Ecosystems and communities change over scales of time and space. Deltaic wetlands are especially dynamic particularly because of the high variability in forcing power by the river itself. This study’s objectives were to report wetland plant community change in a deltaic system to understand processes important to restoration. We describe here the “The Delta Cycle” of plant community change within the Mississippi River’s Balize Delta, U.S.A. A complete delta cycle occurs over wide time scales of years to centuries to even millennia, with sediment delivery being the key coupled with subsidence rates, both dictating mud surface elevations. From 1984 through 2012, plant community change was monitored on 4 “inner deltaic splay” lobes of the Balize Delta which effectively scale up to the entire river Delta Cycle. A total of 55 plant species were identified within the collected 964 plots sampled over the 28 yr study. Annual Total Peak Standing Biomass tracked remarkably at the sites regardless of vegetation type. NMS ordinations were generated to elucidate trajectories of community change on the study lobes over time.
Results/Conclusions
Four ‘foundation’ species dominated the wetland lobes (Salix nigra, Schoenoplectus deltarum, Sagittaria latifolia, Sagittaria platyphilla; ordered from high to low substrate elevation along a lobe). Each of the four species has such precise elevation fidelity they were used as surrogates for elevation change. After a 3 yr primary succession period, S. deltarum dominated most of the next 7 yrs. Species richness dropped after these first 10 yrs as elevations declined as marked by the dominance in turn of the remaining two foundation species. The 4th site, of eventual dominance of only S. platyphilla, established 10 yrs into the study, gradually became open water and served as a space for time substitution for the last stages of the delta cycle. Ordinations confirm a clear 3 phase pattern exists within the delta cycle, (1) a short-term primary colonization community, (2) communities dominated by the two mid-elevation foundation species, but with local areas of atypical local disturbance or elevations supporting an assortment of herbs, and (3) a senescent period of gradual elevation decline back to open water. Few studies have tracked the vegetation on Louisiana’s deltas over such long periods. They result in at better understanding of restoration projects and help with their modeling.