This guide provides instruction on how to measure individual trees and forest stands. Download the Resource for the complete guide with tables and illustrations and a printable version.
Tree diameters are measured at DBH or Diameter breast height (4.5 feet from base of the tree).
The most common (and practical) tools used to measure dbh are the diameter tape (d-tape) and the Biltmore stick.
The total height (in feet) of a tree may at times be important. But, for most loggers, the amount of merchantable wood is what is of interest.
Total Tree Height
To determine the total height of a tree a clinometer is used. The clinometer measures the amount of rise in 100 feet. So the user paces out 100 feet, sights on the top of the tree and the stump and reads the scale on the clinometer. If viewer is uphill from the stump, measure from stump to eye level and add to tree height. If downhill, subtract.
To determine the number of sawlogs or pulpwood in a tree use the Biltmore stick. On one edge is something called a hypsometer which, like the clinometer triangulates the height but in this case in 16’ foot (or partial) logs.
To use the hypsometer, pace 66 feet (1 chain) from the tree. Hold the stick at 25” from eye and line botton of stick with stump - read number of logs or partial logs.
Forest Stands are measured for a variety of reasons including forest management planning, forest health monitoring and timber appraisal.
Each objective requires different information and level of detail.
Because it is not practical to measure an entire forest, most land managers use sampling techniques or small sample plots to gather information about an entire forest. A timber cruise (cruising) is a sampling technique that when applied systematically, is surprisingly accurate.
1. To plan a cruise you need some basic information
- a good base map with boundaries, aerial photos are also useful.
- A sense of the variation (of timber types) within the stand. Walk around the stand to assess whether the forest is uniform (for example a pure white pine stand) or has a lot of variation.
2. Establish sample points
- Forest measurement specialists feel a 10% cruise in a typical NH stand requires 30 points. If the stand has a lot of variability more points should be taken.
- Point centers must be evenly spaced across stand. Do not bias the sample by moving points into more desirable areas.
- The acreage is not as important to the number of points as the variability within the stand is. Start with 30 points. If the stand is variable add more points.
- The distance between the points will be based on the scale of the map. Use a compass and pace (or tape) to move from one point to another.
3. Collect data at sample point
Tools needed: compass, measuring tape, prism (description below), diameter tape or Biltmore stick, hypsometer, tally sheet.
- at point, you may want to poke a flagged stick into the ground (temporarily) to call the point, hold prism over the point and look at trees in a circle around the point. (see Figure 3 above)
- if tree is in, measure its diameter, merchantable height in logs. Record on tally sheet. Use a new tally sheet for each plot. Volumes may be recorded in the field or at office using Tally Sheet chart on page 9
4. Summarize data
- Use the shortcut formulas to determine volumes per acre.
Most New Hampshire loggers have heard the term basal area in relation to the NH timber harvesting laws.
Basal area is the cross sectional area of the stem at 4 ½ feet or breast height.
Basal area is also used by foresters to express the density or crowding within the forest. The prism is also used. To determine Basal area per acre the cruiser simply counts the number of trees that are “in at the point” and multiplies it by the prism factor x10, x15, x20 etc. The average basal area per acre figures can be compared with published “stocking guides” giving to the forest manager guidance on what the best density is for a given stand.