The vegetation of abandoned rice fields and factors influencing it in small valley ('yatsu', in Japanese) heads in the east plain of Lake Kitaura, Ibaraki, Japan, were examined to evaluate the potential of the fields as habitats for indigenous wetland plants. The floristic composition in a 15×5m study area and the importance value of each species, which was evaluated as the frequency of occurrence in 39 0.5×0.5m quadrats set at each study site, were recorded in 32 abandoned rice fields. In total, 230 indigenous (site average 32 spp.) and 25 alien (site average 3 spp.) species were recorded. Seven species that were listed on national or regional red lists were recorded at nine sites. Analyses of environmental factors affecting the vegetation properties using a generalised linear model showed that groundwater level (GWL), light availability index, which was calculated from a spherical photograph taken above the vegetation, and the time since abandonment, had significant effects on both the richness of indigenous species and indigenous wetland species. A significant positive effect of the GWL was also detected for the occurrence of the endangered species. In contrast, the GWL had a significant negative effect on the importance value of the invasive alien species Solidago altissima, which often dominates the fields. The GWL was significantly lower in the fields abandoned with remaining drainage facilities. In conclusion, abandoned rice fields in 'yatsu' valley heads can provide a habitat for wetland plants, including threatened species, unless the drainage facilities remain.
Stream classifications and indicators that are capable of summarizing the complex information of ecological communities provide useful tools in river ecosystem management. However, these tools have not yet achieved practical application here in Japan due to the fact that in many studies, the criteria for selecting stream classifications and indicators are neither objective nor quantitative. Combining model-based clustering and indicator values (IndVal) makes it possible to assess the appropriateness of stream classifications based on the indexability from multiple classifications. Additionally, by establishing threshold values, indicators can be objectively selected. Using these techniques, we examined appropriate data acquisition methods for determining a stream classification system for vegetation at the catchment scale. Additionally, we studied the suitability of methods that were derived solely from either biological or environmental data as well as those that combined the two. We prepared three sets of data that utilized different research zone and scope-setting methods and then created three types of stream classifications from each, ultimately evaluating the appropriateness by the quality of selected indicators and the level of indexability. The most appropriate methods involved those derived from biological and environmental data exhibiting consistently high indexability as well as those that created vegetation maps in certain areas of the distribution over the entire catchment area. Furthermore, the quality of the selected indicators was consistent with the indexability results.
A population of an artificially introduced dandelion species was investigated to follow the early settlement behavior of an introduced species in Japan. At a developed field in the Tokyo Bay Area, many seeds of Taraxacum officinale Weber were sown on artificial soil in 1998, creating a population with density as high as 1×10^2 plants/m^2. In 2006, the population was lower in density. Most of the seedlings appeared in early summer and had died by autumn. A few of the seedlings appeared in autumn and had a relatively high survival rate. The population had a high percentage of pure individuals of the introduced dandelion in 2006, although other populations growing in some major cities in central Japan have high percentages of hybrids between the introduced and a native dandelion species. This is the first documentation of diploid individuals of introduced dandelions growing in Japan; these diploids represented about 15% of the individuals of the population.
In Okinawa-jima Island, we have monitored the population trend of Orii's flying fox Pteropus dasymallus inopinatus for a long time since 2000, and we found a tendency of increasing of observed number of bats. We monthly counted foraging bats in two sites (urban and forested area) using road census methods from September 2001 to August 2009 and from April to March 2004 and 2008, respectively. Threefold increase was found in both areas during 8 and 4 years, and it was found in every season. These results suggest that the bat's population in Okinawa-jima Island is growing, not a spatial heterogeneity in bat's habitat use. The raise of annual growth rate coincided with the decreasing number of typhoons. It seems that the bat population size depends on the frequency of disturbance of typhoons. We should take account of the spreading of agricultural damages and the extinction of this subspecies resulting from unstable fluctuation of populations under the global warming.
We investigated the current distribution of the sika deer population and its impact on vegetation around Mt. Hyonosen, Hyogo Prefecture. Based on a vegetation survey that was conducted at a regional scale, we estimated that understory vegetation in deciduous hardwood forests has declined significantly over mountain ranges on the east- and south-sides of Mt. Hyonosen. A pellet group count survey indicated that there has been an overabundance of sika deer since 1999 in these areas. It is hypothesized that a neighboring population of sika deer with high density expanded into these mountain ranges. Moreover, recent decreases in snow in this region could have promoted population expansion. Vegetation around the peak has not declined yet, but deer grazing has occurred seasonally due to migratory individuals traveling from the foot of the mountain. Signs of deer grazing were observed on 230 plant species, including 13 red-listed species, on Mt. Hyonosen. Moreover, we found that a community of red-listed species had declined because of deer grazing. We note that serious declines in vegetation could expand to the peak of Mt. Hyonosen if management of the deer population is not rapidly introduced.
The Watarase wetland is a floodplain wetland in central Japan, mainly composed of moist tall grassland dominated by Phragmites australis and Miscanthus sacchariflorus. The restoration experiment was conducted to determine whether removal of topsoil, including the rhizomes and seed bank of the invasive species Solidago altissima, would lead to an increase in re-colonization of aquatic and short-lived wetland plants from the soil seed bank. We investigated species composition and vegetation development at the experimental site during 2 years after topsoil removal at five soil depths. At the experimental site, six aquatic and 31 short-lived wetland species, including 14 Red List species, were recorded. This suggests the effectiveness of topsoil removal for restoration of aquatic and short-lived wetland plants. During the study period, nine exotic species, including S. altissima, were recorded, but their species number and abundance decreased remarkably in the second year. Although species number and abundance mostly decreased significantly with removal depth, some species occurred only in deeper layers, suggesting the need to explore the topsoil removal depth required to increase wetland plant diversity for successful restoration.
