Egans Creek Restoration

The area of Egans Creek Greenway south of Jasmine Street and north of Sadler Road was described in an Ecological Assessment in 2002 as a black water stream that flowed through a series of interconnecting canals and intersecting mosquito ditches that drained into a remaining wetland forest community (hydric hammock). Throughout the Greenway, flow in the creek is restricted to the channel due to historic channelization, canal (mosquito ditch) creation, steep banks and adjacent filled berms. There are very few areas along the creek/canals where water can flow out of the banks into the surrounding wetland forests (hydric hammock). In most areas, the creeks and the interconnected ditches and canals effectively drain the surrounding wetland forests (hydric hammock). Steep sided banks allow little vegetation growth along the creek except in some areas of erosion where new vegetation such as cattails can be found.

Trees and shrubs within the black water stream community included an occasional groundsel tree, sugarberry, bigleaf swampweed, wax myrtle and Carolina willow. Common low growing vegetation included alligatorweed, sedge, Columbian waxweed, sand cordgrass and hairy maiden.

The wetland forest community (hydric hammock) dominated throughout the Greenway between the creek/canals and the maritime hammock communities (forests associated with coastal areas). As indicated, they are infrequently flooded during periods of high water and receive surface water runoff from the surrounding higher elevations.

The main characteristic of the wetland forest community was a well-developed mature canopy of sugarberry, red mulberry, red cedar, red bay and cabbage palm with some live oak. The wetland forest community (hydric hammock) located south of Jasmine Street was dominated by a red maple monoculture forest.

One of the primary purposes of the Egans Creek Greenway is to protect the wildlife corridor used by animals moving south from Ft. Clinch State Park. According to the Environmental Assessment in 2002, a total of three amphibian, nine reptile, 23 bird, eight mammal and four fish species were encountered through direct observation and signs of inhabitants (tracks, etc.) during the field survey.

Listed birds observed in the Greenway include the little blue heron, snowy egret, tricolored heron, white ibis, wood stork and roseate spoonbill. In 2007, Egans Creek Greenway became a part of the "Florida’s Great Birding Trail."

Prior to the installation of the tidal barrier at Jasmine Street in 2008, saltwater intrusion into Egans Creek was first becoming evident with red maples dying in 2005.

The outer limits of affected wetland areas were delineated by soil salinity measuring in 2009. The limits of the “affected area” were defined by the presence of dead and stressed red maples, which totaled approximately 60 acres. The majority of salinity impacts appear to have occurred in the northern half of the preserve, which received tidal waters from two large culverts located in the northeast corner of the project area under Jasmine Street. Saltwater entered and was distributed by the existing mosquito control canals that are aligned north-south and east-west within the Greenway. A total of 11 “affected wetland areas” have been identified within the project area.

Since the construction of the tide barrier at Jasmine Street in 2008, the affected areas dominated by dead maple trees appear to be naturally succeeding into more salt tolerant vegetation such as salt bush, wax myrtle and red cedar. Newly established vegetation has grown into the sun exposed low lying areas due to the elimination of shade previously provided by the red maples including cattails, elderberry, swamp hibiscus and flatsedge. These affected areas are most evident in Sections C1, C3, C4 and C5. (see link below for map of affected areas).

Particularly high saline areas were evident by the observation of bare soils with salt crystals on the surface. Vegetation that thrives in these harsh conditions includes yaupon holly, glasswort, marsh elder and giant foxtail. These affected areas are most evident in Sections C2 and C6.

A surprising observance within the affected areas is the natural growth of red maple seedlings. In addition, areas that provided some shading were observed to have the presence of several fern species: royal fern and chain fern. This may be an indication that the soil salinity may be dissolving in the surface soils within those areas. The red maple seedling growth has been observed in Section C1.

Current irregular flooding conditions has the habitat evolving to a mix between vegetation found in a wetland forest and vegetation that is found in the slightly high maritime hammock (coastal forest) without the mature vegetation canopy. The lack of canopy shading has allowed for invasion of exotic vegetation such as chinaberry and Chinese tallow.The maritime forest that remains at a higher elevation surrounding Egans Creek has not been impacted by saltwater intrusion, and the ditching and draining of the wetlands.

