Plant community development as affected by initial planting richness in created mesocosm wetlands

The gain or loss of plant species may alter the development of structural and functional attributes critical to developing or restoring ecosystem services in created mitigation wetlands. A three-year study was conducted in created mesocosm wetlands to determine the role of initial planting richness (IPR) in vegetation community development using five species of plants common to natural and created wetlands in the Virginia Piedmont. The mesocosms were naturally colonized by volunteer species after planting the same as in real-world mitigation wetlands created in the region. At the end of each growing season, all species present were identified, and species richness (S) and cover percentages (i.e., percent total, planted and volunteer species) were measured. Indices for diversity (Shannon-Weiner H′) and prevalence (PI) were calculated. After establishment of planted rhizomes, hydrology was maintained solely by precipitation. However, unintended leaking in six mesocosms in the beginning of the study created two distinctively different hydrologic conditions (i.e., wet vs. dry conditions) that were factored into the final data analysis. Both richness (S) and biodiversity (H′) varied significantly with initial planting richness (IPR). Differences in these two attributes were mainly due to differences between monotypic mesocosms (IPR = 1) and those with the greatest number of species initially planted (IPR = 5). Hydrologic conditions impacted some of the plant community characteristics, including total percent cover being higher in one year and PI being lower both in “wet” conditions. The mesocosms were becoming typical of wetlands with more hydrophytes present over the course of the study. The outcome of the study showed that the mesocosm wetlands were following a similar pattern found in vegetation community development trajectory of newly created mitigation wetlands. The study showed the positive effect of initial planting richness on species richness and diversity in the early development of plant community. Our findings also reinforce the importance of maintaining adequate hydrologic conditions for the early development of vegetation community in created mitigation wetlands.