137-688: Capparis decidua , commonly known as karira , is a useful plant in its marginal habitat. It is a small much-branched tree or shrub . It bears a mass of slender, gray-green leafless branches, the small caducous leaves being found only on young shoots. It rarely exceeds a height of 5 metres (16 feet). The new flush of leaves appears in November–January. Red conspicuous flowers appear in March to April and August–September and ripe by May and October. The pink fleshy berries are readily eaten by birds. It coppices well and produces root suckers freely. It
274-670: A potential evapotranspiration ratio (PET) value of <0.25. However, most lowland tropical forests can be classified as tropical moist or wet forests, which differ in regards to rainfall. Tropical forest ecology- dynamics, composition, and function- are sensitive to changes in climate especially changes in rainfall. Soil types are highly variable in the tropics and are the result of a combination of several variables such as climate, vegetation, topographic position, parent material, and soil age. Most tropical soils are characterized by significant leaching and poor nutrients, however there are some areas that contain fertile soils. Soils throughout
411-409: A symbiotic relationship with Frankia species, a filamentous bacterium that can fix nitrogen from the air, converting it into ammonia . They have actinorhizal root nodules on their roots in which the bacteria live. This process enables the tree to live in low nitrogen habitats where they would otherwise be unable to thrive. The plant hormones called cytokinins initiate root nodule formation, in
548-416: A classic example of parallel evolution . With an estimated 60,000-100,000 species, the number of trees worldwide might total twenty-five per cent of all living plant species. The greatest number of these grow in tropical regions; many of these areas have not yet been fully surveyed by botanists , making tree diversity and ranges poorly known. The majority of tree species are angiosperms or hardwoods. Of
685-503: A drier savanna climate and insufficient rainfall to support dense forests, the canopy is not closed, and plenty of sunshine reaches the ground which is covered with grass and scrub. Acacia and baobab are well adapted to living in such areas. The roots of a tree serve to anchor it to the ground and gather water and nutrients to transfer to all parts of the tree. They are also used for reproduction, defence, survival, energy storage and many other purposes. The radicle or embryonic root
822-650: A half meters, or 59 inches, on average). Amongst this group are the Efe, Aka, Twa , Baka , and Mbuti people of Central Africa. However, the term pygmy is considered pejorative so many tribes prefer not to be labeled as such. Some notable indigenous peoples of the Americas , or Amerindians, include the Huaorani , Ya̧nomamö , and Kayapo people of the Amazon . The traditional agricultural system practiced by tribes in
959-418: A hundred litres are required to make one litre of birch syrup. Various parts of trees are used as spices. These include cinnamon , made from the bark of the cinnamon tree ( Cinnamomum zeylanicum ) and allspice , the dried small fruits of the pimento tree ( Pimenta dioica ). Nutmeg is a seed found in the fleshy fruit of the nutmeg tree ( Myristica fragrans ) and cloves are the unopened flower buds of
1096-401: A new niche. Direct competition will often lead to one species dominating another by some advantage, ultimately driving it to extinction. Niche partitioning is the other option for a species. This is the separation and rationing of necessary resources by utilizing different habitats, food sources, cover or general behavioral differences. A species with similar food items but different feeding times
1233-509: A process closely related to mycorrhizal association. It has been demonstrated that some trees are interconnected through their root system, forming a colony. The interconnections are made by the inosculation process, a kind of natural grafting or welding of vegetal tissues. The tests to demonstrate this networking are performed by injecting chemicals, sometimes radioactive , into a tree, and then checking for its presence in neighbouring trees. The roots are, generally, an underground part of
1370-404: A process known as cladoptosis . The crown is the spreading top of a tree including the branches and leaves, while the uppermost layer in a forest, formed by the crowns of the trees, is known as the canopy . A sapling is a young tree. Many tall palms are herbaceous monocots, which do not undergo secondary growth and never produce wood. In many tall palms, the terminal bud on the main stem
1507-465: A roof over the two remaining layers. It contains the majority of the largest trees, typically 30–45 m in height. Tall, broad-leaved evergreen trees are the dominant plants. The densest areas of biodiversity are found in the forest canopy, as it often supports a rich flora of epiphytes , including orchids, bromeliads, mosses and lichens. These epiphytic plants attach to trunks and branches and obtain water and minerals from rain and debris that collects on
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#17327810291361644-614: A seasonal basis but dwelt primarily in adjacent savanna and open forest environments where food is much more abundant. Other people described as rainforest dwellers are hunter-gatherers who subsist in large part by trading high value forest products such as hides, feathers, and honey with agricultural people living outside the forest. Many indigenous peoples around the world live within rainforests as hunter-gatherers, or subsist as part-time small scale farmers supplemented in large part by trading high-value forest products such as hides, feathers, and honey with agricultural people living outside
1781-422: A second spurt of growth, a Lammas growth may occur which is believed to be a strategy to compensate for loss of early foliage to insect predators. Primary growth is the elongation of the stems and roots. Secondary growth consists of a progressive thickening and strengthening of the tissues as the outer layer of the epidermis is converted into bark and the cambium layer creates new phloem and xylem cells. The bark
1918-489: A significant role in reducing erosion and moderating the climate . They remove carbon dioxide from the atmosphere and store large quantities of carbon in their tissues. Trees and forests provide a habitat for many species of animals and plants. Tropical rainforests are among the most biodiverse habitats in the world. Trees provide shade and shelter , timber for construction, fuel for cooking and heating, and fruit for food as well as having many other uses. In much of
2055-424: A similar growth form, by usually growing larger and having a single main stem; but there is no consistent distinction between a tree and a shrub, made more confusing by the fact that trees may be reduced in size under harsher environmental conditions such as on mountains and subarctic areas. The tree form has evolved separately in unrelated classes of plants in response to similar environmental challenges, making it
2192-467: A single tree species, which will not flourish in the absence of its mycorrhizal associate. Others are generalists and associate with many species. The tree acquires minerals such as phosphorus from the fungus, while the fungus obtains the carbohydrate products of photosynthesis from the tree. The hyphae of the fungus can link different trees and a network is formed, transferring nutrients and signals from one place to another. The fungus promotes growth of
2329-640: A slightly looser definition; while the Joshua tree , bamboos and palms do not have secondary growth and never produce true wood with growth rings, they may produce "pseudo-wood" by lignifying cells formed by primary growth. Tree species in the genus Dracaena , despite also being monocots, do have secondary growth caused by meristem in their trunk, but it is different from the thickening meristem found in dicotyledonous trees. Aside from structural definitions, trees are commonly defined by use; for instance, as those plants which yield lumber. The tree growth habit
