Shiro Tsuyuzaki

Adaptive advantages of ant-dispersed seeds in the myrmecochorous plant Trillium tschonoskii (Liliaceae)

Trillium tschonoskii Maxim. is a myrmecochorous perennial herb which grows in single-species stands in the cool temperate broad-leaved deciduous woodland of Hokkaido, northern Japan. Its many-seeded fruit initially falls close to the parent, over 50% within 20 cm. Ants, principally Myrmica ruginodis and Aphaenogaster japonica, transport seeds to their nests, a mean distance of 64 cm. The nests are overdispersed and short-lived, and are no richer in nitrogen or phosphorus than surrounding soils. There are proportionally more older (3-leaved) than younger (1-leaved) juvenile Trillium plants at distances > 60 cm from the nearest parent plant than at 0-30 or 30-60 cm. This indicates that the relatively short-distance dispersal of T. tschonoskii seeds by ants is sufficient to reduce seedling mortality, by reducing competition between seedlings; and that this is the primary advantage of myrmecochory in this species. This contrasts with previous studies, involving ant species with longer-lived nests, where the main advantage to the plant is nutrient-enhanced seedling microsites.

Seedling establishment patterns on the Pumice Plain, Mount St. Helens, Washington

We examined the factors that control seedling es- tablishment on barren substrates on the pyroclastic flows from Mount St. Helens. From June to September in 1993, we monitored seedling and microhabitat changes in 240 20 cm x 20 cm quadrats on the Pumice Plain. Seedlings emerged in 104 quadrats (43.3 %). The most abundant species were Anaphalis margaritacea, Hypochaeris radicata, Lupinus lepidus and Epilobium angustifolium. Measured site charac- teristics included topography, particle size distribution, ground surface movements, soil water content, organic matter, pH, and presence or absence of dead lupines. Quadrats with seed- lings had higher cover of dead lupines, higher amount of rock and gravel substrate, and a greater cover of rills. More seed- lings emerged where eroded material accumulated. Compared to coarse-textured surfaces, silt surfaces had higher organic matter, held more water, and showed higher pH. However, seedlings became established more frequently on coarse-tex- tured surfaces. In greenhouse experiments, a higher percent- age of Hypochaeris seeds germinated on silt than on sand or gravel. The germination of Anaphalis and Epilobium did not differ with soil texture, but was higher at higher moisture levels. Seedling colonization is more dependent on ground surface microtopography, particle size, and ground movement than on the chemical status of these volcanic deposits.

Species attributes in early primary succession on volcanoes

We predicted that plants that can establish on vol- canic soils with similar disturbance histories will have similar growth characteristics. We tested this prediction by a multi- variate analysis of 27 traits of 84 species found six years after an eruption on Mount St. Helens, Washington State, USA, and Mount Usu, Hokkaido, Japan. These traits include vegetative, life-history, phenological and seed-biology characteristics. Cluster analysis revealed five species groups: annual herbs, perennial forbs, graminoids, shrubs and trees. Each group has distinct vegetative, life-history, and seed-biology traits. Ex- cept for shrubs, which were lacking on Mount Usu, both floras were well represented in each group. On intensely disturbed sites on both volcanoes, perennial forbs, whose development is dependent primarily on well-developed below-ground or- gans and wind-dispersal, expanded their cover more rapidly than did graminoids. These graminoids generally produce gravity-dispersed seeds and have close-set rhizomes and/or shoots. These results suggest that species that can establish during the early stages of succession on each volcano have similar vegetative, life-history, and seed-biology traits.

Environmental deterioration resulting from ski-resort construction in Japan

Ski slopes are commonly established following clearcutting of areas of well-developed forests, scraping off the surface soil, and seeding the entire ground-surface, as forests widely remain in mountainous regions where skiing is developed in Japan. The ski slopes are then sown with seeds of exotic plants in an attempt to prevent soil erosion. However, many bare areas remain, or develop, on ski slopes. Due to this landscape fragmentation, not only deterioration of Nature but also environmental problems develop, including those of water, garbage, and traffic, pollution. The ski-resort concentration occurs mainly in regions of high-quality landscape around urbanized areas, and derives mostly from economic benefits. Yet any regulation of ski-resort construction has unfortunately been delayed. Areas where ski-resorts have been concentrated have a high risk of damage, and further studies of the situation are overdue. We should reconsider the construction, enlargement, and distribution patterns, of skiresorts, and any further development should be based on sound ecological and conservational knowledge rather than mere transient economic considerations.

