1.3 Terrestrial biomes

Terrestrial biomes are Earth's major land ecosystems, shaped by climate, soil, and unique plant and animal communities. From frozen tundra to lush rainforests, these biomes showcase nature's diversity and adaptability to different environmental conditions.

Understanding terrestrial biomes is crucial for grasping global ecology and conservation. Human activities like deforestation and climate change are altering these ecosystems, highlighting the need for sustainable management and protection of Earth's vital landscapes.

Types of terrestrial biomes

• Terrestrial biomes are large regions of land characterized by distinct climate patterns, soil types, and communities of plants and animals
• The distribution of terrestrial biomes is primarily determined by temperature and precipitation, which influence the types of vegetation that can grow in an area
• Major terrestrial biomes include tundra, boreal forests, temperate forests, temperate grasslands, temperate deserts, tropical savannas, and tropical rainforests

Characteristics of terrestrial biomes

Climate in terrestrial biomes

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• Climate is a key factor in determining the distribution and characteristics of terrestrial biomes
• Temperature and precipitation patterns vary significantly across different biomes, ranging from cold and dry conditions in tundra to hot and humid conditions in tropical rainforests
• Seasonal changes in temperature and precipitation also play a role in shaping the structure and function of terrestrial biomes

Soil in terrestrial biomes

• Soil type and quality vary among terrestrial biomes, influenced by factors such as climate, vegetation, and geological history
• In cold biomes like tundra, soils are often thin, nutrient-poor, and underlain by permafrost
• Temperate and tropical biomes generally have more developed soils with higher organic matter content and nutrient availability

Vegetation in terrestrial biomes

• Vegetation structure and composition are adapted to the specific climate and soil conditions of each biome
• Tundra is characterized by low-growing plants like mosses, lichens, and hardy shrubs
• Forests (boreal, temperate, and tropical) are dominated by trees, with varying levels of understory vegetation
• Grasslands and savannas are characterized by grasses and scattered trees or shrubs

Tundra biome

Climate of tundra

• Tundra experiences extremely cold temperatures, with long, harsh winters and short, cool summers
• Annual precipitation is low, typically less than 25 cm (10 inches), and mostly occurs as snow
• Permafrost (permanently frozen ground) is a defining feature of tundra soils

Soil of tundra

• Tundra soils are thin, nutrient-poor, and often waterlogged due to the underlying permafrost
• Soil development is slow due to the cold temperatures and short growing season
• Cryoturbation (mixing of soil layers due to freeze-thaw cycles) is common in tundra soils

Flora of tundra

• Tundra vegetation is adapted to the harsh climate and includes low-growing plants like mosses, lichens, sedges, and dwarf shrubs
• Plants have shallow root systems to avoid the permafrost layer and often grow in dense clumps to protect against wind and cold
• Examples of tundra plants include Arctic willow, bearberry, and cotton grass

Fauna of tundra

• Tundra animals are adapted to the cold climate and scarce resources, with many species migrating or hibernating during the winter
• Large herbivores like caribou and musk oxen graze on tundra vegetation
• Predators such as Arctic foxes, snowy owls, and polar bears hunt smaller animals like lemmings and voles

Boreal forest biome

Climate of boreal forests

• Boreal forests (also known as taiga) experience cold, dry winters and short, cool summers
• Annual precipitation ranges from 40-100 cm (16-39 inches), with most falling as snow during the winter
• Growing seasons are short, typically lasting 3-5 months

Soil of boreal forests

• Boreal forest soils are often acidic and nutrient-poor due to slow decomposition rates in the cold climate
• Soils are typically podzols, characterized by a thick layer of organic matter (litter) on top of mineral soil horizons
• Permafrost may be present in some areas, limiting soil development and drainage

Flora of boreal forests

• Boreal forests are dominated by coniferous trees such as spruce, fir, and pine, which are adapted to the cold climate and nutrient-poor soils
• Understory vegetation is relatively sparse and includes shrubs like blueberry and lingonberry, as well as mosses and lichens
• Deciduous trees like birch and aspen may be present in areas with better soil conditions or following disturbances like fire

