Environmental Constraints on the Restoration Success of Black Mangrove Habitats in the Northern Gulf of Mexico Jonathan M. Willis, Lauren K. Alleman, Christine N. Pickens, Laura C. Hundy, and Mark W. Hester Coastal Plant Ecology Laboratory University of Louisiana at Lafayette Funding provided by Louisiana Board of Regents, CPRA/Sea Grant Coastal Science Assistantship Program NOAA CREST, UL Lafayette & Coastal Plant Ecology Lab
Outline Background Review of manipulative experiments Salinity level Water table depth Chilling/freezing Review of field studies Natural propagule establishment Seedling transplant survival at restoration site Conclusion
Louisiana Salt Marshes Spartina alterniflora (smooth cordgrass) Dominant emergent macrophyte in Louisiana and throughout salt marshes of the Gulf and Atlantic Coasts of N. America
Louisiana Salt Marshes Southern salt marshes and barrier island salt marshes frequently have Avicennia germinans (black mangrove) growing in association with smooth cordgrass
Value of Restoring Black Mangrove Habitat Provides critical woody structure & habitat on barrier islands Source: Scott Walters
Value of Restoring Black Mangrove Habitat Provides critical woody structure & habitat on barrier islands Black mangrove/smooth cordgrass association may provide added ecosystem resilience to disturbance Source: Mike Osland Source: Scott Walters
Black Mangrove Restoration Template ABIOTIC FACTORS BIOTIC FACTORS Hydrology Elevation Tidal Inundation Soil Moisture Water Table Salinity Mangrove Propagule Establishment Nutrients Facilitation Light Level Disturbance Sand Burial Hurricanes Climatic Variance Mangrove Seedling Mangrove Adult Predation Herbivory Fungal Infection Competition Reproduction (per individual) Mangrove Dispersal Accretion Mangrove Population Development Reproduction (per area)
Black Mangrove Restoration Template ABIOTIC FACTORS BIOTIC FACTORS Hydrology Elevation Tidal Inundation Soil Moisture Water Table Salinity Mangrove Propagule Establishment Nutrients Facilitation Light Level Disturbance Sand Burial Hurricanes Climatic Variance Mangrove Seedling Mangrove Adult Predation Herbivory Fungal Infection Competition Reproduction (per individual) Mangrove Dispersal Accretion Mangrove Population Development Reproduction (per area)
Seedling Response to Salinity Level and Water- Table Depth Alleman, L. K., and M.W. Hester. 2011. Refinement of the fundamental niche of black mangrove (Avicennia germinans) seedlings in Louisiana: Applications for restoration. Wetlands Ecology and Management. 19: 47-60.
Salinity Level Experiment 2 seedling age classes 12-month old 24-month old 5 salinity levels 0 ppt 12 ppt 24 ppt 48 ppt 96 ppt 5 replicates 50 total experimental units
Biomass (g) 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 12 month old seedlings 0 24 48 72 96 Salinity Level (ppt) Aboveground Belowground
Biomass (g) 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0 24 month old seedlings 0 24 48 72 96 Salinity Level (ppt) Aboveground Belowground
Water Table Depth Experiment 2 seedling age classes 6-month old 18-month old 5 water table depths 0 cm -15 cm -30 cm -45 cm -60 cm 3 hydrologic regimes static fluctuating bi-weekly fluctuating bi-monthly 5 replicates 150 total experimental units Source: L. Alleman
6-month old seedlings Aboveground Biomass (g) 5 4 3 2 1 0 0-15 -30-45 -60 Water-Table Depth (cm) static biweekly bimonthly
Aboveground Biomass (g) 5 4 3 2 1 0 18-month old seedlings 0-15 -30-45 -60 Water-Table Depth (cm) static biweekly bimonthly
Leaf Characteristics 6-month old seedlings 18-month old seedlings Water Table Depth -30 cm Water Table Depth -60 cm
Chilling/Freezing Injury Experiment 3 Early Life History Stages Dispersal (in salt water) Stranded (on moist sand) Seedling (rooted in moist sand) 3 Exposure Temperatures 5.7 C 2.5 C -6.5 C 4 Durations 2 hours 6 hours 12 hours 24 hours 5 Replicates 180 Total Experimental Units Pickens, C. N., and M. W. Hester. 2011. Temperature tolerance of early life history stages of black mangrove, Avicennia germinans: Implications for range expansion. Estuaries and Coasts. 34: 824-830.
