LOWLAND EVERGREEN RAIN FORESTS

The tall, lush evergreen forests envisioned by most when referring to tropical forests are lowland evergreen rain forests. These forests are characterized by canopies with multiple layers of vegetation and the presence of large canopy emergent trees. Lowland evergreen rain forests generally have very high species diversity, with over 1000 tree species per square kilometre found in the richest forests of Amazonia and southeast Asia. Canopy and emergent trees in lowland evergreen forests often have large spreading crowns with a radius of >20m at maturity, can grow to more than 1min girth, and commonly possess plank-like buttresses important in physical support.

 

Beneath the upper canopy layer are smaller understorey trees, treelets, and a layer of herbaceous ground vegetation. Cauliflory and ramiflory are especially common among understorey trees in lowland tropical rain forests. One also generally finds abundant lianas; woody climbers that germinate in the understorey, but possess climbing mechanisms (such as tendrils or hooks) that allow them to use free-standing trees as support structures. Lianas that reach the canopy thus remain anchored to the forest floor.

Also common are epiphytes; plants that live on other plants (most often trees), but which at no point in their life history are rooted in the ground. Orchids, ferns and bromeliads provide many examples of tropical epiphytes, which enhance tropical diversity immensely (epiphytes are thought to comprise 10% of all vascular plants). Another group of plants characteristic of tropical forests are hemi-epiphytes, which germinate in the canopy, as do epiphytes, but produce roots that grow down the trunk of the host tree to become rooted in the ground. The most important group of tropical hemi-epiphytes are figs (many species of Ficus), the fruits of which are an important resource for many vertebrate species.

TROPICAL FOREST FORMATIONS

The main types of tropical forest are distinguished by differences in the distribution of rainfall throughout the year, by elevation, and by soil type. Tropical forests that experience ever-wet conditions with no month receiving less than 100mm of precipitation are generally referred to as ‘tropical rain forests’, although a distinction is also sometimes made between tropical ‘moist forests’ and ‘rain forests’ in a strict sense that receive annual rainfall in excess of 4000 mm.

The two other main tropical forest types, ‘tropical dry forests’ and ‘semi-evergreen rain forests’, experience an annual dry period. In tropical dry forests (also called ‘monsoon forests’) the dry period is severe, and during this most trees drop their leaves in order to reduce water loss. In semi-evergreen rain forests the seasonal drought is less extreme, and a leafless period does not occur to the same extent.

Within these broad moisture regimes, tropical forests are subdivided on the basis of elevation and soil type, and corresponding differences in forest structure. The distinguishing structural characteristics include canopy height, crown layering and the presence (or absence) of different climbers and epiphytes. Tree buttressing, crown shape, leaf structure, and position of flower/fruit formation are other important physiognomic descriptors of tropical forests.

On a global basis the most important types of tropical moist forest include lowland evergreen rain forests, upper and lower montane rain forests, heath forests, peat swamp forests, freshwater swamp forests and mangroves.

DISTRIBUTION PATTERNS TROPICAL RAINFOREST

The Tropical forests exist with some essential facts of geography and climatic systems. By definition, ‘the tropics’ lie between 23o N and 23o S latitude, the area within which the sun lies directly overhead at some point in its seasonal progression.

The flux of solar energy within this region is high, due to the fact that incoming sunlight is projected at a 90o angle to the surface of the earth. This high solar energy flux results in a high rate of water evaporation over the tropical oceans and of evapotranspiration over tropical land surfaces.



The result is a rising column of warm, moist air at tropical latitudes. As this air rises it cools as a result of the gradient in air pressure through the atmosphere (adiabatic cooling). Water condenses out from this air mass, generating rainfall. The air mass ultimately dries out, and is carried poleward from the tropics as a part of wind circulation patterns known as Hadley cells.

At subtropical latitudes near 23–30o N and S, the now-dry air mass descends, creating a region of high pressure that corresponds closely to the world distribution of deserts. As a consequence of these climatic circulation patterns, the earth’s equatorial zone is warm and wet, corresponding to the broad band of tropical forests found along the earth’s equatorial axis.

