A04_Quirk_NBI_Planting_Design_2024_FINAL_0001.pdf

North Breton Island Restoration Back Barrier Planting Design

Submitted to

U.S. Fish and Wildlife Service

Prepared by

Tracy Quirk, Ph.D.

Department of Oceanography and Coastal Sciences

Louisiana State University

July 2024

Summary

• The back-barrier of North Breton Island (NBI) is relatively stable. Settlement / elevation change rates in backdune and back-barrier marsh habitats of NBI are low;

-0.11 ± 0.08 ft/yr from 2021 to 2023 (settlement plates) and 0.04 ± 0.05 ft/yr from 2023 to 2024 (island elevations).

• While some plants have naturally colonized, most of the backdune/swale and back-barrier marsh remains unvegetated.

• Recommended species based on their presence on Louisiana barrier islands, habitat value for birds (e.g., brown pelican nesting), vegetative mode of reproduction for herbaceous species, ability to stabilize sediment, and general commercial availability are: Spartina alterniflora and Avicennia germinans for the back-barrier marsh, Spartina patens for the back-barrier high marsh and backdune habitats, Paspalum vaginatum, Sporobolus virginicus , Iva frutescens, and Lycium carolinanum for the backdune habitat. Most recommended target species for planting are colonizing NBI naturally but at low densities and in isolated patches.

• Based on a combination of data sources, elevation ranges for target species are generally:

Species Mean range Maximum range Avicennia germinans 0.7 - 1.4 -1.0 - 2.5 Spartina alterniflora 0.5 - 1.5 -1.0 - 2.5 Spartina patens (marsh) 1.5 - 3.0 Spartina patens (dune) 5.0 - 6.0 Paspalum vaginatum 1.0 -5.7 Sporobolus virginicus 3.0 - 8.0 Iva frutescens 2.5 - 6.0+ Lycium carolinianum 2.5 - 6.0+

Elevation (ft, NAVD88)

• NBI elevations average 5.2 ± 0.10 and 2.4 ± 0.13 ft, NAVD88 for the backdune and back-barrier marsh habitats, respectively based on most recent survey points.

• Recommended Avicennia planting area is between 1 and 3 ft, NAVD88 and encompasses 11 acres along the island and 1-acre near the southern lagoon.

Recommended plant spacing is 3 x 3’ in high priority areas (8 acres) and 5 x 5’ spacing for remaining (4 acres).

• Spartina alterniflora is recommended for planting bayward of Avicennia at elevations of 0.5 – 1.5 ft, NAVD88 within an 8 acre area north- and mid-island and a 1-acre area along the tidal lagoon to the south. Recommended plant spacing is 3 x 3’ in high priority areas (4 acres) and 5 x 5’ spacing for remaining (5 acres).

• Spartina patens can be planted along the high elevation back-barrier marsh interior of Avicennia plantings in an area of 2 – 3ft, NAVD88. Spartina patens planting area in the back-barrier marsh is 40 acres. Recommended plant spacing is 3 x 3’ in high priority areas (25 acres) and 5 x 5’ spacing for remaining (15 acres).

• Spartina patens, Paspalum vaginatum, Sporobolus virginicus, Iva frutescens, and Lycium carolinianum can be planted in a 192-acre backdune area ranging from 2.5 and 6 ft, NAVD88 in elevation. Recommended plant spacing is 5 x 10’ planting in blocks along the backdune.

Plan

Recommendations for back-barrier planting of North Breton Island based on recent elevations

The majority of the back-barrier North Breton Island (NBI) is situated at elevations too high to support Avicennia germinans, although Avicennia is a priority species for brown pelican nesting. A relatively large area in the north adjacent to the 2023 Mangrove Planting Area, a thin strip of area along the backbarrier and along a tidal lagoon in the southern part of NBI are at appropriate elevations for Avicennia, accounting for a protective buffer of Spartina alterniflora plantings on the bayside. Avicennia planting area is between 1 and 3 ft, NAVD88 and encompasses 11 acres along the island and 1 acre near the southern lagoon (Fig. 1;

Table 1).