0.8 Significantly greater mortality with: Exposure at -6.5 C 24 hour duration of cold exposure Proportion Dead 0.6 0.4 0.2 0 0.8-6.5 2.5 5.7 Temperature ( C) Proportion Dead 0.6 0.4 0.2 0 2 6 12 24 Duration Exposure (hours)
Dispersal stage propagules tended to have greatest overall survivorship May confer advantage to surviving freeze events when still in dispersal stage (in saline water) 1 0.8 Survivorship 0.6 0.4 0.2 0 Stranded Stage Propagules Dispersal Stage Propagules Seedling Stage 0 7 14 21 28 35 42 49 56 Time (days)
Elevation Survey: Natural Population Alleman, L.K. and M.W. Hester. 2011. Reproductive ecology of Black Mangrove (Avicennia germinans) along the Louisiana coast: propagule production cycles, dispersal limitations, and establishment elevations. Estuaries and Coast. 34: 1068-1077.
Establishment Elevations: Newly Established Propagules vs. Mature Trees Tree Height (cm) 200 180 160 140 120 100 80 60 40 20 0 mature trees (>12-months old) n = 218 newly established propagules (<12-months old) n = 54-0.1 0 0.1 0.2 0.3 0.4 0.5 Elevation (m, NAVD88)
Establishment Elevations: Newly Established Propagules vs. Mature Trees Tree Height (cm) 200 180 160 140 120 100 80 60 40 20 0 mature trees (>12-months old) n = 218 newly established propagules (<12-months old) n = 54-0.1 0 0.1 0.2 0.3 0.4 0.5 Elevation (m, NAVD88)
Mean water level = 0.15 m NAVD88 Mean mangrove elevation (all sites, ages) = 0.23 m NAVD88 0.9 0.8 Low water establishment windows? 0.7 Elevation (m, NAVD88) 0.6 0.5 0.4 0.3 0.2 0.1 0-0.118- Oct- -0.2 08 01- Nov- 08 15- Nov- 08 29- Nov- 08 13- Dec- 08 27- Dec- 08 10- Jan- 09 24- Jan- 09 07- Feb- 09 Date 21- Feb- 09 07- Mar- 09 21- Mar- 09 04- Apr- 09 18- Apr- 09 02- May- 09 16- May- 09 30- May- 09
Elevation Survey: Restored Site
Sampling Strata at Restored Site Zone 1: Lowest Elevation Zone 6: Highest Elevation
Hydrograph of Restored Site
Elevation & Hydrology: Restored Site Zone 1-3: Lowest elevations and greatest percentage of time flooded Zone 5-6: Highest elevations and almost non-existent flooding
Vegetation Cover of Restored Site
Seedling salt tolerance Conclusions 12-month and 24-month old seedlings cannot tolerate 96 ppt Optimal growth between 24 48 ppt, respectively Hydrology Best seedling growth at water-table depth range of 0 to -0.3 m Propagule and adult elevation ranges of 0.16 0.27 m NAVD88 (34% - 15% flooded, respectively) Tolerance to chilling/freezing High mortality of all life stages following 24 hrs at -6.5 C Propagules have greater survivorship when in dispersal stage Marsh platform elevation and associated hydrology is critical Work with succession Once smooth cordgrass established, hydrology should be conducive for natural black mangrove establishment or assisted propagule dispersal
Questions?