Forests and Their Resources

Transcription

1 LESSON 2 Forests and Their Resources Guiding Question: How can resource managers strike a balance between the ecological and economic value of forest resources? List some of the ecological and economical values of forest resources. Describe the costs and benefits of the different methods of timber harvesting. Discuss the current levels of deforestation in the United States and in developing nations. Reading Strategy Before you read, preview Figure 8. Note any questions you have about it, and try to answer them as you read. Vocabulary even-aged, uneven-aged, clear-cutting, seed-tree approach, shelterwood approach, selection system, deforestation, old-growth forest Forests cover about 30 percent of Earth s land sur LESSON PLAN PREVIEW Differentiated Instruction Struggling students create a T-chart to help them understand the value of forests. Real World Students consider how logging could affect their own lives. Inquiry Students research deforestation patterns in various regions of the world Resources Outdoors Activity, How Much Lumber? Modeling Lab, Making Recycled Paper Real Data Online Lesson 11.2 Worksheets and Assessment Chapter 11 Overview Presentation Source: U.S. Geological Survey 330 Lesson 2 face, as you can see in Figure 6. Most of the world s remaining forests are either boreal forest or tropical rain forest. Temperate forests cover a much smaller area, in part because people have already cleared so many of them. Forests provide habitat for countless organisms; help maintain soil, air, and water quality; and play key roles in our planet s biogeochemical cycles. Forests also have long provided people with wood for fuel, construction, paper production, and other uses. Resource managers who manage public or private forests are called foresters. Forest management is called forestry. Foresters aim to balance the ecological importance of forests with the economic importance of forests as resources for wood products. Figure 6 Earth s Forests About 30 percent of Earth s land area is covered with forests (as indicated by the green areas). Most of Earth s forests are boreal forests in the north and tropical rain forests in the south.

2 Forest Resources Forest resources have great ecological and economic value. The complexity of forests makes their resources enormously important, both within their ecosystems and in the world economy. A 2005 survey by the United Nations showed that more than one third of the world s forests were used mostly for timber production. But forests provide a wide variety of other services and products, including conservation of biodiversity; protection of soil and water quality; maintenance of biogeochemical cycles; food; medicine; and social services such as recreation, tourism, education, and conservation of culturally important sites. In addition, some people live in forests and depend on forests for all their needs. Ecological Value Because forests are structur- ally complex, they provide many different habitats for plants and animals. As a result, forest ecosystems have great biodiversity. You can see the complexity of a mature forest s structure and the diverse habitats within it in Figure 7. In general, forests with a greater diversity of plants have a greater diversity of other organisms as well. And in general, mature forests, such as the old-growth forests remaining at Clayoquot Sound, have more biodiversity than younger forests. Forests also provide many vital ecosystem services. Forest plants help prevent soil erosion. They also help regulate the water cycle by slowing runoff, reducing flooding, and purifying water as they take it from the soil and release it to the atmosphere. Forest plants also store carbon and release oxygen, thereby helping to moderate climate. Because they fulfill so many ecological functions, forests are necessary for our survival. Canopy Some animals live in the dense treetop canopy. Leaf-eating insects there provide food for many bird species. Subcanopy Tree-dwelling mammals such as squirrels, sloths, and monkeys eat fruit and leaves in the canopy and subcanopy. Other animals use tree bark, branches, and trunks as places to feed, nest, and rest. Snag Snags are dead or dying trees. Insects feed on snags and then provide food for other animals. Holes in snags provide nest sites and shelter for many vertebrate species. Understory Understory plants, such as rhododendrons, and groundcover plants, such as ferns, provide varied habitats. Stems, leaves, and roots also provide food and shelter. Figure 7 Mature Forest Structure Mature forests have complex structures. The crowns of the largest trees form the canopy, and smaller trees beneath them form the shaded subcanopy and understory. Dead or dying trees, or snags, are valuable for nesting and shelter. Shrubs and groundcover grow just above the forest floor. Forest floor Much biodiversity is found on the forest floor, mostly as insects and decomposers. Forestry and Resource Management 331

