2: Conducting a Woodland Inventory – Activity

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Adobe PDF icon Download a printable version of the activity. Download a printable version of the Tree Tally Form and the Plot Tally Form.

How this helps you:

You typically can rely on a forester to take all the tree measurements needed to help you make woodland management decisions, but engaging in these activities will enable you to:

  • Learn the meaning of tree measurement terminology that may appear in your woodland stewardship plan.
  • Better understand the accuracy and reliability of tree measurements provided by a forester.
  • Assist a forester to take tree measurements (diameter, merchantable height, total height), determine wood volume per tree and per acre, measure basal area per acre and trees per acre, and read a stocking chart to determine if a stand is overstocked or understocked.
  • Monitor your trees and woodland more often.

Part 1 – Tree Measurements

Step 1. Measure tree diameter.

  • Step 1A: Read the chapter Introduction and Tree Measurements section on Tree Diameter (Adobe PDF icon PDF, pages 9-10).

  • Step 1B: Buy a diameter tape from a forestry equipment dealer or make your own. You can make your own from a non-stretch ribbon about 6 feet long. Cover each end with heavy piece of tape to prevent fraying. Place marks every 3.14 inches along its length. Number those marks consecutively 1, 2, 3… Each mark represents 1 inch of stem diameter.

  • Step 1C: Practice measuring stem diameter on trees of different sizes and shapes. To begin, stand on the uphill side of a tree and measure up 4 ½ feet from the ground. Note where this height hits your body so that you can take all diameter measurements at this height. Then measure the diameter of differently shaped trees, referring to Figure 2-1 (Adobe PDF icon PDF, page 10) as needed.

Step 2. Measure tree height.

  • Step 2A: Read about Tree Height (Adobe PDF icon PDF, page 11).

  • Step 2B: Make a hypsometer following instructions in Figure 2-2 (Adobe PDF icon PDF, page 11).

  • Step 2C: Practice measuring total tree height to the nearest foot and merchantable tree height to the nearest 8-feet using your hypsometer and the instructions in Figure 2-2 (Adobe PDF icon PDF, page 11).

Step 3. Evaluate tree defects.

  • Step 3A: Read about Tree Defects (Adobe PDF icon PDF, page 12).

  • Step 3B: Walk through your woodland evaluating defects on the each tree’s butt log (up to17 feet). Compare defects to the drawings in Figure 2-3, Figure 2-4, and photographs provided. Which defects reduce the total volume of usable wood? Which defects just reduce the wood quality?

  • Step 3C: Try estimating the percentage of wood volume in a log that is lost from crooks, cracks, decay, wire and other defects that reduce useful wood volume.

  • Step 3D: If possible, visit a sawmill to watch logs being sawn into lumber. Observe how different types of defects alter the appearance and usefulness of the lumber.

Step 4. Calculate tree volume.

  • Step 4A: Read the section on Tree Volume (Adobe PDF icon PDF, page 12-15).

  • Step 4B: Using your new knowledge, identify a tree by its species, measure its diameter at breast height (DBH) to the nearest inch, measure its merchantable height by counting the number of 8-foot logs, and estimate its percent sound wood (after deducting volume for defects). Record your measurements on the Tree Tally Form (Adobe PDF icon PDF version).

Tree Tally Form
Tree Tally Form

  • Step 4C: Look up the tree volume in board feet on Table 2-1 (Adobe PDF icon PDF, page 13) and the tree volume in cords on Table 2-2 (Adobe PDF icon PDF, page 15). Record those volumes on your Tree Tally Form.

  • Step 4D: Multiply each of those tree volumes by the % useable wood and record the net tree volume on your Tree Talley Form.

  • Step 4E: Practice measuring several trees and calculating their net tree volumes.

  • Step 4F: Your forester may recommend a different volume table designed for local use. Some of these volume tables have already factored in the percent useable wood so you do not need to estimate defect for each tree. Such tables are reasonably accurate for determining the percent useable wood across many trees in a stand, but may not be accurate for an individual tree. Tree measurements are not an exact science!

Part 2 – Stand Measurements

Step 5. Locate plots.

  • Step 5A: Read the section on Stand Measurements (Adobe PDF icon PDF, pages 15-16).

  • Step 5B: Taking stand measurements is generally the role of a forester, but you may be interested in measuring one plot to learn about the process and reliability of measurements and better appreciate the complexities. Identify a tree stand of interest for measuring its volume, growth rate, and stocking. A stand with only a few tree species and where the main canopy trees are more than 5 inches DBH would be very appropriate for learning.

