Biome Notes
1. Tropical Rain Forests – this biome contains at least half the species of terrestrial ecosystems, if not more. Water and temperature are not the limiting factors in tropical rain forests. A very diverse group of plants grow here. The growing season is year round. There is a group of plants that survive by living on the branches of other plants called epiphytes. Some epiphytes send their roots to the ground so they can get more moisture and nutrients. These plants are called hemi-epiphytes.
Two thirds (2/3) of the soil is deficient in phosphorus, potassium, calcium, magnesium and other nutrients. If you remove the vegetation, the soil cannot be farmed except for an extremely short amount of time. The soil contains enough aluminum to be toxic to plants. Most of the roots are in the upper thin layers and as soon as something decomposes, the vegetation takes up the nutrients. All the nutrients are tied up within the vegetation.
The agricultural process carried out here is slash and burn …. Small groups of people go into the forest, clear a small area, plant their crops for 2-3 years, then the nutrients are totally gone so the people move to another location and repeat the process. Once they move from a location, massive erosion may take place, which removes the topsoil that is present. Under this situation, it may take hundreds to millions of years for the topsoil to be formed on the site again by natural processes.
2. Savanna – area with 90-150cm of precipitation per year. Sometimes there are prolonged periods of drought. This is a transition zone between the tropical rain forest and deserts. Animals associated with this biome are large herbivore (grazing…plant eaters) … zebra, wildebeast, and gazelles. Predators are large … lions, cheetahs. The soil is nutrient deficient (poor) and has aluminum that is toxic to larger plant forms like trees.
3. Desert – has less than 25 cm of precipitation per year. The limiting factor here for plants growing and animals surviving is water. Deserts are at 30 degrees North and South latitude. They have vast temperature changes between day and night. The temperature that the soil gains during the day is rapidly lost because of clear nights. The heat is re-radiated back into the atmosphere. Annual plants are abundant only when there is precipitation. After a rainfall these plants germinate rapidly, produce their seeds and disperse them rapidly. The trees and shrubs that do grow here have real deep taproots that extend all the way down to the water table. Plants usually open their stomata (areas where water is lost and gases are exchanged with the atmosphere) at night instead of during the day to reduce evaporation.
Animals spend their days in burrows and feed in the early morning, late afternoon and at night. Camels store water, but cannot survive without man to provide them with the water (by digging deep under the sand) across the distance of a large desert like the Sahara. A unique feature of the camel is that their nose has a tremendous amount of folds in it that collect condensation (as they exhale) and reabsorbs the moisture. Some organisms shut their metabolism down when it gets too hot. This is called estivation (equivalent to hibernation except it is done in hot climates). Many rodents of this biome do this.
4. Temperate Grasslands (Prairies) – highly productive soils that are often converted to agricultural land. They are different from Savanna’s because they have long cold winters (Great Plains of the U.S.) They have large grazing animals like American Bison and Antelope. Grasslands are naturally maintained by grazing animals and periodic fires. Fires are not always harmful to ecosystems. In grasslands, fires cause nutrients to be released from burned plants into the soil and this is beneficial to wildlife.
5. Temperate Deciduous Forests – areas have relatively cold winters, warm summers and adequate precipitation. Places where they occur:
- Southeastern United States (Appalachians and the Smokies)
- Eastern United States
- Canada
- Large regions of Eurasia (Germany)
There is 75-250 cm of precipitation per year. Around Chattanooga, there is an annual rainfall of 132 cm (52 inches). Where you find rainfall below 75 cm is where you get into the grasslands. Where it cools off too much to have temperate deciduous forests you find coniferous forests.
The forest floor has a vast amount of wildflowers. They have to grow really fast and produce their seed before the trees get their leaves and block the sun out of the forest floor. In the springtime, the wildflowers produce magnificent colors.
Scientists think the Chaparral in California was temperate deciduous forest in the past and precipitation patterns changed (decreased) through time.
The climax species of trees in the temperate deciduous forests are oaks and hickories. Animals found here include raccoons, white-tailed deer, wild turkey, black bears, skunks and a variety of reptiles to mention a few.
6. Taiga (Northern Coniferous Forests) – The trees here are spruce, hemlock and fir. This area is characteristic of northern North America (Canada around Montreal). There are long cold winters with short days and little moisture. Summer days are long. You can find marshes, lakes and ponds with willow and birch trees around them. Trees in this biome occur in real tight stands of only a few species.
The unique tree is the nitrogen fixing alder …. capable of converting atmospheric nitrogen into a form of nitrogen other plants can use. These plants are legumes. Alders can colonize an bare soil that is not suitable for other plants. Large animals live here….elk, moose, deer (herbivores)…..predators are bear, lynx, wolves, wolverines, bobcats (carnivores). South of the taiga you would find grasslands or temperate deciduous forests depending on the amount of annual precipitation. To the north you will find the tundra.
7. Tundra – lies between the coniferous forest and permanent ice. Open and boggy areas characterize it. It’s a large area that basically looks the same throughout. Trees are small. Species of willows grow here. The adaptation it has, because you do not have much precipitation and you have cool temperatures the majority of the year, it grows real flat to the surface of the earth. Trees line the streams. You will find grasses and sages scattered throughout the area. You also find lichens (fungus and bacteria or algae in a symbiotic relationship) which caribou feed upon. The annual precipitation is less than 25 cm. Water is frozen and unavailable most of the year. About one foot below the surface of the ground you will find a frozen layer called the permafrost. Massive amounts of waterfowl migrate to the tundra in spring to breed. Large herbivores found in this biome include musk oxen, caribou, and reindeer. Carnivores in this biome include wolves, lynx, and arctic fox. Rodents you find here are lemmings (rise and crash with population growth curves). When the lemmings become too dense they often run into the oceans, off bluffs and kill themselves. The Snowy Owl feeds upon the lemming as the other carnivores do. The lemming is often a primary food source here.