Geographically Comprehensive Assessment of Salt-Meadow Vegetation-Elevation Relations Using LiDAR

Salt meadows are thought to be vulnerable to habitat loss under future sea-level rise (SLR) due to inundation and compression of coastal environments (coastal squeezing). The extent of this threat is poorly understood due to the lack of geographically comprehensive impact assessments. Here, we linked vegetation data for Danish salt meadows to novel very fine-resolution digital elevation models. We developed statistical models relating plant species richness and average salt tolerance to elevation at different spatial scales. The best models were used to quantify potential impacts of SLR on Danish salt-meadow vegetation under five potential 21(st)-century scenarios. Overall, species richness increased with elevation (average r (2) = 0.21), while average salt tolerance decreased (average r (2) = 0.45). Fine resolution (a parts per thousand currency sign10-m) topography was required to fully represent vegetation-elevation relationships. At > 50-m resolutions only feeble links were found. Under the worst scenarios 67-74% of the Danish salt-meadow area was projected to be lost. Notably, the relatively species-rich upper meadows were predicted to shrink drastically. If realized, these impacts may have severe consequences for salt-meadow biodiversity. We note that sedimentation, not accounted for here, may allow some salt meadows to partly keep up with SLR but the extent to which this will occur and where is uncertain.