Restored saltmarshes have low beta diversity due to limited topographic variation, but this can be countered by management

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