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Chapter 5: Biomes - Global Patterns of Life

Overview of Biomes

• Biomes: Defined areas sharing similar climate, topography, and soil conditions, leading to the same biological communities.

• Key determinants of biome distribution include temperature and precipitation.

  • Temperature-controlled biomes often aligned in latitudinal bands.

Types of Terrestrial Biomes

• Major biomes include:

  • Tropical rainforest

  • Subtropical moist forest

  • Temperate rainforest

  • Boreal forests

  • Tropical and subtropical seasonal forests

  • Temperate conifer forests

  • Tundra

  • Tropical grasslands and savannas

  • Temperate broadleaf and mixed forests

  • Deserts and dry shrublands

  • Mediterranean woodlands and scrub

  • Montane grasslands and shrublands

  • Temperate grasslands and savannas

Temperature and Precipitation

• Temperature and precipitation patterns also vary with altitude:

  • Ascending a mountain leads to cooler and wetter conditions, a phenomenon known as vertical zonation.

Tropical Rainforests

• Found in humid tropical regions with complex and diverse biological communities.

  • Characteristics:

    • High rainfall (exceeds 200 cm per year).

    • Uniform temperatures (warm to hot year-round).

    • Soil tends to be thin, acidic, and nutrient-poor.

    • Nutrient recycling occurs rapidly, with most nutrients locked in living organisms.

    • Vulnerable to deforestation as human settlement expands.

    • Host 50% to 66% of all terrestrial species.

Tropical Seasonal Forests

• Characterized by wet and dry seasons with consistent high temperatures.

  • Plants are often drought deciduous, losing leaves in dry periods.

  • Richer soil than tropical rainforests, making them better for agriculture.

  • Many have been altered or destroyed by human activities.

Tropical Savannas and Grasslands

• Feature limited tree cover, dominated by grass, and experience dry seasons prone to fire.

  • Flora has adaptations (deep roots) for surviving drought and fire.

  • Supports migratory grazers such as antelope and wildebeest.

Deserts

• Characterized by low moisture levels (less than 30 cm/year) and erratic precipitation.

  • Adaptations in flora:

    • Water-storing stems and thick epidermis to minimize water loss.

    • Plants bloom only after rare rains.

  • Animal adaptations include nocturnal behaviors and water conservation techniques.

  • Vulnerability noted due to human activities like off-road vehicles and overgrazing.

Temperate Grasslands

• Dominated by grasses and seasonal flowering plants, with few trees.

  • Significant fluctuations in daily and seasonal temperatures.

  • Thick organic soils make them highly productive, much converted to farmland.

  • Overgrazing leads to erosion, impacting the ecosystem.

Temperate Shrubland (Mediterranean)

• Features warm, dry summers and cool, moist winters.

  • Contains evergreen shrubs; fire ecological factor.

  • Known as chaparral in California, facing threats from urban development.

Temperate Deciduous Forests

• Experience lush growth during summer months; trees lose leaves in winter as a temperature adaptation.

  • Historically vast coverage in the eastern U.S. reduced due to timber harvesting.

  • Re-growth occurs with different dominant species.

Temperate Rainforest

• Characterized by cool, rainy conditions often clouded in fog.

  • Significant condensation in the canopy provides moisture to the understory.

  • Home to coniferous forests, such as California's redwoods.

Boreal Forests (Taiga)

• Northern coniferous forests between 50° and 60° N latitude.

  • Dominated by coniferous trees; limited tree growth due to extreme cold and short summers.

Tundra

• Treeless landscapes at high latitudes with a growing season of 2-3 months.

  • Mostly frozen with little water available throughout the year.

Marine Ecosystems

• Cover roughly 75% of Earth's surface; photosynthesis mainly by algae.

  • Upwelling currents enhance nutrient circulation.

Biological Productivity

• Dependent on nutrient availability, light, and depth in marine environments.

  • Key features include vertical stratification related to light and temperature variations.

Coastal Zones

• Communities differ by depth, light, temperature, and nutrients.

  • Coral Reefs:

    • Formed by coral polyps and crucial for biodiversity; face threats from pollution and climate change.

  • Mangroves:

    • Saltwater trees that stabilize shorelines and provide nurseries for aquatic species.

Freshwater Ecosystems

• Lakes: Vertical zones include epilimnion (warm layer) and hypolimnion (cold, deeper layer), with thermoclines acting as thermal barriers.

• Wetlands: Saturated land with high biodiversity, acting as breeding grounds for various species.

• Conservation crucial due to ecological significance.

Human Disturbance on Biomes

• Human activities invade 40% of net terrestrial primary productivity; habitat conversion leads to biodiversity loss.

  • Temperate deciduous forests most affected, while tundra and Arctic deserts remain least human-disturbed.