A biome is a region where organisms live with similar conditions, both geographically and climatically. Biomes bifurcate between aquatic (marine and freshwater) and terrestrial, though land and freshwater are typically classified together because of their proximate geography. Beyond that, land-based biomes are more finely defined by climate, with latitude, elevation, and humidity being significant factors.
Marine biomes are defined by depth, latitude, and water flow. Upwelling cold water that brings nutrients from the deep greatly affects marine life, and so figures as a major factor in defining a marine biome.
There is the typical cacophony of vocabulary in identifying biomes, which traditionally have local names. Temperate grassland, shrubland, prairie (North America), savanna (Australia), steppe (central Asia), pampas (South America) and veld (South Africa) are all the same biome under a different term.
Adding to the nomenclature noise are numerous biome classification schemes. Almost all are exclusively terrestrial biomes. All start with climate and diverge from there.
American botanist and climatologist Leslie Holdridge came up with the concept of life zones in 1947 which emphasized temperature and precipitation. Holdridge updated his design in 1967, complicating it with humidity provinces and regions of altitude and latitude. The result was 38 different life zones which emphasized soil type and climax vegetation (dominant plants).
Holdridge’s scheme does not work well in predicting soil pattern, and especially breaks down when moisture becomes a determining factor; especially in cold climates, whether oceanic or arid. Nonetheless, it has been used in assessing changes in vegetation patterns due to global warming.
American plant ecologist Robert Whittaker developed his terrestrial biome scheme in the late 1950s, focusing on gradients of temperature and precipitation. Whittaker’s approach was a simplification of Holdridge’s, with workable concepts about different communities of plant and animal life. Its simplicity made it popular.
A terrestrial biome scheme by German ecologist Heinrich Walter was published in 1976 with 9 basic biomes, from equatorial to polar. Like Whittaker, Walter’s approach was based on temperature, moisture, and vegetation types. Walter also accounted for seasons.
In 2001 came a team effort by the Worldwide Fund for Nature (WWF), defining 8 terrestrial and freshwater ecozones, along with 13 marine ecozones; 14 terrestrial biomes with 867 terrestrial ecoregions; 13 freshwater biomes; and 11 marine habitat types.
The WWF system is rigged to hierarchical classification: ecozone, biome, ecoregion, ecosystem, biotype (typically plant or animal), and species. It is thus strongly taxonomic and not well-suited to describing biospheric dynamics.
Bizarrely, missing from all extant biome schemes is the endolithic biome: the microscopic life in rock crevices and underneath the surface, where life originated. ~70% of Earth’s bacteria and archaea live in the planet’s crust, not on it.