Chapter I Contents

Page Introduction ...... 3 Background ...... 5 Definition of Degraded Lands ...... 5 Tropical Soils and Climates ...... 5 Scope and Causes of Land Degradation ...... 7 Reclamation Using Trees...... 8

Table Table No. Page I. Tropical Lands Recently Undergoing Severe Desertification ...... 7

List of Figures FijweNo. Page l._Tropical Forests and Woodlands, for the purpose of the Report, are Located at Latitudes South of 23.5° N and North of 23.5° S, and at Other Frost-Free Localities ...... 4 2. The Role of Forests ...... 10 Introduction and Background

INTRODUCTION

Eleven million hectares (ha) of the world’s other uses. Trees protect soil from the effects remaining tropical forests are converted to of tropical heat, rain, and wind. Soil tem- other land uses or to wasteland each year (33). peratures are lower under tree canopies, per- About half of the Earth’s original tropical forest mitting reaccumulation of organic matter that land has thus been altered. Deforestation can restores soil structure and microbiota and en- be beneficial where cleared tropical land can hances moisture- and nutrient-holding abilities. sustain agriculture. Under available farming Bacteria on the roots of some trees produce ni- technologies, however, many remaining tropi- trogen fertilizer, while fungi on tree roots can cal lands cannot sustain agriculture and are convert soil minerals to useful forms. In dry soon abandoned or converted to less produc- areas, trees can help to prevent the rise of tive uses. Often, forests cannot regrow natural- saline ground water (92). Where surface soils ly on these degraded lands. are dry or infertile, deep tree roots can tap un- derground reservoirs of nutrients and water Tropical nations* (fig. 1) have about 650 mil- and bring them to the surface. lion ha of cropland and nearly 2 billion ha of land in various stages of degradation (33,114). In recent years, reforestation efforts have in- Those regions with rapidly growing popula- creased. Of the approximately 11.5 million ha tions—Asia, Central America, North Africa, of planted forest in 1980 in the tropical nations, and the heavily populated parts of East and some 40 percent have been planted since 1976 West Africa—need productive land most des- (33). About 60 percent of this was planted for perately, yet have the most rapid deforestation industrial purposes (lumber, veneer, pulpwood, and extensive areas of degraded land. In many etc.). The other 40 percent was nonindustrial of these places, firewood has become so scarce (fuelwood, watershed protection, etc.). While that certain foods requiring cooking have been it is not known how much of this planting oc- eliminated from the diet. People must use crop curred on degraded land and how much oc- residues and dried dung for fuel, which robs curred on recently cleared primary forests, it the soil of organic matter and nutrients and ac- is probable that a 1arge and increasing propor- celerates erosion. Soil eroded from degraded tion of the reforestation, especially nonindus- lands fills riverbeds and reservoirs, increasing trial planting, is occurring on degraded sites the severity of floods and causing water scar- (37). cities. This background paper discusses techniques The best solution for stopping this trend of to reforest tropical lands and gives special em- land degradation is to prevent inappropriate phasis to degraded lands and community-ori- land-use practices on forested lands. Where ented forestry. It does not address methods to this is not possible, reforestation is one way to manage existing forests, nor does it focus on improve the productivity of many degraded public policies or institutional mechanisms to lands and provide useful products for the peo- sustain tropical forests. Those issues are cov- ple. Trees provide wood, fuel, food, fodder, and ered in a forthcoming OTA report, Technol- ogies To Sustain Tropical Forest Resources, *In this b,~(.k~round paper, tropical lands include all lands lo- and in another background paper, U.S. and in- (:ated at Iatltudes south of 23.5 N and north of 23.5 s. ternational Institutions.