Spartina alterniflora is recommended within the area bayward of Avicennia and generally at elevations of 0.5 – 1.5 ft, NAVD88. Along the back-barrier Spartina alterniflora planting area is 8 acres within a 1-acre area along the tidal lagoon to the south (Fig. 1; Table 1). While elevations are appropriate for Spartina alterniflora within the outlined areas, stability of the substrate and susceptibility to tidal action and scour may be issues along the mid-back-barrier.

Spartina patens can be planted along the high elevation back-barrier marsh interior of Avicennia plantings in a relatively large area in the north and along the barrier at elevations of 2 – 3ft, NAVD88. Spartina patens planting area in the back-barrier marsh is 40 acres (Table 1).

The majority of the backdune (also referred to as swale) habitat of North Breton Island is between 2.5 and 6 ft, NAVD88 and therefore is appropriate for planting backdune species (Figs. 1, 4 & 5). Recommended species include Spartina patens, Paspalum vaginatum, Sporobolus virginicus, Iva frutescens, and Lycium carolinanum (Table 1) Sporobolus virginicus, Iva frutescens, and Lycium carolinanum at higher elevations closer to the dune crest and Spartina patens and Paspalum vaginatum at lower elevations closer to the bay.

Sporobolus virginicus would have higher survivorship than S. patens and P. vaginatum closer to the dune crest where subject to sand burial.

Fig. 1. Planting location options for target species (Avicennia germinans, Spartina alterniflora, Spartina patens, and backdune species, Paspalum vaginatum, Spartina patens, Sporobolus virginicus, Iva frutescens and Lycium carolinianum) based on most recent elevations, North Breton Island.

Table 1. Potential acres and recommended planting densities of target species for North Breton Island.

Recommended spacing for plantings

1) Priority area 1: 3 x 3 spacing (Fig. 2) (equates to approximately 4,240 plants per acre)

High densities planting areas: establish dense vegetation quickly (i.e., pelican nesting habitat) for Spartina alterniflora, Avicennia and Spartina patens

Fig. 2. Typical vegetation layout: 3 x 3’.

Planting area Priority Area US Survey Acres Recommended spacing Est. density

(per acre) Quantity

Back-barrier Spartina alterniflora 1 4 3 x 3 4,240 16,960

5 4 5 x 5 1,750 7,000

Back-barrier Avicennia germinans * 1 9 3 x 3 4,240 38,160

5 2 5 x 5 1,750 3,500

Back-barrier Spartina patens 1 25 3 x 3 4,240 106,000

2 15 5 x 5 1,750 26,250

Back-barrier dune species 3 192

Spartina patens 38 5 x 10 871 33,098

Paspalum vaginatum 38 5 x 10 871 33,098

Sporobolus virginicus 38 5 x 10 871 33,098

Iva frutescens 38 5 x 10 871 33,098

Lycium carolinianum 38 5 x 10 871 33,098

Southern lagoon Spartina alterniflora 4 1 5 x 5 1,750 1750

Southern lagoon Avicennia germinans 4 1 5 x 5 1,750 1750

* Planting density of 2023 Mangrove planting area: 5,333 plants/acre

2) Priority areas 2, 4, &5: 5 x 5 spacing (equates to approximately 1,750 plants per acre)

Moderate density planting areas for Spartina alterniflora, Avicennia, and Spartina patens along back-barrier marsh

3) Priority area 3: 5 x 10 spacing (equates to ~871 plants per acre) planting in mixed species blocks with higher backdune plantings of Sporobolus virginicus, Iva frutescens and Lycium carolinianum and lower backdune plantings of Spartina patens and Paspalum vaginatum (Fig. 3).

Fig. 3. Backdune vegetation layout in higher and lower elevations of the back dune in 5 x 10’ mixed species spacing.

Recommendations for planting areas (in order of priority; Fig. 4)

1) The northern section of NBI is in close proximity to existing core breeding areas of brown pelican and has relatively large areas of appropriate elevations for Spartina alterniflora, Avicennia germinans and Spartina patens in the back barrier marsh. I recommend high density (3 x 3 spacing) plantings in this area, which also will create habitat connectivity to 2023 Avicennia plantings.

2) Spartina patens along length of island (5 x 5 spacing). High likelihood of success.

