2.4 Biomes, zonation and succession

what determines the type of biome in a given area

the climate

what does succession lead to

climax communities

what are biomes

collections of ecosystems sharing similar climatic conditions

what are the main factors governing the distribution of biomes

insolation, precipitation and temperature

what does the tricellular model of atmospheric circulation explain

the distribution of precipitation and temperature influencing structure and relative productivity of different terrestrial biomes

what is zonation

the changes in a community along an environmental gradient due to factors such as changes in altitude, latitude, tidal level or distance from shore

what is succession

the process of change over time in an ecosystem involving pioneer, intermediate and climax communities

what does greater habitat diversity lead to

greater species and genetic diversity

why is gross productivity low in the early stages of succession

due to the unfavourable initial conditions and low density of producers

is there one set climax community

no, there is a set of alternative stable states for an ecosystem

what are the five major types of biome

aquatic (freshwater and marine), deserts, forests, grasslands, tundra

other than climate, what is the other major factor that determines what grows where

the terrain or geography: slope, aspect and altitude

what is climate made up of

general weather patterns, seasons, extremes of weather and other factors

what are the two most important factors that make up a climate

temperature and precipitation

what do ocean currents do

distribute surplus heat energy at the equator towards the poles

what causes the seasons on earth

the earth is tilted 23.5 degrees on its axis

what are the most important abiotic factors influencing biomes or what grows where

insolation, precipitation, temperature

what happens when the P/E ratio is much greater than 1

it rains or snows a lot and evaporation rates are low, there is leaching in the soil when soluble minerals are washed downwards

what happens when the P/E ratio is far less than 1

water moves upwards through the soil and then evaporates from the surface, this leaves salts behind and the soil salinity increases to the point that plants cannot grow (salinization)

what happens when the P/E ratio is approximately 1

the soils tend to be rich and fertile

why do different biomes have different productivity

they have different limiting factors

which latitudes have greater productivity

low ones

why do low latitudes have greater productivity

temperatures are high all through the year, sunlight input is high and precipitation is also high

what would temperate deciduous forests become if precipitation were higher

temperate rainforest

what would temperate deciduous forest become if precipitation were lower

temperate grassland

what are the five ways it is generally agreed that the climate is changing

temperature increase of 1.4-4.5C by 2100, greater warming at higher latitudes, more warming in winter than summer, some areas becoming drier, others wetter, stronger storms

what is the only way organisms can adapt to fast change

to move to areas where it is more favourable

what are the moves occurring as animal try to adapt to rapidly changing conditions

towards the poles where it is cooler, higher up mountains where it is cooler, towards the equator where it is wetter

what are some examples of biomes shifting

in Africa in the Sahel region, woodlands are becoming savannas, in the arctic, tundra is becoming shrubland

why can plants only migrate very slowly

because they need to rely on their seeds being dispersed by wind or animals

what are some natural obstacles to migration

mountain ranges and seas

what are some anthropogenic obstacles to migration

roads, agricultural fields and cities

what are some areas that are predicted to have a high turnover of species due to climate change

the himalayas - as species can move no higher than the land mass, equatorial eastern Africa - with a very drought sensitive climate, the Mediterranean region, Madagascar, The north American great plains and lakes

what are some new opportunities for exploitation of resources due to biome changing

drilling for oil under the Arctic ocean is becoming possible with the decrease in sea ice, the north-west passage for ships between the north pole and north America could become a trade route without icing up

what are tropical rainforests

hot and wet areas with broadleaved evergreen forest

where are tropical rainforests found

within 5 degrees of the equator

what is the typical rainfall in tropical rainforests

2000-5000 mm/yr

what are the average temperatures for tropical rainforests

26-28C

why is there high insolation in tropical rainforests

they are close to the equator

why may nutrients be limiting plant growth in tropical rainforest

rain washed nutrients out of the soil (leaching)

why do plants grow tall in tropical rainforests

they compete for light

describe the multi storey profile of a tropical rainforest

very tall emergent trees, a canopy of others, understorey of smaller trees and shrub layer under this, vines climbers and orchids live on the larger trees and use them for support