CHARACTERISTIC OF INDONESIAN RAINFORESTS

Most of the natural forests in Indonesia, including in tropical rain forests. Tropical rainforests have characteristics that are different from other forests. Indonesia is an archipelago that has over 17,500 islands spread from Sabang to Merauke. Diverse place to grow from forests in Indonesia make Indonesia's tropical forests have a special characteristic of the forest than in the other hemisphere.

Many experts mendiskripsi tropical rainforests as a specific ecosystem, which can only stand firmly with the links between the constituent components as a unified whole. The linkage between the constituent components allows certain forms of forest structure that can provide a specific function as well as economic stability, high biological productivity, hydrological cycles are adequate and others. The reality on the groung, forest type has a very low soil fertility, soil composed of negatively charged clay particles such as kaolinite and illite low.

The condition of forest land also shows the uniqueness and distinctive characteristics. The biological activity of the soil rests on a layer of soil over the top (top soil). The biological activity of these about 80% are in top soil only. The facts indicate that the tropical rainforest ecosystems are fragile ecosystem, because each component can not stand alone. Besides, it was found that some other phenomenon is the existence of high diversity between sites or groups of both the forest and the growth of vegetation (Marsono, 1991).

From these characteristics make tropical forest in Indonesia is very prone to degradation. Tropical forest destruction in Indonesia is estimated at 2 million hectares per year. Tropical forest destruction in Indonesia is caused by various factors both from parties only seek profit alone or from the way management of tropical forests is wrong, because they do not understand about the characteristics of tropical forest itself.

Reduction efforts and prevention of tropical forest destruction in Indonesia is an urgent matter. Otherwise tropical forests will be lost due to logging activities, mining, human settlements, agricultural land clearing, forest fires and conversion to other forms.

Characteristics of Rainforests

Characteristics of rain forests, The temperature in a tropical rain forest varies little. It rarely rises above 95 °F (35 °C) or drops below 64 °F (18 °C). In many regions, the average temperature in the hottest month is only 2 to 5 Fahrenheit degrees (1 to 3 Celsius degrees) higher than the average temperature in the coldest month. Most rain forests receive more than 80 inches (203 centimeters) of rain annually. Some areas may receive more than 250 inches (635 centimeters) of rain each year. Thundershowers can occur more than 200 days a year.

Rain forest soils vary greatly from place to place. In many areas, the soil is acidic and infertile because years of heavy rains have washed out most of the nutrients (nourishing substances). Most rain forest nutrients are part of living plants. Small amounts of nutrients occur in a thin layer of topsoil that contains decaying vegetation.

Rain forest trees have developed several ways of capturing nutrients. For example, they obtain nourishment from rainwater that collects in their leaves or along their trunks and branches. They also withdraw nutrients from their old leaves before they shed them. The roots of most rain forest trees grow close to the surface and quickly absorb soil nutrients before they wash away. Special fungi called mycorrhizae grow in or on many of the roots and help them absorb minerals from the soil.

Rain forests grow in four major layers: (1) the canopy, or top layer; (2) the sub-canopy, a layer of trees just below the canopy; (3) the understory, a shady lower area; and (4) the floor. The tallest trees, known as emergents, grow more than 165 feet (50 meters) tall. The crowns (tops) of these trees dominate the canopy. Emergents receive the greatest amount of sunlight, but they must endure high temperatures and strong winds. The crowns of other trees in the canopy usually form a nearly continuous covering of leaves 65 to 165 feet (20 to 50 meters) above the ground. Some tall trees have large growths called buttresses that extend from the base of the trunk and help support the tree.

More than 70 percent of rain forest animal and plant species reside in the canopy and sub-canopy. Many tree branches have a dense covering of epiphytes, plants that grow on other plants and obtain nourishment from the air and rain. Vines called lianas often climb on or around the trunks and branches of trees.

The shady understory shelters small palms, young trees, and herbaceous (nonwoody) plants that can grow in dim light. Many popular house plants, such as philodendrons, dieffenbachia, and ferns, are developed from species that live in this area. Some scientists believe only 1 percent of the sunlight available to emergent trees reaches the understory.

A thin layer of fallen leaves, seeds, fruits, and branches covers the forest floor. This layer quickly decomposes and is constantly replaced.