3) Mid-island dune plantings with 5 x 10 spacing. High likelihood of establishment success and a lot of available open space for vegetation.

4) Southern lagoon – currently has naturally colonizing areas of Spartina alterniflora and I like it.

5) Spartina alterniflora and Avicennia along back island length (5 x 5 spacing).

Likelihood of survival / establishment uncertain.

Fig. 4. Recommended areas for planting in order of priority.

Cost estimates by species and size

Table 2. Cost and time estimates for grow-out of recommended species.

Considerations

Bird Habitat

The US Fish and Wildlife Service provides the following recommendations for Brown Pelican habitat suitability index for breeding habitat: island covered with greater than 50% woody (0.6–10.7 m height) vegetation (for Florida, Alabama, and Louisiana; Hingtgenet al.

1985). Further, literature analysis and a survey of Louisiana barrier islands indicate that islands that provided persistent pelican nesting habitat were between 25 and 173 acres in size with the shrub and dune habitat ranging from 5 to 50 acres (Visser et al. 2005).

Pelicans preferred nesting in shrubs (i.e., Avicennia germinans and Iva frutescens), and nesting occurred at an average elevation of 1 ft above mean sea level (Visser et al. 2005).

Louisiana barrier islands also support large populations of other nesting colonial seabirds including Royal Terns, Sandwich Terns, Laughing Gulls, Black Skimmers, among others, all of which have formed nesting colonies on NBI. These species nest in open areas of sand, shell or dried seaweed without dense vegetation. Royal and Sandwich terns on other Louisiana barrier islands show high site fidelity for nesting grounds presumably due to the low availability of suitable nesting habitats as well as the relative instability of habitats

Species Size Bid range

(cost per unit) Time for grow-out

Avicennia germinans 4" $7.00 1 yr

1-gallon $10.00 1.5 yr

Spartina alterniflora plug $1.25 -2.50 0.5 yr

Spartina patens 4" $2.50 - 3.25 60 - 90 days

Paspalum vaginatum 4" $2.50 - 3.25 60 days

Sporobolus viginicus 4" $2.50 - 3.26 60 days

Iva frutescens 1-gallon $6.65 - 15.00 1 yr

Lycium carolinianum 4" $5.00 1 yr used (Visser and Peterson 1994). Though spatially consistent nesting grounds for breeding populations on NBI have not been confirmed, planting designs should consider this habitat preference and leave some open areas without dense vegetation.

Island Settlement

Nine settlement plates were installed in 2020 – 2021 prior to the end of island construction in December 2021 (Fig. 5). Four settlement plates were placed on or near the dune crest (MS01, MS02, MS03, and MS07); one plate was placed in the foredune (MS05), and four plates in the backdune (MS04, MS06, MS08, and MS10). Two settlement plate measurements were collected post-construction on 12/23/2021 and 5/16/2023 spanning 509 days.

The one settlement plate on the foredune experienced an annual rate of change of -0.093 ft/yr. The change in elevation of settlement plates on the dune crest was highly spatially variable with a range of +2.15 to -1.25’ (i.e., +1.54 to -0.89 ft/yr; Table 3) from December 2021 to May 2023. The backdune settlement plates experienced an elevation change ranging from +0.17 to -0.34’ or an annual average rate of change of -0.11 ± 0.08 ft/yr (Table 3; Fig. 6).

Fig. 5. Location of nine settlement plates on NBI. Map courtesy of USGS.

Table 3. Settlement plate elevations and change rates post-construction, North Breton Island.

Fig. 6. Annual rate of change in settlement plate elevations in the foredune, dune crest and backdune areas of North Breton Island based on a 509 day interval from 12/23/2021 to 5/16/2023.

