Download Biomes of North America

Biomes of North America
Definitions
1. Biome - a major climax plant formation or group of similar ecosystems.
2. Plant Formation - A general type of plant climax community with a high degree
of similarity, e.g. desert, deciduous forest.
3. Climax community - Community which is capable of replacing itself on a given
site. Results from a successional sequence of communities.
Distribution of biomes is influenced by climatic and geographic factors.
1. The distribution of heat from the sun and the resulting seasons is a major feature
affecting distribution of biomes.
2. The global patters of air circulation also has a major affect; see fig 33.2, pg 785.
3. Geologic factors, such as mountain ranges, interact with the above two factors in
controlling distribution of biomes.
Characteristics of North American Biomes
1. Tundra is characterized by a lack of trees. There are two types of tundra: arctic
and alpine. Both are characterized by a lack of trees.
o The arctic tundra is circumpolar above the arctic circle. There is a narrow
daily temperature range. Permafrost exists, even in the summer months.
Summers have long days of midnight sun. Plants have a very short
growing season.
o The alpine tundra exists at the highest levels of mountains above the
treeline. There is a wide range of daily temperatures, usually no
permafrost, and less variability in daylength (no midnight sun or days
without any sun).
o Example plants: Reindeer Moss (a lichen), blueberries, rhododendron and
dwarf willow "trees". Example animals: Reindeer, caribou, arctic wolves
and foxes, lemmings, shore birds.
2. Taiga (Boreal Forest/Northern Coniferous Forest) is also circumpolar. This biome
exists below the arctic tundra. Permafrost exists in this biome in about 65% of the
area. This area is cold with more precipitation, largely in the form of snow. Very
cold winters and hot summers with wide ranges of temperatures in those seasons.
o Example plants: Spruce, Fir, Pine, Tamarack, Poplar, Aspen
o Example animals: Moose, Black Bear, Lynx, Porcupine
3. Deciduous Forest occurs in the eastern U.S. out to about the Mississippi valley.
Region receives 75-250 cm of rainfall. Climate is temperate with distinct seasons:
warm summers and cold winters. This plant formation is characterized by leaves
falling in the fall of the year.
o Different plant associations characterize the different deciduous forests:
1. Beech-Maple
2. Maple-Basswood
4.
5.
6.
7.
3. Hemlock - Hardwoods
4. Oak - Chestnut* replaced by Hickory (Oak-Hickory)
5. Different associations result from water and temperature
tolerances.
o Stratification readily observed in deciduous forest:
/Understory/Saplings+shrubs/Forest Floor with spring flowers and ferns.
Grasslands (Prairie) occur west of the Mississippi and up to the foothills of the
Rockies Mountains. Rainfall is the limiting factor: 25-100 cm and temperature
range of 50°C in summer to -45°C in winter. Formation made of 3 associations.
o Tall Grass Prairie - 6 feet tall.
o Mixed Grass Prairie. Fig 33.13, pg 791
o Short Grass Prairie.
o Example animals: bison, pronghorn antelope, prairie dog
Deserts are associated with a lack of water, usually less than 10 cm. Extreme
daily variations in temperatures 15-35°C.
o Various life adaptations to desert conditions:
1. Well plants send down deep tap roots to get deep water.
2. Drought avoidance plants shed their leaves in times of stress.
3. Drought evasion plants evade drought conditions by being in the
seed condition during times of drought. Annual plants. Water
required to remove germination inhibitors.
4. Drought tolerance plants have water storage organs they can draw
upon thus tolerating the low water environment.
o Various structural adaptations to desert conditions:
1. thick cuticles
2. fewer stomates
3. water-storage tissues
4. leaves with leathery texture
o Example plants: sagebrush, creosote bush, cacti
o Example animals: kangaroo rat, lizards, snakes / activity at dawn+dusk
Mountain forests occur at the higher elevations in the Rockies and Sierra Nevada
Mountains. The forests are very similar to the taiga biome. Douglas fir and coastal
redwoods. High water availability due to fog and rainfall as it rises up the
mountain.
o Example plants: Douglas Fir, Western red Cedar, Ponderosa Pine
Tropical Rain Forests occur in Central America from the Yucatan Peninsula,
Belize, Guatemala, Nicaragua, Costa Rica and Panama. Rainfall 200-400 cm.
Species diversity is very high (# species/area). Temperatures range 25-32°C and
humidity seldom below 80%. No seasons based on temperature. Broadleaf
evergreen trees dominate with canopy contiguous. Soils not very fertile, all
nutrients bound up in organisms in forest. Soils so waterlogged trees have shallow
root system. Buttresses help. Little light reaches forest floor. Many epiphytes and
lianas.
8.
Wetlands are areas where water covers the soil, or is present either at or
near the surface of the soil all year or for varying periods of time during the year,
including during the growing season. Water saturation
(hydrology) largely determines how the soil develops and the
types of plant and animal communities living in and on the soil.
Wetlands may support both aquatic and terrestrial species. The
prolonged presence of water creates conditions that favor the
growth of specially adapted plants (hydrophytes) and promote
the development of characteristic wetland (hydric) soils.
Wetlands vary widely because of regional and local
differences in soils, topography, climate, hydrology, water
chemistry, vegetation, and other factors, including human
disturbance. Indeed, wetlands are found from the tundra to the tropics and on every
continent except Antarctica. Two general categories of wetlands are recognized: coastal
or tidal wetlands and inland or non-tidal wetlands.