Number of trees

Number of trees in a stand
Forest Measurement and Modelling.

Estimates of the number of trees in a stand may be needed to assess the success of regeneration or as input into an indirect measurement technique (e.g. Tarrif equations for stand volume). The number of trees may also be compared with a management ideal to determine if the stand is over- or under-stocked.

The number of trees in a stand is usually only a useful parameter when the trees are of similar size and age, e.g. a well-regulated plantation.

The number of trees in a stand is often reported as trees / ha and may be calculated from:
  • Fixed area plots;
  • Quadrants;
  • Point-to-plant methods;
  • Point sample.

The number of trees on a fixed area plot is divided by the area of the plot to give an estimate of the trees / ha. A number of randomly selected plots can provide an unbiased estimate of the mean and standard deviation of the stand. The other methods can also provide unbiased estimates when the trees are randomly spaced throughout the stand. However, when the trees are clumped, or gaps occur, these methods may result in biased estimates of the standard deviation.

The point-to-plant method estimates the average area that four trees (or n trees) occupy. From a randomly selected point, nominate the fourth and fifth (n and n+1) trees and measure the distance from the point to these trees. The four (n) trees occupy the space in a circle whose radius is the average of distances between the forth and fifth trees. If four trees occupy X ha, then there are 4/X trees per ha. This method is very fast and particularly useful for estimating the regeneration levels when there are many stems / ha and the distance to the n+1 tree is small.

Point samples estimate the basal area / ha (m2/ha). To estimate the number of trees from a basal area estimate, divide the stand basal area by the average tree basal area.

[number.htm] Revision: 6/1999