1
|
Meyer GA, Leroux SJ. A theory for context-dependent effects of mammalian trampling on ecosystem nitrogen cycling. J Anim Ecol 2024; 93:583-598. [PMID: 38566364 DOI: 10.1111/1365-2656.14066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2023] [Accepted: 02/06/2024] [Indexed: 04/04/2024]
Abstract
Large mammalian herbivores substantially impact ecosystem functioning. As their populations are dramatically altered globally, disentangling their consumptive and non-consumptive effects is critical to advance mechanistic understanding and improve prediction of effects over ecosystem and Earth-system spatial extents. Mathematical models have played an important role in clarifying potential mechanisms of herbivore zoogeochemistry, based mostly on their consumptive effects as primary consumers and recyclers of organic and inorganic matter via defecation and urination. Trampling is a ubiquitous effect among walking vertebrates, but the consequences and potential mechanisms of trampling in diverse environments remain poorly understood. We derive a novel mathematical model of large mammalian herbivore effects on ecosystem nitrogen cycling, focusing on how trampling and environmental context impact soil processes. We model herbivore trampling with a linear positive or negative additive effect on soil-mediated nitrogen cycling processes. Combining analytical and numerical analyses, we find trampling by large mammalian herbivores is likely to decrease nitrogen mineralisation rate across diverse environments, such as temperate grassland and boreal forest. These effects are mediated by multiple potential mechanisms, including trampling-induced changes to detritivore biomass and functioning (e.g. rate of organic matter consumption). We also uncover scenarios where trampling can increase nitrogen mineralisation rate, contingent on the environment-specific relative sensitivity of detritivore mineral-nitrogen release and detritivore mortality, to trampling. In contrast to some consumptive mechanisms, our results suggest the pace of soil nitrogen cycling prior to trampling has little influence over the direction of the trampling net effect on nitrogen mineralisation, but that net effects may be greater in slow-cycling systems (e.g. boreal forests) than in fast-cycling systems (e.g. grasslands). Our model clarifies the potential consequences of previously overlooked mechanisms of zoogeochemistry that are common to all terrestrial biomes. Our results provide empirically testable predictions to guide future progress in empirical and theoretical studies of herbivore effects in diverse environmental contexts. Resolving ecological contingencies around animal consumptive and non-consumptive effects will improve whole-ecosystem management efforts such as restoration and rewilding.
Collapse
Affiliation(s)
- G Adam Meyer
- Department of Biology, Memorial University of Newfoundland and Labrador, St. John's, Newfoundland, Canada
| | - Shawn J Leroux
- Department of Biology, Memorial University of Newfoundland and Labrador, St. John's, Newfoundland, Canada
| |
Collapse
|
2
|
Manninen OH, Myrsky E, Tolvanen A, Stark S. N-fertilization and disturbance exert long-lasting complex legacies on subarctic ecosystems. Oecologia 2024; 204:689-704. [PMID: 38478083 PMCID: PMC10980618 DOI: 10.1007/s00442-024-05524-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2023] [Accepted: 02/03/2024] [Indexed: 04/01/2024]
Abstract
Subarctic ecosystems are subjected to increasing nitrogen (N) enrichment and disturbances that induce particularly strong effects on plant communities when occurring in combination. There is little experimental evidence on the longevity of these effects. We applied N-fertilization (40 kg urea-N ha-1 year-1 for 4 years) and disturbance (removal of vegetation and organic soil layer on one occasion) in two plant communities in a subarctic forest-tundra ecotone in northern Finland. Within the first four years, N-fertilization and disturbance increased the share of deciduous dwarf shrubs and graminoids at the expense of evergreen dwarf shrubs. Individual treatments intensified the other's effect resulting in the strongest increase in graminoids under combined N-fertilization and disturbance. The re-analysis of the plant communities 15 years after cessation of N-fertilization showed an even higher share of graminoids. 18 years after disturbance, the total vascular plant abundance was still substantially lower and the share of graminoids higher. At the same point, the plant community composition was the same under disturbance as under combined N-fertilization and disturbance, indicating that multiple perturbations no longer reinforced the other's effect. Yet, complex interactions between N-fertilization and disturbance were still detected in the soil. We found higher organic N under disturbance and lower microbial N under combined N-fertilization and disturbance, which suggests a lower bioavailability of N sources for soil microorganisms. Our findings support that the effects of enhanced nutrients and disturbance on subarctic vegetation persist over decadal timescales. However, they also highlight the complexity of plant-soil interactions that drive subarctic ecosystem responses to multiple perturbations across varying timescales.
