the sporadic type. Toward the northern latitudinal limit, the distinction between the three tropical montane forest zones in equatorial mountains becomes less clear. This can be explained by temperature conditions: on equatorial mountains, a temperature sum of 85° C months which controls the upper limit of the lower montane forests, and a coldest month mean temperature of-1° C which controls the evergreen broad-leaved trees, appear at c. 2500 and c. 4000 m respectively. The altitudinal range between 2500 m and 3800 m, which is the upper forest limit, is covered by upper montane and subalpine forests. On the other hand, at the latitudinal northern limit, the tropical upper montane and subalpine forests cannot exist because the above mentioned two temperature conditions occur at nearly the same point. Thus, at the northern latitudinal limit of the tropical montane forests, the three zones of equatorial mountains amalgamate into a single subtropical lowland forest community. This is due to the seasonal temperature climate in middle latitudes in, e.g., central Japan and central China.

Effects of nature trails on ground vegetation and understory colonization of a patchy remnant forest in an urban domain.

Effects of nature trails on understory vegetation was studied in a self recovering patchy forest remained in an urban sprawl of central Japan. An adverse impact of soil compaction at surface level, originating basically from human trampling, was found on root development and stem growth of understory colonizers implying a succession deterrence. Ground coverage was reduced with proliferated path web in trampled sites and a few species showed site preference. Management options such as demarcation of trek routes and their rotational use could help revitalize the colonization to further succession process.

Distribution and succession of West Himalayan forest types in the eastern part of the Nepal Himalaya

Distribution of the West Himalayan forest types dominated by Pinus roxburghii, P. wallichiana, and Quercus semecarpifolia is discussed within the pattern of forest distribution in the eastern, humid part of the Nepal Himalaya. All of the principal zonal forests of the western Himalaya are found in the wet eastern Himalaya, where they occur as relict patches on local dry habitats, such as south-facing convex slopes. The successional status of these western Himalayan species changes along the west-to-east gradient of the Himalaya: in the western Himalaya they persist as climax species; from the central to the eastern Himalaya they are pioneer trees in disturbed sites; and in the wet eastern Himalaya they comprise relict patches. The pioneer trees found in the eastern Hima- laya are classified into four ecological types according to their nature: the habit pioneer, the habitat pioneer, the undifferentiated canopy component, and the understory component. The three western Himalayan elements discussed in this study are included in the habitat pioneer type. Species corresponding to each of the four pioneer types can be found throughout wet Southeast Asia, including Japan and tropical Asia.

Patterns of species diversity in rural herbaceous communities under different management regimes, Chiba, central Japan

The patterns of plant species diversity in herbaceous vegetation subjected to various human activities were studied in most of the landscape elements in a rural area of Chiba, central Japan. Twenty-eight transects were sampled in four types of human management-regime (cultivation, trampling, mowing, and abandonment) and were grouped into seven vegetation types using TWINSPAN and DCA analyses. The DCA axis 1 arranged all the transects into a successional order along which biomass and the degree of succession increased. Accumulated number of species increased in a stepwise pattern along the DCA axis 1, in which the dominant plant life-forms were replaced from annuals, to perennials and perennials/tree-saplings depending on different management regimes. The unique species which were confined to a certain management regime, were identified in each site. It is suggested that the coexistence of various successional communities under different human management regimes enhance regional species diversity through maintaining these unique species. Among four types of management regime, mowing sites (especially traditional verge meadows) had most abundant unique, rare species specially adapted to regular cutting. It is suggested that maintaining such traditional mown sites is important to conserve the unique biodiversity of the studied area.

Early herbaceous succession along a topographical gradient on forest clear-felling sites in mountainous terrain, central Japan

Early successional patterns of herbaceous communities in forest clear-felling sites were investigated along a topographical gradient, which included ridge, slope and valley habitat types, in warm-temperate evergreen forest regions of central Japan for 5 years. Three dominant species with wind-dispersed seeds played a major role in the succession: an annual,Crassocephalum crepidioides, a biennial,Erigeron canadensis, and a perennial,Miscanthus sinensis. Pioneer herbs that have a seed-bank strategy, which are common in old field succession, were not found in the mountainous sites. The persistence of the annual or biennial dominants during the very early stages of secondary succession was different in the three topographical habitat types. In the ridge habitat,M. sinensis dominated from the first year state, andC. crepidioides andE. canadensis were less prominent.Crassocephalum crepidioides andE. canadensis became dominant as one moved down the slope. In the valley habitat,C. crepidioides dominated in the first year stage, was succeeded byE. canadensis in the second year, and thenM. sinensis gradually replaced it in later years. As all three wind-dispersed dominants simultaneously invaded in all the habitat types after clear-felling, the different successional patterns along the topographical gradient might have resulted from differences in the establishment ability and the growth rate of the three dominants depending on the three habitat types.

TERTIARY RELIC DECIDUOUS FORESTS ON A HUMID SUBTROPICAL MOUNTAIN, MT. EMEI, SICHUAN, CHINA

The floristic characteristics, age structure and survival modes of Tertiary-relic deciduous forests were analyzed at 1600 m on Mt. Emei (3099 m), Sichuan, China. Three plots were selected to represent typical topographies: Plot 1 at 1620 m on a scree slope, Plot 2 at 1640 m on a slope with moderately rocky soils, and Plot 3 at 1616 m on a gentle slope with less rocky soils. At Plot 1, on the scree slope, the forest was rich in species and dominated by Tertiary remnants and other deciduous trees (Davidia involucrata, Styrax hemsleyana, Cercidiphyllum japonicum var.sinense, Pterocarya hupehensis, Prunus brachypoda, Prunus padus, Tetracentron sinense andStaphylea holocarpa). The relic deciduous tree taxaDavidia, Cercidiphyllum, Tetracentron andEuptelea occupied the unstable concave slopes, where evergreen broad-leaved trees (Castanopsis platycantha andMachilus pingii) were rarely able to survive. On the relatively stable convex slopes of this plot, evergreen trees with small diameter mainly appeared in the subcanopy and shrub layers.Davidia involucrata was the dominant species in this forest. On the slope with moderately rocky soils (Plot 2), the forest was co-dominated by relicDavidia and other deciduous (Styrax andPterocarya), and evergreen trees (Castanopsis andMachilus). On the gentle slope with less rocky soils (Plot 3),Davidia trees were found only in the subcanopy and shrub layers, and the forest was dominated byMachilus, Castanopsis, Styrax andPrunus trees. Regeneration ofDavidia occurs mainly on the scree slope where landslides are most common. The age structure of theDavidia stands indicates that this species is able to survive on the unstable scree habitat due to its strong sprouting ability. The Tertiary-relic deciduous forest on the scree slope is seen to be a topographic climax forest.