Input Template for Content Writers (e-Text) 1. Details of Module and its Structure Module Detail Subject Name Botany Paper Name <Ecology> Module Name/Title <Biogeography> Module Id < Major Terrestrial Biomes > Pre-requisites <Basic knowledge of ecology> Objectives <Characteristics and classification of major Terrestrial Biomes> Keywords <Ecosystem>, <Biomes>, <Forest> Structure of Module / Syllabus of a module (Define Topic / Sub-topic of module ) Terrestrial Ecosystem <Tropical Forest>,<Tropical Savanna>,<Temperate Grassland> <Dessert>,<Temperate Shrubland>,<Temperate Forest>,< Conifer forrest>,< Tundra> <Topic name2> <Sub-topic Name2.1>, <Sub-topic Name2.2> 2 2. 2. Development Team Role Name Affiliation National Coordinator <National Coordinator Name> Subject Coordinator < Prof. Sujata Bhargava > Paper Coordinator < N.S.R. Krishnayya > Content Writer/Author (CW) < Swati Diwakar > Content Reviewer (CR) <CR Name> Language Editor (LE) <LE Name> TABLE OF CONTENTS Introduction 1. Tropical Forests (i) Tropical Rain Forest (ii) Tropical Dry Forest 2. Tropical Savanna 3. Temperate Grassland 4. Dessert 5. Temperate Shrubland 6. Temperate Forest 7. Conifer forrest 8. Tundra 9. References 3 e-Text Major Terrestrial Biomes INTRODUCTION Terrestrial ecosystems can be grouped into broad categories called biomes. Ecologists F. E Clements and V. E. Shelford in 1939 coined the term Biomes for regions with similar distribution of plant, animals and environmental conditions. Biome is one of the largest recognizable ecological units on Earth. There are eight major terrestrial biomes: i. Tropical forest ii. Tropical Savanna iii. Temperate grasslands iv. Desert v. Chaparral (shrublands) vi. Temperate forest vii. Conifer forest (Taiga or boreal forest) and viii. Tundra Figure 1: Biomes on Earth FIGURE 1 The distribution of the biomes types is influenced by the mean annual temperature and mean annual precipitation (Figure 1 and 2). Boundaries between the biome are broad and merge into each other. These categories reflect the relative contribution of three general plant life-forms: Trees, Shrubs and Grasses. These plant forms represent adaptations under different environmental conditions. Within the broad classes of forest ecosystems, leaves are classified into two categories based upon their existence on the trees: Deciduous (leaves that live for only a single growing season or year and Evergreen (leaves that live beyond a year). Similarly, Evergreen leaf types are also classified into two categories: broadleaf type characteristic of tropical rain forests and needle-leaf type characteristic of environment with short growing seasons. 4 Figure 2: Distribution of World’s major Terrestrial Biomes 1. Tropical forests (i) Tropical Rain Forests Ecosystems characteristic of warm, wet climates with no distinct seasonality are dominated by broadleaf evergreen trees and are called tropical rain forest (Figure 3). The tropical rainforests of the world are famous for the greatest number of plants and animals than any other biome on Earth. Tropical forests characterize the equatorial zone. These are found in tropical America, west Africa, Congo basin of Africa and in the Indo-Malayan region of Asia. Climate: Tropical rain forests are restricted to warm temperatures and high rainfall areas in equator between 10° North and South. Average temperatures range from 25-27° C and it varies little from month to month. Annual rainfall ranges from about 2000-4000 mm. Vegetation: Most plants growing in tropical rainforests are woody-stemmed trees and climbers. The tropical rainforest is a broad-leaved evergreen forest with a complex, multi-storeyed structure. The vertical 5 structure of the forest is divided into five general layers: emergent trees, high upper canopy, low tree stratum, shrub understory and a ground layer of herbs and ferns. Conspicuous in the rain forest are the lianas or climbing vines, epiphytes growing up in trees and stranglers growing downward from the canopy to the ground. Many large trees develop buttresses for support. Tropical rain forest supports high levels of primary productivity. Figure 3: Tropical Rain Forest Animal life: Tropical rain forest harbours a great diversity of plants and animals. It covers only 6% of the land surface but accounts for >50 % of all known plants and animal species. The richest area is the lowland tropical forest of peninsular Malaysia containing around 7900 species. Soil: Rainforest soil are nutrient poor, acidic, thin and low in organic matter as the heavy rains leach nutrients from rain forests soils and rapid decomposition in the warm, moist rain forest climate keeps the soil organic matter low. Soils are oxisols characterised by advanced weathering and so have high clay content, deficient in calcium