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  1. Article ; Online: Context‐dependent effects of a reintroduced ungulate on soil properties are driven by soil texture, moisture, and herbivore activity

    Vanessa J. Dodge / Valerie T. Eviner / J. Hall Cushman

    Ecology and Evolution, Vol 10, Iss 19, Pp 10858-

    2020  Volume 10871

    Abstract: Abstract Although there is considerable evidence that large mammalian herbivores influence ecosystem‐level processes, studies have reported such widely varying results that generalizations have remained elusive. Here, we use an 18‐year‐old exclosure ... ...

    Abstract Abstract Although there is considerable evidence that large mammalian herbivores influence ecosystem‐level processes, studies have reported such widely varying results that generalizations have remained elusive. Here, we use an 18‐year‐old exclosure experiment—stratified across a landscape heterogeneous with respect to soil texture, moisture and herbivore activity—to understand the variable effects of tule elk (Cervus canadensis nannodes), a native reintroduced herbivore, on soil properties along the coast of northern California. Elk significantly increased soil bulk density and created a compacted layer at shallow soil depth, while decreasing infiltration rate and pH. The effects of elk on bulk density, penetration resistance, and pH varied with soil type, being least pronounced in coarse, sandy loams, and greatest in loose sand. The effects of elk on nutrient availability varied along gradients of soil texture and moisture. In coarser soils, elk decreased ammonium availability, but increased it in finer soils. Elk also decreased soil moisture content, in part through their positive effect on bulk density, and this effect was most pronounced in coarser soils. Through decreasing soil moisture content, elk also decreased nitrate availability in coarser soils. At greater levels of elk activity (as measured by dung deposition), the elk effect on bulk density was amplified, and this had a corresponding negative effect on nitrate and phosphate availability. Our study has demonstrated that a better understanding of spatial variation in the effects of herbivores on ecosystems can emerge by evaluating their influences across gradients of soil texture, soil moisture, and herbivore activity. These data enabled us to evaluate several frameworks that have been developed to understand the variable effects of herbivores on ecosystems, which is a significant step in reconciling the many competing ideas put forth to explain the context‐dependent effects of large herbivores on grazed ecosystems.
    Keywords context‐dependent effects ; ecosystem processes ; environmental heterogeneity ; long‐term effects ; native ungulate herbivore ; reintroduction ; Ecology ; QH540-549.5
    Subject code 550
    Language English
    Publishing date 2020-10-01T00:00:00Z
    Publisher Wiley
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  2. Article ; Online: Novel fine-scale aerial mapping approach quantifies grassland weed cover dynamics and response to management.

    Carolyn M Malmstrom / H Scott Butterfield / Laura Planck / Christopher W Long / Valerie T Eviner

    PLoS ONE, Vol 12, Iss 10, p e

    2017  Volume 0181665

    Abstract: Invasive weeds threaten the biodiversity and forage productivity of grasslands worldwide. However, management of these weeds is constrained by the practical difficulty of detecting small-scale infestations across large landscapes and by limits in ... ...

    Abstract Invasive weeds threaten the biodiversity and forage productivity of grasslands worldwide. However, management of these weeds is constrained by the practical difficulty of detecting small-scale infestations across large landscapes and by limits in understanding of landscape-scale invasion dynamics, including mechanisms that enable patches to expand, contract, or remain stable. While high-end hyperspectral remote sensing systems can effectively map vegetation cover, these systems are currently too costly and limited in availability for most land managers. We demonstrate application of a more accessible and cost-effective remote sensing approach, based on simple aerial imagery, for quantifying weed cover dynamics over time. In California annual grasslands, the target communities of interest include invasive weedy grasses (Aegilops triuncialis and Elymus caput-medusae) and desirable forage grass species (primarily Avena spp. and Bromus spp.). Detecting invasion of annual grasses into an annual-dominated community is particularly challenging, but we were able to consistently characterize these two communities based on their phenological differences in peak growth and senescence using maximum likelihood supervised classification of imagery acquired twice per year (in mid- and end-of season). This approach permitted us to map weed-dominated cover at a 1-m scale (correctly detecting 93% of weed patches across the landscape) and to evaluate weed cover change over time. We found that weed cover was more pervasive and persistent in management units that had no significant grazing for several years than in those that were grazed, whereas forage cover was more abundant and stable in the grazed units. This application demonstrates the power of this method for assessing fine-scale vegetation transitions across heterogeneous landscapes. It thus provides means for small-scale early detection of invasive species and for testing fundamental questions about landscape dynamics.
    Keywords Medicine ; R ; Science ; Q
    Subject code 710
    Language English
    Publishing date 2017-01-01T00:00:00Z
    Publisher Public Library of Science (PLoS)
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  3. Article ; Online: Grassland compost amendments increase plant production without changing plant communities