The layers of a rain forest continually change. Large old trees die and fall to the ground, leaving a gap in the canopy. Direct sunlight penetrates through to the understory and stimulates the growth of seedlings, saplings, and small trees below. The small trees slowly stretch upward into the canopy. As they branch and expand their crowns, they fill the gaps in the canopy. A mature rain forest consists of a mixture of closed canopies, gaps, and patches of growing trees where the canopy is being rebuilt. The regeneration of many rain forest trees depends on gaps developing regularly in the canopy.

Plants and animals. About 45 percent of the world's plant species occur in tropical rain forests. Scientists have counted over 250 species of trees in small areas of Asian and South American rain forests. A similar plot of land in a northern temperate forest would have only about 10 to 15 tree species. In addition to trees, rain forests support a great variety of bamboos, herbs, and shrubs. Climbing vines, ferns, mosses, and orchids grow directly on the trunks and branches of large trees.

Because of continual moisture and warmth, tropical rain forests stay green all year. Most rain forest trees continually lose old leaves and grow new ones. Only a few species lose all of their leaves for a brief period.

Fish, amphibians, reptiles, birds, and mammals abound in the rain forest and its rivers. However, insects rank as the most plentiful rain forest animals. An individual tree in a South American rain forest may support more than 40 species of ants. Scientists have counted about 1,200 species of beetles living in only 19 tree crowns from Panama.

Plants and animals in the rain forest depend on one another for survival. Many animal groups, especially insects and birds, pollinate the flowers of rain forest trees. Such animals receive food from the flowers' nectar. In return, they pollinate the next flowers they visit. Some trees rely on only one species of insect for pollination. Many rain forest trees also depend on animals to disperse their seeds. In the Amazon rain forest, fish disperse the seeds of some trees.

What is a Rainforest ? | DEFINITION OF RAINFOREST

Frequently Asked Questions About the Rainforest, What is a Rainforest? or Definition of Rainforest. Rainforest is a woodland of tall trees growing in a region of year-round warmth and abundant rainfall. Almost all rain forests lie at or near the equator. They form an evergreen belt of lush vegetation that encircles the planet. German botanist Andreas F. W. Schimper first coined the term rain forest-in German, Regenwald-in 1898.

Tropical rain forests occupy only 6 to 7 percent of the earth's surface. However, they support more than half of the world's plant and animal species (kinds). More kinds of frogs and other amphibians, birds, insects, mammals, and reptiles live in rain forests than in any other area. Scientists believe millions more rain forest species remain undiscovered.

The rain forest provides people with many benefits. Its plants produce timber, foods, medicines, and such industrial products as dyes, fibers, gums, oils, and resins. Rain forests help regulate the earth's climate and maintain clean air. The forests' lush, green beauty and rich wildlife offer a special source of enjoyment.

In addition, rain forests provide homes to millions of people. Such groups as the Yanomami of South America, the Dayaks of Southeast Asia, and the Pygmies of central Africa have lived in rain forests for centuries. They make their living by hunting, fishing, collecting forest products, and farming. Traditional forest peoples have acquired much knowledge about the rain forest's plants and animals.

In spite of these benefits, people cut down thousands of square miles or square kilometers of rain forest each year. This destruction eliminates thousands of species of animals. A number of governments and conservation organizations are working to preserve the rain forests.

Types of Rainforests

Rainforests are found throughout the world, not only in tropical regions, but also in temperate regions like Canada, the United States, and the former Soviet Union. These forests, like tropical rainforests, receive abundant, year-round rainfall, and are characterized by an enclosed canopy and high species diversity, but lack the year-round warmth and sunlight associated with tropical rainforests. However this book focuses on tropical rainforests, and these are the only forest forms discussed here.

Tropical rainforests merge into other types of forest depending on the altitude, latitude, and various soil, flooding, and climate conditions. These forest types form a mosaic of vegetation types which contribute to the overwhelming diversity of the tropics.

