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ABSTRACT Intermittent streams are prevalent worldwide, yet the understanding of drivers of their changing flow patterns remains incomplete. We examined hydrological changes spanning four decades (1982–2020) in Kings Creek, an intermittent grassland stream within the Konza Prairie Biological Station in Kansas, USA. We analysed streamflow data from a US Geological Survey gauge on Kings Creek and three upstream Long Term Ecological Reasearch (LTER) sub‐watersheds with annual, biennial or quadrennial burn frequencies and linked trajectories of woody encroachment to increased evapotranspiration and changes in streamflow. Riparian woody cover doubled in the annually and biannually burned sub‐watersheds and sevenfold in the quadrennially burned watersheds. We observed significant decreases (84%) in daily discharge and number of annual flow days (55%) at the downstream USGS Kings Creek gauge, with similar changes in the LTER sub‐watersheds. The changing riparian cover, propelled by the regional expansion of woody plants, contributed to decreased streamflow by amplifying actual evapotranspiration (ET). Seasonal assessments underscored the critical influence of late summer conditions (July–September), under which increases in ET were linked to rising temperatures and increased evapotranspiration by riparian cover. Our results highlight the significant hydrological impacts of woody encroachment in grasslands and emphasize the importance of long‐term ecohydrological monitoring in unravelling the interplay between climate and vegetation as controls on the hyper‐variable flow patterns in this intermittent stream. Predicting and managing hydrological impacts on the flow of intermittent grassland rivers and streams worldwide requires accounting for the effects of accelerating woody encroachment.
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Trajectories and state changes of a grassland stream and riparian zone after a decade of woody vegetation removal
Abstract Riparian zones and the streams they border provide vital habitat for organisms, water quality protection, and other important ecosystem services. These areas are under pressure from local (land use/land cover change) to global (climate change) processes. Woody vegetation is expanding in grassland riparian zones worldwide. Here we report on a decade‐long watershed‐scale mechanical removal of woody riparian vegetation along 4.5 km of stream channel in a before–after control impact experiment. Prior to this removal, woody plants had expanded into grassy riparian areas, associated with a decline in streamflow, loss of grassy plant species, and other ecosystem‐scale impacts. We confirmed some expected responses, including rapid increases in stream nutrients and sediments, disappearance of stream mosses, and decreased organic inputs to streams via riparian leaves. We were surprised that nutrient and sediment increases were transient for 3 years, that there was no recovery of stream discharge, and that areas with woody removal did not shift back to a grassland state, even when reseeded with grassland species. Rapid expansion of shrubs (Cornus drummondii,Prunus americana) in the areas where trees were removed allowed woody vegetation to remain dominant despite repeating the cutting every 2 years. Our results suggest woody expansion can fundamentally alter terrestrial and aquatic habitat connections in grasslands, resulting in inexorable movement toward a new ecosystem state. Human pressures, such as climate change, atmospheric CO2increases, and elevated atmospheric nitrogen deposition, could continue to push the ecosystem along a trajectory that is difficult to change. Our results suggest that predicting relationships between riparian zones and the streams they border could be difficult in the face of global change in all biomes, even in well‐studied sites.
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- Award ID(s):
- 2025849
- PAR ID:
- 10468450
- Publisher / Repository:
- Ecological Applications
- Date Published:
- Journal Name:
- Ecological Applications
- Volume:
- 33
- Issue:
- 4
- ISSN:
- 1051-0761
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/eap.2830
