Equatorial and Tropical Physical Geography
Realm of the Intertropical Convergence Zone
A Regional Approach
All elements of physical geography integrated in the ecoregion approach of Robert Bailey, UCLA Geographer, U.S. Forest Service
Bailey, 2002
Foundation in Scholarship
Used Extensively
just
The question here: what
scale to use in
interpreting physical
geography ?
macroscale
mesoscale
microscale
Microscale – focused on microclimate and soil control of biography
Useful for helping students understand a field site, but not global patterns
Bailey, 2002 Bailey, 2002
Not microscale
Classic Considerations for Micro-scale• Precipitation
– The Type they get: Rain, Snow, etc.– How much they get: Yearly, monthly, daily– When they get it: seasonality
• Sunlight– Length of day in different seasons– Affect of topography & other local factors– Important for plant life
• Temperature– Daily, Monthly, Yearly averages
• Soil Type– Rocky, Acidic, Sandy, Fertile, etc.
Mesoscale – role landforms influences the ecosystem over broad areas (but not globally)
Tropical Limestone
sometimes, mesoscale
Bailey, 2002Oberlander & Muller, 1974
For a geography perspective, the
macroscale ecoregion scale makes sense
Bailey, 2002
Regions at macroscale derive from temperature & moisture
Macroscale – ecoregions based on climatic zones (e.g. Koeppen climate zones)
Focus in this class is global patterns of ecoregions (occasionally showing
examples from meso- and micro-scales)
Could organize by biomes, but not connected to the process that
controls the geography
Could organize by temp & precip, but not connected to the processes
that create the geography
General circulation perspective
Intertropical Convergence Zone (ITCZ) –brings summer rains in equatorial &tropical latitudes
Subtropical High – brings drought,annually or seasonally
Polar Front – brings precipitation in the midlatitudes
Polar Easterlies – the cold landscapes of tundra and ice caps
Organized by basic climate processes controlling precipitation and temperature
Organization for each section
1st – climate2nd – soils 3rd – landforms& hydrology4th – biogeographywith discussion of geology where defines meso-scale
landform regions and also bringing in HEI (human environment interactions)
Bailey, 2002
Climate of Tropics: Driven by ITCZ and Trade Winds
Typical Day
Starts with clear sky, warming the surface.
By the
afternoon,
Cumulonimbus
produces downpours that stop in the evening.
Little Seasonal Change in Temp
Typical Year
Hadley Cell
Ascending
moist air
condenses
& rains
ITCZ
Equatorial & Tropical
Latitudes influenced by
ITCZ
0º
Descendingwarms & driesIn subtropics
Desertzone
Descendingair warms& dries insubtropics
Desert Zone
Trade winds Trade winds
Global CirculationPatterns
Hadley Cell
See ITCZ & Subtropical High
ITCZ Shifts Seasonally
ITCZ
Shifts
South
ITCZ
Shifts
North
Monsoon Arrives
Monsoon (seasonal wind shift) brings Extreme Peak in
Summer Precipitation
Africa Example
Rain came because the subtropical high (drought) and the
ITCZ (rain) shifted
Prof. Caylor
Notice the lag
Effect. It takes
time to heat
up & draw the
ITCZ into
the Sahel
Further from the ITCZ: Drought during winter from subtropical highproduces “savanna” climate or Aw
ITCZ & entire
circulation shifts N & Sso seebroad peaks
Polar Front Polar FrontITCZ
Wet Summer From ITCZ
Dry Winter From Subtropical High
Also, long periods of drought can occur at the extreme limits of ITCZ
movement
Senegal, Sahel susceptible to long droughts
Summary Climographs
ITCZ ST High ITCZ
Soils of the Tropics
Soils form over tens of thousands of years
Gives you a “map” of the “average” location of rainforests & savanna
Synonym: Oxisol Soils
Process ofLatosol or Oxisol Soils