Additionally, thirty-three elevation points in the back-barrier marsh surveyed in May 2023 were resurveyed in May 2024 (Fig. 7). The mean difference in elevation was 0.04 ± 0.05’ with a median difference of 0.005’ indicating a small annual change in elevation at most

NBI Settlement Plate Location 12/23/2021 5/16/2023 Change (ft) Daily rate of change

(ft/day) Annual rate of change

(ft/yr)

MS-04 Back dune 1.70 1.87 0.17 0.000334 0.122

MS-06 Back dune 4.49 4.18 -0.31 -0.000617 -0.225

MS-08 Back dune 4.00 3.66 -0.34 -0.000668 -0.244

MS-10 Back dune 4.01 3.87 -0.14 -0.000275 -0.100

MS-01 Dune crest 7.49 9.64 2.15 0.004224 1.542

MS-02 Dune crest 6.97 5.73 -1.24 -0.002436 -0.889

MS-03 Dune crest 6.86 6.61 -0.25 -0.000491 -0.179

MS-07 Dune crest 9.00 9.28 0.28 0.000550 0.201

MS-05 Fore dune 5.97 5.84 -0.13 -0.000255 -0.093

Elevation, ft, NAVD88 locations. The largest change was a 1.1’ increase at one location. Fifteen locations (45%) had a net change of less than 0.1’.

Fig. 7. Back-barrier elevations in U.S. ft, NAD83 (colors) in May 2024 and changes from May 2023 to May 2024 as noted. Courtesy of USGS.

Island Elevations

The NAVD88 tidal datum (0.72 ft) approximates mean sea level (MSL, 0.75 ft) at the nearest tidal gage station at Shell Beach, LA. Thus, elevations included in this report approximate elevations relative to MSL - 0.03 ft.

Island elevations during the May and October 2023 and May 2024 surveys ranged from a low elevation of -0.38’ to a high elevation of 11.36’. Dune, swale, and back-barrier marsh elevation averaged 8.4 ± 0.3, 5.2 ± 0.10, and 2.4 ± 0.13’, respectively (Table 4; Fig. 8).

Table 4. Elevations (minimum, maximum, mean and median) of dune, swale, and back-barrier marsh habitats survey plots at North Breton Island during 2023 – 2024 surveys.

Fig. 8. Elevation (‘z’) survey data collected in 2023 with a subset collected in 2024 at North Breton Island in back-barrier, swale and dune habitats. Points with planted vegetation are shown in Red, all other naturally vegetated and non-vegetated points are shown in Blue.

Elevations of the island decline from the dune crest to the back-barrier landward edge (Fig.

5). Points show the most recent island elevations. To interpolate the elevation points across a larger spatial scale, universal kriging was used and illustrates predicted elevation ranges of back barrier NBI (Fig. 5).

NBI Survey 2023-2024 Elevations

Habitat n Min Max Mean Median Dune 25 6.1 11.4 8.4 8.6 Swale 48 3.3 6.6 5.2 5.0 Back barrier marsh 95 -0.4 5.0 2.5 2.5

Elevation (ft, NAD83)

Fig. 9. North Breton Island elevation survey points (May and October 2023 and May 2024) and interpolation of elevations using universal kriging. Elevation values are in U.S. feet. The 2023 mangrove planting area and the estimated location of sand fencing is designated.

Target Species (Justification)

There are a number of plants species that occur on back-barrier islands in Louisiana and along the Gulf Coast. The goal is to select plant species that are common to Louisiana barrier islands, are perennial and/or reproduce vegetatively, provide preferred habitat for birds especially nesting brown pelicans, and are generally commercially available. The target species below are all found naturally colonizing North Breton Island, though presently are at low densities in isolated patches.

Spartina alterniflora is the dominant salt marsh perennial grass species along the US Atlantic and Gulf coasts. Spartina alterniflora is a keystone species, creating foraging habitat for many organisms, stabilizing sediments, facilitating accretion. It is common and naturally colonizes the back-barrier marsh habitats of island in Louisiana and, importantly, can create some protection of plantings of Avicennia slightly inland from tidal scour.

Avicennia germinans is an important back-barrier marsh species in Louisiana and provides habitat for a variety of organism and is a preferred pelican nesting habitat. Survivorship of planted Avicennia can be variable (~60% survivorship in the 2023 Mangrove Planting Area, NBI), but may be improved by planting Spartina alterniflora along the bayside.

Spartina patens is a common and important back-barrier high marsh and dune perennial rhizomatous grass species on Louisiana barrier islands.

