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Biomes

The Ecosystem - Biomes Side 2

Environmental Systems and Societies June 2009

THE ECOSYSTEM - Biomes

By the end of this topic you should be able to:- SYLLABUS

STATEMENT ASSESSMENT STATEMENT CHECK NOTES

2.4

BIOMES

2.4.1 Define the term biome.

2.4.2 Explain the distribution and relative productivity of tropical rainforests, deserts, tundra and any other biome.



BIOMES

BIOME – a collection of ecosystems sharing similar climatic conditions, e.g. tundra, tropical rainforest, desert. The parts of the Earth which are able to support life, collectively termed the biosphere, contain four major habitats:-

• Terrestrial • Marine • Freshwater • Estuarine

Large areas of land with similar conditions and characteristic types of plants adapted to those conditions are called BIOMES. The distribution of these biomes is the result of an interaction between the communities inhabiting them and their physical environment. TEMPERATURE and RAINFALL

i.e.

are important in determining the distribution of biomes. In spite of the vast areas involved, and the complicating effects of mountain ranges, there is a global pattern to these biomes.



The relationship between the major terrestrial biomes and climate is shown below.

Q1. What other important factors would have a large influence on the distribution of

vegetation?



Due to the global differences in climate and limiting factors, the relative productivity of biomes i.e. the rate of energy production, can vary a great deal.

ECOSYSTEM TYPE MEAN NPP (kg m-2 yr-1)

MEAN BIOMASS (kg m-2)

*Tropical rainforest 2.2 45 Tropical deciduous forest 1.6 35

Tropical scrub 0.37 3 * Tropical grassland (savanna) 0.9 4

*Desert 0.003 0.002 Temperate grassland 0.6 1.6 *Temperate forest 1.2 32.5

Boreal forest (coniferous) 1.2 32.5 *Tundra and alpine 0.14 0.6

Open ocean 0.12 0.003 Continental shelf 0.36 0.001

Estuaries 1.5 1 NET PRIMARY PRODUCTIVITY (NPP)

– the amount of energy made available by plants to animals at the herbivore level. NPP depends on the amount of heat, moisture, nutrient availability, competition, the number of sunlight hours, the age of plants and the health of plants. In geographic terms NPP increases towards the equator, water permitting, and declines towards the poles.

BIOMASS

– the dry mass of organic material in organisms or ecosystems, usually per unit area..

The four biomes which we shall study in greater depth are:-

• Tropical rainforests • Tropical grassland (savanna) • Deserts • Tundra

The distribution and relative productivity of each biome must be explained with reference to the prevailing climate and limiting factors (various factors which limit the distribution or numbers of an organism).



Tropical rainforests

DISTRIBUTION OF TROPICAL RAINFORESTS AND OTHER TROPICAL ECOSYSTEMS

CLIMATE

Some features of climates in rainforest areas: • Annual temperatures are high (26-27ºC), owing to the

equatorial location of rainforest areas. • Seasonal temperature ranges are low, 1-2ºC, and diurnal (daily)

ranges are greater, 10-15ºC. • Rainfall is high (>2000 mm per year), intense, convectional,

and occurs on about 250 days each year. • Humidity levels on the ground are high, often 100%. • The growing season is year-round.

VEGETATION • The vegetation is evergreen,

enabling photosynthesis to take place year-round.

• It is layered, and the shape of the crowns vary with the layer, in order to receive light.

• Rainforests are a very productive ecosystem: NPP is about 2200 g/m2/yr, and there is a large amount of stored energy (biomass 45 kg/m).

• The ecosystem is diverse – there can be as many as 200 species of tree per hectare (an area the size of a rugby pitch), including figs, teak, mahogany, and yellow-woods.

SOILS: TROPICAL LATOSOLS



Savannas

CLIMATE • There is no such thing as a ‘typical’ savanna climate. • Rainfall in savanna areas ranges from 500-2000mm per

year with a drought lasting between one and eight months.

• Annual temperature are high (>25ºC). • Summers are hot and wet, winters hot and dry. • Convectional rain occurs in summer. • High temperatures year-round lead to high

evapotranspiration losses.

SOILS: FERRUGINOUS Savanna soils are influenced by distinct seasonal changes in processes. Moreover, they vary with topography. Frequently, sandy and/or leached soils predominate on the upper slopes, clay-based soils on lower slopes. This catena is reflected by changes in vegetation. In places laterite, a hardened layer of iron/aluminium, may limit further soil development and agricultural practices.

