The Tree of Land and Sea

This topic submitted by Audree Riddle ( riddleak@miamioh.edu) at 11:18 PM on 6/9/07.

This barracuda coasts above the corals at Molasses Reef, Key Largo, Florida.

Tropical Field Courses -Western Program-Miami University



“Oh! those mangroves. I never saw one that looked as if it possessed a decent conscience. Growing always in shallow stagnant water, filthy black mud, or rank grass, gnarled twisted, stunted and half bare of foliage, they seem like a crowds of withered, trodden-down old criminals, condemned to the punishment of everlasting life. I can’t help it if this seems fanciful. Anyone who has seen a mangrove swamp will know what I mean”(Davidson, 1998). The mangroves are unique species. A tree that is able to live in saltwater. On the coast of Florida, the mangroves are most plentiful. Striving in areas were the freshwater from the main land and the seawater meet. The different variances of salinity gradient in the water create three different optimal zones for the different species, red, white and black (Cummins, 2007). The three species live very close together, and it is common to find the unique roots, which will be discussed later, intertwine with one another. These trees do not only intertwine by themselves though, “you almost always find coral, mangroves and sea grasses together” (Davidson, 1998). The mangroves are an important part of the intertidal zone and the marine ecosystem.
There are some specific traits that all the mangrove species share, which include environment, root structure, salt extraction and reproduction. The mangroves are very intolerable of low temperatures thus leaving them only to thrive in the tropical and subtropical regions on the world (Burnie, 1988). Their location in the intertidal zone allows them to maintain their salinity balance using the freshwater run off (Arny and Law, There are different types of roots that ground these tropical trees to their environment; stilt-roots and breathing roots are just two of the many names for the different types. The stilt roots arch from the truck into the water (Burnie, 1988). Red Mangroves are the only mangrove species with the stilt-roots but more commonly are referred to as “prop” which is a distinctive feature that attracts artists to use them as subjects. The prop roots create a stilt like system of the trunk with roots sometimes coming from many feet high on the trunk. The high roots make it possible for the roots to take in oxygen from the air. There are large pores, which make this exchange of gasses, on the thick part of the root that is exposed in the air (Lodge, 1994). The stilt roots also have a partnership with sponges that grow on the roots which gives the mangrove nitrogen, and in return the sponges receive carbohydrates (Thomas, 2000). The breathing roots, which also go by the name pneumatophore or peg roots, grow up from the mud and come out above the water during low tide to collect oxygen (Blaxland, 2000). In these environments, the trees especially their roots play an important role to the animals that live in the area. Crabs eat the leaves on the trees and other animals such as snails, fiddler crabs, air breathing fish and marine birds take shelter in the mangrove swamps for protection (Mattson, 1991). The snails eat a great deal of algae off the seedlings, which if too much algae grows, the tree could be stifled. The air breathing fish, the mudskipper, is much like the mangrove living on both land and water (Blaxland, 2000). Due to deforestation by humans of these mangroves, the habitants are losing their home. Not only is the destruction of the mangroves destroying the home to hundreds of species, but the direct connection between land and sea (Maser & Sedell, 1994, 6). It is important because of this connection to understand the mangroves way of repopulating. Which like the majority of the other characteristics of the mangrove has a very interesting seedling process. The seedling grows on the parent, until the propagule, seedling, falls off the parent (Blaxland, 2000). The wind then carries the propagule from the parent’s location until it settles in the tidal waves. The mangroves use water to help pollinate along the shorelines (Tudge, 2005). The waves then carry the propagule to a shore with no significance to its parent location where it can quickly plant itself.
Whereas the large shallow roots which support the trees in the unstable soggy sediment is shared by the three types of mangrove, one of the most important features of the trees are the leaves (Mattson, 1991). Humans commonly use the leaves to distinguish the three species from one another. The same leaves also make it possible for these trees to live in salt water, because of the special salt glands that excretes briny water to get the salt out of the trees system (Thomas, 2000). The leaves of the
The first of the three species is the black mangrove, named for the color of its mature bark. The breathing roots of the black mangrove cover the interior of the mangrove swamps, where the tidal action is slower and the water is shallow when flooding occurs (Lodge, 1994). One is able to distinguish the leaves of the black mangrove by their thick blunt-tip and wedged base, white fuzzy like underside and visible salt grams on the surface (Petrides, 1988). Though the tree is able to intake in the salt water and filter it though the leaves, but the black mangrove is able to withstand high salinity within soil but does not thrive (Cummins, 2007). The flowers of the tree are white and bloom in early summer (Petrides, 1988). Also harvest from the black mangrove is “mangrove honey”, though it has had ups and downs in the market because of hurricane damages’ decease in availability the honey has always maintained high quality (Arny and Law).
The second of the three species is the red mangrove, named for the thin layer under the bark. The mangrove requires the strong “prop” roots for support in the outermost location in the mangrove swamps. This species of mangrove does not need to grow in salt water, though it does manage better in estuaries, where the seawater and freshwater meet (Lodge, 1994). In Florida, the Red Mangrove is considered a shrub reaching 20 feet in height with beautiful yellow flowers blooming in the spring (Arny and Law). The leaves of the red species like the black species has a blunt tip and wedged base, but are on occasion spotted with black on their green underside, not white (Petrides, 1988). The red mangrove even located far from the shore has a lower tolerance level in comparison to the black and white species, they plant themselves in less soil thus able to limit the soil salinity intake (Cummins, 2007).
The last of the three species is the white mangrove, named because it has the lightest bark though it is not white. This third species is the driest of the three remaining high in the mainland (Lodge, 1994). The leaves of the white mangroves are typically 2-3 inches long and the same color on both sides. A detail specific to the white mangrove leave are the paired leavestalk glands (Petrides, 1988). The leave is rounded on both the base and the tip. The leave from the paired leavestalk glands or nectaries excretes sugar. This tree also produces a small fruit which is buoyant making it very easy for them to reproduce along miles of shoreline (Arny and Law). Like the black mangrove, the white mangrove is able to live in water with a high salinity, but likewise does not thrive (Cummins, 2007). There is a fourth mangrove, buttonwood, without specific details, is a relative of the white mangrove. The buttonwood cannot take in as much salt thus is elevated to drier land and commonly used as a landscape peace in south Florida (Lodge, 1994).
Human effects like deforestation and changes in the salinity of the water have huge effects on the trees and cause dieback. The mangroves have an impact on the stability of the coastlines (Cummins, 2007). This is why policies have been created to help protect from the trimming of the mangroves and preserving the trees. It was stated in this Act that 555,000 acres of Mangroves inhabited Florida and 80 percent were privately owned or government property. It was their intent to “protect and preserve mangrove resources valuable to our environment”. Even thought it does continue one to discuss the economical value of the mangroves, which is an important reason to prevent illegal deforesting for private use (Mangrove Trimming and Preservation Act). Humans do not only affect the mangroves directly by cutting them down but they also have an effect on the salinity levels of the water that they grow in. Whereas each mangrove has its own tolerance level for salt intake as mentioned before, the soil salinity is so high in the isles that the trees are not able to filter the salt out, leading to a mangrove dieback.
As in any ecosystem, the alteration of a particular element can alter the lives of all things living in the system, this adds to the importance of maintaining the mangroves of South Florida and the Caribbean to help save species of marine life including the coral reef.