3 ANSWERS Real Data : 130 million tons; 1980: 180 million tons; 1990: 250 million tons; 2000: 350 million tons (answers are approximate) : 38%; : 39%; : 40% 3. About 23% 4. Answers will vary. Real Data From Trees to Paper The invention of the movable-type printing press by Johannes Gutenberg in 1450 created a demand for paper that continues to increase even today. Because most fiber for paper production comes from wood, a high demand for paper results in a high demand for timber. Examine the graph and answer the questions. 1. Interpret Graphs About how many millions of tons of paper and paperboard were consumed worldwide in 1970? 1980? 1990? 2000? 2. Calculate By about what percentage did global consumption increase from 1970 to 1980? From 1980 to 1990? From 1990 to 2000? 3. Calculate According to the United Nations Food and Agriculture Organization, worldwide paper consumption was expected to be about 431 million tons in By what percentage was world paper consumption expected to increase from 2000 to 2010? Economic and Medicinal Value The use of forest resources is essential to our lifestyle. Forests provide timber, which can be made into thousands of economically valuable products. And for thousands of years, wood from forests has fueled the fires that have kept people warm and well fed. Wood has also built the houses that have kept people sheltered. It has built the ships that have carried people and their cultures from one region to another. And wood has enabled us to make paper, which has helped people to share knowledge. Forest plants also provide food and medicine. Many fruits, nuts, spices, and herbs come from forest plants. Forest plants have also yielded many modern medicines. The drug paclitaxel, which treats several kinds of cancer, was discovered in the Pacific yew tree. Madagascar rosy periwinkle, a flowering forest plant that is endangered in much of its range, is the source of treatments for leukemia and Hodgkin s lymphoma. Other cancer treatments and treatments for other illnesses have also been derived from plants. Timber Harvesting There are costs and benefits to every method of timber harvesting. Today, most commercial timber harvesting, or logging, takes place in Canada, Russia, and other nations with large boreal forests, and in nations with large tropical rain forests, such as Brazil. In the United States, most logging takes place in the conifer forests of the West and on the pine plantations of the South, on both private and public lands. Paper and paperboard consumed (millions of tons) Global Consumption of Paper and Paperboard Africa Asia Europe Latin America North America Continent Data from the Food and Agriculture Organization of the United Nations Oceania 4. Propose a Solution List three steps that your school could take to reduce its paper consumption. 332 Lesson 2

4 When timber companies harvest trees, they use one or more of the methods shown in Figure 8 clearcutting, the seed-tree approach, the shelterwood approach, or a selection system. These methods fall into two categories: those that result in even-aged stands of trees and those that result in uneven-aged stands of trees. Even-aged stands result from the regrowth of trees that were mostly all cut at the same time, as with clear-cutting (Figure 9). Uneven-aged stands result from the regrowth of trees that were cut at different times, as with selection systems. Uneven-aged stands typically have more biodiversity, because the regrown trees of different ages offer a greater variety of habitats. But all methods of logging disturb forest communities. Logging changes forest structure and composition, as the larger trees forming the canopy and subcanopy are often removed. Most logging methods also increase soil erosion, which can lead to muddy waterways that degrade animal habitats and lower drinking-water quality. And most methods also increase runoff, sometimes causing flooding, or even landslides. Figure 9 Clear-Cutting During clear-cutting all the mature trees in an area are cut at once. The result is regrowth that is even-aged, like the short trees in the foreground. Figure 8 Timber Harvesting Methods Different methods of timber harvesting lead to different patterns of regrowth. Original forest HARVEST (a) Clear-cutting (b) Seed-tree or shelterwood approach (c) Selection system REGROWTH FOLLOWING HARVEST BIG QUESTION How can we use Earth s resources sustainably? Perspective After students have read about the methods of timber harvesting, ask each student to develop a few questions a timber company executive might consider when determining what method of harvesting to use in a particular area. Have students share and discuss the questions they develop. Forestry and Resource Management 333

