Biomes

I. Biome Basics

A. Climate (temperature and precipitation) affect distribution of plant and animal species around the globe.

B. A biome is a large terrestrial region characterized by similar climate, soil, and plants and animals.

I. Biome Basics

C. Levels of OrganizationPopulation – all the members of one species in

an areaCommunity – all of the members of all of the

different types of species in a regionEcosystem – the biotic and abiotic (soil, water)

factors in a regionBiome – the ecosystem and climate in a region

I. Biome Basics

D. Maps may show specific boundaries of biomes, but it’s important to remember that really biomes may not be uniform at edges, and are often patchy within as well.

E. Climate is made of both temperature and precipitation, and both are important for determining the type of biome that is found in a region.

I. Biome Basics

F. There are three levels of precipitation in a region - lots of rain, a moderate amount of rain, or little rain.

G. There are also three general temperature levels – hot (never freezes), temperate (hot in summer, several months below freezing in winter) and cold (only 3 – 4 months above freezing).

I. Biome Basics

H. The combination of the three levels of precipitation with the three intensities of temperature lead to the nine major terrestrial biomes found on the planet.

Temperature Cold

Forest (taiga/boreal)

Temperate

Forest

Hot/Tropical

Forest

Cold

Grassland (Tundra)

Temperate

Grassland (Prairie)

Hot/Tropical

Grassland (Savannah)

Cold

Desert

Temperate

Desert

Hot

Desert

Precipitation

II. Deserts (no, not Desserts)

A. A desert is a biome with low precipitation, scattered unevenly throughout the year.

B. Usually deserts have hot days and cooler/cold nights. There is little vegetation or cloud cover to trap or store heat.

II. Deserts

C. Desert ecosystems are one of the most fragile types of ecosystem because it takes thousands of years to recover from a disturbance. Plant growth is very slow, there is low species diversity, and very slow nutrient cycling because of low soil bacterial levels.

II. Deserts

D. All deserts get very low precipitation, but there are three types based on average annual temperature

1. Hot/Tropical deserts 2. Temperate deserts 3. Cold deserts

E. About 1/5th of the world’s surface is a desert.

F. Hot/Tropical deserts have very few actual plants (none of the cacti/agave/succulents traditionally associated with deserts).

G. Hot deserts have hard, wind-blown surfaces with lots of rocks. The sand usually has a hard crust, which can be broken with grazing and SUV travel.

H. Dust storms are common, especially if the hard sand crust is broken by human or animal activity.

Sahara Desert

I. The Sahara desert is an example of a hot desert. Temperatures are above freezing year-round, consistently about 20 – 35 C.

J. Temperate deserts have high summertime temperatures, but have several months of freezing weather in the winter. Temperate deserts also tend to get a bit more rain than hot deserts.

Mojave Desert

K. Temperate deserts have the plants traditionally associated with deserts – cacti, agave, and other succulents.

L. The Mojave desert in California is an example of a temperate desert.

M. Cold deserts, such as the Gobi in Mongolia, only get above freezing for 6 or 7 months of the year. Antarctica is considered a cold desert (due to lack of rainfall).

Gobi Desert

III. Grasslands

A. Grasslands are found mostly in the interior of continents. The amount of precipitation in a grassland is greater than what is found in a desert, but not enough generally for trees to grow.

B. A tropical grassland is called a savanna. A savanna is always around 20 C – it never gets below freezing and has a pretty stable warm temperature.

C. Savannas cover about half of Africa, and large areas of Australia, South America, and India.

D. Most savanna grass grows in clumps interspersed with patches of bare ground.

F. Savannas have a wet and dry season, and while mostly grass do have some scattered trees such as acacia.

G. Savannas support lots of different species of hoofed herbivores (zebras, gazelles, giraffes etc) that migrate seasonally and spatially partition resources. The large amount of herbivore biomass also support big predators (cheetahs, lions).

H. Temperate grasslands are called prairies. Prairies are characterized by uneven rains (no rainy/dry seasons), hot summers, and freezing winters.

I. The above-ground portions of prairie grasses die back each year in the winter and decompose, producing thick, rich soils.

J. Prairies are found in the Midwest and in southern Canada (Alberta/Saskatchewan). In Ukraine and Russia temperate grasslands are known as steppes, and in Argentina and Uruguay they are know as pampas. In South Africa temperate grasslands are called veldts.

K. Fire is a very important natural part of prairie ecosystems. Grasses are well adapted to fire – the fire doesn’t burn the roots and grasses quickly grow back.

L. Prairies are very windy and have high evapotranspiration rates. The combination of winds and frequent fires hinders tree growth.

