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

google

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