Terrestrial Biomes Lecture Review
Biological Systems are Hierarchical
Biological systems are organized in a hierarchical order from small to large scales:
Atoms
Molecules and macromolecules
Cells
Tissues
Organs
Organisms
Populations
Communities
Ecosystems
Biosphere
This hierarchy frames how life processes integrate from chemistry to global-scale patterns.
Learning Objectives (Biomes)
Define Ecology and Ecosystem
Ecology: the scientific study of interactions among organisms and their environment.
Ecosystem: a complex, dynamic network of living (biotic) and non-living (abiotic) components interacting as a system.
Describe and distinguish between the large-scale and local factors determining terrestrial biome distribution.
Describe climatic variables that affect the climate in La Crosse (as an example location).
Draw and interpret a climograph of major terrestrial biomes.
Biomes Defined by Predominant Vegetation
Biomes are defined by their predominant plant communities (vegetation), i.e., the type of plants that dominate the landscape.
Conceptual emphasis: vegetation is a visible, integrative indicator of the underlying climate and soil conditions.
Determinants of Terrestrial Biomes
Primary factors:
Temperature
Precipitation
Key secondary/interactive factors:
Altitude (lapse rate: temperature generally decreases with elevation)
Latitude (affects solar angle and day length, thus climate)
Other considerations mentioned in readings: soil properties (nutrients, pH, minerals), sunlight availability, wind (evaporation), and disturbances (fire, floods, etc.).
Global vs Local Influences on Biome Location
Large-scale controls:
Global patterns of temperature and precipitation shaped by latitude and prevailing atmospheric circulation (Hadley cells, Ferrel cell, Polar cells).
Local controls:
Mountains and topography
Bodies of water and coastal effects
Microclimates (small-scale climate variations in a landscape)
Data Snapshot: Locations and Biome Influences
Location data used to illustrate biome distribution (sampled at Belém, Yuma, Denver, Chicago, Dawson, Barrow):
Belém, Brazil: Altitude 16 ext{ m}; Precipitation 279 ext{ cm}; Temperature 26.5^ ext{°C}; Latitude 1^ ext{°}
Yuma, AZ: Altitude 63 ext{ m}; Precipitation 10 ext{ cm}; Temperature 24^ ext{°C}; Latitude 32^ ext{°}
Denver, CO: Altitude 1611 ext{ m}; Precipitation 39 ext{ cm}; Temperature 10^ ext{°C}; Latitude 40^ ext{°}
Chicago, IL: Altitude 205 ext{ m}; Precipitation 89 ext{ cm}; Temperature 9^ ext{°C}; Latitude 42^ ext{°}
Dawson, Canada: Altitude 323 ext{ m}; Precipitation 31 ext{ cm}; Temperature -5^ ext{°C}; Latitude 64^ ext{°}
Barrow, AK: Altitude 9 ext{ m}; Precipitation 11 ext{ cm}; Temperature -12^ ext{°C}; Latitude 71^ ext{°}
Summary question: Which two factors seem to influence terrestrial biomes the most?
Temperature and Precipitation.
How could these data be represented graphically?
A climograph plotting average annual temperature (T{ ext{avg}}, in ^ ext{°C}) on one axis against average annual precipitation (P{ ext{avg}}, in \text{cm}) on the other axis for each location (or a single climograph with multiple biome regions).
Climographs and Temperature-Precipitation Relationships
Temperature and precipitation provide a two-dimensional space to predict biome location.
In climographs, x-axis typically represents time (months) or latitude-related climate cycles, while y-axes show temperature (°C) and precipitation (cm).
Figure concept (described): an arrangement showing various biomes such as Temperate Grassland, Subtropical Desert, Tropical Wet Forest, Desert, Wet Forest, Temperate Forest, Boreal Forest, Arctic Tundra, plotted in relation to their characteristic temperature ranges and precipitation totals.
Notation:
T_{ ext{avg}}: Average annual temperature (in ^ ext{°C})
P_{ ext{avg}}: Average annual precipitation (in cm)
Climograph relationships illustrate that biomes cluster in regions of the T{ ext{avg}}–P{ ext{avg}} space.
Correlation, Causation, and Interactions
Correlation vs. cause and effect:
Temperature and precipitation influence where biomes occur.
Altitude and latitude influence temperature and precipitation (i.e., they are drivers of climate).
Temperature and precipitation do not directly affect altitude and latitude.
Are temperature and precipitation the only factors?
No. Other determinants include soil properties (nutrients, pH, minerals), sunlight availability, wind/evaporation dynamics, and disturbances (fire, floods, tornadoes, volcanoes).
Practical Exercise: Graphing and Prediction
Exercise: Using a sheet of paper, graph which biome would be present based on temperature and precipitation.
Example exercise prompts:
If Chicago area average annual temperature increases by +4 ^ ext{°C} and precipitation decreases, which biome is favored? Likely a shift toward a drier and warmer biome (e.g., temperate grassland or desert) depending on the magnitude of change and thresholds in the climograph.