Fauna of boreal forests

• Boreal forests support a diverse range of animals adapted to the cold climate and coniferous habitat
• Large herbivores include moose, deer, and caribou, which browse on trees and shrubs
• Predators such as lynx, wolves, and bears hunt smaller mammals like snowshoe hares and rodents
• Many migratory bird species, such as warblers and thrushes, breed in boreal forests during the summer

Temperate forest biome

Climate of temperate forests

• Temperate forests experience distinct seasonal changes, with cold winters and warm summers
• Annual precipitation ranges from 75-150 cm (30-59 inches), distributed relatively evenly throughout the year
• Growing seasons are longer than in boreal forests, typically lasting 5-7 months

Soil of temperate forests

• Temperate forest soils are generally fertile and well-developed, with a rich organic layer (humus) and active soil fauna
• Soils are often alfisols or mollisols, characterized by a high base saturation and good drainage
• Soil pH and nutrient availability vary depending on the underlying bedrock and vegetation type

Flora of temperate forests

• Temperate forests are characterized by a mix of deciduous and coniferous trees, with species composition varying by region and elevation
• Deciduous trees like oak, maple, and beech dominate many temperate forests, shedding their leaves in the fall
• Understory vegetation is diverse and includes shrubs, herbaceous plants, and spring ephemerals that take advantage of the high light levels before the canopy closes

Fauna of temperate forests

• Temperate forests support a wide range of animals, including both generalists and specialists
• Large herbivores like deer and elk browse on vegetation, while smaller mammals like squirrels and chipmunks feed on seeds and nuts
• Predators such as bobcats, foxes, and owls hunt smaller animals, while omnivores like bears and raccoons have diverse diets
• Many bird species, including woodpeckers, warblers, and thrushes, are found in temperate forests

Temperate grassland biome

Climate of temperate grasslands

• Temperate grasslands experience hot summers and cold winters, with moderate precipitation
• Annual precipitation ranges from 25-90 cm (10-35 inches), with most falling during the growing season
• Frequent droughts and fires are common in temperate grasslands, shaping the vegetation structure

Soil of temperate grasslands

• Temperate grassland soils are often deep and fertile, with a high organic matter content from the dense root systems of grasses
• Soils are typically mollisols, characterized by a thick, dark surface horizon (A horizon) rich in nutrients
• Soil formation is influenced by the semi-arid climate, with less leaching and weathering compared to wetter biomes

Flora of temperate grasslands

• Temperate grasslands are dominated by a diverse mix of grasses and forbs (non-woody flowering plants)
• Grasses are well-adapted to the frequent fires and grazing by large herbivores, with deep root systems and the ability to resprout quickly
• Examples of temperate grassland plants include big bluestem, switchgrass, and purple coneflower

Fauna of temperate grasslands

• Temperate grasslands support a variety of animals adapted to the open habitat and seasonal changes in resource availability
• Large herbivores like bison, pronghorn, and wild horses graze on the abundant grasses
• Smaller mammals such as prairie dogs, ground squirrels, and badgers create burrows and modify the landscape
• Predators like coyotes, hawks, and ferrets hunt the smaller animals, while omnivores like foxes and skunks have more diverse diets

Temperate desert biome

Climate of temperate deserts

• Temperate deserts experience hot, dry summers and cool winters with minimal precipitation
• Annual precipitation is typically less than 25 cm (10 inches), with most falling as brief, intense rainstorms
• High evaporation rates and large temperature fluctuations between day and night are common

Soil of temperate deserts

• Temperate desert soils are often sandy or rocky, with low organic matter content and limited soil development
• Soils are typically aridisols, characterized by a lack of moisture and the accumulation of salts and carbonates
• Biological soil crust, composed of cyanobacteria, lichens, and mosses, plays a crucial role in stabilizing desert soils and fixing nitrogen

Flora of temperate deserts

• Temperate desert vegetation is sparse and adapted to the harsh, dry conditions
• Plants have various adaptations to conserve water, such as small leaves, thick cuticles, and deep root systems
• Examples of temperate desert plants include cacti, yucca, and sagebrush

Fauna of temperate deserts

• Temperate desert animals are adapted to the extreme temperatures and scarce water resources
• Many animals are nocturnal or crepuscular (active at dawn and dusk) to avoid the heat of the day
• Examples of temperate desert animals include kangaroo rats, rattlesnakes, and roadrunners
• Insects and other invertebrates, such as scorpions and beetles, are also abundant in temperate deserts

