Introduction to Biomes

What are the characteristics of the terrestrial biomes?

What are climate graphs used for?

If we know the general temperature range and precipitation level of an area, what can we predict in the absence of human disturbance?

What is vertical zonation?

Cloud forests occur in high mountains where fog and mist keep vegetation wet all the time.

What type of soil do tropical moist forests tend to have?

Tropical rainforests occur where rainfall is abundant - more than 200 cm (80 in) per year - and temperatures are warm to hot year-round.

It has been estimated that one-half to two-thirds of all species of terrestrial plants and insects live in tropical forests.

Tropical seasonal forests are often called Dry Tropical Forests because they are dry much of the year.

Seasonal forests are often open woodlands that grade into savannas.

What is the difference between grasslands and savannas?

Tropical savannas and grasslands have a rainy season, but generally the rains are less abundant or less dependable than in a forest.

During dry seasons, fires can sweep across grassland, killing off young trees and keeping the landscape open.

Grazing pressure from domestic livestock is an important threat to both the plants and animals of tropical grasslands and savannas.

Deserts occur where precipitation is rare and unpredictable, usually with less than 30 cm of rain per year.

Desert vegetation is sparse, but it can be surprisingly diverse and most desert plants and animals are highly adapted to survive long droughts and extreme heat.

Desert is more vulnerable because sparse, slow-growing vegetation is quickly damaged by off-road vehicles.

Desert soils recover slowly.

Desert is also vulnerable to overgrazing.

What is a major environmental problem in Africa's Sahel region?

In tropical latitudes, temperate (mid-latitude) grasslands occur where there is enough rain to support abundant grass but not enough for forests.

Most grassland is a complex, diverse mix of grasses and flowering herbaceous plants, generally known as forbs.

Deep roots help plants in temperate grasslands and savannas survive drought, fire, and extreme heat and cold.

Deep roots, together with an annual winter accumulation of dead leaves on the surface, produce thick, organic-rich soils in temperate grasslands.

Evergreen shrubs with small, leathery, sclerophyllous (hard, waxy) leaves form dense thickets in temperate shrublands called chaparral.

Scrub oaks, drought-resistant pines, or other small trees often cluster in sheltered valleys in temperate shrublands.

Periodic fires burn fiercely in this fuel-rich plant assemblage and are a major factor in plant succession in temperate shrublands.

In California, the landscape of temperate shrublands is called chaparral, Spanish for “thicket”.

Temperate shrublands are inhabited by drought-tolerant animals such as jackrabbits, kangaroo rats, mule deer, chipmunks, lizards, and many bird species.

Very similar landscapes to temperate shrublands are found along the Mediterranean coast as well as southwestern Australia, central Chile, and South Africa.

Broadleaf forests occur throughout the world where rainfall is plentiful.

In mid latitudes, these forests are deciduous and lose their leaves in winter.

At lower latitudes, broadleaf forests may be evergreen or drought-deciduous.

Coniferous forests grow in a wide range of temperature and moisture conditions.

Coniferous forests often occur where moisture is limited, in cold climates, moisture is unavailable (frozen) in winter, hot climates may have seasonal drought, sandy soils hold little moisture, and they are often occupied by conifers.

Coniferous forests provide most wood products in North America.

Coniferous forests of the Pacific coast grow in extremely wet conditions. The wettest coastal forests are known as temperate rainforests, a cool, rainy forest often enshrouded in fog.

The Coniferous Forest is the largest terrestrial biome, found in the northern parts of Europe, North America and Asia.

Boreal forests, or Northern Forests, lie between about 50° and 60° north.

Mountainous areas at lower latitudes may also have many characteristics and species of the boreal forest.

Dominant trees in boreal forests are pines, hemlocks, spruce, cedar, and fir.

Some deciduous trees are also present in boreal forests, such as maples, birch, aspen, and alder.

These forests are slow-growing because of the cold temperatures and a short frost-free growing season.

The extreme, ragged edge of the boreal forest, where forest gradually gives way to open tundra, is known by its Russian name, Taiga.

Tundra is a treeless landscape that occurs at high latitudes or on mountaintops, has a growing season of only two or three months, and it may have frost any month of the year.

Tundra is a variant of grasslands because it has no trees.

Tundra is a very cold desert because water is unavailable (frozen) most of the year.

