# How Is Biomass Calculated?

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## Introduction to Biomass

Biomass is an amount of biological matter, usually described in terms of net loss or net gain for a specific amount of time. This value is typically expressed in terms of dry weight, or it may be defined in terms of a single element such as carbon or nitrogen. The calculation can be used to assess changes to an individual, a population of individuals or an entire ecosystem. By knowing how to calculate changes in biomass, you can assess the health and fitness of a biological system, such as a forest or wetland.

## Biomass Calculation

It is always important to stipulate the time period for which biomass is calculated. Biomass is usually expressed as a net change in biomass because there can be significant changes to the biomass within the designated time period. The calculation is defined as:

?biomass(net) = increase biomass(gross) – decrease biomass(gross).

By subtracting the decrease in biomass from the gross increase in biomass, the net change in overall biomass for the specified time period is determined.

## Biomass Calculation Uses

The above equation can be used to investigate real world changes in biomass. For example, many forestry and logging experts are interested in the net increase of biomass for a forest stand (a group of trees in the same area that share similar characteristics, including age and size). By taking specific forestry measurements, the approximate gross increase of tree biomass for the stand can be calculated. However, the gross increase in biomass often does not equal the net increase in biomass. If an insect infestation attacked the trees, large biomass losses could occur. Also, storms and other weather could blow down a number of trees, making them useless to the forester. These losses must be assessed and subtracted from the calculated gross increase of tree biomass to truly assess the usable increase of net tree biomass.

#### References

• Principles and Standards for Measuring Primary Production; Timothy Fahey and Allen Knapp; 2007