Environmental Engineering Reference
In-Depth Information
Figure 22.5
Energy flows in natural grassland on the
Canadian prairies.
swept from the same plots. Green leaves and stems were separated from dead shoots. The
distribution of biomass in the various components is given in the left-hand pie chart in
Figure 22.5. These biomass values by themselves do not indicate the annual net primary
productivity (NPP), as productivity is a rate measure of biomass accumulation over time.
Also studies of populations and consumption rates of natural herbivores indicated that 26
g m
−2
of green plant material was consumed during each growing season in the
proportions indicated in the second pie chart in Figure 22.5. Underground parts were
studied by means of soil cores taken at monthly intervals from the same quadrats. They
were divided into 10 cm segments and the soil was removed by washing. An attempt was
made to separate dead material from live material, but it is not easy. It is difficult to
distinguish dead roots from live roots, and to decide what is current and what is old root.
Consequently a conservative estimate of annual root production was arrived at by taking
the difference between maximum and minimum dry weights in each layer, to a maximum
depth of 1·5 m. From Figure 22.5 it can be seen that net radiation for the growing season
of 240 days averaged 17,130 kJ m
−2
day
−1
. The percentage figures on arrows are
percentage net radiation if above the NPP compartment and percentage NPP if below the
NPP compartment. A useful statistic in describing ecosystems is the annual turnover of
