9.2 Terrestrial Biomes and Ecosystems

Earth's diverse terrestrial biomes are shaped by climate, geography, and complex ecological interactions. From tundra to tropical rainforests, each biome supports unique plant and animal communities adapted to specific environmental conditions.

Understanding terrestrial biomes is crucial for grasping Earth's ecosystems. These biomes face threats from human activities like deforestation and climate change, highlighting the need for conservation efforts to protect biodiversity and maintain vital ecosystem services.

Terrestrial Biomes and Characteristics

Major Terrestrial Biomes

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• Tundra characterized by low temperatures, short growing seasons, permafrost, and low-growing vegetation (mosses, lichens, and shrubs)
• Taiga (boreal forest) features cold temperatures, coniferous trees (spruce, fir, and pine), and acidic soils
• Temperate deciduous forests have distinct seasons, moderate temperatures, and trees that lose their leaves annually (oak, maple, and beech)
• Temperate grasslands (prairies and steppes) characterized by grasses, herbaceous plants, occasional trees, and periodic droughts or fires
• Temperate rainforests have mild temperatures, high humidity, and dense vegetation, including tall trees (redwoods and Douglas firs) and understory plants
• Tropical rainforests feature high temperatures, abundant rainfall, and immense biodiversity, with tall trees forming a dense canopy and numerous understory layers
• Tropical savannas have warm temperatures, seasonal rainfall, and a mix of grasses and scattered trees (acacia and baobab)
• Chaparral characterized by hot, dry summers and mild, wet winters, with drought-resistant shrubs and small trees (sage and manzanita)
• Deserts have low precipitation, extreme temperatures, and sparse vegetation adapted to conserve water (cacti and succulent plants)

Characteristics of Terrestrial Biomes

• Terrestrial biomes are large, distinct ecological communities characterized by their dominant vegetation, climate, and geography
• Vegetation in each biome is adapted to specific environmental conditions, such as temperature, precipitation, and soil type
• Climate patterns, including temperature and precipitation, largely determine the distribution and characteristics of terrestrial biomes
• Biomes support diverse communities of plants and animals that interact through complex food webs and ecological relationships
• Terrestrial biomes play crucial roles in global biogeochemical cycles, such as the carbon and water cycles, and provide essential ecosystem services

Factors Influencing Biome Distribution

Climatic Factors

• Temperature affects the length of the growing season and the types of plants that can survive in a given area
• Precipitation influences the amount of water available for plant growth and determines the vegetation structure and composition
• Latitude influences the amount of solar radiation received, affecting temperature and seasonality (higher latitudes experience colder temperatures and shorter growing seasons compared to equatorial regions)
• Altitude affects temperature and precipitation, with higher elevations generally experiencing cooler temperatures and increased precipitation, resulting in distinct biomes at different elevations within the same region (montane forests)
• Ocean currents can moderate coastal climates, creating milder conditions and influencing the distribution of biomes (temperate rainforests)

Geographic Factors

• Topography, including mountains and valleys, can create rain shadows and microclimates that influence local biome distribution
• Soil characteristics, such as nutrient content, pH, and water retention, can affect the types of plants that can grow in an area and, consequently, the biome type
• Proximity to large water bodies, such as oceans and lakes, can moderate temperatures and increase humidity, influencing the distribution of coastal and riparian biomes
• Natural barriers, such as mountain ranges and deserts, can limit the dispersal of species and create distinct biomes on either side
• Geologic history, including past climate changes and tectonic events, has shaped the distribution and evolution of terrestrial biomes over long timescales

Adaptations and Interactions in Biomes

Plant Adaptations

• Tundra plants grow low to the ground, have shallow root systems, and use the sun's energy efficiently during the short growing season; many reproduce asexually to conserve energy
• Taiga plants, such as coniferous trees, have needle-like leaves to reduce water loss and allow snow to slide off easily, and thick bark to protect against cold temperatures
• Temperate deciduous forest plants have broad leaves to maximize photosynthesis during the growing season and drop their leaves to conserve energy during the dormant season; many have thick bark to protect against fire
• Temperate grassland plants have extensive root systems to access water and nutrients in the soil, and many are adapted to periodic fires (underground storage organs or fire-resistant seeds)
• Tropical rainforest plants have adapted to high humidity and competition for light by developing buttress roots, drip tips on leaves, and epiphytic growth habits
• Desert plants conserve water through various means, such as having small leaves, deep root systems, and the ability to store water in their stems (cacti)

Animal Adaptations and Interactions

• Animals in each biome have adapted to the specific conditions and resources available (tundra animals have thick fur or feathers for insulation, while desert animals are often nocturnal to avoid extreme heat)
• Biotic interactions, such as predation, competition, and symbiosis, shape the structure and dynamics of ecosystems within each biome
• In the African savanna, the grazing of large herbivores (zebras and wildebeests) maintains the grasslands and supports predators (lions and hyenas)
• Migratory animals, such as birds and large mammals, connect different biomes and play important roles in nutrient cycling and seed dispersal
• Pollination and seed dispersal by animals are critical for the reproduction and distribution of plants in many biomes (insects, birds, and mammals)
• Decomposers, such as fungi and bacteria, break down dead organic matter and recycle nutrients back into the soil, supporting plant growth and ecosystem productivity

Human Impacts on Biomes

Habitat Alteration and Destruction

• Deforestation, particularly in tropical rainforests and temperate forests, leads to habitat loss, biodiversity decline, soil erosion, and altered carbon cycles, contributing to climate change and the loss of ecosystem services
• Agriculture and livestock grazing can lead to the conversion of grasslands, savannas, and forests into croplands or pastures, resulting in habitat fragmentation, soil degradation, and changes in species composition
• Urbanization and infrastructure development can cause habitat destruction, fragmentation, and pollution, affecting local and regional biodiversity and ecosystem functions

Climate Change and Invasive Species

• Climate change, driven by human activities (fossil fuel combustion and land-use changes), can shift the distribution of biomes, alter species ranges, and disrupt ecological interactions, leading to biodiversity loss and changes in ecosystem services
• Invasive species, often introduced by human activities (trade and travel), can outcompete native species, alter ecosystem dynamics, and cause economic damage
• Overexploitation of resources, such as overhunting, overfishing, and unsustainable harvesting of plants, can lead to population declines, local extinctions, and cascading effects on ecosystem structure and function

Pollution and Conservation Efforts

• Pollution, including air, water, and soil contamination, can have detrimental effects on the health of organisms and the functioning of ecosystems across various biomes
• Acid rain, caused by sulfur dioxide and nitrogen oxide emissions, can acidify soils and water bodies, damaging plants and aquatic ecosystems
• Conservation efforts, such as protected areas, sustainable land management practices, and ecosystem restoration projects, can help mitigate the negative impacts of human activities on terrestrial biomes and promote the preservation of biodiversity and ecosystem services
• International agreements, such as the Convention on Biological Diversity and the United Nations Framework Convention on Climate Change, aim to address global environmental challenges and support the conservation of terrestrial biomes