2466-563: A specified height. In wider definitions, the taller palms , tree ferns , bananas , and bamboos are also trees. Trees are not a monophyletic taxonomic group but consist of a wide variety of plant species that have independently evolved a trunk and branches as a way to tower above other plants to compete for sunlight. The majority of tree species are angiosperms or hardwoods; of the rest, many are gymnosperms or softwoods. Trees tend to be long-lived, some reaching several thousand years old. Trees evolved around 370 million years ago, and it
2603-579: A study published in 2020 in the journal Nature. In 2019 they took up a third less carbon than they did in the 1990s, due to higher temperatures, droughts and deforestation. The typical tropical forest may become a carbon source by the 2060s. Despite the negative effects of tourism in the tropical rainforests, there are also several important positive effects. Deposits of precious metals ( gold , silver , coltan ) and fossil fuels ( oil and natural gas ) occur underneath rainforests globally. These resources are important to developing nations and their extraction
2740-484: A tree is any plant with the general form of an elongated stem, or trunk, which supports the photosynthetic leaves or branches at some distance above the ground. Trees are also typically defined by height, with smaller plants from 0.5 to 10 m (1.6 to 32.8 ft) being called shrubs , so the minimum height of a tree is only loosely defined. Large herbaceous plants such as papaya and bananas are trees in this broad sense. A commonly applied narrower definition
2877-725: A trend towards declining populations in rainforests, for example, reptiles that feed on amphibians and reptiles. This trend requires close monitoring. The seasonality of rainforests affects the reproductive patterns of amphibians, and this in turn can directly affect the species of reptiles that feed on these groups, particularly species with specialized feeding, since these are less likely to use alternative resources. Efforts to protect and conserve tropical rainforest habitats are diverse and widespread. Tropical rainforest conservation ranges from strict preservation of habitat to finding sustainable management techniques for people living in tropical rainforests. International policy has also introduced
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#17327810291363014-604: A tropical rainforest is stratified into layers, each hosting unique ecosystems . These include the emergent layer with towering trees, the densely populated canopy layer, the understory layer rich in wildlife, and the forest floor , which is sparse due to low light penetration. The soil is characteristically nutrient-poor and acidic. Tropical rainforests have a long history of ecological succession , influenced by natural events and human activities. They are crucial for global ecological functions, including carbon sequestration and climate regulation. Many indigenous peoples around
3151-440: A vast diversity in plant and animal species. The root for this remarkable speciation has been a query of scientists and ecologists for years. A number of theories have been developed for why and how the tropics can be so diverse. Interspecific competition results from a high density of species with similar niches in the tropics and limited resources available. Species which "lose" the competition may either become extinct or find
3288-436: A wide range of edible fruits are found in the tropics. Other commercially important fruit include dates, figs and olives. Palm oil is obtained from the fruits of the oil palm ( Elaeis guineensis ). The fruits of the cocoa tree ( Theobroma cacao ) are used to make cocoa and chocolate and the berries of coffee trees, Coffea arabica and Coffea canephora , are processed to extract the coffee beans. In many rural areas of
3425-416: A wide range of shapes and sizes, in response to environmental pressures including climate and predation. They can be broad or needle-like, simple or compound, lobed or entire, smooth or hairy, delicate or tough, deciduous or evergreen. The needles of coniferous trees are compact but are structurally similar to those of broad-leaved trees. They are adapted for life in environments where resources are low or water
3562-552: A widespread diverse group of which the only survivor is the maidenhair tree Ginkgo biloba . This is considered to be a living fossil because it is virtually unchanged from the fossilised specimens found in Triassic deposits. During the Mesozoic (245 to 66 million years ago) the conifers flourished and became adapted to live in all the major terrestrial habitats. Subsequently, the tree forms of flowering plants evolved during
3699-415: A widespread root network at the surface for more efficient uptake of nutrients in a very nutrient poor and competitive environment. Most of the nutrients within the soil of a tropical rainforest occur near the surface because of the rapid turnover time and decomposition of organisms and leaves. Because of this, the buttress roots occur at the surface so the trees can maximize uptake and actively compete with
3836-557: Is a flavouring obtained from distilling bark from the roots of the sassafras tree ( Sassafras albidum ). The leaves of trees are widely gathered as fodder for livestock and some can be eaten by humans but they tend to be high in tannins which makes them bitter. Leaves of the curry tree ( Murraya koenigii ) are eaten, those of kaffir lime ( Citrus × hystrix ) (in Thai food ) and Ailanthus (in Korean dishes such as bugak ) and those of
3973-516: Is a rudimentary stalk and neatly folded miniature leaves, ready to expand when the next growing season arrives. Buds also form in the axils of the leaves ready to produce new side shoots. A few trees, such as the eucalyptus , have "naked buds" with no protective scales and some conifers, such as the Lawson's cypress , have no buds but instead have little pockets of meristem concealed among the scale-like leaves. When growing conditions improve, such as
4110-416: Is a sudden movement of sap at the end of the winter as trees prepare to burst into growth. In North America, the sap of the sugar maple ( Acer saccharum ) is used in the production of maple syrup . About 90% of the sap is water, the remaining 10% being a mixture of various sugars and certain minerals. The sap is harvested by drilling holes in the trunks of the trees and collecting the liquid that flows out of
4247-505: Is also found in the southern hemisphere, as for example in the Eastern Australia temperate forest, characterised by Eucalyptus forest and open acacia woodland. In tropical regions with a monsoon or monsoon-like climate, where a drier part of the year alternates with a wet period as in the Amazon rainforest , different species of broad-leaved trees dominate the forest, some of them being deciduous. In tropical regions with
Capparis decidua - Misplaced Pages Continue
4384-528: Is an evolutionary adaptation found in different groups of plants: by growing taller, trees are able to compete better for sunlight. Trees tend to be tall and long-lived, some reaching several thousand years old. Several trees are among the oldest organisms now living. Trees have modified structures such as thicker stems composed of specialised cells that add structural strength and durability, allowing them to grow taller than many other plants and to spread out their foliage. They differ from shrubs , which have
4521-458: Is an example of niche partitioning. The theory of Pleistocene refugia was developed by Jürgen Haffer in 1969 with his article Speciation of Amazonian Forest Birds . Haffer proposed the explanation for speciation was the product of rainforest patches being separated by stretches of non-forest vegetation during the last glacial period. He called these patches of rainforest areas refuges and within these patches allopatric speciation occurred. With
4658-418: Is continually replaced by a living layer of cells called the cork cambium or phellogen. The London plane ( Platanus × hispanica ) periodically sheds its bark in large flakes. Similarly, the bark of the silver birch ( Betula pendula ) peels off in strips. As the tree's girth expands, newer layers of bark are larger in circumference, and the older layers develop fissures in many species. In some trees such as
