On our Central America cruise we spend time inside the neotropical rainforests of Costa Rica and Panama when we visit places such as Manuel Antonio National Park, Corcovado National Park, and Barro Colorado Island in Lake Gatun, Panama.
Tropical rainforests are found near the equator where there is more direct sunlight hitting the land and sea than anywhere else. The heat causes evoporation, the warm water-laden air rises, and when it cools, condenses taking the form of droplets and clouds form. The clouds then produce rain, and near the equator where tropical rainforests are found, it rains more than ninety days a year with strong sun usually shining between the storms. The water cycle repeats often along the equator.
The main plants in this ecosystem are trees, and in the rain forest, some rain never gets past the trees to the shorter plants at lower levels and the ground below. Tropical rainforest trees can reach heights of more than 164 feet, and at this height, often form a canopy through which little light passes. The forest understory therefore receives at times only 2% of the original sunlight.
The temperature in a rain forest rarely gets higher than 93 °F (34 °C) or drops below 68 °F (20 °C); average humidity is between 77 and 88%; rainfall averages bewteen 50 to 260 inches (125 to 660 cm.) yearly. There is usually a brief season of less rain where the rainforest receives as little as 10 centimeters / 4 inches of rain, and this is a very stressful time for plants and animals alike. It has been thought that in the rain forests, 50% of the precipitation comes from its own evaporation, but recent studies are starting to change that idea. What we do know, however, is that a lot of the rain that falls, never reaches the ground. Instead it stays in the upper levels, caught by the leaves of the trees themselves, the vines which have used the trees as scaffolding to reach the sunlight, or the innumerable species of epiphytic plants which grow along the branches or trunks.
The average temperature of a rain forest is about 77° Fahrenheit (25°Celcius) year-round, and never drops below 64° Fahrenheit (17° Celcius). Rain forests feel so hot because of the high humidity, more than actaul temperature. The other reason is because of their location near the equator where there is more solar radiation. Tropical rainforests are never found in climates which have temperatures that drop below freezing.
The plants that make up the understory of a rain forest have adapted to the small amount of sunlight that they receive and the water runoff from the dripping leaves above.
When the rainforests were first explored by outsiders from northern climes, they were amazed by the dense growth, trees with giant buttresses, vines, and epiphytes. It was interpreted to indicate the presence of rich soils, filled with nutrients. Today we know that the soil of the tropical rainforests is shallow, very poor in nutrients and almost without soluble minerals. Thousands of years of heavy rains have washed away the nutrients in the soil. We know now that nutrients generally stay in a tropical rainforest ecosystem by being recycled and and used immediately by living matter and in a thin, barely perceptable layer of decomposing leaf litter. Various species of decomposers like insects, bacteria, and fungi make quick work of turning dead plant and animal matter into nutrients. These nutrients are taken up the moment they become available to the living plants. A study in the Amazon rainforest found that 99% of nutrients are held in root mats of living plants. When a rainforest is burned or cut down the nutrients are removed from the ecosystem. The soil can only be used for a very short time before it becomes completely depleted of all nutrients.
Tropical rainforests support 7% of the earth’s species on less than .5% of its land, and on our Costa Rica and Panama cruise we are indeed fortunate to visit some of the finest and well-protected tropical rainforests in Central America. Tropical rainforests produce 40% of Earth's oxygen and cover about 6% of the earth's surface, yet they are home to over half the world's species! Come and expore them with us!
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