8.3 Terrestrial Biomes

Tropical rainforests are found near the equator and are the most biologically diverse terrestrial biome. They have warm, stable temperatures year-round (20°C to 34°C) and receive 250 to over 450 cm of rainfall annually. Even in drier months, rainfall remains high compared to other biomes. The consistent warmth and sunlight support year-round plant growth so these forests are highly productive.

Rainforests are structured in vertical layers which creates a wide range of habitats. Common plants include broadleaf trees, vines, ferns, and epiphytes (plants that grow on other plants). Animals include jaguars, sloths, toucans, monkeys, frogs, and countless insect species. Many animals live in the canopy and rarely descend to the ground (OpenCurriculum, n.d.).

Tropical rainforests are vital for global biodiversity and climate regulation, but they face serious threats from deforestation and habitat loss.

Savannas are grasslands with scattered trees, and they are located in Africa, South America, and Northern Australia. Savannas are hot, tropical areas with temperatures averaging from 24°C to 29°C and an annual rainfall of 50-120 cm. Savannas have an extensive dry season so trees do not grow well. The open landscape allows sunlight to reach the ground, supporting a rich layer of grasses and herbaceous plants. Since fire is an important source of disturbance in this biome, plants have evolved well-developed root systems that allow them to quickly re-sprout after a fire.

Savannas support a wide variety of large herbivores, including elephants, giraffes, zebras, antelope, and wildebeest. These animals are often migratory, moving in herds in search of water and fresh grazing areas. The biome also supports many predators, such as lions, cheetahs, hyenas, and vultures, which rely on the abundance of herbivores for food. Smaller animals like meerkats, ground birds, and insects also thrive in this environment (OpenCurriculum, n.d.).

Deserts are dry biomes that receive less than 30 cm of precipitation per year. Most desserts are subtropical and found around 30° latitude north and south of the equator. These regions are known for their extreme heat, low humidity, and sparse vegetation.

Temperatures in deserts can exceed 40°C during the day but drop sharply at night due to the lack of cloud cover. The intense sunlight and dry air create harsh conditions for life, yet many organisms have evolved remarkable adaptations to survive. Plants in deserts are typically succulents, such as cacti and other plants that store water to help them during dry seasons. These plants often have thick, waxy cuticles, spines instead of leaves, and shallow but widespread roots to quickly absorb water from light rains. Animals in deserts are also well-adapted to conserve water and avoid heat. Many are nocturnal, active only at night when temperatures are cooler. Typical desert animals include lizards, snakes, and rodents (OpenCurriculum, n.d.).

In addition to subtropical deserts there are cold deserts that experience freezing temperatures during the winter and any precipitation is in the form of snowfall.

The chaparral is a shrubland biome found in California, along the Mediterranean Sea, and along the southern coast of Australia. These areas experience hot, dry summers and mild, wet winters. Annual precipitation typically ranges from 65 to 75 centimetres, most of which falls during the winter months.

Temperatures in the chaparral can vary widely. Summer temperatures often exceed 30 °C, while winter temperatures are usually mild, ranging from 10 to 15°C. The long dry season and frequent droughts make fire a natural and important part of the chaparral ecosystem. Many plants are adapted to survive and even regenerate after periodic wildfires. The chaparral is a fragile biome that can be easily damaged by human activity like fire suppression, which disrupts natural fire cycles and leads to more intense wildfires.

Vegetation in the chaparral is dominated by dense, woody shrubs and small trees with tough, leathery leaves that reduce water loss. Some species have seeds that only germinate after exposure to fire (OpenCurriculum, n.d.).

Animals in the chaparral are adapted to the dry conditions and often avoid the heat by being active at night or during cooler parts of the day. They include rodents, lizards, and a variety of birds and insects. Most chaparral animals are small because the densely growing trees make it difficult for very large animals to move through. The largest animals are deer, which browse on the leaves of chaparral trees (OpenCurriculum, n.d.).

Temperate grasslands are found in the interiors of continents, including the prairies of North America and the steppes of Eurasia. Annual precipitation typically ranges from 25 to 90 cm, which is enough to support grasses but not large stands of trees.

Temperate grasslands experience seasonal temperature extremes. Summers are often hot, with temperatures above 30°C, while winters can be very cold, with temperatures well below freezing. Periodic droughts and fires are common and play an important role in maintaining the grassland ecosystem by preventing the growth of woody plants.

