Effects of Elk Herbivory on Vegetation and Nitrogen Processes

Schoenecker, Kathryn A.; Singer, Francis J.; Zeigenfuss, Linda C.; Binkley, Dan; Menezes, Rômulo S. C.

doi:10.2193/0022-541x(2004)068[0837:eoehov]2.0.co;2

Cited by 42 publications

(47 citation statements)

References 46 publications

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“…Some movement of N down slope is likely to occur through hydrological processes, but since this is a semi-arid system, transport via water could be limited. Just as wild grazers play a crucial role as transporters of organic matter and nutrients in many systems (Frank et al 1994;Walker et al 2003;Schoenecker et al 2004;Holdo et al 2007), we suggest that domestic herds must have played a similar role in the Mongolian steppe for millennia. Currently, the livestock herds largely sort themselves across the topographic gradient, with sheep and goats foraging more often on steeper, upper slopes.…”

Section: Discussionmentioning

confidence: 84%

Legumes mitigate ecological consequences of a topographic gradient in a northern Mongolian steppe

et al. 2011

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Topography should create spatial variation in water and nutrients and play an especially important role in the ecology of water-limited systems. We use stable isotopes to discern how plants respond both to ecological gradients associated with elevation and to neighboring legumes on a south-facing slope in the semi-arid, historically grazed steppe of northern Mongolia. Out of three target species, Potentilla acaulis, Potentilla sericea, and Festuca lenensis, when >30 cm from a legume, all showed a decrease in leaf δ(15)N with increasing elevation. This, together with measures of soil δ(15)N, suggests greater N processing at the moister, more productive, lower elevation, and more N fixation at the upper elevation, where cover of legumes and lichens and plant-available nitrate were greater. Total soil N was greater at the lower elevation, but not lichen biomass or root colonization by AMF. Leaf δ(13)C values for P. acaulis and F. lenensis are consistent with increasing water stress with elevation; δ(13)C values indicated the greatest intrinsic water use efficiency for P. sericea, which is more abundant at the upper elevation. Nearby legumes (<10 cm) moderate the effect of elevation on leaf δ(15)N, confirming legumes' meaningful input of N, and affect leaf δ(13)C for two species, suggesting an influence on the efficiency of carbon fixation. Variation in leaf %N and %C as a function of elevation and proximity to a legume differs among species. Apparently, most N input is at upper elevations, pointing to the possible importance of grazers, in addition to hydrological processes, as transporters of N throughout this landscape.

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Section: Discussionmentioning

confidence: 84%

Legumes mitigate ecological consequences of a topographic gradient in a northern Mongolian steppe

et al. 2011

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“…However, areas used by livestock had comparatively lower belowground investment and higher aboveground investment, a pattern which is related to grazing-mediated variation in plant community composition . These results show that, despite qualitative similarities, it may be diYcult to readily extrapolate insights from natural ecosystems to livestock production systems and vice versa, because quantitative eVects of grazers may vary between diVerent plant communities (e.g., North American prairies, Schoenecker et al 2004; East African savannas, Augustine and McNaughton 2006).…”

Section: Discussionmentioning

confidence: 96%

“…Since the above-and belowground aspects have seldom been studied alongside soil nutrients (Biondini et al 1998;Schoenecker et al 2004), particularly in multi-species natural communities, our results provide a simultaneous assessment of herbivore control over material and energy Xow through grazing ecosystems. The hypothesized eVects of Ungrazed resin N (mg g -1 ) Grazed resin N (mg g -1 ) d 1:1 line herbivores on NAP and nutrient dynamics (de Mazancourt et al 1998) are well supported by Weld experiments (e.g., Ritchie et al 1998;Biondini et al 1998;Chapman et al 2003).…”

Section: Discussionmentioning

confidence: 99%

“…Studies have also investigated the relationships between grazingrelated changes in NBP and in soil N dynamics [e.g., North American tallgrass prairie (Johnson and Matchett 2001)]. But, very few studies have approached the inter-related aspects of NAP and NBP vis-à-vis soil N availability simultaneously (Biondini et al 1998;Schoenecker et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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Herbivore effects on above- and belowground plant production and soil nitrogen availability in the Trans-Himalayan shrub-steppes

Bagchi

Ritchie

2010

Oecologia

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Large mammalian herbivores may have positive, neutral, or negative effects on annual net aboveground plant production (NAP) in different ecosystems, depending on their indirect effects on availability of key nutrients such as soil N. In comparison, less is known about the corresponding influence of grazers, and nutrient dynamics, over annual net belowground plant production (NBP). In natural multi-species plant communities, it remains uncertain how grazing influences relative allocation in the above- and belowground compartments in relation to its effects on plant nutrients. We evaluated grazer impacts on NAP, NBP, and relative investment in the above- and belowground compartments, alongside their indirect effects on soil N availability in the multiple-use Trans-Himalayan grazing ecosystem with native grazers and livestock. Data show that a prevailing grazing intensity of 51% increases NAP (+61%), but reduces NBP (-35%). Grazing also reduced C:N ratio in shoots (-16%) and litter (-50%), but not in roots, and these changes coincided with increased plant-available inorganic soil N (+23%). Areas used by livestock and native grazers showed qualitatively similar responses since NAP was promoted, and NBP was reduced, in both cases. The preferential investment in the aboveground fraction, at the expense of the belowground fraction, was correlated positively with grazing intensity and with improvement in litter quality. These results are consistent with hypothesized herbivore-mediated positive feedbacks between soil nutrients and relative investment in above- and belowground compartments. Since potentially overlapping mechanisms, such as N mineralization rate, plant N uptake, compositional turnover, and soil microbial activity, may contribute towards these feedbacks, further studies may be able to discern their respective contributions.

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“…Stewart et al (2006), in a companion study to this paper, reported herbivore optimization by North American elk in this same montane ecosystem, and observed increases in NAPP at low levels of herbivory in forbs, graminoids, and shrubs. Herbivory by elk has also been implicated both in increasing and decreasing rates of nutrient cycling in soils (Singer and Schoenecker 2003;Schoenecker et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Population density of North American elk: effects on plant diversity

et al. 2009

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Large, herbivorous mammals have profound effects on ecosystem structure and function and often act as keystone species in ecosystems they inhabit. Density-dependent processes associated with population structure of large mammals may interact with ecosystem functioning to increase or decrease biodiversity, depending on the relationship of herbivore populations relative to the carrying capacity (K) of the ecosystem. We tested for indirect effects of population density of large herbivores on plant species richness and diversity in a montane ecosystem, where increased net aboveground primary productivity (NAPP) in response to low levels of herbivory has been reported. We documented a positive, linear relationship between plant-species diversity and richness with NAPP. Structural equation modeling revealed significant indirect relationships between population density of herbivores, NAPP, and species diversity. We observed an indirect effect of density-dependent processes in large, herbivorous mammals and species diversity of plants through changes in NAPP in this montane ecosystem. Changes in species diversity of plants in response to herbivory may be more indirect in ecosystems with long histories of herbivory. Those subtle or indirect effects of herbivory may have strong effects on ecosystem functioning, but may be overlooked in plant communities that are relatively resilient to herbivory.

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Effects of Elk Herbivory on Vegetation and Nitrogen Processes

Cited by 42 publications

References 46 publications

Legumes mitigate ecological consequences of a topographic gradient in a northern Mongolian steppe

Legumes mitigate ecological consequences of a topographic gradient in a northern Mongolian steppe

Herbivore effects on above- and belowground plant production and soil nitrogen availability in the Trans-Himalayan shrub-steppes

Population density of North American elk: effects on plant diversity

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