and phosphorus. Tropical soils tend to be bright red in both A and B horizon due to oxides of iron along with oxides of aluminium and manganese. (ii) Tropical Dry Forests Tropical dry forest includes semi-evergreen, dry evergreen, semi deciduous forests. This is a series of plant communities along an environmental gradient toward increasing aridity. Tropical dry forests of all types are found in climate regions that are warm year round and experience several months of severe drought during low sun period. They are often neglected as attention focuses on 6 the wet evergreen forests of the tropics. They deserve treatment as separate biome because it hosts a different group of plants and animals that do either neighboring tropical savannas or rainforests. Figure 4: Tropical Dry Forest The broadleaf evergreen forests are replaced by the dry tropical forests. Dry tropical forests undergo varying lengths of dry season. During the dry season, the drought deciduous trees and shrubs drop their leaves (Figure 4). New leaves are grown at the onset of the rainy season. The largest proportion of tropical dry forest is found in Africa and South America. Most dry tropical forests have been lost to agriculture and grazing and other disturbances. 2. Tropical Savanna Tropical Savannas are characteristic of semiarid regions with seasonal rainfall. The term Savannas is used to describe range of vegetation types in the drier tropics and subtropics (Figure 5). Climate: Tropical savannas occur north and south of tropical dry forests within 10° to 20° North & South of the equator. Savannas are associated with a warm continental climate with distinct seasonality in precipitation and a large variation in total rainfall per year. Seasonal drought combines with another important physical factor, fire. Fire helps maintain the tropical savannah as a landscape of grasslands and scattered trees. 7 Figure 5: Tropical Savanna Vegetation: It is characterized by a vegetation cover of grasses with scattered shrubs or trees. Such vegetation is characteristics of regions with alternating wet and dry seasons. Frequent fires have selected for fire resistance in the savanna flora. Savannas are characterised by two layer vertical structure due to the ground cover of grasses and the presence of shrubs or trees. Productivity and decomposition is savanna ecosystems are closely tied to the seasonality of precipitation. Animal life: Savannas support a large variety of herbivores. The tropical savanna is populated by wandering animals that move in response to seasonal and year-to year variations in rainfall and food availability. The African Savanna is dominated by a large and diverse ungulate fauna of atleast 60 species such as wildebeest, giraffes, and zebras. The wandering consumers of the Australian savannas include kangaroos. Living on the herbivore fauna are large number of carnivores such as Lion, leopard, cheetah and Hyena. Soil: Deeply weathered, low nutrient acidic soil are characteristic of such biomes. 3. Temperate Grasslands The natural grasslands of the world occur in the multitudes in midcontinent regions, where annual precipitation declines as air masses move inward from the coastal environments. In the northern hemispheres, examples of such regions are Prairies of North America and Steppes of central Eurasia. In the southern hemisphere, grasslands are represented by the pampas of Argentina and veldt of high plateaus of southern Africa. 8 Figure 6: Temperate Grassland Climate: Natural grasslands occupy regions where rainfall ranges from 25-80 cm per year. The temperate grasslands climate is one of the recurring droughts and the diversity of vegetation cover reflects the difference in the amount of rainfall. The maximum precipitation usually occurs in summer during the height of the growing season. The grasslands are tallest and most productive where mean annual precipitation is greater than 800 mm and mean annual temperature in above 15° C winters in temperate grasslands are generally cold and summers are hot. Vegetation: The most visible feature of grassland is tall, green and short lived herbaceous growth that develops in springs and dies in autumn (Figure 6). Drought and high summer temperatures encourage fires. Grassland consists of an ephemeral herbaceous layer that arises from crowns, nodes and rosettes of plants hugging the ground. The height of the vegetation varies from about 5cm in dry, short grass prairies to over 200 cm in the wetter, tall grass prairies. The ground layer and below ground root layer are the other two major strata of grasslands. They have highly developed roots layer that extend deep into the soil. Animal Life: Grasslands support a diversity of animal life with both invertebrate and vertebrate herbivores including