Essential Forestry Measurement Tools

Diameter Tape

Measuring a tree's diameter is fundamental to managing, buying, and selling standing timber. Diameter tape, or D-tape, is used primarily to measure a tree's diameter, usually at breast or chest height, the most common measurement made by tree professionals. This tape has regular length measurements on one side and diameter conversions on the other. It is small and easily fits in a forester's cruiser vest.

Tree Calipers

Calipers usually offer more precise data when measuring tree and log diameters. They serve the same purpose as diameter tape, but because they are often large and cumbersome they are usually only used in forest research where exactness is necessary.

Tree diameter calipers come in many sizes and materials. A small plastic caliper that measures 6.5 inches would be much less expensive than an aluminum caliper that measures 36 inches.

Clinometer

The only other measurement that is as important as a tree's diameter is its total and merchantable height. A clinometer is basic forest inventory tool for determining merchantable and total tree heights.

A clinometer can also be used to measure slope, which helps in laying out road grades, measuring tree heights on a slope, measuring topographic relief, and in preliminary surveying measurements.

A clinometer usually measures height either in percentages or topographic scales. To use this tool, you look into the clinometer with one eye while using the other to line up the instrument reference line with the tree reference points (butt, logs, total height).

Logger Tape

A logger tape is a self-retracting reel tape primarily used to make land measurements of felled timber. The tape is generally built to withstand rough treatment.

Angle Gauge

An angle gauge is used to select or tally trees in what is called variable area plot sampling. The gauge allows foresters to quickly determine which trees fall inside or outside of the plot. Gauges come in several shapes and serve the same purpose as a cruising prism.

Prism

A prism is an ingenious, wedge-shaped piece of glass that will deflect the tree trunk image when viewed. Like an angle gauge, this optical device is used to tally trees in variable area plot sampling. Prisms are available in a range of dimensions to best fit the size of the trees you are sampling. Prisms are not used to tally dense sapling regeneration.

Compass

The compass is an essential part of every forester's toolkit. It is not only used to run and maintain property boundary lines but also to safely orient oneself in unfamiliar forests and wildlands.

A hand-held compass is adequate for most compass work and is compact and easy to carry. When more accuracy is needed, a staff compass can be useful.

Surveyor's Chain

The fundamental tool for horizontal land measurement used by foresters and forest owners is the surveyor's or Gunter's chain, which has a length of 66 feet. This metal "tape" chain is often divided into 100 equal parts, which are called "links." The "chain" and "link" are used as units of measurement, with 80 chains corresponding to one mile.

Increment Borer

Foresters use tree borers to extract core samples from trees to determine age, growth rate, and tree soundness. Borer bit length normally ranges from 4 to 28 inches, and diameter normally ranges from 4.3 mm to 12 mm.

An increment borer is the least invasive way to count tree rings. It works by extracting a very small (0.2 inch in diameter) straw-like sample that runs from the bark to the pith of the tree. Though this hole is small, it can still introduce decay in the trunk. To prevent this, trees are limited to one bore every six years, and the extracted core is reinserted into the core hole after it has been examined.

Biltmore Stick

The "Biltmore stick," or cruiser stick, is an ingenious device used to measure trees and logs. It was developed around the turn of the century and was based on the principle of similar triangles. The stick is still very much a part of every forester's toolkit and can be purchased at any forestry supply center. You can even make your own.

These "woodland sticks" come in a variety of designs and are made of fiberglass or wood. They can be used to determine tree diameters and board foot volume. Some are designed to serve as walking sticks as well.