Dynamics and sustainability of the inner Mongolia typical steppe - ecosystem responses to grazing and climate

Abstract

The purpose of this study is to examine interactions of historic, present, and future climate patterns, vegetation patterns, and grazing practices to better comprehend and predict the sustainability and resilience of the Mongolian steppe grassland ecosystem. This study will utilize SAVANNA (a dynamic, spatially extensive ecosystem model) to understand, interpret, and predict how future grazing, soils, vegetation, and climate patterns interact to affect ecosystem sustainability and resilience. Field results suggest that production of these grasslands has declined with increased grazing intensity. This information was incorporated in the model structure to examine future stability and resilience of this vegetation system. This analysis also used Savanna to simulate both vegetation and livestock production, which gave further insight into potential effects management, climate, and grazing on the sustainability of grassland systems. Simulations that examined the effects of livestock density on vegetation showed a moderate level of grazing (~50% of vegetation removed) was sustainable for this particular system. This region was resilient to light and moderate levels of grazing; however, higher grazing intensities, in combination with low precipitation events, resulted in decreased herbaceous net primary production and increased shrub net primary production. Once initiated, these patterns continued even by an after-the-fact removal of grazing from this region. When predicted climate change scenarios were utilized in model simulations, results showed this grazing system was most sensitive to changes in precipitation patterns; however combinations of precipitation, temperature, and CO2 had synergistic effects on herbaceous production. Greater increases in temperature put a larger stress on the sustainability of herbaceous vegetation, which resulted in unsustainable herbaceous biomass-alleviated only by a reduction in grazing intensity. Only increased precipitation, CO2, or the combination of the two lessened the effects of a large increase in temperature. Simulations with climate change indicate that grazing increases the vulnerability of sustainable grassland systems to climate change. Therefore management must change grazing rates when net primary production is decreased to maintain grassland sustainability.