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 CB

Solar Energy

Rainy Season

Seasonal shift in rainy/dry seasons

Global Air Circulation & Regional Climates• Properties of air and water.

Cell 3 South

Cold,dry air falls

Moist air rises — rain

Cell 2 South

Cool, dryair falls

Cell 1 South

Moistair rises,cools, andreleasesmoistureas rain

Cell 1 North

Cool, dryair falls

Cell 2 North

Moist air rises — rain

Cell 3 NorthCold, dryair falls

Polar cap

Arctic tundra

60°

30°

0°

30°

60°

Polar cap

Evergreenconiferous forest

Temperate deciduousforest and grassland

Desert

Tropical deciduousforest

EquatorTropical rain forest

Tropical deciduous forest

DesertTemperate deciduousforest and grassland

Terrestrial Biomes of the World

• Tundra• Boreal Forest• Temperate Forest• Prairies and

Grasslands

• Chaparral• Desert• Tropical Forest• Tropical Mountains

Biome – a large geographical region having a defining climate to which plants show a similar physiological adaptation.

Temperature and precipitation regulate plant growth, thus the regional distribution of biomes.

Global Distribution of Terrestrial Biomes

Global Net Primary Productivity For 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

Net Primary Production of Terrestrial Biomes

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 < -12C).• 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 ± 2C– 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

AlpineTundra

TropicalForest

Tropical Forest Temperate Deciduous Forest

Northern Coniferous Forest

Arctic Tundra

LowHigh Moisture Availability

Lo

wH

igh

Elevatio

n

Tropical Mountains