4795-503: Is developed by the Indian banyan . Many large trees have buttress roots which flare out from the lower part of the trunk. These brace the tree rather like angle brackets and provide stability, reducing sway in high winds. They are particularly prevalent in tropical rainforests where the soil is poor and the roots are close to the surface. Some tree species have developed root extensions that pop out of soil, in order to get oxygen, when it
4932-414: Is estimated that there are around three trillion mature trees in the world currently. A tree typically has many secondary branches supported clear of the ground by the trunk, which typically contains woody tissue for strength, and vascular tissue to carry materials from one part of the tree to another. For most trees the trunk is surrounded by a layer of bark which serves as a protective barrier. Below
5069-644: Is extremely drought-resistant and tolerates some frost. It can be found in arid regions in North Africa , the Middle East , and South Asia , including the Thar desert . Khair city in Uttar Pradesh, India is famous for Kair trees. The fruit and young buds can be eaten raw. Its spicy fruits are used for preparing vegetables , curry and fine pickles and can attract helpful insectivores ;
5206-603: Is generally between 1500 and 2500 m while the upper limit is usually from 2400 to 3300 m. Tropical freshwater swamp forests , or "flooded forests", are found in Amazon basin (the Várzea ) and elsewhere. Rainforests are divided into different strata, or layers, with vegetation organized into a vertical pattern from the top of the soil to the canopy. Each layer is a unique biotic community containing different plants and animals adapted for life in that particular strata. Only
5343-486: Is inelastic. Eventually the growth of a tree slows down and stops and it gets no taller. If damage occurs the tree may in time become hollow. Leaves are structures specialised for photosynthesis and are arranged on the tree in such a way as to maximise their exposure to light without shading each other. They are an important investment by the tree and may be thorny or contain phytoliths , lignins , tannins or poisons to discourage herbivory. Trees have evolved leaves in
5480-424: Is not available in the soil because of excess water. These root extensions are called pneumatophores , and are present, among others, in black mangrove and pond cypress. The main purpose of the trunk is to raise the leaves above the ground, enabling the tree to overtop other plants and outcompete them for light. It also transports water and nutrients from the roots to the aerial parts of the tree, and distributes
5617-521: Is often given priority to encourage economic growth. Mining and drilling can require large amounts of land development , directly causing deforestation . In Ghana , a West African nation, deforestation from decades of mining activity left about 12% of the country's original rainforest intact. With the invention of agriculture , humans were able to clear sections of rainforest to produce crops, converting it to open farmland . Such people, however, obtain their food primarily from farm plots cleared from
Capparis decidua - Misplaced Pages Continue
5754-458: Is ready to eat when the process is complete, having been tenderised and flavoured by the smoke it has absorbed. In the cold process, the temperature is not allowed to rise above 100 °F (38 °C). The flavour of the food is enhanced but raw food requires further cooking. If it is to be preserved, meat should be cured before cold smoking. Wood has traditionally been used for fuel, especially in rural areas. In less developed nations it may be
5891-428: Is related to climatic conditions; growth normally ceases when conditions are either too cold or too dry. In readiness for the inactive period, trees form buds to protect the meristem , the zone of active growth. Before the period of dormancy, the last few leaves produced at the tip of a twig form scales. These are thick, small and closely wrapped and enclose the growing point in a waterproof sheath. Inside this bud there
6028-407: Is scarce. Frozen ground may limit water availability and conifers are often found in colder places at higher altitudes and higher latitudes than broad leaved trees. In conifers such as fir trees, the branches hang down at an angle to the trunk, enabling them to shed snow. In contrast, broad leaved trees in temperate regions deal with winter weather by shedding their leaves. When the days get shorter and
6165-402: Is that a tree has a woody trunk formed by secondary growth , meaning that the trunk thickens each year by growing outwards, in addition to the primary upwards growth from the growing tip . Under such a definition, herbaceous plants such as palms , bananas and papayas are not considered trees regardless of their height, growth form or stem girth. Certain monocots may be considered trees under
6302-471: Is the first part of a seedling to emerge from the seed during the process of germination . This develops into a taproot which goes straight downwards. Within a few weeks lateral roots branch out of the side of this and grow horizontally through the upper layers of the soil. In most trees, the taproot eventually withers away and the wide-spreading laterals remain. Near the tip of the finer roots are single cell root hairs . These are in immediate contact with
6439-452: Is the only one to develop, so they have unbranched trunks with large spirally arranged leaves. Some of the tree ferns, order Cyatheales , have tall straight trunks, growing up to 20 metres (66 ft), but these are composed not of wood but of rhizomes which grow vertically and are covered by numerous adventitious roots . The number of trees in the world, according to a 2015 estimate, is 3.04 trillion, of which 1.39 trillion (46%) are in
6576-450: Is the result of heavy heat and moisture forming oxides of iron and aluminium, which are insoluble in water and not taken up readily by plants. Soil chemical and physical characteristics are strongly related to above ground productivity and forest structure and dynamics. The physical properties of soil control the tree turnover rates whereas chemical properties such as available nitrogen and phosphorus control forest growth rates. The soils of
6713-534: Is the result of phosphorus levels in the soils, precipitation, high temperatures and the extensive microorganism communities. In addition to the bacteria and other microorganisms, there are an abundance of other decomposers such as fungi and termites that aid in the process as well. Nutrient recycling is important because below ground resource availability controls the above ground biomass and community structure of tropical rainforests. These soils are typically phosphorus limited, which inhibits net primary productivity or
6850-545: The Amazon rainforest ) are called carbon sinks . As major carbon reducers and carbon and soil methane storages, their destruction contributes to increasing global energy trapping , atmospheric gases. Climate change has been significantly contributed to by the destruction of the rainforests. A simulation was performed in which all rainforest in Africa were removed. The simulation showed an increase in atmospheric temperature by 2.5 to 5 degrees Celsius. Some species of fauna show
6987-515: The Cretaceous period. These began to displace the conifers during the Tertiary era (66 to 2 million years ago) when forests covered the globe. When the climate cooled 1.5 million years ago and the first of four glacial periods occurred, the forests retreated as the ice advanced. In the interglacials , trees recolonised the land that had been covered by ice, only to be driven back again in
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#17327810291367124-704: The Equator . They are a subset of the tropical forest biome that occurs roughly within the 28° latitudes (in the torrid zone between the Tropic of Cancer and Tropic of Capricorn ). Tropical rainforests are a type of tropical moist broadleaf forest , that includes the more extensive seasonal tropical forests . True rainforests usually occur in tropical rainforest climates where no dry season occurs; all months have an average precipitation of at least 60 mm (2.4 in). Seasonal tropical forests with tropical monsoon or savanna climates are sometimes included in
