Stand Volume and Growth:
Getting the Numbers

2. Measuring stand volume and growth

Table 1 summarizes the necessary steps for measuring your stand, how to accomplish those steps, and the tools you’ll need to perform the task. Steps 1 through 4 explain the information in Table 1.

Step 1: Identify distinct stands Carefully select the area or stand you wish to sample. It should be relatively uniform in stocking (trees per acre or space between trees) and in size of trees. EC 1133 explains a procedure for dividing up your land into logical stand types. You can do this on an aerial photo, but you must verify your decisions on the ground by walking through the stand.

Here are some examples of how to deal with different stand characteristics: • If you have a timber stand with an area containing smaller diameter trees and another area where the trees are consistently and substantially larger (6 inches DBH or greater than the smaller trees), treat those two areas as separate stands. • If you have a few larger diameter trees mixed uniformly into a younger stand, sample it as one stand, but estimate the volumes separately based on different tarif numbers measured from the large and small trees. Combine the results to obtain total stand growth and yield. • If you have a distinct smaller area (1 to 3 acres) with poor stocking in a larger well-stocked area, exclude the smaller area from your sample and volume estimate and measure it separately. • If you have several ¼ to ½-acre openings scattered through a larger stand that is otherwise a uniform stand, sample the entire area. The confidence you place on your estimate may be lowered, but the numbers you generate will be more accurate than if you ignored the openings. • If you have a mixed species stand of conifers and hardwoods, sample each species separately and combine the volumes for total stand growth and yield.

Step 2: Choose a sampling plan Once you determine which areas are similar enough to be sampled together as stands, it’s time to make your sampling plan. In order to avoid any bias, it is imperative you locate samples with a predetermined system that relies on systematic measurements.

If you wander through your stand and pick likely looking spots, your estimates will be inaccurate. As EC 1133 shows you, mark intended plot locations on your photo or map. One plot per 1 to 2 acres will generally give you a good estimate for uniform stands, but more diverse stands will require a minimum of 1 plot per acre.

Step 3: Estimate the plot size you’ll need Your objective is to select a plot size that will give you five to eight sample trees per plot. The proper plot size to use for sampling depends on the number of trees per acre, which is directly related to distance between trees.

Before you leave for the field to begin this process, use Table 2 as a checklist to ensure that you have the proper equipment.

To begin, refer to the sampling plan you determined for the stand under step 2. Locate on the ground the point where you’ll start the sample.

Measure a straight line, in your planned compass direction, to the first plot center. The dots in Figure 1 represent trees in a hypothetical stand. An asterisk (*) marks the center point for your plot. Note that the plot center does not need to be a tree. It is simply the point where your measurement indicates the location of the plot center.

From your plot center, proceed to measure all the trees within a 26’ 4” radius. This is a 1/20th acre plot size and will often give you the proper number of trees per plot. If you do not achieve the desired five to eight trees after recording plot 1, don’t change your plot size as of yet.

Proceed along your planned compass direction, and in plot 2 measure the number of trees within the 26’ 4” plot radius. If you continue to have too many or too few sample trees after measuring 3 or 4 plots, then you should return to Plot 1 and adjust your plot size accordingly.

Remember: It is much better to have a few too many trees than not enough, so be sure you have an adequate plot size. Eight to 10 trees per plot may seem to be a lot of trees to measure and record, but it is much better than getting only two to four trees per plot and risk getting an inaccurate volume estimate.

Once you have obtained the proper plot size, continue with your sampling plan for the entire stand.

Step 4: Collect plot information Establish a plot (see Figure 2): Using point * as your plot center and the plot radius you determined on step 3, identify the trees within your plot. It’s not necessary to mark the entire outer limits of the plot, nor is it necessary to measure the distance to trees that are clearly “in” the plot. From the plot center, measure the distance only to trees that are near the perimeter.

As you traverse your compass line and reach the location for your next plot, immediately locate the plot center. Do not deviate from your compass line! Moving the plot center one way or the other to get more trees in the plot may overstate the actual stand volume. A temporary marker at the plot center (a flag or stick) is fine for most purposes. Establish a more permanent plot center if you have a long-range plan to sample the same stand repeatedly.

Measure tree diameters Recording Plot Trees: Moving in a clockwise direction from your compass line, begin recording the trees in the plot. Remember the first tree you measured so you don’t accidentally count it a second time. A tree is “in” the plot if its center falls inside the plot boundary. Measure DBH (tree diameter at breast height, 4.5 feet from the ground on the uphill side of the tree) and record these numbers on the Plot Trees section of the Tree Tally Card. Figure 3 is a completed Tree Tally Card for the Coleman’s Conifers. (A blank card is available in appendix C).