    Rebecca Ryals / Valerie T. Eviner / Claudia Stein / Katharine N. Suding / Whendee L. Silver

    Ecosphere, Vol 7, Iss 3, Pp n/a-n/a (2016)

    2016  

    Abstract: Abstract Compost amendment to grassland is a novel strategy proposed and demonstrated to increase ecosystem carbon (C) storage. However, the effects of compost applications on biomass production and plant diversity are not well known. We assessed impacts ...

    Abstract Abstract Compost amendment to grassland is a novel strategy proposed and demonstrated to increase ecosystem carbon (C) storage. However, the effects of compost applications on biomass production and plant diversity are not well known. We assessed impacts of a one‐time compost amendment over 4 yr on plant dynamics in two grazed grassland ecosystems in California: a coastal prairie and valley grassland. The valley grassland was dominated by exotic annual grasses and had significantly lower species diversity than the coastal prairie, which consisted of a mix of perennial and annual grasses and forbs. We observed large and persistent increases in aboveground biomass. Over the 4 study years, aboveground biomass from compost‐amended plots increased by 76% ± 21% at the valley grassland and 41% ± 21% at the coastal prairie, compared with controls. Plant N content was also greater from compost‐amended plots. There were no major shifts in species richness or abundance at either grassland site. Overall, plant communities at both grasslands were relatively resistant to the compost addition, but responses of some individual species were observed. Notably at the valley grassland, the abundance of forbs decreased slightly, while the abundance of grasses increased. The abundance of two noxious weeds did not change as a result of the compost amendment. Our results suggest that a single application of composted organic matter used to sequester C provided cobenefits to grassland plant dynamics. The compost amendments produced sustained increases in plant productivity and forage production as well as plant N content without greatly affecting the diversity of these exotic annual grasslands.
    Keywords annual grasslands ; carbon sequestration ; Carthamus lanatus ; compost amendment ; diversity ; Elymus caput‐medusae ; Ecology ; QH540-549.5
    Subject code 580
    Language English
    Publishing date 2016-03-01T00:00:00Z
    Publisher Wiley
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  4. Article ; Online: Impacts of introduced Rangifer on ecosystem processes of maritime tundra on subarctic islands

    Mark A. Ricca / A. Keith Miles / Dirk H. Van Vuren / Valerie T. Eviner

    Ecosphere, Vol 7, Iss 3, Pp n/a-n/a (2016)

    2016  

    Abstract: Abstract Introductions of mammalian herbivores to remote islands without predators provide a natural experiment to ask how temporal and spatial variation in herbivory intensity alter feedbacks between plant and soil processes. We investigated ecosystem ... ...

