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A . Forest Biomes: Forests cover approximately 26%-29% of the Earth’s continental surface; 2/3 of the leaf area of land plants (for photosynthesis); contain 70 % of all the carbon present in living organisms on the Earth.
1. Common Characteristics of Forests• Dominated by trees• Have the highest
levels of animal & plant biodiversity found on land.
• Stratified plant levels: canopy/ understory/floor
2. Major Types of ForestsA. Tropical Zone Forests:
• Tropical Rain Forests - located directly on or near the equator. (Remember the tropical zone) Do not have a winter Two seasons may be present. (Wet and Dry) Temperature varies very little from month to month.
(20°C to 30°C/68°F to 86°F) Rainfall is usually evenly distributed throughout the
year. The soil tends to be nutrient-poor and acidic. Decomposition occurs very rapidly. Most trees are evergreens, 70 – 110 ft tall, have
very shallow roots and buttressed trunks.
•Seasonal rainforest: short dry period in a very wet tropical region
•Semi-evergreen forest: longer dry season (The upper tree story consists of
deciduous trees, while the lower story is still evergreen).
•Monsoon deciduous forest: the length of the dry season increases further as
rainfall decreases (all trees are deciduous).
•Major Threats to Tropical Forests:Unregulated loggingReplacement of forest for farmland. Usually plantations of a single species of tree or shrub (Palm trees in Indonesia; Cassava in Brazil; Bananas in Central America)Building of roads increases access and increases the amount of settlement by humans.
B. Temperate Zone Forests:• Temperate Deciduous Forests: Defined seasons with a distinct winter. Moderate climate and a growing season of 4-6 frost-free
months. Temperature varies from -30° C to 30° C (-22°F to 86°F). Precipitation (75-150 cm 30-60 in) is distributed evenly
throughout the year. Soil is fertile, enriched with decaying litter.
•Temperate Rainforests:mild winters, high annual precipitation (greater than 200 cm).Can be dominated by conifers (needle and cone bearing trees), broad leaved evergreens, broad-leaved deciduous, or a combination of all types.
• Chaparral (Mediterranean Forest)Precipitation is concentrated in winter, less than 100 cm per
year. Fire and drought prone.Combination of scrub trees, grasses and cacti.
• Boreal forest (taiga)Represent the largest terrestrial
biome.Occurring between 50 and 60
degrees north latitudes. Seasons are divided into short,
moist, and moderately warm summers and long, cold, and dry winters.
Temperatures are very low.Precipitation is primarily in the
form of snow, 40-100 cm annually. Soil is thin, nutrient-poor, and
acidic.Canopy permits low light
penetration, and as a result, understory is limited.
• Major Threats to Temperate Forests:Close to large areas of human population (North
America/Europe/Asia)Affected by acid rain from the burning of fossil fuels. Logging and clearing for farmland. Introduction of non-native species (Gypsy moth, Emerald
Ash Borer) Forest fires
• There are no forests biomes in the Polar Zone. The Arctic Circle is typically the latitudinal tree line for
Boreal forests. (There are no land masses near the Antarctic Circle and there are no trees on Antarctica)
Altitudinal tree lines vary depending on the latitude. Lower at higher latitudes and higher at lower latitudes.