By Norma Kline

Have you noticed the wide array of tools used by foresters and wondered which ones might be useful for a small landowner? The decision to purchase forestry tools will depend on a landowner’s general interest in hands-on woodland management. Basic tools to consider include a compass for orienting, a loggers tape to measure distances and a woodland stick to estimate diameter and height. Other options include a diameter tape which can easily fit in a pocket and a clinometer used for height as well as slope. If you are interested in learning more about these tools check out the extension publications below in the reference section of this article. There are also more specialized and even more expensive tools like rangefinders that use laser technology; these are handy but would likely be most cost effective for professional use.

This article discusses increment borers and how they can help assess stand growth. Increment borers are used to extract a narrow wood core from a tree. The extracted core provides a clear view of the tree’s annual growth rings. Some increment borers are quite long, up to two feet or more and are generally used to core to the center of larger trees to determine their age. These long increment borers are expensive, over $600 and are cumbersome to carry. Luckily many landowners already have a good idea of tree age from planting records or by inspecting landscape changes using historical imagery in Google Earth.

Increment borers are useful for more than determining tree age. A very short (6 inch long) increment borer can be used to quickly assess how fast trees have been growing in the last 5-10 years. While even a short increment borer is pricey (approximately $200) it might be a worthwhile tool for landowners interested in monitoring the growth of young stands. Observing recent growth gives a good idea of competition (crowding) in a stand; as trees start to crowd each other, growth slows and the tree rings become closer together (Figure 1). In an even-aged stand, comparing the recent growth of dominant trees (trees that stick out above their neighbors) versus suppressed trees (trees that are completely overtopped) will show a marked difference in growth rings. The growth rings of a dominant tree will be more widely spaced than a suppressed tree. Dominant trees have more access to resources (light, nutrients, and moisture) than the overtopped trees. This process of tree competition where some trees become dominant is called differentiation. Self-thinning occurs when suppressed trees eventually die.

Landowners can intervene before growth slows by thinning the stand to decrease density. Thinning a stand helps free up resources, allowing the remaining trees to grow larger. A landowner can check how density is effecting growth by examining increment cores. Visual indicators of stand health are also helpful. As stand density increases, the length of the green crowns starts to shorten. Other indications of increased density are fewer shrubs and forbs growing in the understory. Landowners can quantify stand density by measuring tree diameter and numbers of trees in plots. This data can then be compared to a density diagram to to help make future management decisions (see references below). The decision to thin a stand will ultimately depend on landowner objectives.

The three pieces (handle, bit, extractor) of an increment borers fit together as a streamlined unit (Figure 2). To assemble, unscrew the extractor and gently slide out the bit and insert the bit through the handle (closing the latch). Start the borer into the tree at breast height (4.5 feet above ground) by exerting pressure and turning the handle clockwise (Figure 3). Make sure to keep the borer horizontal and continue turning the handle until the borer is about 2 to 4 inches into the tree (this should be enough to observe recent growth). Carefully insert the extractor into the core and turn the handle one half-turn counterclockwise to loosen the core for removal.

Extract the core (Figure 4) and observe the growth rings (Figures 5 and 6). An increment borer requires care to ensure many years of use. Be careful not to damage the cutting tip of the borer. If a piece of the core gets stuck near the tip, try to extract it in the same way you would remove the core. Never use the metal tip of the extractor or anything metal to dislodge a stuck piece from the cutting end. Starting the borer into another tree can help dislodge a stuck core. To avoid misplacing the extractor, tie a piece of bright colored ribbon to the extractor. Read more about the topics discussed in the links below.

Reference for further reading.

Tools for Measuring Your Forest. EC 1129. https://catalog.extension.oregonstate.edu/ec1129

Measuring Your Trees. EM 9058. https://catalog.extension.oregonstate.edu/em9058

Competition and Density in Woodland Stands. EM9206. https://catalog.extension.oregonstate.edu/em9206

Basic Forest Inventory Techniques for Family Forest Owners. PNW 630. https://catalog.extension.oregonstate.edu/pnw630

Trade-name products and services are mentioned as illustrations only. This does not mean that the Oregon State University Extension Service either endorses these products and services or intends to discriminate against products and services not mentioned.