Freshwater Swamps. Contents

Transcription

1 Freshwater Swamps Intermediate and Senior Contestants should study the following description to prepare for the Ecosystem Quiz station in the Florida 4-H Annual Forest Ecology Contest Contents Overview and History... 2 Environmental Factors effecting Freshwater Swamps... 3 Flora and Fauna of Freshwater Swamps... 5 Benefits of freshwater swamps Human impact of freshwater swamps Summary

2 Overview and History Introduction Wetlands, including both swamps and marshes, once covered over half of the land in Florida and were widely distributed throughout the Southeastern United States. While much of this land has been drained, dredged, or developed there are still approximately 3 million acres of wetlands remaining in Florida. It is estimated that as much as 10% of the state is currently swampland. These forested wetlands are found along rivers and streams, near lakes and ponds, and in low drainage areas throughout the state. They are often intermingled with other ecosystems and represent a mosaic of diverse habitats. The most common type of swamp in Florida is the cypress dome. It is called a dome because the tallest trees grow in the middle of the stand and shorter ones grow at the outer edges. This gives a dome appearance to the shape of the tree stand. Studies have shown that the trees in the middle grow faster than those at the edge, but the reason is still a mystery. Swamps may be classified as either river swamps or still-water swamps. River swamps have a surface flow of water at least part of the year. They generally have a shorter hydroperiod than still-water swamps with more frequent dry periods in between. River swamps are usually formed from the overflow of rivers or streams. In dry seasons, when water levels drop, these swamps have a mucky, peatlike soil. Swamps with short hydroperiods and flowing water have higher levels of dissolved oxygen and faster rates of organic matter removal. Additionally, water in river swamps is usually clearer and less acidic than in still-water swamps. Hardwood species are more likely to grow in these wetlands than in still-water swamps. About one-third of the swamps in Florida are classified as river swamps. Most of these are found in Northern Florida. Still-water swamps have little or no noticeable water flow. These swamps are fed by rainwater or groundwater and have a longer hydroperiod than river swamps. The soil remains saturated 2

3 most of the time and has layers of clay underneath. A layer of peat is usually formed on the floor of cypress swamps, the most common type of still-water swamp in Florida. Leaf and plant litter decomposes more slowly in water-logged swamps. A build up of organic matter can decrease nutrient availability and reduce the availability of oxygen to soil. Oxygen levels in the water are low so that few species can survive flooding for long periods of time. The trees and plants that do well in these swamps have adapted to flooding and low oxygen levels. Water in still-water swamps is murkier and darker than in river swamps, partly a result of the slow-moving water and partly because of tannins, substances that seep into the water from plant roots. These substances give the water a characteristic tea-colored look that earned it the name of black water. Environmental Factors effecting Freshwater Swamps There are four key environmental elements that help to define different types of swamps. Each of these environmental elements affects the plant and animal community of a swamp. All must be considered when defining what type of swamp is being studied. 1. Hydroperiod The first element is called the hydroperiod, or length of time that the land is flooded. Swamps are defined as fresh water, woody communities with water throughout most or all of the growing season. As transitional habitats between upland areas and aquatic systems, there is much variation among presence of water. Some stay wet most of the year while others have more frequent dry periods. A swamp s source of water affects its nutrient supply, hydroperiod, and flow rate. Swamps, which are fed entirely by rainfall, fluctuate with wet and dry seasons and have relatively short hydroperiods. A cypress dome is a good example of this type of 3

4 swamp. Swamps that are flooded most of the year, such as those with groundwater supply have a long hydroperiod. Swamps with long hydroperiods generally have fewer plant species and less vegetation than short hydroperiod swamps. 2. Type of accumulated organic matter and soils The type of accumulated organic matter is the second environmental element to consider. A cypress swamp will have different companion plants than a hardwood swamp. Each type of swamp represents a community of plants that grow well together and provide habitat for certain wildlife. As the plant community s change so do the insects and animals that will live there. Swamp soils are generally a poorly drained mixture of sand, organic matter, and clay that forms layers and slows down the seepage of water. Rainwater may collect and be held in place by pockets of clay in the substrate. The water will slowly leach down to the water table over a period of weeks or months. 3. Water Quality The third key element in defining swamps is water quality. The quality of water may be affected by the source of the water, the rate of flow, nutrient and ph levels, and a number of other factors. Swamp water is more acidic in some types of swamps than in others depending on the vegetation and the soils and geology that the water comes in contact with. For example, swamp water from sandy soils in pine flatwoods will be almost 10,000 times more acidic than swamp water that has been in contact with limestone. Swamps fed by deeper ground water, like springs and seeps, have clearer water than swamps fed with shallow groundwater or surface runoff. Bacteria that decay leafs and other plant parts that fall into swamps remove oxygen from swamp water. The shade from swamp trees hinders algae from putting back the oxygen; so swamps especially stagnate swamps, have low oxygen levels that limit the types of fish that can survive in them. 4

