Extirpation or Coexistence? Management of a Persistent Introduced Grass in a Prairie Restoration

Abstract Introduced perennial grasses are one of the greatest constraints to prairie restoration. Herbicides suppress but do not eliminate introduced grasses, so we explored the interaction of herbicide with two additional controls: heavy clipping (to simulate grazing) and competition from native species. A 50‐year‐old stand of the introduced perennial grass Agropyron cristatum (crested wheatgrass) in the northern Great Plains was seeded with native grasses and treated with herbicide annually for 7 years in a factorial experiment. Clipping was applied as a subplot treatment in the final 3 years. Both herbicide and clipping significantly reduced the cover of A. cristatum, but clipping produced an immediate and consistent decrease, whereas herbicide control varied among years. The cover of A. cristatum decreased significantly with increasing cover of a seeded native grass, Bouteloua gracilis (blue grama), suggesting that both top‐down (i.e., grazing) and bottom‐up (i.e., resource competition) strategies can contribute to A. cristatum control. No treatment had any effect on the seed bank of A. cristatum. Even in the most effective control treatments, A. cristatum persisted at low amounts (approximately 5% cover) throughout the experiment. The cover of B. gracilis increased significantly with seed addition and herbicide, and, after 7 years, was similar to that in undisturbed prairie. The total cover of native species increased significantly with clipping and herbicide, and species richness was significantly higher in plots receiving herbicide. Clipping season had no effect on any variable. In summary, no method extirpated A. cristatum, but clipping reduced its cover by 90% and doubled the cover of native species. Extirpation might not be a realistic goal, but relatively simple management allowed coexistence of native species.     

Does Management for Duck Productivity Affect Songbird Nesting Success?

ABSTRACT Habitat management for ducks has significantly influenced prairies and wetlands used by other species. However, the effects of management on other species have not been clearly assessed. We present the first study to compare the nesting success of ducks with the productivity of coexisting passerines. We evaluated effects of cattle grazing, subdivision of fields, habitat edges, year, and vegetation structure on duck and songbird nesting success in 32 mixed-grass prairie fields in southern Alberta, Canada. Duck and songbird nesting success were not correlated. Duck nesting success was influenced by timing of grazing and vegetation structure, and tended to be higher in wetter years, whereas nesting success of most songbirds was not influenced by vegetation structure or grazing, and was sometimes higher in drier years. Local habitat management for ducks cannot be assumed to benefit songbirds. However, some management strategies, such as those that promote tall grass and short litter, might benefit both taxa.     

Effects of livestock exclusion on in‐stream habitat and benthic invertebrate assemblages in montane streams

1. Stream and riparian ecosystems in arid montane areas, like the interior western United States, are often just narrow mesic strands, but support diverse and productive habitats. Meadows along many such streams have long been used for rangeland grazing, and, while impacts to riparian areas are relatively well known, the effect of livestock grazing on aquatic life in streams has received less attention. 2. Attempts to link grazing impacts to disturbance have been hindered by the lack of spatial and temporal replication. In this study, we compared channel features and benthic macroinvertebrate communities (i) between 16 stream reaches on two grazed allotments and between 22 reaches on two allotments where livestock had been completely removed for 4 years, (ii) before and after the 4‐year grazing respite at a subset of eight sites and (iii) inside and outside of small‐scale fenced grazing exclosures (eight pairings; 10+ year exclosures) in the meadows of the Golden Trout Wilderness, California (U.S.A.). 3. We evaluated grazing disturbance at the reach scale in terms of the effects of livestock trampling on per cent bank erosion and found that macroinvertebrate richness metrics were negatively correlated with bank erosion, while the percentage of tolerant taxa increased. 4. All macroinvertebrate richness metrics were significantly lower in grazed areas. Bank angle, temperature, fine sediment cover and erosion were higher in grazed areas, while riparian cover was lower. Regression models identified riparian cover, in‐stream substratum, bank conditions and bankfull width‐to‐depth ratios as the most important for explaining variability in macroinvertebrate richness metrics. 5. Small‐scale grazing exclosures showed no improvements for in‐stream communities and only moderate positive effects on riparian vegetation. In contrast, metrics of macroinvertebrate richness increased significantly after a 4‐year period of no grazing. 6. The success of grazing removal reported here suggests that short‐term removal of livestock at the larger, allotment meadow spatial scale is more effective than long‐term, but small‐scale, local riparian area fencing, and yields promising results in achieving stream channel, riparian and aquatic biological recovery.