Laterization soil development
Oberlander & Muller, 1984
Soil Name
OxisolLatosol(synonyms indifferentclassifications)
Clay type(kaolinite)Not holdnutrients
Oxisol Profiles
• Little organic matter
• Red from iron oxides
• Loose & friable texture
Paradox: Poor soils because few nutrients, yet great rainforests
Why? Natural nutrient recycling
With Deforestation
• organic matter leached• nutrients lost• Gradual loss of fertility
British Honduras, Maize Yield (lb./acre)Virgin soil 1500-2000Second year 1200Third year 800
With deforestation• soil structure hardened by desiccation and
compaction into laterite
• Can make “laterite” by drying out the soil
Deforestation has always occurred: traditional swidden (slash and burn)
agriculture – burn to release nutrients and move to another plot
Problem is AcceleratingIndustrial farming in Brazil
Expansion around Towns,Mambasa, Congo
Bolivia,
Tierras Bajas
Population Growth
No chance for recovery, as in slash and burn
Rondonia
Brazil
Deforestation impacts Global Warming through CO2 release
Positive spin: invest in rainforests
Net Effect
Eco-friendly efforts exist, butsmall in aerial extent
Shade-grown coffeeEcotourism
Brazil Nut
Landscapes of the Tropics
1. Laterite duricrusts & bornhardts
2. Waterfalls are common
3. Feral relief
4. Tropical Karst
5. Deep weathering - susceptible to erosion after deforestation
Just as bricks made, when soil
dried – dry season can turn soil into a laterite “duricrust”
Laterite duricrusts & bornhardtsseen in savanna landscapes
Bornhardts
Bornhardts emerge
Step 1: graniteweathered insubsurface
Step 2: oncegranite exposeddomes “grow” oremerge abovelaterite
A savanna landscape
Spizkoppe, Namibia
Kopje
Bornhardts keep
“growing” until they get so large, latent fractures open up and create kopjes
Waterfalls are common
General explanation: rivers need hard “tools” in the bedload to erode resistant rock.
Weathering so intense that rivers load is mostly sand, silt and clay, not hard cobbles or boulders
Angel Falls Venezuela, 979 mIguazu Falls, Argentina
Sipi Falls, Uganda Victoria Falls,
Zimbabwe
Feral relief
Steep landscapes
made by landsliding
from intense rains
in places like Hawaii
Andes where a lot
of relief exists
Steep slopes made possible by vegetation holding soil to steep faces
Intense rains saturates slopes and landslides rush down slopes
Flat valleys eroded by torrential floods
Landslides strip
trees
Net effect is relief gone wild (feral)
Kauai(GoogleEarth)
Mt Rotui, Moorea
Rarotonga, Cook Islands
Tropical KarstKarst occurs in
all climates from
limestone
dissolving,
but tropical karst
has special forms
due to
abundant water
And
organic acids
Cockpit Karst
Jamaica, Cockpit Country
ESRI/GIS helps to see the joints (fractures) that intersect to set the pattern
Stone ForestYunnan, China
Organic
acids
decay
base
Tower Karst (with relief)
Guilin, China Malaysia
Halong Bay, Vietnam Nearby Restaurant
Deep weathering – creates susceptibility to erosion after
deforestationWeathering
Profiles
Very
Deep
Under
Forest
Cover
With deforestation
Overland flow of water produces gullying
Deforestation leads to landsliding
Banana, Brazil
Costa Rica
Biogeography of the Tropics
Tropical Rainforest – no or minor dry season
Tropical Savannas – major dry season
Tropical Rainforest
• Contain as many species of plants and animals as all other types of ecosystems combined
• 4 mi2 area - 750 species of trees, 1500 species of flowering plants
The Tropical & Equatorial Rain Forest
The world’s most biologically-diverse biome
Great Variety in Forest Types
Biogeography Generalizations
Missouri Botanical Garden
1. Smooth bark to inhibit other plants
2. Lianas (vines)
3. Leaves have Drip Tips
4. Buttress
