Woody Vegetation Removal Stimulates Riparian and Benthic Denitrification in Tallgrass Prairie
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Expansion of woody vegetation into areas that were historically grass-dominated is a significant contemporary threat to grasslands, including native tallgrass prairie ecosystems of the Midwestern United States. In tallgrass prairie, much of this woody expansion is concentrated in riparian zones with potential impacts on biogeochemical processes there. Although the effects of woody riparian vegetation on denitrification in both riparian soils and streams have been well studied in naturally wooded ecosystems, less is known about the impacts of woody vegetation encroachment in ecosystems that were historically dominated by herbaceous vegetation. Here, we analyze the effect of afforestation and subsequent woody plant removal on riparian and benthic denitrification. Denitrification rates in riparian soil and selected benthic compartments were measured seasonally in naturally grass-dominated riparian zones, woody encroached riparian zones, and riparian zones with woody vegetation removed in two separate watersheds. Riparian soil denitrification was highly seasonal, with the greatest rates in early spring. Benthic denitrification also exhibited high temporal variability, but no seasonality. Soil denitrification rates were greatest in riparian zones where woody vegetation was removed. Additionally, concentrations of nitrate, carbon, and soil moisture (indicative of potential anoxia) were greatest in wood removal soils. Differences in the presence and abundance of benthic compartments reflected riparian vegetation, and may have indirectly affected denitrification in streams. Riparian soil denitrification increased with soil water content and NO3 −. Management of tallgrass prairies that includes removal of woody vegetation encroaching on riparian areas may alter biogeochemical cycling by increasing nitrogen removed via denitrification while the restored riparian zones return to a natural grass-dominated state.
Keywordswoody encroachment denitrification riparian vegetation nitrogen removal prairie streams tallgrass prairie
We thank M. Arango, J. Taylor, and R. Ramundo for laboratory assistance. Identification of vegetation was performed by B. Vanderweide. We thank the volunteers who assisted with woody vegetation removal. This manuscript was greatly improved by two anonymous reviews. This research was supported by the NSF Long Term Ecological Research Program at Konza Prairie Biological Station, Grant # DEB-0823341 and Kansas State University. This is publication #12-465-J from the Kansas Agricultural Experiment Station.
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