We evaluated the key constraints in restoring the vegetation of abandoned overgrown woodland that developed on once semi-natural grassland by analyzing the seed bank persistence of typical semi-natural grassland species. Approximately half of the grassland species recorded in the above-ground vegetation in typical semi-natural grassland were either scarce or absent in the soil seed bank. This scarcity indicates that the potential for grassland species restoration using the soil seed bank may be limited. Conversely, more than half of the grassland species recorded in the soil seed bank produced long-term persistent seeds, which may insure population re-establishment after restoration, even if the plants have disappeared from the vegetation. One year after the restoration treatment, 11 new grassland species emerged in the restored site. These new populations were suspected of having arisen from long-term persistent seeds in the soil, seeds dispersed from the edge vegetation, or 'bud-bank' or vegetative parts in the soil. The results of this study emphasize the importance of information not only on seed bank persistence but also on other traits related to plant reproduction or regeneration for the effective restoration of semi-natural grassland communities.
Between June 22 and October 18, 2010, 300 water systems on Okinawa Island covering a length of 340km were explored in order to record the distribution of 31 taxa of alien aquatic organisms and 41 taxa of native fish. They were confirmed mainly by visual observation while walking up the river on foot. The alien aquatic organisms were distributed mainly in the southern part of the island, although a few were seen in the northeastern part of the island. The tilapia (Oreochromis spp.), guppy, and carp were found in 141, 120, and 54 water systems, respectively. The sailfin catfish, redbelly tilapia, and red-eared slider turtle were distributed mostly in the southern part of the island, which has a high human population density. Ornamental fish such as the danio, platy, and small snakehead were found only in the northern part of the island, which has a low human population density. Endangered species and native fish were found mainly in the northern and central-western parts of the island. The swordtail is an alien fish that has an extensive distribution in the northern part of the island, and it is feared that it might influence some endangered species.
This study clarified the present situation with respect to the effects of sika deer, Cervus nippon, on the forest vegetation in the Zenki region, Mt. Ohmine (Shimokitayama, Nara prefecture). The forest structure, deer population density, and dwarf bamboo, Sasa borealis, vegetation on the forest floor were surveyed. A forest census conducted in 2005 revealed that the size structure of 1443 stems over 1.3m in height showed an inverse-J shape in the 1.08-ha plot. Bark-stripped stems (≥5cm in diameter at breast height) were seen in 18 of 54 species (33.3%) and 144 of 1023 trees (14.1%). The population densities of sika deer in September and October 2008, estimated based on the fecal accumulation rate tecnique, were 11.2 and 24.0 head/km^2, respectively. The mean stem density of S. borealis was 0.0023±0.0159 stem/m^2 (mean±1SD, n=432) in 2009. In comparison with the density recorded in 1983 around the study plot (11.3±5.7 stem/m^2, n=184), the S. borealis vegetation had declined markedly. Therefore, we postulate that sika deer severely affected the forest floor vegetation, i.e., S. borealis vegetation, tree regeneration, and herbaceous plant growth.
By examining histologically prepared sections of incisor teeth, we aged 698 sika deer that were harvested on the Shiretoko Peninsula, Hokkaido, between December 2007 and April 2010. We found a disproportionate lack of animals aged 5 years old and younger, particularly those born in 2004 and 2005, in samples from Cape Shiretoko and Rausu on the northern and eastern parts of the peninsula. Winterkill counts in the area suggest that the overwinter climate was the main source of mortality. This pattern was less pronounced in other parts of the peninsula, likely due to differences in overwinter carrying capacities within the study area.
Bombus terrestris is a commercialized pollinator in many countries. In Japan, its colonies have been used in numerous greenhouses since 1991. However, new queens escape from the greenhouse colonies easily and naturalize. The invasion range of B. terrestris has been expanding annually. We captured 11 B. terrestris queens in Hamanaka, Akkeshi District, Hokkaido, on 11 June 2010. This is the first record of B. terrestris in this region. Three of the 11 captured queens had pollen cakes on their hind legs, showing that each of these queens had founded colonies in the area. We found the queens on the edge of the Kiritappu wetland. Since B. terrestris is a powerful immigrant, we predict that it will invade the wetland in the near future. B. terrestris also competes with native Japanese bumblebees for several resources (e.g., nesting sites and native flowers for nectar and pollen). Therefore, the invasion of B. terrestris into the Kiritappu wetland will probably pose serious risks for its unique ecosystem, including native bumblebees, plants, and animals.
I previously (Takatsuki, 2009) proposed the following question: Although bears are often regarded as umbrella species, is this actually true? So far, I have not been able to find scientific evidence in support of this, and I feel that conservation activities should be based on scientific approaches. Indeed, this opinion is in accordance with that of S. Boutin (2005) in his review of the ecological effects of carnivores in boreal forests of Nordic countries, in which he discussed several effects of bears on ungulates, hares, rodents, and vegetation through cascade effects. Boutin emphasized that a "fine-filter" conservation approach that focuses on particularly charismatic carnivores often overlooks ecological processes and that carnivore-oriented conservation requires large refuges. However, actual refuges are often too small for such large carnivore species, particularly in Europe. Such approaches that focus only on carnivores as umbrella species risk the loss of endangered species or organisms requiring particular ecological processes. For biodiversity conservation, a "coarse-filter" approach that focuses on ecological processes such as wild fires, logging, and succession is more important and effective. Given that the social conditions of Japan in terms of biological conservation are often more similar to those of Europe than of North America, a "coarse-filter" approach may be more appropriate for bear conservation in Japan.