Chapter 2 Importance of Tropical Forests

Chapter 2

Importance of Tropical Forests

PageHighlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Social and Economic Context . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

Water and Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Hydrology in Tropical Regions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Local Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Tropical Agriculture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

Basic Human Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Wood for Fuel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44Other Basic Human Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Employment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Commercial Forest Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Wood. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48Products for Medicine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50Other Forest Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Endangered Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Migratory Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52

Political Implications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Importance to Future Generations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

Chapter p references. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Table

Table No. Page2. Estimated Annual Person-day Requirements for Various Forestry Operations . . 47

List of Figures

Figure No. Page9. Tropical Forests and Woodlands Are Located at Latitudes South of 23.5° N

and North of 23.5° S, and at Other Frost-Free Localities . . . . . . . . . . . . . . . . . . . 3810. Age-Sex Composition of More Developed

and Less Developed Regions, 1980 and 2000. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3911. The Role of Forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

Importance of Tropical

Chapter 2

Forests

The potentially renewable productivity oftropical forests will become increasingly im-portant over the next 30 years as the tropical .nations’ population grows from 2 billion to4 billion people.

Tropical forests support economic develop- .ment. They sustain production on land thatrapidly loses productivity if they are re-moved and they can restore the productivityof degraded land.

●

Economic development in tropical nationsis important to the people of the UnitedStates for humanitarian reasons and becauseof our economic ties with these nations.

Industrial wood and other forest products

earn substantial foreign exchange for tropi-cal nations that trade with the United States.

Tropical forest resources provide food, fuel,medicines, and other basic human needs formillions of people who live in and near them.

Where fuel wood is not available, agricultur-al lands are damaged as people have to burncrop residues and manure that would other-wise be used as fertilizer.

The highly diverse tropical forests containplants and animals that have great potentialvalue for medicine, agriculture, and otherindustries. These will be more valuable asindustries come to rely more on biotech-nology.

SOCIAL AND ECONOMIC CONTEXT

Tropical nations face a dilemma. Forestsmust be cut and cleared to increase productionin the near term, but the loss of forests canreduce productivity in the long term.

About 76 nations, containing about half theworld’s population (2 billion), are located en-tirely or largely within the tropical latitudes(fig. 9). These nations are characterized by fast-growing populations, low per capita incomes,and agrarian economies. Some of their agricul-ture is subsistence farming in upland areaswhere soils have low fertility or are dry. Someis commercial agriculture on the more fertileand generally irrigated alluvial plains of majorriver valleys. The success of both types of agri-culture is linked to the status of 1.2 billion hec-tares (ha) of moist tropical forest and 800 mil-lion ha* of drier open woodlands.

● This report refers to land area in hectares (ha), One hectareequals 2.47 acres. One square kilometer equals 100 ha. Onesquare mile equals 259 ha. Thus 1.2 billion ha of moist tropicalforest is 3 billion acres or 4.6 million square miles.

Because the population structure in tropicalcountries is dominated by young people, foodand other needs are growing faster than popu-lation (fig. 10). For example, food productionin developing nations needs to increase byabout 4 percent per year, while population isgrowing at about 2 percent. The age structurealso means that population growth has a built-in momentum that will prevent the numbersfrom stabilizing until well into the next cen-tury, if then (80).

Part of the needed gains in agricultural pro-duction can come from improved irrigation,crop breeding, and technical inputs that en-hance agricultural yields. But average yieldsprobably cannot increase every year by 4 per-cent. Two percent gains may be possible, butto sustain even that rate over several decadeswill be very difficult. Consequently, the amountof land farmed and grazed will have to beexpanded and people will continue to clear for-ests to produce food and other goods.

37

38 ● Technologies to Sustain Tropical Forest Resources

Ch. 2—Importance of Tropical Forests . 39

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Population growth rates and the number ofyoung people in tropical populations also resultin a rapidly growing labor force. But in mosttropical nations, it does not seem likely thatindustry and commercial agriculture will beable to sustain growth of over 2 percent peryear in job opportunities. Thus, substantialnumbers of people will turn to the forests—either clearing them for conventional farmingand grazing, or managing them for forestry andagroforestry production.

The need for food and jobs is direct and com-pelling, while the environmental services pro-vided by tropical forest resources affect tropi-cal people indirectly and forest loss becomesapparent slowly. In the long term, tropical peo-ple need the watershed protection, preserva-tion of habitat and genetic diversity providedby the forests (fig. 11).

One approach to accommodate the conflict-ing needs of tropical people is to accelerate eco-nomic development of resources outside theforest to provide food, goods, jobs, and foreignexchange. This would reduce the need to ex-ploit and clear tropical forests. While this mayhave the greatest effect in the long run, thesetypes of technologies (e.g., improving tropicalagriculture) are outside the scope of thisassessment.

A second approach is to direct the use of for-est resources so that both sets of needs—pro-vision of food, jobs, and national income andmaintenance of the forests’ environmentalservices—are fulfilled.

WATER AND CLIMATE

Hydrology in Tropical Regions

Most rainfall in the Tropics occurs where thenortheast and southwest trade winds converge.This Inter-Tropical Convergence Zone is intrin-sically unstable, oscillating to the north andsouth of the Equator, causing an erratic rain-fall pattern with sharp seasonal contrasts (49).When tropical rains do fall, storms are moreviolent than those in temperate areas. Morewater falls per storm, quickly saturating thesoil. Consequently, a larger proportion of therainfall runs off the soil surface. Furthermore,in tropical storms raindrops are larger, thushaving great kinetic energy and high erosivepower (1,59). For example, in areas of theAmazon Basin where annual rainfall averages2,100 millimeters per year and land slope isabout 15 percent, erosion removes only about360 kilograms of soil per hectare per year fromforested land. But after the forest is cleared,erosion increases 100 times (43).

