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Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes

S. J. Sharp, KATE DAVIDSON, C. Angelini Orcid Logo, H. S. Fischman, S. Pennings Orcid Logo, Mike Fowler Orcid Logo, John Griffin Orcid Logo

Journal of Ecology

Swansea University Authors: KATE DAVIDSON, Mike Fowler Orcid Logo, John Griffin Orcid Logo

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Abstract

Large grazers modify vegetated ecosystems and are increasingly viewed as keystone species in trophic rewilding schemes. Yet, as their ecosystem influences are context‐dependent, a crucial challenge is identifying where grazers sustain, versus undermine, important ecosystem properties and their resil...

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Published in: Journal of Ecology
ISSN: 0022-0477 1365-2745
Published: Wiley 2024
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URI: https://cronfa.swan.ac.uk/Record/cronfa67530
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Yet, as their ecosystem influences are context‐dependent, a crucial challenge is identifying where grazers sustain, versus undermine, important ecosystem properties and their resilience. Previous work in diverse European saltmarshes found that, despite changing plant and invertebrate community structure, grazers do not suppress below‐ground properties, including soil organic carbon (SOC). We hypothesised that, in contrast, eastern US saltmarshes would be sensitive to large grazers as extensive areas are dominated by a single grass, Spartina alterniflora. We predicted that grazers would reduce above‐ and below‐ground Spartina biomass, suppress invertebrate densities, shift soil texture and ultimately reduce SOC concentration. We tested our hypotheses using a replicated 51‐month large grazer (horse) exclusion experiment in Georgia, coupled with observations of 14 long‐term grazed sites, spanning ~1000 km of the eastern US coast. Grazer exclusion quickly led to increased Spartina height, cover and flowering, and increased snail density. Changes in vegetation structure were reflected in modified soil texture (reduced sand, increased clay) and elevated root biomass, yet we found no response of SOC. Large grazer exclusion also reduced drought‐associated vegetation die‐off. We also observed vegetation shifts in sites along the eastern US seaboard where grazing has occurred for hundreds of years. Unlike in the exclusion experiment, long‐term grazing was associated with reduced SOC. A structural equation model implicated grazing by revealing reduced stem height as a key driver of reduced soil organic carbon. Synthesis: These results illustrate the context dependency of large grazer impacts on ecosystem properties in coastal wetlands. In contrast to well‐studied European marshes, eastern US marshes are dominated and structured by a single foundational grass species resulting in vegetation and soil properties being more sensitive to grazing. Coastal systems characterised by a single foundation species might be inherently vulnerable to large grazers and lack resilience in the face of other disturbances, underlining that frameworks to explain and predict large grazer impacts must account for geographic variation in ecosystem structure.</abstract><type>Journal Article</type><journal>Journal of Ecology</journal><volume>0</volume><journalNumber/><paginationStart/><paginationEnd/><publisher>Wiley</publisher><placeOfPublication/><isbnPrint/><isbnElectronic/><issnPrint>0022-0477</issnPrint><issnElectronic>1365-2745</issnElectronic><keywords>Biodiversity, blue carbon, ecosystem resilience, horses, multifunctionality, Spartina alterniflora, Sporobolus alterniflorus, trophic cascade</keywords><publishedDay>2</publishedDay><publishedMonth>9</publishedMonth><publishedYear>2024</publishedYear><publishedDate>2024-09-02</publishedDate><doi>10.1111/1365-2745.14407</doi><url/><notes>Research Article</notes><college>COLLEGE NANME</college><CollegeCode>COLLEGE CODE</CollegeCode><institution>Swansea University</institution><apcterm>Another institution paid the OA fee</apcterm><funders>Division of Environmental Biology, Grant Number: OCE‐1832178</funders><projectreference/><lastEdited>2024-09-02T15:56:02.9452877</lastEdited><Created>2024-09-02T15:30:20.2122014</Created><path><level id="1">Faculty of Science and Engineering</level><level id="2">School of Biosciences, Geography and Physics - Biosciences</level></path><authors><author><firstname>S. 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spelling v2 67530 2024-09-02 Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes f382f4045afe626492fe3c0e4766c41b KATE DAVIDSON KATE DAVIDSON true false a3a29027498d4b43a3f082a0a5ba16b4 0000-0003-1544-0407 Mike Fowler Mike Fowler true false 9814fbffa76dd9c9a207166354cd0b2f 0000-0003-3295-6480 John Griffin John Griffin true false 2024-09-02 Large grazers modify vegetated ecosystems and are increasingly viewed as keystone species in trophic rewilding schemes. Yet, as their ecosystem influences are context‐dependent, a crucial challenge is identifying where grazers sustain, versus undermine, important ecosystem properties and their resilience. Previous work in diverse European saltmarshes found that, despite changing plant and invertebrate community structure, grazers do not suppress below‐ground properties, including soil organic carbon (SOC). We hypothesised that, in contrast, eastern US saltmarshes would be sensitive to large grazers as extensive areas are dominated by a single grass, Spartina alterniflora. We predicted that grazers would reduce above‐ and below‐ground Spartina biomass, suppress invertebrate densities, shift soil texture and ultimately reduce SOC concentration. We tested our hypotheses using a replicated 51‐month large grazer (horse) exclusion experiment in Georgia, coupled with observations of 14 long‐term grazed sites, spanning ~1000 km of the eastern US coast. Grazer exclusion quickly led to increased Spartina height, cover and flowering, and increased snail density. Changes in vegetation structure were reflected in modified soil texture (reduced sand, increased clay) and elevated root biomass, yet we found