Grassland Biomes

location, structure and functions

The 8 major biomes ofthe world

The temperate grassland biome

Prairies of North America

Pampas of South America Veldt of

South Africa

Russian / Mongolian Steppes

AustralianBush

Canterbury Plains, NZ

Steppe terrain in Russia and Mongolia• Undulating land dominated

by grasses• Large trees and shrubs are

mainly absent

Steppe climate

What do you think the general climate is likethroughout the year and why? (think aboutfactors such as latitude)

Cool temperate climate for steppe grasslands(warm temperate climate for Veldt)

Steppe climateWhat annual temperature range would you expect and why? (think about factors such ascontinentality)

Mean annual temperatures ranging from –15 inwinter to +20 in summer. Continental interiorresults in low temperatures during winter.

Steppe climateHow important would you think precipitation isfor grassland biomes? Why? Would they behigh rainfall biomes? Why / why not?

Precipitation is a dictating factor on grasslandbiomes and grass type – more rain generallymeans taller grasses. Low precipitation (notenough for trees) of around 250-500mm per year. More precipitation in western steppethan in east as there are less rain-bearingwinds. 75% of all precipitation falls during thesummer months.

Typical Steppe climate graph

What problems could this factor of low precipitation bring?

Threats of drought and fire.

Steppe climate

Temperate grassland soils

Chernozem (black earth) type

• Very deep, dark in colour with fertile upper layers• Nutrient rich from decay of surface matter in winter and

due to decay of deep, wide-branching roots – especially important for recycling of Ca.

• Approx 2m-deep grass rooting system helps keep the soil structure stable and intact (tightly-knit ‘sod’) reducing soil erosion and protecting underground stems and buds from winter frost and snow.

• Roots reach right down to the water table so there is a net upward movement of water.

• Ideal soils for farming but prone to wind erosion if ecosystem balance is not maintained.

A Horizon 0-50cmsOrganic matter on top. Strong drying action by winds. Crumbly black topsoil. Matted, random root network with accumulation of mull humus and bases Ca, Ng, Na, K and some Fe, Al and Si. Grasses extract and return minerals. Many biota such as earthworms – nutrient mixing and aids drainage. B1 Horizon 50-100cmsFine vertical roots. Slight leaching of nutrients especially after spring snow melt and summer storms. Loess

B2 Horizon 100-160cmsCalcification occurs - nodules of CaCo3 form. Loess

C Horizon 160-200cmsweathered parent rockLime-rich parent rock 200cms

Last lesson …• Where are the major areas of grassland biomes to be found?

• In terms of climate, what type of biome is Steppe?

• What did we find out about the climate in the Steppe biome?

• What type of soil is generally found in this area?

• Are these soils infertile? Why / Why not?

Why no trees?

• Thick grass cover – prevents tree seeds from taking hold.

• Low precipitation inhibits tree growth.• Fire destroys any trees that may take hold –

underground stems and buds of perennial grasses not affected by fire (as opposed to trees and shrubs that have above-ground stems and buds).

• Grazing animals quickly destroy emerging shrubs and sapling trees.

• Grasses are hardy and quick growing.

Steppe biodiversity

Low flora and faunadiversity when comparedwith tropical grasslandssuch as savanah.• Blue gramma and buffalo grass• Sagebrush and speargrasses

Flora

What advantages do you thinkthese grasses have for survival inthe environment that they live in?

• Narrow, spine-like leaves• Waxy or downy surfaces• Long, water-seeking roots• Below-ground stems and buds• Seeds easily dispersed by wind• Some grasses and their seeds release

inhibitory chemicals

FaunaLower biodiversity thantropical grasslands …

Small mammals(mainly rodents) • Gophers• Rabbits• FoxesOther mammals• Goats, antelope• HorseAlso• Reptiles• Birds• Many insect varieties

GPP and NPP in temperate grasslands

• Gross primary productivity is the amount of energy trapped in organic matter during a specified interval at a given trophic level.

• Net primary productivity is the amount of energy trapped in organic matter during a specified interval at a given trophic level less that lost by the respiration of the organisms at that level.

Tropical rainforest – 15000 Kcal/m2/yr

Comparative NPP rates in different biomes

Temperate forest – 5000 Kcal/m2 /yr

Temperate grasslands – 2000 Kcal/m2/yr

Desert – 500 Kcal/m2/yr

Nutrient Cycling

• In addition to energy, ecosystems also contain cycles of nitrogen and other plant nutrients, such as phosphates and potassium.

• The pattern of plant nutrients can be shown as a diagram. Nutrients are derived from weathered rock or in dissolved in rainfall and they may be lost from the system by leaching, in runoff or through harvesting of crops.

• Most nutrients are recycled within the system through plant uptake, leaf fall (and other “fallout” from plants and animals) and decomposition.

• Nutrients are stored in the biomass, the litter and the soil in variable quantities depending on the type of ecosystem and seasonal changes.

Mineral recycling

L

B

S

B

L

S

Tropical rainforest Steppe nutrient storage nutrient storage

S

B

L

Input dissolvedin rainfall

Release as litter decomposes

Uptake byplants

Loss in runoff

Fall out astissues die

Input weatheredfrom rock

Loss byleaching