Paspalum vaginatum and Sporobolus virginicus are both important backdune and swale perennial rhizomatous grass species on Louisiana barrier islands

Iva frutescens is a high salt marsh shrub common in backdune habitats on Louisiana barrier islands and has been found to be an important nesting habitat for pelicans (Visser at el. 2005).

Lycium carolinianum is an evergreen woody vine native to beaches and back-barriers in Louisiana. Can tolerate salt spray and provides nesting habitat for brown pelican.

Range of elevations of target species

Avicennia germinans

Based on NBI elevation and vegetation survey and data (Table 3) from West Dernier Island in 2015 (Table 4), Avicennia is generally found between –0.4 to 2.5 ft, NAVD88 with an average between 0.71 and 1.4 ft.

Spartina alterniflora is found at similar elevations to Avicennia, between -0.4 and 2.5 ft, with an average of 1.4 ft, NAVD88 on NBI (Table 3; Fig. 6) and an average of 1.4 ft in West Dernier (Table 4).

Spartina patens is found between 1.45 and 3.00 ft in marsh habitats and on NBI in backdune/swale habitats between 4.8 and 6.1 ft and an average of 5.4 ft (Table 5; Fig. 6).

Spartina patens on West and East Dernier and West Timbalier islands occurred at elevations between 1.4 and 5.9 ft (Table 4).

Paspalum vaginatum on NBI occurred at elevations of 1.4 to 5.7 ft and on West Dernier between 1.0 and 3.7 ft (Tables 3 & 4).

Sporobolus virginicus only occurred in one vegetation plot on NBI at 7.8 ft (Table 5).

Iva frutescens – In marshes, the most robust shrubs are flooded less than 6 to 7% of the growing season and are not found in areas flooded more than 30% of the time (Thursby and Abdelrhman 2004).

Lycium carolinianum – grows at similar elevation range as Iva frutescens.

Fig. 10. Elevation of plant species in vegetation survey plots in May 2023 in back-barrier, swale and dune habitats at North Breton Island.

Table 5. Elevations (minimum, maximum, mean and median) of plant species in vegetation survey plots at North Breton Island, May 2023.

Table 6. Minimum, maximum and mean elevation of target species based on survey points in May 2015 on West and East Denier and West Timbalier islands (Quirk, unpublished data).

NBI Survey 2023 Plant species elevations

Species n Min Max Mean Median Avicennia germinans (L.) L. 6 -0.4 2.5 1.4 1.7 Cakile constricta Rodman 3 4.8 4.9 4.8 4.8 Cucumis melo L. 2 4.8 5.5 5.2 5.2 Cynodon dactylon (L.) Pers. 2 6.1 6.4 6.2 6.2 Cyperus L. 4 4.5 7.8 6.0 5.9 Cyperus odoratus L. 3 4.8 5.5 5.0 4.8 Distichlis spicata (L.) Greene 3 1.4 5.5 3.9 4.8 Dysphania ambrosioides (L.) Mosyakin & Clemants 1 5.7 5.7 5.7 5.7 Eleusine indica (L.) Gaertn. 2 5.1 6.3 5.7 5.7 Fimbristylis castanea (Michx.) Vahl 8 3.5 5.0 4.4 4.6 Morus L. 1 5.7 5.7 5.7 5.7 Panicum amarum Elliott 18 4.5 10.4 7.6 7.3 Panicum repens L. 2 5.7 6.1 5.9 5.9 Paspalum vaginatum Sw. 5 1.4 5.7 2.7 2.1 Physalis angulata L. 1 5.7 5.7 5.7 5.7 Pluchea odorata (L.) Cass. 1 5.7 5.7 5.7 5.7 Portulaca oleracea L. 6 4.1 5.0 4.6 4.8 Sesuvium portulacastrum (L.) L. 16 3.3 9.8 5.3 4.7 Spartina alterniflora Loisel. 6 -0.4 2.5 1.4 1.7 Spartina patens (Aiton) Muhl. 5 4.8 6.1 5.4 5.5 Sporobolus virginicus (L.) Kunth 1 7.8 7.8 7.8 7.8

Elevation (ft, NAD83)