    Abstract Abstract Introductions of mammalian herbivores to remote islands without predators provide a natural experiment to ask how temporal and spatial variation in herbivory intensity alter feedbacks between plant and soil processes. We investigated ecosystem effects resulting from introductions of Rangifer tarandus (hereafter “Rangifer”) to native mammalian predator‐ and herbivore‐free islands in the Aleutian archipelago of Alaska. We hypothesized that the maritime tundra of these islands would experience either: (1) accelerated ecosystem processes mediated by positive feedbacks between increased graminoid production and rapid nitrogen cycling; or (2) decelerated processes mediated by herbivory that stimulated shrub domination and lowered soil fertility. We measured summer plant and soil properties across three islands representing a chronosequence of elapsed time post‐Rangifer introduction (Atka: ~100 yr; Adak: ~50; Kagalaska: ~0), with distinct stages of irruptive population dynamics of Rangifer nested within each island (Atka: irruption, K‐overshoot, decline, K‐re‐equilibration; Adak: irruption, K‐overshoot; Kagalaska: initial introduction). We also measured Rangifer spatial use within islands (indexed by pellet group counts) to determine how ecosystem processes responded to spatial variation in herbivory. Vegetation community response to herbivory varied with temporal and spatial scale. When comparing temporal effects using the island chronosequence, increased time since herbivore introduction led to more graminoids and fewer dwarf‐shrubs, lichens, and mosses. Slow‐growing Cladonia lichens that are highly preferred winter forage were decimated on both long‐term Rangifer‐occupied islands. In addition, linear relations between more concentrated Rangifer spatial use and reductions in graminoid and forb biomass within islands added spatial heterogeneity to long‐term patterns identified by the chronosequence. These results support, in part, the hypothesis that Rangifer population persistence on islands is facilitated ...
    Keywords Alaska ; Aleutian ; alternative state ; caribou ; irruption ; isotope ; Ecology ; QH540-549.5
    Subject code 550
    Language English
    Publishing date 2016-03-01T00:00:00Z
    Publisher Wiley
    Document type Article ; Online
    Database BASE - Bielefeld Academic Search Engine (life sciences selection)

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  5. Article: Livestock grazing regulates ecosystem multifunctionality in semi‐arid grassland

    Ren, Haiyan / Adam B. Cobb / Gail W. T. Wilson / Gaowen Yang / Shuijin Hu / Valerie T. Eviner / Weiyang Gui / Yingjun Zhang / Yongfei Bai

    Functional ecology. 2018 Dec., v. 32, no. 12

    2018  

    Abstract: Livestock grazing has been shown to alter the structure and functions of grassland ecosystems. It is well acknowledged that grazing pressure is one of the strongest drivers of ecosystem‐level effects of grazing, but few studies have assessed how grazing ... ...

    Abstract Livestock grazing has been shown to alter the structure and functions of grassland ecosystems. It is well acknowledged that grazing pressure is one of the strongest drivers of ecosystem‐level effects of grazing, but few studies have assessed how grazing pressure impacts grassland biodiversity and ecosystem multifunctionality (EMF). Here, we assessed how different metrics of biodiversity (i.e., plants and soil microbes) and EMF responded to seven different grazing treatments based on an 11‐year field experiment in semi‐arid Inner Mongolian steppe. We found that soil organic carbon, plant‐available nitrogen and plant functional diversity all decreased even at low grazing pressure, while above‐ground primary production and bacterial abundance decreased only at high levels of grazing pressure. Structural equation models revealed that EMF was driven by direct effects of grazing, rather than the effects of grazing on plant or microbial community composition. Grazing effects on plant functional diversity and soil microbial abundance did have moderate effects on EMF, while plant richness did not. Synthesis. Our results showed ecosystem functions differ in their sensitivity to grazing pressure, requiring a low grazing threshold to achieve multiple goals in the Eurasian steppe. A plain language summary is available for this article.
    Keywords arid lands ; biodiversity ; community structure ; ecological function ; ecosystems ; field experimentation ; functional diversity ; grazing effects ; grazing intensity ; livestock ; microbial communities ; nitrogen ; primary productivity ; soil ; soil microorganisms ; soil organic carbon ; steppes ; structural equation modeling ; China
    Language English
    Dates of publication 2018-12
    Size p. 2790-2800.
    Publishing place John Wiley & Sons, Ltd
    Document type Article
    Note JOURNAL ARTICLE
    ZDB-ID 2020307-X
    ISSN 1365-2435 ; 0269-8463
    ISSN (online) 1365-2435
    ISSN 0269-8463
    DOI 10.1111/1365-2435.13215
    Database NAL-Catalogue (AGRICOLA)

