Refinement of the fundamental niche of black mangrove (Avicennia germinans) seedlings in Louisiana: Applications for restoration

Black mangrove (Avicennia germinans) occurs at the northern boundary of its North American range in the coastal salt marshes and barrier islands of Louisiana. This species provides important habitat and sustainability to Louisiana's coastal salt marshes via its woody structure and extensive root system. Refinement of the physiological tolerances of A. germinans seedlings to salinity, sand burial and hydrologic regime provides valuable insight into the fundamental niche of A. germinans and thereby the potential for increased restoration success in coastal and back-barrier salt marshes. We subjected two age classes of A. germinans seedlings used in restoration (young seedlings of 6 or 12 months of age, and older seedlings of either 18 or 24 months of age) to abiotic stressors frequently encountered at coastal restoration sites: (1) elevated salinity levels, from 0 to 96 ppt, (2) sediment burial, from 0 to +20 cm, and (3) varying water levels, ranging from 0 cm to -60 cm. A. germinans seedlings displayed a non-linear response to each environmental factor, with greatest biomass occurring between low and moderate levels of stress or disturbance (i.e., between 24 and 48 ppt salinity, 0 to +10 cm burial, and -15 to -30 cm water level). The two age classes displayed similar physiological tolerances; however, older seedlings may confer an advantage due to greater total biomass and reserves, most notably in response to burial. We suggest that this refinement of the fundamental niche be utilized as a guideline for improved restoration success in micro-tidal environments within black mangrove's range.