Tropical forests protect soil and modulatewater flows in several ways. The canopy ofleaves intercepts rainfall and provides tempor-

ary water storage. In addition, organic litter onthe soil surface and the porous topsoil storewater. The organic litter in closed tropical for-ests is typically 10 to 30 centimeters thick andthe topsoil has a high organic material content(49,61). These mechanisms minimize the im-pacts of intense rainstorms, reduce peak storm-flows, and help mitigate flooding.

The effects of forest cover on streamflowhave been measured in tropical regions. In amoist montane forest in Kenya, for example,water measurements were taken on two adja-cent 600 ha valleys for over 25 years. When onevalley was cleared for a tea plantation—leavingthe steeper slopes and riverbanks under forest—the immediate effect was a fourfold increasein peak stormflow. Even after installing con-servation practices (e.g., contour planting, cut-off drains, cover crops), stormflows remaineddouble that measured in the undisturbed forest,although the total flows were small (49). Simi-larly, an experiment was conducted in Indiaon a forest which had been reduced to waste-land by fuelwood cutting and overgrazing.When the severely eroded Siwalik hills of

Ch. 2—importance of Tropical Forests • 41

Figure Il.—The Role of Forests

1..Ecological effects

SOURCE: World Bank, Forestry Sector Policy Paper (Washington, D. C.: World Bank, 1978).

25-287 0 - 84 - 4

42 • Technologies to Sustain Tropical Forest Resources

Chandigah were reforested, the peak rate offlow from the watershed was reduced 73 per-cent and total flow was reduced 28 percent (73).

In dry environments where tree canopies areopen, forests are less effective in protecting thesoil and modulating water flows, but their in-fluence is still beneficial. Open forests provideshade and act as windbreaks. They reduce soilsurface temperatures and wind erosion and sta-bilize streambanks. They can anchor shiftingsand dunes that can otherwise destroy crop-lands and irrigation systems, In coastal plains,trees can prevent the rise of saline ground wa-ter. Trees in arid areas, however, may throughevapotranspiration leave less water availablefor human uses (49).

Local Climate

Tropical forests also can affect local climate.In moist forests with closed canopies, tran-spiration of water extracted from the soil andthe direct evaporation of intercepted rainfallcool the surrounding air. The resulting cool-ing effect is pronounced, increasing the occur-

rence and persistence of mists. Thus, the heatflux from a closed tropical forest in the dry sea-son is only half that from similar land coveredwith subsistence crops or rough pasture (49).Crops cultivated in and near the forest are like-ly to enjoy greater soil moisture content thanthose on cleared land, provided that they areplanted beyond the root-spread of the trees.Similarly, windbreaks and shade trees can im-prove microclimates for crops in dry areas.

Some mountain forests in low rainfall areascollect useful amounts of water by condensationfrom mists and release the water as “drip-fall,”sometimes giving rise to perennial streams (49).However, the belief that forests actually causerain is questionable. (One recent study in theAmazon reports that a significant part of therain falling there is water evaporated from theforest, but the results have not been verifiedby other studies.) The dessication that is so fre-quently a consequence of large-scale forest des-truction is due to the hydrological damagecaused by loss of infiltration and undergroundstorage. In general, forests thus have a criticallyimportant influence on the reception of rain-fall, but not on its generation (49).

TROPICAL AGRICULTURE

The populations of tropical nations generallyare concentrated on the coastal plains and inthe valleys of the great rivers. Most forests inthese areas already have been cleared for crop-lands. Much of this land is irrigated by oldsystems that control the drainage of seasonalfloodwaters. Land that is irrigated with newersystems uses large dams to store excess flood-water and can produce more than one crop peryear,

The most productive tropical agriculture isbased on annual flooding, but it fails when thefloods are severe. New high-yielding crop vari-eties of the Green Revolution are short-stemmed and so require precise control ofwater levels. Excessive flooding also can resultin shortages of reservoir water for irrigationin the following dry season. Further, the ac-

celerated siltation that accompanies abnormalfloods can fill reservoirs, canals, and streamchannels, reducing the precision of water con-trol in subsequent years. Thus, the Green Rev-olution not only increased production from thebest tropical croplands but also increased sus-ceptibility to damage by floods and siltation.This makes watershed protection provided bytropical forests even more important.

Unfortunately, recent decades have been atime of rapid deforestation in many tropical na-tions. Consequently, river flows have becomemore erratic, flood damage to crops and struc-tures has been severe, and siltation of water-ways and reservoirs has increased (49).

The modulating effect of forests on stream-flow and the consequences for agriculture are

most evident when the protective forests havebeen destroyed. In Pakistan, for example, some70 million people depend on 14 million ha ofirrigated land in the Indus Basin for food. Theirrigation depends on river flow, but deforesta-tion on the Indus’ headlands has resulted in in-creased peak flows during the monsoons, fol-lowed by water shortages during the dry sea-son, With World Bank funding, two dams, theMangla and the Tarbella, were constructed forhydropower, flood control, and irrigation.Careful studies of sedimentation rates hadindicated that these dams would repay con-struction costs by providing benefits for manydecades. However, parts of both watershedshave suffered uncontrolled deforestation and

these reservoirs are filling with sediment attwice the expected rate (49]. Similarly, siltationis expected to reduce the lifetime of the Hira-kud reservoir in India from 110 years to 35years (57).

In India, the area of agricultural land dam-aged each year by floods continues to increaseas deforestation occurs. The area of moist for-est cleared each year is about 147,000 ha (29),and the area flooded has risen 18 percent overthe past 10 years, from 22 million to 26 millionha (72). Clearing of forests over the past 20years in India has caused flood and erosiondamage estimated at U.S.$36 billion in 1982.This estimate includes loss of topsoil, loss of

44 . Technologies to Sustain Tropical Forest Resources

nutrients, loss of property to floods, and short-ened reservoir lifetimes (57).

