Contents

Idea

As defined by Wikipedia:

Biomass, in ecology, is the mass of living biological organisms in a given area or ecosystem at a given time. Biomass can refer to species biomass, which is the mass of one or more species, or to community biomass, which is the mass of all species in the community. It can include microorganisms, plants or animals. The mass can be expressed as the average mass per unit area, or as the total mass in the community.

How biomass is measured depends on why it is being measured. Sometimes the biomass is regarded as the natural mass of organisms in situ, just as they are. For example, in a salmon fishery, the salmon biomass might be regarded as the total wet weight the salmon would have if they were taken out of the water. In other contexts, biomass can be measured in terms of the dried organic mass, so perhaps only 30% of the actual weight might count, the rest being water. For other purposes, only biological tissues count, and teeth, bones and shells are excluded.

In stricter scientific applications, biomass is measured as the mass of organically bound carbon (C) that is present. The total live biomass on earth is about 560 billion tonnes C, (see B Groombridge et al) and the total annual primary production of biomass is just over 100 billion tonnes C/yr.

The total global live biomass has been estimated as 560 billion tonnes C, most of which is found in forests.

Details

Most of this biomass is found on land, with only 5 to 10 billion tonnes C found in the oceans.

On land there is about 1,000 times more plant biomass (phytomass) than animal biomass (zoomass). About 18% of this plant biomass is eaten by the land animals. However in the ocean the animal biomass is nearly 30 times larger than the plant biomass. Most ocean plant biomass is eaten by the ocean animals.

The total biomass of bacteria is estimated to equal that of plants. The number of prokaryotes on Earth is estimated to be around five million trillion trillion, or $5 \times 10^{30}$, accounting for at least half the global biomass.

References

• M. Rodell et. al Earth Interactions Volume 9 (2005) Global Biomass Variation and Its Geodynamic Effects: 1982–98

ABSTRACT: Redistribution of mass near Earth’s surface alters its rotation, gravity field, and geocenter location. Advanced techniques for measuring these geodetic variations now exist, but the ability to attribute the observed modes to individual Earth system processes has been hampered by a shortage of reliable global data on such processes, especially hydrospheric processes. To address one aspect of this deficiency, 17 yr of monthly, global maps of vegetation biomass were produced by applying field based relationships to satellitederived vegetation type and leaf area index. The seasonal variability of biomass was estimated to be as large as 5 $kg m^-2$. Of this amount, approximately 4 $kg m^-2$ is due to vegetation water storage variations. The time series of maps was used to compute geodetic anomalies, which were then compared with existing geodetic observations as well as the estimated measurement sensitivity of the Gravity Recovery and Climate Experiment (GRACE). For gravity, the seasonal amplitude of biomass variations may be just within GRACE’s limits of detectability, but it is still an order of magnitude smaller than current observation uncertainty using the satellite-laser-ranging technique. The contribution of total biomass variations to seasonal polar motion amplitude is detectable in today’s measurement, but it is obscured by contributions from various other sources, some of which are two orders of magnitude larger. The influence on the length of day is below current limits of detectability. Although the nonseasonal geodynamic signals show clear interannual variability, they are too small to be detected.

• Biomass, Wikipedia.

• B. Groombridge and M. D. Jenkins, Global Biodiversity: Earth’s Living Resources in the 21st century, World Conservation Monitoring Centre, World Conservation Press, Cambridge, 2011, page 11.