ES 4 - Biomes

Topic 4 - Biomes

Biomes

-          Areas sharing similar climate, topographic and soil conditions, basic types of biological communities

-          Biome distribution determinant: precipitation & temperature (latitudinal bands)

Altitude depends on temp & precipitation

Vertical zonation (vegetation zones defined by altitude)

Tropical rainforest

-          Humid; support most complex & biologically rich biomes

-          Cloud forest: high mountains, fog & mist continually wet vegetation

-          Tropical rainforest: >200 cm or 80 inch / year; warm temp.

-          1/2 to 2/3 of all species dwells

-          Soil

o   Thin, acidic, nutrient poor

o   90% nutrients in organisms

o   Rapid decomposition & nutrient cycling

o   Soil cannot support continued cropping & rain erosion

o   Rapid deforestation due to immigration

Tropical Seasonal Forest

-          Many tropical regions are characterized by wet and dry seasons with hot temperatures year round.  These support tropical seasonal forests.

-          Brown and dormant much of the year but become green during the rainy season

-          Many of the plants are drought deciduous, i.e. they lose their leaves when it is dry.

-          Few of the tropical seasonal forests remain in their  natural state as humans use fire to clear the land in the dry season and settle there.

-          Soil is richer than rainforest, therefore more productive land for agriculture.

Tropical Savannas and Grasslands

•          Grasslands with sparse tree cover are called savannas. 

•          Rainfall amounts do not support forests

•          Dry season prone to fire

•          Plants with deep, long-lived roots and other adaptations to survive drought, heat, and fire

•          Many migratory grazers such as antelope, wildebeest, or bison

Desert

•          Characterized by low moisture levels (less than 30 cm per year) and precipitation that is infrequent    and unpredictable from year to year. 

•          Have wide daily and seasonal temperature fluctuations.

•          Plants exhibit water conservation characteristics such as water-storing stems, thick epidermis to reduce water loss, and salt tolerance.

•          Many plants bloom and set seed only after spring rains.

•          Animals also have adaptations.  Many are nocturnal and able to conserve water.

•          Deserts are vulnerable.

•          Slow growing vegetation is damaged by off road vehicles. It takes decades for desert soils to recover.

•          Overgrazing - Livestock are destroying the plants of the southern Sahara.   Without plants the land cannot retain what little rainfall there is and it becomes more barren.

Temperate Grasslands

-          Communities of grasses and seasonal herbaceous flowering plants

-          Few trees due to inadequate rainfall

-          Large daily and seasonal temperature fluctuations

-          Thick organic soils

-          Much converted to farmland.  Tallgrass prairies in the U.S. are now mostly farms.

-          Overgrazing is a threat because it kills the plants and permits erosion to occur.

Temperate Shrubland (Mediterranean)

-          Characterized by warm, dry summers and cool, moist winters

-          Evergreen shrubs, scrub oaks, pines

-          Fires are a major factor in plant succession.

-          Referred to as chaparral in California

-          High number of unique species

-          Human homes built in chaparral harm endangered wildlife and burn periodically.

-          Also found along Mediterranean coast, southwestern Australia, central Chile and South Africa

Temperate Deciduous Forest

-          Temperate regions support lush summer plant growth when water is plentiful.

-          Deciduous trees lose their leaves in winter as an adaptation to freezing temperatures.

-          Eastern half of U.S. was covered with broad leaf deciduous forest when European settlers arrived.  Much of that was harvested for timber.

-          Areas in U.S. have re-grown, although the dominant species are different

-          Areas in Siberia severely threatened now, may be region with greatest rate of deforestation in the world today

Boreal Forests

•          Boreal Forest - Northern Coniferous Forest

v  Broad band of mixed coniferous and deciduous trees between 50° and 60° N latitude

v  Dominated by pines, hemlock, spruce, cedar  and fir with some deciduous trees mixed in

•          Taiga - Northernmost edge of boreal forest

v  Extreme cold and short summers limit the growth rate of trees.  A tree that is 4 inches (10 cm) in diameter may be over 200 years old.

Marine Ecosystem

-          Oceans cover 3/4 of Earth’s surface.

-          Photosynthesis is carried out by algae or free floating plants (phytoplankton).  Greatest amount of photosynthesis near the coast where nutrients wash in.

