Environmental Engineering Reference
In-Depth Information
above-ground biomass. In the prairie ecosystem this is the annual turnover of shoot
biomass, where
In this calculation total above-ground biomass includes the mean standing crops of green
shoots, dead shoots plus litter
Another useful descriptor of rates of turnover is
mean residence time
, which is simply the
reciprocal of the annual turnover rate, when the turnover rate is expressed as a decimal
fraction. Thus:
ECOSYSTEM PRODUCTION
Our knowledge of the production ecology of ecosystems has increased enormously since
the start of the International Biological Programme (IBP) in the 1960s. This world-wide
programme to learn more about the world's biomass was based on the theme 'the
biological basis of productivity and human welfare'. The aim was to solve the
fundamental equations of production ecology:
where GPP is gross primary production, NPP is net primary production, NEP is net
ecosystem production, R (A) is autotroph respiration, R (H) is heterotroph respiration and
B is biomass. Table 22.4 shows data on the primary biological productivity of the world's
main ecosystem types. This table shows the area of each of the named biomes, the mean
rate of NPP for each, the mean biomass of each, and the total biomass of each (mean
biomass × area).
In terms of the degree of dominance at the global scale, Table 22.5 shows the
proportion of the world's biomass which is found within each biome. Tropical forests
contain two-thirds of the world's biomass, and a further quarter is held within temperate
and boreal forests. Grassland contains only 5 per cent, whilst aquatic ecosystems are