Origin of plants recovering on the volcano Usu, northern Japan, since the eruptions of 1977 and 1978

The vegetation near the summit of the volcano Usu was destroyed during eruptions in 1977 and 1978 by 1–3 m thick layers of volcanic deposits. Thereafter, the vegetation gradually recovered and by 1984 134 plant species were recognized of which 95 species had established by vegetative reproduction, 18 by seed immigration from elsewhere, 5 by artificial introduction for soil erosion control and 17 species from viable seeds buried in the former topsoil. The summit area was still covered by thick layers of volcanic ash, which were however rapidly eroded by rains. Vegetatively reproducing plants such as Petasites japonicus var. giganteus and Polygonum sachalense contribute more effectively to the revegetation process than plants of other types of origin.

Mortality and growth of trees in peat-swamp and heath forests in Central Kalimantan after severe drought

Lowland forests in Central Kalimantan, Indonesian Borneo, are endangered by land conversion and the increasing frequency of severe drought. Knowledge of the tolerance of tropical trees to drought is urgent for the management of these lowland habitats. The short-term effects of drought on tree demography (mortality and growth) were investigated in an ever-wet riparian peat-swamp forest and a heath forest on coarse sandy soil after the 1997 El Nino Southern Oscillation (ENSO) event. This drought was unusually severe because little rain fell during the following rainy season. However, forest-wide mortality following the drought (1997–1999) was not critically high in the peat-swamp (6.13% yr−1) or heath (4.26% yr−1) forest. In both forests, standing trees frequently died during the dry season following the drought. The riparian peat-swamp forest was not flooded until 1998, after the prolonged drought in 1997. The hummock–hollow microtopography resulted in differential mortality of peat-swamp trees. On tall hummocks, standing death increased two-fold (4.99% yr−1) during the dry season, whereas uprooting decreased by one-third (0.85% yr−1) during the following rainy season. In contrast, tree growth was not affected by hummock height. Common canopy species were concentrated on tall hummocks and died standing more often than did understory species found in hollows, indicating species-specific mortality after the drought. The large stand basal area relative to the forest-wide growth rate in diameter suggested less resilience to drought by peat-swamp (45.6 m2 ha−1 and 0.0186 ln[cm] yr−1) than heath (27.9 m2 ha−1 and 0.0232 ln[cm] yr−1) forest. A single severe drought did not cause dramatic changes in the peat-swamp and heath forests; however, an increasing frequency of droughts similar in severity to that of the 1997 ENSO event may have the potential to alter the community structure and dynamics, leading to a consistent decline in Bornean lowland forests.

Vegetation development patterns on skislopes in lowland Hokkaido, northern Japan

Abstract The Japanese montane zones are usually covered with well-developed forests, and most ski resorts are constructed there. Therefore, the construction of skislopes requires the destruction of forest ecosystems. To detect vegetation development patterns on skislopes, I assessed vegetation on seven skislopes in the lowland of Hokkaido Island, Japan, using 155 2 m×2 m plots. The surrounding vegetation was mostly consisted of broad-leaved forests with a floor of dwarf bamboo, Sasa senanensis. The skislopes were established 5–28 years before the surveys by scraping off the topsoil and subsequent artificial seeding. The data of vegetation analyzed by TWINSPAN resulted in six different grassland types: (A) Miscanthus sinensis–Hypochaeris radicata, (B) introduced herbs with low richness, (C) introduced herbs, (D) Artemisia montana, (E) M. sinensis–Pueraria lobata–A. montana, and (F) Solidago gigantea var. leiophylla. H. radicata and S. gigantea var. leiophylla were alien species. Vegetation dominated by introduced grasses for erosion control, such as Dactylis glomerata and Poa pratensis, should be initial vegetation on the skislopes. Most tree pioneer species established in the vegetation type A, that was most natural vegetation in the skislopes. Type A seemed to proceed from types B and C, and species richness was the highest. Therefore, this type should be preferable for the management and restoration of skislope vegetation. Type D established on newer skislopes, while types E and F established on older skislopes. Results including detrended correspondence analysis suggested that those vegetation types D–F proceeded to distorted succession, i.e. biological invasion changed native successional sere. Based on these results, I recommended that the restriction of alien invasion and careful monitoring on M. sinensis grasslands are required to restore the natural vegetation.