Flood control and irrigation also are impor-tant in Central America. By the year 2000,Costa Rica and Panama plan to expand theirirrigated areas by 180 percent and 340 percent,respectively (45). Yet, in these countries defor-estation is rapid and uncontrolled. In manyCentral American locations, water needs forirrigation, consumption, industry, and naviga-tion are reaching the limits of low-season flows.Half of the region’s forests have been cleared inthe past 25 years and water flows are becomingmore erratic as deforestation continues (26,45,77]. Similarly, in Africa along a broad belt bor-dering the equatorial humid tropical forest andalong the Gulf of Guinea, the forests are beingdestroyed. Consequently, several nations in theregion are expected to suffer agricultural watershortages before the end of the century (77).

In addition to watershed protection for thecurrent year’s crops, forests have longer termvalues for agriculture. Farmers throughout theworld are using more high-yielding crop vari-eties. In fact, about half the increase in agri-cultural production in recent decades can beattributed to plant breeding (81). The relianceon high-yielding varieties has reduced the ge-netic diversity of agricultural systems and soincreased the risk of catastrophic damage fromdiseases, pests, and other stresses. Yet, no greatincrease in crop failures has occurred. This is

due to new methods of crop protection and theability of crop breeders to respond to threatsquickly by breeding new traits into the crops—traits sometimes obtained from wild relatives

in the tropical forests. For example, a recentimprovement in resistance of peanuts to leaf-spot was derived from breeding crop varietieswith wild forms from the Amazon region. Theestimated benefit from this one improvementis $500 million per year (47).

The peanut is just one of many crops withancestors in tropical forest areas (58). Othercultivated tropical plants include plantains,yams, tare, cassava, sugarcane, potatoes, andcowpeas. Tree crops with tropical forest an-cestors and relatives include oil palm, rubber,coffee, cocoa, and many important fruits.These tropical plants account for at least halfthe calories consumed by people in the Tropics(47), as well as many commodities importantto the U.S. economy. Future gains in produc-tivity from breeding these important agricul-tural crops may depend on the genes in theirwild progenitors and, thus, on the continuedexistence of tropical forests and associated nat-ural areas.

For the people of the Tropics, damage fromincreased flooding and siltation and the poten-tial loss of crop breeding opportunities meanpoorer nutrition, slower economic progress,and less prospect of achieving prosperous,stable economies. For the United States, thismeans the affected nations are less able to tradeinternationally. The developing nations alreadyare a major market—and the fastest growingmarket—for U.S. exports. Their purchasesfrom the United States in 1982 were valued at$82.7 billion, over one-third of all U.S. exports(82).

BASIC

Wood for Fuel

Wood is the most important source of

Brazil and Mexico, where oil and gas provide Fuelwood, however, is becoming harder anda greater share of total fuel than wood). One harder to find. Some 100 million people alreadyand one-half billion people in developing coun- are experiencing acute fuelwood scarcity andtries meet 90 percent of their energy needs with another billion are affected by lesser shortages

Ch. 2—lmpotance of Tropical Forests Ž 45

Photo credit: R?. C. Ghosh

Collecting firewood in the dry, open forests of MadhyaPradesh, India is arduous labor for women. Because thequantity collected is greater than the annual growth,

finding enough wood takes more andmore time each year

(30). In some countries, it can take up to 300person-days of work to satisfy one household’sannual fuelwood needs—forcing some dramat-ic changes in lifestyle. For example, many fam-ilies in Upper Volta eat only one cooked mealeach day, and in Senegal, quick cooking cereal(e.g., rice) has replaced more nutritious, butslower cooking, foods (e.g., millets) (64). Fewerfamilies can avoid the “luxury” of boiling theirwater (76) and some are forced to keep childrenout of school to search for wood.

Fuelwood shortages are forcing increasingnumbers of people to burn animal dung andagricultural wastes, with adverse impacts onland productivity. It has been estimated thatif the cow dung burned for fuel in Asia, Africa,and the Near East were used for fertilizer, grainproduction could increase by 20 million tonsa year (4).

Other Basic Human Needs

The exact number of people living in andnear tropical forests, relying on the productivi-ty of forests to supply their basic needs, is notknown. The U.N. estimates that about 28 mil-lion people practice shifting cultivation in theclosed tropical forests of Asia, 20 million inAfrica, and 40 million in Latin America—total-ing some 88 million people (31). This meanssome 3 to 4 percent of the total agriculturalpopulation in Asia, about 10 percent in Africa,and 35 percent in Latin America, work insidethe closed forests. These estimates include eth-nic populations practicing shifting cultivationas a traditional way of life. They do not includenonagricultural people who are purely huntersand gatherers, nor people who recently movedinto forests. This can be significant, since intropical Asia, at least, squatters probably out-number shifting cultivators.

Many millions of additional people live indrier, mixed tree and grassland environments(open woodlands). These people are typicallylivestock herders and dryland farmers; yet, theytoo are directly dependent on the woodland en-vironment. Their livestock feed on trees and

Photo credit: U.S. Agency for Intemational Development

As fuelwood becomes more scarce, the burning of animaldung increases, depriving the land of nutrients

46 Ž Technologies to Sustain Tropical Forest Resources

bushes, especially during dry seasons whengrasses provide poor fodder. People living inopen woodlands use wood for cooking, boilingwater, heating, drying crops, and as fuel forsmall industries. Open woodland dwellers, likethe people of the closed forests, use trees andwild plants for medicines, soaps, and manyother basic needs (86).

Food from the forests—both closed andopen—meets a significant part of the world’snutritional needs. Meat from wild animals,fruits, nuts, honey, insects, fungi, and foliageare all important forest food sources. At least500 species of edible leaves are used in Africaalone (42). “Bush meat,” including rodents andreptiles as well as wild ungulates and othermammals and birds, supply as much as 75 per-cent of the animal protein consumed in sometropical regions (20).

Forest trees and vegetation are the main ma-terials used in the Tropics to build homes andbuildings. In many rural societies, wood fre-quently is preferred even when other materialsare available (91). Local wood also serves aspoles, fences, stakes, furniture, tools, and uten-sils. Substitutes for these products are rarelyavailable in subsistence cultures. Various fibersderived from forest vegetation are also impor-tant, especially for household use. Rattans, forexample, are climbing palms used for cane fur-niture, baskets, mats, and similar uses.

