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Terrestrial Biomes
Global Air Circulation & Regional Climates
• Uneven heating of the Earth’s Surface
– Air is more heated at the equator and less at
the poles.
Global Air Circulation & Regional Climates
• Seasonal changes in temperature and
precipitation
Insolation
A
B
C
Solar Energy
Rainy
Season
Seasonal shift in rainy/dry seasons
Global Air Circulation & Regional Climates
• Properties of air and water.
Cell 3 North
Cold, dry
air falls
Moist air rises — rain
Polar cap
Cell 2 North
Arctic tundra
Evergreen
60° coniferous forest
Temperate
deciduous
forest and grassland
Deser
30°
Tropical deciduoust
forest
0°
Equator
Cool, dry
air falls
Cell 1 North
Moist
air rises,
cools,
and
releases
moisture
as rain
Tropical
rain forest
Tropical deciduous forest
30°
Desert
Temperate deciduous
forest and grassland
60°
Cool, dry
air falls
Cell 2 South
Polar cap
Cold,
dry air
falls
Cell 1 South
Moist air rises — rain
Cell 3 South
Terrestrial Biomes of the World
Biome – a large geographical region having a defining
climate to which plants show a similar physiological
adaptation.
•
•
•
•
Tundra
Boreal Forest
Temperate Forest
Prairies and
Grasslands
•
•
•
•
Chaparral
Desert
Tropical Forest
Tropical Mountains
Temperature and precipitation
regulate plant growth, thus the
regional distribution of biomes.
Global Distribution of
Terrestrial Biomes
Global Net Primary
Productivity For
Terrestrial Biomes
Net Primary Production of Terrestrial Biomes
Biome
NPP (g C/m2/yr)
Tropical Rain Forest
900
Tropical Dry Forest
675
Temperate Evergreen Forest
585
Temperate Deciduous Forest
540
Boreal Forest
360
Tropical Grasslands
315
Cultivated land (USA)
290
Chaparral
270
Prairie
225
Tundra
225
Desert
32
Extreme Desert
1.5
Tundra
• Windswept expanses where nothing
stands taller than grasses and sedges.
• Average temperature is -5°C.
– Water is held as ice for most of the year;
growing season is from May to August
– Plant growth is inhibited
– Decomposition and nutrient cycling is very
slow; soils are rich in organic matter
– Each year, only the top meter defrosts, below
that the ground remains frozen year round Permafrost
Tundra
• The organic rich soil in the tundra called peat.
• Due to the short growing season, all growth and
reproduction must happen in a short period.
• Young shoots are thus loaded with nutrients
– Makes good grazing
– Food is so abundant at this time that wading birds,
ducks, geese and swans commonly migrate to the
tundra; herds of caribou and reindeer arrive and
support biting flies, midges, and mosquitoes.
– Insects spend the winter as eggs, larvae or pupae.
– Birds usually feast on the abundant newly-hatched
insects
Tundra
• Although there are a lot of individual birds,
mammals, and insects, there are not many types
of species.
• Few plant species have evolved to withstand the
harsh tundra climate.
• Tundra has a low species diversity (# of species)
– Naturally low diversity does not mean unimportant.
– Tundra is essential to the well-being of animals
such as ducks, geese, seals, polar bears, and
caribou
• Recovery from disturbance takes a long time
– Tracks from vehicles are visible for several months
Tundra
Boreal Forest
• Great fir forest of Canada and northern
Eurasia.
• Vegetation type is defined by seasonal
expansion and contraction of the Arctic
and continental polar air masses.
– Polar air in the winter, continental air in the
summer
– Very cold winters, relatively warm summers so
trees can survive
Boreal Forest
• Many trees look like Christmas trees, not oak
trees
– Shape of tree is related to the ability to shed snow
– Broken trees are not good competitors
• Leaf morphology is important
– Needles are more durable, can photosynthesize
year round
– conserve heat more efficiently
• Boreal forests are low in species diversity, but
not as low as tundra
Boreal Forest
Temperate Forest
• Can be divide into evergreen and
deciduous forest types.
• Generally have a moist cool climate.
– Sometimes referred to as temperate rain
forests
• Contain giant redwoods and Douglas fir
– Redwoods can reach 120 m (~360 ft) in height.
– High-quality wood makes these forests a
valuable timber resource
• Old Growth Forest
Temperate Forest (Deciduous)
• Hot summers, cool winters (minimum
temp rarely < -12°C).
• Rain is plentiful (75 – 200 cm / yr), long
growing season, fertile soil, moderate
diversity.
• Species include oak, beech and maple.