5 A Tree s History 1 Examine the photo of the tree-trunk slice, or tree cookie, below. Observe the light-colored and darkcolored rings. Each pair of rings represents a year of the tree s growth. 2 Observe areas A and B. Note any differences. 3 Observe Area C, which was blackened by a fire. Analyze and Conclude 1. Calculate Approximately how old was this tree when it was cut down? 2. Infer Areas A and B were both produced by four years of growth. What conditions might account for their difference? 3. Interpret Visuals How are the ring widths in Area C different from the widths elsewhere? Given these differences, explain how the tree grew after the fire. 4. Communicate Using evidence from this tree cookie, write a paragraph that summarizes the history of the tree. Include as many details as possible in your paragraph. C B Clear-Cutting From the 1950s through the 1970s, timber was largely harvested by clear-cutting, a method in which all of the trees in an area are cut at once. Clear-cutting is generally the most cost-efficient method for timber companies, but it also has the greatest impact on forest ecosystems. Clear-cutting results in even-aged stands of regrowth. Sometimes clear-cutting can mimic the effects of natural disasters such as fires, tornadoes, or windstorms that knock down large areas of trees. Usually, however, clear-cutting destroys or displaces entire communities of organisms, causes soil erosion, and increases the penetration of sunlight to ground level. Because it changes light, precipitation, wind, and temperature conditions, clear-cutting can lead to a new microclimate. The new microclimate allows different types of plants to replace those of the original forest. Essentially, clear-cutting sets in motion secondary succession in which the resulting climax community may turn out to be different from the original climax community. Seed-Tree and Shelterwood Approaches When timber is harvested with the seed-tree approach, small numbers of mature and healthy seed-producing trees are left standing so that they can reseed the logged area. In the shelterwood approach, small numbers of mature trees are left in place to provide shelter for seedlings as they grow. Although both methods are less harmful to forest communities than clear-cutting, both lead to regrowth that is mostly even-aged. Selection Systems Selection systems, in contrast, result in unevenaged stands of regrown trees. In a selection system, only some of the trees in a forest are cut at once. Selection systems include single-tree selection, in which trees spaced widely apart are cut one at a time, and group selection, in which small patches of trees are cut. Timber companies pursued a form of selection harvesting at Clayoquot Sound after old-growth advocates applied pressure and the government researched the issue. Not wanting to bring a complete end to logging when so many local people depended on the industry for work, the activists promoted a method they considered more environmentally friendly. After some research, the government agreed. However, selection systems are by no means ecologically harmless. Moving trucks and machinery over roads and trails to get to individual trees compacts the soil and disturbs the forest floor. In addition, selection methods are unpopular with timber companies because they are more expensive than clear-cutting. For example, cut trees must sometimes be removed by helicopters. Loggers dislike selection systems because they are more dangerous than clear-cutting. In clear-cutting, loggers are largely protected from falling trees by the heavy machinery they operate; when cutting selectively, loggers must spend more time on the ground, in danger both from equipment and from falling trees. A Reading Checkpoint What are two different selection systems? 334 Lesson 2