Collapse
Affiliation(s)
- Outi H Manninen
- Arctic Centre, University of Lapland, Pohjoisranta 4, 96100, Rovaniemi, Finland.
| | - Eero Myrsky
- Arctic Centre, University of Lapland, Pohjoisranta 4, 96100, Rovaniemi, Finland
| | - Anne Tolvanen
- Natural Resource Institute Finland, Paavo Havaksen Tie 3, 90570, Oulu, Finland
| | - Sari Stark
- Arctic Centre, University of Lapland, Pohjoisranta 4, 96100, Rovaniemi, Finland
| |
Collapse
|
3
|
Swain M, Leroux SJ, Buchkowski R. Strong above-ground impacts of a non-native ungulate do not cascade to impact below-ground functioning in a boreal ecosystem. J Anim Ecol 2023; 92:2016-2027. [PMID: 37565516 DOI: 10.1111/1365-2656.13993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2022] [Accepted: 07/28/2023] [Indexed: 08/12/2023]
Abstract
1. Experimental studies across biomes demonstrate that herbivores can have significant effects on ecosystem functioning. Herbivore effects, however, can be highly variable with studies demonstrating positive, neutral or negative relationships between herbivore presence and different components of ecosystems. Mixed effects are especially likely in the soil, where herbivore effects are largely indirect mediated through effects on plants. 2. We conducted a long-term experiment to disentangle the effects of non-native moose in boreal forests on plant communities, nutrient cycling, soil composition and soil organism communities. 3. To explore the effect of moose on soils, we conduct separate analyses on the soil organic and mineral horizons. Our data come from 11 paired exclosure-control plots in eastern and central Newfoundland, Canada that provide insight into 22-25 years of moose herbivory. We fit piecewise structural equations models (SEM) to data for the organic and mineral soil horizons to test different pathways linking moose to above-ground and below-ground functioning. 4. The SEMs revealed that moose exclusion had direct positive impacts on adult tree count and an indirect negative impact on shrub percent cover mediated by adult tree count. We detected no significant impact of moose on soil microbial C:N ratio or net nitrogen mineralization in the organic or mineral soil horizon. Soil temperature and moisture, however, was more than twice as variable in the presence (i.e. control) than absence (i.e. exclosure) of moose. Overall, we observed clear impacts of moose on above-ground forest components with limited indirect effects below-ground. Even after 22-25 years of exclusion, we did not find any evidence of moose impacts on soil microbial C:N ratio and net nitrogen mineralization. 5. Our long-term study and mechanistic path analysis demonstrates that soils can be resilient to ungulate herbivore effects despite evidence of strong effects above-ground. Long-term studies and analyses such as this one are relatively rare yet critical for reconciling some of the context-dependency observed across studies of ungulates effects on ecosystem functions. Such studies may be particularly valuable in ecosystems with short growing seasons such as the boreal forest.
Collapse
Affiliation(s)
- Makayla Swain
- Department of Biology, Memorial University of Newfoundland, St John's, Newfoundland, Canada
| | - Shawn J Leroux
- Department of Biology, Memorial University of Newfoundland, St John's, Newfoundland, Canada
| | | |
Collapse
|
4
|
Koltz AM, Gough L, McLaren JR. Herbivores in Arctic ecosystems: Effects of climate change and implications for carbon and nutrient cycling. Ann N Y Acad Sci 2022; 1516:28-47. [PMID: 35881516 PMCID: PMC9796801 DOI: 10.1111/nyas.14863] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Arctic terrestrial herbivores influence tundra carbon and nutrient dynamics through their consumption of resources, waste production, and habitat-modifying behaviors. The strength of these effects is likely to change spatially and temporally as climate change drives shifts in herbivore abundance, distribution, and activity timing. Here, we review how herbivores influence tundra carbon and nutrient dynamics through their consumptive and nonconsumptive effects. We also present evidence for herbivore responses to climate change and discuss how these responses may alter the spatial and temporal distribution of herbivore impacts. Several current knowledge gaps limit our understanding of the changing functional roles of herbivores; these include limited characterization of the spatial and temporal variability in herbivore impacts and of how herbivore activities influence the cycling of elements beyond carbon. We conclude by highlighting approaches that will promote better understanding of herbivore effects on tundra ecosystems, including their integration into existing biogeochemical models, new applications of remote sensing techniques, and the continued use of distributed experiments.
