Top-down and sideways: Herbivory and cross-ecosystem connectivity shape restoration success at the salt marsh-upland ecotone

Abstract

Wetland restoration provides remarkable opportunities to understand vegetation dynamics and to inform success of future projects through rigorous restoration experiments. Salt marsh restoration typically focuses on physical factors such as sediment dynamics and elevation. Despite many demonstrations of strong top-down effects on salt marshes, the potential for consumers to affect salt marsh restoration projects has rarely been quantified. Recently, major restoration projects at the Elkhorn Slough National Estuarine Research Reserve in central California, USA provided an opportunity to examine how herbivory influences restoration success. We quantified the strength of consumer effects by comparing caged to uncaged plantings, and compared effects among plant species and sites. We used camera traps to detect which herbivores were most common and how their abundance varied spatially. Beyond characterizing consumer effects, we also tested management strategies for reducing negative effects of herbivory at the restoration sites, including caging, mowing, and acoustic playbacks of predator sounds. We found extremely strong consumer effects at sites with extensive stands of exotic forbs upland of the high marsh; uncaged restoration plants suffered heavy herbivory and high mortality, while most caged plants survived. Brush rabbits (Sylvilagus bachmani) were by far the most frequent consumers of these high marsh plants. Our work thus provides the first evidence of mammal consumers affecting salt marsh restoration success. Mowing of tall exotic forb cover adjacent to the marsh at one restoration site greatly reduced consumption, and nearly all monitored plantings survived at a second restoration site where construction had temporarily eliminated upland cover. Playbacks of predator sounds did not significantly affect restoration plantings, but restoration efforts in marsh communities vulnerable to terrestrial herbivory may benefit from concurrent restoration of predator communities in the upland habitats surrounding the marsh. A landscape approach is thus critical for recognizing linkages between terrestrial and marine vegetation.

Rapid enhancement of multiple ecosystem services following the restoration of a coastal foundation species

“…Transplanting/seeding foundation species (marsh plants, juvenile mangroves, oysters, corals, etc.) from areas where they are thriving to areas where they are scarce is a common restoration approach (Davis and Short 1997, Jaap 2000, Gilman and Ellison 2007, Pritchard et al 2015, Wasson et al 2021) used to enhance foundation species coverage and the ecosystem services and functions they provide.…”

“…As human populations continue to grow in coastal areas, the impact of human activities on the foundation species that define coastal marine environments has intensified (Barbier et al 2011, Kirwan and Megonigal 2013. Such impacts include effects of agriculture (Wasson et al 2021) and urban development (Coverdale et al 2013), diversion of freshwater inputs (Kennish 2002), and overfishing (Altieri et al 2012) leading to trophic downgrading (Estes 2011, Kéfi 2012. Global effects of ocean acidification on coral reefs (Bellwood et al 2004), sea level rise on tidal marshes (Thorne et al 2018a, b) and rising sea surface temperature effects on seagrass (Zimmerman and Hill 2015) and kelp forests (Muth et al 2019, Rogers-Bennett andCatton 2019) are some prime examples of how humans are contributing to the loss of foundation species and the services they provide.…”

Long‐term study reveals top‐down effect of crabs on a California salt marsh

“…2019) and comparatively few on consumer effects (Boyer and Fong 2005, Armitage and Fong 2006, Wasson et al. 2021). The role of consumers in woody perennial marsh systems, like those found along the Pacific Northwest Coast of the United States, Europe, Australia, South Africa, and South Asia (Kadereit et al.…”

“…systems Tyrrell 2012, Moore 2019). On the west coast of the United States, there have been many studies on bottom-up processes in tidal marshes (Thorne et al 2014, 2018, Janousek et al 2017, Osland et al 2019 and comparatively few on consumer effects (Boyer and Fong 2005, Armitage and Fong 2006, Wasson et al 2021. The role of consumers in woody perennial marsh systems, like those found along the Pacific Northwest Coast of the United States, Europe, Australia, South Africa, and South Asia (Kadereit et al 2007), is likely to operate at considerably longer timescales than herbaceous grass-dominated systems, thus providing a novel perspective on consumer effects.…”

Rewilding and restoring nature in a changing world

“…Features of interest included in this Collection span from bacteria through large vertebrates (e.g., wild dogs, elephants) to ecosystems and their functions. These articles also showcase a range of methodological approaches from a series of small-scale field experiments (Wasson et al [7]), wildlife tracking and remote sensing (Mata et al [8]), and large-scale models to predict restoration outcomes (D'Acunto et al [9]).…”