3 4 ● Background Paper #1: Reforestation of Degraded Lands Ch. l—introduction and Background ● 5

BACKGROUND

To understand the constraints on existing re- report, * a simple but useful breakdown of trop- forestation techniques and the potentials of ical areas divides it into three types: 1) hot, wet new ones, it is first necessary to define land lands, 2) arid/semiarid lands, and 3) mountain- degradation, briefly describe tropical soils and ous lands. climates, and discuss the causes of land deg- Most tropical soils on hot, wet lands have sig- radation and benefits of reforestation. nificant fertility problems. Year-long high tem- peratures and high rainfall combine to accel- Definition of Degraded Lands erate the removal of nutrients needed by plants Degradation of tropical land is a physical, from rock materials and soil mineral particles. chemical, and biological process set in motion The residual minerals tend to be composed by activities that reduce the land’s inherent pro- mostly of aluminum, silicon, iron, oxygen, and ductivity. This process includes accelerated water—a chemical composition so restricted erosion and leaching, decreased soil fertility, that many food or tree crops will have stunted diminished natural plant regeneration, dis- growth or will not survive. An estimated 2 per- rupted hydrological cycle, and possible salini- cent of the soils of hot, wet lands, if cleared zation, waterlogging, flooding, or increased of vegetation, will irreversibly harden on dry- (119), drought risk, as well as the establishment of ing severely limiting reestablishment of weedy plants that displace more desirable plant any vegetation (67). species, Evidence that the degradation process In arid/semiarid lands, soil nutrients needed is advancing includes, for example, a reduc- by many plants become available to plants with tion in the water-holding ability of the soil, a sufficient water (16). However, if most of the decrease in the amount of soil nutrients avail- water evaporates from the soil surface rather able to plants, a reduction of the soil’s ability than percolating down, dissolved solids or salts to hold nutrients, or soil compaction or surface can accumulate at or near the land surface in hardening. concentrations that many plants will not toler- This definition implies a strong interrelation- ate (43). ship between inappropriate land-use practices Mountainous lands** are cooler than the and land degradation. In some places degrada- other two categories and exist in both wet and tion is manifest (e. g., erosion and desertifica- dry climates. Because they have steep slopes, tion), whereas in others it is inferred (e.g., their soils are easily eroded. Much of the rain- declining crop yields). fall in the wetter regions runs off the land sur- face rather than percolating into the ground. Tropical Soils and Climates Consequently, soils in mountainous lands are likely to be rocky and thin, except perhaps on Although the chemical, physical, and bio- the lower slopes (16), logical processes that occur in the tropics are the same as those elsewhere in the world, the rates often are accelerated. Tropical air, soil, and water temperatures are higher; rainfall is more intense and erratic; and the growing sea- *See Van Wambeke (1 19) and Fripiat and Herbillon (36) for son is longer than in temperate parts of the more detailed information. These are good references on soils world. These factors affect tropical forests and of the hot wet tropics. They not only contain the commonly cited their soils. Further, they can place severe con- information on agriculture, soil names, etc., but also provide dis- cussions of mineralogical and chemical processes. straints on certain land uses. Although detailed * *Elevated areas throughout the tropics typically from 750 soil descriptions are beyond the scope of this meters and abet’e. 6 ● Background Paper #1: Reforestation of Degraded Lands

Photo credit. B C Stone for the National Academy of Sciences

Severely degraded lands on Guam which were once covered by tropical forests Erosion has uncovered large expanses of infertile soil

Photo credit OTA staff Barren landscapes on islands along the south coast of China reflect deforestation that occurred hundreds of years ago Ch. l—/ntroduction and Background ● 7

