Turnover and change in plant species composition in a shielded salt marsh following variation in precipitation and temperature

Questions: Temperature and precipitation variation between years may affect plant species composition directly or indirectly. We wish to investigate whether salt marsh edaphic conditions and plant species composition change as a result of climatic variation. Further, whether areas with the largest edaphic variations also experience the largest change in species composition and turnover. Finally, do temperature and precipitation variations change the way the plant community is able to respond to natural edaphic gradients?. Location: Bygholmengen, a shielded salt marsh in Vejlerne, Denmark, Northern Europe. Methods: Botanical surveys were conducted and soil samples collected from 40 plots during a wet and dry summer to register changes in vegetation cover, species richness composition and edaphic factors (moisture, nutrients, salinity). These data were used to calculate dissimilarities in species composition, temporal turnover and environmental dissimilarity between years. A linear mixed-effects model was used to link species richness with the measured edaphic factors. Results: We found that the precipitation and temperature variations altered the edaphic conditions; furthermore, the vegetation cover and species richness decreased when conditions were dry whereas the number of salt marsh species increased. Further, species composition changed significantly between years, and sampling plots that experienced the least edaphic change also retained more species between years. Species richness responded more to changes in nutrient availability during wet than dry conditions. Conclusion: Our results pointed toward the climatic variations, and subsequent change in edaphic conditions, being responsible for the significant change in species composition as areas with the least change in edaphic factors retained most species between years. Dry conditions favored salt marsh-adapted species and the extent to which increased nutrient levels led to a higher species richness decreased in dry compared to wet conditions.