The tropical forest zone

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The tropical forest zone contains 1.76 billion ha, divided into six ecofloristic zones: the tropical rain forests, the moist deciduous forests, the dry zone, the very dry zone, the desert zone and the hill and mountain forests. Table 8 presents the regional distribution of these six categories. Ninety-six percent of tropical forests occur in the following four formation types.

Tropical rain forests are found in areas with more than 2 500 mm of annual rainfall. They are evergreen, luxuriant and rich in animal and plant species. More than half the world's 718.3 million ha of rain forests are located in two countries: Brazil (41 percent) and Indonesia (13 percent). Rain forest composition and structure vary with distance from the ocean, distance from rivers, altitude and geographic position.

Moist deciduous forests occur in areas with an annual rainfall of 1 000 to 2 000 mm. Forest structure varies depending on the amount and distribution of rain, the type of soil and the length of the dry season. Some dominant tree species may lose their leaves towards the end of the dry season. This forest type is generally less diverse than rain forest.

Dry zone forests are found in tropical areas receiving between 500 and 1 000 mm of rainfall per year. They are relatively open and include thornland, shrubland, savannah and other short and sparse woody vegetation. Dry zone forests tend to be fragile and are easily degraded. More than half are in Africa. Dry forest types include oak, mesquite, piņon-juniper, maquis and acacia.

Tropical upland forests are forests above 800 m and include cloud forests (montane rain forests), which are shorter, floristically simpler and more heavily laden with mosses and lichens than lowland rain forests. Tropical upland species are similar to temperate forest species. The upland zone covers the Himalayas, parts of Myanmar, Thailand and Viet Nam, the highlands of Mexico, the Andes and the highlands of Ethiopia and mountains around Lake Victoria.

More than 200 million people live in clearings in tropical forests. They include groups who have lived in the same forest for generations, often referred to as indigenous or tribal peoples; people who have recently moved into the area, often described as settlers or squatters; and people who live part-time in the forest working as small-scale harvesters of forest products." These forests contribute to food security by providing sources of food, income, jobs, fuelwood, medicine and construction materials. Hunting for forest wildlife provides a significant proportion of the protein requirements of forest dwellers and the rural poor in many countries.

Table 8: Area of tropical forest formation, 1990

Region Total forest area Rain forest Moist deciduous Dry deciduous Hill and mountain Very dry Desert
 

('000 ha)

Africa 527586 86616 251143 92527 35256 58660 3385
Asia 310597 177371 41832 41108 47163 37 3085
Latin America and Caribbean 918116 454309 294306 44944 121895 1045 1616
TOTAL 1756299 718297 587281 178579 204314 59742 8086

Source: FAO

Forests also provide important indirect services. For example, forests surrounding towns, villages and communities offer critical soil erosion protection on hillsides and near streams. Deforestation in nearby watersheds may lead to flooding of lowland areas, displacement of populations and reductions in food production, as happened recently in Thailand and Madagascar."

Tropical deforestation. The rates, causes and effects of deforestation differ greatly from one country or region to another. These differences are due to population density and growth rates, the extent and quality of forest resources, levels and rates of development, the structure of property rights and cultural systems. Recent estimates suggest that nearly two-thirds of tropical deforestation worldwide is due to farmers clearing land for agriculture." Table 9 provides data on deforestation rates by region for the four major forest zones. As FAO points out in its recent book on sustainable forest management (footnote 5, p. 252), tropical forests are not being destroyed for trivial reasons. They are being cleared to provide expanding populations with land for food and cash crops. Many growing economies depend on wood products as a source of jobs, income, tax revenue and export earnings. Logging concessions and industrial roundwood production, from which sawnwood, panels and pulp and paper originate, provide these opportunities.

The largest losses of forest area are taking place in the tropical moist deciduous forests, the zone best suited for human settlement. In the decade 1981 to 1990, an estimated 61 million ha were deforested, which is more than 10 percent of the remaining moist deciduous area. The proportion of moist deciduous area still forested is 46 percent (only 29 percent in Asia). In contrast, 76 percent of the world's rain forest zone is still covered in forest. During the past decade, the total area of rain forest cut was 46 million ha.

TABLE 9A: Forest cover and deforestation in the tropical zone

Region Total land area Forest area 1980 Forest area 1990 Annual change in area 1981-90 Annual rate
of change
 

(million ha)

(%)

Africa 2 236 568 527 -4.1 -0.7
Asia 892 350 311 -3.9 -1.2
Latin America 1 650 992 918 -7.4 -0.8
WORLD TOTAL 4 778 1 910 1 756 -15.4 -0.8

 

TABLE 9B: Deforestation in the tropical rain forest zone

Region Total land area of zone Total forested area 1990 Annual deforestation 1981-90
  (million ha) (million ha) (% of zone) (million ha) (% of zone)
Africa 118.5 86.6 73 0.5 0.5
Asia 306.0 177.4 58 2.2 1.1
Latin America 522.6 454.3 87 1.9 0.4
WORLD TOTAL 947.1 718.3 76 4.6 0.6

 

TABLE 9C: Deforestation in the moist deciduous zone

Region Total land area of zone Total forested area 1990 Annual deforestation 1981-90
  (million ha) (million ha) (% of zone) (million ha) (% of zone)
Africa 653.6 251.1 38 2.2 0.9
Asia 144.6 41.8 29 0.7 1.5
Latin America 491.0 294.3 60 3.2 1.0
WORLD TOTAL 1 289.2 587.2 46 6.1 1.0

 

TABLE 9D: Deforestation in the dry and very dry zones

Region Total land area of zone Total forested area 1990 Annual deforestation 1981-90
  (million ha) million ha) (% of zone) (million ha) (% of zone)
Africa 823.1 151.2 18 1.1 0.7
Asia 280.6 41.1 15 0.5 1.1
Latin America 145.4 46.0 32 0.6 1.3
World total 1 249.1 238.3 19 2.2 0.9

