Grazing Effects on the Composition, Diversity, and Function of Wet Meadow Grasslands in Manitoba, Canada

Wet grasslands are an important element of rangeland communities around the world and are key in the provision of many ecosystem services, including interception of runoff, filtration of pollutants, storage of carbon, and maintenance of wildlife habitat. In the northern Great Plains, wet grasslands are often more productive than upland grasslands and are an important source of seasonal forage or hay. As climates continue to limit growing conditions and yields of upland forages, grazing pressure on wet grasslands may increase. Our research focused on a wet meadow rangeland in Manitoba, Canada to test how the timing and intensity of grazing affect the composition, diversity, and function of plants and soils. Our results demonstrate that the effects of grazing on wet meadow grasslands depend on its timing and intensity. Early grazing shifted the composition of plants, increasing the abundance of weedy and invasive species, including foxtail barley (Hordeum jubatum). The effect of grazing on plant diversity also depended on its intensity. As a result, the spatial heterogeneity of wet grasslands increased following early, intense grazing but decreased following late-season grazing. Although the effect of grazing on a number of soil variables did not differ among grazing treatments, early, intense grazing increased soil bulk density. Our results demonstrate that late-season, moderate-intensity grazing can sustain the diversity and function of wet meadow grasslands. Our research also highlights the negative impacts of early-season, intense grazing on the proliferation of weedy and invasive plants. As changing climates across the Great Plains continue to increase grazing pressure on marginal rangelands, adaptive management must focus on increasing the resilience of wet grasslands. Our work points to an important gap in our understanding of interactions among grazing, ecosystem services, and belowground production in wet meadow grasslands.