6 Deforestation Deforestation may help nations develop, but it can be ecologically destructive in the long run. We all depend on wood, from the herder in Nepal cutting trees for firewood to the American high school student using tons of paper while earning a diploma. For such reasons, people have cut forests for timber for thousands of years. Forests are also cleared to make way for farming. Deforestation is the clearing of a forest and the replacement of it by another land use. It has altered the landscapes and ecosystems of much of our planet. Deforestation has provided warmth, shelter, and trade for many human communitites, even as it has caused soil degradation and species population declines for other communities. The negative effects of deforestation are greatest in tropical regions because of the potential massive loss of biodiversity, and in arid regions because of loss of soil productivity. In addition, deforestation has a global impact. It adds carbon dioxide (CO 2 ) to the atmosphere in two ways. CO 2 is released when plant matter is burned or decomposed, and after burning, less vegetation remains to use CO 2. Because CO 2 in the atmosphere contributes to the greenhouse effect that can cause global warming, widespread deforestation can contribute to global warming. ANSWERS Quick Lab 1. About 28 years old 2. Sample answer: Rainfall and temperature; the years in which Area A grew might have had more rainfall and temperatures that were better suited for growth 3. The tree added more new wood on the side away from the fire than on the side of the fire. 4. Answers will vary. Answers should account for differences in the widths of the tree rings (specifically the areas marked A and B ), mention the fire and how it damaged the outmost growing regions of the tree in Area C, and mention the fact that the tree survived the fire (as evidenced by continued growth in other parts of tree). Reading Checkpoint Single-tree selection and group selection United States Deforestation for timber and farmland enabled the United States to expand across the continent. The vast deciduous forests of the East were virtually stripped of their trees by 1850, making way for countless small farms. Timber from eastern forests built the cities of America s East Coast. Later, midwestern cities such as Chicago were constructed with timber cut in the forests of Wisconsin and Michigan. The Industrial Revolution As the U.S. farming economy shifted to an industrial one, wood was used to fuel the Industrial Revolution. Logging operations moved south to Texas, Florida, and the Carolinas. Once most mature trees there were cut, timber companies moved west, cutting the continent s biggest trees in the Rocky Mountains, the Sierra Nevada, the Cascade Mountains, and the Pacific Coast ranges. By the early 1900s, very little old-growth forest forest that has never been logged remained in the United States, as you can see in Figure 10. Figure 10 Deforestation in the United States When Europeans began colonizing the area that would become the United States (left map), the entire eastern half and large parts of the western half were forested (green). By 1920, the vast majority of these forests had been cut (right map) Source: Williams, M Americans and their forests. Cambridge: Cambridge University Press. As adapted by Goudie, A., The human impact. Cambridge, MA: MIT Press. Forestry and Resource Management 335

7 Today Today, not even the largest oaks and maples in eastern North America, or even most redwoods of the California coast, are old-growth trees. The scarcity of old-growth trees in North America today explains the concern that scientists have for old-growth ecosystems and the passion with which environmental advocates have fought to preserve them in areas such as Clayoquot Sound. While some former farms and pastures of eastern North America are slowly regaining forest cover, this process is basically secondary succession. Once old-growth forest is cut, it may need hundreds of years of undisturbed growth in order to recover. ANSWERS Lesson 2 Assessment For answers to the Lesson 2 Assessment, see page A 17 at the back of the book. Developing Nations Old-growth tropical rain forests still remain in many developing nations, and these nations are in the position the United States once was: They have a vast frontier that they can develop and use for income. Today s advanced technology, however, has allowed these nations to exploit their resources much faster than the United States did. As a result, deforestation has been rapid in the tropical rain forests of developing nations, such as Brazil and Indonesia (Figure 11). Because rain forests are the most diverse biomes, a great diversity of species some perhaps still undiscovered are being affected by, or even lost to, deforestation. And recall that large-scale forest loss has global consequences. It can worsen global warming by increasing carbon dioxide in the atmosphere, especially if trees are cleared by burning, as they often are in tropical rain forests. Figure 11 Rainforest Deforestation Brazil produces more charcoal than any other nation. Both farmed trees and rainforest trees are cut and burned to make charcoal. About 350,000 Brazilians work in unhealthy, often exploitative conditions in the charcoal industry Review What is one way a forest is ecologically valuable? What is one way a forest is economically valuable? 2. Compare and Contrast How are clear-cutting and the shelterwood approach similar? How are they different? How do both differ from selection systems? 3. Predict What, generally, is the current level of deforestation in the United States? In developing nations? How would you expect the deforestation in developing nations to change in the next 100 years? Explain. 4. People in developed nations often warn people in developing nations to stop destroying rain forests. People of developing nations often respond that this is hypocritical, because many of the developed nations became wealthy by deforesting their land and exploiting its resources. What would you say to the leader of a developing nation that is seeking to clear much of its forest? 336 Lesson 2