EQUATORIAL EVERGREEN RAINFOREST VS. MOIST FOREST

There are two major types of wet tropical forests: equatorial evergreen rainforests and moist forests, which includes monsoon forests and montane/cloud forests. Equatorial rainforests, often considered the "real rainforest," are characterized by more than 80 inches (2,000 mm) of rain annually spread evenly throughout the year. These forests have the highest biological diversity and have a well-developed canopy "tier" form of vegetation. Roughly two-thirds of the world's tropical wet forests can be considered the equatorial type. These forests are near the equator where there is very little seasonal variation and the solar day is a constant length all year round. The greatest expanses of equatorial rainforest are found in lowland Amazonia, the Congo Basin, the Southeast Asian islands of Indonesia, and Papua New Guinea.

Tropical moist forests are found at a greater distance from the equator where rainfall and day length vary seasonally. These forests get "only" 50 inches (1,270 mm) of rain annually and are markedly distinguished from equatorial rainforests by a cooler dry season. During this dry season, many trees shed some or even all their leaves, creating a seasonal reduction of canopy cover and allowing more sunlight to reach the forest floor. The increased sunlight reaching the forest floor allows the growth of vigorous understory vegetation not found in lowland equatorial forest. Such moist forest is found in parts of South America, the Caribbean, West Africa, and Southeast Asia, especially Thailand, Burma, Vietnam, and Sri Lanka.

PRIMARY VS. SECONDARY FOREST

Throughout this site, other books, and discussions about tropical rainforest, the term "primary forest" is used. Primary forest refers to untouched, pristine forest that exists in its original condition. This forest has been relatively unaffected by human activities. Primary rainforest is often characterized by a full ceiling canopy and usually several layers of understory. The ground floor is generally clear of heavy vegetation because the full canopy allows very little light, necessary for plant growth, to penetrate. Occasionally, when a canopy tree falls, a temporary "light gap" is opened in the canopy, allowing growth of floor and understory species. Primary forest is the most biologically diverse type of forest.

Secondary forest is rainforest that has been disturbed in some way, naturally or unnaturally. Secondary forest can be created in a number of ways, from degraded forest recovering from selective logging, to areas cleared by slash-and-burn agriculture that have been reclaimed by forest. Generally, secondary forest is characterized (depending on its level of degradation) by a less developed canopy structure, smaller trees, and less diversity. Due to the lack of a full canopy, more light will reach the floor, supporting vigorous ground vegetation. "Jungle" is the term often applied to secondary forest with dense ground growth, but it is also applied to some tropical moist forests where seasonal variations permit thick ground growth.

Primary versus total forest cover for selected tropical countries

		Total land area		Total forest cover 2005				Primary forest cover 2005				Total deforestation 1990-2005		Loss of primary forest 1990-2005
Country		(1000 ha)		(1000 ha)		% of total land area		(1000 ha)		% of total land area		% of 1990 forest cover		% of 1990 primary forest cover
Bolivia		109,858		58,740		54.2		29,360		26.7		-6.5		-6.5
Cambodia		18,104		10,447		59.2		322		1.8		-19.3		-58.0
Congo		34,200		22,471		65.8		7,464		21.8		-1.1		-1.1
Costa Rica		5,110		2,391		46.8		180		3.5		-6.7		-29.4
Ghana		23,854		5,517		24.2		353		1.5		-25.9		0.0
Guatemala		10,889		3,938		36.3		1,957		18.0		-17.1		-17.0
Malawi		11,848		3,402		36.2		1,132		9.6		-12.7		-34.5
Malaysia		32,975		20,890		63.6		3,820		11.6		-6.6		0.0
Nigeria		92,377		11,089		12.2		326		0.4		-35.7		-79.0
Senegal		19,672		8,673		45		1,598		8.1		-7.2		-9.2
Thailand		51,312		14,520		28.4		6,451		12.6		-9.1		0.0
Brazil		851,488		477,698		57.2		415,890		48.8		-8.1		-9.7
Colombia		113,891		60,728		58.5		53,062		46.6		-1.2		-1.5
Côte d'Ivoire		32,246		10,405		32.7		625		1.9		1.8		0.0
Liberia		11,137		3,154		32.7		129		1.2		-22.3		0.0
Madagascar		58,704		12,838		22.1		10,347		17.6		-6.2		-1.5
Mexico		195,820		64,238		33.7		32,850		16.8		-6.9		-15.3
Panama		7,552		4,294		57.7		3,023		40.0		-1.9		-18.4
Papua New Guinea		46,284		29,437		65		25,211		54.5		-6.6		-13.7
Peru		128,522		68,742		53.7		61,065		47.5		-2.0		-2.9
Philippines		30,000		7,162		24		829		2.8		-32.3		0.0
Sri Lanka		6,561		1,933		29.9		167		2.5		-17.7		-35.0

