Line plot survey

Line plot survey is a systematic technique of laying out sample plots in a forest inventory within a rectangular grid. It is also an application of systematic sampling, similar to statistical properties as random sampling, but often easier to carry out.^[1]

Surveys typically are to collect information about seedlings, shrubs, invasive species, signs of wildlife, need for fertilization, timber species count, and/or similar purposes. For statistical control, all sample plots are a precise radius, typically 4 to 8 feet (120 to 240 cm), and must not include features outside each sampling circle.

Method

The method is used for forest inventories to accurately estimate the volume standing in a forested tract without counting every single item. Inventory specialists set up a line or bearing on their hand compass and determine how many plots to take on this survey line. This is done by determining the distance between survey lines (B), the distance between plots (D), and the surface area (A) in the tract. The number of samples to take is

The survey starts in a random distance by picking two random numbers between [0 and B] and [0 and D] for the first plot and line location. Then measure the length to the first plot, survey and repeat. Once at the boundary, turn 90° and continue on to the next transect.

Uses

The line plot survey has the advantage of insuring the inventory includes an even outlay and includes everything in the forested tract.

Examples of this are stand regeneration surveys to assess what is growing in a forest. Transect azimuth of 300° using plots one chain apart in one tenth acre then perhaps moving four chains to the next plot while still on the 300° (degree) bearing.

References