Bibliography

1996 Mangrove Trimming and Preservation Act, Florida Statutes, http://www.dep.state.fl.us/water/wetlands/docs/mangroves/mtpa96.pdf.

Arny, Nancy P. and Law Beverly E. University of Florida. Cooperative Extension Service. Institute of Food and Agricultural Sciences. http://www.sfrc.ufl.edu/Extension/pubtxt/for43.htm.

Blaxland, Beth. Mangroves. (2002). Chelsea House Publishers: Broomall.

Burnie, David. Eyewitness Books TREE. (1988). Alfre A. Knopf: New York.

Davidson, Osha Gray. The Enchanted Braid: Coming to Terms with Nature on the Coral Reef. (1998). John Wiley & Sons, Inc.: New York.

Lodge, Thomas. The Everglades Handbook: Understanding the Ecosystem. (1994). St. Lucie Press: Delray Beach.

Maser, Chris & Sedell, James R. From the Forest to the Sea: The Ecology of Wood in Streams, Rivers, Estuaries, & Oceans. (1994). St. Lucie Press: Delray Beach.

Mattson, Robert A. The Living Ocean. (1991). Enslow Publishers, Inc.: Hillside.

Petrides, George A. The Field Guide to Eastern Trees: Eastern United States and Canada. (1988). Houghton Mifflin Company: Boston.

Thomas, Peter. Trees: Their Natural History. (2000). Cambridge University Press: Cambridge.

Tudge, Colin. A Natural History of What Trees Are, How They Live, and Why They Matter: The Tree. (2005). Crown Publishers: New York.


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