Importance of Microtopography in Determining Plant Community Distribution in Baltic Coastal Wetlands

This study investigated microtopography and edaphic factors to ascertain their use as determinants for identifying the location and extent of plant community types in internationally important Baltic coastal wetlands in Estonia. Plant community types were identified, and abundance and frequency of plant species were recorded within 105 1-m2 quadrats at two sites. Within each quadrat, a real-time kinematic differential GPS (dGPS) was used to record elevation; soil moisture, organic matter, particle size, pH, salinity, nitrogen (N), phosphorus (P), and potassium (K) were also measured. A significant difference was recorded for elevation in six of the seven different plant communities: Reed Swamp, Clubrush Swamp, Lower Shore grassland, Upper Shore grassland, Tall Grassland, and Scrub and Developing Woodland. Median elevation differences between plant communities were between 0.04 m and 0.19 m. Soil moisture and salinity were related to elevation, and all three significantly influenced plant community location. A Canonical Correspondence Analysis confirmed that elevation and soil moisture influenced the distribution of five of the seven community types, while the remaining two communities were strongly related to either pH and salinity or organic matter, N, and K, respectively. Microtopography was found to strongly affect the distribution and extent of Baltic coastal wetland plant communities because of the relationship between sea-level and site hydrology. Rising sea levels may profoundly affect the distribution of plant communities in these wetlands, and the quantification of the elevation differences between the plant communities in this study provides an important baseline for predicting their future location and extent.