Top-down vs. bottom-up control on vegetation composition in a tidal marsh depends on scale

Kelly Elschot, Anke Vermeulen, Wouter Vandenbruwaene, Jan P. Bakker, Tjeerd J. Bouma, Julia Stahl, Henk Castelijns, Stijn Temmerman

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

The relative impact of top-down control by herbivores and bottom-up control by environmental conditions on vegetation is a subject of debate in ecology. In this study, we hypothesize that top-down control by goose foraging and bottom-up control by sediment accretion on vegetation composition within an ecosystem can co-occur but operate at different spatial and temporal scales. We used a highly dynamic marsh system with a large population of the Greylag goose (Anser anser) to investigate the potential importance of spatial and temporal scales on these processes. At the local scale, Greylag geese grub for below-ground storage organs of the vegetation, thereby creating bare patches of a few square metres within the marsh vegetation. In our study, such activities by Greylag geese allowed them to exert topdown control by setting back vegetation succession. However, we found that the patches reverted back to the initial vegetation type within 12 years. At large spatial (i.e. several square kilometres) and temporal scales (i.e. decades), high rates of sediment accretion surpassing the rate of local sea-level rise were found to drive long-term vegetation succession and increased cover of several climax vegetation types. In summary, we conclude that the vegetation composition within this tidal marsh was primarily controlled by the bottom-up factor of sediment accretion, which operates at large spatial as well as temporal scales. Topdown control exerted by herbivores was found to be a secondary process and operated at much smaller spatial and temporal scales.

Original languageEnglish
Article numbere0169960
JournalPLoS One
Volume12
Issue number2
DOIs
Publication statusPublished - 1 Feb 2017

Funding

This work was funded by the Netherlands Organization for Scientific Research (NWOZKO, project 83908320). It forms part of the research programme BE SAFE, which is financed by the Netherlands Organisation for Scientific Research (NWO; grant 850.13.011), Deltares, Boskalis, Van Oord, Rijkswaterstaat, World Wildlife Fund and HZ University of Applied Science, of which T.J. Bouma is a principal investigator. This work is part of the UA-BOF DOCPRO awarded to S. Temmerman. There was no additional external funding received for this study. The funders had no role in study design, data collection and analyses, decision to publish or preparation of the manuscript.

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