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© T. M. Whitmore
TODAY•Physical Geography sub-regions of
South America (continued)Chilean “Mediterranean”“Temperate” (marine west coastal)
ChileDry lands of Southern ConeHumid “temperate” southeastern
SAAmazonia & central lowland SA
© T. M. Whitmore
LAST TIME-Questions?•Physical Geography sub-regions
Middle American (Mesoamerican) Highlands
Middle American lowlands & Caribbean
Coastal deserts of PeruAndean Highlands
© T. M. Whitmore
Mediterranean climate zone of Chile
•~ 30º - 40º South – thus NOT in tropics
•Landforms
•Climate: Cfbso-called “Mediterranean” climate
zone because it resembles the climate of the Mediterranean (and coastal southern California)
•VegetationMuch like Spain or S. CaliforniaGreat for Med. Crops (wine!)
Santiago
An
des
NASA World Wind
Chile’s vineyards
© Oregan Stqte University
Chilean viniculture
© T. M. Whitmore
Marine West Coastal South America
•~ 40° and farther south along west coast
•Landforms very narrow Andes
•Climate: CfbCool; seasonal temp swing; littl
e seasonal precip difference
•Vegetationa forest landscape (mostly pines)
NASA World Wind
*
© T. M. Whitmore
© T. M. Whitmore
Dry lands of the Southern Cone
•Patagonia (southern-most area)leeward rain shadow; little precip (
Bs or Bw); seasonal temp swing; step-like plateaux with very steep
canyons and spectacular mtns; very windy
•Chaco and Eastern Andes piedmont (also Bs climate)sloping plains and piedmonts,
grasslands with scrub
© T. M. Whitmore
Westerlies(moist winds)
Rai
n sh
adow
NASA World Wind
*
; ~ 45º S45º S
© T. M. Whitmore
© Secretaría de Turismo de Sarmiento
© T. M. Whitmore
Humid temperate South America
•Landforms– famous location of Pampasplains and low sloping uplands
•Climate: Cfamoderate seasonal temp swing; little sea
sonal precip difference
•Vegetationnot a forest landscape but tall grasses
•SoilsSuperior soils (mollisols) on Pampas with
great stored natural fertility
Note silt in “Rio de la Plata”
Pam
pas
NASA World Wind
© T. M. Whitmore
© T. M. Whitmore
© T. M. Whitmore
Mollisol(great fertility)
Mollisols in the great grasslands
© T. M. Whitmore
Amazonia & central lowland SA•Landforms“Highlands” Vast low lying river basins
•ClimatesEquatorial:
Af – warm & wet constantlyTropical wet/dry:
Aw – warm with seasonal rainsavannah or cerrado
© T. M. Whitmore
NASA World Wind
Amazon Basin
Rio Negro
Rio Amazon
winds
windsDry ---- Wet
Dry ---- Dry
Wet ---- Dry
© T. M. Whitmore
Equatorial climate
© T. M. Whitmore
© T. M. Whitmore
Amazonia & central lowland SA II
•Vegetation Equatorial rainforestsWet-dry tropical vegetation: open
forests & savannas
© T. M. Whitmore
© T. M. Whitmore
Equatorial rainforests
•Richest terrestrial biome on earth
•> 1 million higher plant and animal species (10 – 20% of world’s total); even more if micro fauna and flora and insects added
•Very diverse (>60 different species of large trees in 1 ha); > 600 total species/haDiversity => relative scarcity of any
particular species in any area
•Highest total of biomass per ha on earth
© T. M. Whitmore
Equatorial rainforests II•Broadleaved trees in multi-story
canopy
•Rapid “recycling” of plant nutrientsWarm temps and much rain =>
“leaching” of nutrients from soils (many of these are among the world’s worst)
•Access via rivers (or increasingly) by roads
© T. M. Whitmore
© T. M. Whitmore
Nutrient flows in forests
Solar energy
© T. M. Whitmore
© T. M. WhitmoreAmazon meeting the Río Negro
© T. M. Whitmore
Savanna (or Cerrado)
•Seasonal rain => grasslands with occasional trees
•Most rapidly transforming landscape in South America (agriculture – soy beans)
© T. M. Whitmore
Cerrado (savanna)
© T. M. Whitmore
Amazonian Soils
•Terra firme (dry land) soils in AmazoniaAncient “shield” rocksRapid nutrient recyclingCalled “oxisols” or “ultisols”
•Alluvial soils based on silt deposited along river flood plains of Amazon and its tributariesWhite water riversVárzea (flood plain)
© T. M. Whitmore
OxisolUltisol
(this soil is from NC)
“White” W
ater Rivers
© T. M. Whitmore
© T. M. Whitmore
Amazonian Soils II
•Anthropogenic soilsRaised fieldsTerra preta do Indio soils
Terra preta do Indio
Neighboring oxisolTerra preta do Indio
© T. M. Whitmore
Soils and fertility
•4 major parts to soils Organic matter alive and dead
(partly decomposed = humus)Inorganic matter — sand, silt, and
clayWaterAir
© T. M. Whitmore
Soils and fertility II•Major plant nutrients from:
Solar energy (visible wavelengths)Air – the CO2 part provides carbon
(C)Water provides: hydrogen (H) &
oxygen (O) Only absorbed through roots
Soils (and fertilizers): phosphorus (P); nitrogen (N); and potassium (K)
© T. M. Whitmore
Soil nutrients (N, P, & K)
•Must be dissolved in water for roots to absorb
•Available to plants only in the form of ions:Cations (+ charge) Anions (- charge)
© T. M. Whitmore
Soil nutrients
•Most important soil based nutrients:Nitrogen (N)Potassium (K)Phosphorus (P)Plus about 10 micro-nutrients
• Importance of clay and humus (serve as sites to which cations and anions attach)
•Note role of nitrogen-fixing bacteria
© T. M. Whitmore
Cation Exchange Capacity (CEC)
•Measure of ability of a soil to retain and exchange nutrient ions
•CEC associated with some clays and humus
•CEC is very low in oxisols and ultisols
•Storage of basic cations defines fertile soils
•Aluminum is especially toxic and found in acidic soils
© T. M. Whitmore
Slash/burn agriculture in Amazonia
•Recall the forest energy/nutrient flows
•Slash & burn (swidden, milpa, roza y quemar, etc.) agriculture redirects nutrient flows
•Slash-burn-plant-fallow-repeat
Nutrient flows in forests
Nutrient Flows in slash & burn Agriculture
Ash in newly cut swidden awaiting planting
Cleared swidden surrounded by 1 yr re-growth; N. Belize
© T. M. Whitmore
Soil problems in swidden agriculture •Much is lost due to burning process –
especially critical is nitrogen (in the NOx in the smoke)
•Ash is rapidly carried away by rains (worse in hilly places)Thus fertility boost last only 1-3 yrs
•Even where fertility is better, weed and pest invasions limit use
• If fallowing is sufficient for forest re-growth => all is OK if not problemsTo get 1 ha farmer must have 20+
ha available•Role of clearing for pasture
Crop yrs 3-4 Crop yrs 3-4Crop yrs 3-4
Crop yrs 1-2& 5-6
Crop yrs 5-6
Crop yrs 7-8
Crop yrs 9-10
Crop yrs 10-12
Crop yrs 5-6
Crop yrs 1-2& 7-8
Crop yrs 1-2& 13-14
10 yrs fallow
5 yrs fallow
3 yrs fallow