Our Tropical Rainforest
OverviewMost of the natural vegetation of American Samoa fits into the category of tropical rainforest. Tropical rainforests are found throughout the world in areas of warm climates and sufficient to plentiful year-round rainfall. The Samoan tropical rainforest originally extended from just inland of the shore up to the summits of the highest mountains, except on those peaks where soil factors or weather factors have created scrubby vegetation in which life forms other than tall trees are predominant.
Students will be able to:
1. Define the vocabulary terms tropical rainforest, native, and endemic.
2. Identify five different tree species that live in American Samoa's tropical rainforest ecosystem.
3. Describe how our actions can threaten the health of our tropical rainforest ecosystem.
4. Learn about the role of the National Park of American Samoa in conserving our tropical rainforest.
One of the significant characteristics of tropical rainforests is high species diversity. Tropical rainforests are home to the majority of the world’s plant species. The flora of Samoa (the sum of the plants occurring in the archipelago) comprises about 550 native flowering plants, 215 fern species, and 13 fern ally species. About two thirds of these species are found in American Samoa. They can be divided into two types: endemic species (restricted to Samoa) and indigenous species (not restricted to Samoa).
The level of endemism of the native flowering plants in Samoa is estimated to be about 30% at the species level. Areas to the west such as Indonesia and Malaysia have much larger floras, a characteristic that can be attributed to their much larger areas, older age, and to what is called a “filter effect” in which chance and distance limit the number of species successfully reaching (and becoming established in) the faraway islands of Polynesia.
Another characteristic of tropical rainforests is the presence of unusual life forms. One of the most unique is that of epiphytes, plants that grow on trees, usually in order to get closer to the sunny canopy, but which do no harm to the “host” plant. When the conditions in the forest are extremely wet, as they are in the montane forest and cloud forest, epiphytes may even cover the trees. The most prevalent group of epiphytes is the orchid family, which comprises 65 species in American Samoa (many of which are not epiphytes but grow on the forest floor). Epiphytic ferns comprise the second most abundant group of epiphytes in the Territory.
The vegetation of Samoa is not homogenous, because zones of plant combinations can be discerned. It is difficult, however, to make sense of the differences we can see in the pattern of plants, and even more difficult to determine where the boundaries are between the different types of vegetation. The vegetation can generally be divided into a number of categories called “plant communities.” A plant community is a unit of similar vegetation distinguished from other plant communities by its structure and habitat. Eight natural plant communities can be recognized in American Samoa: (1) Littoral Strand, (2) Marsh, (3) Freshwater Forest, (4) Mangrove Forest, (5) Lowland Forest, (6) Montane Forest, (7) Montane Scrub, and (8) Summit Scrub. Several other disturbed types of vegetation can also be recognized.
Littoral Strand comprises the forest, scrub, and herbaceous zones growing directly on the seashore. Its component species are seawater dispersed and widespread on Pacific shores. Marsh, Freshwater Forest, and Mangrove Forest are classified as “wetlands,” but they comprise only a small percentage of the overall land area of American Samoa. Lowland and Montane Forest together comprise the “tropical rainforest” that once covered over 90% of Samoa.
Montane Scrub and Summit Scrub are unique. Montane scrub comprises the vegetation on the summits and upper slopes and ridges of Tutuila on geologic areas called “trachyte plugs,” which have a characteristic chalky soil that appears to cause stunted vegetation. Its scattered, stunted trees are embedded in a dense matrix comprising shrubs, ferns, and lianas. Epiphytes also abound in this community, sometimes covering the stunted trees.
A plant community that is in equilibrium with its environment, when its form and flora change little with time (barring major disturbance), is called a “climax plant community.” A climax forest is often confused with “primary forest,” which is the natural and undisturbed forest in an area. However, nearly all of the mature forests in Samoa are better described as climax rather than primary forest, since in ancient times much of the interior of the islands was inhabited and cleared for cultivation before being abandoned early in the European Era (after 1830).
Native tropical forests serve several important functions in American Samoa and throughout the tropics. First, they provide protection from soil erosion, which leads to a higher quality of drinking water. Second, they are home to a majority of the world’s plant and animal species. Third, they serve as home to animals, such as pigeons and flying foxes, and plants, such as Tahitian chestnut (ifi), that have traditionally been a major part of the local diet.
Unfortunately, the forests of American Samoa are seriously threatened. The most dangerous threats, direct or indirect, are the actions of people. Due to rapid population growth, the existence of communities such as mangroves, wetlands, and some kinds of lowland forest have been nearly eliminated. Alien plant and animal species also threaten to out compete and reduce the abundance of some native species.
1. Large piece of white paper, 15 ft. x 3 ft.
2. Pencil and paper for each student
3. Index cards
4. Chalk or whiteboard
6. Meter stick
7. Art Whistler's The Samoan Rainforest
Handouts & Worksheets
1. Plants of the Rainforest Rubric
Introduce Inquiry Question?
What is a tropical rainforest?
Ask: Have you ever heard the term tropical? If yes, where and how did you hear about it? If not, what do you think it means? Write the term on the board and explain the word to understand its meaning. Explain that tropical refers to climate found in regions close to the equator characterized by high temperatures and no winter snow. Tell students that tropical ecosystems show a high level of diversity among the living things that live there.
Ask: Have you ever heard the term rainforest? If yes, where and how did you hear about it? If not, what do you think it means? Write the term on the board and explain the word to understand its meaning, as you did with tropical. Explain that rainforest refers to a forest that receives a high amount of rainfall. To illustrate the concept of rainforest, show students the images of the National Park of American Samoa’s native rainforest.
Activity 1: Rainforest Mural
Have students arrange their seats in a circle. In advance of the lesson, write these plant names in five columns on the board: 1) niu (coconut); 2) lau fala (pandanus); 3) nonu (noni); 4) ifilele; 5) asi. Hang the piece of large paper in a part of the classroom where students can work on it with ease. Draw light pencil marks on the paper to divide it vertically into five segments.
Discuss with students what they know about rainforests. Review these facts: rainforests are usually found in the tropics and they receive from 4-8 meters of rain per year, five times the rainfall of some states in the United States. Use a meter stick to visually demonstrate this amount. Rainforests are home to 50% of the 5-10 million species of plants in the world. Ask a volunteer why plant species are important. Inform students that plants are used as a vital ingredient in many medicines; quite a few cancer treatments, for example, are dependent on plants found in the rainforest. Furthermore, many plants in the rainforest have yet to be identified and studied, so we don't yet know their potential value. Discuss why public awareness of rainforest plants is important to the continuation of their existence.
Divide students into five groups. Inform them that they are going to make a mural to raise awareness of some species of plants in the rainforest. Assign one of the tree species columns on the board to each group. Ask students to assign each student a role— Leader, Researchers, and Artists.
Direct groups to find each of their plant species on the list, using Art Whistler’s Tree book. Researchers should list down on an index card a fact about their tree species and two of its main uses in Samoan culture. Artists should draw a picture of their tree species onto the group's space on the mural paper. Ask groups to talk over the main uses of the plant so that everyone understands its uses. Caution them that if they do not understand a use, they should not list it and the Leader should use classroom resources, such as a dictionary, to help clarify the information they have found.
Each Leader will present his or her group's segment of the mural, explaining their tree species and their uses. As a class, come to a consensus about a title for the mural (e.g. “Some Important Plants of the Rainforest,” “We Need These Plants.”)
Conclusion with Inquiry Question
What is a tropical rainforest?
Encourage your family and friends to plant native trees around your home and in your community. Talk to them about the various uses for native Samoan trees.