• PRODUCTIVITY is production per unit time.
energy per unit area per unit time (J m-2 yr-1)
biomass added per unit area per unit time (g m-2 yr-1)
• PRODUCTION is the incorporation of energy
and materials into the bodies of organisms
• BIOMASS is the mass of organic material in
organisms of ecosystems.
• Usually expressed per unit area.
• Standing crop = ecosystem biomass.
GROSS PRODUCTIVITY (GP)
• is the total gain
in energy or
• Could be
or absorption in
NET PRODUCTIVITY (NP)
• is the gain in energy or biomass per
unit time remaining after allowing for
• Organisms use some of the energy they
capture to keep themselves growing
and alive (metabolism).
• The energy used by organisms for
essential tasks is called RESPIRATORY
ENERGY, and eventually it is released
to the environment as heat.
NP = GP – respiration
(for both producers and consumers)
When energy is released from ATP it is lost
as heat. (2nd Law of Thermodynamics)
GROSS PRIMARY PRODUCTIVITY (GPP)
• is the quantity of matter produced, or solar energy
fixed, by photosynthesis in green plants
• measured per unit area per unit time.
[Chemosynthesis and non-green plant autotrophs too]
• Energy enters an ecosystem through
• Only 2% of the light energy falling on a tree
is captured and turned into chemical
energy (glucose) by photosynthesis.
• The rest is reflected, or just warms up the
tree as it is absorbed.
Net Primary Productivity (NPP)
• The quantity of biomass potentially
available to consumers in an ecosystem.
• It is measured in unit of mass or energy per
unit area per unit time.
• Plants have to use some of the energy they
capture to keep themselves growing and
NPP = GPP - respiration
SECONDARY PRODUCTIVITY (SP)
• biomass gained by
• Not all food eaten is
into an animals body.
• Unassimilated food =
feces or droppings
SP = food eaten – fecal loss
In a food web you can
usually assume that:
• The energy input into
an organism = GP.
• The energy output to
the next trophic level =
• The difference between
GP and NP = R and/or
loss to decomposers.
1. Harvest method - measure biomass and
express as biomass per unit area per unit
2. CO2 assimilation - measure CO2 uptake
in photosynthesis and release by
3. O2 production - Measure O2 production
Measuring Primary Productivity
Radioisotope method - use C14 tracer in
5. Chlorophyll measurement - assumes a
correlation between amount of chlorophyll and
rate of photosynthesis.
What affects productivity?
• The least productive ecosystems are
those with limited heat and light
energy, limited water and limited
• The most productive ecosystems are
those with high temperatures, lots of
water, light and nutrients.
Swamps and marshes
Tropical rain forest
Northern coniferous forest (taiga)
Woodland and shrubland
Lakes and streams
Tundra (arctic and alpine)
800 1,600 2,400 3,200 4,000 4,800 5,600 6,400 7,200 8,000 8,800 9,600
Average net primary productivity (kcal/m2/yr)
Three years of satellite data on the earth’s GP.
LAND: high = dark green low = yellow
OCEAN: high = red IB/ESS blue
Not used by humans
Human use of
Lost or degraded land
Author-Guru Altered by human activity