no response of SOC. Large grazer exclusion also reduced drought‐associated vegetation die‐off. We also observed vegetation shifts in sites along the eastern US seaboard where grazing has occurred for hundreds of years. Unlike in the exclusion experiment, long‐term grazing was associated with reduced SOC. A structural equation model implicated grazing by revealing reduced stem height as a key driver of reduced soil organic carbon. Synthesis: These results illustrate the context dependency of large grazer impacts on ecosystem properties in coastal wetlands. In contrast to well‐studied European marshes, eastern US marshes are dominated and structured by a single foundational grass species resulting in vegetation and soil properties being more sensitive to grazing. Coastal systems characterised by a single foundation species might be inherently vulnerable to large grazers and lack resilience in the face of other disturbances, underlining that frameworks to explain and predict large grazer impacts must account for geographic variation in ecosystem structure. Journal Article Journal of Ecology 0 Wiley 0022-0477 1365-2745 Biodiversity, blue carbon, ecosystem resilience, horses, multifunctionality, Spartina alterniflora, Sporobolus alterniflorus, trophic cascade 2 9 2024 2024-09-02 10.1111/1365-2745.14407 Research Article COLLEGE NANME COLLEGE CODE Swansea University Another institution paid the OA fee Division of Environmental Biology, Grant Number: OCE‐1832178 2024-09-02T15:56:02.9452877 2024-09-02T15:30:20.2122014 Faculty of Science and Engineering School of Biosciences, Geography and Physics - Biosciences S. J. Sharp 1 KATE DAVIDSON 2 C. Angelini 0000-0002-6669-5269 3 H. S. Fischman 4 S. Pennings 0000-0003-4757-7125 5 Mike Fowler 0000-0003-1544-0407 6 John Griffin 0000-0003-3295-6480 7 67530__31231__a74024b3660e4eacbce914c97e8196f7.pdf 1365-2745.14407.pdf 2024-09-02T15:30:20.1714790 Output 2627761 application/pdf Version of Record true © 2024 The Author(s). This is an open access article under the terms of the Creative Commons Attribution License CC-BY. true eng http://creativecommons.org/licenses/by/4.0/
title Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
spellingShingle Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
KATE DAVIDSON
Mike Fowler
John Griffin
title_short Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
title_full Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
title_fullStr Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
title_full_unstemmed Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
title_sort Large grazers suppress a foundational plant and reduce soil carbon concentration in eastern US saltmarshes
author_id_str_mv f382f4045afe626492fe3c0e4766c41b
a3a29027498d4b43a3f082a0a5ba16b4
9814fbffa76dd9c9a207166354cd0b2f
author_id_fullname_str_mv f382f4045afe626492fe3c0e4766c41b_***_KATE DAVIDSON
a3a29027498d4b43a3f082a0a5ba16b4_***_Mike Fowler
9814fbffa76dd9c9a207166354cd0b2f_***_John Griffin
author KATE DAVIDSON
Mike Fowler
John Griffin
author2 S. J. Sharp
KATE DAVIDSON
C. Angelini
H. S. Fischman
S. Pennings
Mike Fowler
John Griffin
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publishDate 2024
institution Swansea University
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1365-2745
doi_str_mv 10.1111/1365-2745.14407
publisher Wiley
college_str Faculty of Science and Engineering
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hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Biosciences, Geography and Physics - Biosciences{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Biosciences, Geography and Physics - Biosciences
document_store_str 1
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description Large grazers modify vegetated ecosystems and are increasingly viewed as keystone species in trophic rewilding schemes. Yet, as their ecosystem influences are context‐dependent, a crucial challenge is identifying where grazers sustain, versus undermine, important ecosystem properties and their resilience. Previous work in diverse European saltmarshes found that, despite changing plant and invertebrate community structure, grazers do not suppress below‐ground properties, including soil organic carbon (SOC). We hypothesised that, in contrast, eastern US saltmarshes would be sensitive to large grazers as extensive areas are dominated by a single grass, Spartina alterniflora. We predicted that grazers would reduce above‐ and below‐ground Spartina biomass, suppress invertebrate densities, shift soil texture and ultimately reduce SOC concentration. We tested our hypotheses using a replicated 51‐month large grazer (horse) exclusion experiment in Georgia, coupled with observations of 14 long‐term grazed sites, spanning ~1000 km of the eastern US coast. Grazer exclusion quickly led to increased Spartina height, cover and flowering, and increased snail density. Changes in vegetation structure were reflected in modified soil texture (reduced sand, increased clay) and elevated root biomass, yet we found no response of SOC. Large grazer exclusion also reduced drought‐associated vegetation die‐off. We also observed vegetation shifts in sites along the eastern US seaboard where grazing has occurred for hundreds of years. Unlike in the exclusion experiment, long‐term grazing was associated with reduced SOC. A structural equation model implicated grazing by revealing reduced stem height as a key driver of reduced soil organic carbon. Synthesis: These results illustrate the context dependency of large grazer impacts on ecosystem properties in coastal wetlands. In contrast to well‐studied European marshes, eastern US marshes are dominated and structured by a single foundational grass species resulting in vegetation and soil properties being more sensitive to grazing. Coastal systems characterised by a single foundation species might be inherently vulnerable to large grazers and lack resilience in the face of other disturbances, underlining that frameworks to explain and predict large grazer impacts must account for geographic variation in ecosystem structure.
published_date 2024-09-02T15:56:01Z
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