 

TABLE 9E: Deforestation in the tropical upland formations

Region Total land area of zone Total forested area 1990 Annual deforestation 1981-90
  (million ha) (million ha) (% of zone) (million ha) (% of zone)
Africa 169.2 35.3 21 0.3 0.8
Asia 102.6 47.2 46 0.6 1.2
Latin America 429.1 121.9 28 1.6 1.2
World total 700.9 204.4 29 2.5 1.1

Note: Table 9A gives figures on forest cover in the tropical zone as a whole, including forests growing in zones not regarded as zones of natural forest growth, such as deserts or alpine areas. The data for Tables 9B to 9E are restricted to the zones of natural forest growth. The sums of the figures in these tables do not necessarily agree with Table 9A. Source: FAO, op. cit., footnote 5, p. 252.

Plantations

The available data on tree plantation areas suggest that the 100 million ha of plantations in the world provide for 7 to 10 percent of the world's present commercial wood consumption." An additional 14 million ha of rubber and coconut oil palm plantations are not included in the area of forest plantations. These are mainly in Asia and the wood obtained from them is increasingly important.

Statistics on plantations must be treated with caution because some reports use figures based on the accumulated area planted without any deductions for the areas felled. in other cases, figures are based simply on the numbers of seedlings distributed to farmers or communities and not on the numbers planted or surviving. On the other hand, the figures may omit the numbers of trees planted by farmers from their own seedlings.

Plantations cannot provide the full range of goods and services supplied by a natural forest. They are tree crops, analogous to agricultural crops, with a simplified ecology of one or, at most, a few species usually chosen for their yield and ease of management. The primary purpose of most plantations is to produce wood or other products quickly and cheaply. Their role, which is a highly valuable one, complements national or global forestry management strategies.

Plantations can be highly productive. The increment of timber from a tropical plantation may be 30 ml per hectare compared with 2 to 8 ml per hectare from a managed natural forest. Annual yields of up to 70 ml per hectare have been attained in Brazil from clones of hybrids of eucalyptus species. Such figures must be treated with caution, however (see Box 12). Experience shows that the yields assumed at the planning stage of many plantations are overestimated, often by a factor of two or more .20 Tree plantations that are well planned and managed can be highly productive and are ideal for supporting large-scale wood industries.

In tropical countries, the net area of plantations (taking into account the estimated survival rates) is estimated to be about 30 million ha, counting industrial and community plantations but not including trees planted by farmers themselves on their own lands. The area dedicated to plantations is growing at an average rate of around 2.6 million ha per year; about half of this area is in communally owned plantations.

A recent review of tropical plantations concluded that planning is generally poor, particularly for vital issues such as matching species and site. The study also noted that plantation projects are often designed in haste, with scant attention paid to important issues because of time and financial constraints.

Temperate countries also have numerous examples of plantations that have failed or sites that have been degraded because large blocks of single-species plantations have been established, unsuitable species have been introduced and even-aged plantations have been planted. Case-studies describe improperly managed temperate plantations as degrading key natural habitats, increasing soil erosion, modifying local hydrological cycles, intensifying pest and disease attacks and elevating levels of agrochemical pollution.

In the developing countries, further development of plantation forestry is constrained by the shortage of land. With expanding farming populations using all the unforested land for food production, the areas available for plantations are becoming increasingly restricted. The experience of the past two decades demonstrates that degraded or "waste" land may be the only resource available to the landless poor. There are, however, large areas where the natural forest has been badly degraded or where soil fertility has been lost through overcultivation, which could be used for plantations.

BOX 12: MALAYSIA'S COMPENSATORY PLANTATION PROGRAMME


Malaysia has a long history of experience with tree plantations. To meet projected timber requirements, the country established teak plantations in its northern peninsula in the late 1950s. A decade later, fast-growing tropical pine plantations were planted to provide longfibre pulp for an expanding pulp and paper industry. Prime lowland natural forest was cleared to plant Pinus caribaea, P. merkusii and Araucaria spp.

In the 1980s, a number of factors prompted policy-makers to expand plantations. First, revised projections made it clear that natural forests alone could not entirely meet the growing demand for logs. The initial growth rates and production estimates of the country's selective management system proved to be overoptimistic. Second, three-decades of agricultural development had reduced much of Malaysia's natural production forests to less productive and harder to manage hilly areas. Third, over-harvesting in many areas resulted in a significant backlog of secondary forest in need of silvicultural treatment and rehabilitation.

The government responded by establishing the Compensatory Forest Plantation Programme. As the name suggests, this large-scale programme was intended to compensate for the declining timber production from Malaysia's natural forests by establishing 188 000 ha of fast-growing, utility-grade tree plantations. As development programmes converted natural forests to agricultural and other uses, the timber would be used by an expanding wood processing industry. An important objective of the compensatory plantation programme was to maintain timber production at levels that could support the country's wood processing capacity.

In the early 1980s, international donors promoted fast-growing species such as Acacia mangium, Gmelina arborea and Paraserianthes flacataria as a means of relieving pressure on natural forests. The Malaysian Government accepted funding to plant these species even though the performance of the principal species to be planted, Acacia mangium, was largely unproven in Malaysia. Nor was this species well established in domestic or international markets.

Over time, problems with the performance of A. mangium became evident. Although the tree grows rapidly, it has poor form, is vulnerable to heartrot and is not a reliable source of utility-grade timber. To date, its wood appears to be more suitable for wood chips, a much lower-value end use. As a result, the government has halted the Compensatory Forest Plantation Programme.



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