In the northwestern Amazon forest alone, atleast 1,300 plant species have been used bynative people as medicines and drugs (62). Tra-ditional healers in Southeast Asia use some6,500 plants as treatments for malaria, stomachulcers, syphilis, and other disorders, and alsoas sedatives and emetics (50). A number ofthese plants identified and tested by native peo-ple through generations of trial and error yieldexceptionally promising compounds whenscreened in modern laboratories (21,24).

Forests also protect both inland and coastalwaters, providing another important benefit topeople. After deforestation, increased runoffaccelerates erosion and carries excessiveamounts of sediment to nearby lakes, reser-voirs, and streams. For example, as early as

1904 erosion resulting from deforestation wasresponsible for clogging the once-navigable Riodas Velhas in Brazil to such an extent that evencanoes ran aground (87). Today, deforestationis much more widespread in Brazil, and othernavigable rivers such as the Cuiaba and Sa˜oFrancisco have large parts filled with silt fromeroded forest soils (3,8). Inland waterway trans-portation is further damaged by the seasonaldrying up of local streams that can be a con-sequence of deforestation (18,88).

Increased erosion caused by deforestationhas accelerated siltation of the Panama Canal’ssystem of reservoirs at the same time that accel-erated runoff has diminished water storage inthe Canal’s watershed. During a 1977 drought,the canal was closed to large vessels becauseof low water, a situation that experts believemay occur with increasing frequency unlesswatershed forest cover is restored (85).

Another impact of deforestation on tropicalwaterways relates to the release of nutrientsfrom the forest biomass and soil. Organic mat-ter production is sharply reduced under non-forest conditions. Further, the soluble nutrientsfrom the ash of burned forests and from rapidlydecomposing soil organic matter are easilyleached from soil by heavy rainfall. The result-ing increased nutrient content of runoff canaccelerate the growth of noxious plants andalgae in nearby lakes, canals, and rivers. Aquat-ic weeds block canals and pumps in irrigationprojects. Also, they interfere with hydroelectricproduction, waste water through evapotran-spiration, hinder boat traffic, increase water-borne disease, interfere with fishing and fishculture, and clog rivers and canals so thatdrainage is severely retarded and floods result.

In India, for example, plants reduce waterflow in some large irrigation projects by asmuch as four-fifths. Rafts of water hyacinthweighing as much as 300 tons float over ricepaddies in Bangladesh during floods. When thewater recedes, the weeds settle and kill the ger-minating rice. Maintaining forested water-sheds would reduce erosion and runoff, reducepopulations of aquatic weeds, and reduce thecost of maintaining waterways.

Ch. 2—lmpotance of Tropical Forests ● 4 7

Forests also act as a buffer against the forceof typhoons and other violent storms in coastalzones. Tropical Asia, for example, suffers anaverage of 57 typhoons each year, causingstorm damage that averages $2.8 billion (92).Forests reduce the destructive energy of thesestorms by deflecting wind and reducing theoccurrence of landslides and other environ-mental damage.

Tropical storms are most violent in coastalareas, typically the areas that are most popu-lated. Yet coastal forests are being eliminatedmore rapidly than most other types of tropicalforests, with sometimes devastating effects (45).For example, Bangladesh has a coastal zone of20,000 square kilometers that supports 20 mil-lion people. This nation’s coastal areas wereextensively cleared in the 1960’s, leaving littleprotective forest. When a severe typhoonstruck in 1970, 150,000 Bangladeshis drowned(35,65). Each year, typhoons and floods to-gether claim the lives of 200,000 people anddestroy many hundred thousand hectares ofcrops (92). A portion of these lives and cropscould be saved if forest cover were maintainedand enhanced (45).

About 15.5 million ha of mangrove forestsgrow along coastlines and in estuaries in trop-ical America, Asia, and Africa (31). These for-ests have several important functions asidefrom acting as a coastal buffer against storms,seawash, and floods. They also process sewage,absorb nutrients and heavy metals, and precip-itate sediments, Most importantly, they provideideal breeding and nursery grounds for variousfish, molluscs, and crustaceans. Many valuableshrimp species breed at sea, after which theyoung move into mangroves where they seekfood and protection. Mangroves also providenurseries for such commercially importantfishes as mullet, grunts, and milkfish (66).

labor because site preparation usually involvesmore cutting and tree removal than does har-vest (63). Table 2 is a summary of estimatedannual person-day requirements for variousforest plantation operations in World Bankprojects.

Some tropical governments view tree plant-ing as a way to reduce unemployment (33). Forexample, planting programs are planned withemployment as a major benefit in various areasof Brazil. In the states of Minas Gerais andEspirito Sante, a large work force plants100,000 ha/yr by hand, and in the Amazon re-gion two large companies only do hand-plant-ing. Similarly, large-scale, labor-intensive pro-grams have been developed in Colombia, Vene-zuela, the Philippines, the Republic of Congo,and other Asian and African countries, andsmaller programs are under way in Guatemalaand Honduras (89).

Forestry and agroforestry require protectionand management and so provide even moreemployment opportunities. Using agroforestrysystems including cultivated crops, several treecrops, and livestock on a 100-ha farm in India,employment is estimated to rise from 20 to 50people at the final, sustained yield stage. Thus,agroforestry systems to reclaim 5 million ha ofIndia’s degraded lands might employ 2 millionpeople (57). Furthermore, forest products couldserve as the basis for cottage industries, provid-ing more employment and producing goods fordomestic use and export.

