Toshiya Ohkuro

Indicator species and functional groups as predictors of proximity to ecological thresholds in Mongolian rangelands

We focused on responses to grazing by individual species and functional groups in relation to ecological thresholds in Mongolian rangelands, with repeated measures from the same ecological sites to account for rainfall variability. At all sites, even under rainfall fluctuations, there were robust combinations of indicator species that could be used to forewarn managers to take action to minimize the probability of crossing ecological thresholds. Depending on the landscape condition of each site, the cover of functional groups, which shared traits of perennial life history, grass or forb growth form, linear leaf shape, and alternate leaf attachment, or the cover of functional groups of woody shrubs dramatically decreased before an ecological threshold was crossed. Thus, across all sites, the responses of certain functional groups to grazing appeared to predict the crossing of an ecological threshold. The ecological indicators derived in this study should help to improve land managers’ ability to prevent adverse changes in states before ecological thresholds are reached.

Sheep gain and species diversity: in sandy grassland, Inner Mongolia

Abstract A grazing experiment was conducted from 1992 to 1996 at a sandy grassland in the Horqin sandy land, located in the northeastern part of China. The grassland had been grazed by sheep for many years before the experiment at an intensity of 4.5 sheep ha−1. The experiment consisted of 4 grazing treatments: no grazing (0 sheep ha−1), light grazing (2 sheep ha−1), moderate grazing (4 sheep ha−1) and overgrazing (6 sheep ha−1). Plant species diversity, plant biomass, soil properties, and sheep liveweight under various grazing treatments were examined. Overgrazing resulted in considerable decreases in both species diversity and plant biomass. As a result, sheep liveweight gain decreased significantly in the last 3 years of the experiment in the overgrazing treatment. No grazing and light grazing treatments had higher species diversity as well as higher biomass production than moderate grazing and overgrazing treatments. The results indicate that light sheep grazing is sufficient for the recovery of overgrazed grassland in this region and for the maintenance of plant species diversity. The proper grazing intensity should be 2–3 sheep or sheep equivalents per hectare for the sandy grassland in Inner Mongolia.

Spatial pattern of grazing affects influence of herbivores on spatial heterogeneity of plants and soils

With our enhanced understanding of the factors that determine biodiversity and assemblage structure has come increasing acknowledgment that the use of an appropriate disturbance regime to maintain spatial heterogeneity is an effective conservation technique. A herbivore’s behavior affects its disturbance regime (size and intensity); this, in turn, may modify the associated spatial heterogeneity of plants and soil properties. We examined whether the pattern of spatial disturbance created by the Siberian marmot (Marmota sibirica) affects the spatial heterogeneity of vegetation and soils at a colony scale on the Mongolian steppe. We expected that the difference in management between two types of area (protection against hunting marmots vs. hunting allowed) would result in different behavioral patterns; therefore, we estimated the patterns of spatial disturbance separately in protected and unprotected areas. We then surveyed plant communities and soil nutrients in these areas to assess their spatial heterogeneity. We found that disturbance of both vegetation and soil was more concentrated near marmot burrows in the unprotected area than in the protected area. In addition, the degrees of spatial heterogeneity of vegetation and soil NO3-N were greater in the unprotected area than in the protected area, where disturbance was more widely distributed. These results indicate that the spatial pattern of disturbance by herbivores affects the spatial heterogeneity of vegetation and soil properties through changes in the disturbance regime. Our findings also suggest that the intensity of disturbance is more important than its size in determining community structure in Mongolian grasslands.

Vegetation in a Post-Ecological Threshold State May Not Recover after Short-Term Livestock Exclusion in Mongolian Rangelands