The Food and Agriculture Organization of the United Nations estimates that primary forests now account for 36 percent of total forest area, but are being lost or modified at a rate of 6 million hectares a year through deforestation or selective logging. Selective logging, where only one or two valuable tree species are harvested from an area, was recently found to be degrading forests in the Amazon twice as fast as deforestation figures indicate.

Scientists do not know how long it takes for secondary forest to attain the structure and levels of biodiversity of primary forest. A recent study by conducted as part of the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA) determined that trees in the Central Amazon may, on average, be several hundred years old, suggesting that primary forests take a long time to develop.


LOWLAND VS. MONTANE FOREST

Lowland tropical rainforest refers to the majority of tropical rainforest, that is, forest which grows on flat lands at elevations generally less than 3,300 feet (1,000 m)—although elevation may vary. Lowland primary forest, often characterized by more than five forest tier levels, is usually taller and more diverse than montane forest. It has a greater diversity of fruiting trees; hence more animals specially adapted to feed on their fruits and more large mammals. Lowland rainforest is far more threatened than montane forest because of its accessibility, more suitable soils for agriculture, and more hardwoods valuable as timber. In many countries, virtually all lowland primary forest is gone, while montane forest still remains.

Tropical montane rainforest is forest that grows on mountains and above an altitude of 3,300 feet. High montane forest, above 6,600-10,000 feet (2,500-3,000 meters) in elevation, is often manifested as "cloud forest," forest that receives the majority of its precipitation from mist or fog that passes up from the moist, humid lowlands. The trees of cloud forests are typically shorter than those of lowland forest resulting in a less-developed canopy. Nevertheless, cloud forest trees are heavily burdened with epiphytes that thrive with the abundance of moisture from the passing fog. Trees in places like the lower elevations of the Andes in Ecuador, Peru, Colombia, and Venezuela; Central America (Monteverde in Costa Rica in particular); Borneo (Mount Kinabalu); and Africa (Ethiopia, Kenya, Rwanda, Zaire, Uganda), are frequently green with dense moss and beautiful, often rare, orchids.

Patches of cloud forests tend to have many endemic species, because they are often isolated from other sections of cloud forest by valleys and ridges. These species are prevented from migrating to other forest areas by these obstacles to the sides, by the lowland forest below, and by steep cliffs above. Cloud forests are home to an abundance of hummingbirds, frogs, and epiphytes like orchids, bromeliads, and mosses. Many of these species are endemic to a single locality, like the Golden toad of Monteverde, Costa Rica, a species which is now believed to be extinct. Cloud forests generally lack an abundance of large-bodied mammals due to the small number of fruiting trees.

Tropical montane forests are especially in the South American Andean region, where much of the forest has been cleared for agriculture. Of the continent's endangered species, a disproportionate number of those are found in yungas, the regional name for tropical montane forests in the Andes. These forests have also been little studied.

Above 10,000 feet (3,300 m), cloud forest may give way to sub-alpine and alpine forest. These habitats have less rain, fewer trees, and reduced biodiversity compared with lower elevation forests.

Chart showing percentage cover of world forests. Rainforests are a subsection of "Tropical forests".

OTHER TYPES OF FOREST

SEASONAL OR MONSOON FOREST
Monsoon forests are tropical moist or seasonal rainforests found primarily in Asia (India/Sri Lanka to China), West and East Africa, Northern Australia, and Eastern Brazil. In this type of forest there is a distinct cooler dry season and a distinct wet season. These forests tend to be less diverse and more dwarfed in terms of tree size in comparison to typical equatorial rainforests.

Monsoon forests are highly threatened worldwide by clearing for cultivation, especially in West Africa, where over 90 percent of the coastal rainforests and the monsoon forests have been cleared.