Table 2.—Estimated Annual Person-day Requirementsfor Various Forestry Operations

Plantation designSpacing: 600-2,000 trees per hectare (ha)

(more for energy plantations)

Task Person-days

Employment

Forest management and forest products in-dustries can be a major source of employmentin tropical countries. Industrial wood harvestin tropical forests takes about 60 person-daysper hectare. Planting trees takes even more

Nursery work/1,000 plants. . . . . . . . . . . . . . . . . . . . . . . . 7-13Land clearing and burning/haa . . . . . . . . . . . . . . . . . . . 10-50Pitting for planting/ha . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15Weeding/ha/yr a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-36Pruning/ha ., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15Thinning, , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11aThese measures vary greatly according to site conditions.SOURCE: P.J. Wood, J. Burley, and A. Grainger, “Technologies and Technology

Systems for Reforestation of Degraded Tropical Lands, ” OTA com-missioned paper, 1982,

48 • Technologies to Sustain Tropical Forest Resources

Mangroves

Mangrove forests are important-economically and ecologically. However, mangrove ecosys-tems can be damaged by human activity. Deforestation of watershed areas can accelerate deposi-tion of sand, silt, and clay in alluvial areas; changes in the pattern and volume of freshwater runoffcan be attributed to irrigation, roadbuilding, and other such projects; coastal engineering prac-tices may bring about a change in tidal flushing regimes. Other major stresses include pollutantssuch as pesticides and insecticides used in large agricultural projects and recurring oil spills dueto the exploitation and transportation of offshore oil.

Several mangrove species are highly valued as firewood because they burn evenly with littlesmoke, and as charcoal because they have high caloric value. Charcoal for commercial sale is themain mangrove product in several Asian countries. Mangrove poles are used extensively for ruralhouses, foundations, and scaffolding of urban construction because the wood of many mangrovespecies is durable and resistant to termites (14). In recent years, mangrove has been harvested forwoodchips to be used in chipboard manufacture, newspaper, and as a source of cellulose for rayon(71). The conversion of mangrove land to aquacuhure ponds also is increasing, which could havepotential to increase fish production. However, improper site selection and poor design could havesubstantial negative impacts.

Management of mangrove forests can be complicated. In clearcut mangrove areas, increasedtemperatures and evaporation can raise soil salinity so that mangroves are unable to regrow. Handplanting of seedlings is possible but costly. Selective felling systems that retain trees below certaindiameters often involve rather complicated regulations that may be difficult to administer. Naturalregeneration can be enhanced by clearcutting narrow strips so that nearby trees can provide seeds.

The pressure to clear additional mangrove forest areas for agricultural, industrial, and aqua-cultural purposes will continue and the demand for fuelwood and poles will increase. Short- andlong-term socioeconomic impacts of all alternative uses of mangrove forest areas must be evalu-ated to determine the optimum uses. It is only partly known, for instance, to what extent marinespecies are affected by removal of mangrove forests. Improved understanding of this importantinteraction could have significant forest management payoffs.

COMMERCIAL FOREST PRODUCTS

Wood

The principal commercial products of trop-ical forests are timber and fuelwood. Tropicalhardwoods are used to produce lumber for con-struction, poles, pilings, railway ties, props inmines, and panel products such as plywood,veneer, fiberboard, and particle board. Hard-wood is also important for finished goods suchas furniture and paper products. In addition,some softwoods from tropical forests are usedfor lumber and pulp.

Most tropical forest wood is used within thecountry of origin and the economic value ofthis domestic consumption is difficult to assess.

Value estimates exist for the 6 percent of thecommercial tropical wood harvest that is ex-ported. The total value of wood and wood prod-uct exports from the tropical nations has in-creased by about 500 percent in the past 10years (32). Indonesia’s wood exports in 1980earned some $1.9 billion, The value of woodexports for Malaysia was $2 billion in 1980; forthe Philippines, $415 million; for Brazil, $8I6million; for the Ivory Coast, $415 million [32].

World trade in tropical wood is significantto the economies of both the producing andconsuming nations. The largest single importeris Japan. Several other large importers—e. g.,Singapore, Hong Kong, and South Korea—

Ch. 2—lmportance of Tropical Forests ● 4 9

reexport most of the wood to industrialized na-tions after partial or complete processing.

The United States is the second largest im-porter of tropical wood products and little ofthis wood is reexported. U.S. hardwood im-ports in 1978 amounted to $682 million, withtropical countries (principally Southeast Asia)supplying 82 percent of the total. Imports oftropical wood (logs, lumber, plywood, and ven-eer) averaged $430 million annually from 1974to 1978, Although the dollar value of these im-ports seems high, on a volume basis they ac-count for only 1 to 2 percent of all wood usedin this country (85). U.S. demand for tropicalwood has been growing at rates well above ourpopulation and the gross national productgrowth rates.

Both in the Tropics and in the importing na-tions, industrial hardwood is used mostly in the

housing industry, so industrial demand fortropical wood has grown at a rate that generallyfollows housing starts. The paper industry isthe other major wood user, but it primarily usessoftwoods, for which the United States andCanada are major producers. Many tropical na-tions import paper, and the papermills locatedin the Tropics still import most of their soft-wood pulp from the temperate zone. Sometropical nations have begun to use their ownnatural pine forests, pine plantations, and, ina few cases, hardwoods as a source of pulp.But tropical forests still produce no more than10 percent of the world’s paper and paper-board.

This is likely to change in the next few dec-ades. New technologies, some developed by theU.S. Forest Products Laboratory and U.S. for-est industry, make it possible to produce high-quality paper pulp from 100 percent hard-

Photo credit: H. Bollinger

Wood, a major export item for Malaysia, is no longer restricted to sawlogs. Here 8-year-old Albizia falcataria trees(a legume species) are harvested for export to the Japanese pulp and paper market

50 . Technologies to Sustain Tropical Forest Resources

woods and from a mixture of many hardwoodspecies (84). International demand for tropicalhardwood chips is expected to rise substantial-ly as the new technologies are installed inpapermills in wood-scarce Japan and in Eur-ope, where wood shortages are anticipated.Japan already uses hardwood chips for overhalf of its pulpwood needs (46).

Demand for hardwoods for paper productionalso will increase within those tropical nationsthat have growing economies. As income in-creases, demand for paper products rises rapid-ly among relatively poor consumers as long aswood supplies are abundant (17).