7261-841: The Indigenous peoples of the Americas , the Congo Pygmies in Central Africa, and several tribes in Southeast Asia, like the Dayak people and the Penan people in Borneo . Food resources within the forest are extremely dispersed due to the high biological diversity and what food does exist is largely restricted to the canopy and requires considerable energy to obtain. Some groups of hunter-gatherers have exploited rainforest on
7398-522: The Mesozoic era supercontinent of Gondwana . The separation of the landmass resulted in a great loss of amphibian diversity while at the same time the drier climate spurred the diversification of reptiles. The division left tropical rainforests located in five major regions of the world: tropical America, Africa, Southeast Asia, Madagascar, and New Guinea, with smaller outliers in Australia. However,
7535-414: The annual growth rings There may also be rays running at right angles to growth rings. These are vascular rays which are thin sheets of living tissue permeating the wood. Many older trees may become hollow but may still stand upright for many years. Trees do not usually grow continuously throughout the year but mostly have spurts of active expansion followed by periods of rest. This pattern of growth
7672-749: The genetic variation used in evading the damage caused by new pests is still derived from resistant wild stock. Tropical forests have supplied 250 cultivated kinds of fruit , compared to only 20 for temperate forests . Forests in New Guinea alone contain 251 tree species with edible fruits, of which only 43 had been established as cultivated crops by 1985. In addition to extractive human uses, rain forests also have non-extractive uses that are frequently summarized as ecosystem services . Rain forests play an important role in maintaining biological diversity , sequestering and storing carbon , global climate regulation, disease control, and pollination . Half of
7809-552: The pine ( Pinus species) the bark exudes sticky resin which deters attackers whereas in rubber trees ( Hevea brasiliensis ) it is a milky latex that oozes out. The quinine bark tree ( Cinchona officinalis ) contains bitter substances to make the bark unpalatable. Large tree-like plants with lignified trunks in the Pteridophyta , Arecales , Cycadophyta and Poales such as the tree ferns, palms, cycads and bamboos have different structures and outer coverings. Although
7946-671: The spider monkey ( Ateles sp.), African giant swallowtail ( Papilio antimachus ), three-toed sloth ( Bradypus tridactylus ), kinkajou ( Potos flavus ), and tamandua ( Tamandua tetradactyla ). The emergent layer contains a small number of very large trees , called emergents , which grow above the general canopy , reaching heights of 45–55 m, although on occasion a few species will grow to 70–80 m tall. Some examples of emergents include: Hydrochorea elegans , Dipteryx panamensis , Hieronyma alchorneoides , Hymenolobium mesoamericanum , Lecythis ampla and Terminalia oblonga . These trees need to be able to withstand
8083-498: The " world's largest pharmacy ", because over one quarter of natural medicines have been discovered within them. It is likely that there may be many millions of species of plants, insects and microorganisms still undiscovered in tropical rainforests. Tropical rainforests are among the most threatened ecosystems globally due to large-scale fragmentation as a result of human activity. Habitat fragmentation caused by geological processes such as volcanism and climate change occurred in
8220-540: The 12,000 years since the start of human agriculture, the number of trees worldwide has decreased by 46%. There are approximately 64,100 known tree species in the world. With 43% of all tree species, South America has the highest biodiversity, followed by Eurasia (22%), Africa (16%), North America (15%), and Oceania (11%). In suitable environments, such as the Daintree Rainforest in Queensland , or
8357-405: The Amazon is based on swidden cultivation (also known as slash-and-burn or shifting cultivation) and is considered a relatively benign disturbance. In fact, when looking at the level of individual swidden plots a number of traditional farming practices are considered beneficial. For example, the use of shade trees and fallowing all help preserve soil organic matter , which is a critical factor in
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#17327810291368494-612: The Andean foothills, and volcanic areas of Southeast Asia, Africa, and Central America. Oxisols, infertile, deeply weathered and severely leached, have developed on the ancient Gondwanan shields . Rapid bacterial decay prevents the accumulation of humus. The concentration of iron and aluminium oxides by the laterization process gives the oxisols a bright red color and sometimes produces minable deposits (e.g., bauxite ). On younger substrates, especially of volcanic origin, tropical soils may be quite fertile. This high rate of decomposition
8631-620: The English oak ( Quercus robur ) and 306 species of invertebrate on the Tasmanian oak ( Eucalyptus obliqua ). Non-native tree species provide a less biodiverse community, for example in the United Kingdom the sycamore ( Acer pseudoplatanus ), which originates from southern Europe, has few associated invertebrate species, though its bark supports a wide range of lichens, bryophytes and other epiphytes. Trees differ ecologically in
8768-546: The European bay tree ( Laurus nobilis ) and the California bay tree ( Umbellularia californica ) are used for flavouring food. Camellia sinensis , the source of tea, is a small tree but seldom reaches its full height, being heavily pruned to make picking the leaves easier. Wood smoke can be used to preserve food. In the hot smoking process the food is exposed to smoke and heat in a controlled environment. The food
8905-667: The Iban "kenyalang" and the Kenyah "mamat". Pygmies who live in Southeast Asia are, amongst others, referred to as " Negrito ". Yam , coffee , chocolate , banana , mango , papaya , macadamia , avocado , and sugarcane all originally came from tropical rainforest and are still mostly grown on plantations in regions that were formerly primary forest. In the mid-1980s and 1990s, 40 million tons of bananas were consumed worldwide each year, along with 13 million tons of mango. Central American coffee exports were worth US$ 3 billion in 1970. Much of
9042-476: The abundance of rainfall changes throughout the year creating distinct moist and dry seasons. Tropical forests are classified by the amount of rainfall received each year, which has allowed ecologists to define differences in these forests that look so similar in structure. According to Holdridge's classification of tropical ecosystems, true tropical rainforests have an annual rainfall greater than 2 m and annual temperature greater than 24 degrees Celsius, with
9179-523: The animal and plant waste. The understory layer lies between the canopy and the forest floor. The understory is home to a number of birds, small mammals, insects, reptiles, and predators. Examples include leopard ( Panthera pardus ), poison dart frogs ( Dendrobates sp.), ring-tailed coati ( Nasua nasua ), boa constrictor ( Boa constrictor ), and many species of Coleoptera . The vegetation at this layer generally consists of shade-tolerant shrubs, herbs, small trees, and large woody vines which climb into
9316-496: The arrival of warmer weather and the longer days associated with spring in temperate regions, growth starts again. The expanding shoot pushes its way out, shedding the scales in the process. These leave behind scars on the surface of the twig. The whole year's growth may take place in just a few weeks. The new stem is unlignified at first and may be green and downy. The Arecaceae (palms) have their leaves spirally arranged on an unbranched trunk. In some tree species in temperate climates,
