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: Scott Walters Source: Mike Osland

ABIOTIC FACTORS BIOTIC FACTORS

Mangrove Propagule Establishment

Mangrove Seedling

Mangrove Population Development

Mangrove Adult

Black Mangrove Restoration Template

Predation • Herbivory • Fungal Infection

Facilitation

Competition

Accretion

Hydrology • Elevation • Tidal Inundation • Soil Moisture • Water Table • Salinity

Reproduction (per individual)

Reproduction (per area)

Nutrients

Light Level Mangrove

Dispersal Disturbance

• Sand Burial • Hurricanes • Climatic Variance

ABIOTIC FACTORS BIOTIC FACTORS

Mangrove Propagule Establishment

Mangrove Seedling

Mangrove Population Development

Mangrove Adult

Black Mangrove Restoration Template

Predation • Herbivory • Fungal Infection

Facilitation

Competition

Accretion

Hydrology • Elevation • Tidal Inundation • Soil Moisture • Water Table • Salinity

Reproduction (per individual)

Reproduction (per area)

Nutrients

Light Level Mangrove

Dispersal Disturbance

• Sand Burial • Hurricanes • Climatic Variance

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

12 month old seedlings

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 24 48 72 96Salinity Level (ppt)

Biom

ass

(g)

AbovegroundBelowground

24 month old seedlings

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

0 24 48 72 96Salinity Level (ppt)

Biom

ass

(g)

AbovegroundBelowground

Source: L. Alleman

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

Water Table Depth Experiment

6-month old seedlings

0

1

2

3

4

5

0 -15 -30 -45 -60Water-Table Depth (cm)

Abo

vegr

ound

Bio

mas

s (g

)s taticbiweeklybimonthly

18-month old seedlings

0

1

2

3

4

5

0 -15 -30 -45 -60Water-Table Depth (cm)

Abo

vegr

ound

Bio

mas

s (g

)s taticbiweeklybimonthly

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

0.2

0.4

0.6

0.8

2 6 12 24

Duration Exposure (hours)

Prop

ortio

n D

ead

0

0.2

0.4

0.6

0.8

-6.5 2.5 5.7

Temperature (°C)Pr

opor

tion

Dea

d

Significantly greater mortality with: Exposure at -6.5 C 24 hour duration of

cold exposure

Dispersal stage propagules tended to have greatest

overall survivorship

0

0.2

0.4

0.6

0.8

1

0 7 14 21 28 35 42 49 56Time (days)

Surv

ivor

ship

Stranded Stage Propagules

Dispersal Stage Propagules

Seedling Stage

May confer advantage to surviving freeze events when

still in dispersal stage (in saline water)

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

020406080

100120140160180200

-0.1 0 0.1 0.2 0.3 0.4 0.5Elevation (m, NAVD88)

Tree

Hei

ght (

cm)

mature trees (>12-months old)newly established propagules (<12-months old)

n = 218 n = 54

020406080

100120140160180200

-0.1 0 0.1 0.2 0.3 0.4 0.5Elevation (m, NAVD88)

Tree

Hei

ght (

cm)

mature trees (>12-months old)newly established propagules (<12-months old)

n = 218 n = 54

Establishment Elevations: Newly Established Propagules vs. Mature Trees

Mean water level = 0.15 m NAVD88 Mean mangrove elevation (all sites, ages) = 0.23 m NAVD88

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

18-Oct-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

21-Feb-09

07-Mar-09

21-Mar-09

04-Apr-09

18-Apr-09

02-May-

09

16-May-

09

30-May-

09

Date

Ele

vatio

n (m

, NA

VD

88)

Low water establishment windows?

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

Conclusions Seedling salt tolerance

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?