Terrestrial Biomes

Weather - particular set of physical properties of the Earth’s troposphere:

–Temperature, pressure, humidity, precipitation, sunshine, cloud cover, wind direction and speed

Climate – a region’s general pattern of atmospheric or weather conditions, including seasonal variations and weather extremes over a long period.

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

Climate and its Effects

Climate

the average weather patterns for an areaOver a long period of time (30 - 1,000,000 years).

is

It is determined by

Average Precipitation Average Temperatureand

which are influenced by

latitude altitude ocean currents

and affects

where people live how people livewhat they

grow and eat

Four Global Temperature Regimes

• Tropical

• Temperate

• Subpolar

• Polar

Hot

Cold

Four Plant Types

• Succulent – vertical orientation on most parts, no leaves, store water, photosynthesis in tissue– Cactus

• Broadleaf Evergreen – keep most of their broad leaves year-round– Tropical trees

• Broadleaf Deciduous – drop their leaves when it gets cold (dry in the tropics) – Oak, maple, pecan

• Coniferous (cone-bearing) Evergreen Plants – keep their narrow pointed leaves (needles) all year– Pine, spruce, fir

• Forest – dominated by trees– A lot of precipitation needed

• Scrubland – small deciduous trees and shrubs– Some precipitation needed

• Grassland – dominated by grasses– Does not need as much precipitation as a forest– Usually needs disturbance to limit tree growth

• Grazing, fire

• Desert – dominated by succulents– Very little precipitation

Biome Types

‘For plants, precipitation generally is the limiting factor that determines whether a land area is desert, grassland, or forest.’

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

Boundary lines between biomes are not as distinct as implied here.

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

Desert

Desert Biomes

• Evaporation exceeds precipitation• Three types of desert depending on

average temperature– Tropical (Saudi Arabia)

• Always hot– Temperate (Reno, Nevada)

• Cool winter / hot summer– Polar (Northwest China)

• Cold winter / hot summer

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

DesertTropical deciduous

forest

EquatorTropical rain forest

Tropical deciduous forest

DesertTemperate deciduousforest and grassland

Deserts

Mostly found in areas that Hadley cells bring dry air.

Desert

Can also be caused by a rainshadow

Desert

• Soils– Often well draining (sand)– Often saline– Thin layer of organic matter

• Diversity– Low, but varies with precipitation

Desert Survival

• ‘Beat the heat’ and ‘Every drop of water counts’

Desert Vegetation

• Low-growing, CAM photosynthesis, waxy, reduced leaves

• Shallow roots (organic layer), long roots along waterways

• Allelopathy/well-spaced (chemical competition)

• Drought-resistant seeds.

Desert Vegetation

Desert plants can not escape the sun. Evolution has shaped them to minimize exposure to the sun.

Desert Vegetation

• Annual desert wildflowers and grasses store much of their biomass in seeds during dry periods and can remain inactive sometimes for years

• In only a few weeks after a rain:– Germinate, grow, flower, produce new seed, die

• Desert mosses and lichens– Can dry out completely and remain dormant

until the next rain (sometimes for years)– Some museum specimens have been known to

recover and grow after 250 years w/o water

Desert Animals

• Desert animals usually hide from the full strength sun and come out when the temp is lower– Some can become dormant during periods of extreme

heat and drought

• Seed eaters (herbivores) are common– Birds, ants, rodents

• Higher level carnivores:– Snakes, lizards, hawks, owls, coyotes, and some

foxes (precipitation dependant)

• Water conservation / recycling is key– Kangaroo rat

Grassland, Tundra, and Chaparral Biomes

• Enough average annual precipitation to allow grass to grow– Erratic precipitation and fires (and sometimes wind)

keep large stands of trees from forming

• Three types of grasslands determined by a combination of precipitation and temperature:– Tropical, temperate, and polar

Tropical Grassland / Savanna

• Warm temperatures, low to moderate precipitation, and a prolonged dry season (seasonally wet/dry)

• Have some deciduous trees that drop their leaves during the dry season– African savanna – acacia tree– Australian savanna (bush) – eucalyptus tree

• African savanna has large herds of hooved animals:– Grazers – grass and herb eaters (Thompson’s gazelles,

wildebeests, zebras) – Browsers – twig and leaf eaters (elephants, giraffes)– Reduce competition by eating different parts of the

vegetation

Temperate Grassland

• Seasonal extremes of hot and cold, precipitation falls unevenly throughout the year, windy– Can get very dry in summer and fall: promotes fire

• Except along rivers, tree growth is limited by:– Drought, occasional fires, and intense grazing

• Soil is very rich in nutrients– Most of above ground biomass dies each year– Great for growing crops (this can lead to high erosion rates)

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.

• 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.

• Cover about 10% of the Earth’s land surface, just south of the arctic polar ice cap

• Most of the year: bitterly cold, very windy, covered with ice and snow– Winters are long and dark

• Covered by low-growing plants, mosses, and dwarf woody shrubs adapted to– Lack of sunlight and water, freezing temperatures, and

constant high winds– Most growth occurs during the 6 – 8 week summer

growing season (almost 24 hr photoperiod)

Polar Grasslands / Arctic Tundra

Polar Grasslands / Arctic Tundra

• Average temperature is -5°C.– Water is held as ice for most of the year– Decomposition and nutrient cycling is very

slow; soils are very rich in organic matter (but poor in usable N and P)

– Each year, only the top meter defrosts, below that the ground remains frozen year round – Permafrost

– Water at the surface thaws, but cannot permeate the permafrost layer – mosquitoes like this!

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

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– Fires important

• 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

Forest Biomes

• Moderate to high average annual precipitation

• Three types depending on temperature:– Tropical, temperate, boreal (polar)

• All contain trees and various types of vegetation

Tropical Rain Forest

• Broadleaf evergreen forest found near the equator

• Warm annual mean temperature (little month to month deviation), high humidity, almost daily rainfall

• Distinct layers based on need for sunlight– Emergent layer – tallest trees (most sunlight)– Canopy – top of tall trees– Understory – small trees– Shrub – shrubs and short plants– Forest Floor – ground layer (least sunlight)

Tropical Rain Forest • Huge diversity (Different layers support different life)

– Perhaps 50 - 80% of all terrestrial organisms on Earth inhabit these 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

– Remember – nutrient poor soil!

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 Rain Forest

Tropical Deciduous Forests

• A little farther away from the equator

• Wet / Dry season– Lower canopy– Deciduous trees drop their leaves during the dry

year (some drought resistant evergreen trees)

• Long dry season areas = tropical scrub forests– Small deciduous trees and shrubs

Temperate Deciduous Forest

• Moderate average temperatures that change seasonally– Long, warm summers– Cold, but not too severe winters– Abundant precipitation, often spread evenly throughout

the year

• Dominated by broadleaf deciduous trees– Oak, maple, hickory, sycamore, and poplar– Relatively slow decomposition = high soil nutrients– More sunlight hits the forest floor

• Rich diversity of plant life at ground level

http://www.chenowith.k12.or.us/whs/mwc/tforest2.jpg

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

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