General Characteristics
Bottomland hardwoods are one of the lowest and wettest types of
hardwood forests. They are generally found along the edges of lakes and rivers and in sinkholes. Bottomland forests represent a transition between drier upland hardwood forest and very wet river floodplain and wetland
forests. While trees and plants in this ecosystem cannot tolerate long periods of flooding (as in a swamp), they are flooded periodically when water levels rise. There is much variety among bottomland hardwood
forests, based on slope of the land, soil type, water availability, and climate. Deciduous trees of various ages grow in these forests. They often grow in distinct layers, with an overstory of dominant tree species
(core species), an understory of companion trees and shrubs, and a groundcover layer of herbaceous plants. These diverse communities are known for their species richness and may support from two to five times more
species of both plants and animals than either pine forests or upland hardwood forests. While the types of plants and animals found across Florida vary, there is no "peninsula effect" (declining number of species from
north to south) in the bottomland hardwood forests. Bottomland hardwood forests constantly change and are altered over time by natural disturbance and climatic changes. They are characterized by infrequent,
low-intensity fire, poorly to well-drained soils, and frequent flooding. Bottomland hardwoods may be underwater part of the year and completely dry during droughts. When wet, they provide important habitat for young
fish, insects, crayfish, worms, and micro-organisms. Nutrients increase during these periods as floodwaters drop sediment and organic matter. When dry, the soil is able to release stored-up nutrients and take in oxygen.
Soil within bottomland hardwoods varies from clay-rich organic mixtures in the panhandle and northern peninsula, to coarse, nutrient-poor sands in south Florida. The central region and southern peninsula have
intermediate, sandy soil with some clay deposits. The nutrient content of the soil is determined by the amount of leaf litter and other organic matter present on the forest floor. Because the forest is full of
deciduous trees there is much leaf litter and other organic matter on the ground. This increases the nutrient levels of the soil as the litter decays. While most Florida soils have low nutrient content and are not as
rich as soils farther north, bottomlands have some of the best soils in Florida. Forests with nutrient-rich soils generally have a greater variety of plant species.
Wildlife of Bottomland Forests
Nutrient-rich hardwood forests also support more wildlife, since these ecosystems have lots of flowering and fruiting plants and an abundance of natural cover for
animals. Both food and shelter are available year-round. A wide variety of ground birds and songbirds use bottomland hardwoods. Wild turkey, chuck-will's widow, woodcock, and many ducks can be seen in these habitats.
Wood ducks like to nest in the trees in bottomland forests. Also using the forests are several species of woodpeckers and owls, wood warblers, cardinals, blue jays, vireos, wrens, and others. Mammals found in
bottomland ecosystems may include white-tailed deer, black bear, wild hog, raccoon, skunk, fox, otter, mink, gray squirrel, and fox squirrel. The presence of these mammals may be limited by the size of the forest, since
larger animals need more space. Several species of snakes live in these hardwood forests including coral snake, cottonmouth, eastern diamondback rattlesnake, and many non-poisonous varieties. Box turtles and mud
turtles live in the moist areas, while many frogs, skinks, and fish breed in the shallow waters and vegetation. Hardwood trees are also preferred nesting sites for various cavity dwellers, such as owls, woodpeckers,
and squirrels. Along with the resident species of wildlife, many migrating birds and waterfowl use bottomland hardwoods each year. Several threatened or endangered species may be found in these habitats, including the
Florida panther and both Bachman's and Swainson's warblers. Environmental Factors
Environmental factors such as floods, fires, and climate changes affect the composition of plants within natural communities. Bottomland hardwood forests are a complex natural community with many beneficial
ecological functions. Regular flooding along river basins creates a natural flow-through system that connects the headwaters of rivers to coastal estuaries. Nutrients, silt, and tiny organisms move between waterways
within the system. Flooding of low-level areas in bottomland hardwoods provides a place for excess water to go, which helps to control major flooding of main river channels. The wet underground soils also help to filter
out pollutants and recharge the water table. The Role of Flooding
