Abstract
Abstract Question How multiple abiotic stress factors combined with herbivory affect interactions within plant communities is poorly understood. We ask how large herbivore grazing affects the direction of plant–plant interactions along an environmental gradient in a salt marsh. Location Grazed (cattle) and ungrazed salt marshes of the Dutch Wadden Sea island Schiermonnikoog. Here, patches of tall plant communities, dominated by the tough, unpalatable species Juncus maritimus Lam., are found alternating with low‐statured, intensively grazed plant communities. Methods Along the inundation gradient, we measured plant species composition and plant species traits (specific leaf area, specific root length, maximum height and abundance) inside and outside J. maritimus patches in grazed and ungrazed areas. In addition, we measured soil structure parameters (bulk density, soil porosity, clay depth), multiple limiting conditions for plant growth (soil salinity, soil redox, plant canopy light interception), plant biomass, presence of herbivores and abundance of soil macro‐detritivores. Results Under grazing, the palatable grasses Elytrigia atherica (Link) Kerguélen and Festuca rubra L. were positively associated with J. maritimus , while shade‐intolerant Puccinellia maritima (Huds.) Parl. and Juncus gerardii Loisel. were negatively associated with this species. Furthermore, macro‐detritivore presence was higher inside J. maritimus patches. In ungrazed areas E. atherica and F. rubra were negatively associated with J. maritimus , while P. maritima and J. gerardii were rare. In both grazed and ungrazed conditions the directions of species associations were independent of the inundation gradient. Analysis of species traits and abiotic conditions suggested that associational resistance (a facilitation type) was important in grazed areas. In ungrazed areas, light competition was the likely dominant process. Conclusions The direction of species associations within these salt marsh communities was strongly affected by grazing, not by the underlying stress gradient. Measurement of species traits indicated that plant–plant interactions shifted from competitive to facilitative under grazing. Besides grazing, cross‐trophic facilitation of soil disturbing macro‐detritivores may play an important – thus far ignored – role in structuring plant communities.
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Claims 12
Claim · model-written summary
Under grazing, Elytrigia atherica was positively associated with J. maritimus.
- Taxon
- Elytrigia atherica
Elymus athericuse0 - Interactor
- J. maritimus
Juncus maritimuse0other - Outcome
- associated with J. maritimuse0
- Direction
- positivelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under grazing, the palatable grasses Elytrigia atherica (Link) Kerguélen and Festuca rubra L. were positively associated with J. maritimus”
Claim · model-written summary
Under grazing, Festuca rubra was positively associated with J. maritimus.
- Taxon
- Festuca rubra
Festuca rubrae0 - Interactor
- J. maritimusJuncus maritimuse0other
- Outcome
- associated with J. maritimuse0
- Direction
- positivelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Under grazing, the palatable grasses Elytrigia atherica (Link) Kerguélen and Festuca rubra L. were positively associated with J. maritimus”
Claim · model-written summary
Under grazing, Puccinellia maritima was negatively associated with J. maritimus.
- Taxon
- Puccinellia maritima
Puccinellia maritimae0 - Interactor
- J. maritimusJuncus maritimuse1other
- Outcome
- associated with this speciese0
- Direction
- negativelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“shade‐intolerant Puccinellia maritima (Huds.) Parl. and Juncus gerardii Loisel. were negatively associated with this species”
e1“Under grazing, the palatable grasses Elytrigia atherica (Link) Kerguélen and Festuca rubra L. were positively associated with J. maritimus”
Claim · model-written summary
Under grazing, Juncus gerardii was negatively associated with J. maritimus.
- Taxon
- Juncus gerardii
Juncus gerardiie0 - Interactor
- J. maritimusJuncus maritimuse1other
- Outcome
- associated with this speciese0
- Direction
- negativelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“shade‐intolerant Puccinellia maritima (Huds.) Parl. and Juncus gerardii Loisel. were negatively associated with this species”
e1“Under grazing, the palatable grasses Elytrigia atherica (Link) Kerguélen and Festuca rubra L. were positively associated with J. maritimus”
Claim · model-written summary
Macro-detritivores were more common inside J. maritimus patches.
- Taxon
- J. maritimusJuncus maritimuse0
- Interactor
- macro‐detritivoree0other
- Outcome
- macro‐detritivore presencee0
- Direction
- highere0
- Setting
- inside J. maritimus patchese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“macro‐detritivore presence was higher inside J. maritimus patches”
Claim · model-written summary
Without grazing, E. atherica and F. rubra were negatively associated with J. maritimus.
- Taxon
- E. athericaElymus athericuse0
- Interactor
- J. maritimusJuncus maritimuse0other
- Outcome
- associated with J. maritimuse0
- Direction
- negativelye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In ungrazed areas E. atherica and F. rubra were negatively associated with J. maritimus”
Claim · model-written summary
Without grazing, P. maritima and J. gerardii were rare.
- Taxon
- P. maritimaPuccinellia maritimae0
- Outcome
- raree0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“while P. maritima and J. gerardii were rare”
Claim · model-written summary
Species association directions were independent of inundation gradient under either grazing condition.
Verbatim
e0“In both grazed and ungrazed conditions the directions of species associations were independent of the inundation gradient”
t0“plant communities”
Claim · model-written summary
Trait and abiotic analyses suggested associational resistance in grazed areas.
Verbatim
e0“Analysis of species traits and abiotic conditions suggested that associational resistance (a facilitation type) was important in grazed areas”
t0“plant communities”
Claim · model-written summary
Light competition was inferred as the dominant process without grazing.
Verbatim
e0“In ungrazed areas, light competition was the likely dominant process”
t0“plant communities”
Claim · model-written summary
Grazing shifted plant interactions from competitive to facilitative.
Verbatim
e0“plant–plant interactions shifted from competitive to facilitative under grazing”
t0“plant communities”
Claim · model-written summary
The authors suggest soil-disturbing macro-detritivores may facilitate plant communities.
Verbatim
e0“cross‐trophic facilitation of soil disturbing macro‐detritivores may play an important – thus far ignored – role in structuring plant communities”