Temperate deserts are in the midlatitudes, meaning they experience seasonal temperature variations.

Many temperate desert plants are succulents, meaning they have thickened, fleshy parts for storing water. Succulent plants also grow

very slowly. Saguaro cacti, Carnegiea giganteaSonoran Desert, Arizona, USA. Saguaros will grow 75 years before sprouting an arm.

Polar deserts are located near the poles in areas where harsh winds carry away any moisture. The little precipitation that falls takes the form of ice or snow.

Most of the interior of Antarctica is considered a polar desert.

250 year-old mummified seal carcass. McMurdo Dry Valley, Antarctica.

Grasslands tend to have moderate levels of net primary productivity. Significant seasonal

changes in temperature or precipitation.

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Tropical grasslands, also called savannas, are located near the equator. Transition areas between tropical forests and subtropical deserts.

Savannas have consistent temperatures. The seasons are instead based on precipitation.

Serengeti

National

Park,

Tanzania,

Africa.

Temperate grasslands, called prairies in North America, are farther away from the equator and experience seasonal temperature shifts.

Badlands National

Park, South

Dakota, USA.

Prairie plants have adapted to the cold winter and frequent absence of precipitation by developing root systems that can be several feet deep. This enables prairie plants to recover

quickly from drought or wildfire, while the slow growing trees cannot.

Compass Plant,

Silphium

laciniatum

Photos from

National

Geographic

Missouri

Goldenrod,

Solidago

missouriensis

Polar grasslands, also called tundra, are below freezing most of the year. Limiting factor is

temperature.

Due to the short growing season, only the top layer of soil actually thaws and can support plant life. The rest is permanently

frozen soil, called permafrost.

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Spitsbergen, Norway. Photo by John Shaw.

There is a growing season in the tundra, but it is only a few months long. Only small plants and lichens grow there.

8Ilulissat, Greenland. Photo from mvfram.blogspot.pt

Forest biomes have the most consistent precipitation and are dominated by hardwood trees. High net primary

productivity.

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The emergent layer consists of the tallest trees that reach above all others.

The canopy is the outermost layer of leaves within a group of trees. Most of the animal life is found here.

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The understory consists of vegetation immediately below the canopy.

The shrub layer consists of shorter plants that utilize the 5% of sunlight that passes through the canopy. Mostly small shrubs and seedlings.

The forest floor is mostly home to decomposers due to the lack of sunlight.

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Phallus indusiatus, Veiled Lady Fungus

Tropical rainforests receive the greatest amount of rainfall of any other biome and are consistently warm. Few abiotic limiting

factors for plant growth.

Nutrient cycles occur very rapidly in rainforests due to the rapid growth of both producers and decomposers. Increased leaching of

nutrients in soil due to rainfall.

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Iguaçu Falls, border of Brazil, Argentina, and Bolivia.

Temperate rainforests receive a comparable amount of precipitation to tropical ones, but are in higher latitudes. One example is the Northern

Pacific coast of the United States and Canada, which has two geographic advantages: Located on the windward side of the

Olympic mountain range.

Receives constant moisture from the wind currents off the Pacific ocean.

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Issaquah, Washington, United States

Deciduous forests experience a winter that reaches below freezing oran intense dry season that requires the trees to drop their leaves. Like rainforests, these mostly contain broadleaf trees which have more

surface area for absorbing sunlight.

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White oak, Quercus alba.

An example of a broadleaf tree.

Norway spruce, Picea abies.

An example of a needle leaf tree.

The leaves of broadleaf trees lose moisture rapidly through transpiration, so they will shed their leaves cold winters or dry seasons.

15Dandenong Ranges, Australia.

Boreal forests, also called taiga, have coniferous trees, which are much more well-adapted to the long, cold, dry winters. Needle-shaped leaves have a waxy

coating that retains moisture in the winter.

The cone shape of the trees allows accumulated snow to slide to the ground.

Fairbanks, Alaska, United States.

Mediterraneanbiomes are forests and scrublands with highly seasonal precipitation. Nearly all

precipitation occurs in the winter months.

Summers are completely dry, leading to wildfires.

17Chaparral – Payson, Arizona, USA

Biomes are dynamic – they change as the Earth changes. This process is called succession.

Ecosystem succession takes two forms, depending on the starting point.

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Primary succession occurs when a new ecosystem develops where there was none before.

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Early stages: Weathering breaks down rock. Erosion by wind and

water. Dissolving of rock by

acidic rainfall. Biological breakdown by

lichens and mosses.

Lichens and mosses are considered pioneer speciesbecause they are the first organisms to populate an area in the early stages of succession.

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Middle stages: Intermediate species like grasses and other wildflowers dominate the area. Seeds carried in by wind

and animals.

Grow quickly, short lifespans.

Niche generalists.

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Late Stages: Climax species populate and dominate the ecosystem. Tend to be niche

specialists.

Grow slowly, long lifespans.

Continue to dominate the ecosystem until another disruption occurs.

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Secondary succession occurs following the disruption of an existing ecosystem. Fire, flood, volcanic eruption, clear-cutting, etc.

Similar to primary succession, but without the need to create soil. Climax community is reached much faster than primary succession.

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The ecosystems around Mount St. Helens fully revegetated within 30 years of the eruption.

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