By Jerilyn WatsonFrom VOA Learning English, this is Science in the News. I'm Faith Lapidus.And I'm Shirley Griffith. This week, we tell about Everglades National Park in the American state of Florida.When many people think of Florida, images of sandy coastlines or fun theme park rides come to mind. Yet about an hour south of Miami lies a natural wilderness different from anywhere else in the United States.Everglades National Park is the largest subtropical wilderness in the country. The park is home to several rare and endangered species. It is also the third largest national park in the lower 48 states, after Death Valley and Yellowstone. Each year, more than one million people visit the Everglades.In 1947, President Harry Truman spoke at the official opening of Everglades National Park. He said the goal of creating the park was to protect forever a wild area that could never be replaced.The Everglades is considered one of the great biological wonders of the world. The expansive wetlands stretch across more than 600,000 hectares. It is a place where plants and animals from the Caribbean Sea share an ecosystem with native North American species.Nine different environments exist within the Everglades. They include mangrove and cypress swamps, estuaries and coastal marshes.In the 1940s, Marjory Stoneman Douglas wrote a book called, "The Everglades: River of Grass." She described the area as, "the liquid heart of Florida."Unlike most other national parks, Everglades National Park was created to protect an ecosystem from damage. The Everglades is home to about 15 species that federal officials say are threatened and endangered. They include the Florida panther, the American crocodile and the West Indian manatee.In addition, more than 350 bird species and 300 species of fresh and saltwater fish live within the park. The Everglades is also home to 40 species of mammals and 50 reptile species.Visitors to the Everglades will see many exotic plants. They include what is said to be the largest growth of mangrove trees in the western world. Gumbo-limbo trees, known for their peeling red skin, strangler figs and royal palms are also among the area's plant life. The country's largest living mahogany tree also lives in the Everglades.Sawgrass grows in some areas of the park. Be careful – sawgrass is very sharp, with teeth just like a saw. It can grow up to four meters tall.With about one and one-half meters of rainfall each year, plants and trees never stop growing in the Everglades.The dry, winter season is the favorite of most visitors, when insects like mosquitoes are less of a problem. The rainy season lasts from June to November. There are many ways to explore the Everglades. Visitors can see alligators while hiking the Anhinga Trail.The Everglades is one of the only places on Earth where freshwater alligators and saltwater crocodiles live in the same area. Visitors using canoes or airboats are likely to see large groups of wading birds like the wood stork or the great blue heron. It is even possible to see flamingos in the Everglades.Some visitors might enjoy riding bicycles through Shark Valley. Others may want to move slowly through shallow waters where they can see insects and wildlife up-close. Park guides also lead visitors on tram rides.Experts say changes to the Everglades are threatening several different kinds of wildlife. They say the threats are a result of actions the United States government began more than 50 years ago, and settlers began even earlier.The National Park Service says that early colonial settlers and land developers believed the Everglades had little value. The settlers had plans to remove water from the area. In the 1880s, developers began digging canals to reduce water levels.At the time, they did not understand the complexity of the Everglades' ecosystem. As a result, they were not prepared for all the work and caused environmental problems. The ecosystem, however, was able to survive.Even larger efforts to drain the wetlands continued between 1905 and 1910. Farms were built on large pieces of land. This led to increased development, with more people moving to the Everglades and also more visitors.More changes came in 1948. At that time, Congress approved the Central and South Florida Project. As part of the plan, the Army Corps of Engineers built roads, canals and water-control systems throughout South Florida.The project was aimed at providing water and flood protection for developed areas and agriculture. Workers built a huge system of waterways and pumping stations to control the overflow of Lake Okeechobee, north of the Everglades.Today, some of South Florida's early wetland areas no longer exist. Populations of wading birds have been reduced by 90 percent. Whole populations of animals are in danger of disappearing. The endangered creatures include the manatee, the Miami blackhead snake, the wood stork and the Florida panther.In recent years, environmental experts have learned about the damage to the Everglades. Some experts say the balance of nature there has been destroyed.Thirteen years ago, Congress approved a plan to restore and improve the Everglades. Federal, state and other organizations are partners in the Comprehensive Everglades Restoration Plan. Thomas Van Lent is a scientist with The Everglades Foundation, a not-for-profit group. He says the restoration efforts are moving forward. For example, many roads have been removed.Early in 2010, ground was broken on the Picayune Strand Restoration Project. The goal of the project is to re-establish natural water flow across more than 22,000 hectares of wetland. Workers removed water from that area in the early 1960s. At the time, the goal was to develop the land for homes. However, the development failed, and healthy wetlands were harmed.Project organizers hope to re-create wetlands in Picayune Strand and nearby lands by redirecting the flow of water in that area. At the same time, they are seeking to re-establish natural water flow to the Ten Thousand Islands National Wildlife refuge.Project officials are working to improve the size and ecosystems of nearby lands. The area includes the Collier Seminole State Park and the Florida Panther National Wildlife Refuge. If the goals are met, the project should help threatened and endangered animals.For example, the population of one big cat has been falling in recent years. Panthers once existed in much greater numbers. But too much hunting, loss of panther homelands and vehicle strikes have reduced their population.Wildlife experts are working to increase the number of panthers and other animals at risk. Scientists also want to remove Burmese pythons from the Everglades. Pythons have no natural enemies in the area.No one knows how many of these huge snakes live in and around the Everglades. Burmese pythons are native to Southeast Asia. Python owners apparently left their unwanted snakes in the Everglades years ago.Scientist Thomas Van Lent says pythons have been found along the sides of roads, as if thrown there from vehicles. Some of the creatures are big enough to eat bobcats and small deer.Mr. Van Lent says it is very difficult to find pythons in the Everglades, and hunting them has not proved very effective. "Other animals and people usually find the snakes when they step on them by accident," he adds. Other methods like trapping also have not solved the problem.The future of the wild, beautiful and sometimes threatening Everglades is not clear. However, efforts to protect the area are continuing so people from all over the world may continue visiting this biological treasure.This Science in the News was written by Jerilyn Watson. Our producer was June Simms.With Shirley Griffith, I'm Faith Lapidus. Read and listen to our programs on our website, 51voa.com. And you can see videos about Everglades National Park and projects to protect and improve the park at www.evergladesplan.org. Join us again next week for more news about science on the Voice of America.