© 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