Which of the following is NOT considered a principal biome?

Wetlands are unique ecosystems that are often classified differently from principal biomes. Principal biomes, such as forests, savannas, and grasslands, are large ecological areas characterized by distinct climate conditions, flora, and fauna. Each of these biomes supports a variety of life forms and has specific environmental characteristics.

Forests, for instance, are defined by their dense tree coverage and are categorized into various types based on climate, such as tropical, temperate, or boreal forests. Savannas are grassland ecosystems with scattered trees, found in regions with seasonal rainfall. Grasslands, often referred to as prairies or steppes, consist primarily of grasses with few trees and are adapted to specific climate conditions differing from those of forests or savannas.

In contrast, wetlands, which include areas such as marshes, swamps, and bogs, are characterized by saturated soils and standing water at least part of the year. They serve various ecological functions, including water filtration and habitat for wildlife, but they do not fit neatly into the established categories of the principal biomes. Therefore, wetlands are typically considered as a distinct category rather than a principal biome themselves.