9453-437: The bark functions as a protective barrier, it is itself attacked by boring insects such as beetles. These lay their eggs in crevices and the larvae chew their way through the cellulose tissues leaving a gallery of tunnels. This may allow fungal spores to gain admittance and attack the tree. Dutch elm disease is caused by a fungus ( Ophiostoma species) carried from one elm tree to another by various beetles. The tree reacts to
9590-463: The broader definition. Tropical rainforests ecosystems are distinguished by their consistent, high temperatures, exceeding 18 °C (64 °F) monthly, and substantial annual rainfall. The abundant rainfall results in nutrient-poor, leached soils, which profoundly affect the flora and fauna adapted to these conditions. These rainforests are renowned for their significant biodiversity . They are home to 40–75% of all species globally, including half of
9727-440: The clove tree ( Syzygium aromaticum ). Many trees have flowers rich in nectar which are attractive to bees. The production of forest honey is an important industry in rural areas of the developing world where it is undertaken by small-scale beekeepers using traditional methods. The flowers of the elder ( Sambucus ) are used to make elderflower cordial and petals of the plum ( Prunus spp. ) can be candied. Sassafras oil
9864-764: The community. The initial disturbance is often a natural phenomenon or human caused event. Natural disturbances include hurricanes, volcanic eruptions, river movements or an event as small as a fallen tree that creates gaps in the forest. In tropical rainforests, these same natural disturbances have been well documented in the fossil record, and are credited with encouraging speciation and endemism. Human land use practices have led to large-scale deforestation. In many tropical countries such as Costa Rica these deforested lands have been abandoned and forests have been allowed to regenerate through ecological succession. These regenerating young successional forests are called secondary forests or second-growth forests. Tropical rainforests exhibit
10001-465: The cone for years waiting for a trigger event to liberate it. Fire stimulates release and germination of seeds of the jack pine , and also enriches the forest floor with wood ash and removes competing vegetation. Similarly, a number of angiosperms including Acacia cyclops and Acacia mangium have seeds that germinate better after exposure to high temperatures. The single extant species of Ginkgophyta ( Ginkgo biloba ) has fleshy seeds produced at
10138-442: The driving force moving the decomposable carbon from the litter to the soil. Respiration rates are highest early in the wet season because the recent dry season results in a large percentage of leaf litter and thus a higher percentage of organic matter being leached into the soil. A common feature of many tropical rainforests is the distinct buttress roots of trees. Instead of penetrating to deeper soil layers, buttress roots create
10275-424: The ease with which they can be found by herbivores. Tree apparency varies with a tree's size and semiochemical content, and with the extent to which it is concealed by nonhost neighbours from its insect pests . In ecosystems such as mangrove swamps, trees play a role in developing the habitat, since the roots of the mangrove trees reduce the speed of flow of tidal currents and trap water-borne sediment, reducing
10412-755: The eastern and central Amazon as well as the Southeast Asian Rainforest are old and mineral poor whereas the soils of the western Amazon (Ecuador and Peru) and volcanic areas of Costa Rica are young and mineral rich. Primary productivity or wood production is highest in western Amazon and lowest in eastern Amazon which contains heavily weathered soils classified as oxisols. Additionally, Amazonian soils are greatly weathered, making them devoid of minerals like phosphorus, potassium, calcium, and magnesium, which come from rock sources. However, not all tropical rainforests occur on nutrient poor soils, but on nutrient rich floodplains and volcanic soils located in
10549-492: The easy movement of larger animals such as: ungulates like the okapi ( Okapia johnstoni ), tapir ( Tapirus sp.), Sumatran rhinoceros ( Dicerorhinus sumatrensis ), and apes like the western lowland gorilla ( Gorilla gorilla ), as well as many species of reptiles, amphibians, and insects. The forest floor also contains decaying plant and animal matter, which disappears quickly, because the warm, humid conditions promote rapid decay. Many forms of fungi growing here help decay
10686-454: The emergent layer is unique to tropical rainforests, while the others are also found in temperate rainforests . The forest floor , the bottom-most layer, receives only 2% of the sunlight. Only plants adapted to low light can grow in this region. Away from riverbanks, swamps and clearings, where dense undergrowth is found, the forest floor is relatively clear of vegetation because of the low sunlight penetration. This more open quality permits
10823-615: The end of the glacial period and increase in atmospheric humidity, rainforest began to expand and the refuges reconnected. This theory has been the subject of debate. Scientists are still skeptical of whether or not this theory is legitimate. Genetic evidence suggests speciation had occurred in certain taxa 1–2 million years ago, preceding the Pleistocene . Tropical rainforests have harboured human life for many millennia, with many Indigenous people in South and Central America, who belong to
10960-664: The ends of short branches on female trees, and Gnetum , a tropical and subtropical group of gymnosperms produce seeds at the tip of a shoot axis. The earliest trees were tree ferns , horsetails and lycophytes , which grew in forests in the Carboniferous period. The first tree may have been Wattieza , fossils of which were found in New York state in 2007 dating back to the Middle Devonian (about 385 million years ago). Prior to this discovery, Archaeopteris
11097-461: The far north of the northern hemisphere is moist taiga or northern coniferous forest (also called boreal forest). Taiga is the world's largest land biome , forming 29% of the world's forest cover. The long cold winter of the far north is unsuitable for plant growth and trees must grow rapidly in the short summer season when the temperature rises and the days are long. Light is very limited under their dense cover and there may be little plant life on
11234-480: The food produced by the leaves to all other parts, including the roots. In the case of angiosperms and gymnosperms, the outermost layer of the trunk is the bark , mostly composed of dead cells of phellem (cork). It provides a thick, waterproof covering to the living inner tissue. It protects the trunk against the elements, disease, animal attack and fire. It is perforated by a large number of fine breathing pores called lenticels , through which oxygen diffuses. Bark
11371-437: The forest and hunt and forage within the forest to supplement this. The issue arising is between the independent farmer providing for his family and the needs and wants of the globe as a whole. This issue has seen little improvement because no plan has been established for all parties to be aided. Agriculture on formerly forested land is not without difficulties. Rainforest soils are often thin and leached of many minerals, and
11508-745: The forest canopy are widely recognized as important for the establishment and growth of rainforest trees. It is estimated that perhaps 75% of the tree species at La Selva Biological Station, Costa Rica are dependent on canopy opening for seed germination or for growth beyond sapling size, for example. Tropical rainforests are located around and near the equator, therefore having what is called an equatorial climate characterized by three major climatic parameters: temperature, rainfall, and dry season intensity. Other parameters that affect tropical rainforests are carbon dioxide concentrations, solar radiation, and nitrogen availability. In general, climatic patterns consist of warm temperatures and high annual rainfall. However,