– Produce a new batch of leaves each year
• Not as expensive as ‘freeze-proofing’ them
• Early spring, a lot of light hits the forest
floor and spring ephemerals take
advantage of this.
• Soils make good farmland and supports
good lumber
Prairies and Grasslands
• Climatically similar to temperate forests
but are dryer.
– Precipitation ranges from a low 40 mm (plants
seldom grow taller than 0.5m) to a high of 80
cm (plants can grow more than 2 m – tall grass
prairie).
• Home to numerous herbivores
– Grazing is an important ecological factor in
these areas
• Heat and aridity become important
evolutionary factors
– Panting, sweating, large ears,
evapotranspiration
Prairies and Grasslands
• Native grazers prevented any single plant from
out competing the others.
– Introduced domestic grazers (cattle or sheep for
example) have different grazing patterns and the
floristic composition has been resorted.
• Soils are very rich – America’s bread basket.
• Fire is an important component of grasslands.
– Some areas may burn every three to five years
(lightning)
– Keeps trees from becoming established
– Stopping these fires can alter the community,
allowing trees to grow.
Chaparral
• Wet and mild winter climate, dry and mild
summer
– Found in coastal California, Israel, parts of South
America and Australia
– Mediterranean climate
• The summer drought is what drives this
biomes ecology
• Plants either limit the water they lose, or gain
as much water as possible
Chaparral
• Plants can limit water loss by producing small
hard green leaves
– Hardness due to a waxy outer covering used to
prevent water loss
– Most of these plants are evergreen, so they can
photosynthesize during the wet part of the year
– By retaining leaves year round – they are able to
take advantage of all rainfall
• Plants can gain as much water as possible
– Deep tap roots
– Extensive root system (bare ground between
plants)
Chaparral
• Eradication of top predators when these
areas are settled leads to a proliferation of
herbivores.
– Sometimes, native herbivores have been
replaced with goats
– Goats are indiscriminate browsers and kill
many of the plants they eat
– Overgrazing has reduced many Mediterranean
hillsides to bare rock with very few patches of
vegetation
– Urbanization in California
Chaparral
Desert
• Dry air descends usually at Latitudes 20 –
30° North and 20 – 30° South.
– Too dry to support most life forms
• Cloudless skies permit wide temperature
fluctuations
– 50° C during the day, near 0° C at night.
• Desert plants and animals must be
obsessive about water retention
Desert
Rainshadow
Desert
• Desert animals usually hide from the full
strength sun and come out when the temp
is lower.
– Top predators are usually snakes and lizards –
need less water than mammals
– Camels have a highly developed nasal
structure that prevents water loss and its hair
is efficient at reflecting the sun’s heat.
• Desert plants can not escape the sun.
– Evolution has shaped them to minimize
exposure to the sun
Desert
Desert
• Desert plants are also designed to retain
as much water as possible.
– Stem and leaves appear to be thick and fleshy,
skin very leathery.
– Needles create microclimate in still air.
– Extensive root network; leaves are recycled
Desert
Tropical Forest
• Key feature is constant temperature
– Average temperature from one month to the
other is usually within ± 2°C
– However, daytime temp may be 34° C during
the day and 20° C at night.
• Much rain: annual rainfall ranges from
2,000 mm to 15,000 mm (79 – 591 inches;
1.6 inches per day).
• Wet and dry seasons
– Length of dry season determines the areas
ecology
Tropical Forest
• Long Dry Season
– Dry season = 6-8 months
– Many trees drop their leaves during the dry
season not to escape cold, but to prevent
overheating
• Short Dry Season
– Dry season < 3 months
– Tropical rain forest: 2,300 – 5,000 mm of rain
per year (extreme years some places may get
15,000 mm = 50 feet).
Tropical Forest (Rain)
• Huge diversity
– Perhaps 50 - 75% of all organisms on Earth inhabit
theses forests.
– Temperate forest may have 20 - 30 tree species per
hectare (2.47 acres); rain forests can support more
than 350 – 450 tree species per hectare
• To fit that many tress each species may only be
represented once or twice
• Most productive terrestrial biome
– High temp, moisture, uninterrupted growing
season
– Decomposers / nutrient cycling
Tropical Rain Forest
Tropical Mountains
• Go from tropical forest to shrubs to ice as
you move up in altitude.
– Similar phenomena seen as you move from the
equator north
Tropical Mountain
High
Alpine
Tundra
Elevation
Low
Tropical
Forest
Tropical Forest
High
Temperate
Deciduous Forest
Northern
Coniferous Forest
Moisture Availability
Arctic Tundra
Low
Tropical Mountains