Question

Arrange the following ecosystems in increasing order of mean NPP (Tonnes/ha/year).
a. Tropical deciduous forest
b. Temperate coniferous forest
c. Tropical rainforest
d. Temperate deciduous forest

Answer 1

Introduction to net primary productivity

Gross primary productivity refers to the rate of production of organic matter during photosynthesis.

Net primary productivity (NPP) refers to the remainder of the gross production which is left after its use by the producers in the process of respiration.

It is the biomass that is available to the heterotrophs in an ecosystem for consumption.

The productivity in tropical forests is always higher than that in the temperate forests because nitrogen-fixing bacteria are more active in the tropical regions.

Tropical deciduous forests

The annual net primary productivity of tropical deciduous forests is high but not as high as tropical rainforests as the trees of the forest shed all their leaves during the fall season.

Thus they are incapable of producing organic matter by photosynthesis during that period.

Temperate coniferous forest

Temperate coniferous forests have much less net primary productivity compared to temperate deciduous forests.

This is because the trees in the coniferous forests do not have a dense canopy and have leaves with lesser surface area.

This results in lesser photosynthesis and organic matter production.

Tropical rainforest

Tropical rain forests have the highest net primary productivity due to the availability of abundant light and water throughout the year and the presence of a wide variety and number of plants.

The NPP of tropical rain forests is around $2200{\text{gm}}^{-2}{\text{year}}^{-1}$.

Temperate deciduous forests

Temperate deciduous forests have lesser productivity compared to tropical deciduous forests because the amount and intensity of light available in the temperate zones is much less.

Increasing order of NPP

The order in which net primary productivity increases in forest ecosystems is -

$\text{Temperate coniferous forests}<\text{Temperate deciduous forests}<$
$\text{Tropical deciduous forests}<\text{Tropical rainforest}$

Or,
$b<d<a<c$

Final answer
$\left(d\right)b<d<a<c$.