Tropical savanna biome

Climate of tropical savannas

• Tropical savannas experience hot temperatures year-round, with distinct wet and dry seasons
• Annual precipitation ranges from 50-130 cm (20-50 inches), with most falling during the wet season
• The length of the dry season varies, but can last several months

Soil of tropical savannas

• Tropical savanna soils are often nutrient-poor and heavily weathered due to the high temperatures and seasonal rainfall
• Soils are typically oxisols or ultisols, characterized by a high clay content and low fertility
• Termites play a significant role in soil turnover and nutrient cycling in tropical savannas

Flora of tropical savannas

• Tropical savannas are characterized by a continuous layer of grasses and scattered trees or shrubs
• Grasses are fire-adapted and quickly resprout after burning, while trees have thick bark and deep root systems to survive fires and drought
• Examples of tropical savanna plants include acacia trees, baobab trees, and elephant grass

Fauna of tropical savannas

• Tropical savannas support a diverse array of animals, many of which are adapted to the seasonal changes in resource availability
• Large herbivores like elephants, giraffes, and zebras graze on the abundant grasses and browse on trees and shrubs
• Predators such as lions, cheetahs, and hyenas hunt the herbivores, while smaller carnivores like jackals and wild dogs target smaller prey
• Many bird species, including ostriches, secretary birds, and oxpeckers, are found in tropical savannas

Tropical rainforest biome

Climate of tropical rainforests

• Tropical rainforests experience hot, humid conditions year-round, with little seasonal variation in temperature
• Annual precipitation is high, typically exceeding 200 cm (79 inches), and is relatively evenly distributed throughout the year
• Humidity levels are consistently high, often above 80%

Soil of tropical rainforests

• Tropical rainforest soils are often nutrient-poor and heavily weathered due to the high temperatures and abundant rainfall
• Soils are typically oxisols or ultisols, characterized by a high clay content and low fertility
• Despite the low soil quality, the rapid nutrient cycling between plants and the soil supports the high biodiversity of tropical rainforests

Flora of tropical rainforests

• Tropical rainforests are characterized by a complex, multi-layered structure with a high diversity of plant species
• The canopy layer is dominated by tall, broadleaf evergreen trees, while the understory contains smaller trees, shrubs, and herbaceous plants
• Epiphytes (plants that grow on other plants) and lianas (woody vines) are abundant in tropical rainforests
• Examples of tropical rainforest plants include bromeliads, orchids, and figs

Fauna of tropical rainforests

• Tropical rainforests support an incredible diversity of animal life, with many species found nowhere else on Earth
• Arboreal (tree-dwelling) animals like monkeys, sloths, and birds are common, adapted to life in the complex canopy
• Large mammals such as tapirs, jaguars, and gorillas inhabit the forest floor, while countless invertebrates, amphibians, and reptiles occupy various niches
• Many species have evolved complex relationships, such as mutualisms between plants and their pollinators or seed dispersers

Human impacts on terrestrial biomes

Deforestation of terrestrial biomes

• Deforestation, the removal of forests for timber, agriculture, or development, is a major threat to terrestrial biomes, particularly tropical rainforests
• Clearing forests leads to habitat loss, fragmentation, and degradation, threatening biodiversity and altering ecosystem functions
• Deforestation also contributes to climate change by releasing stored carbon and reducing the capacity of forests to absorb atmospheric CO2

Desertification of terrestrial biomes

• Desertification is the process by which drylands (arid, semi-arid, and sub-humid areas) become increasingly degraded and unproductive
• Overgrazing, unsustainable agriculture, and climate change can all contribute to desertification
• Desertification leads to soil erosion, loss of vegetation cover, and reduced biodiversity, ultimately impacting the livelihoods of millions of people

Conservation of terrestrial biomes

• Conservation efforts aim to protect and restore terrestrial biomes and their associated biodiversity
• Strategies include establishing protected areas, promoting sustainable land management practices, and restoring degraded habitats
• Engaging local communities and addressing socio-economic factors are crucial for successful conservation outcomes
• International agreements, such as the Convention on Biological Diversity, provide frameworks for global cooperation in conserving terrestrial biomes