Lecture 7: Notes

Lecture 7: Vegetation biomes William S. Currie, Assoc. Prof. SNRE
Topics
1. Global circulation and continental effects
2. Soils and soil development
3. Global scale vegetation biomes
4. Regional, landscape, and local scale patterns
—>Triangulate Annual/Seasonal Climate with Types of Vegetation and Soil Development
These 3 all interact
Lecture skims over several entire fields of science:
-General circulation of the atmosphere
-Climate science
-Biogeography
-Soil science

I. Global circulation and continental effects
Regional to continental scale controls on temperature and moisture (#1)
-Location relative to Hadley cells, i.e. vertical and latitudinal movements of air and moisture in the atmosphere, exert strong effects on climate
-These can vary seasonally as the Hadley cells move northward and southward
(See Ricklefs fig 4.5)
Sun heats most efficiently at equator
—>warm air rises and colder air from N/S fills in behind it
-this creates cycling air flows (N/S are in opposite directions)
-A simple principle with far-reaching effects:
warm air can hold a lot more water vapor than cold air can (fig. 4.4)
Rising warm air creates rainfall zones because as it rises it cools
then the moisture condenses to fall as rain
-Solar radiation at the Earth’s surface: Warm deserts are self-reinforcing at a large scale
Dry air cannot produce clouds -> more radiation reaches the surface-> more heat->dry air
Lack of clouds in desert also produces cold night since heat is not trapped
-But annual averages don’t tell the whole story, because Hadley cells shift up and down, to some extent, with the seasons

*Intriguing idea: migrating birds are really just trying to stay in the “same area” in a climate area
Could say that they are staying in place while the planet moves

Regional to continental scale controls on temperature and moisture (#2)
-Location relative to continental centers and edges, oceans and ocean currents, and large-scale horizontal circulation in the atmosphere
– all exert strong controls on regional climate.
Example A: Where continents are larger, seasonal temperatures tend to vary more
-land absorbs/releases lots of heat-> creates fluctuations
-oceans distribute heat more evenly and absorb/release more steadily
Example B: The Bermuda High, and clockwise circulation (in the atmosphere) around it,
bring moisture to the eastern US.
Proximity to edge vs centre of continents and distance to ocean are important
Example C: Asian monsoon brings warm, moist air to higher latitudes in SE Asia
Continent warms more than the ocean in summer
Then the heat rises upward drawing water from the oceans
Example D: Warm ocean currents bring moist air to the Pacific NW of North America, where there are temperate rainforests.

Regional to continental scale controls on temperature and moisture (#3)
-Hadley cells, locations and sizes of continental masses, ocean currents, and horizontal atmospheric circulation … these all interact
-These interactions can produce idiosyncratic regional-scale climate patterns that have altered as the continents have moved (due to plate tectonics) and the surface/atmosphere has gone through warming and cooling periods

Example: Polar ice caps are a relatively recent phenomenon, caused by:
Having a continental land mass at the South Pole
Land temp fluctuates more than water-> colder now than before there was land
Having the Arctic Ocean closed off from the circulation of the Pacific and Atlantic Oceans,
thus unable to receive heat from the lower latitudes via ocean currents

II. Soils and soil development
Soil:
-Sometimes defined as
“A natural product formed from weathered rock by the action of climate and organisms”
-But soil also contains mineral grains, organic matter, water, air, living microorganisms,
and nutrient elements so it is more complex than the first definition implies

-Organic matter serves many functions:
Source and exchange site for nutrient cycling
Energy source for heterotrophic microorganisms in soil
Source of organic acids important in soil development
Influences soil structure, pore space, and water holding capacity

Jenny’s soil-formation equation (1941)
Soil formation = f(Cl, O, R, P, T)
-Cl: climate
-O: organisms (including vegetation and microorganisms)
-R: relief (or topography) –on flat land soil stays in place and weathers; steep land soil slides
off and must be replaced so it is “young soil”
-P: parent material (rock, sand, gravel)
-T: time –especially interacts w/ climate and vegetation
–age affects the properties of soil

Levels of soil called Horizons
O=Organic at the top; can be thick or thin
A=area with roots, holds water and nutrients
E= elluviation; not always present; moves materials down from A to B
B= area w/ materials deposited by A; where primary minerals convert to secondary
C= area of parent material

Soil taxonomy is a system of classification used in the US. The highest taxonomic level are these Orders: Alfisols, Aridosols, Entisols, Histosols, Inceptisols, Mollisols, Oxisols/Andisols, Spodosols, Ultisols, Vertisols (AKA “Great Groups”)
-terms refer to the age of soil

Important soil-forming processes:
Podsolization: cool areas w/ rain -> upper layer nutrients leach downward
Laterization: warm and moist -> nutrients leach away into water and out of soil
Calcification: cool to hot areas w/ no water to carry minerals downward
-> minerals get left on the surface or at the water level in the soil
Gleization: cool and moist -> wet soil

III. Vegetation biomes
1.Whittaker’s biome depictions (slide)
Average annual temperature and precipitation
~5 C separates boreal forest from temperate
~20 C separates temperate from tropical and subtropical

2.Walter biome definitions
Based on seasonality of temperature and precipitation
3.Walter climate diagrams
Show seasonal patterns of temperature and precipitation
Ideal for plants = precipitation during the warm periods -> ”growing seasons”

Temperate seasonal forest (slide)

Spodosol, temperate forest, northern MI (slide)
-Shows heavily leached E horizon (white) and B horizon directly beneath

Soil formed through lateritic processes (Andisol or Oxisol) (slide)

Tropical rain forest in Ecuador, Amazon basin

Tropical seasonal forest or savanna

IV. Regional, landscape, and local scale patterns
Controls on climate at a particular location

We talked about:
Global scale effects (ice ages, global warming)
Latitude (Hadley cells, seasons)
Location relative to large land masses
Ocean currents and prevailing winds (example: Bermuda H brings moisture to SE US)

Now talk about:
Orographic effects
E.g Orographic lifting carries warm moist air up on west side of Sierras
East side of Sierras experience a “rain shadow”
Topographic effects: Elevation and aspect

Topographic and orographic effects control local climates and microclimates
Topographic effects: Aspect (NSW or East-facing)
In northern hemisphere:
-south-facing aspect gets more sunlight, more temp extremes, often drier
-north-facing aspect is cooler, with less temp extremes, often wetter
E.g San Gabriel Mtns north of LA

Elevational zones mimic latitudinal zones
- Shown in class: Merriam’s life zones (slide)
Lines across elevation are slanted because rain/dry affects temps
Highest elevation (alpine zone) is similar to an arctic zone
Second highest Hudsonian zone is like Canada

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