11645-401: The forest floor, although fungi may abound. Similar woodland is found on mountains where the altitude causes the average temperature to be lower thus reducing the length of the growing season. Where rainfall is relatively evenly spread across the seasons in temperate regions, temperate broadleaf and mixed forest typified by species like oak, beech, birch and maple is found. Temperate forest
11782-555: The forests. Peoples have inhabited the rainforests for tens of thousands of years and have remained so elusive that only recently have some tribes been discovered. These indigenous peoples are greatly threatened by loggers in search for old-growth tropical hardwoods like Ipe, Cumaru and Wenge, and by farmers who are looking to expand their land, for cattle(meat), and soybeans, which are used to feed cattle in Europe and China. On 18 January 2007, FUNAI reported also that it had confirmed
11919-425: The fruits and either discard the seeds, or swallow them so they pass through the gut to be deposited in the animal's droppings well away from the parent tree. The germination of some seeds is improved when they are processed in this way. Nuts may be gathered by animals such as squirrels that cache any not immediately consumed. Many of these caches are never revisited; the nut-casing softens with rain and frost, and
12056-480: The ground underneath trees there is shade, and often there is undergrowth, leaf litter , and decaying wood that provide other habitat. Trees stabilise the soil, prevent rapid run-off of rain water, help prevent desertification, have a role in climate control and help in the maintenance of biodiversity and ecosystem balance. Many species of tree support their own specialised invertebrates . In their natural habitats, 284 different species of insect have been found on
12193-557: The ground, the roots branch and spread out widely; they serve to anchor the tree and extract moisture and nutrients from the soil . Above ground, the branches divide into smaller branches and shoots. The shoots typically bear leaves, which capture light energy and convert it into sugars by photosynthesis , providing the food for the tree's growth and development. Trees usually reproduce using seeds . Flowering plants have their seeds inside fruits, while conifers carry their seeds in cones, and tree ferns produce spores instead. Trees play
12330-489: The ground. Tropical rainforests exhibit high levels of biodiversity. Around 40% to 75% of all biotic species are indigenous to the rainforests. Rainforests are home to half of all the living animal and plant species on the planet. Two-thirds of all flowering plants can be found in rainforests. A single hectare of rainforest may contain 42,000 different species of insect, up to 807 trees of 313 species and 1,500 species of higher plants. Tropical rainforests have been called
12467-421: The ground. Trees use a variety of methods of seed dispersal . Some rely on wind, with winged or plumed seeds. Others rely on animals, for example with edible fruits. Others again eject their seeds (ballistic dispersal), or use gravity so that seeds fall and sometimes roll. Seeds are the primary way that trees reproduce and their seeds vary greatly in size and shape. Some of the largest seeds come from trees, but
12604-413: The growth of the fungus by blocking off the xylem tissue carrying sap upwards and the branch above, and eventually the whole tree, is deprived of nourishment and dies. In Britain in the 1990s, 25 million elm trees were killed by this disease. The innermost layer of bark is known as the phloem and this is involved in the transport of the sap containing the sugars made by photosynthesis to other parts of
12741-447: The heartwood are blocked in some species. Heartwood is usually darker in colour than the sapwood. It is the dense central core of the trunk giving it rigidity. Three quarters of the dry mass of the xylem is cellulose , a polysaccharide , and most of the remainder is lignin, a complex polymer . A transverse section through a tree trunk or a horizontal core will show concentric circles of lighter or darker wood – tree rings. These rings are
12878-472: The heavy rainfall can quickly leach nutrients from area cleared for cultivation. People such as the Yanomamo of the Amazon , utilize slash-and-burn agriculture to overcome these limitations and enable them to push deep into what were previously rainforest environments. However, these are not rainforest dwellers, rather they are dwellers in cleared farmland that make forays into the rainforest. Up to 90% of
13015-487: The hot temperatures and strong winds that occur above the canopy in some areas. Several unique faunal species inhabit this layer such as the crowned eagle ( Stephanoaetus coronatus ), the king colobus ( Colobus polykomos ), and the large flying fox ( Pteropus vampyrus ). However, stratification is not always clear. Rainforests are dynamic and many changes affect the structure of the forest. Emergent or canopy trees collapse, for example, causing gaps to form. Openings in
13152-411: The inserted spigots; the sap is then heated to concentrate the flavour. Similarly in northern Europe the spring rise in the sap of the silver birch ( Betula pendula ) is tapped and collected, either to be drunk fresh or fermented into an alcoholic drink. In Alaska, the sap of the sweet birch ( Betula lenta ) is made into a syrup with a sugar content of 67%. Sweet birch sap is more dilute than maple sap;
13289-400: The inside. The newly created xylem is the sapwood . It is composed of water-conducting cells and associated cells which are often living, and is usually pale in colour. It transports water and minerals from the roots to the upper parts of the tree. The oldest, inner part of the sapwood is progressively converted into heartwood as new sapwood is formed at the cambium. The conductive cells of
13426-445: The large surface areas these roots create provide support and stability to rainforests trees, which commonly grow to significant heights. This added stability allows these trees to withstand the impacts of severe storms, thus reducing the occurrence of fallen trees. Succession is an ecological process that changes the biotic community structure over time towards a more stable, diverse community structure after an initial disturbance to
13563-528: The largest tree, Sequoiadendron giganteum , produces one of the smallest tree seeds. The great diversity in tree fruits and seeds reflects the many different ways that tree species have evolved to disperse their offspring. For a tree seedling to grow into an adult tree it needs light. If seeds only fell straight to the ground, competition among the concentrated saplings and the shade of the parent would likely prevent it from flourishing. Many seeds such as birch are small and have papery wings to aid dispersal by
13700-582: The maintenance of soil fertility in the deeply weathered and leached soils common in the Amazon. There is a diversity of forest people in Asia, including the Lumad peoples of the Philippines and the Penan and Dayak people of Borneo. The Dayaks are a particularly interesting group as they are noted for their traditional headhunting culture. Fresh human heads were required to perform certain rituals such as
13837-409: The mixed podocarp and broadleaf forest of Ulva Island, New Zealand , forest is the more-or-less stable climatic climax community at the end of a plant succession, where open areas such as grassland are colonised by taller plants, which in turn give way to trees that eventually form a forest canopy. In cool temperate regions, conifers often predominate; a widely distributed climax community in
13974-519: The next glacial period. Trees are an important part of the terrestrial ecosystem , providing essential habitats including many kinds of forest for communities of organisms. Epiphytic plants such as ferns , some mosses, liverworts, orchids and some species of parasitic plants (e.g., mistletoe ) hang from branches; these along with arboreal lichens, algae, and fungi provide micro-habitats for themselves and for other organisms, including animals. Leaves, flowers and fruits are seasonally available. On
14111-420: The old lineages of flowering plants called basal angiosperms or paleodicots ; these include Amborella , Magnolia , nutmeg and avocado , while trees such as bamboo, palms and bananas are monocots . Wood gives structural strength to the trunk of most types of tree; this supports the plant as it grows larger. The vascular system of trees allows water, nutrients and other chemicals to be distributed around
