You will also need to find a reasonable turnover rate for your location. The turnover rate is the rate at which living plant material dies and becomes plant litter (dead leaves, wood, roots, etc. which later become incorporated into soils). This is usually determined as the ratio of the amount of dead plant litter produced in a given year to the total amount of plant biomass present (the standing stock or pool size of plant biomass). In some cases, plants only live for one year or less (plants known as annuals). For these plants, their entire biomass dies each year, so the turnover rate is 1. In other words, 100% of their total biomass turns over each year. For plants that live more than a year - called perennials, the turnover rate will usually be some number between 0 and 1. For example, for many grasses, the above-ground portion of the plants die each year, but the roots can persist from one year to the next. Hence, the turnover rate for grasslands might be closer to 0.5, meaning that 50% of total biomass dies each year. For much larger and longer-lived plants like trees (some of which can live for hundreds or even thousands of years!), plant litter produced each year [twigs and branches that die and fall to the ground] is often a small fraction of the total biomass. The turnover rate in forests can be as low as 0.02 (2 % of standing live biomass dies each year).

Finally, in many cases, the amount of dead plant litter produced each year is approximately equal to the amount of new plant biomass that is grown. This often occurs when an ecosystem has matured and is no longer accumulating biomass, such as in an old-growth forest. In these cases, the turnover rate can be estimated using the growth rate divided into the total biomass because this will yield the same number as the death rate divided into the total biomass.

In order to complete this exercise, you will need to know the turnover rate for your chosen vegetation type or biome.