VEGETATION Savanna vegetation is xerophytic (adapted to drought) and pyrophytic (adapted to fire). Grasses predominate on sandy, leached soils, while trees may be found in moister areas, such as valleys. Growth is rapid in summer (NPP 900g/m2/yr).

Fire (natural and as a result of human activity) reduces the biomass store (4 kg/m). Grasses are well adapted because the bulk of their biomass is beneath ground level and they regenerate quite quick burning.

NUTRIENT CYCLE • The biomass store less than that of

the tropical rainforest due to a shorter growing season.

• The litter store is small due to fire. This means that the soil store is relatively large.

The savanna nutrient cycle differs from the tropical rainforest nutrient cycle due to the combined effects of the seasonal drought and the occurrence of fire. Consequently there is: (i) a lower nutrient availability (ii) a reduced biomass store (iii) a small litter store (iv) a relatively soil store



Distribution of arid and semi-arid environments

In desert areas a shortage of rainfall and high temperatures lead to a soil water deficit. Aridity is defined using the water balance. In arid regions there is a deficit in water balance over the year. In semi-arid areas the water balance fluctuates between the positive and negative.



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Example questions

1. The tundra contains many shallow lakes and bogs because:-

A. there is heavy snowfall in winter

B. weathering of rocks occurs unevenly

C. there is a lot of water from melting glaciers

D. the ground is mostly impermeable

2. For most desert areas, which of the following is correct?

Gross Primary

Productivity

Net Primary

Productivity

Biomass

A Low Low Low

B High High High

C Low Low High

D High High Low

3. The main deserts of the world are found at

A. latitudes between the tundra and temperate forests

B. lower latitudes than temperate and tropical forests

C. latitudes between the temperate and tropical forests

D. higher latitudes than the tundra



4. Which one of the following is most likely to have the highest gross primary

productivity?

A. An area of tundra in Norway

B. A area of tropical rainforest in Malaysia

C. A temperate forest in northern Canada

D. An area of desert in Australia

5. Describe the global distribution of tropical rainforest and tundra, explaining how abiotic factors influence the vegetation. (10 marks)

6.



KEY WORDS

TERM DEFINITION

ABIOTIC FACTOR A non-living, physical factor that may influence an organism or ecosystem, e.g. temperature, sunlight, pH, salinity, precipitation etc.

BIODIVERSITY The amount of biological or living diversity per unit area. It includes the concepts of species diversity, habitat diversity and genetic diversity.

BIOMASS

The mass of organic material in organisms or ecosystems, usually per unit area. Sometimes the term “dry weight biomass” is used where mass is measured after the removal of water. Water is not organic material and inorganic material is usually relatively insignificant in terms of mass.

BIOME A collection of ecosystems sharing similar climatic conditions, e.g. tundra, tropical rainforest, desert.

BIOSPHERE

That part of the Earth inhabited by organisms, i.e. the narrow zone (a few kilometres I thickness) in which plants and animals exist. It extends from the upper part of the atmosphere (where birds, insects and wind-blown pollen may be found) down to the deepest part of the Earth’s crust to which living organisms venture.

BIOTIC FACTOR A living, biological factor that may influence an organism or ecosystem, e.g. predation, parasitism, disease, competition.

COMMUNITY A group of populations living and interacting with each other in a common habitat.

ECOSYSTEM A community of interdependent organisms and the physical environment they inhabit.



ENVIRONMENT An organism’s physical and biological surroundings.

FOOD WEB The interconnection of organisms within several food chains.

HABITAT The environment in which a species normally lives.

LATITUDE The angular distance from the equator (i.e. north or south of it) as measured from the centre of the Earth (usually in degrees).

INSOLATION The amount and duration of incoming solar radiation.

PHOTOSYNTHESIS The process by which autotrophs (plants) make their own food by converting light energy into chemical energy.

PRODUCTIVITY, GROSS PRIMARY (GPP)

The quantity of organic matter produced, or solar energy fixed, by photosynthesis in green plants per unit area per unit time.

PRODUCTIVITY, NET PRIMARY (NPP)

Gross primary productivity less the biomass or energy lost by plants through respiration (R): NPP = GPP – R. The quantity of biomass potentially available to consumers in an ecosystem is indicated by NPP. It is measured in units of mass or energy per unit area per unit time.

PRODUCITIVTY, SECONDARY

The biomass gained by heterotrophic organisms, through feeding and absorption, measured in units of mass or energy per unit area per unit time.

RESPIRATION The breakdown of food to release energy.

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