IGAPÒ FOREST

Flooded forest in Brazil | more Photo by R. Butler

Igapò forest is rainforest that is regularly inundated for extended periods during the flood season (sometimes considered permanently flooded rainforest). The best known of such forests are found in the Amazon Basin where they make up about 2 percent of the total rainforest. Igapò forest trees are shorter than those of non-flooded forest because of the instability caused by the wet, poorly drained soils (hence it is sometimes known as "swamp forest") and characterized by certain tree species like Cecropia, Ceiba, and Mauritia palms (also known as the aguaje palm). Many igapò tree species have stilt roots and flying buttresses to lend structural support. Igapò forest is flooded (4-10 months of the year) and flooding is usually predictable. Fish play an important role in seed dispersal in this forest system.

VÀRZEA FOREST
Vàrzea forests are floodplain forests which flood seasonally. Unlike swamp forests, varzeà forests have relatively rich soils from the annual replenishment of nutrients from whitewater rivers. Because these forests are more suitable for agriculture than typical rainforest, they are some of the most threatened. Even in the Amazon where vast majority of such forests are found, vàrzea are disappearing rapidly for development.

Floodplain forests, especially those located on river banks and islands, are often short-lived due to the meandering nature of tropical lowland rivers which eat away at the forests' base. According to Amazon Headwaters, a book by Michael Goulding and his colleagues, research in Peru suggests that most floodplain forests are rarely older than 200 years and may have turnover rates exceeding 1.6 percent, implying an average tree life of 63 years. For this reason, floodplain forests are nearly always in some stage of succession with pioneer species like Cecropia being replaced with Kapok (Ceiba) and fig trees further away from the river.

HEATH FOREST
Heath forests are found on well-drained, sandy soils that are extremely nutrient-poor. These forests are characterized by certain tree species tolerant of the poor, acidic soil conditions and are considerably "stunted" in comparison with typical rainforests. More light reaches the forest floor making for dense tree growth. Heath forests, also known as blackwater or caatinga forests, are drained by blackwater rivers and are found primarily in the Amazon Basin (the Rio Negro drainage), but also in parts of Asia.

PEAT FOREST  [news and information on peatlands]
Peat forest is found in small parts of Africa, northeastern South America, and large areas in southeast Asia (especially Borneo and Sumatra). These swamp forests appear in places where dead vegetation becomes waterlogged and accumulates as peat. The peat acts as a sort of sponge withholding moisture at times of little rainfall and absorbing monsoon rains. When peat swamp forests are drained for agricultural projects, they become highly susceptible to combustion. Under the dry el Niño conditions of 1997-98, thousands of fires raged in the peat swamps of Indonesia. Fires in peat swamps are extraordinarily difficult to extinguish because the conflagration continues in the deeper layers of peat.

TERRA FIRME FOREST
Terra Firme literally means "firm earth" and refers to rainforest that is not inundated by flooded rivers. This forest is noticeably taller and more diverse (>400 species/hectare in some areas) than igapò or flooded forest. It is found only on dry, well-drained soils and is characterized by such species as Brazil nut trees, Rubber trees, and many tropical hardwood trees.

MANGROVE FOREST [news and information on peatlands]
Mangrove forest is found in silt-rich, saline (brackish water) habitats worldwide, generally along large river deltas, estuaries, and coastal areas. It is characterized by low tree diversity, almost exclusively mangroves, with a low broken canopy. Mangroves are evergreen trees and shrubs that are well adapted to their salty and swampy habitat by having breathing roots (pneumatophores) that emerge from the oxygen-deficient mud to absorb oxygen.

Mangroves in Honduras. Photo by R. Butler. More mangrove photos

Mangrove swamps are home to numerous bizarre amphibious fish species like the mudskippers of eastern Africa to Australia and Anableps, the so-called four-eyed fish of the New World. Mudskippers are renowned for their preference for terrestrial haunts over aquatic realms. These fish spend more time on floating debris, tree toots, and plants than they do in the water where they only go to escape predators. Watching a group of Mudskippers reminds the observer of what our ancestors must have looked like when they first left the ocean for life on land. Mudskippers are highly intelligent fish that feed primarily on insects and crustacean.

