Terrestrial Biomes

What Are the Characteristics of Earth’s Terrestrial Biomes?

Defining a Biome

Although just 29 percent of Earth’s surface is land, there is incredible diversity in that small percentage. From deserts to forests, and from tropical rain forests to rolling grasslands, terrestrial biomes differ greatly in location, extent, biodiversityglossary term (opens in a new window), and abiotic factors. A biomeglossary term (opens in a new window) is a large region characterized by its climate and organisms. A biome can consist of many different ecosystems.

There are great differences in the latitudeglossary term (opens in a new window), altitude, and geography among Earth’s terrestrial biomes. Therefore, climate conditions vary significantly among these biomes. For example, biomes located close to the equator experience warmer temperatures than biomes located closer to the poles.

Temperature and amount of precipitation, which are properties of climate, primarily determine which organisms live in a biome. Climate determines the types of plant species that can live in a region. Plant life, in turn, partly determines the animal species that live there.

The major terrestrial biomes on Earth include deserts, tundra, taigas, rain forests, deciduous forests, grasslands, and chaparrals.

Terrestrial Biomes

Different climates result in diverse plant and animal life across biomes. What features can be used to compare terrestrial biomes?

Desert Biome

Deserts cover about one-fifth of Earth’s land surface. The word desert conjures up images of dry, arid landscapes with sand and dust. This is a valid description for many deserts. Desert biomes receive little rainfall, usually less than 25 centimeters annually. The rain that does fall on deserts is sporadic and may be in the form of heavy downpours. Some deserts can go an entire year with no rain. The average annual temperatures of hot, dry deserts range from 20°C to 25°C. Extreme highs may reach to 49°C (120°F) or even higher. At night the temperature drops rapidly. Desert soils are often sandy or gravelly. They are well drained, and surface water is usually present for only short periods. Where water is present for long periods, it will form a water hole or oasis. Water may be found below the surface at dry river beds and vegetation often follows these dry water courses.

The Sahara Desert is the world’s most extensive hot desert. It covers about 9,200,000 square kilometers across North Africa. It is extremely dry, receiving less than 2.5 centimeters of rainfall per year. The Sahara Desert is also very hot. During summer months, the Sahara commonly reaches temperatures of 50°C (122°F). The highest temperature recorded was 58°C (136°F)!

The Sahara Desert

The Sahara Desert covers most of North Africa. How does the Sahara Desert compare with other large deserts?

Life is sparse in most deserts. Relatively few living things are adapted to withstand the heat and drought of this biome, but there are some species that are adapted to the dry, harsh environment. Desert plants tend to be low-lying bushes or woody trees that are able to tolerate the heat and lack of water. Desert plant species store water and nutrients in their stems and leaves. These plants are called succulents. Many desert succulents are cacti. Cacti have evolved many adaptations to desert life. They store water in their stems. These stems are often covered in waxy substances to reduce water loss. They also lower water loss by having a shape that reduces their surface area, and by having modified leaves that form spines. These spines provide them with protection. Many desert plants have extensive root systems to collect the scarce water. Other plants store nutrients below ground in taproots or corms.

Many desert plants have very short life cycles that are adapted to the infrequent rain. After a rainstorm the seeds of the plants will quickly germinate. The plants will grow rapidly. They will flower and seed in a few weeks. Their seeds will remain in the soilglossary term (opens in a new window), perhaps for many years, until it rains again.

Like plants, desert animals must be adapted to high temperatures and little water. Many desert animals such as reptiles and small rodents spend the hottest hours of the day burrowed underground where temperatures are cooler. Other desert species like bats, snakes, and larger rodents are completely nocturnal, waiting for the cool night hours to become active. Structural adaptations to heat include systems for recycling water within the body, and cooling surfaces such as large ears. Some desert species move with changes in precipitation, following blooms in vegetation. Many species have adapted their life cycle to periods when food and water are more plentiful.

Defining Deserts

Desert biomes are characterized by low rainfall and extreme conditions. What common adaptations have plants and animals evolved to survive in desert biomes?

Not all deserts are hot. In fact, the largest desert in the world, Antarctica, is frozen. Cold deserts also exist in Greenland and around the Arctic Circle. They have long, extremely cold winters with little snowfall. The average winter temperature of cold deserts ranges between –2° and 4°C (28° to 39°F) with the coldest temperature ever recorded on Earth being in Vostok, Antarctica, at –89°C (–128°F).

Similar to dry deserts, there is little life in cold deserts. In the summer months, there is barely enough heat for small lichens and mosses to grow. The most common animals include species of invertebrates. In summer these provide food for many species of migratory birds. Mammals are mainly small rodents and their predators. Some cold deserts are home to foxes and coyotes. The cold desert of Antarctica is one of the few places in the world where penguins can be found.

Taiga Biome: the Boreal Forest

The taiga is the largest terrestrial biome. It is located just below the Arctic Circle, below the tundra, and stretches across parts of Europe, Asia, and North America. Similar to the tundra, taigas have extremely cold winter temperatures averaging below freezing for half of the year. However, there is more snowfall in the taiga biomeglossary term (opens in a new window) than the tundra. The summers are warm and humid due to rainfall, but they are very short. The majority of the precipitation in the taiga falls as rain in the summer. This sets the conditions for huge coniferous forests to grow. In fact, the taiga is sometimes called a boreal forest biome.

The coniferous forests of the taiga are made up of evergreen trees that produce their seeds in cones. Their leaves are long, thin needles with a waxy coating that helps prevent water loss and helps protect the needles from freezing temperatures. The forests of the taiga are densely packed because the coniferous trees grow close together for protection from cold and wind. However, this makes them vulnerable to wildfires that can easily spread from tree to tree.

Mountain Forest

Coniferous forests flourish in the cold climate found at high altitudes. Why are evergreen conifers adapted to remain green and able to photosynthesize year-round?

Many herbivorous animals of the taiga feed mainly on the seeds produced by the coniferous trees. These animals include squirrels, insects, and seed-eating birds like finches and sparrows. Herbivores such as moose and beavers eat tree bark, aquatic vegetation, and plant shoots and roots. The variety of herbivores living in the taiga attract predators such as wolves, bobcats, and raptors.