M. Most prairies worldwide are gone, because the soil is so good for agriculture.

N. Because of an abundance of grass but a lack of shelter from predators, temperate grassland animal populations are similar worldwide. Most are dominated by herbivorous plant-eating grazers called ungulates (hoofed mammals). Deer and buffalo are examples. Top predators include lynx, coyotes, and fox.

O. Cold grassland is called arctic tundra. During most of the year these treeless plains are bitterly cold, swept by frigid winds, and covered by ice and snow. Most precipitation falls as snow.

P. The biome is characterized by a thick spongy mat of low growing grasses, mosses, and tiny shrubs. Most growth happens during a 7 to 9 week summer.

Q. Because tundra is so cold, permafrost forms. Permafrost is soil that is frozen more than 2 consecutive years.

R. During the summer, permafrost keeps melted snow and ice from soaking into the ground, so tundra has many summer bogs and little lakes, which is the perfect environment for mosquitoes and black flies.

S. These flies feed large groups of migratory birds, and large herds of elk and caribou come for the summer to feed off tundra plants.

T. As global warming causes some of the permafrost to melt, large amounts of methane and carbon dioxide are released. Melting permafrost makes the ground marshy and causes soil substance as well.

Alaskan Tundra

IV. Forests

A. Areas of the world that receive the highest amounts of rainfall support forests (trees need a lot of water!).

B. Tropical rainforests are found in hot, tropical climates around the equator that never get below freezing.

C. Rainforest climates are characterized by hot humid weather, with very frequent (if not daily) rain.

IV. Forests

D. Tropical rainforests have very high NPP – although rainforests cover only about 2% of the planet, it is estimated they contain about half of the plant and animal species on Earth.

E. There are many specialized niches and distinct layers in the rainforest – allowing much speciation to occur.

IV. Forests

F. Temperate deciduous forests grow in areas that have great seasonal change – long warm summers with cold winters with several months of freezing temperatures. Precipitation is abundant and spread pretty evenly throughout the year.

G. Deciduous trees such as maple, oak, hickory, and beech survive the winters by dropping their leaves in the fall.

IV. Forests

H. Because these trees drop so many leaves each year, and decomposition is relatively slow, this ecosystem accumulates a thick layer of leaf litter. Leaf litter is nutrient rich and forms a thick, excellent layer of soil.

I. Leaf litter also insulates the forest floor, providing food and shelter for many bugs, as well as a rich area for decomposers and beneficial bacteria and fungi.

J. Fallen leaves also suppress weed and invasive plant growth and prevent soil erosion.

K. Leaf litter is critical to supporting plant growth, providing habitat for bugs and bacteria, and improving soil water retention/percolation and infiltration for this ecosystem.

IV. Forests

L. Evergreen coniferous forests, also called boreal forests or taiga, are found in areas with high rainfall but cold temperatures (around 60 N latitude).

M. These forests are found in major areas in northern Canada, Europe, and Asia. As you increase in altitude, they are also found on major mountain ranges.

N. Winters are long and cold, and often dry as well. Summers are short but the sun can shine for up to 19 hours a day in far northern latitudes.

O. Most boreal forests are dominated by a few species of coniferous (cone-bearing) evergreen trees, such as spruce, pine, or fir.

IV. Forests

P. Species diversity is low in this biome because few organisms can survive the intense cold and dry winters.

Q. Soil conditions are very different here – pine trees do lose needles, but they are waxy and acidic, and decompose very slowly. The soil is usually acidic and nutrient poor.

V. Chaparral

A. Chaparral biomes are found on coasts with maritime climates (moderate temperatures, long winter rainy season, prevailing winds coming from oceans).

B. Also called temperate shrubland, vegetation consists of dense shrubs or low growing trees with leathery leaves.

Chaparral near Malibu, CA

V. Chaparral

C. Fire is a normal part of this ecosystem - during the hot dry summers fires are sparked by thunderstorms and spread quickly. Many chaparral plants only sprout or drop their seeds after a fire.

D. Many humans live in this biome because the climate is so nice, but summer fires and the resulting spring mudslides are a constant worry.

VI. Mountains

A. Mountains or steep/high lands cover about 1/4th of the world’s surface. Going up in elevation changes biomes in a similar way to going up in latitude.

B. As you go up mountains, you will see first coniferous forest, then tundra. Tundra found in mountains is called alpine tundra, while tundra found at high latitudes is called arctic tundra.

VI. Mountains

C. Because of the steep slopes, mountain soil is very easily eroded.

D. Mountains play important roles in Earth’s climate (rain shadow effects) and snow and ice on their tops increases earth’s albedo (ability to reflect instead of absorb heat).

VI. Mountains

E. Mountains are very important in the water cycle as well – they store water as ice and snow in the winter, and release it to rivers in the spring and summer.

F. About 1.2 billion people live in mountain ranges or on their edges, and 4 billion people depend on mountain systems for some or all of their water.