Flooding plays a major role in maintaining bottomland hardwood hammocks. Changes between wet
and dry periods help to maintain the health of the ecosystem and eliminate species that cannot tolerate both. Frequent flooding in bottomland forests promotes the storage of water within organic matter for use in dry
periods. It also slows down the decay of vegetative matter, allowing nutrients to build up. Floodwaters bring sediments and nutrients that settle into the soil. During drought periods leaf litter decays quickly
because the soil is exposed to oxygen. This allows the nutrients to be released so plants and trees can use them. Floodwaters also help many trees to disperse their seeds. Some seeds are carried directly by water,
while others may be eaten by fish or other wildlife and dispersed to new locations indirectly. Baldcypress seeds are dispersed exclusively by water. The trees and plants found in this ecosystem are well adapted to the
presence of water. Some species have physical features that allow them to get enough oxygen during wet periods. For example, baldcypress have knees that help the trees to take in oxygen, even while growing in water. The Role of Fire
Wildfires do not affect bottomland forests very often, but they still contribute to changes in the trees and plants that grow there. When the
forest is dry enough to burn, the fire can remove built-up leaf litter and groundcover and release nutrients back into the soil. The dead leaves are fairly moist and burn slowly, unlike the dry, flammable leaf litter in
sandhill or scrub forests. Infrequent fires allow the establishment of many slow-growing hardwoods. However, long-term exclusion of fire can lead to an excessive accumulation of plant material. This
build-up of organic matter becomes fuel during drought periods, which may result in high-intensity fires that damage the tree canopy and endanger wildlife and humans. If the fire is severe enough, it may destroy the
dominant hardwoods and provide opportunity for other types of plants and trees to establish in the area. This would change the ecosystem from bottomland hardwoods to a community of faster growing pioneer species, such
as pines and herbaceous plants. Geographic Distribution
In the bottomland forests of the panhandle and far northern Florida, the trees resemble the ones
growing in the Appalachian Mountains and Piedmont regions farther north. Dominant trees here are a mixture of hardwoods, such as American beech and white oak along with various evergreens. Fewer plants grow on the
ground than in hardwood stands farther south. Hardwood forests in northern Florida have one of the largest numbers of species per unit area in the United States. The central region and southern peninsula of Florida
have more evergreen species, denser groundcover, and many varieties of ferns and epiphytes (air plants). Some of the most common dominant trees are live oak, water hickory, swamp chestnut oak, and red maple. The
southern regions of Florida are characterized by many tropical species of trees and plants and the largest number of epiphytes in the United States. These include numerous ferns, bromeliads, and orchids. Dominant trees
in south Florida bottomland forests are most often live oak and cabbage palm. Human Impact
For hundreds of years Florida was characterized by vast forests of
longleaf pine and wiregrass, with bottomland hardwoods where the soil and climate allowed them to grow. Many of the ancient hardwood communities have been replaced with other land uses or forest types, either
naturally or because of human activity. As populations have increased in Florida, bottomland hardwood forests have been drained and used for agricultural purposes or residential development. Water from bottomland
forests is sometimes pumped for irrigation of agricultural crops. This may lower the water levels and damage the health of the ecosystem. Runoff from agricultural and urban areas has had a serious impact on the water
quality and health of many bottomland forests. Excessive amounts of nutrients within the water may result in low oxygen levels and die-offs of fish, insects, micro-organisms, and plants.
Summary
Bottomland hardwood forests represent a rich and diverse ecosystem with many benefits to the environment, humans, and wildlife. These beautiful natural communities help to maintain healthy
water systems, fertile soil, and habitat for numerous species of wildlife and must be carefully managed and protected to ensure their preservation. While bottomland hammocks may be
found scattered throughout Florida, some good examples of these ecosystems may be seen in Ichetucknee River State Park, O'Leno State Park, Apalachiocola National Forest, San Falasco Hammock, Suwannee River State Park,
Dead Lakes State Recreation Area, Wakulla Springs State Park, St. Marys National Wildlife Refuge, Faver-Dykes State Park, Silver River State Park, and the Myakka River State Park. |