roots to
support giant
trees
5. Prop & Stilt
roots to allow
growth in wet soils
6. Epiphytes
grow on trees
(e.g.orchids)
7. Bromeliads
are epiphytes
with a plant
structure that
can cup water
Drip Tip
Epiphyte (Orchid) Stilt Roots (Mangroves)
Strangler
Fig
Epiphytes, Lianas common
Source: http://www.world-builders.org/lessons/less/biomes/rainforest/tropi_rain/tropgifs
Tropical Rain Forest Vegetation
Layers in the Tropical Rain Forest Canopy
Canopy Layer
•Continuous layer (about 45 m)
•Most have buttressed trunks
•Especially high diversity of plants and animals
•Same tree found once or twice per square kilometre
•Lianas (vines) connect trees
•Epiphytic vegetation common -28,000 species (eg. mosses, bromeliads, ferns, orchids)
•Abundant fauna (eg. monkeys, sloths, bats, treefrogs, ants, beetles, parrots, hummingbirds and snakes)
Understorey Layer
•Receives 2-5% of incident light (blocked by canopy)
•Understorey plants photosynthesize most efficiently under low light (low respiration rates)
•Layer consists of small trees (eg. dwarf palms) and seedlings of taller trees
•Low wind: insect pollination, strong smelling and conspicuous flowers often on trunks
•Abundant fauna (eg. insects, snakes, frogs, parakeets, leopards, jaguars etc.)
Forest Floor•Approximately 1% of light incident upon the canopy
•100% relative humidity, less temperature variation
•Rapidly-decomposing organic matter
•Few flowering plants
•Fungi thrive on decomposing organic matter
•Large mammals forage for roots and tubers (eg. tapirs)•Many insects (eg. termites, cockroaches, beetles, centipedes, millipedes, scorpions and earthworms)
ButtressedTrunks
Helps supportlarge tree biomass, weight of water andepiphytes
Massive changes in water height(100 cm = 1m, 2000 cm = 20 m)
Amazon Forests associated with flooding different• Igapò: swamp forest, flooded by typically blackwater
rivers for extended periods (4-10 months).• Vàrzea: flooded forest, covers at least 60,000 square
miles (154,400 sq. km) of the Amazon, flooded seasonally by whitewater rivers and has richer soils than igapò and correspondingly, is good for agriculture.
Adaptation to Amazon’s Pulses
• Floating Meadows- always have access to sunlight and can readily use the nutrients of whitewater rivers..
• Inundated Tree species adapt -- Some species show continuous production of new leaves, other species defoliate completely or do not show any change in leaf production during the year at all.
Amazing Specializations
Anteater, El SalvadorFruit bat & roll in seed dispersal
of trees
Few limits on moisture or tempfor animals
3-toed Sloth Antbird
Fruit Bat Howler Monkey
Caiman Emerald Tree Boa
Piranha Scarlet Macaw
Online Resources
Video Clips from
Planet Earth
More online videos
Ecogeeks
Tropical SavannasAt fringe of the ITCZ, intensewet season of varying length
• East African savannas (e.g. Serengeti Plains)
• Llanos of Venezuela
• Cerrado of Brazil
• Pine savannas of Belize
Generalizations
• Perennial grasses (tall, 1-2 m at maturity)
• Open canopy of trees can form
(a) when soils are poor (e.g. laterite)
(b) with regular burning
(c) with regular grazing (e.g. clearing by large mammals like elephants that open woodlands to grass grazing.
Thick Perennial Grass
Typically distinguished by dominant tree-type (e.g. Acacia savanna)
Termite Mounds Common
Classic Baobob Tree
Trees in low, wetter areas
Role of Elephants in Clearing Scrub
Courtesy of K. Caylor
Fire turns trees to grasslands
West Africa
Yucatan
Savanna AnimalsGiraffe
Water holes in dry season
Gemsbok (Oryx gazella)Example of how survive long drought
• Eats succulents like tsama melons and cucumbers
• Digs 1m to eat roots & tubers
• Raise body temp to 113 F to avoid sweating