Terrestrial Biomes: Climate, Soil, Vegetation, and Human Influence

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Life on Land: Terrestrial Biomes

Introduction

Terrestrial biomes are large ecological areas on the Earth's surface, each defined by distinctive climate, soil, vegetation, and animal life. Understanding the distribution and characteristics of these biomes is fundamental to the study of ecology and environmental biology.

Large-Scale Patterns of Climatic Variation

Climates and the Distribution of Terrestrial Biomes

Climate is the primary factor determining the global distribution of terrestrial biomes. Variations in temperature and precipitation create distinct environments that support different types of plant and animal communities.

Climate: The long-term pattern of temperature and precipitation in a region.
Biome: A large ecological community defined by its climate, soil, and living organisms, especially the dominant vegetation.
Climatic diagrams: Graphical representations showing average monthly temperature and precipitation, used to characterize biomes.
Example: Tropical rain forests occur in regions with high, year-round rainfall and stable temperatures, while deserts are found in areas with low precipitation and high temperature variability.

Other Factors: Microclimate and Soil

Microclimate and Soil as Foundations of Terrestrial Biomes

While climate sets the broad boundaries for biomes, local variations in microclimate and soil properties further influence the distribution and characteristics of ecosystems within each biome.

Microclimate: The climate of a small, specific place within a larger area, which can differ from the general climate of the region.
Soil: The upper layer of earth in which plants grow, consisting of organic matter, minerals, gases, liquids, and organisms.
Soil properties: Include texture, fertility, pH, and organic matter content, all of which affect plant growth and ecosystem productivity.
Example: In deserts, soils are often low in organic matter and nutrients, while in temperate grasslands, soils can be deep and fertile.

Natural History and Geography of Biomes

Overview of Major Terrestrial Biomes

The Earth's major terrestrial biomes include tropical rain forest, desert, Mediterranean woodland and shrubland, temperate grassland, and boreal forest. Each biome is characterized by its location, climate, soil, vegetation, and the degree of human influence.

Major Terrestrial Biomes

Tropical Rain Forest

Tropical rain forests are among the most biologically diverse and productive ecosystems on Earth, found near the equator.

Location: Within 10° latitude of the equator, including Southeast Asia, West Africa, and Central and South America.
Climate: Little temperature variation; annual rainfall exceeds 2000 mm, distributed evenly throughout the year.
Soil Properties: Soils are typically nutrient-poor, acidic, and thin due to heavy rainfall causing leaching and rapid decomposition. Mycorrhizal fungi help plants obtain nutrients.
Vegetation: Dominated by tall, evergreen trees (often 40 m high), with high plant and animal diversity.
Human Influence: Exploited for timber, agriculture, and medicinal resources; significant deforestation and habitat loss.
Example: The Amazon Rainforest in South America.

Desert

Deserts are arid regions with extreme temperature fluctuations and low precipitation, covering about 20% of Earth's land surface.

Location: Bands at 30°N and 30°S latitude, in continental interiors or rain shadows of mountains.
Climate: Precipitation is less than evaporation; temperature can be hot or cold.
Soil Properties: Soils are low in organic matter (lithosols), but may have nutrient-rich 'islands' under shrubs. Some areas have high salt accumulation due to evaporation.
Vegetation: Sparse or absent; plants have adaptations such as small leaves, dense hairs, or dormancy to reduce water loss.
Human Influence: Increasing due to agriculture, urbanization, and desertification from overuse.
Example: The Sahara Desert in Africa.

Mediterranean Woodland and Shrubland

This biome is characterized by mild, wet winters and hot, dry summers, and is found on several continents.

Location: Occurs in regions such as California, the Mediterranean Basin, parts of Australia, and South Africa.
Climate: Cool, moist winters and springs; hot, dry summers.
Soil Properties: Fragile soils with moderate fertility.
Vegetation: Evergreen trees and shrubs, many of which are fire-resistant due to frequent fires.
Human Influence: Long history of human settlement, agriculture, and urban development.
Example: The chaparral of California.

Temperate Grassland

Temperate grasslands are extensive, fertile regions dominated by grasses, with periodic droughts and fires.

Location: Widespread from 30° to 55° latitude, including North America (prairies), Eurasia (steppes), and South America (pampas).
Climate: Precipitation ranges from 300 to 1000 mm annually; experiences periodic droughts.
Soil Properties: Soils are often deep and fertile, making them ideal for agriculture.
Vegetation: Dominated by herbaceous grasses; high productivity and diversity.
Human Influence: Most have been converted to farmland, leading to loss of native vegetation and soil organic matter.
Example: The North American prairies.

Boreal Forest (Taiga)

The boreal forest is a cold, northern biome dominated by coniferous trees and characterized by long winters and short summers.

Location: Broad band between 50° and 65°N latitude, primarily in the Northern Hemisphere (Canada, Russia, Scandinavia).
Climate: Cold, long winters; short, cool summers; moderate precipitation.
Soil Properties: Soils are thin, acidic, and low in fertility due to slow decomposition at low temperatures and low pH.
Vegetation: Dominated by evergreen conifers; relatively high animal density and diversity.
Human Influence: Historically low, but increasing due to logging and resource extraction.
Example: The Siberian taiga.

Summary Table: Major Terrestrial Biomes

Biome	Location	Climate	Vegetation	Human Influence
Tropical Rain Forest	~10° N/S of Equator	Wet, stable temperature	Trees, high diversity	High (deforestation, agriculture)
Desert	~30° N/S	Dry, hot or cold	Sparse or absent	Increasing (urbanization, agriculture)
Mediterranean Woodland & Shrubland	~40° N/S	Cool, wet winters; hot, dry summers	Evergreen shrubs, fire-adapted	High (agriculture, urbanization)
Temperate Grassland	30°–55° N/S	Moderate, periodic droughts	Grasses, high productivity	Very high (converted to farmland)
Boreal Forest	50°–65° N	Cold, long winters	Coniferous trees	Increasing (logging, resource extraction)

Key Concepts and Applications

Reading Climate Diagrams: Climate diagrams plot monthly temperature and precipitation, helping to identify biome types and seasonal patterns.
Soil-Vegetation Relationships: Soil fertility and structure influence the types of plants that can thrive in each biome.
Human Impact: Human activities such as agriculture, deforestation, and urbanization are altering biomes worldwide, often reducing biodiversity and ecosystem services.

Additional info: The notes above expand on brief points from the original slides, providing definitions, examples, and a summary table for clarity and completeness.