Yu Yoshihara

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.

Differential responses and mechanisms of productivity following experimental species loss scenarios

Experiments that simulate nonrandom species loss from natural communities can offer a fundamentally different understanding of the impacts of species loss on ecosystem function and their underlying mechanisms compared to seeding experiments where species are randomly assembled from a local species pool. We examined the mechanisms underlying changes in primary productivity following experimental species loss scenarios in Mongolian grassland. The range of species loss scenarios was based on natural patterns of species abundance that reflect the species’ contributions to ecosystem processes. We found a clear reduction in productivity due to species loss only when species were lost randomly. Grassland productivity was relatively robust following nonrandom species loss scenarios. Even in the context of density compensation, the decrease in dominant trait values for leaf height would explain the reduction in productivity with random species loss. In contrast, the maintenance of dominant trait values of key productivity traits such as leaf dry matter content and leaf height might contribute to the maintenance of productivity in response to nonrandom species loss. Our experiment demonstrated that the responses and mechanisms of primary productivity to species loss differ according to the scenarios of species loss in natural grassland communities. The effects of diversity on productivity might be weak in mature natural systems when species loss is nonrandom. Understanding the consequences of realistic species loss on ecosystem functioning based on field-based removal experiments will give insights into real conservation strategies in the face of global biodiversity change.

Local-scale disturbance by Siberian marmots has little influence on regional plant richness in a Mongolian grassland

Our objective was to examine the relative importance of local-scale disturbance by Siberian marmots in increasing regional (landscape-wide) plant richness. We used an additive diversity partitioning framework and quantified species richness patterns of grassland plant communities affected by marmot disturbance across different spatial scales: within and among on- and off-marmot-mound subsites, among sites, and among landscape units (corresponding to α and three levels of β richness). Values of β richness among subsites and β richness among landscape units were similar to those expected by chance. This suggests that plant species are randomly distributed among subsites and among landscape units, despite the prediction based on previous studies that local-scale disturbance by Siberian marmots and its interactive effects with landscape contexts disproportionately influence spatial patterns of plant species. Of the spatial components of regional richness, only the β richness among sites was significantly different from the expected value, probably reflecting the differential spatial pattern of disturbance by marmots at a site scale. The β richness among landscape units contributed the most to regional richness, whereas β richness among subsites and among sites contributed less. Thus, our results suggest that local-scale disturbance by Siberian marmots has little influence on regional plant richness in a Mongolian grassland.

Role of tussock morphology in providing protection from grazing for neighbouring palatable plants in a semi-arid Mongolian rangeland

Background: Palatable plants in rangelands may be protected from herbivore grazing by the presence of less palatable neighbouring plants. The protective role of benefactor species on palatable species often collapses under heavy grazing, but the underlying mechanism—the relationship between the reduced protective role and grazing damage to benefactor species—remains unclear. Aims: To clarify whether the protection of surrounding palatable species conferred by a less palatable tussock grass (Achnatherum splendens) is reduced under heavy grazing, focusing on the changes to tussock morphology caused by grazing. Methods: In the Mongolian steppe, we measured the morphological traits of A. splendens tussocks, plant density of palatable graminoids and grazing damage in three A. splendens microhabitats (inside, adjacent to, and outside tussocks) under light and heavy grazing areas. Results: A. splendens tussocks had smaller basal area and culm height, and greater culm density under heavy grazing. The densities of palatable graminoids adjacent to and inside tussocks were equal to or lower than those outside, but grazing damage decreased inside tussocks. Additionally, plant establishment inside tussocks was negatively related to A. splendens culm density, probably owing to competition for space within the tussocks. Conclusions: Our results indicate that the collapse of positive grass–grass interactions results from the decline in neighbouring benefactor plants through the morphological changes caused by grazing.

Effects of soil-salt accumulation on sheep body weight in Mongolian grassland: evidence of excess salt in plant and wool samples

The aim of this study was to examine the effects of accumulated soil salt on livestock production in Mongolian grasslands. In saline and control areas, we compared soil salinity, sodium concentrations in plants and wool, and body weights of ewes. Mean soil salinity, sodium concentrations, and growth retardation were greater in the high-salinity area than in the control region. Increased retention of sodium in wool samples was evidence of excess dietary sodium. These results reflect sodium overflow from soil to sheep via plants, and this overflow can diminish livestock productivity in saline areas.

