Climate change shuffles species’ ranges and creates novel interactions that may either buffer communities against climate change or exacerbate its effect. Coastal plant communities such as salt marshes are likely to be affected by climate change via changing precipitation patterns, warming temperatures, and sea-level rise (SLR). Rising sea levels affect the distribution of stress from both salinity and inundation, and shifting stresses are likely to affect plant interactions. For instance, facilitation can become more prevalent in salt marshes under stressful conditions while competition is stronger in benign environments. SLR may have one of several possible effects on plant communities, depending on the predominant stresses in a given community. To determine how Mediterranean-climate salt marsh communities are affected by SLR, we transplanted marsh turfs to lower elevations to simulate SLR. We then manipulated cover of the dominant species, Salicornia pacifica, to determine how the strength of its interactions with the rest of the plant community varies with SLR.
Results/Conclusions
We found that both S. pacifica and the subordinate species were affected by inundation. Subordinate species cover and diversity were both reduced at low elevations in the presence of S. pacifica compared to when it was removed, suggesting that the competitive effect of S. pacifica on subordinate species is strongest at low elevations. This result may be specific to marshes in Mediterranean climates, as we found that salinity decreased at low elevations in contrast to expectations in climates with greater rainfall. In Mediterranean-climate marshes, rising sea levels lead to stronger competition with the dominant species which will reduce cover and diversity of subordinate species. This suggests that plant-plant interactions will exacerbate the effects of SLR on marsh communities rather than ameliorating it.