what is stratification

the division of the forest into distinct layers

what are epiphytes

plants that grow on other plants and use them for support

what are primary forests

those that are not logged by humans

why are there many niches and habitats for animals in tropical rainforests

there are so many plant species and a stratification of them

what kind of roots do plants have in tropical rainforests and why

they have shallow buttress roots to support them and because most nutrients are near the surface

how much of the NPP of terrestrial ecosystems is produced by tropical rainforests

about 40%

when is the growing season in tropical rainforests

all year round

why is there no net gain in large mature trees in tropical rainforests

all the glucose made in photosynthesis is used in respiration

how much of the human population lives in the tropics and the subtropics

more than 50%

what human activities destroy the forest

commercial logging and clear felling to convert the land to grazing cattle

what are some examples of tropical rainforests

amazon rainforest, congo in Africa, Borneo rain forest

what are deserts

dry areas which are usually hot in the day and cold at night

why are deserts usually hot in the day and cold in the night

the skies are clear and there is little vegetation to insulate the ground

what are the three types of deserts

tropical, temperate, cold

how much of the earths surface is covered by deserts

20-30%

where are deserts generally found (latitude)

about 30 degrees north and south of the equator

what factor is limiting in deserts

precipitation (water)

what is the average precipitation in deserts

less than 250mm per year

why are desert soils rich in nutrients

they are not washed away

what are most plants in the desert

cacti and succulents

what are some of the adaptations of desert plants to their environment

leaves reduced to spines, thick cuticles to reduce transpiration

what are the dominant animals in deserts

reptiles

how can small mammals survive in deserts

by adapting to be nocturnal

how is irrigation possible in deserts

by tapping underground water stores or aquifers

what is desertification

when an area becomes a desert, either through overgrazing, overcultivation or drought

what are some examples of deserts

Sahara, Gobi, Namib

what are temperate grasslands

fairly flat areas dominated by grassesand herbaceous plants

where are temperate grasslands found

in centres of continents 40-60 degrees north of equator

what is the P/E ratio in temperate grassland

P=E or P is slightly more than E

why is the temperature range high in temperate grasslands

they are not near the sea to moderate temperatures

why are temperate grasslands probably not a climax community

they are arrested by grazing animals

what does decomposed vegetation form in temperate grasslands

a mat with high levels of nutrients

what types of animals are found in temperate grasslands

burrowing animals, kangaroo, bison, antelopes, wolves, coyotes

are trees found in temperate grassland

no

what is the net productivity of temperate grassland

600g/m^2/yr

what are temperate grasslands used for by humans

cereal crops

what are cereals

annual grasses

what is an example of when overcropping brought about an ecological disaster

the dust bowl in 1930s america, overcropping and drought led to soil being blown away on the great plains

what is the effect of overgrazing on temperate grassland

it reduces them to desert or semi-desert

what are some examples of temperate grassland

north american prairies, russian steppes, pampas in argentina, veld in south africa

what are temperate forests

deciduous forests with a mild climate

where are temperate forests found

between 40-60 degrees north and south of the equator

what is the P/E ratio of temperate forests

P is greater than E

what is the rainfall in temperate forests

500-1500mm per year

what is the temperature range in temperate rainforests

-30-30C

what are the most common dominant species in temperate forests in britain

oaks

what is the growing season of trees in temperate forests

6-8 months

how much do trees grow per year in temperate forests

about 50cm per year

do woodlands show stratification

yes

what is beneath the canopy in woodlands

a lower shrub layer between 5 and 20 metres

what is the forest floor covered in in temperate forests

a thick undergrowth of brambles, grass, bracken and ferns

what are common epiphytes in temperate forests

mistletoe, mosses, lichens and algae

why is the soil brown in temperate forests

due to the leaching of humus and nutrients and the mixing by biota

which biome has the second highest NPP

temperate forests

why is the NPP of temperate forests lower than that of tropical rainforests

due to leaf fall in the winter, frozen soils can limit water, temperatures and insolation are lower in the winter too

what is an example of a temperate forest

US Pacific northwest

what is the tundra

a biome that is cold, low precipitation, long dark winters

how much of earths land surface is covered by tundra

10%