-          Organisms die and fall to sea floor where the nutrients are used in deep ocean ecosystems. 

-          Upwelling currents circulate nutrients from the ocean floor back to the surface.

-          Vertical stratification is a key feature.

-          Light and temperature decrease with depth and deep ocean species often grow slowly.

-          Cold water holds more oxygen than warm water so productivity is often high in cold oceans such as the North Atlantic.

-          Ocean systems classified by depth and location to shore:

-          Benthic -  bottom

-          Pelagic - water column above the bottom

-          Area near shore is known as littoral zone

Surface to Hadal Zone Communities

-          Open ocean is a biological desert except for areas where nutrients are distributed by currents e.g. Sargasso Sea in the Atlantic

-          The deepest layer of the ocean (hadal zone) contains communities of tube worms, mussels, etc. supported by microbes that capture chemical energy from thermal vents on the ocean floor.  These organisms are adapted to extreme temperatures (350^oC) and intense pressure.

Coastal Zones

-          Communities vary with depth, light, temperature and nutrient concentration.

-          Coral Reefs - Aggregations of coral polyps that live symbiotically with algae.  Their calcium rich skeletons build up the reef.

-          Found in shallow water as light must penetrate for algal photosynthesis.

-          Threatened by trash, sewage, urban runoff, industrial waste, introduced pathogens and global warming.  Global warming causes coral bleaching in which corals expel their algal partners and then die.

-          One third of coral reefs have already been destroyed and 60% of the remaining reefs will probably be dead by 2030 ( 2006 UNESCO Conference).

-          Economically important due to tourism.

Mangrove

-          Mangroves are trees that grow in saltwater along tropical coastlines.

-          Help stabilize shoreline

-          Nurseries for fish, shrimp

-          Can be cut for timber

Tidal Environments

-          Estuaries - bays or semi-enclosed bodies of brackish water that form where rivers enter the ocean

-          Salt marshes - coastal wetlands flooded regularly or occasionally by seawater

-          Both are nutrient rich and biologically diverse.

-          2/3 of marine fish and shellfish rely on estuaries for spawning and development.

-          Threatened by sewage from coastal cities

Tide Pools

-          Depressions in a rocky shoreline that are flooded at high tide but retain some water at low tide

-          Wave action prevents most plant growth, but animals can be found in tidal pools.

-          Diverse specialized species adapted to the harsh conditions.

Barrier Islands

-          Narrow islands made of sand that form parallel to a coastline

-          Provide protection from storms, waves, tides

-          Since they are made of sand, they should not be built on, but they are.  Oftentimes, storms destroy the buildings.

-          About 20% in the US have been developed.

Freshwater Ecosystems

-          Lakes

-          Freshwater lakes have distinct vertical zones.

-          Epilimnion - warm upper layer

-          Hypolimnion - cold, deeper layer that does not mix

-          Thermocline - distinctive temperature transition zone that separates warm upper layer and deeper cold layer

-          Benthos - bottom

Wetlands

-          Land surface is saturated or covered with water at least part of the year.

-          Swamps - Wetlands with trees.

-          Marshes - Wetlands without trees.

-          Bogs and Fens - Waterlogged soils that tend to accumulate peat. Bogs fed by precipitation, while fens are fed from groundwater.  Nutrient poor with low productivity, but many unusual species.

-          Water usually shallow enough to allow full sunlight penetration, so the majority of wetlands have high productivity.

-          Trap and filter water, and store runoff.

-          Conservation is very important due to rich biodiversity.  Wetlands are the breeding grounds for birds. One of the greatest areas of concern for biologists.

-          May gradually convert to terrestrial communities through succession

Human Disturbance

-          By some estimates, humans preempt about 40% of net terrestrial primary productivity.

-          Conversion of habitat to human use is single largest cause of biodiversity loss.

-          Temperate deciduous forests are the most completely human-dominated biome.  Tundra and Arctic Deserts are the least disturbed.

-          About half of all original wetlands in the U.S. have been degraded over the past 250 years.

Tropical Savannahs & Grasslands

Deserts

Temperate Grasslands

Temperate Deciduous Forests

Temperate Rainforests

Boreal Forests

Tundra