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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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The long shadow of woody encroachment: An integrated approach to modeling grassland songbird habitat
Abstract Animals must track resources over relatively fine spatial and temporal scales, particularly in disturbance‐mediated systems like grasslands. Grassland birds respond to habitat heterogeneity by dispersing among sites within and between years, yet we know little about how they make post‐dispersal settlement decisions. Many methods exist to quantify the resource selection of mobile taxa, but the habitat data used in these models are frequently not collected at the same location or time that individuals were present. This spatiotemporal misalignment may lead to incorrect interpretations and adverse conservation outcomes, particularly in dynamic systems. To investigate the extent to which spatially and temporally dynamic vegetation conditions and topography drive grassland bird settlement decisions, we integrated multiple data sources from our study site to predict slope, vegetation height, and multiple metrics of vegetation cover at any point in space and time within the temporal and spatial scope of our study. We paired these predictions with avian mark‐resight data for 8 years at the Konza Prairie Biological Station in NE Kansas to evaluate territory selection for Grasshopper Sparrows (Ammodramus savannarum), Dickcissels (Spiza americana), and Eastern Meadowlarks (Sturnella magna). Each species selected different types and amounts of herbaceous vegetation cover, but all three species preferred relatively flat areas with less than 6% shrub cover and less than 1% tree cover. We evaluated several scenarios of woody vegetation removal and found that, with a targeted approach, the simulated removal of just one isolated tree in the uplands created up to 14 ha of grassland bird habitat. This study supports growing evidence that small amounts of woody encroachment can fragment landscapes, augmenting conservation threats to grassland systems. Conversely, these results demonstrate that drastic increases in bird habitat area could be achieved through relatively efficient management interventions. The results and approaches reported pave the way for more efficient conservation efforts in grasslands and other systems through spatiotemporal alignment of habitat with animal behaviors and simulated impacts of management interventions.
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- Award ID(s):
- 2025849
- PAR ID:
- 10547669
- Publisher / Repository:
- ESA
- Date Published:
- Journal Name:
- Ecological Applications
- Volume:
- 34
- Issue:
- 3
- ISSN:
- 1051-0761
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract In the Central Great Plains of North America, fire suppression is causing transitions from grasslands to shrublands and woodlands. This woody encroachment alters plant community composition, decreases grassland biodiversity, undermines key ecosystem services, and is difficult to reverse. How native grazers affect woody encroachment is largely unknown, especially compared to domesticated grazers. Bison were once the most widespread megafauna in North America and are typically categorized as grazers, with negative effects on grasses that indirectly benefit woody plants. However, bison can negatively impact woody plants through occasional browsing and mechanical disturbance. This study reports on a 30‐year experiment at Konza Prairie Biological Station, a mesic grassland in the Central Great Plains of North America, under fire suppression and experimental presence/absence of bison. Based on remote sensing, deciduous tree canopy cover was lower with bison (6% grazed vs. 16% ungrazed). Shrub land cover showed no difference (42% grazed vs. 41% ungrazed), while herbaceous land cover was higher with bison (51% grazed vs. 40% ungrazed). Evergreen tree canopy cover (Juniperus virginianaL.), which decreases biodiversity and increases wildfire risk, was approximately 0% with bison compared to 4% without bison. In the survival trial ofJ. virginianaseedlings, we found a 40% overwinter mortality with bison, compared to 5% mortality without bison. Compared to ungrazed areas, native plant species richness was 97% and 38% higher in bison‐grazed uplands and lowlands, respectively. Species evenness and Shannon's index were higher in the bison treatment in uplands, but not in lowlands. Bison affected community composition, resulting in higher cover of short grass species and lower tree cover. While grazers are generally assumed to favor woody plants, we found that bison had the opposite effect at low fire frequencies. We argue that the large size of bison and their behaviors account for this pattern, including trampling, horning, and occasional browsing. From a conservation perspective, bison might hamper tree expansion and increase plant diversity in tallgrass prairies and similar grasslands.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1002/eap.2954
