Sizing up reserves

If you wanted to create a tropical rain forest reserve in South America that was large enough to protect most of the species that live there, how big would the reserve have to be? No one really knows for sure, but scientists working in Brazil may have an answer sometime in the next few years These scientists are in the midst of a 20-year study to find out what happens when parts of a rain forest are cut down and how the use of the remaining forest affects the plants and animals that live there. By looking at some of the data these scientists have collected so far, your kids will discover some of the ways tropical rain forest destruction affects certain species. And they'll also learn some of the ways species in a rain forest community interact and how much space it might take to preserve them.

Before you get started, copy the diagram in the margin onto a chalkboard or a sheet of easel paper. Then begin by having the kids imagine that a road is going to be built right through the middle of a huge section of tropical rain forest. Also, some of the forested land is going to bee converted into pastures for cattle and farmland for crops.

Ask the kids how life in the forest might be affected by these changes. (Some animals might be killed on the road; others might move into less developed areas; more development might come into the area because of the access the road provides, causing further destruction of the rain forest; entire species could become extinct.) List their answers on a chalkboard or sheet of easel paper.

After the kids have made some predictions, try the following demonstration to get them thinking about some of the other changes that can occur when parts of a forest are cut down. (This demonstration works best with a group of at least 20 kids.)

CHOPPING DOWN THE FOREST

Have the kids stand close together in a big group in an open area of the room. Tell them that each one of them is a tree, and together they represent a huge tract of undisturbed tropical rain forest. Have one child in the center of the forest describe what he or she sees when looking "through the trees." Can he or she see the forest edge? you? the rest of the room? Is there much light down near the floor? (Point out that, in many tropical rain forests, the canopy is so thick that little sunlight reaches the forest floor.) Then turn a small electric fan on low at the edge of the forest and ask the center child if he or she can feel a breeze.

Now "chop down" part of the forest by having some of the kids near the edge move aside. (Pick kids from each "side" of the edge.) Ask the center child to report any changes in what he or she can see. Turn the fan on low again, and ask if the center child can feel a breeze. Once part of the forest has been cut down, the center child should notice more light near the floor, should find it easier to see through the trees to the edge of the forest, and should be able to feel a much stronger breeze. If none of these changes occur, chop down some more of the trees at the edge.

After the demonstration, ask the kids what has happened to the area that used to be the middle of the forest. (It's now at or near the forest's edge.) Then ask them how this shift from forest middle to forest edge might affect the life within the forest. Point out that many of the plants and animals that were adapted to living in the middle of the forest might not be able to survive at the forest edge. Can the kids think of reasons for this? (Changes in temperature, moisture level, air circulation, and so on would occur at the forest's new edge. For example, the former "middle of the forest" would now receive much more sunlight than before, raising the overall temperature of the area. The area would also receive more wind, which could make the new edge drier than when it was part of the forest's middle.) Again, list the kids' answers on the chalkboard or a piece of easel paper.

Now tell the kids that some scientists in Brazil are studying what happens to the life in a rain forest when part of the forest is cut down. Then, using the information under "What's Happening in Brazil?" on page 404, explain the Biological Dynamics of Forest Fragments Project. Make sure the kids understand that the forest in the area where the scientists are working was going to be cut down anyway. But by directing where the loggers cut, the scientists have been able to create reserves, or forest "islands," of specific sizes. Show the kids the diagram you copied earlier to give them a better idea of what it is these scientists are doing.

Also explain that the scientists are trying to figure out how big a reserve might have to be in order to protect as many of the species that live in a rain forest as possible. For example, could most of the plants and most of the birds, mammals, amphibians, and other animals found in the Brazilian rain forest survive in a 2500-acre (1000-ha) reserve or would it take a 25,000-acre (10,000-ha) reserve? Or one that's even larger? (Note: Explain that new research shows that some species are so specialized that they may become extinct if even a small area in certain parts of a rain forest is destroyed.)