  • Step 5C: Your plot must be located randomly within a stand, so while standing on the edge of the stand, take a compass bearing (azimuth) that will enable you to enter the stand, and walk 100 feet (or any pre-determined distance) into the stand following that azimuth. Put a stake in the ground to indicate your plot center.

  • Step 5D: You will measure trees on a 1/10 acre circular plot with a radius of 37.25 feet around the plot center. Be prepared to measure this radius using a tape measure or measured length of string attached to the plot center stake.

  • Step 5E: Use the Plot Tally Form (Adobe PDF icon PDF version) to record measurements in your plot.

Plot Tally Form
Plot Tally Form

Step 6. Measure basal area.

  • Step 6A: Read the section on Stand Density and Basal Area (Adobe PDF icon PDF, page 17).

  • Step 6B: Buy an angle gauge from a forestry equipment supplier or make your own 10-factor stick-type angle gauge using directions in Figure 2-6 (Adobe PDF icon PDF, page 16 – 17). Actually you can make an angle gauge from any small object of known width, such as a washer, penny, or thumb held at a fixed distance from your eye. Use the following formula to calculate the distance to hold the object from your eye for a 10-factor angle gauge:

    Distance from eye = width of object x 33

    For example, a thumb with a width of 0.75 inches should be held 24.75 inches away from your eye (0.75 x 33 = 24.75). You can maintain that distance while using the tool by stretching a string of the appropriate length between your eye and the object.

  • Step 6C: Most foresters use a prism to measure basal area, but an angle gauge is easier to learn, so we will describe its use here.

  • Step 6D: Use the angle gauge to measure basal area. An angle gauge is attached to a stick or chain so that you can place it at precisely the correct distance from one eye. Using the chain or stick, hold the angle gauge at the appropriate distance from your eye. Face toward a distinctive tree or a known direction (e.g., north, east…) and look at a single tree stem at breast height (4 ½ feet above ground) through the angle gauge. If the tree stem is wider than your gauge, count that tree. Turn your body to the right and look at the next visible tree stem. If that tree is wider than your angle gauge, count that tree. Continue turning to the right peering at every visible tree stem until you arrive back at your starting point.

  • Step 6E: How many trees did you count that were wider than your angle gauge? If you are using a 10-factor angle gauge, multiply the number of trees by 10 to calculate your basal area per acre based on that one plot. Record that basal area on your Plot Tally Form on the line provided near the top of the form.

  • Step 6F: Repeat this basal area measurement at several randomly located places in a stand. Average those measurements to determine the average basal area of a stand.

  • Step 6G: The recommended basal area for a particular forest type may be found in your woodland stewardship plan or in Chapter 6: Managing Important Forest Types (Adobe PDF icon PDF, page 55).

Step 7. Count trees per acre.

  • Step 7A: Face toward a distinctive tree or a known direction (e.g., north, east…). Use your tape measure or string to measure to the edge of the plot, a distance of 37.25 feet from the plot center. Count all trees larger than 4 inches diameter within 37.25 feet of the plot center. Continue re-measuring the plot radius as needed to determine which trees are within the plot. Record that tree count on your Plot Tally Form on the line provided near the top of the form. Multiply the number of trees per plot by 10 to determine the number of trees per acre and record that number on your Plot Tally Form.

Step 8. Measure tree DBH and height and calculate volume.

  • Step 8A: Use the skills you learned in Steps 1 through 3 above to measure the DBH and merchantable height of all trees in the plot that meet the minimum standards for merchantability, usually 4 inches DBH for pulpwood or 9 inches DBH for sawtimber. Evaluate each tree’s defects and estimate its percent useable wood.

  • Step 8B: Record on the Plot Tally Form (Adobe PDF icon PDF version) each tree’s

    • Species
    • DBH
    • merchantable height
    • percent useable wood.
  • Step 8C: Using the knowledge you learned in Step 4 above, calculate the tree volume and net tree volume of each tree in the plot. For simplicity you may wish to consider all trees to be suitable for sawtimber and use only Table 2-1 (Adobe PDF icon PDF, page 13) to calculate volume of the plot. Or you can consider all trees to be suitable for pulpwood and use only Table 2-2 (Adobe PDF icon PDF, page 15) to calculate volume of the plot.