Species Island n min max mean Avicennia germinans West Dernier 4 0.38 1.60 0.71 Avicennia germinans West Timbalier 1 3.67 3.67 3.67 Paspalum vaginatum West Dernier 8 1.04 3.24 1.90 Spartina alterniflora West Dernier 7 0.20 4.00 1.40 Spartina patens West Dernier 8 1.44 2.77 1.62 Spartina patens East Dernier 17 2.67 5.89 4.62 Spartina patens West Timbalier 7 2.07 5.45 3.51 z (ft, NAVD88)

Relevant plant species information for use in NBI restoration (USDA NRCS)

Avicennia germinans

• Active growth period: year round

• Growth rate: rapid

• Life span: long

• Adapted to coarse textured soils: no

• Adapted to fine textured soils: yes

• Anaerobic tolerance: high

• Salinity tolerance: high

• Planting density per acre: 320 – 640

• Commercial availability: routinely available

Spartina alterniflora

• Active growth period: spring and summer

• Growth form: rhizomatous

• Mature height: 3.5 ft

• Life span: moderate

• Adapted to coarse textured soils: yes

• Adapted to fine textured soils: yes

• Anaerobic tolerance: high

• Salinity tolerance: high

• Planting density per acre: 2,728 – 40,000

• Vegetative spread: moderate

Spartina patens

• Growth form: rhizomatous

• Mature height: 2.0 ft

• Life span: long

• Adapted to coarse textured soils: yes

• Adapted to fine textured soils: yes

• Anaerobic tolerance: high

• Salinity tolerance: high

• Planting density per acre: 4,000 – 43,000

Paspalum vaginatum

• Active growth period: summer

• Growth form: rhizomatous

• Mature height: 0.1 ft

• Life span: moderate

• Adapted to coarse textured soils: no

• Adapted to fine textured soils: yes

• Anaerobic tolerance: high

• Salinity tolerance: medium

• Propagated by seed: yes

• Seed per pound: 413,000

• Planting density per acre: 4,800 – 40,000

• Commercial availability: routinely available

• Survivorship low in areas of active sand burial

Sporobolus virginicus

• Active growth period: year round

• Growth form: rhizomatous

• Mature height: 2 ft

• Life span: long

• Adapted to coarse textured soils: yes

• Adapted to fine textured soils: yes

• Anaerobic tolerance: medium

• Salinity tolerance: high

• Moisture use: low

• Planting density per acre: 1,000 – 16,000

Iva frutescens

• Growth rate: moderate

• Life span: long

• Adapted to coarse textured soils: yes

• Adapted to fine textured soils: yes

• Anaerobic tolerance: high

• Salinity tolerance: high

• Planting density per acre: 1,200 – 2,700

Lycium carolinianum

• Active growth period: spring

• Growth rate: slow

• Life span: moderate

• Adapted to coarse textured soils: yes

• Adapted to fine textured soils: yes

• Anaerobic tolerance: high

• Salinity tolerance: medium

• Planting density per acre: 2,728 – 3,450

• Commercial availability: routinely available

References

Hingtgen, T. M., R. Mulholland, and A. V. Zale . 1985. Habitat Suitability Index Models:

Eastern Brown Pelican. US Fish and Wildlife Service Biological Report 82(10.90). 20. p.

Snedden, G. A., Cretini, K., & Patton, B. (2015). Inundation and salinity impacts to above-and belowground productivity in Spartina patens and Spartina alterniflora in the Mississippi River deltaic plain: Implications for using river diversions as restoration tools. Ecological Engineering, 81, 133-139.

Thursby, G. B. and M. A. Abdelrhman. 2004. Growth of the marsh elder Iva frutescens in relation to duration of tidal flooding. Estuaries 27: 217 – 224.

Visser, J. M. and G. W. Peterson. 1994. Breeding populations and colony site dynamics of seabirds nesting in Louisiana. Colonial Waterbirds 17: 146-152.

Visser, J. M., Vermillion, W. G., Evers, D. E., Linscombe, R. G., & Sasser, C. E. (2005). Nesting habitat requirements of the Brown Pelican and their management implications. Journal of Coastal Research, 21(2), e27-e35.

APPENDIX

2015 Elevation and vegetation survey locations and data for West Dernier, East Dernier and West Timbalier islands (Quirk, unpublished data).