14248-515: The ongoing challenge of balancing conservation with human development needs. Tropical rainforests are hot and wet. Mean monthly temperatures exceed 18 °C (64 °F) during all months of the year. Average annual rainfall is no less than 1,680 mm (66 in) and can exceed 10 m (390 in) although it typically lies between 1,750 mm (69 in) and 3,000 mm (120 in). This high level of precipitation often results in poor soils due to leaching of soluble nutrients in
14385-592: The only fuel available and collecting firewood is often a time-consuming task as it becomes necessary to travel further and further afield in the search for fuel. It is often burned inefficiently on an open fire. In more developed countries other fuels are available and burning wood is a choice rather than a necessity. Modern wood-burning stoves are very fuel efficient and new products such as wood pellets are available to burn. Tropical rainforest Tropical rainforests are dense and warm rainforests with high rainfall typically found between 10° north and south of
14522-514: The past, and have been identified as important drivers of speciation. However, fast human driven habitat destruction is suspected to be one of the major causes of species extinction. Tropical rain forests have been subjected to heavy logging and agricultural clearance throughout the 20th century, and the area covered by rainforests around the world is rapidly shrinking. Tropical rainforests have existed on earth for hundreds of millions of years. Most tropical rainforests today are on fragments of
14659-516: The plant also is used in folk medicine and herbalism . It can be used in landscape gardening , afforestation and reforestation in semidesert and desert areas; it provides assistance against soil erosion . Tree In botany , a tree is a perennial plant with an elongated stem , or trunk , usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth , plants that are usable as lumber or plants above
14796-585: The plant and reduce water loss. Both the production of wood and the production of cork are forms of secondary growth. Trees are either evergreen , having foliage that persists and remains green throughout the year, or deciduous , shedding their leaves at the end of the growing season and then having a dormant period without foliage. Most conifers are evergreens, but larches ( Larix and Pseudolarix ) are deciduous, dropping their needles each autumn, and some species of cypress ( Glyptostrobus , Metasequoia and Taxodium ) shed small leafy shoots annually in
14933-409: The plant, and without it trees would not be able to grow as large as they do. Trees need to draw water high up the stem through the xylem from the roots by capillary action , as water continually evaporates from the leaves in the process of transpiration . If insufficient water is available the leaves will die. The three main parts of trees include the root, stem, and leaves; they are integral parts of
15070-529: The presence of 67 different uncontacted tribes in Brazil, up from 40 in 2005. With this addition, Brazil has now overtaken the island of New Guinea as the country having the largest number of uncontacted tribes. The province of Irian Jaya or West Papua in the island of New Guinea is home to an estimated 44 uncontacted tribal groups. The pygmy peoples are hunter-gatherer groups living in equatorial rainforests characterized by their short height (below one and
15207-524: The rainfall in the Amazon area is produced by the forests. The moisture from the forests is important to the rainfall in Brazil , Paraguay , Argentina Deforestation in the Amazon rainforest region was one of the main reason that cause the severe Drought of 2014–2015 in Brazil For the last three decades, the amount of carbon absorbed by the world's intact tropical forests has fallen, according to
15344-403: The rapid uptake of other trees. These roots also aid in water uptake and storage, increase surface area for gas exchange, and collect leaf litter for added nutrition. Additionally, these roots reduce soil erosion and maximize nutrient acquisition during heavy rains by diverting nutrient rich water flowing down the trunk into several smaller flows while also acting as a barrier to ground flow. Also,
15481-437: The rest, many are gymnosperms or softwood trees; these include conifers , cycads , ginkgophytes and gnetales , which produce seeds which are not enclosed in fruits, but in open structures such as pine cones , and many have tough waxy leaves, such as pine needles. Most angiosperm trees are eudicots , the "true dicotyledons", so named because the seeds contain two cotyledons or seed leaves. There are also some trees among
15618-428: The roots and helps protect the trees against predators and pathogens. It can also limit damage done to a tree by pollution as the fungus accumulate heavy metals within its tissues. Fossil evidence shows that roots have been associated with mycorrhizal fungi since the early Paleozoic , four hundred million years ago, when the first vascular plants colonised dry land. Some trees such as Alder ( Alnus species) have
15755-464: The seeds on the surface of water. Mangroves often grow in water and some species have buoyant fruits with seeds that start germinating before they detach from the parent tree. These float on the water and may become lodged on emerging mudbanks and successfully take root. Other seeds, such as apple pips and plum stones, have fleshy receptacles and smaller fruits like hawthorns have seeds enclosed in edible tissue; animals including mammals and birds eat
15892-434: The soil particles and can absorb water and nutrients such as potassium in solution. The roots require oxygen to respire and only a few species such as mangroves and the pond cypress ( Taxodium ascendens ) can live in permanently waterlogged soil. In the soil, the roots encounter the hyphae of fungi. Many of these are known as mycorrhiza and form a mutualistic relationship with the tree roots. Some are specific to
16029-466: The specifics of the origin of rainforests remain uncertain due to an incomplete fossil record. Several biomes may appear similar-to, or merge via ecotones with, tropical rainforest: Moist seasonal tropical forests receive high overall rainfall with a warm summer wet season and a cooler winter dry season. These forests usually fall under tropical monsoon or tropical savanna climates. Some trees in these forests drop some or all of their leaves during
16166-471: The start of the dry season. Many deciduous trees flower before the new leaves emerge. A few trees do not have true leaves but instead have structures with similar external appearance such as Phylloclades – modified stem structures – as seen in the genus Phyllocladus . Trees can be pollinated either by wind or by animals, mostly insects. Many angiosperm trees are insect pollinated. Wind pollination may take advantage of increased wind speeds high above
16303-534: The supporting plants. The fauna is similar to that found in the emergent layer, but more diverse. It is suggested that the total arthropod species richness of the tropical canopy might be as high as 20 million. Other species inhabiting this layer include many avian species such as the yellow-casqued wattled hornbill ( Ceratogymna elata ), collared sunbird ( Anthreptes collaris ), grey parrot ( Psitacus erithacus ), keel-billed toucan ( Ramphastos sulfuratus ), scarlet macaw ( Ara macao ) as well as other animals like
16440-413: The surviving seeds germinate in the spring. Pine cones may similarly be hoarded by red squirrels , and grizzly bears may help to disperse the seed by raiding squirrel caches. The seeds of conifers, the largest group of gymnosperms, are enclosed in a cone and most species have seeds that are light and papery that can be blown considerable distances once free from the cone. Sometimes the seed remains in
