Abstract

Restored habitats, such as saltmarsh created through managed realignment, sometimes fail to meet targets for biological equivalence with natural reference sites. Understanding why this happens is important in order to improve restoration outcomes.Elevation in the tidal frame and sediment redox potential are major controls on the distribution of saltmarsh plants. We use niche models to characterize 10 species’ responses to these, and test whether differences in species occurrence between restored and natural saltmarshes in the UK result from failure to recreate adequate environmental conditions.Six species occurred less frequently in recently restored marshes than natural marshes. Failure of restored marshes to achieve the elevation and redox conditions of natural marshes partially explained the underrepresentation of five of these species, but did not explain patterns of occurrence on older (>50 years) restored marshes.For all species, an effect of marsh age remained after controlling for differences in environmental conditions. This could be due to differences in successional mechanism between restored and natural marshes. In recently restored marshes, high‐marsh species occurred lower in the tidal frame and low‐marsh species occurred higher in the tidal frame than in natural marshes. This supports the hypothesis that competition is initially weaker in restored marshes, because of the availability of bare sediment across the whole tidal frame. Species that establish outside their normal realized niche, such as Atriplex portulacoides, may inhibit subsequent colonization of other species that occurred less frequently than expected on older restored marshes. Synthesis and applications. Niche models can be used to test whether abiotic differences between restored sites and their natural counterparts are responsible for discrepancies in species occurrence. In saltmarshes, simply replicating environmental conditions will not result in equivalent species occurrence.

Highlights

  • The creation of new habitat through restoration is an important strategy to compensate for loss or degradation of natural and semi-­natural ecosystems (Young, 2000)

  • Niche models can be used to test whether abiotic differences between restored sites and their natural counterparts are responsible for discrepancies in species occurrence

  • Patch-­scale experimental studies have demonstrated the role of competition in setting upper and lower elevation limits of saltmarsh plants (Hacker & Bertness, 1999; Pennings, Grant, & Bertness, 2005), so we predict that reduced competition would allow pioneer species to grow higher in the tidal frame, and upper-m­ arsh species lower in the tidal frame

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Summary

| INTRODUCTION

The creation of new habitat through restoration is an important strategy to compensate for loss or degradation of natural and semi-­natural ecosystems (Young, 2000). Some restored sites are high in the tidal frame or have oxic sediments (Brooks, Mossman, Chitty, & Grant, 2015; Mossman et al, 2012a), so differences in environmental conditions may not fully account for the discrepancies If they do, future restoration schemes should seek to manipulate topography prior to flooding so that elevation and redox conditions more closely match those in natural marshes. Patch-­scale experimental studies have demonstrated the role of competition in setting upper and lower elevation limits of saltmarsh plants (Hacker & Bertness, 1999; Pennings, Grant, & Bertness, 2005), so we predict that reduced competition would allow pioneer species to grow higher in the tidal frame, and upper-m­ arsh species lower in the tidal frame Such shifts in realized niche on restored marshes could have longer term consequences for vegetation development. We examine plant communities from 22 saltmarshes including natural (reference), MRs (50 years post breach), and use niche modelling to examine (1) whether differences in elevation and redox potential are sufficient to explain differences in species distribution between restored and natural marshes and (2) whether any shifts in niche position between natural marshes and MRs are consistent with the expected signatures of altered successional processes

| MATERIALS AND METHODS
| DISCUSSION
Findings
G Observed Expected
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