FOREST BIOMES

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.