MAJOR ECOSYSTEM TYPES

1) Arid and semi-arid zone ecosystems

>> Grasslands and savannahs
Grassland ecosystems are areas dominated by grasses, grass-like plants and woody plants and are further characterized by periodic drought, fire and large herbivore grazing. Soils are usually marked by low fertility. In particular, savannahs are characterized by a dominant grassy ground layer which can be present in treeless plains, open woodlands, and closed-canopy woodlands. The earth’s land surface is composed of 20 per cent grasslands with temperate grasslands representing one forth of the area and savannas the remainder.

>> Warm desert and semi-desert
Hyper-arid desert ecosystems have irregular rainfall with periodic droughts lasting several years. The Sahara desert represents nearly 70 per cent of the global hyper-arid total. Semi-desert areas are dominated by succulents and other xerophytic plants and are often characterized by sparse or absent tree cover. Rainfall in arid and semi-arid areas varies from less than 200 to a maximum of 800 mm annually.

>> Tundra communities and cold desert biomes
Non-humid areas are composed of cold regions and drylands and represent 61 per cent of the Earth’s total land surface. Cold regions include polar and tundra areas as well as certain high mountains and plateaus and compose 14 per cent of the non-humid area total. Temperatures remain below freezing for a period long enough to restrict plant growth and liquid water is usually unavailable for a significant part of the year.

2) Coastal, marine and freshwater ecosystems

>> Mangroves
A hybrid terrestrial / marine ecosystem, mangroves are composed of shrubs, trees, and ferns living in or adjacent to the intertidal zone. Mangroves are predominantly tropical and are rarely found beyond the latitudes 30°N and 30°S with the most diverse systems located in Southeast Asia.

>> Coral reefs
Composed of calcium carbonate, corals are most abundant in shallow marine environments usually characterized by warm low-nutrient waters. Coral reefs are among the most diverse ecosystems in the world with over 450 different coral species identified in Southeast Asia alone.

>> Seagrasses
Found in shallow coastal areas between the Arctic and Antarctic, seagrasses are flowering plants that live submerged in seawater. Entire ecosystems are founded on their high productivity as they provide an important source of food for many organisms.

>> Pelagic or open-ocean communities
Founded on the activity of plankton, which supports a large number of free-swimming organisms, pelagic communities occupy a greater area than any other major community on earth. Characterized by vertical gradients that fluctuate seasonally or as often as daily, the community responds to variations in the physical and chemical variations of seawater.

>> Deep-sea communities
Deep-sea communities exist in permanent darkness at depths greater than 3000 meters. Such areas are marked by low biomass, although sampling techniques indicate small organism diversity near the sea bottom is relatively high.

>> Rivers
Bodies of freshwater draining from elevated land toward sea level, rivers show considerable variation in water flow, underlying geology, altitude and (in the case of large river systems) latitude. While there can be a wide range of habitats within an individual river, some rivers are marked by continual change while others have been in continuous existence for millions of years.

>> Lakes
Lakes are mainly glacial in origin. As a rule, they are geologically short-lived, typically changing or disappearing within 100,000 years. As a result, lake ecosystems are often less complex - less evolved - than others.

>> Wetlands
Wetlands are characterized by permanent or seasonal shallow waters and large aquatic plants and are usually categorized into one of four major types: bogs, fens, marshes, and swamps. Bogs are peat-producing wetlands in most climates in which organic matter has accumulated over long periods. Fens, also peat-producing wetlands, are usually supplied by mineral-rich groundwater. Marshes and swamps are inundated areas with herbaceous emergent vegetation or forested wetlands where little or no peat production occurs.

3) Forest ecosystems

>> Boreal and temperate needleleaf forests
This forest type covers a larger area than any other. Species diversity is usually relatively low and dominated by a small number of tree species. However, diversity among organisms such as lichens and mosses is usually relatively high. Serving as major reservoirs of organic carbon, these forests are significant in the carbon cycle both above and below ground.

>> Temperate broadleaf and mixed forests
Structurally more complex than needleleaf forests with considerably higher species diversity, the temperate forests are generally representative of warmer latitudes. Aboveground biomass is lower than that of temperate needleleaf with below ground biomass being intermediate.

>> Tropical moist forests
The most diverse ecosystems on earth, tropical moist forests contain an estimated 60 per cent of all species. Diversity is extremely high with as many as 300 tree species per hectare in areas such as the western Amazon. Such forests account for nearly one third of the annual global terrestrial net primary production.

>> Tropical dry forests
Characteristic of tropical areas affected by seasonal drought, tropical dry forests are often composed of a deciduous forest canopy. Sparse trees and parkland occupy areas in transition from forested to non-forested landscapes and most tropical dry forests have lower species diversity than tropical moist forests.

>> Forest plantations
Forest plantations were usually intended for the production of timber and pulpwood and often consist of only one species. Not usually important as a habitat for native species, such systems can maintain nutrient capital and soil structure as well as serve to protect watersheds.

4) Mountain ecosystems

Mountains and highlands represent one quarter of the earth’s land surface. Mountain ecosystems are susceptible to change from such environmental influences as landslides, avalanches, lava flows and torrents and are slow to recover. Recently, climate change has led to the rapid melting of glaciers and icecaps in many mountain ranges. Mountain ecosystems are often highly biodiverse, with large numbers of endemic species.

5) Agricultural ecosystems

Agricultural land represents 38 per cent of earth's land area and is predominantly characterized by permanent pastures. Agricultural ecosystems do contribute to soil structure protection and air and water quality. However, wetland drainage, field consolidation and the creation of idle areas, among other agricultural practices, have greatly reduced wild biodiversity. Habitat and genetic diversity within agricultural ecosystems has also declined.

 

Online resources:

Major Biomes of the World
Contains detailed descriptions of Earth's major ecosystems

 

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