Guest Commentary | Making it in the Shade: The Hardwood Hammock Ecosystem in Florida
Nestled between pine flatwoods, prairies and wetlands, Florida’s mesic hardwood or oak hammock ecosystems are unique upland forests. These ecosystems, often referred to as “hammocks,” form on upland rises typically 10-15 feet above sea level, providing a cool, shady and moist environment due to the wide canopies and dappled light underneath the oak trees. Hammocks are vitally important, offering habitat for a range of species, and the ecosystem plays a key role in water regulation and nutrient cycling as the water moves from upland areas to the coasts.
Oak hammocks, as the name suggests, are prevailed by broadleaf hardwood trees such as live oak (Quercus virginiana), laurel oak (Quercus laurifolia) and water oak (Quercus nigra). The hardwood hammock forests predominantly develop in areas with rich, well-drained soil, often along riverbanks, floodplains or old coastal dunes. The dense tree canopy forms a shady understory, and moisture persists throughout the year. This is the reason for oak hammocks’ lush atmosphere compared to drier, more fire-prone environments like pine flatwoods.
Another characteristic of oak hammocks is their resistance to fire. Unlike pine forests that thrive with regular burns, oak hammocks are fire-intolerant due to their dense canopy and thick leaf litter. This lack of fire encourages the growth of a multilayered forest structure; canopy, understory, and ground cover, supporting a rich diversity of plant and animal life.
The plant diversity in oak hammocks is incredible. American holly (Ilex opaca), southern magnolia (Magnolia grandiflora), sweetgum (Liquidambar styraciflua), and cabbage palm (Sabal palmetto) combine in the canopy with oaks. In the dappled understory saw palmetto (Serenoa repens), beautyberry (Callicarpa americana), wild coffee (Psychotria nervosa), along with numerous native ferns, mosses, and grasses thrive and form a complex patchwork of biodiversity and complexity.
There are also numerous mycorrhizal relationships in the oak hammock with different fungal species. If you are lucky enough to be wandering through these forests a couple of days after a rain you can often discover numerous mushrooms from the mycelium in the soil that negotiate the complex relationships between plants and cycle nutrients from fallen branches and leaves.
In the canopies and boughs above epiphytes, such as Spanish moss (Tillandsia usneoides) and resurrection fern (Pleopeltis polypodioides), drape from tree limbs, thriving in the humid, shady environment. Wildflowers like spiderwort (Tradescantia ohiensis), and partridge pea (Chamaecrista fasciculata) bloom along the edges, adding bursts of color that attract pollinators.
Oak hammocks support a wide variety of wildlife. White-tailed deer, raccoons, bobcats, and gray foxes find food and shelter within the dense vegetation. Reptiles such as the eastern box turtle and various snake species, including black racers and rat snakes, are commonly seen. Amphibians like green tree frogs and southern toads thrive in the moist ground layer.
Birds also find food, rest and home in the hammocks. Species such as barred owls, red-shouldered hawks, woodpeckers, and warblers nest in the pinnacles of the oaks. Migratory birds use oak hammocks as critical stopover habitats, feeding on the rich insect life and berries.
Gopher tortoises, a species more commonly associated with upland environments, burrow near hammock edges also. At times, oak hammocks border wetlands or rivers, and provide corridors between water sources as well as islands of respite from the fires in the pine flatwoods.
These careful, slow growing ecosystems that rely on a careful balance of ecological threads are at risk due to shifting forces. The most significant threat is habitat loss due to development.
As higher ground is more desirable and Florida’s population continues to expand, these refuges are cleared for housing and infrastructure. This fragments the ecosystem and isolates populations.
Invasive species pose another major threat. Non-native plants such as air potato (Dioscorea bulbifera) and Chinese tallow tree (Triadica sebifera) can outcompete native vegetation and alter the structure of the forest canopy. Some areas are so well colonized with invasive species that a monoculture is created.
There are also invasive animals that have significant impacts. Invasive feral hogs damage the forest floor by turning the soil by rooting, and wallowing. This destroys sensitive native plant communities that rely on balanced soil structure. These exposed areas also become more susceptible to erosion. These areas are often colonized by invasive plants such as Cesar weed (Urena lobata) which has been transported by hitching a lift in the fur of the wild hogs.
Climate change adds further stress. Shifts in rainfall patterns and increased temperatures can impact the range of oak hammocks or increase their susceptibility to pests and disease. Additionally, sea level rise and saltwater intrusion threaten coastal hammocks, particularly those growing on dune ridges near shorelines.
The oak hammock is a verdant, lush oasis of shade and biodiversity that is filled with life. Their ecological value, aesthetic beauty, and cultural importance necessitate preservation. Through conservation efforts, responsible land-use planning, and invasive species control, we can protect these treasures for the enjoyment of many.
David Outerbridge is director of UF/IFAS Extension Lee County. Contact him at douterbridge@ufl.edu.
To reach DAVID OUTERBRIDGE, please email news@breezenewspapers.com