Click here to see a diagram of the affected areas (labeled C1 through C11).

FDOT’s ultimate goal of the Egans Creek restoration project is to reestablish a forested wetland system (hydric hammock) with ecological and aesthetic qualities equal to or better than the freshwater system that was impacted.

A healthy hydric hammock (wetland forest) community has a well-developed mature canopy of primarily sugarberry, red mulberry, red cedar, red bay and cabbage palm with some red maple and live oak.

Trees and shrubs that can be common and sometimes abundant in the hydric hammock (wetland forest) community include devils walking stick, groundsel tree, sugarberry, yaupon, Virginia willow, red cedar, red mulberry, red bay, cabbage palm, Carolina willow and American elder. Common groundcovers and vines may include blackberry, the exotic Japanese honeysuckle, Florida betony, Colombian waxweed, marsh pennywort, Virginia creeper and frostweed.

A healthy hydric hammock (wetland forest) community can contain diverse wildlife because of the food sources and cover. Important food sources can include a variety of fruits and seeds including wax myrtle, red cedar, red maple and hackberry. The infrequent flooding does not allow the full life cycle of amphibians. Amphibians that could be found in this community could include salamanders and frogs, such as the dwarf salamander, southern dusky salamander, narrow mouth toad, spadefoot toad, tree frogs (green, gray, and squirrel), southern toad, spring peeper, little grass frog and southern leopard frog. Reptiles that may be found in this community include green anole, ground skink, southeastern five-lined skink, rough green snake, rat snakes, water snakes and crayfish snakes. The American alligator may be found within the creek/canals along with aquatic turtles. Box turtles may be found in the hammock communities.

A diverse bird and mammal population could exist within a healthy hydric hammock (wetland forest) community to take advantage of the diversity of fruit, seed, and canopy insect populations for food and the tree canopy for nesting. The proximity of water-related and forest-related communities increase the chance for high diversity of wildlife. Water related birds (e.g. ibises, herons and egrets) could be found near the water and woodland birds (e.g. owls, warblers, vireos, flycatchers and woodpeckers) could be found within the hammock community. Mammals that could frequent a healthy hydric hammock (wetland forest) community include raccoon, cotton mouse, golden mouse and gray squirrel.

The present system does not contain the physical elements of a black water stream with an interconnected hydric hammock (wetland forest) system. The vegetation community evolved into a red maple dominated system that also could not sustain the animal diversity that could occur in a healthy hydric hammock (wetland forest) community. It is recommended that the range of vegetation be monitored and maintained during the restoration and natural growth process so that the system can develop into a more healthy community for the diverse wildlife.

The overall restoration goal for Egans Creek Greenway will support a variety of native plants and animals. The Greenway will continue to provide flood protection, recreation and other economic benefits for the public. The ecological resources, including plant and animal communities, will have a natural diversity and abundance, and exotic plant species will be reduced. Particularly, the Greenway will favor use by birds for foraging and nesting, and have a sustainable population of wildlife with special focus to attract protected species.

Alternatives for restoration activities under consideration are:

1) Natural recruitment: Monitor the progress of natural succession and allow nature to "take its course."

2) Aesthetic planting: Plant salt tolerant species in zones of high visibility and monitor for successful establishment.

3) Full planting: Revegetate the entire affected area with species appropriate to current soil salinity levels.

Natural recruitment (Alternative 1) will provide the greatest success rate for revegetation, will result in greater diversity of species (more wildlife), and reduce the overall level of disturbance, thus minimizing increased invasion from exotic species. Emerging seedlings of freshwater species (maple, sugarberry and cedar) will naturally find the least affected soils and may outgrow transplants (plants taken from other sources and moved to Egans Creek) over the long term of 10 to 20 years, returning the Greenway to the target habitat through the remnant seed bank.