5 4. Fire The fourth element is the frequency of fire. Fire helps to define a swamp by controlling build-up of vegetation and affecting the type of plants and trees that will grow there. Many species, such as pond pine and titi, depend on occasional fires to regenerate. These species have developed adaptations to protect them from fire damage. Pond pine trees have a layer of thick, shaggy outer bark that protects the inner bark. After a burn both kinds of trees are quick to resprout from adventitious roots or shoots. All swamps burn at least occasionally; however, some may have fires only three or four times in a hundred years. Swamps that have frequent fires have less build-up of organic matter and support different species of plants than swamps with infrequent fire regimes. How often a swamp burns is largely determined by the type of fuel that is present and the length of the hydroperiod. Swamps with lots of peat will burn slowly for a long time. These low-intensity fires help to limit the build-up of flammable fuels and release nutrients back into the soil. However, slow burning fires in peat also kill many roots, and therefore, many plants. Fire is less common in drier swamps that have short hydroperiods. Organic matter decomposes faster in these environments so there is less accumulation of plant fuels. Flora and Fauna of Freshwater Swamps Trees and Plants Some of the factors that determine which plants grow in a swamp are its hydroperiod, fire history, geographic location, water quality, and level of human disturbance. The longer a swamp is filled with water, the more stressful conditions for become for plants.therefore, swamps with shorter hydroperiods tend to have a greater variety of species, while swamps with long hydroperiods may be dominated by only one or two species. Long hydroperiods are stressful because water covering 5

6 swamp soils hinders oxygen uptake by wetland plant roots. Many plants that can survive in swamps have developed unique adaptations for supplying oxygen to their roots. For example, cypress trees have developed pneumatophores, more commonly referred to as knees. Cypress knees are part of the root system that projects out of the water. They are thought to function like a snorkel, transporting air to submerged roots. Other adaptations for supplying oxygen to submerged roots are special roots called adventitious roots that grow out from the plant above the water and special spongy tissues called aerenchyma, which can transport air from plant parts above the water. For many swamp plants submerged roots are not a problem. Swamps are home to numerous air plants like Spanish moss, butterfly orchids, and several ferns. Tree trunks, old stumps and fallen logs also provide elevated growing sites. Geographic location and temperature range are also key factors in determining which plants will grow in a swamp. Certain species of epiphytes are common to South Florida swamps but are unable to withstand the colder temperatures of North Florida. Melaleuca and Brazilian pepper, invasive non-native tree species, are also limited to warm, South Florida wetlands since they cannot tolerate freezing temperatures. Cypress, the most common wetlands tree in Florida, is the dominant species in most swamps since it is highly flood-tolerant. However, cypress trees require occasional dry-downs to allow their seeds to germinate in the mucky, saturated soil. There are two types of cypress trees in Florida swamps. Bald cypress grows best in swamps along rivers and streams while pond cypress is found in still-water swamps. In areas of south Florida, for example Big Cypress Swamp and the Everglades, poor growing conditions stunt the growth of pond cypress. Cypress trees there only grow to about 10 feet tall and these wetlands are called dwarf or pigmy swamps. Cypress trees can grow up to 150ft tall and live over 500 years. Native Americans often used them for dugout canoes because of 6