Fuelwood and charcoal enter commerce forboth household use and industry. Wood fuelshave become much more important for indus-tries in tropical nations since the rapid rise infossil fuel costs. Wood is the least expensiveenergy source available for many cottage in-dustries and charcoal the highest quality localsource for some uses. For example, Brazil has1.5 million ha of eucalyptus plantations estab-lished to supply charcoal to the iron and steelindustry in the state of Minas Gerais (31).

The Philippine Government is planning twolarge wood-consuming industrial facilities inthe province of Ilocos Norte. The first of a num-ber of 3-megawatt “dendrothermal” electricpowerplants dependent on wood from fast-growing trees as boiler fuel is under construc-tion. Another project that will involve two largepig-iron blast furnaces and will rely on char-coal from local wood is being planned (36).

Products for Medicine

The importance of the tropical forests, espe-cially the moist forests, as a source for medi-cines is largely a result of their high biologicaldiversity. Some of these forests contain com-munities of species that have existed for 60 mil-lion years, making them the oldest continuous-ly established land ecosystems known. Theirgreat age and ecological stability have allowedevolution to proceed in a relatively undisturbedmanner, and it is probably due to this stablehistory that tropical moist forests developedtheir extreme biological richness (45).

Because tropical moist forests contain somany species, each species must compete withand defend itself against many potential ene-mies, and one way to do this is by developingalliances (e.g., symbiosis) with other species.Thus, tropical forest species are highly interac-tive. The millions of plant and animal speciesalso have had time to develop complex chemi-cals that help them interact with other species.It is because of these “biologically active”chemicals that the tropical forests are consid-ered Earth’s richest storehouses of potentialdrugs.

Today, medical science is highly dependenton chemicals produced naturally by plants.One-fourth of all U.S. prescriptions containingredients from higher plants (27). In 1974, theUnited States imported $24.4 million worth ofmedicinal plants to produce about $3 billionworth of drugs. The commercial value of theseproducts is over $8 billion per year. When non-prescription items are included, the valuedoubles (28).

Although chemical screening has been doneon less than 1 percent of the tropical species,already some 260 South American plants havebeen identified as having potential for fertilitycontrol. Some 1,400 tropical forest species arebelieved to have anticancer properties (7,16,21,68,70). The National Cancer Institute hasscreened about 35,000 higher plant species foractivity against cancer. As of 1977, about 3,000of these had demonstrated reproducible activi-ty and a smaller number were appropriate forclinical trials (23). Rotenoids from the roots oftropical trees, for example, are being testedclinically in the United States as antitumordrugs.

One tropical plant, the rosy periwinkle, hashad a profound effect on treatment of leuke-mia. In 1960, people suffering this diseasefaced one chance in five of remission. But be-cause of two drugs developed from the rosyperiwinkle, the chances of remission are nowfour in five (41). Tabebuia serratifolia, Jacaran-da caucana, and Croton tiglium are tropicaltrees, and each produces a unique anti-cancercompound whose effectiveness has beenproved in the laboratory (51).

Ch. 2—lmportance of Tropical Forests ● 5 1

Tropical forest plants are significant in treat-ing other medical problems, notably hyperten-sion (2,41,44,67). D-tubocurasine, made fromthe South American vine Chondrodendron to-rnentosum, is widely used as a muscle relax-ant in surgery in the United States, Chemistshave been unable to produce it syntheticallyin a form having all of the characteristics ofthe natural product (52). The drug’s supply,therefore, continues to rely on extracts fromwild plants.

Tropical forest animals are also necessary tomedical science. Primates are the most impor-tant group. They are used widely in medicalresearch and pharmaceutical trials.1 Tropicalprimates are especially important because oftheir similarity to humans. For example, re-search into malaria, cardiovascular diseases,cancers, hepatitis, and other diseases common-ly uses rhesus monkeys, longtail macaques,squirrel monkeys, chimpanzees, African greenmonkeys, and owl monkeys.

Some 34,000 primates were imported into theUnited States in 1977 for drug safety tests anddrug production (5). Virus-free polio vaccineperhaps is the most important of the drugs pro-duced this way, using many thousands of trop-icaI forest African green monkeys, The Cen-tral and South American owl monkey is theonly known nonhuman animal suitable for ma-laria chemotherapy and immunology studies(5). Few of these important animals are raisedin captivity; most are captured, and they arebecoming scarce as their forest habitat is be-ing destroyed.

Other Forest Products

Tropical forests provide abroad array of non-wood products.z Some are produced in planta-tions of selected tree species. Others are gath-ered in natural forests and brought to marketthrough a diffuse system of collectors andmiddlemen. These are often called “minor for-est products, ” although their importance fre-quently is greater than that term implies. Forexample, tropical forests provide essential oils,exudates, gums, latexes, resins, tannins, sterols,waxes, esters, acids, phenols, alcohols, edibleoils, rattans, bamboos, flavorings, sweeteners,spices, balsams, pesticides, and dyestuffs.

Few nations have collected data on the com-mercial value of these nonwood forest prod-ucts. One exception is India, where nonwoodforest products are worth about $135 millionper year, equivalent to one-fifth of the value ofindustrial timber (48,69). Indian forests alsoproduce a substantial quantity of animals usedfor food, scientific research, and other pur-poses. In Indonesia, rattans generate an exporttrade worth up to $5 million per year. Theworld trade in rattan end products now totals$1.5 billion (22,37).

World trade in essential oils and spices fromtropical forest plants, such as camphor, cassia,cardamon, citronella, and cinnamon, exceeds$1 billion per year. The United States now im-ports about 10,000 tons per year of these kindsof oils and spices, with a value of over $100million (24,54,55). A systematic investigation ofthe many nonwood forest products used by theforest-dwelling people of the Tropics mightlead to increased use of these materials and fur-ther enhance the economic importance of theforests.

