1. Spatial heterogeneity of species (beta diversity) is an important attribute of ecological communities, but is less frequently considered when assessing restoration success than other aspects of diversity (gamma and alpha). Differences in beta diversity between restored and natural sites may arise due to differences in environmental heterogeneity.

2. We use a nested sampling design to survey plant communities and environmental conditions (elevation, redox potential and metrics of topography) on four pairs of restored and natural saltmarshes. We assess whether there are differences in both alpha and beta diversity between natural and restored sites, and analyse their environmental drivers.

3. Topography was an important driver of plant alpha diversity and beta diversity. The effects of topography were partly indirect, mediated though changes in redox potential, but topography also influenced plant communities independently of both elevation and redox.

4. Restored saltmarshes were less heterogeneous in topography than natural marshes. This reduced topography was reflected in lower beta diversity; plant communities 1 m apart in natural marshes were as dissimilar as those found 20 m apart in restored marshes.

5. Large-scale topographic manipulation carried out at one site a decade after initial restoration successfully increased topographic heterogeneity and increased beta diversity when surveyed three years after manipulation. These changes were still evident when resurveyed after a further two years.

6. Synthesis and applications. Increasing environmental heterogeneity can improve restoration outcomes by increasing beta diversity on restored sites. The effect of environmental heterogeneity is likely to be particularly strong within intertidal habitats where small changes in topography can determine whether a species can occur at a given location. Topographic manipulation is a feasible post-restoration technique that can be applied to ensure restored saltmarshes better meet policy targets of biological, physical and functional equivalence with natural marshes.

17-Nov-2021

Vegetation percentage cover and environmental data collected in nested sampling grids in restored and natural saltmarsh in Freiston Shore, Orplands, Tollesbury and Deveraux Farm. Elevation data have been processed to calculate relative tidal height and topography metrics.

This data package contains:

• Data - Data collected in nested sampling grids.
• Four R scripts: Alpha diversity analysis.R (analysis of differences in and environmental drivers of alpha diversity), Dissimilarity loess fits.R (bootstrapped loess model fits and Mantel tests of relationships between distance matricies), Dissimilarity beta diversity analysis.R (summarises and produces graphs from bootstrapped loess figures) and Partitioned beta diversity analysis.R (analyses of beta diversity using additive partitioning).
• Files DVN_Ele etc - Bootstrapped loess model fits (i.e. output of Dissimilarity loess fits script). R code thinks these are in a folder called Boots.

Figures in the paper are produced by the following scripts:

• Fig. 1 - not produced. Needs download of Environment Agency Lidar data. Quadrat locations (panel c) are provided in Data.csv.
• Fig. 2 - produced by Partitioned beta diversity analysis.R
• Fig. 3 - produced by Dissimilarity beta diversity analysis.R
• Fig. 4 - produced by Dissimilarity beta diversity analysis.R