Collapse
Affiliation(s)
- Amanda M. Koltz
- Department of BiologyWashington University in St. LouisSt. LouisMissouriUSA,The Arctic InstituteCenter for Circumpolar Security StudiesWashingtonDCUSA,Department of Integrative BiologyUniversity of Texas at AustinAustinTexasUSA
| | - Laura Gough
- Department of Biological SciencesTowson UniversityTowsonMarylandUSA
| | - Jennie R. McLaren
- Department of Biological SciencesUniversity of Texas El PasoEl PasoTexasUSA
| |
Collapse
|
5
|
Fire, Herbivores, and Vegetation Type Shape Soil Biochemistry in Sodic Patches of a Semi-Arid Savanna Ecosystem. LAND 2022. [DOI: 10.3390/land11081148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
In the Kruger National Park (KNP), the lower slopes of catenas have open patches referred to as sodic patches. Fire and herbivores are dominant mediators of vegetation in sodic patches. The effect of fire and herbivores on soil properties of sodic patches remains largely understudied. Moreover, the co-existence of trees and grasses and how they influence savanna soils is an important but poorly understood phenomenon in ecology. Therefore, the present study aimed to determine the influence of 20 years of fire, herbivores, vegetation type, and their interaction on soil biochemistry of sodic patches on the Nkuhlu exclosures in the Kruger National Park, South Africa. We found a higher main effect of fire on available phosphorus, cation exchange capacity, and soil organic matter. The presence of herbivores caused an increase in soil exchangeable cations (K+, Ca2+, Na+, and Mg2+), organic matter, cation exchange capacity, and microbial activity. Tree canopies had a higher effect on total nitrogen, exchangeable Ca and Mg, soil organic matter, and cation exchange capacity than open grassland zones. Our results indicate that changes in vegetation structure due to fire and herbivores and their secondary impact on soil properties should be taken into consideration in managing savannas. Moreover, fire and herbivores play an important role in the maintenance of vegetation type (trees and grasses) in sodic patches.
Collapse
|
6
|
Aggerbeck MR, Nielsen TK, Mosbacher JB, Schmidt NM, Hansen LH. Muskoxen homogenise soil microbial communities and affect the abundance of methanogens and methanotrophs. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 827:153877. [PMID: 35218841 DOI: 10.1016/j.scitotenv.2022.153877] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 02/09/2022] [Accepted: 02/10/2022] [Indexed: 06/14/2023]
Abstract
Grazing herbivores may affect soil microbial communities indirectly by impacting soil structure and vegetation composition. In high arctic environments, this impact is poorly elucidated, while having potentially wide-reaching effects on the ecosystem. This study examines how a key arctic herbivore, the muskox Ovibos moschatus, affects the soil microbial community in a high arctic fen. Environmental DNA was extracted from soil samples taken from grazed control plots and from muskox exclosures established 5 years prior. We sequenced amplicons of the 16S rRNA gene to provide insight into the microbial communities. We found that in the grazed control plots, microbial communities exhibited high evenness and displayed highly similar overall diversity. In plots where muskoxen had been excluded, microbial diversity was significantly reduced, and had more uneven intra-sample populations and overall lower ecological richness and evenness. We observed that the composition of microbial communities in grazed soils were significantly affected by the presence of muskoxen, as seen by elevated relative abundances of Bacteroides and Firmicutes, two major phyla found in muskox faeces. Furthermore, an increase in relative abundance of bacteria involved in degradation of recalcitrant carbohydrates and cycling of nitrogen was observed in grazed soil. Ungrazed soils displayed increased abundances of bacteria potentially involved in anaerobic oxidation of methane, whereas some methanogens were more abundant in grazed soils. This corroborates a previous finding that methane emissions are higher in arctic fens under muskox grazing. Our results show that the presence of large herbivores stimulates soil microbial diversity and has a homogenizing influence on the inter-species dynamics in soil microbial communities. The findings of this study, thus, improve our understanding of the effect of herbivore grazing on arctic ecosystems and the derived methane cycling.
Collapse
Affiliation(s)
| | - Tue Kjærgaard Nielsen
- Department of Plant and Environmental Science, University of Copenhagen, 1871 Copenhagen, Denmark
| | - Jesper Bruun Mosbacher
- Department of Ecoscience, Aarhus University, 4000 Roskilde, Denmark; Arctic Research Centre, Aarhus University, 8000 Aarhus, Denmark
| | - Niels Martin Schmidt
- Department of Ecoscience, Aarhus University, 4000 Roskilde, Denmark; Arctic Research Centre, Aarhus University, 8000 Aarhus, Denmark
| | - Lars Hestbjerg Hansen
- Department of Plant and Environmental Science, University of Copenhagen, 1871 Copenhagen, Denmark.
