Topic 1.2: Terrestrial Biomes Flashcards

Definition and Core Characteristics of Biomes

• Biomes are geographical areas characterized by a shared combination of average yearly temperature and precipitation patterns, which together define a region's climate.
• Climate refers specifically to the long-term trends and averages of annual temperature and precipitation in a given area.
• Temperature and precipitation ranges serve as the two primary defining characteristics of any biome:
  • Tropical Rainforest: Defined by consistently warm temperatures and extremely high annual rainfall.
  • Desert: Defined primarily by very low annual precipitation. Although deserts often experience high temperatures, the defining factor distinguishing them from tropical rainforests is the scarce rainfall.
  • Tropical Seasonal Forest (Savannah): Annual precipitation ranges from approximately $60\,cm$ or $75\,cm$ up to $280\,cm$, with average annual temperatures ranging from $18^\circ\text{C}$ to $29^\circ\text{C}$.

Adaptations of Organisms to Biome Climates

• Plant and animal communities residing within a biome possess specialized biological adaptations essential for surviving its specific climatic conditions.
• Desert Adaptations:
  • Camels: Store energy in the form of fat inside their humps, allowing them to endure extended periods without access to external food and energy sources.
  • Cacti: Possess thick, waxy cuticles (outer coatings) that minimize water loss caused by evaporation in high-heat, low-moisture environments.
• Grassland Adaptations:
  • Shrubs and Wildflowers: Develop long, deep root systems capable of storing substantial energy reserves underground. When periodic wildfires devastate the above-ground vegetation, these deep root energy stores allow the plants to rapidly regrow.

Geographic Distribution and Latitudinal Patterns of Biomes

• The worldwide spatial distribution of biomes follows predictable geographic patterns determined largely by latitude and distance from the Equator, which dictate light intensity and temperature:
  • Cold and Dry Biomes (Tundra and Boreal Forest):
  • Located far from the Equator, concentrated around $60^\circ$ latitude and further north.
  • Characterized by low annual precipitation and low average temperatures.
  • Temperate Biomes (Temperate Grassland and Temperate Seasonal Forest):
  • Concentrated in the middle latitudes between $30^\circ$ and $60^\circ$ latitude.
  • Experience moderate annual rainfall and moderate temperatures year-round, featuring warm summers and cool winter seasons.
  • Tropical Biomes (Tropical Rainforest and Tropical Seasonal Forest / Savannah):
  • Concentrated around the Equator ($0^\circ$ latitude).
  • Characterized by direct solar radiation year-round, resulting in consistently warm temperatures and high annual precipitation.

Nutrient Availability Across Biomes

• Soil nutrient availability is a crucial biome characteristic that dictates which plant species—and how many species—can survive in an ecosystem.
• Tundra:
  • The soil remains permanently frozen year-round as permafrost, except for a thin surface layer known as the active layer that thaws annually to support plant growth.
  • Permanently frozen soil severely restricts the decomposition of organic matter by decomposers, preventing the recycling of essential soil nutrients.
  • Frozen conditions result in low soil nutrient levels and low liquid water availability, limiting survival to very few plant species, which subsequently limits animal diversity.
• Tropical Rainforest:
  • Possesses surprisingly nutrient-poor soil despite high plant density and high biomass production.
  • Rapid nutrient uptake occurs because dense plant populations compete intensely for resources, immediately absorbing soil nutrients as soon as organic matter decomposes.
• Boreal Forest (Taiga):
  • Characterized by cold temperatures and dominated by coniferous trees such as pine, spruce, and aspen.
  • Features nutrient-poor soils because low temperatures throughout much of the year restrict the activity of decomposers (such as earthworms and fungi), slowing the decomposition of dead organic matter and nutrient cycling.
• Temperate Seasonal Forest:
  • Found extensively in areas such as West Michigan and across much of the United States.
  • Features high soil nutrient levels due to the abundance of broadleaf deciduous trees (such as oaks and maples) that shed their leaves every autumn.
  • Accumulation of leaf litter on the forest floor, combined with moderate temperatures, promotes rapid decomposition and continuous nutrient replenishment in the soil.

Climate Change and Shifts in Biome Distribution

• Biome boundaries are dynamic and shift geographically in response to global climate changes driven by human activities.
• Mechanisms of Biome Shifts:
  • Rising global temperatures cause previously frozen northern soils to thaw, expanding the suitable growing habitat for large tree species further north.
  • Warm temperatures cause biomes to lose their southern geographic ranges, as southern regions become too warm for cold-adapted native tree species.
• Boreal Forest and Aspen Distribution Shifts:
  • Historical range baseline for aspen trees was documented from $1971$ to $2000$.
  • Climate modeling predicts a substantial northward shift in aspen range between $2071$ and $2100$.
  • Regions in the northern United States and southern Canada are projected to become too warm to support characteristic boreal tree species like aspen and spruce.
• Direct Observational Evidence:
  • Comparative photographs taken of the exact same Arctic plot of land in $1962$ and $2004$ document tree lines and boreal forest vegetation creeping steadily northward into previously frozen terrain.

Concept Explanation Skill Application

• Skill Practice Exercise:
  • Task: Identify one characteristic of a biome and explain how that characteristic determines the community of organisms found in that biome.
• Operational Philosophy:
  • "Think like a mountain, write like a scholar."