Plant species diversity and forage quality as affected by pasture management and simulated cattle activities

Grazed pastures have been historically used in Japan for animal production with little concern to biodiversity. However, pasturing has significant effects on biodiversity and productivity because it produces gaps in the distribution of vegetation due to animal activities. We hypothesized that different grazing activities would have effects on the diversity of plant species and forage quality in different ways and that the sward type would modify these effects. Therefore, we attempted to predict the diversity of plant species and changes in total nutrient content per area at the time since treatment on the basis of simulations of cattle activities in three pastures with different vegetation compositions. We created three ground types (grazed areas, cleared ground, and undisturbed areas) in three pastures (improved, partially improved semi-natural, and semi-natural pasture) and recorded the percentage cover of each plant within the plots. We repeatedly calculated the biodiversity indices from these community data by varying the sampling probabilities for each ground type, which provided us with the expected species diversity indices with the changing proportions of each ground type. Furthermore, we investigated the dry matter and forage qualities. For improved and partially improved semi-natural pasture, our models predicted that plant diversity increased as a saturating function of the proportion of cleared ground and grazed area relative to the undisturbed area, although our models also showed exponential curves for the semi-natural pasture. Forage samples from cleared ground plots and semi-natural pasture had the lowest forage quality among all pastures. Based on the predicted effects of cattle pasturing on the plant species biodiversity and forage quality, it may be more beneficial to maintain a small proportion of cleared ground in the improved pasture during intensive grazing.

Recent pasture management determines biodiversity and productivity, and past management determines forage quality

ABSTRACT Agro-ecosystem management focuses on developing grassland systems that meet sustainable productivity and biodiversity targets. Pasture management affects productivity and biodiversity, but the effects of previous management impacts are difficult to predict. Our objective was to identify the effects of key management factors and their timing on current biodiversity and productivity in public pastures in northeastern Japan. We surveyed pasture management histories (stocking rate, mowing frequency, fertilizer application and pasture renovation by plowing) from 1991 to 2010. We divided the data into periods and examined productivity, forage quality and biodiversity (plants and burrowing rodents). We included these parameters into generalized linear models, and found that recent fertilization level, mowing frequency and renovation were the most important factors affecting plant species diversity. In contrast, recent and past stocking rates were the dominant factors for productivity and forage quality, respectively. Thus, biodiversity and productivity were affected by different factors, suggesting that pasture management can balance the competing goals of biodiversity conservation and productivity improvement. From the effects of pasture management on biodiversity, forage productivity and quality, avoiding intensive pasture management is a practical application. In addition, a time lag effect of grazing pressure on forage quality should be considered during future pasture management.

Prescribed burning experiments for restoration of degraded semiarid Mongolian steppe

Prescribed burning has been a successful ecosystem restoration tool worldwide. In this study, we burned two different degraded Mongolian grasslands in spring: sparsely vegetated Argalant (ARG) and Hustai National Park (HNP), dominated by the unpalatable forb Artemisia adamsii. We investigated soil properties, seed bank, seedling density, vegetation, biomass, and forage quality before and/or after burning in the grasslands. Burning weakly affected soil properties and significantly reduced seed bank density. Seedling density of Chenopodium aristatum was greater and that of Cleistogenes squarrosa was lower in burned than in unburned plots of HNP, although C. squarrosa showed greater vegetative growth in burned plots. The floristic composition showed small changes after burning, depending on the pre-burning vegetation, but cover of A. adamsii decreased after burning in both ARG and HNP. Thus, the reduced seed bank density by burning led to weak responses of vegetation composition to burning due to strong vegetative growth. However, burning suppressed the unpalatable forb (A. adamsii) and hastened palatable grass (C. squarrosa) productivity, which would be attractive for livestock production, especially for overgrazed areas with low forage palatability. Our findings illustrate the possibility of using spring prescribed burning as a restoration tool in degraded Mongolian steppe, as well as the importance of site-specific conditions for understanding postfire recovery.