7 their large size. Some canoes could hold up to thirty people. Early settlers logged much of the cypress timber from Florida swamps. The logs were floated down rivers, such as the Suwannee and the St. John s, and used for building homes and forts. Even into the early 1900s cypress wood was widely used for shingles, water pipes, and grave markers. Most of the cypress that is harvested today is sold as landscaping mulch and decorative lumber. Common swamp hardwoods include swamp tupelo, white and pop ash, loblolly bay, sweetbay magnolia, red maple, willow, sweetgum, and certain oaks. Common wetland plants such as cattails, arrowhead, yellow primrose, and pickerelweed with its bright purple flowers decorate the edges of the swamp. Drier areas feature shrubs like holly, wax myrtle, and gallberry. Together these plants form an interesting and diverse natural community. Not all of the plants that are found in Florida swamps are welcome residents. Several species of non-native trees and plants have managed to invade swamplands and threaten to displace much of the native vegetation. Melaleuca is one example of an invasive exotic tree that has already taken over thousands of acres of wetlands. These trees are both flood-tolerant and fire-resistant and they manage to recolonize easily and rapidly after a fire. This gives Melaleuca trees a competitive advantage over many native plants and allows it to spread very quickly. Other invasive plants in swamps include water hyacinth, water lettuce, and hydrilla, one of the worst invaders of wetlands in the Southeast. Old world climbing fern and para grass are two more non-native plants that have established in many forested wetlands and threaten the health and stability of the natural plant communities. Wildlife in freshwater swamps Swamps provide a variety of resources for wildlife including food, shelter, drinking water, and nesting sites. While a many animals can be found in swamps, most of these animals only use the 7

8 swamp part of the time. They are generally not life-long residents and often use neighboring habitats as well. Many insects, fish, reptiles, and amphibians need the still, swampy waters to reproduce. Others come to forage in the shallow water and wet, mucky substrate. In return, the wildlife act as seed dispersers and transporters of nutrients to other ecosystems as they move between habitats. Swamplands are home to many microscopic life forms such as insect larvae and tiny snails. These critters form the base of the food chain and are eaten by larger animals like fish and frogs. The food chain continues as still larger animals, such as birds and mammals, come to swamps to feed on the many frogs, lizards and snakes. These eerie-looking wetlands may seem still and quiet but they are actually teeming with wildlife activity. While swamps are flooded the aquatic animals may be spread out but during dry-down periods many of the tiny fish, insects, and amphibians are concentrated into small pools that continue to hold water. These refuge pools serve as prime fishing and foraging areas for herons, egrets, osprey, and kingfishers. A wide variety of birds may be seen in swamplands, especially during spring and fall migration times when many non-resident species stop for food and water to help them continue their journey. River swamps that border bottomland hardwood forests are particularly attractive to many birds because of the large population of insects that are found there and the abundance of nuts, acorns from the hardwoods. Other birds that commonly use freshwater swamps in Florida include white ibis, red-winged blackbird, boat-tailed grackle, wild turkey, woodpeckers, owls, warblers, and nine different species of herons. The Mississippi and swallow-tailed kites will only breed in swamps. Wood ducks nest in the buttressed trunks of cypress trees and hardwoods. Wood storks and several of the herons and egrets use swamps as rookeries. They can often be seen roosting in large groups and tending their noisy young. Bald eagles and short-tailed hawks soar through the skies in search of food. Roseate spoonbills 8

9 wade and forage along the edges of many South Florida swamps and the rare and unusual limpkin, a bird that is only found in North Florida and South Georgia, forages for snails along the edges of wetlands on its long, stilt-like legs. Swamps are important to many rare birds like the endangered wood stork and threatened bald eagle. In all, twelve species of swamp birds are considered rare, threatened, or endangered. Amphibians such as frogs and salamanders are often the dominant animals in still-water swamps. One reason still-water swamps are good frog habitat is that low oxygen conditions make it difficult for fish that prey on frogs to survive there. Since frogs and toads need water to breed they all spend at least part of their life cycle in wetlands. On a warm spring or summer evening the breeding calls of frogs may fill the night air around a swampy wetland. While river swamps have fewer frogs and lizards there are more arboreal, or tree-climbing species found there. Swamps are used by several snakes including mud snakes, water snakes, and the highly venomous cottonmouth. Tree snakes, an arboreal reptile, are also common in hardwood swamps. Several species of turtles may be found sunning along the edges or swimming in the shallow waters of freshwater swamps. There are a total of 15 species of reptiles and amphibians from Florida swamps that are currently listed as threatened or endangered. The American alligator was once listed as an endangered species in Florida but efforts to protect and rebuild alligator populations have been very successful. Today alligators are a common sight in Florida swamplands. Mammals that commonly use swamps include raccoon, rabbit, otter, bobcat, white-tailed deer, nutria, beaver, and several smaller rodents. Occasionally rare or endangered species like the Florida panther or black bear may be seen using the habitat. The mangrove fox squirrel and mink are two other endangered animals that are sometimes found in swamps. No discussion of the wildlife in Florida swamps would be 9

