Basic Forest Measuring Tools Used by Foresters

An Essential List of Equipment Used to Measure Forests and Trees

 Here is a list of the basic tools, instruments and equipment necessary to measure a tree or an entire forest. Measuring tree diameters and heights, determining tree stem count and stocking levels, following compass mapping directions and boring age cores are essential. I have purchasing sources listed and linked.

Tree Diameter Tapes and Volume Tables
Tree Diameter Tapes and Volume Tables. Photo by Steve Nix, Licensed to About.com

Measuring a tree's diameter and height is fundamental to managing, buying and selling standing timber. There are two tape configurations, the diameter tape and calipers and they have various but important uses.

The diameter tape or D-tape is used primarily to measure a tree's diameter usually at breast or chest height (DBH) and is the most common tree measurement made on a tree by tree professionals. This tape has regular length measurements on one side and diameter conversions on the other using a hook is on the end of the tape for easy attachment to a tree. It is small and easily fits in a forester's cruiser vest (buy from Amazon).

Forestry Suppliers English Fabric Diameter Tape (buy from Amazon)

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

With calipers, you read the diameter at DBH (diameter breast high, 4.5 feet), then take a second reading at right angles to the first reading, and average the two readings.

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

Tree Calipers from Ben Meadows More »

Measure tree heights and slope
A Suunto Clinometer. Suunto-Amazon.com

The only other measurement made of a tree is as important as its diameter is also a tree's 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, to accurately measure tree heights on a slope, measuring topographic relief and in preliminary surveying measurements..

Suunto PM5/66PC Clinometer with Percent and Topo Scales (buy from Amazon)

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

A tree height reading has to be measured from a set distance from the tree.  Usually, the percent scale is used because the distance to measure from is in multiples or fractions of 100. 

logger's tape or self-retracting reel tape is primarily used to determine land measurements and felled timber and is generally built to withstand rough treatment. This automatic return reel tape is most often used to measure accurate distances to sample trees for tree heights and measuring felled logs.

66'/20M Spencer Logger Tape (buy from Amazon) More »

cruzall_anglegauge.JPG
An Angle Gauge. wikimedia commons

Angle gauges and prisms are used to select or tally trees in what is called variable area plot sampling.  The variable plot method is generally faster than fixed area plot sampling where you measure every tree on a circular radius equivalent to a part of an acre or hectare.

The gauge usually has basal area per acre factors (BAF) of 5 to 40.  The average diameter of the trees to be sampled is what determines which BAF to use.  The angle gauge comes in several shapes and serves the same purpose as a cruising prism (see cruising prism below). 

Cruising Angle Gauge (buy from Ben Meadows)

A prism is an ingenious wedged shaped piece of glass that will deflect the tree trunk image when viewed. That image either falls "in" or "out" by the deflection of the tree image through the glass as compared to the image.

Like an angle gauge , this optical device is used to tally trees in variable area plot sampling.  These prisms are also available in a range of basal area factors (BAF) to best fit the size of the trees you are sampling.  You select a BAF to give you 4 to 10 trees per sample plot.  The smaller the trees, the smaller the BAF to use.  Prisms are not used to tally dense sapling size regeneration. 

Calibrated Wedge Prism (buy from Ben Meadows)

  More »

Brunton Compass
Brunton Compass. Amazon.com

 The compass is a mandatory part of a forester's tool inventory. Compasses are not only used to run and maintain property boundary lines and define management units but a must for safe orienteering in unfamiliar forests and wildlands. 

Compasses used for forest work should have a way to set declination. The up-to-date magnetic declination for your area can be found by typing "magnetic declination" into a search engine and selecting the geomagnetic data site.

 A hand-held compass is adequate for most compass work and is compact and easy to carry. There is a time when more accuracy is necessary so a staff compass, a Jacob staff and a Gunter's chain would be needed.  

3 Compasses Selected by Foresters​ (buy from Amazon)

The fundamental unit of horizontal land measurement used by foresters and forest owners is the surveyors' or Gunter's chain  (Buy from Ben Meadows) with a length of 66 feet. This metal "tape" chain is often scribed into 100 equal parts which are called "links".

The important thing about using the "chain" is that it is the preferred unit of measure on all public U.S. More »

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Measuring Tree Age and Growth - The Increment Borer

Tree Core Samples
Tree Core Samples. Steve Nix, Licensed to About.com

Foresters use these 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 and takes a small (0.200 inch diameter) straw-like sample 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 core is reinserted into the core hole.

Tree Increment Borers (buy from Forestry Suppliers)

The Biltmore or Cruiser's Stick
The Biltmore or Cruiser's Stick - Determining Diameter. Photo by Steve Nix

The "Biltmore stick" or cruiser stick is an ingenious device used in cruising and measuring trees and logs and to estimate lumber. It was developed around the turn of the century based on a principle of similar triangles. The stick is still very much a part of a timber owner's tool kit and can be purchased at any forestry supply center. You can even make your own.

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

Scribner Tree & Log Scale Stick (buy from Amazon) More »