A second amphibious species found in mangrove forests is the Anableps. a species widespread in the New World from Central America to northern South America. Most notable about its physical features is its double-lobed eyes which allow it to see both above and below the water line as it swims along the water surface. The Anableps, too, regularly leaves the water to perch on tree roots and rocks.

Mangrove forests are some of the most threatened ecosystems on the planet because of their proximity to the ocean (prime resort/development property) and the tendency for local people and governments to undervalue the services they provide. A recent study by the Food and Agriculture Organization of the United Nations found that 20 percent of the world's mangrove forests have disappeared since 1980, mostly due to farming, harvesting for timber and charcoal, freshwater diversion, real estate development, and conversion for tourism.

According to the Environmental Justice Foundation, about 38 percent of global mangrove deforestation is linked to shrimp farm development. Mangrove clearing for commercial shrimp and prawn hatcheries is particularly prevalent in Southeast Asia. Ironically this form of aquaculture has come at the expense of the natural fish and shrimp hatchery.

The destruction of mangrove forest has dire implications for the fisheries industry, since these forests provide an important spawning ground and serve as a nursery for many commercially important species. In addition, mangrove forest protects coastal regions against storm damage and erosion. Research conducted following the 2004 tsunami in Asia found that areas forested with mangroves suffered considerably less damage than areas without tree vegetation.

Mangrove forests are slow to recover from clearing and degradation. For example, seismic lines only a few meters wide in the mangrove forest of Nigeria were still visible by air a decade after they were cut.


Review questions:

• What is the difference between primary and secondary forest?
• True or false—Cloud forest is found in mountainous areas.
• True or false—flooding is common in the Amazon rainforest.
• Why are mangrove forests important?
• Why are mangrove forests being destroyed?

KINDS OF FORESTS

Many systems are used to classify the world's forests. Some systems classify a forest according to the characteristics of its dominant trees. A needleleaf forest, for example, consists of a forest in which the dominant trees have long, narrow, needlelike leaves. Such forests are also called coniferous (cone-bearing) because the trees bear cones. The seeds grow in these cones. A broadleaf forest is made up mainly of trees with broad, flat leaves.

Forests in which the dominant trees shed all their leaves during certain seasons of the year, and then grow new ones, are classed as deciduous forests. In an evergreen forest, the dominant trees grow new leaves before shedding the old ones. Thus, they remain green throughout the year.

In some other systems, forests are classified according to the usable qualities of the trees. A forest of broadleaf trees may be classed as a hardwood forest because most broadleaf trees have hard wood, which makes fine furniture. A forest of needleleaf trees may be classed as a softwood forest because most needleleaf trees have softer wood than broadleaf trees have.

Many scientists classify forests according to various ecological systems. Under such systems, forests with similar climate, soil, and amounts of moisture are grouped into formations. Climate, soil, and moisture determine the kinds of trees found in a forest formation. One common ecological system groups the world's forests into six major formations. They are (1) tropical rain forests, (2) tropical seasonal forests, (3) temperate deciduous forests, (4) temperate evergreen forests, (5) boreal forests, and (6) savannas. 

Tropical rain forests grow near the equator, where the climate is warm and wet the year around. The largest of these forests grow in the Amazon River Basin of South America, the Congo River Basin of Africa, and throughout much of Southeast Asia.

Of the six forest formations, tropical rain forests have the greatest variety of trees. As many as 100 species-none of which is dominant-may grow in 1 square mile (2.6 square kilometers) of land. Nearly all the trees of tropical rain forests are broadleaf evergreens, though some palm trees and tree ferns can also be found. In most of the forests, the trees form three canopies. The upper canopy may reach more than 165 feet (50 meters) high. A few exceptionally tall trees, called emergents, tower above the upper canopy. The understory trees form the two lower canopies.

The shrub and herb layers are sparse because little sunlight penetrates the dense canopies. However, many climbing plants and epiphytes crowd the branches of the canopies, where the sunlight is fullest.

Most of the animals of the tropical rain forests also live in the canopies, where they can find plentiful food. These animals include such flying or climbing creatures as bats, birds, insects, lizards, mice, monkeys, opossums, sloths, and snakes.

