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

AbstractBackground: 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.Keywords: Achnatherum splendensmicrohabitatMongolian rangelandplant palatabilityplant–plant interactiontussock morphology AcknowledgementsWe are grateful to T. Osawa for his comments on an earlier version of this manuscript, and we also wish to thank D. Kubo for his help in the field survey.Additional informationFundingThis study was financially supported by the Global Environmental Fund of the Ministry of the Environment of Japan [D–1105 "Biodiversity of dryland ecosystem and sustainability of nomadic production in Northeast Asia"] and the Mitsui & Co. Ltd., Environment Fund [R10–B196 "Developing 'restoration manuals' for sustainable use of ecosystem services in drylands of Northeast Asia"].Notes on contributorsAsuka KoyamaAsuka Koyama is a plant ecologist with research interests in plant–plant interactions and the mechanisms of plant community structuring.Yu YoshiharaYu Yoshihara is an assistant professor, and his research interests are the biological and environmental interactions between animals, plants and soils in grasslands, ranging from arid (Mongolia) to humid environments (Japan).Undarmaa JamsranUndarmaa Jamsran is an associate professor, and her major research interests are rangeland ecosystems and management.Toshiya OkuroToshiya Okuro is a professor, and his research interests are centred on land degradation processes and the ecological evaluation of desertification control measures in semi-arid regions.