Tropical forest • They occur near the equator (between latitudes . ⁰ at north and . ⁰ at south). • The major characteristic of tropical forests is their distinct seasons.
Only two seasons are present (rainy and dry). Winter is absent. The length of daylight is about hours and varies little. • The average annual temperature ranges between ° C and °C.
• Precipitation is evenly distributed throughout the year with annual rainfall exceeding mm. • Soil is nutrient-poor and acidic. Decomposition is rapid and soils are subject to heavy leaching. • Tree canopy is multilayered and continuous, allowing little light penetration.
• Flora is highly diverse: one square kilometer may contain as many as different tree species. Trees are - m tall, with buttressed trunks and shallow roots, mostly evergreen, with large dark green leaves. Common vegetation are orchids, bromeliads, vines (lianas), ferns, mosses, and palms. • They are characterized by the greatest diversity of fauna which includes birds, bats, small mammals, and insects.
More than half of earth’s tropical forests have already been destroyed. Fig. . Forest biome Temperate forest • These forests occur in eastern North America, northeastern Asia and western and central Europe.
• Have well-defined seasons with a distinct winter. Moderate climate and a growing season of - days during - frost- free months distinguish temperate forests. Historically biomes are known to move as climate changes. A classic example is the Sahara Desert, which years ago was supposed to be a lush landscape with river flowing through it.
Accordingly, appropriate fauna like Hippos, Giraffes, Crocodiles lived amid abundant trees. Over course of time the climate dried out. It has now become the planets largest desert. The animals have migrated out to adjacent regions with more favourable conditions.
(Source: National Geography) XII Std Biology-Zoology Chapter- XII Std Biology-Zoology Chapter- Organisms and Populations • Annual temperature varies from - ° C to °C. • Precipitation ( - mm) 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 under storey vegetation and stratification of animals.
• Flora is characterized by - tree species per km . Trees have broad leaves that are lost annually such as oak, hickory, beech, hemlock, maple, basswood, cottonwood, elm, willow, and spring-flowering herbs. • Fauna consists of squirrels, rabbits, skunks, birds, deer, mountain lion, bobcat, timber wolf, fox, and black bear. Only scattered remnants of original temperate forests remain today.