In the present study, we tested the potential irreversibility of vegetation dynamics in Mongolian rangelands using well-studied plant communities that exist along grazing gradients, in which ecological thresholds (defined as the points or zones at which disturbance should be limited to prevent drastic changes in ecological conditions) exist in terms of the compositional changes along these gradients. To accomplish this, we removed livestock grazing impacts by establishing exclosures along a grazing gradient at two study sites located in Mandalgobi and Bulgan, Mongolia. Each exclosure was established in the summer of 2004 at a location with either a post-ecological threshold state or a pre-ecological threshold state. We examined general patterns of temporal change in vegetation for the permanent plots inside and outside each exclosure at each site between 2005 and 2010. The trajectories of floristic composition in the permanent plots outside and inside each exclosure were similar from 2005 to 2010, indicating that the trajectories were mainly associated with annual rainfall and annual phenological changes in the plant communities. Post-threshold states at both sites did not reach their respective target community for restoration, indicating the lack of restorability despite livestock exclusion. Moreover, ordination separated the trajectories of floristic composition for the permanent plots inside exclosure in the post-threshold state from those in the pre-threshold state. Thus, our results suggest that vegetation in a post-threshold state may not recover after short-term livestock exclusion in Mongolian rangelands.

Comparison of the Species Compositions between Past and Present Semi-Natural Miscanthus sinensis Grassland in the Kanto Plain

Semi-natural grassland maintained by traditional agricultural practices like mowing and burning has been widely decreased due to urban development and abandonment for more than 50 years, causing the loss of habitats of many native grassland species. In this study, we aimed to evaluate the vegetation of Miscanthus sinensis grassland currently remaining in the eastern part of the Kanto Plain by comparing it to the vegetation of the past extracted from data on regional flora compiled in the 1970s and 1980s. As a result, it became clear that the vegetation of the remaining Miscanthus sinensis grassland established on former arable or reclaimed lands was totally different from the species composition of past semi-natural grassland. Miscanthus sinensis grassland still maintained by agricultural practices remains on the steep slopes between uplands and lowlands where there are paddy fields located at the bottom of the narrow valley called ‘Yatsu’. This vegetation, however, was also significantly different to that of the past, lacking many native perennials selected as indicator species for past semi-natural grassland.

Changes in Topographical Features and Soil Properties after Exclosure Combined with Sand‐Fixing Measures in Horqin Sandy Land, Northern China

In a field experiment we evaluated the effects of exclosure and sand-fixing measures on land restoration of shifting sand dunes in a semi-arid, sandy grassland located in Northern China. We fenced an area of about 2.1 ha, enclosing 2 shifting sand dunes—one large and the other small. In 1996, on each dune we applied 2 sand-fixing measures developed in China—burying wheat straw in a checkered pattern (Sc) and planting seedlings of a sand-fixing shrub, Artemisia halodendron (Ar). Changes in the topographical features and soil properties were then monitored for 6 years. The effectiveness of the sand-fixing measures was assessed by monitoring the topographical features and soil properties. Sand dune fixation took 1 year, and a biological soil crust with high contents of soil organic carbon and fine particles (clay+silt) was formed within 3 years. These results are consistent with those reported in previous studies, confirming that such crusts reduce wind erodibility. The effectiveness of exclosure alone, without the other measures, was also implied, especially for the small dune, based on the changes in the topographical features and soil properties outside the exclosure, where a “no-grazing” policy had been implemented from 2000. The rate of soil restoration was higher on the small dune than on the large dune. This was due to the differences in the initial soil conditions caused by the topographical features, suggesting that the capacity of a site to reverse desertification by itself depends on the dune size. Sc was slightly more effective than Ar, presumably because Ar inhibited the invasion of other plant species, whereas Sc allowed invasion of various species. Although the soil properties in the very thin surface crust were restored, the restoration of the soil properties in deeper layers was not significant even after 6 years. It would take a longer time (e.g., 10 to 20 years) for the restoration of the soil properties in deeper layers to sustain more intensive land use in this region.

Studies on the Habitat Distribution of Wild Fruit Vaccinium uliginosum in connection with the ForestDestruction caused by Volcanic Eruptions on Mt. Kusatsu-Sirane, Central Japan

崩壊地や火山荒原など強度の自然撹乱が生じている地域では, 極相に達しない発達段階の植生が持続する。こうした条件下で成立する植生の保全に際しては, 撹乱体制と植生動態の関係を把握することが重要である。本研究では草津白根山を事例地域として, 火山活動による周期的な自然撹乱が植生に及ぼす影響を調査した。その結果, 火山活動による植生退行がクロマメノキ自生地の成立・維持に大きく寄与していることが明らかとなった。