Construction activities for this alternative include felling (selective removal) of dead snags and treatment and removal of exotic invasive plants. These activites could begin within about nine months. Additional activities would include surveying of recruits for species composition and densities, mapping of recruitment by communities, monitoring of exotic invasive species regrowth for continued removal and examination of recruitment patterns for potential modification to the restoration plan.

Aesthetic planting (Alternative 2) (Recommended) carries the benefits of natural recruitment but adds short term benefit by reducing the appearance of a devastated landscape in areas immediately visible to the public. Selective planting of larger transplants chosen for tolerance to salinity levels in specific planting locations would more quickly restore the desired aesthetic of the Greenway in the 5 to 10 year term.

Construction activities for this alternative include 1) felling (selective removal) of dead snags, 2) treatment and removal of exotic invasive plants and 3) planting of trees and shrubs in selected locations of high visibility. These activites could begin within nine to 18 months depending on season. Planting should be scheduled at the optimum season (during dormancy), typically between November and April. Dormant season planting allows the plants to begin root growth without the need to sustain vegetative function and gives the plant time to adjust to transplant conditions prior to committing resources to other plant functions (leafing out, flowering, and fruiting).

Locations for transplants would be chosen in the field to minimize disturbance to desired emerging recruits and would be sampled for salinity concentrations to optimize the chance for survival. Based on the densities of the emerging natural vegetation, planting densities are anticipated to be between 30 and 60 transplants per acre for canopy trees and large understory shrubs.

Full planting (Alternative 3) carries the highest costs and the greatest risk for success. It also produces the greatest level of disturbance and the most demanding commitment for short and mid-term management. Mid-sized transplants would require location of specific planting sites with appropriate salinity levels to maximize establishment success and avoid large scale failures. Analysis of salinity levels have indicated reductions, especially in shallow, 3-inch sampling locations, but deeper planting holes may encounter higher salinity levels that would impact nursery grown transplants that have not been acclimated, having been grown with freshwater irrigation.

This alternative would have a similar schedule to Alternative 2. Transplant locations would also be field identified and sampled for salinity, minimizing disturbance and taking advantage of the current natural revegetation of the site. Average planting densities for full site planting of canopy trees are anticipated to be greater than 60 transplants per acre because of the increased open character of the interior regions of the site and the increased opportunities for planting of smaller sized transplants.

All three alternatives would include the selected felling (removal) of the majority of dead snags (trees) to improve the visual character of the greenway while retaining suitable habitat for cavity nesting birds and other wildlife. Future monitoring is proposed to be conducted annually for soil salinity and vegetation survival / diversity. Exotic vegetation would be monitored and chemically treated to an extent that it would be most effective. Detailed plans would be incorporated into the restoration plan.

All alternatives are likely to achieve the target goal of establishing a healthy forested wetland system within the long term of 20 years. In all cases, a monitoring plan is essential to provide data for future modifications or additions to the restoration plan and the management of invasive species, which is a critical component of the success of the restoration effort.

Once a restoration alternative has been selected and design is underway, a Value Engineering (VE) team will evaluate the alternative to identify opportunities and recommend concepts that may improve stakeholder value in terms of cost, constructability and basic functionality. The VE Team, which will be an independent team, will document their analysis performed to support decisions related to the planned alternative design. Additionally, the VE Team will summarize existing conditions, document the purpose and need for the project, as well as document other engineering, environmental and social data related to the preliminary restoration alternative.

The major components of the restoration are salinity reduction and freshwater vegetation re-establishment. To measure the progress of these efforts, surface water elevation and salinity are continuously being monitored by automated gauges. Soil salinity and vegetation observations are being documented by observation/measurement through the impacted area by use of a grid map. To date, data collection has occurred twice in a two-year interval but will be repeated more frequently as proactive measures are introduced to accelerate vegetation re-establishment.

