Dr. Largen

• Biomes
• terrestrial climax communities with wide distribution
• with similar ecosystem structure, niches, habitats, types of organisms
• defined largely by regional variations in climate
• strong relationship between climate and life suggests that
• if we know climate of an area
• we can predict what biome will be found there
• approximate biomass
• approximate productivity
• dominant types of organisms
• distribution of biomes results from interaction of
• physical features of the earth
• two key physical factors
• amount of solar heat
• global atmospheric circulation
• together these factors dictate local climate
• two most important climatic factors are
• precipitation
• temperature

• Biomes
• terrestrial climax communities with wide geographic distribution
• concept is useful for describing in broad terms
• general structure of the ecosystem
• types of niches present
• of same type from different areas will exhibit variations in exact species present
• affected by two nonbiological factors
• temperature
• precipitation

• major biomes of the world
• desert
• grassland
• savanna
• Mediterranean shrublands (chaparral)
• tropical dry forest
• tropical rainforest
• temperate deciduous forest
• taiga or boreal forest
• tundra

• deserts
• dry
• precipitation is <25 cm/yr
• time and form of precipitation varies among deserts
• can be cool/cold during parts of year
• temperature can vary greatly during 24-hour period
• vegetation is sparse
• survival depends on water conservation
• organisms have evolved adaptations to help them survive
• restricting activity to times of year when water is present
• avoiding high temperatures by living in deep, cool, & moist (sometimes) burrows
• emerging only at night when temperatures are lower, especially if active year round
• drinking large quantities of water when it is available (camels) & then survive long, dry periods
• world’s great deserts are located in interiors of continents
• Sahara in Africa
• Gobi in Asia
• Great Sandy Desert in Australia
• Grasslands
• also known as temperate grasslands, prairies, steppes
• widely distributed throughout temperate regions
• ~ halfway between equator & poles
• precipitation is ~ 25cm -75cm per year
• tend to be windy with hot summers, cold to mild winters
• grasses make up 60%-90% of vegetation
• trees rare except along water courses due to need for greater amount of water
• in many grasslands, fire is important force in
• preventing invasion of trees
• releasing nutrients from dead plants into soil
• contributing to high fertility of grassland soils
• once covered much of interior North America, widespread in Eurasia & South America
• often highly productive when converted to agricultural use
• many agricultural lands of US & Canada were originally occupied by grasslands (prairies)
• roots of perennial grasses characteristically penetrate far into soil
• grassland soils, therefore, tend to be deep and fertile
• temperate grasslands often populated by herds of grazing mammals
• in North America, huge herds of bison and pronghorns once inhabited prairies
• herds are almost all gone now
• most of prairies have been converted into richest agricultural region on earth
• Savanna
• extensive grasslands spotted with occasional trees or patches of trees
• precipitation is 50cm-150cm /yr
• occurs seasonally
• period of heavy rainfall followed by prolonged drought
• results in seasonally structured ecosystem
• predominant plants are grasses
• with widely spaced, drought resistant trees
• many animals and plants are active only during rainy season
• fire is common
• trees tend to be fire-resistant
• increasingly being converted to agricultural use
• causing inhabitants of savannas to struggle to survive
• Mediterranean shrublands
• also known as chaparral.
• precipitation is 40-100 cm/yr.
• wet, cool winters and hot, dry summers.
• typical of Mediterranean coast and coastal southern California.
• vegetation dominated by woody shrubs adapted to hot, dry summers.
• fire is a common feature.

• Tropical dry forest
• precipitation range is 50-200 cm/yr
• many exhibit monsoon climate
• several months of heavy rainfall followed by dry periods
• ranging from a few to 8 months in length.
• due to highly seasonal rainfall
• plants must be drought resistant
• Tropical rainforest
• precipitation is >200cm/yr
• temperatures are warm and relatively constant, no frost
• located near the equator
• South America, Africa, southeast Asia

• most diverse ecosystems on earth
• contain ~ half of all species of terrestrial plants and animals
• in 1sq mi of tropical forest in Rondonia, Brazil there are 1200 species of butterflies
• 2X number found in U.S. & Canada combined
• communities are diverse
• each kind of organism is often represented in a given area by only a few individuals
• typical to find that individuals of same species are separated by 1km or more
• most nutrients tied up in biomass, not the soil
• they don’t make good farmland
• are being destroyed
• under intense pressure from logging and agriculture
• even though they don’t make good farmland
• many species in rainforests have never been seen by humans
• during our lifetime, a quarter of world’s species will disappear with rainforests
• temperate deciduous forests
• precipitation is 75cm-100cm/yr
• evenly distributed
• warm summers, mild winters
• plants grow actively for ~1/2 year
• northeastern US, eastern Canada, Eurasia
• often populated by deer, beaver, bear, raccoon
• generally have lower number of species but a higher number of individuals per species
• trees are major producers
• Taiga
• also known as northern coniferous forest, or boreal forest
• precipitation is 25cm-100cm per year
• climate is humid due to low evaporation resulting from generally low temperatures
• winters are long and cold
• soil freezes in winter
• has very short growing season for farming so few people live there
• most common trees are conifers such as spruce, fir, larch, etc/
• needle-shaped leaves limit moisture loss
• pyramid shape accommodates snow
• one of largest ecosystems on earth
• located in a ring that extends across vast areas of Asia and North America
• populated by many types of large mammals and carnivores such as moose, elk, deer, wolves, bear, lynx
• has been used for fur trapping and lumber production
• tundra
• located north of taiga and south of polar ice
• precipitation is <25cm/yr
• subsurface soil layer is permanently frozen
• known as permafrost
• doesn’t allow water to sink into soil
• resulting in waterlooged soil
• boggy
• extremely cold and windy
• spring and summer temperatures usually less than 10°C (50°F)
• enormous ecosystem that covers 1/5^th of earth’s land area
• no trees
• plants are usually less than 20cm (8 in) tall
• populated by large grazing mammals such as musk-oxen, caribou, reindeer and carnivores such as wolves, foxes, lynx