The plant assemblages that develop on saltmarshes restored by managed realignment are not equivalent to those on natural marshes, even after over half a century of development. It is important to understand why this difference occurs in order to improve restoration outcomes. One possible explanation is that we fail to successfully replicate the environmental conditions found in natural marshes. Alternatively, plant communities on restored saltmarshes may differ from on natural marshes due to differences in biotic interactions. We investigate the potential roles of these in restoration success using a combination of field sampling, experiments and niche modelling.
Results/Conclusions
By applying niche models of the distribution of ten plant species in restored and natural saltmarshes, we found that differences in elevation and redox potential explained some but not all of the discrepancies in plant occurrence. Another environmental difference, revealed by both remote sensing and field measurements, is that restored saltmarshes lack the local topographic heterogeneity found in natural marshes. This appears important for plant communities as it is reflected in lower beta diversity in restored marshes. We also conducted a field experiment to test the effect of local topographic variation; as well as altering redox conditions it exerted an independent effect on plant survival. Plant community assembly on restored marshes may also differ from that on natural marshes due to differences in biotic interactions arising from the availability of bare sediment at all elevations. This may lead to succession following an inhibition model, where potential dominant species such as Atriplex portulacoides suppress the establishment of other species such as Limonium vulgare. In our field experiment, Limonium, Plantago and Triglochin (all rare on restored sites) failed to colonise plots even when environmental conditions were suitable, but did persist if planted, suggesting limitations to colonisation rather than abiotic unsuitability. We conclude with recommendations for restoration practise.