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  6. Article: Impacts of introduced Rangifer on ecosystem processes of maritime tundra on subarctic islands

    Ricca, Mark A / A. Keith Miles / D. P. C. Peters / Dirk H. Van Vuren / Valerie T. Eviner

    Ecosphere. 2016 Mar., v. 7, no. 3

    2016  

    Abstract: Introductions of mammalian herbivores to remote islands without predators provide a natural experiment to ask how temporal and spatial variation in herbivory intensity alter feedbacks between plant and soil processes. We investigated ecosystem effects ... ...

    Abstract Introductions of mammalian herbivores to remote islands without predators provide a natural experiment to ask how temporal and spatial variation in herbivory intensity alter feedbacks between plant and soil processes. We investigated ecosystem effects resulting from introductions of Rangifer tarandus (hereafter “Rangifer”) to native mammalian predator‐ and herbivore‐free islands in the Aleutian archipelago of Alaska. We hypothesized that the maritime tundra of these islands would experience either: (1) accelerated ecosystem processes mediated by positive feedbacks between increased graminoid production and rapid nitrogen cycling; or (2) decelerated processes mediated by herbivory that stimulated shrub domination and lowered soil fertility. We measured summer plant and soil properties across three islands representing a chronosequence of elapsed time post‐Rangifer introduction (Atka: ~100 yr; Adak: ~50; Kagalaska: ~0), with distinct stages of irruptive population dynamics of Rangifer nested within each island (Atka: irruption, K‐overshoot, decline, K‐re‐equilibration; Adak: irruption, K‐overshoot; Kagalaska: initial introduction). We also measured Rangifer spatial use within islands (indexed by pellet group counts) to determine how ecosystem processes responded to spatial variation in herbivory. Vegetation community response to herbivory varied with temporal and spatial scale. When comparing temporal effects using the island chronosequence, increased time since herbivore introduction led to more graminoids and fewer dwarf‐shrubs, lichens, and mosses. Slow‐growing Cladonia lichens that are highly preferred winter forage were decimated on both long‐term Rangifer‐occupied islands. In addition, linear relations between more concentrated Rangifer spatial use and reductions in graminoid and forb biomass within islands added spatial heterogeneity to long‐term patterns identified by the chronosequence. These results support, in part, the hypothesis that Rangifer population persistence on islands is facilitated by successful exploitation of graminoid biomass as winter forage after palatable lichens are decimated. However, the shift from shrubs to graminoids was expected to enhance rates of nitrogen cycling, yet rates of net N‐mineralization, NH4+ pools, and soil δ¹⁵N declined markedly along the chronosequence and were weakly associated with spatial use within islands. Overall plant and soil patterns were disrupted but responded differently to intermediate (50 yr) and long‐term (100 yr) herbivory, and were correlated with distinct stages of irruptive population dynamics.
    Keywords ammonium ; biomass ; chronosequences ; Cladonia ; ecosystems ; forage ; forbs ; graminoids ; herbivores ; islands ; lichens ; mammals ; mineralization ; mosses and liverworts ; nitrogen ; nitrogen cycle ; plant communities ; population dynamics ; predators ; Rangifer tarandus ; shrubs ; soil fertility ; soil properties ; spatial variation ; stable isotopes ; summer ; tundra ; winter ; Alaska ; Aleutian Islands
    Language English
    Dates of publication 2016-03
    Size p. .
    Publishing place Ecological Society of America
    Document type Article
    ZDB-ID 2572257-8
    ISSN 2150-8925
    ISSN 2150-8925
    DOI 10.1002/ecs2.1219
    Database NAL-Catalogue (AGRICOLA)

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