熱帯雨林の事実：層、生物多様性、動物と気候

Rainforest Facts: Layers, Biodiversity, Animals & Climate | Rainforest Concern | Rainforest Concern Rainforests are among the most important and most misunderstood ecosystems on Earth. This section answers the foundational questions: what rainforests are, how they work, and why they matter, and other information. What is a rainforest? A rainforest is a forest that receives over 1,800mm (70 inches) of rainfall per year, and has a largely closed canopy that keeps the interior (the space below the canopy) humid and shaded year-round. Either tropical or temperate, rainforests cover just 6% of the Earth's land surface but are home to more than half of the world's plant and animal species. Tropical rainforests are characterised by consistently warm temperatures (typically 24–27°C year-round), extraordinary biodiversity, and a layered structure: the forest floor, understory, canopy, and emergent layer, each hosting its own community of species. Tropical rainforests are found in a band around the equator - across Central and South America (most famously the Amazon basin), Central Africa (the Congo Basin), and Southeast Asia (Borneo, Sumatra, and New Guinea). Rainforests are extraordinarily biodiverse, are a globally significant carbon storage, and have critical roles in regional and global water cycles. What are the different layers of a rainforest? The rainforest canopy is divided into four main layers. From top to bottom these are the emergents, the canopy, the understory and the forest floor. These layers act as four interconnected vertically stacked habitats, fostering immense biodiversity. “ Emergents ” are extremely tall trees which can grow to heights of over 80m (but are more typically closer to 50m) protruding from the forest canopy. In the Amazon rainforest the tallest emergent species is the Angelim Vermelho - the largest specimen ever measured was 88.5m tall with a 9.9m trunk circumference and estimated to be over 400 years old. The forest canopy is a mostly continuous cover of foliage formed by adjacent treetops, approximately 10m thick. Although not all tall as the emergents, canopy trees are large, up to 45m tall. These trees are intertwined with lianas and hold flowering plants (called epiphytes) on their branches. This plant diversity hosts countless invertebrate species. These and the trees’ fruits and foliage feed thousands of bird, reptile and mammal species. The canopy is the most biodiverse forest layer. Understory plants tolerate dim conditions; only about 5% of the sunlight shining on the canopy reaches the understory. Generally they have evolved large leaves to maximise photosynthesis. The understory contains the saplings that when fully grown will form the canopy and emergent layers. When a canopy tree falls, the understory and forest floor experience a period of explosive plant growth due to the spike in available light. Although not as biodiverse as the canopy, the understory houses abundant insect life and larger climbing animals, such as jaguars and anaconda. The forest floor is relatively dark; on average only 2% of sunlight reaches this rainforest layer through the canopy and understory. Only plants evolved to tolerate very dim conditions can exist on the forest floor. Most tropical rainforests have surprisingly poor quality soils as rapid bacterial decay preventing humus accumulation. There are exceptions; rainforests that flood on a yearly basis, in Amazonia termed várzea or igapó, have relatively rich soils. Minerals (such as phosphorus from the Andes) and nutrients are deposited by the yearly floods, fertilising the soil and fuelling rapid plant growth. The layers of the forest are connected and maintained in a perpetual cycle. Tree roots bind the soil together, while the canopy and trunks protect the soil from the erosive force of heavy rains. When an emergent or canopy tree dies, its trunk falls to the forest floor, where it decays and the nutrients it contains are recycled, fuelling fresh growth. If trees are removed from the forest (see deforestation, logging) their nutrients and physical protections are removed too. The unprotected soil is simply washed away in heavy rains, causing blockages and floods in lowland rivers, while leaving upland earth dry and unnaturally nutrient poor. Forest layers by Alan Dun Where are the world's rainforests located? Tropical rainforests are found in a belt around the equator, between the Tropic of Cancer and the Tropic of Capricorn (23.5° North and South of the Equator), across South and Central America, Central Africa, Southeast Asia and Oceania. They cover around 6% of the world's land surface, yet contain more than half of our planet’s plant and animal species. The Amazon Rainforest is our planet’s largest rainforest, alone covering almost 526 million hectares of primary forest (as per Global Forest Watch) across nine South American countries. Temperate rainforests occur at higher latitudes - in coastal regions of North America (the Pacific Northwest of the USA and Canada), southern Chile, New Zealand, Norway, and parts of the UK (including Scotland and Wales, where Rainforest Concern is actively working). They are cooler and less biodiverse than their tropical counterparts. What is biodiversity and why does it matter? Biodiversity is a technical term used to describe the variety of living things in a given space. Biodiversity is most commonly used to refer to the diversity of plants and animals (for example in a patch of rainforest), but also refers to the genetic diversity within species all the way up to ecosystem-level diversity. Not all forests are equal; protected virgin forest will always be more biodiverse than plantations or even replanted forest after decades of plant growth and fauna recolonisation. Biodiverse habitats are more stable than similar habitats lacking biodiversity, innately possessing a resilience to change due to their greater capacity for adaptation. When biodiversity is lost from a habitat, that habitat becomes less stable, less productive and less able to recover from disturbance. In natural habitat conservation, biodiversity is core to conservation effectiveness; the more biodiversity a conservation measure protects, the more effective that conservation measure has been. Rainforest Concern has been building reserves for over three decades, always targeting forests of high biodiversity, including rare and threatened species. Examples include the Neblina Reserve , Bosque de las Madres Corridor Project and the Nasampulli Reserve . What animals live in rainforests? Tropical rainforests are extraordinarily biodiverse, although the exact number of tropical rainforest species is unknown, with estimates ranging from from 3 to 50 million species. This has been estimated to include two-thirds of Earth’s flowering plant species and 62% of global terrestrial vertebrate species, as determined by a peer reviewed 2021 study (see R. Pillay et al., Frontiers in Ecology and the Environment, 2022). Many thousands of tropical rainforest species are waiting to be discovered. Rainforest mammals include some of Earth’s most fascinating and unique: jaguars, giant river otters, tapirs, giant anteaters, and more than a dozen species of monkey. Flowering plants and insects feed the vast majority of bird life, providing fruit, nectar, and the insect communities that depend on them. As two-thirds of all flowering plant species are found in rainforests, rainforests host a vast diversity of birds, which form food chains including predatory and scavenging birds. The Amazon Rainforest alone hosts over 1,300 bird species, including macaws, harpy eagles, toucans, and hummingbirds. Insects are by far the most numerous group in tropical rainforests: a single hectare of rainforest may contain more than 480 tree species, and a single tree in the Amazon rainforest may harbour more species of ants than the entire British Isles. 11 threatened and rare species Rainforest Concern’s projects conserve include: Black and Chestnut eagle (Isidor’s eagle, Spizaetus Isidori ). Endangered (IUCN) due to habitat destruction, evidence suggests just 250-999 mature adults exist across their native range. Rainforest Concern’s Neblina Reserve protects several breeding pairs. Olinguito ( Bassaricyon neblina , Near Threatened). Discovered in 2013, the discovery of the olinguito was the first identification of a new mammal species of the order Carnivora in the Americas in 35 years. Longnose Stubfoot toad ( Atelopus longirostris , Critically Endangered) - this species is so rare it was presumed extinct for decades, until its 2016 rediscovery near Neblina. Andean or Spectacled bears ( Tremarctos ornatus , Vulnerable), protected in Neblina. A 2017 camera trap survey revealed twice the number of bears than had been estimated based on Neblina’s area. Oncilla ( Leopardus tigrinus , Vulnerable). This species is threatened by deforestation and conversion of habitat to agricultural land. Protected in Neblina. Baird's tapir ( Tapirus bairdii , Endangered) is in decline due to habitat loss, water pollution, poaching and disease transmission from domestic animals. This species is protected by the Rainforest Concern Bosque de las Madres project. Great green macaw ( Ara ambiguus , Critically Endangered). It is estimated that between 1900 and 2000, 90% of this species’ original habitat has been lost in Costa Rica. This species is protected by the Rainforest Concern Bosque de las Madres project. Arapaima ( Arapaima gigas ). A peer-reviewed study found that arapaima numbers were depleted or overexploited at 93% of the sites examined in 2014. Responsible management and fishing can lead to a boom in arapaima numbers and associated biodiversity, as illustrated by the work of Rainforest Concern’s partners Instituto Juruá. Arapaima numbers have increased by 55x in the lakes of the Instituto Juruá partner communities. Jaguar ( Panthera onca , Near Threatened, IUCN). threatened by loss and fragme