Plant community dynamics on the volcano Mount Koma, northern Japan, after the 1996 eruption

A small eruption occurred in the early spring of 1996 on the summit of Mount Koma, northern Japan, 67 years after the 1929 catastrophic eruption. To identify damage on the plant communities and recovery patterns, we established 400 50 × 50 cm permanent plots in four locations along the gradient of the thickness of tephra produced in 1996: non-disturbed (N), weakly disturbed (W), middle disturbed (M), and heavily disturbed (H). Annual monitoring was conducted from 1996 to 2001. Gullies and rills formed in M and H, indicating that the ground surface movements were more intense there. Mean vascular plant species richness increased from H to N, but did not increase from 1996 to 2001 in any location. In an area where tephra thickness was 10 cm, the recovery was mostly conducted by the species that could have survived during the eruption. A shrub,Salix reinii, was the leading species in most sites throughout most years. Large perennial herbs,Polygonum weyrichii, P. sachalinense andMiscanthus sinensis were common in the disturbed areas, in particular in M and H. Those three species develop large underground organs and enlarge clonally, suggesting that the tolerance to ground surface stability is the most important trait for the recovery of those species.Carex oxyandra established not only by vegetative regeneration but also by seedling regeneration. A short forb,Campanula lasiocarpa, could establish only in W by seedling regeneration. Mosses and lichens were predominant in plots in N and W, but less represented and not greatly increasing their cover in M and H up to 2001. We concluded that the community recovery was delayed in all the disturbed areas, mostly due to low seedling establishment. Only a few specific species established by vegetative reproduction. Disturbance gradients such as thickness of tephra and/or ground surface stability have determined plant community structure and development.

Influence of a non-native invasive tree on primary succession at Mt. Koma, Hokkaido, Japan

The slopes of Mt. Koma in Japan are undergoing primary succession as a result of a 1929 eruption. Understory vegetation below a non-native invasive tree species, Larix kaempferi, a native tree, Betula ermanii, and in the open were compared to determine if the non-native tree species was influencing species composition. Larix canopies are significantly larger than Betula canopies. Vegetation under Larix canopies had significantly greater richness and diversity than vegetation in the open, vegetation under Betula was intermediate but was significantly greater than the open in diversity. Vegetation cover was highest under Betula and significantly lower in the open. Larix canopy size was positively correlated with size and number of Salix reinii shrubs. Betula canopy size was positively correlated with size but not with number of Salix reinii shrubs. Species assemblages in the three sites are slightly different as shown by DCA. Due to the limited species pool on Mt. Koma the greatest possible extent of differences between the three microsites is not large. At this point Larix certainly appears to be accelerating succession for the non-tree species. If Larix persists on the slopes then succession would be permanently deflected towards a Larix forest. This would be a case of succession being deflected towards dominance by the introduced species.

Woody plant establishment during the early stages of volcanic succession on Mount Usu, northern Japan

The establishment patterns of woody plants were investigated on the volcano Usu, 9 years after the 1977–1978 eruptions. The former vegetation was covered by a 1–3 m thick volcanic deposit. Trees producing wind-dispersed seeds capable of long distance dispersal, such as Populus maximowiczii, Betula platyphylla var. japonica, Salix hultenii var. angustifolia, and Salix sachalinensis, were dominant. Most trees were only 2–4 years old in 1986, suggesting that chances for seedling establishment were restricted. The tree heights did not differ significantly among the species, while lengths of annual shoots differed due to herbivore preferences. Trees were established at higher densities on gravel-dominated pumice surfaces than on fine-textured surfaces. Tree density was not greatly affected by the nutrient content of deposits. From 1987 to 1990, tree height increments did not differ between the gravel and non-gravel areas. Ground surface texture is an important factor in determining seedling establishment in the early stages of volcanic succession, and nutrient status is unimportant.