Tree Survey: Point-Centered Quarter Sampling Method

Overview

A number of methods are available for sampling forest communities. Point-centered quarter is one such method. It is used to gather information on the density, frequency, and coverage of tree species found in a forest. This information provides the ability to estimate the number of individual trees encountered, how often a certain tree occurs, how common the tree is compared to other trees, and the size of the tree. Compared to the standard plot analysis, the point-centered quarter method is more efficient, which is a major advantage. In a fixed-area plot sampling, a small portion of the total area of the forest is examined. In this small subsample, the density is determined directly by counting and identifying each tree. The ratio between size of the subplot and the overall forest size is used to determine the density for the entire forest.

Procedure

1. Tree Survey

Establish a 150 m transect in the forest.
Place a stake every 50 m. Each stake (point) represents the center of four compass directions (N, E, W, S) that divide the sampling site into four quarters.
In each quarter, the distance is measured from the stake to the nearest tree ≥ 40 cm, regardless of species. Only one large tree per quarter should be measured, so a total of 16 trees are recorded in the large tree category. Record the distance in cm for each.

Results

The point-centered quarter tree survey method produces three quantitative measures: the relative density, the relative frequency, and the relative basal area. These three values are added together to give the Importance Value of that species. This is then converted to a relative importance value (Table 5).

The importance value of a species can reach a maximum of 300 in a survey that only finds one species present. A high importance value does not necessarily mean that the spec

Application and Summary

Tree surveys are an important technique for both private and public stakeholders. They can provide helpful information to allow land managers to make informed decisions. A community may want to do a tree inventory to determine if there is a need for a forestry program. For example, the survey may reveal many dead or diseased trees (Figure 3) and indicate the need for more plantings. The survey may also help the community set up a maintenance schedule to prevent damage from hazardous trees. Lastly, the su

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