Biomass (ecology)

Biomass 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 some applications, biomass is measured as the mass of organically bound carbon (C) that is present. In 2018, Bar-On et al. estimated the total live biomass on Earth at about 550 billion (5.5×1011) tonnes C, most of it in plants. In 1998 Field et.al. estimated the total annual net primary production of biomass at just over 100 billion tonnes C/yr. The total live biomass of bacteria was once thought to be about the same as plants, but recent studies suggest it is significantly less. The total number of DNA base pairs on Earth, as a possible approximation of global biodiversity, is estimated at 5.3e37, and weighs 50 billion tonnes. Anthropogenic mass (human-made material) is expected to exceed all living biomass on earth at around the year 2020. Ecological pyramid An ecological pyramid is a graphical representation that shows, for a given ecosystem, the relationship between biomass or biological productivity and trophic levels. A biomass pyramid shows the amount of biomass at each trophic level. A productivity pyramid shows the production or turn-over in biomass at each trophic level.