Life on Land: Terrestrial Biomes

Introduction

Terrestrial biomes are large ecological areas on the Earth's surface, with distinct climate, soil, vegetation, and animal life. Understanding biomes is fundamental in general biology, as they illustrate how climate and geography shape the distribution and diversity of life.

Large-Scale Patterns of Climatic Variation

Climate and Biome Distribution

Climate, defined by long-term patterns of temperature and precipitation, is the primary factor determining the global distribution of terrestrial biomes. These patterns result from the Earth's position relative to the sun, atmospheric circulation, and geographical features.

• Climate Diagrams: Visual representations showing average temperature and precipitation throughout the year for a location.

• Latitude: Many biomes are distributed according to latitude, with tropical biomes near the equator and temperate/polar biomes at higher latitudes.

• Example: Tropical rain forests are found near the equator, while boreal forests are located in northern latitudes.

Other Factors: Microclimate and Soil

Microclimate and Soil as Foundations of Biomes

Microclimate refers to the climate of a small, specific area, which can differ from the general climate of the region. Soil properties, including fertility, texture, and organic matter, also play a crucial role in shaping biomes.

• Microclimate: Influenced by local topography, vegetation, and water bodies.

• Soil Properties: Affect plant growth and ecosystem productivity. Key properties include nutrient content, pH, and drainage.

• Example: Desert soils are often nutrient-poor and have low organic matter, while temperate grasslands have deep, fertile soils.

Natural History and Geography of Biomes

Major Terrestrial Biomes

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

Tropical Rain Forest

Location and Climate

Tropical rain forests are found within 10° latitude of the equator, primarily in Southeast Asia, West Africa, and Central and South America. They experience little temperature variation and high, evenly distributed annual rainfall (about 2000 mm).

• Climate: Warm and wet year-round; minimal seasonal changes.

• Soil Properties: Soils are typically nutrient-poor, acidic, and thin due to heavy rainfall causing leaching and rapid decomposition. Mycorrhizae (fungal symbionts) help plants obtain nutrients.

• Vegetation: Dominated by tall, evergreen trees (average height ~40 m), with high plant and animal diversity.

• Human Influence: Exploited for timber, agriculture, and medicine; significant habitat loss due to deforestation.

Desert

Location and Climate

Deserts are typically found in bands at 30°N and 30°S latitude, covering about 20% of Earth's land surface. They occur in continental interiors, rain shadows, or regions with high evaporation.

• Climate: Precipitation is low and often less than evaporation; temperature can be hot or cold.

• Soil Properties: Soils are low in organic matter (lithosols), but nutrient islands may exist under shrubs. Some regions have saline soils due to poor drainage and evaporation.

• Vegetation: Sparse or absent; plants have adaptations such as small leaves, dense hairs, and dormancy to conserve water.

• Human Influence: Increasing intrusion and desertification due to human activities.

Mediterranean Woodland and Shrubland

Location and Climate

This biome occurs on all continents except Antarctica, notably in California, the Mediterranean Basin, and parts of Australia. It features cool, moist winters and hot, dry summers.

• Climate: Seasonal rainfall, with most precipitation in fall, winter, and spring.

• Soil Properties: Fragile soils with moderate fertility.

• Vegetation: Evergreen trees and shrubs; many plants are fire-resistant due to frequent fires.

• Human Influence: Extensive history of agriculture, urbanization, and habitat modification.

Temperate Grassland

Location and Climate

Temperate grasslands are widely distributed from 30° to 55° latitude, found in North America, Eurasia, and South America. They experience moderate precipitation (300–1000 mm) and periodic droughts.

• Climate: Moderate rainfall, periodic droughts.

• Soil Properties: Deep, fertile soils, ideal for agriculture.

• Vegetation: Dominated by herbaceous plants (grasses); high productivity.

• Human Influence: Most converted to farmland; loss of organic matter due to agriculture.

Boreal Forest (Taiga)

Location and Climate

Boreal forests cover over 11% of Earth's land area, primarily between 50° and 65°N latitude in the Northern Hemisphere. They have long, cold winters and short summers.

• Climate: Cold, with moderate precipitation; long winters, short growing season.

• Soil Properties: Low fertility, thin, and acidic soils; slow decomposition due to low temperature and pH.

• Vegetation: Dominated by evergreen conifers; relatively high animal density.

• Human Influence: Historically low, but increasing due to logging and resource extraction.

Summary Table: Major Terrestrial Biomes

Additional info:

• Mycorrhizae are symbiotic associations between fungi and plant roots, enhancing nutrient uptake in poor soils.

• Desertification refers to the process by which fertile land becomes desert, typically due to drought, deforestation, or inappropriate agriculture.

• Climate diagrams are essential tools for visualizing biome climate patterns; students should practice interpreting them.