Be sure to read the key that explains the Tree Tally Card’s dot-tally system. Record diameters to the nearest full inch. If a tree measures exactly at the ½ inchmark, round the diameter down to the nearest full inch. Make a mental note of this decision and when encountering the next tree measuring at the ½ inchmark, record the diameter up to the nearest full inch. Repeat this process as necessary.

THIS SECTION GOES ALONGSIDE THE COLLECT PLOT INFORMATION Estimating plot size Ready to estimate plot size and location, you arrive at the first plot center by pacing off from the stand boundary. You will be able to measure virtually any timber stand with a 1/50th , 1/20th , or 1/10th acre plot. A 1/20 acre plot will be used as the default. After measuring 3 or 4 plots, you may find there are too few or too many trees per plot, so you return to Plot 1 and adjust the plot size accordingly. Stands that fall outside this suggested plot range should be discussed with a professional forester before proceeding with the sampling.

Recording tarif trees: The first tree on each plot is your tarif tree. Your tarif tree should be representative of the other trees in the stand. If the first tree is supressed, dead, or has a broken top, go to the second tree in the plot and use it as your tarif tree. You have already recorded its diameter on the Plot Trees section of your Tree Tally Card. You must now record its diameter and total height on the Tarif Trees section of the Tree Tally Card.

Pick a direction where you can see the top of the tree. Your estimates will be more accurate if you take your observations from about the same level as the base of the tree. Record its height to the nearest 5 foot increment on the Tarif Tree section of the Tree Tally Card. See EC 1129 for more information on measuring the heights of your trees.

Take increment cores for stand age and growth rates: If you have not determined the age of your stand from old records or by counting the growth rings on existing stumps, now is the time. If counting rings on an existing stump, remember to add the number of years since the stump was made.

To determine stand age using an increment borer, bore exactly horizontal into the center of the tree at breast height. Bore slightly more distance than the tree’s radius (bore 8 inches if the tree’s radius is 7 inches). You can recognize the center of the tree by viewing the direction of the slight arc in the growth rings from the extracted core (see Figure 5). Depending on site conditions, to properly determine stand age you will have to add 6 to 10 years (6 years for a high site, 10 years for a low site) to the number you obtained from your increment core. This number represents the number of years it took for the tree to grow to breast height.

Next, use your increment borer to take a growth rate measurement from your tarif tree. You can use the same core sample used in determining stand age. If you didn't use a core for the stand age, you need to bore only far enough to see the most recent 5 to 10 years growth (2 to 4 inches).

Count five growth rings from the outermost ring, and measure the distance in tenths of an inch (see Figure 3). Record this measurement in the 4th column of the Tarif Trees section of the Tree Tally Card.

You can store cores in a plastic straw and examine them later, but it’s important to label them properly and examine them before they dry out and shrink.

Use your compass and proceed to the second plot. Repeat all the steps used in measuring your Plot Trees and Tarif Trees on each of the other plots and record the information on your Tree Tally Card.

THIS SECTION GOES ALONGSIDE THE TARIF INFO. Taking plot data You’re ready to record plot information. (You’ll need to refer to Figures 1 and 2). You identify nine “in” trees on plot number 1 (see Figure 1). The 1st tree measures 12.2 inches DBH, so tally a dot under Plot Trees on plot number 1 next to 12 inches DBH. The 2nd tree is 13.3 inches and you tally a 13. The 3rd tree is 10.2, so tally a 10. The 4th tree is 14.1 and you tally a 14. The last tree on the plot is 15.4 inches DBH and you tally a 15-inch tree as the final plot tree.

Now you need the tarif tree for plot number 1. Remember: the first “in” tree on the plot is your tarif tree. The 1st tree measures 8.2 inches DBH, so you record an 8 in the DBH column under Tarif Trees. You measure its height as 84 feet, so record an 85 in the Height column. This tree had non-uniform growth over the past 10 years, so you measure the distance from the outermost 5 rings and find 2/10ths inch radial growth. Record this value in the radial growth column of the Tarif Trees.

The Tree Tally Card shows a completed sample of 10 plots for our example stand. The next step is to find a comfortable place to calculate the Tree Tally Card data and turn it into some valuable stand volume and growth information.

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