Forests are one of the most important natural resources on this earth. Covering the earth like a green blanket these forests not only produce innumerable material goods, but also provide several environmental services which are essential for life.
It is estimated that forests covered l/4th of the earth’s entire land area in 1940 and l/5th in 1980. There are approximately 1.2 billion hectares of open wood lands and Savannah and nearly 2.5 billion hectares of closed forest.
Present-day forest biomes or biological communities that are dominated by trees and other woody vegetation (Spurr and Barnes), can be classified according to numerous characteristics, with seasonality being the most widely used. Distinct forest types also occur within each of these broad groups. There are three major types of forests, classed according to latitude:
1. Tropical Forests:
Tropical forests are characterised by the greatest diversity of species. They occur near the equator, within the area bounded by latitudes 23.5 degrees N and 23.5 degrees S. One of the major characteristics of tropical forests is their distinct seasonality: winter is absent, and only two seasons are present, i.e., rainy and dry. The length of daylight is 12 hours and varies little.
Temperature is on average 20-25°C and varies little throughout the year: the average temperatures of the three warmest and three coldest months do not differ by more than 5 degrees.
Precipitation is evenly distributed throughout the year, with annual rainfall exceeding 2000 mm.
Soil is nutrient-poor and acidic. Decomposition is rapid and soils are subject to heavy leaching.
Canopy in tropical forests is multilayered and continuous, allowing little light penetration.
Flora is highly diverse: one square kilometer may contain as many as 100 different tree species. Trees are 25-35 m tall, with buttressed trunks and shallow roots, mostly evergreen, with large dark green leaves. Plants such as orchids, bromeliads, vines (lianas), ferns, mosses, and palms are present in tropical forests.
Fauna include numerous birds, bats, small mammals, and insects. More than half of tropical forests have already been destroyed.
2. Temperate Forests:
Temperate forests occur in eastern North America, northeastern Asia, and western and central Europe. Well-defined seasons with a distinct winter characterise this forest biome. Moderate climate and a growing season of 140-200 days during 4-6 frost-free months distinguish temperate forests.
Temperature varies from – 30°C to 30°C.
Precipitation (75-150 cm) is distributed evenly throughout the year.
Soil is fertile, enriched with decaying litter.
Canopy is moderately dense and allows light to penetrate, resulting in well-developed and richly diversified understory vegetation and stratification of animals.
Flora is characterised by 3-4 tree species per square kilometer. Trees are distinguished by broad leaves that are lost annually and include such species as oak, hickory, beech, hemlock, maple, basswood, cottonwood, elm, willow, and spring-flowering herbs.
Fauna is represented by squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and black bear.
Only scattered remnants of original temperate forests remain.
3. Boreal Forests:
Boreal forests, or taiga, represent the largest terrestial biome. Occuring between 50 and 60 degrees north latitudes, boreal forests can be found in the broad belt of Eurasia and North America: two-thirds in Siberia with the rest in Scandinavia, Alaska, and Canada.
Seasons are divided into short, moist, and moderately warm summers and long, cold, and dry winters. The length of the growing season in boreal forests is 130 days.
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.
Flora consists mostly of cold-tolerant evergreen conifers with needle-like leaves, such as pine, fir, and spruce.
Fauna include woodpeckers, hawks, moose, bear, weasel, lynx, fox, wolf, deer, hares, chipmunks, shrews, and bats.