‘See ongoing OTA assessment “Alternatives to Animal Usein Testing and Experimentation. ”

‘See Workshop Proceedings on Plants: The Potentials for Ex-tracting Protein, Medicines, and Other Useful Chemicals (Wash-ington, D. C,: U.S. Congress, Office of Technology Assessment,OTA-BP-F-23, September 1983), for additional information.


Endangered Species

Tropical habitats contain a significant num-ber of the world’s endangered species. As dis-cussed earlier, tropical moist forests are boththe most biologically complex and species-di-verse* biome on Earth. The complexity is bothdynamic (highly interactive) and stable (able tomaintain itself for long periods). Yet the stabil-ity depends on an important provision—thatexternal forces do not exceed certain criticalthresholds. Human intervention may easily ex-ceed these thresholds.

Because of geographic confinements andspecialized ecological requirements, tropicalmoist forest species are unusually susceptibleto extinction (46). Many species are found inonly one small area, so even a limited amountof deforestation can exterminate entire species.Further, species are highly interdependent. Forexample, Brazil nuts are probably the mostcommercially significant food gathered fromforests. The nuts will grow only where a par-ticular type of bee lives, as only this bee canpollinate Brazil nut flowers. The bee, in turn,lives only where a particular type of orchid isfound, because it must obtain a chemical fromthe orchid to attract its mate. Thus, the tree hasnot been domesticated away from the forestwhere the bees and the orchids are found. Fur-ther, for some of the nuts to serve as seeds, thenuts must be chewed by a rodent to soften thefruit, allowing seed germination. Thus, Brazilnut tree reserves must be large enough to sup-port a breeding population of this rodent. Suchcomplex systems of interdependence areanother reason why entire species can bethreatened by small changes (75).

At least three-quarters of the projected ex-tinctions worldwide until the end of the cen-tury are expected to occur in tropical moist

“Biological diversity includes two related concepts, geneticdiversity and ecological diversity. Genetic diversity is the amountof genetic variability among individuals in a single species,whether the species exists as a single interbreeding group or asa number of populations, strains, breeds, races, or subspecies.Ecological diversity (species richness) is the number of speciesin a community of organisms. Both kinds of diversity are fun-damental to the functioning of ecological systems (17).

forests. Degradation and destruction of tropi-cal forests and woodlands could precipitate afundamental shift in the course of evolution(45). Of more certain concern is the loss ofpotential resources, not only chemicals andanimals that may be used directly in medicine,agriculture, and other industries but also ge-netic information with great potential for bio-technology development.

Migratory Animals

Tropical forests provide habitats for many ofthe world’s migratory and endangered species.About two-thirds of the birds that breed inNorth America migrate to Latin America or theCaribbean for winter (74). In general, foresthabitats are more important for migratoryspecies than was previously thought. Many mi-gratory species winter in tropical highlands—areas that have been rapidly preempted foragriculture. Since migratory species concen-trate often in smaller areas in winter, the ef-fects of clearing 1 ha of forest in Mexico prob-ably are equivalent to clearing 5 ha in theNortheastern United States (74).

Migratory species have economic, environ-mental, and esthetic values in the UnitedStates. For instance, some migratory birds playan important role in integrated pest manage-ment systems for agriculture in the EasternUnited States, yet they could become morescarce as their wintering grounds in the Trop-ics are lost to deforestation.

Climate

The question of whether tropical deforesta-tion can disrupt the stability of world climatesis highly controversial. The scientific under-standing of the climate effects of deforestationis still theoretical. When forests are removed,more solar heat is reflected back into space (the“albedo” effect). Some scientists believe thatthis can lead to changes in global patterns ofair circulation, with potential impacts on agri-culture (53,60).


Another effect of forests on global climate istheir role as a carbon reservoir in the carboncycle. As large areas of forest are converted tononforest, the carbon that had been stored inwood and in organic material in the topsoil isreleased to the atmosphere as carbon dioxide.When croplands, grasslands, or degradedbrush replace moist forest, the new vegetationstores much less carbon, Thus, net annual de-forestation adds carbon dioxide to the atmos-phere (90).

The concentration of carbon dioxide in theatmosphere has been increasing for severaldecades, apparently more from burning fossilfuels than from deforestation, Scientists agreethat continued increases in atmospheric car-

bon dioxide will produce a “greenhouse effect”leading to a global warming trend. Doublingof the atmospheric carbon dioxide would prob-ably raise the average global climate by severaldegrees centigrade. Some scientists hypothe-size that increased cloud cover and other en-vironmental change will confound the green-house effect. The effects of such trends onagriculture or on the world’s hydrological sys-tems are unknown. Likewise, the role of theworld’s forests and the effect of substantialdeforestation are still uncertain. Some scien-tists consider deforestation to be a significantfactor in the concentration of atmospheric car-bon dioxide, while others do not (10,12,15,19,34,90).

POLITICAL IMPLICATIONS

Stability of the renewable natural resourcebase in tropical countries affects both the eco-nomic viability of U.S. investments overseasand the political stability of the host nations.Foreign assistance projects funded by the U.S.Government and development projects fundedby the U.S. private sector are being undercutby flooding, siltation of reservoirs, pest out-breaks, and other problems associated with de-forestation. For example, the reservoirs usedto operate the Panama Canal are rapidly fillingwith silt (85), as are hydroelectric reservoirs inPakistan, Thailand, the Philippines, Indonesia,and many other nations (49).

Food and jobs are critical for political stabil-ity in developing nations and both are reducedby inappropriate deforestation. Food suppliesand employment can be increased in the longrun, however, by reforestation of degradedland and by forest management. Frontiers of

human settlement, with relatively untappedsupplies of natural resources, historically area source of new employment opportunities. To-day, however, the remaining frontiers are most-ly infertile or dry lands unable to support largenumbers of people using current technologies.Thus, many rural unemployed persons migrateto the cities. As unemployment climbs, changesin the distribution of income within societiesfurther aggravate social inequities and politicalstresses (11).