Afterward pass out copies of the charts and graphs so the kids can see some of the things that have happened in the isolated reserves of the Forest Fragments Project. Explain that the charts and graphs show real data that the scientists have collected from 2.5-acre (1-ha) and 25- acre ( 10-ha) reserves during the reserves' first two years of isolation. Then pass out copies of page 407 and have the kids answer the questions using the charts and graphs.

When the kids are finished, ask them if any of the changes they predicted earlier occurred in the reserves the scientists studied. Talk about the changes, then go over the answers to the questions (see the end of this activity). As you go over the answers, discuss the fact that all animals and plants depend on specific physical conditions in their habitats in order to survive. For example, when light conditions changed in the forest areas the scientists were studying, many of the butterfly species that had lived in the forest's interior disappeared. And trees that were once in the interior were damaged and even knocked over by increased wind.

Also point out that all animals and plants depend on other species in order to survive and reproduce. For example, monkeys that eat fruit were absent or very rare in the reserves because many of the fruit trees they depended on had been chopped down. (There were still some fruit trees left, but not enough to support the monkeys year round.)

You might also want to explain that animals need a certain amount of space in order to find all the food and water they need to survive. For example, herds of white-lipped peccaries need thousands of acres. (For more about how much space certain animals need, see "A Home in the Range" on pages 43-45 of NatureScope: Amazing Mammals-Part I.)

Finally, ask the kids if they think either the 2.5- or 25-acre ( 1- or 10-ha) reserve would be large enough to preserve the variety of life found in the Brazilian rain forest the scientists are studying. Tell them that even though the Forest Fragments Project is far from over, scientists are predicting that a Brazilian rain forest reserve would probably have to cover millions of acres in order to protect most of the species that live there.

WHAT'S HAPPENING IN BRAZIL?

In 1977, Dr. Thomas Lovejoy of World Wildlife Fund (WWF) was looking for a place to try an experiment. He wanted to find out what happens when a tropical rain forest is separated by roads, pastures, and other human developments. He also wanted to try to find out how much forest it might take to make a reserve large enough to support the plants and animals that normally live in a rain forest.

Lovejoy knew that, under Brazilian law, any land development project in the Amazon region of Brazil must leave half of the area forested. He discovered some land that was going to be converted to pasture and asked if he could direct which parts of the total area would be converted to pasture and which ones would be left undisturbed. The local government, Brazilian scientists, and the ranchers agreed to cooperate.

In 1979, scientists from WWF and Brazil's National Institute for Amazon Research began mapping out more than 20 areas within the virgin rain forest. These areas would eventually become reserves of varying sizes: 2.5, 250, and 2500 acres ( l, 10, 100, 1000 ha). There was also one 25,000-acre ( l 0,000-ha) reserve. Then, with help from more scientists and some of the ranchers, they obtained a "before" picture of each future reserve by taking an inventory of the plants and animals in each one.

Finally, in 1980, the ranchers started cutting down the forest. The reserves, once part of a continuous forest, became isolated "islands" of trees. And the scientists immediately started monitoring the changes that occurred in each "island." So far only 10 of the reserves have been isolated or separated from the continuous forest. The scientists are planning to continue the experiment until at least l999.

BRANCHING OUT: MEASURING THE DIFFERENCE

Temperature variation between the edge of a forest and its interior occurs in all forests-not just in tropical rain forests. To help your kids see how temperatures vary between the inside and outside of a forest, take them to a nearby woodlot and have them measure the temperature at the edge of the woods, just inside the woods, and 50 feet ( l 5m) or more into the woods.

You can also measure differences in evaporation rate and soil moisture. To get an idea of differences in evaporation rate, hang one wet cloth inside the forest and one outside and see how long it takes each to dry. And to determine soil moisture differences you can just feel the soil both inside and outside the forest. (In general, soil in a forest holds more moisture than that outside a forest.) After taking your measurements, discuss the fact that many of the animals and plants that are adapted to conditions within a forest often can't survive outside a forest, even at its edge.