General location of major climate types
GEO 101, April 1, 2014
Finish B climates
A: Tropical climates
E: too cold for trees
D: long winter
H
C: long summer
Treeline
B: arid
Freezeline
A: never freezes
Hypothetical continent
What is where and why?
60°
Four Major Causes of Arid Climates
1. Location near subtropical high pressure belt
30°N or 30°S
30°
2. Location in continental interior
0°
3. Location behind mountain barriers
4. Location near cold ocean currents
30°
60°
No “B” climates at
high latitudes. Why?
Location of “B” climates
Desert plants cope with water deficiency in two ways
1. Drought evaders: annual plants that have a short
life after it rains. Spend most time as dormant
seeds.
2. Drought resistors: perennial plants that tough it out
and have adaptations that enable them to live with
very little water. These are called xerophytic plants.
STH, Interior, Mt. barriers, Cold currents
1
Drought evaders
Drought resistors
Annuals
Perennial xerophytes
Characteristics of xerophytes
Characteristic spacing of xerophytes (ocotillo)
North
American
Cactaceae
African
Euphorbiaceae
Foliage…most can be shed during drought
sparse
small needle shaped leaves
waxy coatings
hairs
or...no leaves just green stems, succulents
Photosynthesis – CAM pathway common
stomates open at night to take in CO2
close in day to reduce water loss
photosynthesis uses daylight and CO2
stored the night before
Example of
convergent
evolution
Sonoran Desert has more rain and more vegetation
Characteristics of xerophytes, contd.
Roots
deep rooted (160’ mesquite)
and/or widespread shallow roots
Growth habit
relatively short
succulent
spiny or toxic
2
Namib Desert
Kangaroo rat
Desert animals
Most nocturnal
Get water from food
Most are small
Lizard
How they do it....
Body temperature range 98-108
Blood volume kept high at expense of tissue fluid
Can safely lose 40% of body water weight
Urine thick, feces dry
BS or Steppe climates
transition between tall-grass prairies and true desert
vegetation
short grasses
bunch grasses
good pasture
overgrazed easily
vulnerable to desertification
Short grass prairie associated with BS climate
Spring greening
3
Desertification of arid and semi-arid lands
“A” = Tropical climates = never freezes
Process whereby productive potential of arid or semi-arid
land falls by 10% or more, primarily due to human activities.
Three tropical climate subtypes
60°
30°
Af: Tropical rainforest climate
“f” means no dry season, doldrums
seasonless, monotonous, high humidity
tropical rainforest, broadleaf evergreen, selva
multistoried
upper Amazon, northern Congo basin, East Indies
0°
30°
60°
Am: Tropical Monsoon (“m” = monsoon)
short but not severe dry season
summer rainfall maximum (onshore winds)
tropical rainforest, broadleaf evergreen
less dense, more deciduous trees
primarily coastal locations, east side of continent
Af
Am
Aw
Aw: Tropical savanna (wet & dry, winter dry)
“w” = dry winter
influenced by doldrums and subtropical high
grassland, thorn scrub
dormant season due to drought
What do these all have in common?
Small group question: What leaf shape/shedding habit do
you expect to find in each of these and why?
4
Af: tropical rainforest biome
Epiphytes: plants that “perch” on the branches
orchids, bromeliads
Af: tropical rainforest biome
≠ Jungle
Broadleaf evergreens
Vines (lianas) common
Tropical rainforest is multistoried, competition for light
Af: tropical rainforest biome
Arboreal animals
Pollen vector ≠ wind
Low stress
High diversity
Lemur
Fruit bat
Examples of tropical tree
root systems.
Buttresses are common
Tropical Leaves
often have
drip tips
5
Despite lush growth, tropical rainforest soils are poor.
Nutrients are washed away by the constant rain.
Recycling is rapid.
Nutrients stored in biomass of forest itself.
Distribution of organic carbon
Temperate Forest
Tropical Forest
Impact of tropical forest clearance
1. Releases stored CO2
2. Destroys carbon “sink”
3. Destroys transpiration mechanism
4. Increases erosion
 Tropical rainforest soils are poor.
 Nutrients stored in biomass.
Tropical Monsoon (Am)
Found primarily along eastern coastlines
Result of seasonal reversal of winds
Onshore, bringing rain in summer
Offshore, bringing drier conditions in winter
Desertification
: loss of
productive
potential due
to human
activity
No severe drought
Long growing season (it’s tropical)
Forest not as tall or diverse as Af
Broadleaf deciduous trees lose leaves in dry season
Can happen in
A climates as
well as in arid
climates
6
Aw = Tropical savanna
Biomes:
Plant formations associated with major climate types.
Period of severe drought
long dry season during
“winter” low sun season
High temps. = high PET
Located between Af and B
Tropical rainforest
Tropical savanna
Desert
Temperate grassland
Temperate forest
Mediterranean scrub
Boreal forest
Tundra
Ice
Aw
Aw: dry period is so long that broadleaf deciduous trees
cannot earn enough during wet season to pay for
leaves. Needleleaf trees or small leaves are best.
Trees are dormant in dry season.
Grasses and shrubs dominate
EF
ET
Df
Cs
B
Aw
Af
Aw
B
Cs
Df
ET
EF
Baobab or Upside-Down Tree grows in Africa and Australia.
The legend says that after it was planted by God it kept
moving, so God replanted it upside down
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EF
Where is Aw located ?
Where is Aw located ?
ET
What causes it to be
predictably wet and dry?
What causes it to be
predictably wet and dry?
Df
Cs
Pressure belts follow direct
vertical rays of sun.
Pressure belts follow direct
vertical rays of sun.
B
Aw
In July, when sun is north of
Equator, ITCZ affects Aw 
rain in summer.
In July, when sun is north of
Equator, STH affects Aw 
dry in S. Hemis. winter.
Af
Aw
In January, when sun is
south of Equator,
Subtropical High affects Aw
 dry in winter.
In January, when sun is
south of Equator, ITCZ
affects Aw  rain in S.
Hemis. summer.
B
Cs
Df
EF
ET
Df
Cs
B
Aw
Af
Aw
B
Cs
Df
ET
ET
EF
EF
Changes in vegetation along precipitation gradient in “A”
E
A
D
Af
Am
Aw
B
C
Decreasing precipitation 
A
Decreasing precipitation 
Mangrove: tropical, low energy coastal, woody plants,
tolerate saltwater
Mangrove
Global mangrove distribution
8
Environmental issues associated with A climates
Mangrove destruction for aquaculture/wood chips
Deforestation for agriculture / ranching
Honduras
Shrimp ponds, Indonesia
9