One consequence of the inability of develop-ing country governments to create sufficientjobs is that people emigrate to countries withslower population growth and greater per capi-ta resources. The flow of refugees from Haitito Florida is sometimes cited as an example ofthe economic and social disruption caused, inpart, by tropical deforestation and consequentenvironmental deterioration (9).

IMPORTANCE TO FUTURE GENERATIONS

Tropical forests have particular importance without expensive inputs of irrigation water orto future generations. With few exceptions fertilizers. But scientific study of naturalpresent agriculture systems cannot accomplish ecosystems, in concert with applied researchsustained productivity on infertile or dry sites to develop technologies, possibly can discover


how sustainable agriculture can be achievedon this land. Such research has hardly begunand it is a slow process. Thus, the tropicalforests serve future generations by the infor-mation they reveal to science and by maintain-ing the quality of the land until sustainablesystems for more intensive use are developed.

The Tropics are thought to be the repositoryof two-thirds of the world’s approximately 4.5million plant and animal species, only about500,000 of which have been named. Thatmeans that about 2.5 million of the tropicalspecies are yet unknown to science (58). * Theseunknown species are resources of incalculableimportance for the future. Undoubtedly, newsources of food, drugs, fuel, and products lieundiscovered in tropical forests.

Although vertebrates are generally thoughtto be well known on a worldwide basis, onlyabout 60 percent of the estimated 5,000 speciesof fish in the fresh waters of South Americahave been scientifically described and named,even though these comprise a large proportionof the diet of local people. A principal sourceof meat for Paraguayan farmers is a peccary,made known scientifically only in 1977 (58).

Tropical forests offer potential resources forplant breeding, genetic engineering, and otherbiotechnologies. Because farming environ-ments are constantly changing as pests or plantdiseases threaten or as weather changes, agri-culture relies on the continued input of genet-ic diversity for plant improvement. Germplasmis the resource to which plant breeders turn fordesirable characteristics—resistance to pests orstress, or improved growth qualities. A Peru-vian species, for example, contributed “riperot” resistance to American pepper plants anda wild melon in India was the source of resist-ance to powdery mildew that threatened de-struction of California’s melon crop (47). Awild relative of the potato from Peru has beenknown for decades to be highly resistant to in-

*No one knows how many species exist. Some estimates putthe figure as low as 2 million; many converge on a figure of 5million to 10 million; if tropical insect species are included, thenumber could be closer to 30 million (40).

sects because of sticky hairs on its leaves, butthis resistance has not been useful to agricul-ture because the wild plant cannot be crossedwith domesticated kinds of potatoes. Now thesticky-hair characteristic is expected to betransferred with new biotechnology methods.If it works, the result could be new potatostrains that have a much reduced need for pes-ticide applications. This implies substantialgains in production of this important food andattendant environmental benefits from reducedinsecticide use, It is not possible to predict withaccuracy what germ plasm will be needed inthe future.

With the gradual consumption of fossil fuelsand other nonrenewable resources, the UnitedStates and other nations are expected to turnincreasingly to biological systems for industrialand chemical feedstocks and for solutions topollution and other environmental problems(78,79). Some complex chemicals and somemore simple biological processes can be in-vented in the laboratory, but most have to befound in nature.

Genetic materials and basic systems foundin nature can be reproduced or adapted withbioengineering techniques. New techniques forcloning plants and micro-organisms alreadyare enabling laboratory biologists to screen ex-isting organisms for their production of usefulchemicals much more rapidly and efficientlythan in the past. The newly developing tech-niques for genetic manipulation offer oppor-tunities to adapt existing organisms to newuses (79).

For example, tropical forests have a greaterproportion of alkaloid-bearing plants than anyother biome (6,39,56). Many of the plant speciescontain hydrocarbons as well as carbohydratesin their tissues. These plant tissues can be re-newable sources for many chemicals, includ-ing fuels, now derived from nonrenewable fos-sil sources (13,38). Since tropical forest speciesusually are restricted to small geographic areas,opportunities are lost wherever the forests areremoved before their unique biota has beenidentified, screened, and assessed for useful-ness (83).


Political InterestsU.S. Stake

The United States has strong commitmentsto world peace, economic and social stabil-ity, and maintenance of the Earth’s basiclife-support systems, commitments thatrequire concern about the integrity andlong-term productivity of the global naturalresource base, including the tropical forestcomponent.The United States is party to a broad arrayof international resolutions, strategies, andagreements that call on all participating na-tions to promote and undertake improvedmanagement of the forest resource.U.S. public institutions and private firms

in Tropical Forests

●

●

programs are being affected adversely bydeforestation-related problems.The United States and other nations haveraised humanitarian concerns about indig-enous populations whose cultures and veryexistence may be threatened by destructionof the forests.The United States increasingly is beingrequested by governments and internaltional development organizations to pro-vide technical assistance and financial sup-port for forest-related activities in develop-ing countries.

Environmental Interests●

●

●

U.S. public institutions have statutory andpolicy responsibilities to protect and man-age wisely the environment and naturalresources of our Nation, as well as those ofother areas within and outside U.S. juris-diction in which U, S.-sponsored or U. S.-assisted activities are carried out.The United States shares, with South andCentral America and the Caribbean area,hundreds of species of migratory animals,including birds, insects, marine turtles, andmammals, whose survival depends to vary-ing degrees on tropical forests.The United States is committed to helpingpreserve the world’s flora, fauna, and vul-nerable ecosystems by virtue of domesticlegislation and national policies, and bybeing party to a large number of interna-tional conventions and agreements. Princi-pal among these measures are the Endan-gered Species Act of 1973, the Conventionon International Trade in Endangered Spe-cies of Wild Flora and Fauna, and the Con-vention on Nature Protection and WildlifePreservation in the Western Hemisphere.Large-scale destruction of the Earth’s rainforests runs a risk of triggering global cli-mate change, with uncertain but potentiallyadverse consequences for world food pro-duction and human well-being,


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Chapter 2 Importance of Tropical Forests

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