Salinity reduction:

• Prevent salt water from inundating the area. A tide barrier was constructed at Jasmine Street in 2008 allowing surface runoff from rainfall to flush salinity through the system.
• The level and distribution of salinity in soils is the result of time-dependent interactions of rainfall, evaporation and water movement in and through the soil, seeping and drainage into the existing ditches. There may be some uptake by vegetation, but that will not be the major pathway of salinity reduction. Halophytic plants, those that uptake and compartmentalize salts from the soil, need to be harvested and removed from the site to be an effective strategy for salt reduction.

Vegetation re-establishment:

• Removing dead trees. Selective removal of dead trees to promote re-vegetation while leaving sufficient standing dead trees as wildlife habitat.
• Natural vegetation growth is occurring and will be an important element of the restoration; especially in areas that are difficult to access and are not visible from private property or public trail/use areas.
• Planting desirable freshwater species: Planting will be used to accelerate tree/shrub coverage (especially in high visibility areas) and promote ecological diversity.
• Removing invasive and nuisance plants. Removal of undesirable plants/trees in naturally restoring and planted areas.

The Egans Creek Restoration Plan will be based on compiled data from salinity monitoring, field observations and technical publication research. The critical component to the restoration plan is the anticipated short- and long-term affect of soil salinity conditions to the vegetation. Although the construction of the tide barrier at Jasmine Street is preventing tidal influence into the project site, it is unknown how long saline conditions will sustain in the soil. Soil salinity will presumably diminish through time.

Although most salt-tolerant vegetation is referenced to the tolerance of salt-spray, research has shown that salt tolerance levels in roots were three to four times higher than in leaves. The plants recommended are placed into four relative salt tolerance categories: highly tolerant, tolerant, moderately tolerant and sensitive. Tolerance described for each plant species recommended is summarized in Table 1. In reality, there are no clear cut guidelines between the tolerance categories for plant species.

Potential native vegetation may be planted to supplement the affected areas to provide habitat enhancement include dahoon holly, American holly, yaupon holly, southern red cedar, sweetgum, wax myrtle, blackgum and sycamore. These plant species were selected based on vegetation type, wetland status, salt tolerance, common occurrence for the area and nursery availability.

Once the plan is implemented, vegetation and soil sampling testing will continue to take place to evaluate the salt content in the soil. A possible second phase may require more freshwater vegetation be planted once salinity has been reduced and if target goals have not been met.

Alternative 1- Natural recruitment

The aesthetic condition in the affected areas is likely to be characterized by open areas of mixed vegetative communities in the short term (1-5 years) with diverse grasses and forbs interspersed with shrub thickets and emerging tree saplings in areas of higher elevations. It is anticipated that this will transform into a primary succession forested community in the midterm (5 -15 years) characterized by tree canopies of less than 30 feet tall. Secondary succession hardwood forest is likely to be substantially populated throughout the affected areas within the long term (15 -20 years).

The ecological conditions are characterized by diverse communities of mixed vegetation supporting a wide range of wildlife slowly transforming into a more homogenous mix of forest species, reducing the biodiversity of the site over time and thus supporting a less diverse animal population in the long term.

Alternative 2- Aesthetic planting (Recommended)

The aesthetic condition of the affected areas is likely to mimic that of Alternative 1 except in those areas that are planted to produce a visual impact in the short term. Those areas are anticipated to block views of the impacted areas with forest species, primarily evergreen trees and shrubs and will provide a “forest view’ from strategic view sheds along the Greenway.

The ecologic condition is anticipated to approximate the description above except for the possibility of increased evergreen cover and nesting opportunities afforded by the “buffer” plantings.

Alternative 3- Full planting

The aesthetic condition of the affected areas is likely to be characterized by open areas of managed vegetation suppressed in order to protect planted transplants from competition. It is anticipated that this managed landscape will accelerate the succession of the forest communities by providing a faster canopy of shade and reduce the term of secondary succession by approximately 5 years.

The ecologic condition is anticipated to be considerably less supportive of wildlife due to the disturbance of natural fruiting/seed cycles from management of competitive recruits. Overall biodiversity will likely be reduced in all time frames of the restoration.