Scope and Causes of productivity is greatly decreased. After 1 to 5 Land Degradation years, the land typically is abandoned by farm- ers who move on to other areas. The land then In much of the open woodlands of arid and reverts to secondary forest, vines, brush, or semiarid areas, overgrazing and repeated fires grasses of low nutritive value. Land abandon- have converted the vegetation to a degraded ment is caused by decreasing crop yields and fire climax stage. Consequently, soils become increasing weed control problems (57). Nor- dry and little woody regeneration occurs. Fire- mally, these farmers (shifting cultivators) allow tolerant vegetation—often unpalatable to ani- fallow periods of 10 to 15 years, thus giving mals—persists, leading to a desert-like state. To- enough time for soils to recuperate some pro- day, there are few undisturbed woodlands or ductivity, However, in a growing number of savannas in these regions. An estimated 20.5 places, increased population pressures lead to million hectares (ha) of tropical arid lands, an shortening of these periods. Food production area about the size of South Dakota, become is then greatly decreased, leading to even decertified every year. To date, an estimated stronger pressures to clear more forest. Such 1.56 billion ha of tropical land have undergone effects of acute population pressure are evident desertification (table I). in Haiti, El Salvador, and parts of the Philip- pines and Indonesia (131). Detailed descrip- Desertification occurs in the savanna region tions of tropical agriculture and its effect on of North Africa as well as in the savannas of soils include: Laudelout (71); Nye and Green- southern tropical Africa and northeast Brazil. land (88); Jurien and Henry (60); Watters (123); In the Sudan and elsewhere in North Africa, Sanchez (104); Lal and Greenland (69]. the populations of grazing animals—including goats, sheep, cattle, and camels—number in the Population growth rates in tropical countries millions and their grazing intensity has severe- are the world’s highest. Growing numbers and ly impaired natural regeneration of forests and rising aspirations lead to more than propor- forage (28), Consequently, people have had to tional increases in the demand for food, fuel, range farther in search of fodder for their fodder, and building materials (15). Population animals and wood for cooking and heating growth also requires increased land for ur- (131). banization and village expansion, energy pro- Forest degradation and loss under the rainy duction, and transportation (14). and seasonal environments may not be so se- With few exceptions, such as the river valleys vere as under the arid and semiarid environ- of West Africa where river blindness is being ments, but the effects on people are similar. eradicated, most of those lands that can sus- There are approximately 156 million ha of tain stable agriculture probably have been tropical moist forest, 181 million ha of forest cultivated. Remaining unused lands are those fallow, and 84 million ha of deforested water- already degraded, or those too infertile for con- sheds available for reforestation (131 ). When tinuous farming without constant infusion of areas cleared by agriculturalists are exposed high-cost inputs such as commercial fertilizer. to abundant rainfall, erosion, and leaching, soil Without these inputs, the land becomes suscep- tible to degradation, thus reducing the standard of living (49,108). Table 1 .—Tropical Lands Recently Undergoing Severe Desertification (million hectares) In recent years, some developing countries Region Total decertified area have been planning and encouraging move- Latin America. . . . 701,8 ment of people, usually into sparsely occupied Africa, ...... 685.0 Virgin tropical forests, Two examples are India and Pakistan . 170.0 Brazil’s planned colonization of the Amazon 1,556.8 Total ...... Basin via the Transamazon highway and Indo- SOURCE United NatIons, UN Conference on Desertification: Round-Up, Plan of Action and Resolutions (New York United Nat Ions, 1978) nesia’s colonization of its outer islands (49,108). In both cases, people are moved between re- some may be impossible to reclaim. In addi- gions that are geographically and geologically tion, reforestation of degraded lands may not different and thus they are ill-equipped to cope be so profitable, in financial terms, as reforesta- with the new environment. Consequently, in- tion of rich, fertile lands. However, in many appropriate land use practices have led to de- countries, fertile sites are reserved for agricul- creased crop yields. Forest clearing exposed tural activities. Given the dwindling amount the lands to heavy erosion and depleted the of good lands and the increasing demands for soil’s nutrient supply, leading to land degrada- forest products, it is necessary to consider all tion and to indebtedness and landlessness for alternatives. Reforestation is an alternative that the people. has the potential to rehabilitate the degraded soils and provide many goods and services for The expansion of lands under cultivation will industrial and local needs. continue, given the rising pressures. More lands will become degraded and subsequently abandoned. To break this cycle, some of these Reclamation Using Trees degraded lands can be reclaimed via reforesta- tion. Tree planting of degraded lands is not a For degraded sites it is often advantageous panacea to deforestation or inappropriate land to plant trees because of their ability to use uses. Some degraded lands will be difficult and water and nutrients inaccessible to plants with Ch. 1— Introduction and Background ● 9 — shallow roots and because they supply a mul- Soils under forest cover often have high or- titude of products: wood, fuel, fodder, and ganic matter content. Land-use practices that others. Moreover, a tree canopy acts as a buf- jeopardize the soil’s organic content therefore fer against the direct impact of raindrops on can have adverse effects on successful}’ refor- the soil. The litter and humus layers underlying esting degraded lands. the forest absorb moisture, allowing water to The living network of roots near the surface infiltrate the ground and recharge the ground of forest soils provides mechanical support for water supply (92). Trees, by shading the soil, steep slopes; this root network is the main con- reduce soil temperatures and thus promote ac- tribution to slope strength and prevention of cumulation of organic matter and retard possi- landslides (100). Consequently, trees are par- ble soil hardening, ticularly valuable for watershed protection and The presence or absence of organic matter for arresting desertification in areas of mov- in any soil is an important factor in the soil’s ing soils (e. g., sand dunes). Some trees act as productivity. Soil organic matter is important soil improvers as well as soil protectors. to soil productivity because it: Leguminous trees and forbs have the capacity to enrich soil with nitrogen. Legume trees have ● contributes to the development of soil ag- nutrient-rich leaves which can be used as fod- gregates, which enhance root development der or mulch (80,81). and reduce the energy needed to work the soil; There are many reasons for planting trees. • increases the air- and water-holding ca- Provision of goods for household and industrial pacity of the soil, which is necessary for use (see fig. 2) is equally as important as reha- plant growth and helps to reduce erosion; bilitative factors. For local needs, a tree species ● releases essential plant nutrients as it with several attributes or a mixture of tree spe- decays; cies can be planted to obtain multiple benefits • holds nutrients from fertilizer in storage —e. g., ability to enrich soil fertility, wood suit- until the plants need them; and able for fuel and poles, and nutritious leaves ● enhances the abundance and distribution for fodder. of vital soil biota (90). 10 . Background paper #1: Reforestation of Degraded Lands