10 complete without mentioning insects. The slow-moving waters are important to dragonflies, mosquitos, and many flies and beetles that need water to breed. Their larvae stay in the water, or on the aquatic plants nearby, until they are ready to hatch and fly away. Fish eat the insects and their larvae while they are in the water. Many frogs, lizards, and snakes feed on the abundant insects as they hatch, or emerge. Since so many insects breed in these forested wetlands there are often lots of biting insects around swamps. Caution should be used when you visit these wetlands and insect repellant is a must! Benefits of freshwater swamps Freshwater swamps are valuable wetlands that offer many important benefits including flood control, groundwater recharge, pollution cleanup, wildlife habitat, and recreation. Many swamps are located alongside rivers and provide areas for storage of excess water during floods. Some swamps collect rainwater, runoff, and shallow groundwater during wet periods and help to recharge the aquifers beneath Florida during dry periods. Swamps also help to remove water pollutants. As water filters through wetland vegetation and soils, nutrients, sediments, and pollutants are removed. Wetlands improve water quality in several ways. For example, low oxygen levels in swamp water and soils promote the removal of nitrate-nitrogen through denitrification. Nitrate is formed from the combination of one nitrogen atom with three oxygen atoms. Free oxygen atoms like the ones we breathe are rare in swamp water. But swamp bottom bacteria can breathe with the oxygen atoms in nitrate. In this bacterial breathing process, nitrate is broken apart (denitrified) and the nitrate s nitrogen atoms are released to the air as a gas. Nitrate from human and animal wastes can leach into groundwater supplies and contaminate wells. Human babies are susceptible to nitrate poisoning, known as blue baby disease. High levels of nitrate in drinking water can prevent 10

11 oxygen from being carried through the blood and in severe cases babies turn blue from a lack of oxygen. Additionally, low oxygen levels and organic soils can promote other biochemical reactions that can detoxify other pollutants. Wetland plants also uptake nutrients for their growth. But plant material falling into swamp water is slow to decompose. This results in a build up of organic soils where nutrients are trapped. Wetland plants also slow water movement allowing pollutant particles to settle out. Scientists, engineers and biologists have long recognized the water quality improvement properties of wetlands and have created wetlands to help purify wastewater and storm water runoff. Swamps also provide critical habitat for many wildlife and serve as breeding and refuge areas for countless species. Plants, birds, fish, and invertebrates such as freshwater shrimp, crayfish, and clams require the habitats provided by swamps. Upland creatures like the Florida panther depend on food production from lowland swamps Additionally, freshwater swamps serve as a valuable recreation location for Florida visitors. Millions of people visit swamps each year to take part in activities such as bird watching, camping, fishing, boating, and hiking. Human impact of freshwater swamps As the population of Florida has grown many thousands of acres of swampland have been logged and drained for residential and agricultural uses. Much of the once wet and mucky land has been filled in and used for growing crops, grazing livestock, or building homes. Where swampland once was there are fields of sugarcane, citrus orchards, or pastureland. Much of the remaining wetlands have been polluted by run-off from farms and urban areas. More than 50% of the original wetlands in the state have already been destroyed. 11

12 Human activities have altered drainage patterns, destroyed wildlife habitat, and interfered with the natural filtration systems of the wetlands. The Everglades National Park is one example of a swamp that has been altered significantly by human activities. More than 1/3 of the land area in the Everglades is freshwater marsh and cypress swamp. Extensive draining, dredging, and canal-building has reduced swamplands and affected the natural draining and filtering processes of the ecosystem. Most of these activities were conducted before the Everglades became a National Park in Summary Freshwater swamps are classified according to four environmental factors: hydroperiod, soil, water quality, and fire. They are home to numerous plant species that are adapted to annual flooding, the most notable of which is cypress. Swamps also provide habitat for a diverse range of wildlife from insects to mammals, including 15 species of reptiles and amphibians from Florida swamps that are currently listed as threatened or endangered. Additionally, these forested wetlands provide valuable benefits to man. They act as natural water collection areas and help to recharge the water table and underlying aquifers. They filter out pollutants and purify the water that seeps down through them. They also help to control flooding and maintain water quality. Many swamps produce valuable timber and wood products while others are used for recreational activities like fishing and bird-watching. These special ecosystems are an important part of our Florida landscape and must be carefully managed and preserved to maintain their health and continued environmental benefits. Some examples of freshwater swamps in Florida may be seen at Blue Cypress Water Management Area, Collier-Seminole State Park, Fakahatchee Strand State Preserve, Highlands Hammock State Park, Tosohatchee State Reserve, Big Cypress National Park, and Everglades National Park. 12