16577-661: The temperature begins to decrease, the leaves no longer make new chlorophyll and the red and yellow pigments already present in the blades become apparent. Synthesis in the leaf of a plant hormone called auxin also ceases. This causes the cells at the junction of the petiole and the twig to weaken until the joint breaks and the leaf floats to the ground. In tropical and subtropical regions, many trees keep their leaves all year round. Individual leaves may fall intermittently and be replaced by new growth but most leaves remain intact for some time. Other tropical species and those in arid regions may shed all their leaves annually, such as at
16714-408: The tree, but some tree species have evolved roots that are aerial . The common purposes for aerial roots may be of two kinds, to contribute to the mechanical stability of the tree, and to obtain oxygen from air. An instance of mechanical stability enhancement is the red mangrove that develops prop roots that loop out of the trunk and branches and descend vertically into the mud. A similar structure
16851-432: The tree. It is a soft spongy layer of living cells, some of which are arranged end to end to form tubes. These are supported by parenchyma cells which provide padding and include fibres for strengthening the tissue. Inside the phloem is a layer of undifferentiated cells one cell thick called the vascular cambium layer. The cells are continually dividing, creating phloem cells on the outside and wood cells known as xylem on
16988-404: The trees to capture sunlight. Only about 5% of sunlight breaches the canopy to arrive at the understory causing true understory plants to seldom grow to 3 m (10 feet). As an adaptation to these low light levels, understory plants have often evolved much larger leaves. Many seedlings that will grow to the canopy level are in the understory. The canopy is the primary layer of the forest, forming
17125-482: The tropical rainforests fall into two classifications which include the ultisols and oxisols . Ultisols are known as well weathered, acidic red clay soils, deficient in major nutrients such as calcium and potassium. Similarly, oxisols are acidic, old, typically reddish, highly weathered and leached, however are well drained compared to ultisols. The clay content of ultisols is high, making it difficult for water to penetrate and flow through. The reddish color of both soils
17262-492: The tropics or sub-tropics , 0.61 trillion (20%) in the temperate zones , and 0.74 trillion (24%) in the coniferous boreal forests . The estimate is about eight times higher than previous estimates, and is based on tree densities measured on over 400,000 plots. It remains subject to a wide margin of error, not least because the samples are mainly from Europe and North America. The estimate suggests that about 15 billion trees are cut down annually and about 5 billion are planted. In
17399-426: The typical Yanamomo diet comes from farmed plants. Some action has been taken by suggesting fallow periods of the land allowing secondary forest to grow and replenish the soil. Beneficial practices like soil restoration and conservation can benefit the small farmer and allow better production on smaller parcels of land. The tropics take a major role in reducing atmospheric carbon dioxide . The tropics (most notably
17536-728: The uptake of carbon. The soil contains microbial organisms such as bacteria, which break down leaf litter and other organic matter into inorganic forms of carbon usable by plants through a process called decomposition. During the decomposition process the microbial community is respiring, taking up oxygen and releasing carbon dioxide. The decomposition rate can be evaluated by measuring the uptake of oxygen. High temperatures and precipitation increase decomposition rate, which allows plant litter to rapidly decay in tropical regions, releasing nutrients that are immediately taken up by plants through surface or ground waters. The seasonal patterns in respiration are controlled by leaf litter fall and precipitation,
17673-403: The vascular system which interconnects all the living cells. In trees and other plants that develop wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth. Because this growth ruptures the epidermis of the stem, woody plants also have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork cells to protect the surface of
17810-429: The water depth and creating suitable conditions for further mangrove colonisation. Thus mangrove swamps tend to extend seawards in suitable locations. Mangrove swamps also provide an effective buffer against the more damaging effects of cyclones and tsunamis. Trees are the source of many of the world's best known fleshy fruits. Apples, pears, plums, cherries and citrus are all grown commercially in temperate climates and
17947-437: The wind. Ash trees and maples have larger seeds with blade shaped wings which spiral down to the ground when released. The kapok tree has cottony threads to catch the breeze. The flame tree Delonix regia shoots its seeds through the air when the two sides of its long pods crack apart explosively on drying. The miniature cone-like catkins of alder trees produce seeds that contain small droplets of oil that help disperse
18084-575: The winter dry season, thus they are sometimes called "tropical mixed forest". They are found in parts of South America, in Central America and around the Caribbean , in coastal West Africa , parts of the Indian subcontinent , and across much of Indochina . These are found in cooler-climate mountainous areas, becoming known as cloud forests at higher elevations. Depending on latitude, the lower limit of montane rainforests on large mountains
18221-626: The world have inhabited rainforests for millennia, relying on them for sustenance and shelter, but face challenges from modern economic activities. Conservation efforts are diverse, focusing on both preservation and sustainable management. International policies, such as the Reducing Emissions from Deforestation and Forest Degradation ( REDD and REDD+ ) programs, aim to curb deforestation and forest degradation. Despite these efforts, tropical rainforests continue to face significant threats from deforestation and climate change , highlighting
18358-457: The world's animal and plant species, and two-thirds of all flowering plant species. Their dense insect population and variety of trees and higher plants are notable. Described as the "world's largest pharmacy", over a quarter of natural medicines have been discovered in them. However, tropical rainforests are threatened by human activities, such as logging and agricultural expansion, leading to habitat fragmentation and loss . The structure of
18495-465: The world, forests are shrinking as trees are cleared to increase the amount of land available for agriculture. Because of their longevity and usefulness, trees have always been revered, with sacred groves in various cultures, and they play a role in many of the world's mythologies . Although "tree" is a common word, there is no universally recognised precise definition of what a tree is, either botanically or in common language. In its broadest sense,
18632-769: The world, fruit is gathered from forest trees for consumption. Many trees bear edible nuts which can loosely be described as being large, oily kernels found inside a hard shell. These include coconuts ( Cocos nucifera ), Brazil nuts ( Bertholletia excelsa ), pecans ( Carya illinoinensis ), hazel nuts ( Corylus ), almonds ( Prunus dulcis ), walnuts ( Juglans regia ), pistachios ( Pistacia vera ) and many others. They are high in nutritive value and contain high-quality protein, vitamins and minerals as well as dietary fibre. A variety of nut oils are extracted by pressing for culinary use; some such as walnut, pistachio and hazelnut oils are prized for their distinctive flavours, but they tend to spoil quickly. In temperate climates there
18769-455: Was the earliest known tree. Both of these reproduced by spores rather than seeds and are considered to be links between ferns and the gymnosperms which evolved in the Triassic period. The gymnosperms include conifers, cycads, gnetales and ginkgos and these may have appeared as a result of a whole genome duplication event which took place about 319 million years ago. Ginkgophyta was once
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