Sampling And Statistics

Estimations of total values from plot sample data

Assume we have sampled n plots in a treatment unit (stand). On each plots, all trees have been measured. The stand has area A and we want to estimate some stand variable Y, given as a value per area unit Y_ha. Then the estimated value of Y is

where
estimated value in plot i, and
inventoried area of plot i

We then compute the estimated value of Y by simply multiplying with A (assuming that A is known):

In a prognosis, growth is computed for each plot separately, one period at a time (although treatments may be coordinated between plots). A prognosis model often include some variables that describe the density of the tree cover. For example, total basal area and stem density are common variables in growth functions, expressed as basal area per ha (m²)/ha) and number of trees per ha (trees/ha). Therefore, it is practical to keep all density variables at the plot level to a per ha-value.