Arctic Tundra is an expansive biome that has low productivity because it has a short growing season.

During midsummer, 24-hour sunshine supports a burst of plant growth and an explosion of insect life in arctic tundra.

Alpine Tundra occurs on a near mountain top and has environmental conditions and vegetation similar to arctic tundra. These areas have a short, intense growing season.

Many alpine tundra plants also have deep pigmentation and leathery leaves to protect against the strong ultraviolet light in the thin mountain atmosphere.

Coral reefs and estuaries are among the world's most productive and diverse ecosystems.

Vertical stratification is a key feature of aquatic ecosystems, mainly because light decreases rapidly with depth, and communities below the photic zone (light zone, often reaching about 20 m deep) must rely on energy sources other than photosynthesis to persist.

Temperature also decreases with depth in aquatic ecosystems.

Deep ocean species often grow slowly in part because metabolism is reduced in cold conditions, affecting the amount of oxygen and other elements that can be absorbed in water.

Phytoplankton are microscopic floating algae that carry on photosynthesis and zooplanktons are small, weakly swimming animals that feed on phytoplankton.

Benthic communities occur on the bottom of the ocean, while pelagic zone communities are found in the water column.

The epipelagic zone, where photosynthetic organisms are found, is the uppermost layer of the pelagic zone.

Below the epipelagic zone are the mesopelagic (meso = medium), and bathypelagic (bathos = deep) zones.

The deepest layers of the ocean are the Abyssal Zone (to 4,000 m) and Hadal Zone (deeper than 6,000 m).

Littoral Zones are shorelines, and the Intertidal Zone is the area exposed by low tides.

Coral Reefs are among the best-known marine ecosystems because of their extraordinary biological productivity and their diverse and beautiful organisms.

Mangroves are trees that grow in salt water and occur along calm, shallow, tropical coastlines around the world.

Mangrove forests or swamps help stabilize shorelines and they are also critical nurseries for fish, shrimp, and other commercial species.

Estuaries are bays where rivers empty into the sea, mixing fresh water with salt water.

Salt marshes are shallow wetlands flooded regularly or occasionally with seawater and occur on shallow coastlines, including estuaries.

Tide Pools are depressions in a rocky shoreline that are flooded at high tide but retain some water at low tide.

These areas remain rocky where wave action prevents most plant growth or sediment (mud) accumulation in tide pools.

Barrier Islands are low, narrow, sandy islands that form to parallel to a coastline, occurring where the continental shelf is shallow and rivers or coastal currents provide a steady source of sediments.

Freshwater ecosystems vary according to depth and light penetration, which control size and types of vegetation.

Freshwater ecosystems are often small but they are disproportionately important in biodiversity.

Like marine environments, freshwater lakes have distinct vertical zones.

The Benthos is the bottom of a freshwater lake, occupied by a variety of snails, burrowing worms, fish and other organisms.

The Epilimnion is a warmer upper layer that is mixed by wind and warmed by the sun, while the Hypolimnion is a colder, deeper layer that is not mixed.

The Thermocline is the sharp temperature boundary between the epilimnion and hypolimnion.

The Mesolimnion is below the thermocline, where the water is much colder.

Wetlands are shallow ecosystems in which the land surface is saturated or submerged at least part of the year.

Wetlands have vegetation that is adapted to grow under saturated conditions.

Swamps are also known as wooded wetlands, while marshes are wetlands without trees.

Bogs are areas of saturated ground, and usually the ground is composed of deep layers of accumulated, undecayed vegetation known as peat.

Fens are similar to bogs except that they are mainly fed by groundwater, so that they have mineral-rich water and specially adapted plant species.

Humans have become dominant organisms over most of the earth, damaging or disturbing more than half of the world's terrestrial ecosystems to some extent.

Humans preempt about 40 percent of the net terrestrial primary productivity of the biosphere either by consuming it directly, by interfering with its production or use, or by altering the species composition or physical processes of human-dominated ecosystems.

Conversion of natural habitat to human uses is the largest single cause of biodiversity losses.

The greatest impacts of human disturbance have been in Europe, parts of Asia, North and Central America, and islands such as Madagascar, New Zealand, Java, Sumatra, and those in the Caribbean.

Temperate broadleaf forests are the most human-dominated biome, with 81.9% human dominated.

Tundra and arctic desert have the lowest human-dominated biome, at 0.3%.