Manipulating the system: How large herbivores control bottom‐up regulation of grasslands

Frank, Douglas A.; Wallen, Rick L.; Hamilton, E. William; White, P. J.; Fridley, Jason D.

doi:10.1111/1365-2745.12884

Cited by 35 publications

(31 citation statements)

References 58 publications

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“…Moreover, enhanced leaf tissue nitrogen during the growing season (Fig. 3 B ) increases photosynthetic activity, which prolongs plant growth (23, 29). If bison grazing can both accelerate and extend plant green-up at large scale, it may alter the progression of the green wave itself across the landscape.…”

Section: Resultsmentioning

confidence: 99%

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Migrating bison engineer the green wave

Geremia

Merkle

Eacker

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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Newly emerging plants provide the best forage for herbivores. To exploit this fleeting resource, migrating herbivores align their movements to surf the wave of spring green-up. With new technology to track migrating animals, the Green Wave Hypothesis has steadily gained empirical support across a diversity of migratory taxa. This hypothesis assumes the green wave is controlled by variation in climate, weather, and topography, and its progression dictates the timing, pace, and extent of migrations. However, aggregate grazers that are also capable of engineering grassland ecosystems make some of the world's most impressive migrations, and it is unclear how the green wave determines their movements. Here we show that Yellowstone's bison (Bison bison) do not choreograph their migratory movements to the wave of spring green-up. Instead, bison modify the green wave as they migrate and graze. While most bison surfed during early spring, they eventually slowed and let the green wave pass them by. However, small-scale experiments indicated that feedback from grazing sustained forage quality. Most importantly, a 6-fold decadal shift in bison density revealed that intense grazing caused grasslands to green up faster, more intensely, and for a longer duration. Our finding broadens our understanding of the ways in which animal movements underpin the foraging benefit of migration. The widely accepted Green Wave Hypothesis needs to be revised to include large aggregate grazers that not only move to find forage, but also engineer plant phenology through grazing, thereby shaping their own migratory movements.

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Section: Resultsmentioning

confidence: 99%

“…At each site, we used a paired design of naturally grazed grassland (treatment) and exclosed grassland (control) to measure net aboveground production, grazing intensity, standing crop, and plant nutrients. We made measurements using established methods (29, 36–38). For controls, we placed 3 semipermanent 9-m 2 fenced exclosures at each site.…”

Section: Methodsmentioning

confidence: 99%

Migrating bison engineer the green wave

Geremia

Merkle

Eacker

et al. 2019

Proc. Natl. Acad. Sci. U.S.A.

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“…During the experimental period, resource availability was possibly the main contributor to variations in ANPP under different grazing intensities, since some factors can be excluded such as fire history and co-evolutionary history that were not significantly affected by grazing intensity in this study. It has been reported that the dominant factors affecting resource availability in grassland ecosystems are precipitation, air temperature, nutrient availability, and soil water content (Frank et al, 2018). Previous studies have indicated that precipitation has a positive (Lezama et al, 2014; Lu et al, 2017) or neutral (Wang et al, 2012; Eldridge et al, 2016) effect on primary production in grasslands on a regional scale; in contrast, the timing of rainfall events and precipitation periods are key factors to affect ANPP on a plot scale (Knapp et al, 2012).…”

Section: Discussionmentioning

confidence: 99%

Productive Overcompensation of Alpine Meadows in Response to Yak Grazing in the Eastern Qinghai-Tibet Plateau

et al. 2019

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Understanding the interaction between large herbivores and pasture production, especially with respect to the grazing optimization hypothesis, is critical for pasture management and generating theoretical and testable predictions. However, the optimization hypothesis remains contradictory in alpine meadows on the Qinghai-Tibet Plateau (QTP). In this study, we tested the grazing optimization hypothesis using four yak-grazing intensities (no grazing, light grazing, moderate grazing and heavy grazing) in alpine meadow habitats from 2015 to 2017. The results indicated that species diversity did not differ significantly among grazing regimes during the experimental period. However, the aboveground net primary production (ANPP) under moderate grazing consistently significantly exceeded that in control enclosures over 3 years, confirming the grazing optimization hypothesis. Levels of overcompensation varied among grazing intensities and years, and grazing-induced plant compensation may only occur in the short term. The enhanced regrowth of Poaceae and Cyperaceae induced by yak grazing might contribute to the overall level of overcompensation by plant community. Our results strongly support the grazing optimization hypothesis in the context of alpine meadows grazed by yaks, emphasizing the complex interactions between ANPP, herbivores and other ecological factors in alpine meadows on the QTP. These findings provide new insights for the development of an ecological conservation strategy that will help restore this fragile ecosystem and balance the seemingly incompatible requirements of animal husbandry.

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“…The effects of herbivory on plant biomass should interact with nutrient availability and precipitation in grasslands (Anderson et al, 2018; Frank et al, 2018; McNaughton et al, 1989). The net effect of grazers on biomass across years at a site can alter biomass-precipitation relationships in different ways.…”

Section: Introductionmentioning

confidence: 99%

“…If grazing enhances production by releasing the plant community from light limitation (Borer, Seabloom, et al, 2014), nutrients will have smaller effects on sensitivity when grazers are excluded. In spite of all these possible mechanisms, the generality and degree to which grazing by mammalian herbivores modulates the relationship between grassland biomass and interannual variation in precipitation has not been quantitatively evaluated (Campbell and Stafford Smith, 2000; Frank et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Multiple resource limitations explain biomass-precipitation relationships in grasslands

Bharath

Fay

et al. 2021

Preprint

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Interannual variability in grassland primary production is strongly driven by precipitation, nutrient availability and herbivory, but there is no general consensus on the mechanisms linking these variables. If grassland biomass is limited by the single most limiting resource at a given time, then we expect that nutrient addition will not affect biomass production at arid sites. We conducted a distributed experiment manipulating nutrients and herbivores at 44 grassland sites in 8 regions around the world, spanning a broad range in aridity. We estimated the effects of 5-11 years of nutrient addition and herbivore exclusion treatments on precipitation sensitivity of biomass (proportional change in biomass relative to proportional change in rainfall among years), and the biomass in the driest year (to measure treatment effects when water was most limiting) at each site. Grazer exclusion did not interact with nutrients to influence driest year biomass or sensitivity. Nutrient addition increased driest year biomass by 74% and sensitivity by 0.12 (proportional units), and that effect did not change across the range of aridity spanned by our sites. Grazer exclusion did not interact with nutrients to influence sensitivity or driest year biomass. At almost half of our sites, the previous year's rainfall explained as much variation in biomass as current year precipitation. Overall, our distributed fertilization experiment detected co-limitation between nutrients and water governing grasslands, with biomass sensitivity to precipitation being limited by nutrient availability irrespective of site aridity and herbivory. Our findings refute the classical ideas that grassland plant performance is limited by the single most limiting resource at a site. This suggests that nutrient eutrophication will destabilize grassland ecosystems through increased sensitivity to precipitation variation.

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Manipulating the system: How large herbivores control bottom‐up regulation of grasslands

Cited by 35 publications

References 58 publications

Migrating bison engineer the green wave

Migrating bison engineer the green wave

Productive Overcompensation of Alpine Meadows in Response to Yak Grazing in the Eastern Qinghai-Tibet Plateau

Multiple resource limitations explain biomass-precipitation relationships in grasslands

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