Conceptual takeaway: Small changes in temperature and precipitation can shift biomes across boundaries in the (T{ ext{avg}}, P{ ext{avg}}) space.
Temperature and Precipitation: Quantitative Examples
Typical biome regions by latitude/precipitation patterns (illustrative):
High latitude (Arctic): Arctic tundra – very low temperatures, very low precipitation, high variability.
Mid latitude (Temperate regions): Temperate forest or boreal forest depending on moisture; precipitation ranges from low to high with moderate variability.
Low latitude (Tropical): Tropical wet forest – high temperatures, very high precipitation, sometimes high variability depending on region.
Variation in climate parameters by latitude:
High latitude climate characteristics (e.g., Barrow, Alaska): Temperature very low with high variability; precipitation very low overall.
Mid latitude climate characteristics (e.g., Chicago): Moderate temperatures and moderate precipitation with moderate variability.
Low latitude climate characteristics (e.g., Belém, Brazil): High temperatures with high precipitation totals and variations.
Regional Climatic Mechanisms and Visualizations
Global patterns: Solar-driven air circulation and precipitation
Energy from the sun heats air most at the equator.
Warm, moist air rises near the equator and cools, condenses, and falls as rain.
Cooler, dry air descends back to the surface, creating dry zones at around 30° latitude.
Hadley cell dynamics: warm air rises at equator, moves poleward at high altitude, cools and sinks around 30° latitude, returning equatorward at the surface.
This circulation drives major precipitation belts and desert regions.
Local modifiers of climate:
Mountains: air rising over mountains cools and rains on the windward side; rain shadow on the leeward side.
Oceans and large bodies of water: maritime climates, onshore breezes bring humidity and rain.
Microclimates: small-scale variations due to surface features and vegetation.
Example: Cascade Mountains rain shadow creates dry conditions east of the range; onshore moisture brings rain on the western slopes.
Key Concept Check: Climate Questions
Why are places along the equator hotter than higher latitudes?
Because the angle of incoming sunlight is generally more direct at the equator, delivering more solar energy per unit area.
What determines the global positions of desert biomes?
Solar-driven atmospheric circulation: Dry air subsides around 20–30° N/S, creating desert conditions by inhibiting cloud formation and rainfall.
What is the main factor dictating Earth's temperature distribution?
The amount of sunlight per unit area (solar insolation) is the primary driver of global temperature patterns.
Deserts are found roughly 20–30 degrees from the equator because:
Winds carry warm dry air to the desert (described mechanism).
Wisconsin is cold in January and warm in July because:
The Earth's axis is tilted; the Northern Hemisphere is tilted toward the Sun in July, increasing insolation.
Quick Summary of Climatic Variability by Latitude
High latitude (Arctic tundra):
Temperature: very low, large seasonal variation
Precipitation: very low; often snow rather than rain; high variation
Mid latitude (Temperate forests/grasslands):
Temperature: moderate; distinctive seasons
Precipitation: moderate and variable; capable of supporting diverse biomes
Low latitude (Tropical wet forests):
Temperature: high and relatively constant
Precipitation: high and often very high; strong seasonality in some regions
Worked Relationships and Formulations (LaTeX)
Climatic factors in biome distribution can be conceptualized as a function of two primary variables:
T_{ ext{avg}} = average annual temperature in ^ ext{°C}
P_{ ext{avg}} = average annual precipitation in cm
Biome location can be viewed as a mapping: ext{Biome} = f\left(T{ ext{avg}}, P{ ext{avg}}, ext{soil}, ext{sunlight}, ext{disturbance}, ext{microclimate}
ight)
Hadley cell concept (qualitative):
Warm air rises near the equator, leading to precipitation; dry air descends around 30° latitude, creating deserts.
This can be summarized as a circulation loop with ascending moist air near the equator and descending dry air at subtropical latitudes.
Practice Questions (from the transcript)
Two areas with the same temperature and precipitation can have different vegetation because:
A) They have different nutrients in the soil
B) One is windier than the other
C) They receive different amounts of rain
D) A and B
E) All of the above
Answer: D (A and B) because with identical temperature and precipitation, soil nutrients and wind influence vegetation and microclimates.
What determines the global positions of desert biomes?
Answer: Winds carry warm, dry air to desert regions (i.e., the Hadley circulation and subtropical high-pressure zones).
Wisconsin is cold in January and warm in July because:
Answer: The Earth's axis of rotation is tilted so that the Northern Hemisphere is tilted toward the Sun in July.
Notes on Climax and Usage
These notes synthesize the presented material to provide a coherent framework for understanding terrestrial biomes, their drivers, and how to visualize and predict biome distributions using temperature and precipitation data, along with local modifiers (soil, sunlight, wind, disturbances).
Practical takeaways:
Temperature and precipitation are the primary predictors of biome location, but not the only determinants.
Altitude and latitude influence temperature and precipitation patterns, thereby shaping biome distributions.
Local factors (soils, microclimates, mountains, oceans) can modify or override general regional patterns.