Sanibel Island rice rat project
Introduction
Since 2015, we conducted vegetation sampling on Sanibel Island Florida in July-August as part of a cooperative project between FWC, the University of Florida, J.N. Ding Darling National Wildlife Refuge, and the Sanibel-Captiva Conservation Foundation. We documented 109 species of vascular plants across 54 sampling grids on the island. Data will be used to inform restoration efforts, habitat management decisions, and ongoing research on habitat selection and use of the Sanibel Island rice rat (Oryzomys palustris sanibeli).
Upland Habitat scientist conducted sampling on 54 pre-determined locations, or grids. The grids were stratified into three generalized habitat types – freshwater wetland, transitional zone, and mangrove forest, with 18 grids for each habitat type.
Habitat Descriptions
Our sampling grids were stratified across three different generalized habitat types. Broad descriptions of these habitats are available below. Please be aware that variations within each habitat type were common, so these are summary descriptions only. Detailed accounts of all variations of each habitat type are beyond the scope of this document.
Freshwater Wetlands
The freshwater wetland sites were all located on the “inland” portions of the island. The majority of these sites were flooded during our sampling period, with water depths occasionally surpassing 1 meter. The characteristic signature of these sites was the overwhelming dominance of sand cordgrass (Spartina bakeri). The Spartina typically created a thick groundcover and was nearly always greater than 1 meter in height. High cover classes for litter were common at these points, as the clumps of Spartina generally contained large volumes of standing dead blades of grass. The Spartina was also interspersed with giant leather fern (Acrostichum danaeifolium). Jamaica swamp sawgrass (Cladium jamaicense) was also common, along with southern cattail (Typha domingensis) where the water was deepest. Other frequently encountered herbaceous species were Virginia saltmarsh mallow (Kosteletzkya pentacarpos), lateflowering thoroughwort (Eupatorium serotinum), and saltmarsh morning-glory (Ipomoea sagittata). Woody species were infrequent in the freshwater wetlands, and were most often encountered when points approached the border between a wetland and a hardwood forest. The most common woody species in the freshwater sites were wax myrtle (Myrica cerifera), sea myrtle (Baccharis halimifolia), and buttonwood (Conocarpus erectus). Brazilian pepper (Schinus terebinthifolia), a noxious invasive species, was encountered at a small proportion of the freshwater sites. Although traditional fire regimes have been altered by human activity, we were given the impression that prescribed fire would ideally be applied to these sites on a 1-3 year rotation.
Transitional Zones
The transitional sites are difficult to define, simply by nature of being areas of transition between different habitat types. They are best described as interspersed patches of several different vegetative communities, including pine rockland, upland mixed woodland, rockland hammock, maritime hammock, and mangrove swamp (FNAI 2010). Descriptions of the mangrove portions of the transition zones will be omitted here, as mangrove swamps will be described in detail in the next subsection. Water depth also varied greatly within the transition zones – some points were completely dry, while other had water depths up to 0.75 meters. Percent cover of litter was nearly always 100%, as the ground was typically carpeted with fallen leaves and branches. Bare ground was sparse and infrequent.
Herbaceous species were virtually nonexistent in the interior portions of the transitional zones. Where these areas graded into the freshwater wetlands, we encountered giant leather fern, Jamaica swamp sawgrass, and sand cordgrass. Buttonwood was by far the most common woody species on these grids. Other frequently encountered woody species were white indigoberry (Randia aculeata), cabbage palm (Sabal palmetto), and Florida swampprivet (Forestiera segregata). Brazilian pepper was also quite common on some of the transitional sites. Also of note was the occurrence of joewood (Jacquinia keyensis), a State-Threatened species that we found on three of the transitional sites.
Mangrove Swamp
The mangrove swamps were by far the least floristically diverse of our sites. Groundcover was sparse and consisted primarily of saltwort (Batis maritima) and perennial glasswort (Sarcocornia ambigua). The most common woody species by far were the three species of mangroves: red mangrove (Rhizopora mangle), black mangrove (Avicennia germinans), and white mangrove (Laguncularia racemosa). Water depth in the mangroves was most commonly between 3-10 centimeters but was subject to tidal influence. Percent cover of litter was nearly always 100%, as the ground was covered in a mucky layer of partially decomposed plant matter. Bare ground was extremely infrequent. Fire is not typically a component of the mangrove swamp ecosystem.