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
Climate and its
Effects
is
the average weather patterns for an area
Over a long period of time
(30 - 1,000,000 years).
It is determined by
Average Precipitation
and
Average Temperature
which are influenced by
latitude
altitude
ocean currents
and affects
where people live
how people live
what they
grow and eat
Four Global Temperature Regimes
Hot
• Tropical
• Temperate
• Subpolar
Cold
• Polar
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
Biome Types
• 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
‘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
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
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
Deserts
Cold, dry
air falls
Cell 3 North
Moist air rises — rain
Polar cap
Cell 2 North
Arctic tundra
Evergreen
60° coniferous forest
Temperate deciduous
forest and grassland
Desert
30°
Tropical deciduous
forest
Tropical
0° Equator rain forest
Mostly found in areas that
Hadley cells bring dry air.
Cool, dry
air falls
Cell 1 North
Tropical deciduous forest
30°
Desert
Temperate deciduous
forest and grassland
60°
Cell 1 South
Cool, dry
air falls
Cell 2 South
Polar cap
Cold,
dry air
falls
Moist
air rises,
cools, and
releases
moisture
as rain
Moist air rises — rain
Cell 3 South
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.
Polar Grasslands / Arctic Tundra
• 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
• 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 ± 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 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
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
High
Alpine
Tundra
Elevation
Low
Tropical
Forest
Tropical Forest
High
Temperate
Deciduous Forest
Northern
Coniferous Forest
Moisture Availability
Arctic Tundra
Low
Tropical Mountains