Research summary
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[ Interests | Volcano | Secondary succession (skislope, mining, wildfire, and animal)| Wetland and conservation ]
- Research interests
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Major interests are to understand how determinants on plant community structures change with space and time. The keywords of my interests may be: succession, community dynamics, and disturbance. To understand these, I have surveyed mostly in disturbed areas, including volcanoes, wetlands, forests and skislopes. These ecosystems are suitable for clarifying the mechanisms on plant community structure and function, because the ecosystems are relatively simple and the environmental factors are detectable. I am trying to make a comprehensive model that can describe all successional sere from early to late stages of succession.
- (1) Revegetation patterns after volcanic eruptions
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Mount Usu
Revegetation patterns
My major researches have been conducted on Mount Usu, northern Japan, which erupted in 1977 and 1978. I monitored vegetation dynamics by permanently marked plots from 1983 to the present on Mount Usu, (42°32'N, 140°50'E, 727 m in elevation), after the 1977-78 eruptions which destroyed the pre-eruption vegetation by 1-3 m thick accumulations of ash and pumice.
Most species establishing on the summit area were derived from vegetative reproduction throughout the volcanic deposits. Vegetative reproduction plays a major role on increases in cover. In particular, large perennials, Polygonum sachalinense and Petasites japonicus var. giganteus, of which seeds were frequently provided from the own community, had vegetatively recovered from the caldera rim soon after the eruptions, and remarkably contributed the revegetation. Although long-distance seed-dispersal species, such as willows and birches, immigrated to the crater basin, their cover increase was slow. Those trees expanded roots shallower than the large perennials. Most trees invaded the crater basin soon after the eruptions, while the tree growth was restricted by nutrients and mammalian herbivore. The fate of perennials was dependent on the types of rhizome and stolon systems. Erosion created gullies that removed these deposits and frequently exposed the old original soil. Most annuals were supplied from the seedbank and woody species originated via immigration, indicating that the plant source greatly determines the species composition of establishing vegetation.
Seedbank
Seed extraction method is imporoved to collect seeds quickly with high recovery rate. Using this method, I extracted buried seeds from the former topsoil and confirmed that seedlings of 14 species (8 annuals and 6 perennials) emerged from seeds buried in the topsoil. The seeds have survived more than 30 years under thick tephra. Nearly all the annuals originated from the seedbank but diminished a few years later. The nitrogen-fixing and stoloniferous perennials, Trifolium repens and Lotus corniculatus var. japonicus, were derived only from the seedbank, and have gradually increased in cover. The seedbank was the major source of annuals and of nitrogen-fixing perennials. Succession in the gullies was substantially different from that which occurred outside the gullies where plants mostly originated from seed immigration and vegetative reproduction from surviving plants. The photo shows Hypericum erectum that survived for more than 30 years under the tephra.
Since the former topsoil was exposed by erosion, ephemeral annuals and well-rooted perennials were successful there. Owing to the expansion of once-established perennials, the plant cover was increasing acorss time. Ground surface movements strongly restricted increases in plant cover and the distance from source vegetation was the principal determinant of plant density. Due to differences in disturbance intensity, successional rates were higher on the stable substrates outside gullies and lower on the exposed original topsoil in some gullies. The relationships between species and environments were confirmed by ordination, e.g., CCA, and the results indicated that the seedling establishment pattern was mostly determined by ground surface stability and seedling growth was restricted by nutrients. The analyses of species diversity evaluated by density and cover supported the results.
Flora on Mount Usu after the 1977-78 and 2000 eruptionsMount Koma
A small-scaled eruption occurred on Mount Koma, Hokkaido, in 1995, and an extensive eruption took place in 1929 and completely destroyed the former vegetation. On the summit area, I set up 400 50 cm × 50 cm permanent plots in 1996. Now, the monitoring is annually conducted. The vegetation change is totally slow for the first five years. Here I am monitoring plant community dynamics with reference to:
Biological invasion
Facilitation and inhibition
Symbiosis between vascular plants and fungi
Plant-animal interactions Flora on Mount Koma after the 1996 eruptionsMount St. Helens
The vegetation data six years after the eruption (1986) was compared with the vegetation on Mount Usu six years after the eruptions (1984). The resembled vegetation was developed in the similarly disturbed areas even in geographically distinct regions. The vegetation development was greatly restricted by gully development, due mostly to ground surface instability. Although seedling establishment was restricted by ground surface instability, texture and microtopography, the seedling growth seemed to be restricted by the texture of volcanic deposits, i.e., they could not penetrate their roots into silt particles.