The dominant vegetation consists of grasses that are adapted to survive grazing, fire, and dry conditions. Many have deep root systems that help them access water and recover quickly after disturbances. Temperate grasslands support a variety of grazing animals and their predators. Common animals include bison, antelope, and small mammals such as prairie dogs and rabbits. Predators like wolves, coyotes, and foxes are also found in these ecosystems. Many animals are adapted to open landscapes and use burrows for shelter and protection (OpenCurriculum, n.d.).

Because of their rich, fertile soils, temperate grasslands have been heavily converted to agriculture, especially for growing grains like wheat and corn. As a result, much of the original grassland habitat has been lost and many native species are now threatened (OpenCurriculum, n.d.).

Temperate forests are the most common biome in eastern North America, Western Europe, Eastern Asia, Chile, and New Zealand. These areas experience four distinct seasons (spring, summer, autumn, and winter) with temperatures that range between –30^oC and 30^oC throughout the year. Precipitation is relatively constant throughout the year and ranges between 75 cm and 150 cm.

The dominant vegetation in temperate forests includes deciduous trees, such as oak, maple, beech, and birch, which lose their leaves each fall. In some mixed forests, coniferous trees like pine, spruce and fir are also common. The trees of the temperate forests leaf out and shade much of the ground; however, more sunlight reaches the ground in this biome than in tropical rainforests because trees in temperate forests do not grow as tall. As a result, the understory contains mosses, ferns, various herbaceous plants, and shrubs. The forest floor is often rich in organic material due to the seasonal leaf drop. As the thick layer of leaf litter decays, nutrients are returned to the soil. The leaf litter also protects soil from erosion, insulates the ground, and provides habitats for invertebrates and their predators (OpenCurriculum, n.d.).

Temperate forests support a wide variety of animal life. Common mammals include deer, raccoons, squirrels, and black bears. There are also insects, amphibians, reptiles, and birds. Many animals in this biome are adapted to seasonal changes, with some hibernating or migrating during the winter months (OpenCurriculum, n.d.).

Boreal forests, or coniferous forests, are found in the high northern latitudes just below the Arctic Circle, stretching across Canada, Alaska, Russia, and Scandinavia. These forests experience long, cold winters and short, cool summers. Annual precipitation ranges from 40 to 100 cm and usually takes the form of snow.

Temperatures in boreal forests are cold for most of the year. Winter temperatures often drop well below freezing, while summer temperatures are mild, typically ranging from 10 to 20°C. The growing season is short, usually lasting only a few months.

The vegetation is dominated by coniferous trees such as spruce, fir, pine, and cedar which are well adapted to cold conditions. These trees retain their needle-like leaves so can begin photosynthesis earlier in the spring than deciduous trees. It also takes less energy to warm a narrow needle than a broad leaf which further allows evergreens to start growing during cooler temperatures. The forest floor is often covered with mosses, lichens, and low shrubs (OpenCurriculum, n.d.).

Animal life in the boreal forest includes species adapted to cold and seasonal changes. Common mammals include moose, wolves, snowshoe hares, and bears. Through the summer there are also many insects and birds. Caribou spend their winters there. The boreal forest is too cold for amphibians or reptiles (OpenCurriculum, n.d.).

Boreal forests store large amounts of carbon because these slow-growing tree species are long-lived. This makes them important for climate regulation, however they are often affected by human activities like logging and mining.

The Arctic tundra is found in the far northern regions of the world, including parts of Alaska, Canada, Greenland, and northern Russia. It is the coldest of all biomes and is characterized by long, harsh winters and short, cool summers. Temperatures can drop below –30°C in winter and rarely rise above 10°C in summer. Annual precipitation is typically less than 25 cm and mostly falls as snow. The growing season is very short and lasts only about 2 months.

Plants in the Arctic tundra are generally low to the ground and include low shrubs, grasses, mosses, lichens, and small flowering plants. A defining feature of the tundra is permafrost, a layer of permanently frozen soil beneath the surface. The top layer of soil thaws in the summer, but deeper layers do not so water cannot soak into the ground. This leaves the soil soggy and creates many bogs, lakes, and streams (OpenCurriculum, n.d.).

Few animals live in the tundra year-round. Those that remain have adapted to the extreme cold, including polar bears, arctic foxes and arctic hares. Insects such as mosquitoes can survive the winter as pupae and are very numerous in summer. Many species of birds and large herds of caribou migrate to arctic tundra each summer. There are no amphibians or reptiles. The Arctic tundra is a fragile ecosystem that is highly sensitive to climate change. Warming temperatures are causing permafrost to thaw, which can release stored carbon and further accelerate global warming (OpenCurriculum, n.d.).