Figure 2.— The Role of Forests

< . Controlled runoff, water Catchment r I supplies, trrlgatlon, soil Y protection 4 fertllily, oxygen

* < Recreation, tourism, Ecology and wild national parks, protection Ecological effects — - I life conservation of endangered species of flora and fauna

Windbreaks, shelter belts, dune fixation, reclamation of eroded lands

— Fuelwood and a Cooking, heating, and charcoal household uses

Shifting cultivation, forest — Agricultural uses r 1 grazing, nitrogen fixation, mulches, fruits and nuts L

Housing, buildings, - Building poles L construction, fencing, furniture

Plt saw!ng and Jolnery, furniture, con- Indigenous consumption sawmilling struction, farm buildings I i

Ropes and string, - Weaving materials baskets, furniture,

4 furnishings 4 Serlculture, aplcul - Silk honey, wax Iac ture, erlculture

Carving, Incense, chemicals glassmaking I L 8 {t J

Naval stores tannin, . Gums, resins. turpentine, distillates and OIIS resin, essential oils &

Reduction agent for steel- 9 Charcoal r 1 making, chemicals, poly vinyl chloride [PVC) dry cells 6

Transmission poles I pitprops 1 I 1 T Lumber joinery, furniture 1 I Industrial uses l— Sawlogs packing. ‘shlpbuilding * dt h mining, construction sleepers I Plywood, veneer, furniture, Veneer logs 4 containers. construction I H 1 1 I J

Newsprint. paperboard. prlntlng and writing paper - Pulpwood . containers, packaging

● dissolving pulp, distillates textiles and clothing

Particle board fiberboard Residues A wastepaper I

SOURCE World Bank 1978