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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.