Rainforests - Statistics & Facts

Biodiversity and the rainforest's layers

Many of the statistics relating to biodiversity in the rainforest vary depending on the age of the information, the source, and methodology. The nonprofit Mongabay states that rainforests cover just two percent of the earth's surface, but are home to 50 percent of all life on land. One single hectare of rainforest land may be home to as many as 480 different plant species, compared to temperate forests where the majority of trees may belong to just 5-10 species.

Forest floor: the rainforest can be split into several layers, the lowest of which is the forest floor, which is home to much of the rainforest's small invertebrate population, such as insects, worms, and millipedes. Perhaps surprisingly, rainforests tend to have quite infertile topsoil, and its flora obtain nutrients from other sources. The darkness and humidity of the lower levels, aided by animal activity, means that leaves decompose in around six weeks, whereas they can take years in more moderate or subarctic forests - because of this, nutrients are recycled between plants and animals in an incredibly interdependent ecosystem, rather than absorbed from the soil as in other ecosystems.

Understory: Above the floor is the layer known as the understory, which is made up of young and shorter trees, shrubs, and plants. Light levels in this section are still quite low, and many of the plants have large leaves and emit strong odors to attract animals and insects, to facilitate pollination. Additionally, the fact that these plants require little direct sunlight is why they make some of the most common and durable houseplants sold today. This section of the rainforest is often more open than the floor below or canopy above, making it home to a variety of bird, bat, and flying insect species, while the high humidity also makes it a perfect environment for amphibians and reptiles. Historically, the word jungle was used when referring to rainforests as a whole, but in the past half century jungle has increasingly referred to this section alone, or similar environments such as mangroves.

Canopy: The upper layer of the rainforest is the canopy, which acts as the rainforest's roof, and is responsible for blocking sunlight and trapping humidity. It is home to the largest variety of animal species in the rainforest, with some, including heavier bird and monkey species, spending almost their entire lives in the rainforest's upper levels. Here they are sustained by drinking rainwater and condensation from plants, as well as the many fruits, nuts, and edible insects are found at this level. The canopy can occupy an area ranging anywhere between 20 and 50 meters above the forest floor, depending on the height of the forest itself. In cases where individual trees rise above the canopy, this is referred to as the emerging layer, which may eventually spread out and increase the height of the rainforest over extended periods of time. As the rainforest is home to so many unique species of plant and animal, the removal of just one tree can affect all layers of the rainforest, and the the removal of entire areas may lead to the extinction of these species as they struggle to migrate or adapt.

Rainforests and the water cycle

In many ways, rainforests are self-contained ecosystems, with their own climate and weather patterns. Their high humidity means that large quantities of water evaporate to form clouds every day, and the majority of this water is then released back into the forest as rain (hence the name "rainforest") - for example, between 50 and 80 percent of all moisture in the Amazon rainforest is contained within its own water cycle. Because of its foliage and cloud cover, temperatures remain fairly steady, at around 30°C (86°F) during the day, and 20°C (68°F) at night. Despite this, the water that escapes from this ecosystem may influence weather patterns across oceans - studies have shown a link between water from the Congo rainforest in Central Africa falling on the United States' Midwest, and similar intercontinental connections have been found elsewhere. Because of this, threats to the sustainability of rainforests in one region should be considered a global challenge, as its consequences may have a ripple effect across the world.

Rainforests, the carbon cycle and deforestation

Like the water cycle, the rainforest’s influence on the balance between oxygen (O₂) and carbon dioxide (CO₂) in the atmosphere is mostly self-contained, but happens on such a large scale that its influence can still be felt across the globe. Throughout their lifetimes, plants generally release similar amounts of oxygen (through photosynthesis) and carbon dioxide (through cellular respiration) into the atmosphere, although the volume of oxygen produced is slightly higher. For rainforests, the majority of the CO₂ it absorbs is produced by its own biodiversity, vast quantities of CO₂ are expired each night when no photosynthesis can occur, and this is then reabsorbed during daytime.

Although over 85 percent of the world's carbon is stored in the ocean, terrestrial sources have played a larger part in absorbing and storing carbon from the atmosphere (known as carbon sequestration) in the past 250 years, since the incredible increase in human-made carbon emissions through industrialization. Rainforests are among the most important sources of carbon sequestration on the planet due to their vegetation density, and they act as massive carbon sinks that store large quantities of carbon in its soil and vegetation - as deforestation occurs, this not only reduces large areas of vegetation that help maintain the balance between O₂ and CO₂ levels in the atmosphere, but it also releases large quantities of carbon that has been stored in the soil and plants (sometimes for centuries or longer). Additionally, as more carbon is expelled via the burning of fossil fuels and deforestation, more heat is trapped in the atmosphere, and higher temperatures in plants may result in an acceleration of cellular respiration (CO₂ output) and a deceleration in photosynthesis (O₂ output). Higher temperatures also increase the frequency and severity of forest fires, with fires in the Amazon garnering increased public attention in recent years, and even becoming a major issue in Brazil's 2022 election - in mid-2023, the Lula da Silva administration announced sweeping reforms to halt illegal deforestation and to reach zero net deforestation by 2030.

As deforestation is occurring at a higher rate in rainforests than any other type of forest, preventing further tree loss is one of many necessary steps to save the planet. Rainforests have provided humans with food, shelter, and energy for millennia, but the technological advances in recent centuries have made the extraction of resources unsustainable. Almost half of deforestation occurs through converting land for subsistence farming, and many poorer societies are forced to do this to produce food for growing populations, especially as climate change exacerbates food instability. However, over half of all deforestation in the world is for commercial farming, logging, and fuel, which can be incredibly profitable for businesses and governments, and contributes to a large share of land grabbing in Africa. Major reforestation initiatives have been undertaken in an attempt to restore the rainforest and fight climate change, although a large share of reforestation is for commercial purposes, such as palm oil production, and these forests do not provide the same plant diversity or habitat as rainforests. Climate change exacerbates the impact of deforestation and wildfires, and vice versa, therefore many international organizations set ambitious targets to reduce carbon emissions and limit deforestation in the future. There is some optimism that rainforests and rainforest species will be protected through these measures, however, previous targets of this nature were actually followed by an increase in deforestation rates, therefore it remains to be seen what the long-term impact of conservation and green initiatives will have on the world's rainforests.