| |
Collapse
|
7
|
Wedegärtner REM, Lembrechts JJ, Wal R, Barros A, Chauvin A, Janssens I, Graae BJ. Hiking trails shift plant species' realized climatic niches and locally increase species richness. DIVERS DISTRIB 2022. [DOI: 10.1111/ddi.13552] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Affiliation(s)
| | - Jonas J. Lembrechts
- Research Group of Plants and Ecosystems (PLECO) University of Antwerp Wilrijk Belgium
| | - René Wal
- Department of Ecology Swedish University of Agricultural Sciences Uppsala Sweden
| | - Agustina Barros
- Instituto Argentino de Nivología Glaciología y Ciencias Ambientales (IANIGLA), CONICET, CCT‐Mendoza Mendoza Argentina
| | - Aurélie Chauvin
- Department of Biology Norwegian University of Science and Technology Trondheim Norway
| | - Ilias Janssens
- Research Group of Plants and Ecosystems (PLECO) University of Antwerp Wilrijk Belgium
| | - Bente Jessen Graae
- Department of Biology Norwegian University of Science and Technology Trondheim Norway
| |
Collapse
|
8
|
Kristensen JA, Svenning JC, Georgiou K, Malhi Y. Can large herbivores enhance ecosystem carbon persistence? Trends Ecol Evol 2021; 37:117-128. [PMID: 34801276 DOI: 10.1016/j.tree.2021.09.006] [Citation(s) in RCA: 27] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2021] [Revised: 09/18/2021] [Accepted: 09/21/2021] [Indexed: 12/28/2022]
Abstract
There is growing interest in aligning the wildlife conservation and restoration agenda with climate change mitigation goals. However, the presence of large herbivores tends to reduce aboveground biomass in some open-canopy ecosystems, leading to the possibility that large herbivore restoration may negatively influence ecosystem carbon storage. Belowground carbon storage is often ignored in these systems, despite the wide recognition of soils as the largest actively-cycling terrestrial carbon pool. Here, we suggest a shift away from a main focus on vegetation carbon stocks, towards inclusion of whole ecosystem carbon persistence, in future assessments of large herbivore effects on long-term carbon storage. Failure to do so may lead to counterproductive biodiversity and climate impacts of land management actions.
Collapse
Affiliation(s)
- Jeppe A Kristensen
- Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, OX1 3QY, UK; Center for Biodiversity Dynamics in a Changing World (BIOCHANGE) and Section for Ecoinformatics and Biodiversity, Department of Biology, Aarhus University, DK-8000 Aarhus C, Denmark.
| | - Jens-Christian Svenning
- Center for Biodiversity Dynamics in a Changing World (BIOCHANGE) and Section for Ecoinformatics and Biodiversity, Department of Biology, Aarhus University, DK-8000 Aarhus C, Denmark
| | | | - Yadvinder Malhi
- Environmental Change Institute, School of Geography and the Environment, University of Oxford, Oxford, OX1 3QY, UK
| |
Collapse
|
9
|
Väisänen M, Tuomi M, Bailey H, Welker JM. Plant and soil nitrogen in oligotrophic boreal forest habitats with varying moss depths: does exclusion of large grazers matter? Oecologia 2021; 196:839-849. [PMID: 34080051 PMCID: PMC8292301 DOI: 10.1007/s00442-021-04957-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2020] [Accepted: 05/28/2021] [Indexed: 11/25/2022]
Abstract
The boreal forest consists of drier sunlit and moister-shaded habitats with varying moss abundance. Mosses control vascular plant-soil interactions, yet they all can also be altered by grazers. We determined how 2 decades of reindeer (Rangifer tarandus) exclusion affect feather moss (Pleurozium schreberi) depth, and the accompanying soil N dynamics (total and dissolvable inorganic N, δ15N), plant foliar N, and stable isotopes (δ15N, δ13C) in two contrasting habitats of an oligotrophic Scots pine forest. The study species were pine seedling (Pinus sylvestris L.), bilberry (Vaccinium myrtillus L.), lingonberry (V. vitis-idaea L.), and feather moss. Moss carpet was deeper in shaded than sunlit habitats and increased with grazer exclusion. Humus N content increased in the shade as did humus δ15N, which also increased due to exclusion in the sunlit habitats. Exclusion increased inorganic N concentration in the mineral soil. These soil responses were correlated with moss depth. Foliar chemistry varied due to habitat depending on species identity. Pine seedlings showed higher foliar N content and lower foliar δ15N in the shaded than in the sunlit habitats, while bilberry had both higher foliar N and δ15N in the shade. Thus, foliar δ15N values of co-existing species diverged in the shade indicating enhanced N partitioning. We conclude that despite strong grazing-induced shifts in mosses and subtler shifts in soil N, the N dynamics of vascular vegetation remain unchanged. These indicate that plant-soil interactions are resistant to shifts in grazing intensity, a pattern that appears to be common across boreal oligotrophic forests.
Collapse
Affiliation(s)
- Maria Väisänen
- Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland. .,Arctic Centre, University of Lapland, Rovaniemi, Finland.
| | - Maria Tuomi
- Department of Arctic and Marine Biology, UiT The Arctic University of Norway, Tromsø, Norway
| | - Hannah Bailey
- Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland
| | - Jeffrey M Welker
- Ecology and Genetics Research Unit, University of Oulu, Oulu, Finland.,Department of Biological Science, University of Alaska Anchorage, Anchorage, AK, USA.,UArctic, Rovaniemi, Finland
| |
Collapse
|