Each biome, or community of plants and animals in a certain climate, has life-forms characteristic of that place. For instance, the plants and animals that inhabit the Amazon rain forest are completely distinct from those in the Arctic tundra. However, not everyone agrees on exactly what constitutes a biome, and defining them presents a challenge.
Biomes are sometimes confused with similar ecological concepts, such as habitats and ecosystems. Ecosystems are the interactions between biota, such as plants and animals, within the environment, and many ecosystems can make up a single biome. Nutrient and energy flow also play a critical role in ecosystems. A habitat, on the other hand, is specific to a population or species; it is the area in which that group lives. Meanwhile, biomes describe life on a much larger scale than either habitats or ecosystems.
The term "biome" was first used in 1916 by Frederic E. Clements, an American ecologist, to describe the plants and animals in a given habitat. In 1939, it was further defined by Clements and fellow ecologist Victor Shelford. Over time scientists continued to expand and refine the definition of biome and related concepts in the burgeoning field of ecology, and in 1963, Shelford characterized the following biomes: tundra, coniferous forest, deciduous forest, grassland, and desert. Later, ecologist Arthur Tansley created a separate definition for ecosystems, which was more inclusive of biological processes than the definition of a biome.
What unites all biome definitions is that biomes can be differentiated by the organisms residing there and by the climate, as well as the fact that the organisms within a biome share adaptations for that particular environment. Climate is a major factor in determining types of life that reside in a particular biome, and there are several factors that influence climate, such as latitude, geographic features, and atmospheric processes disseminating heat and moisture.
The number of biomes that exist is debated by scientists. While some aspects of the definition are widely agreed upon (climate and resident life), some definitions broaden to include factors, such as biodiversity and human activity. Although definitions may not be consistent, several types of biomes typically emerge from the definitions: tundras, deserts, grasslands, deciduous forests, coniferous forests, tropical rainforests, and aquatic.
The tundra are located at the northernmost parts of the globe and is defined by long, cold winters and cool summers. The animals and plants that reside here have evolved adaptations that allow them to survive in this frigid environment, such as thick fur and the ability to hibernate.
Located in both cold and warm climates across the globe, deserts are defined by their dryness, and life in these areas is adapted to a lack of water and nutrients.
The grassland biome, which is found on every continent except Antarctica, is characterized as being flat and grassy, with very little tree cover. Large mammals that graze, such as elephants or bison, inhabit these areas, along with small mammals, birds, and predators.
Coniferous Forest Biomes
These areas—known as taigas or boreal forests—experience long, cold winters, short summers, and heavy precipitation. Within this biome, the primary vegetation types are conifers and evergreen trees. Sometimes this category is split into another category known as the temperate forest, which does not experience temperatures as cold. One example of this warmer forest would be the west coast of North America, a humid forest system home to redwoods and cedars.
Deciduous Forest Biomes
Located in eastern North America, Western Europe, and northeastern Asia, this biome is marked by broad-leafed trees, such as maple and oak, that lose their leaves seasonally as the temperatures begin to drop. Overall, these regions are temperate, but still have a distinct winter season.
Tropical Rainforest Biomes
These equatorial regions are warm and wet with diverse vegetation that forms a canopy. Leaf litter on the ground and the humid conditions create a layer of nutrients above the low-quality soil, which allows for the growth of a wide variety of vegetation. In fact, tropical rainforests are famous for hosting vast amounts of biodiversity.
There are numerous ways to classify aquatic biomes, and often freshwater and saltwater biomes are defined separately; factors used for classification include water depth, temperature, and salinity. The terrestrial biomes are typically classified by vegetation types, but this method can be difficult to apply to aquatic environments, which do not have as much visible plant life.
Limitations of Defining Biomes
Although biomes are often thought of as distinctly defined regions, in reality, they are not clearly delineated. Biomes do not typically have precise boundaries; instead, there are frequently transition zones between biomes. These zones are referred to as ecotones, and they can be naturally occurring or created by humans.
Further, many biome definitions exclude humans. However, some scientists believe that human presence is an integral part in defining biomes, and they posit that most biomes are actually primarily influenced by humans. Similarly, scientists are beginning to recognize how the results of human activities, such as habitat destruction and climate change, will change how biomes are defined in the future.