  • Step 8D: Add up the net tree volume of every tree to determine total net tree volume of the plot.

  • Step 8E: Multiply the total net tree volume of the plot by 10 to determine total net volume per acre.

Step 9. Evaluate stand density with a stocking chart.

  • Step 9C: Go to the appropriate stocking chart based on your species composition. Using the basal area per acre and trees per acre shown on your Plot Tally Form, look for the intersection of those two lines on the stocking chart. If those lines intersect near the A line on the stocking chart, your stand may be overstocked and would grow more rapidly if thinned. Follow the nearest line for average stand diameter down to the B line to learn what the optimum stocking level would be. You can interpolate distances between lines.

Part 3 – Site Quality

Description: A site is a contiguous area with a more or less uniform combination of biological, climatic, and soil conditions. The quality of a site determines how well trees will grow. Common factors that determine a site are soil fertility and texture, moisture, climate, slope, and aspect. Site characteristics and their effects are explained more fully in Chapter 3: How Trees and Woodlands Grow (Adobe PDF icon PDF, page 28). In this chapter we focus on evaluating site conditions by evaluating and measuring tree attributes.

Step 10. Estimate site quality from existing trees.

  • Step 10A: Read the introduction to Site Quality and the section on Tree Quality (Adobe PDF icon PDF, page 20).

  • Step 10B: It sometimes is possible to evaluate site quality by looking at the condition of existing trees. This evaluation is most appropriate on a site where there has been little disturbance by logging, wind or other destructive forces and where the stand is fairly mature. If you have a mature, undisturbed stand of trees, then look at the tree stems. Mature trees on a good site tend to be taller, have straighter stems, fewer limbs on main stems, and longer merchantable stem heights, compared to trees of the same species on poor sites. Mature trees on poor sites tend to be relatively short with main stems that are often crooked or forked, and limby.

  • Step 10C: Evaluating existing trees is unreliable on sites that have been logged, even if there are existing mature trees, because past harvests may have high-graded the stand by removing the best trees and leaving the poorest quality trees. Other disturbances such as wind, floods, or fires also can badly damage trees and give a false indication of the underlying site quality.

Step 11. Measure site index.

  • Step 11C: Then look for a tree in your plot of your chosen species that has its crown in a dominant or co-dominant position in the canopy (see Figure 2-9, Adobe PDF icon PDF, page 20).

  • Step 11D: Measure the total height of that tree to the nearest foot.

  • Step 11E: Determine the age of that same tree to the nearest year. One of these methods for aging trees may be useful to you:
    • If the tree was planted, there may be a record of the planting date.
    • Or you could cut the tree down and count tree rings (see Figure 2-10, Adobe PDF icon PDF, page 21)
    • Or you could work with a forester who has an increment borer that can extract a core of wood (pencil shaped) on which you can count rings (see Figure 2-11, Adobe PDF icon PDF, page 21).
    • Or if you have a conifer tree that grows one whorl (layer) of branches each year, you can count whorls (see Figure 2-12, Adobe PDF icon PDF, page 21).
  • Step 11F: Using your total tree height and age, refer to the appropriate site index curves for your chosen species and find where the lines for those measurements intersect. Locate the curve closest to the intersection (you may interpolate between curves) and follow that curve to the right side of the chart. Read the site index on the right axis. This is the total height to which a tree could be expected to grow in 50 years regardless of its current age or height. If your site index is low among the set of curves, it is a poor site for your chosen species. If your site index is high among the set of curves, it is a very good site for your chosen species.

  • Step 11G: If the site index is low for the species of interest, you will be forewarned to limit your investments in that stand or to convert the stand to a different species that is better suited to the site.

  • Step 11H: If the site index is high for the species of interest, you can be more assured that your investments in management (e.g., thinning, pruning, regeneration) will pay off.

Step 12. Use understory plants as site indicators.

  • Step 12A: Read the section on Understory Plants as Site Indicators (Adobe PDF icon PDF, page 22).

  • Step 12B: Associations of understory plants have proven reliable as indicators of site quality. But a well-trained forester is required to make this evaluation because it requires the ability to identify dozens of understory plant species and access to books of information that relate the plant species to site quality. Appropriate indicator plants have not been determined in all locations. This method is appropriate for stands of any age, including stands that have been harvested or damaged. It is most convenient to use understory plants as site indicators during the growing season when indicator plants are visible.

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