Other volcanoes
I had chances to observe Mts Ruapehu, Tarawera, and others located in North Island, NZ, and Mt Pinatubo in the Philippines.
- (2) Secondary succession patterns modified by human impacts
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Secondary succession is often damaged by human impact. To understand the complex mechanisms, I selected two habitats, skislopes and abandoned pastures. Both of the habitats are greatly influenced by land modification, e.g., scrapping off the ground surface, and introduction of exotic grasses. It must be fate that most plant communities received human impact, and thus we should not neglect the effects on ecosystems.
Skislopes
I surveyed more than 20 skislopes in Niigata and Hokkaido Prefectures, Japan. Bare areas developed soon after the skislope establishment and occasionally persisted due to soil erosion, although artificial seeding was widely conducted. Woody plants invaded bare areas and Miscanthus sinensis grassland. Human impact types, slope gradient, vegetation status surrounding skislopes, ground surface movements were related to the vegetation development. In particular, ground surface movements were conspicuous in most skislopes. Owing to the soil movements, tree invasion and vegetation cover were low. Abandoned pastures On Shiretoko Peninsula, Hokkaido, Japan, the relationship between the standing vegetation and seedbank structure was determined. The vegetation development was restricted by thin soil. Small seedbank developed and seemed to contribute the revegetation little, and thus the revegetation slowed.
One of the problems on revegetation on volcanoes, skislopes and wetlands in Japan is that many of those are located in national parks and reserves. For example, Mount Usu is located in Toya-Shikotsu National Park, and a couple of skislope are in Niseko-Syakotan-Otaru Kaigan Quasi-National Park. To promote forestation after 1977-78 eruptions on Mount Usu, Picea glehnii was transplanted on the crater basin. However, this species is not distributed on the mountain!
Wildfire
We set up permanent plots near Fairbanks, AK, USA, in 2005. The forests dominated by Picea mariana were burned by the 2004 wildfire (Boundary Fire). We confirmed that albedo can not recover if plant cover on the ground surface does not recover. Vegetation zonation on palsas was measured in 2006. These data are compared with satellite data.
Smoke-induced seed germination for 40 species in Hokkaido was examined. Only a few species enhanced germination by smoke, but this does not mean zero.Abandoned pastures
On Shiretoko Peninsula, Hokkaido, Japan, the relationship between the standing vegetation and seedbank structure was determined. The vegetation development was restricted by thin soil. Small seedbank developed and seemed to contribute the revegetation little, and thus the revegetation slowed.
Animal disturbances
I have survyed the following animasl, although these are not always related to disturbances. Ant that is of course animal was also surveyed.
- Deer: the effects of over-grazing on vegetation structure on Nakajima Island near Mount Usu. Lava tubes (pits) is an important topography to conserve high biodiversity
- Yak: over-grazing effects on wetland vgetation in China
- Lemming: vegetation modified by lemming on and around baidzharakhs (relic mounds), Siberia
- Mouse: The characteristics of faunal make-up and abundance of rodents 17 years after volcanic eruptions
- Crow: seed dispersal by crow on a volcano
- (3) Wetland community structures
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Wetlands are one of the crucial ecosystems for keeping biodiversity. I measured vegetation and its related environmental factors in Ruoergai marshland located in central and north-eastern parts of China, north-eastern Siberia, and a couple of wetlands in Hokkaido
Island of Japan.In Ruoergai marshland, the largest wetland in China, vegetation zonation was clearly observed along the water table or depth gradient. However, the effects of water table differ between habitats. In low-elevated sites, Carex meyeriana tussocks were well-developed, and the upper parts of tussocks contributed high species diversity. The vegetation received heavy yak grazing.
The community structure of Larix olgensis forest was surveyed in a western part of Mount Changbai peatland, northeastern China. This forest regenerated spontaneously perhaps because safes site for seedling emergence was rare in time.
In northwestern Siberia, I measured vegetation development patterns and its related environmental factors, such as soil pH, texture, hardiness, and slope. Methane emission patterns were compared with vegetation types.
Peat-swamp forest in Indonesia was also surveyed with reference to microtopogranphy.
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