What's a Biome?

To make sense of complexity, humans often need to categorize, or group, things. We have food groups, sexes, eye colors, ages, and movie genres, to name a few. We categorize all types of things, whether they are ideas or objects, and whether they are small or large. One of the largest things that we try to categorize may be the types of environments found on Earth.

The natural world is more varied than we can imagine, and one way to try to make this variation easier to handle is to put different environment types into groups. We can divide our surroundings many ways—by how much water there is, by how warm it is, or by the types of plants or animals we find there. Depending on what characteristics we choose to describe an environment, the groupings we end up selecting may be different.

Usually we group the different natural areas on Earth into categories based on plant and animal life and how they are able to survive in that part of the world. Making groups based on living organisms can be very complicated. We already know of over 1.7 million species of organism, and there are likely over 17 million that exist. But again, by grouping organisms with similar adaptations together, we can see through some of the complexity and have a chance to better understand the living Earth. 

A biome is a type of environment that is defined by the types of organisms that live there. We can also think of these as life zones ("bio" means life). Dividing land up in this way lets us talk about areas that are similar, even if they’re on different continents. But depending on whom you talk to, the way we divide up the world into separate biomes differs.

Biome vs. Biome

Biome categories can be broad or narrow. When we say forest, you may picture a cool, quiet area with pine trees, where bears, deer, and rabbits wander around. Or instead, you might imagine a wet, dark, and noisy rainforest, where you can see monkeys, parrots, and big cats.

According to some people, all forest types belong in one group – the forest biome. But others think that temperate forests (seasonally cold) with pine trees, are very different from tropical rainforests, with dense, leafy canopy and lots of rain. This difference of opinion means that the number of biomes can range anywhere from 5 to 20 biomes.

How Different is Different?

If we take a closer look at these temperate and rain forests, we see that they differ quite a bit in the amount of rain they get and in their temperatures. Tropical rainforests are warm and don't experience a winter season. But temperate forests have a defined winter, with snow and temperatures below zero.

With those cold temperatures, the plants and animals in temperate rainforests have to have adaptations to deal with cold weather. Do those groups seem different enough to you to be in a separate biome?

Don't worry, there is no right or wrong answer. This method of categorizing is one of convenience, and sometimes it just depends on why you're dividing the groups.

Biomes of the World

In order to give you a small taste of the huge diversity of the types of environments out there, we divide the world up into only nine biomes. Just remember that these groups could also be divided into nearly 20 biomes. That means that within each of these biomes there is a range of temperature and weather conditions, and we also find some organisms that are adapted to only part of the biome and others that are adapted to the full range of conditions within the boundaries we are defining.

Tropical Rainforest

You probably picture tropical rainforest as a jungle, where it stays warm all year. There are too many animals to count and the huge numbers of trees keep their leaves year-round. Many of these forests get so much rain that there isn't even much of a dry season – more like a rainy season and a rainier season.

Temperate Forest 

This is the kind of forest where there are four relatively distinct seasons. Many of the trees shed their leaves in the fall and become inactive through the cold winter. In these forests, you find deer, woodpeckers, and bears, some of which hibernate through the winter.

Desert

Deserts make up the hottest biome, but can also get cold temperatures in winter. Such temperature swings make this an extreme environment, where many animals have to burrow underground to find more stable temperatures in order to survive. Plants and animals here must be able to withstand long periods without water.

Tundra

Tundra is flat and cold with low plants like grass and moss that only grow during the short summer. A thick layer of ice lies just below the shallow soil (permafrost) all year around, and trees cannot penetrate it to anchor their roots. Many birds visit the tundra in the summer to nest, but most escape the winter by migrating to warmer areas. Mice and other small mammals stay active during the winter in protected tunnels under the snow.

Taiga (Boreal Forest) 

Taiga is the largest land (terrestrial) biome in the world.  It is made up of mainly conical-shaped evergreen trees with needle-like leaves. These trees are called conifers because their seeds are clumped into cones. The taiga has long, cold winters when most mammals hibernate and birds migrate, or leave the area because the winters are too cold for them to stay. Animals like weasels, grouse and rabbits that do not migrate or hibernate grow dense feathers or fur and turn white to match the snow.

Grassland  

Sometimes called plains or prairie, grasslands are almost entirely short to tall grasses with no trees. This land type gets just enough rain to help grasses, flowers, and herbs grow, but stays dry enough that fires are frequent and trees cannot survive. Here we find large mammals that often travel together in huge herds.

Savanna

These tree-studded grasslands receive enough seasonal rainfall so that trees can grow in open groups or singly throughout. The animals living here have long legs for escaping predators and usually are seen in herds. A combination of fire and grazing animals are important for maintaining the savannah.

Freshwater

This water biome is named for the low concentration of salt found in the water. This includes most ponds, streams, lakes, and rivers. Because salt is important to body function, the plants and animals here have many adaptations that help them save salt.

Marine

This water biome is the largest biome in the world, as it includes the five major oceans that cover 70% of the Earth. Marine water has high levels of salt, so animals and plants living here have adaptations that help them get rid of salt or take on water.

Virtual Biomes

Take a virtual look inside some of these biomes using a computer, smart phone, tablet, or Google Goggles. Our first two virtual biomes are the desert and rainforest. Compare how the two are different and how they are the similar. Write up your results in our biologist notebook.

Additional images from Wikimedia via Adrien Facélina and Pam Brophy.