Classifying Terrestrial Biomes

Without plate tectonics and a hot spot on the Nazca plate, the Galápagos Islands would not exist. Terrestrial by definition means land and volcanic activity birthed these islands in the middle of the Pacific Ocean. Climate varies greatly on and between islands, which produces habitat diversity for the archipelago's many endemic terrestrial species. This is a SMALL section of Volcan Sierra Negra on Isla Isabela, measuring 7.2 x 9.3 km and has the second largest volcanic caldera in the world.

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The biome concept organizes large-scale ecological variation. Terrestrial biomes are distinguished primarily by their predominant vegetation, and are mainly determined by temperature and rainfall. Precipitation amounts affect the types of plants that can be found; trees require large amounts of precipitation whereas grasses do not. Precipitation amounts and types also impact how much weathering of rocks and minerals occurs, for soil formation. Temperature affects decomposition rates, which in turn impacts how much organic matter is incorporated into soil.

Over time, an ecosystem tends to go through the stages of primary succession. However, natural disruptions AND climate AND soil texture influence what the climax community will be. For example, frequent fires are detrimental to trees (wood is a fuel for fires) and only allow for non-woody plants and grasses to dominate. If the ground is frozen majority of the year, then plants with roots will struggle to anchor in soil.

If the climax community are trees...

the biome is going to be a forest. The type of forest depends on the average temperature. All forests receive large volumes of precipitation because trees require large quantities of water. Forests tend to have greater species diversity near the equator and this decreases as you approach the sub-polar zones.

Biomes with high precipitation will be a forest. Tropical forests are in the tropics, temperate forests are in mid-latitude zones and boreal forests are in the (sub)polar northern hemisphere.

If the climax community are grasses...

the biome is going to be a grassland. The type of grassland depends on temperature. Grasslands receive varying, seasonal precipitation and just little enough to not become a forest. Some hardier trees can survive and be found in grasslands. In temperature zones, oak trees (Quercus spp.) can survive seasonal wildfires and attempts at uprooting them. In tropical zones, acacia trees (Acacia spp.) tend to be the dominant large vegetation in savannas.

Grasslands receive just little enough precipitation that trees do grow here. If trees do start growing or establishing, natural fires and controlled burns can kill those trees and prevent succession of this biome into forests.

If the climax community are woody shrubs and succulents...

the biome will be a desert. All deserts are classified as having extreme temperatures and little precipitation. 'Extreme' does not simply imply extreme heat, but also extreme cold and extreme fluctuations between daytime and nighttime temperatures. The desert biome is a dry, terrestrial biome. It consists of habitats that receive very little rainfall each year, generally less than 50 centimeters. The desert biome covers about one-fifth of the Earth's surface and includes regions at a variety of latitudes and elevations.

If the climax community has patchy, low-to-ground vegetation and is largely treeless...

the biome will be a tundra. Tundras are classified as being cold and receiving little precipitation. The vegetation is small because the growing seasons tend to be very brief due to the tilt of Earth's axis. The ground is permanently frozen (permafrost), which resists the penetration of root systems in the soil. There are special types of tundras that have similar characteristics— alpine tundras and páramos, existing above the treeline– but the limit to plant growth and size are temperature and oxygen levels at higher elevations.

For most of the year, the tundra biome is a cold, frozen landscape. This biome has a short growing season, followed by harsh conditions that the plants and animals in the region need special adaptations to survive. Tundra form in two distinct cold and dry regions.