Sampling design must be carefully done to ensure that usable data are collected. Sometimes, the variation in tree size or age class may dictate using more than one plot size or sampling method, at the same time and the same plot center.

The technique for using more than one plot size around the same plot center is called “nested plots”. Various sized plots are used to sample different ages or tree sizes around the same plot center.

A simple example may be a stand of 50 year old hemlock that has been thinned and has seeded in an under-story. One might use a 20 Basal Area Factor Proportion Plot to sample the 50 year old element and a 100th acre fixed area plot to sample the seedlings. Additionally, there may be six very large Western Red Cedar trees over 100 inches in diameter. The entire population of this component of the stand could be 100% cruised.

The example above uses a combination of prism, fixed area plots and 100% cruising. If there were more of the trees 100 inches and larger in the stand, and we were not sure how many, a strip cruise could be used to sample those trees.

SuperACE 98 allows the combining of Basal Area Factors, up to three fixed area plots, up to three strip widths, 100% and one fixed area plot for seedlings. Each plot size must be taken at each plot center. If a plot size is blank, nothing is recorded, but the computer will consider the plot part of the total sample.

Each component of the stand needs to be identified prior to the cruise. The sampling system must match the components involved.

Success depends on using simple ground rules, documenting those rules and training the cruisers.

“Nested Plots” can improve the accuracy of a cruise and ensure that necessary data are collected.