Tropical seasonal forests grow in certain regions of the tropics and subtropics. These regions have a definite wet and dry season each year or a somewhat cooler climate than that of the tropical rain forest. Such conditions occur in Central America, central South America, southern Africa, India, eastern China, and northern Australia and on many islands in the Pacific Ocean.

Tropical seasonal forests have a great variety of tree species, though not nearly as many as the rain forests. They also have fewer climbing plants and epiphytes. Unlike the trees of the rain forest, many tropical seasonal species are deciduous. The deciduous trees are found especially in regions with distinct wet and dry seasons. The trees shed their leaves in the dry season.

Tropical seasonal forests have a canopy about 100 feet (30 meters) high. One understory grows beneath the canopy. Bamboos and palms may form a dense shrub layer, and a thick herb layer blankets the ground. The animal life resembles that of the rain forest.

Temperate deciduous forests grow in eastern North America, western Europe, and eastern Asia. These regions have a temperate climate, with warm summers and cold winters.

The canopy of temperate deciduous forests is about 100 feet (30 meters) high. Two or more kinds of trees dominate the canopy, and another 15 to 25 kinds may be present. Most of the trees in these forests are broadleaf and deciduous. They shed their leaves in fall. The understory, shrub, and herb layers may be dense. The herb layer has two growing periods each year. Plants of the first growth appear in early spring, before the trees have developed new leaves. These plants die by summer and are replaced by plants that grow in the shade of the leafy canopy.

Large animals of the temperate deciduous forests include bears, deer, and, rarely, wolves. These forests are also the home of hundreds of smaller mammals and birds. Many of the birds migrate south in fall, and some of the mammals hibernate during the winter.

Some temperate areas support mixed deciduous and evergreen forests. In the Great Lakes region of North America, for example, the cold winters promote the growth of heavily mixed forests of deciduous and evergreen trees. Forests of evergreen pine and deciduous oak and hickory grow on the dry coastal plains of the Southeastern United States.

Temperate evergreen forests. In some temperate regions, the environment favors the growth of evergreen forests. Such forests grow along coastal areas that have mild winters with heavy rainfall. These areas include the northwest coast of North America, the south coast of Chile, the west coast of New Zealand, and the southeast coast of Australia. Temperate evergreen forests also cover the lower mountain slopes in Asia, Europe, and western North America. In these regions, the cool climate favors the growth of evergreen trees.

The strata and the plant and animal life vary greatly from one temperate evergreen forest to another. For example, the mountainous evergreen forests of Asia, Europe, and North America are made up of conifers. The coastal forests of Australia and New Zealand, on the other hand, consist of broadleaf evergreen trees.

Boreal forests are found in regions that have an extremely cold winter and a short growing season. The word boreal means northern. Vast boreal forests stretch across northern Europe, Asia, and North America. Similar forests also cover the higher mountain slopes on these continents.

Boreal forests, which are also called taiga, have the simplest structure of all forest formations. They have only one uneven layer of trees, which reaches up to about 75 feet (23 meters) high. In most of the boreal forests, the dominant trees are needleleaf evergreens-either spruce and fir or spruce and pine. The shrub layer is spotty. However, mosses and lichens form a thick layer on the forest floor and also grow on the tree trunks and branches. There are few herbs.

Many small mammals, such as beavers, mice, porcupines, and snowshoe hares, live in the boreal forests. Larger mammals include bears, caribou, foxes, moose, and wolves. Birds of the boreal forests include ducks, loons, owls, warblers, and woodpeckers.

Savannas are areas of widely spaced trees. In some savannas, the trees grow in clumps. In others, individual trees grow throughout the area, forming an uneven, widely open canopy. In either case, most of the ground is covered by shrubs and herbs, especially grasses. As a result, some biologists classify savannas as grasslands. Savannas are found in regions where low rainfall, poor soil, frequent fires, or other environmental features limit tree growth. 

The largest savannas are tropical savannas. They grow throughout much of Central America, Brazil, Africa, India, Southeast Asia, and Australia. Animals of the tropical savannas include giraffes, lions, tigers, and zebras.

Temperate savannas, also called woodlands, grow in the United States, Canada, Mexico, and Cuba. They have such animals as bears, deer, elk, and pumas.

Source : World Book 2005