Using an Increment Borer to Take Core Sample
When you age a pine tree, you basically count the growth rings you see in the cross section of the tree. Each year, the tree will put on a summer ring and a winter ring. The summer ring is whitish, and the winter ring is brownish. It is easiest to count the dark rings. I have counted over 200 rings on large pine trees.
If you want to know how old a tree is in your yard, you probably don’t want to cut the tree down. There is a tool that is called an Increment Borer. This tool enables you to take a core sample (cylindrical plug) out of the tree. The tool has a hollow tube with threads on the end that is a little smaller than a pencil which is screwed into the tree. Once screwed into the tree to the depth of half the diameter of the tree (center of tree), another part of the borer is inserted into the tube to wedge the core. Then the borer is backed out a few turns to break the sample free. The wedge is then pulled out bringing the core sample out so you can see the sample plug. When the sample is extracted, the increment borer is then screwed back out. There will be a small hole in the tree that will fill up with sap and close back up. There is no damage to the tree.
What You can Learn from the Core Sample
Now that you know how to take the sample and you have the core to examine, it is time to analyze the sample. Many things can be learned form the core sample. What you now have is the history of the tree.
First, you count the rings, giving you the age of the tree almost. The first few years the tree does not have rings. For loblolly and slash pines, we add two years. For longleaf pines, we add three years. The rings are called “growth rings”. These rings may be wide for fast growth or very close during survival mode. We can tell when there were drought years by the rings. We can tell when the trees were thinned by the increase in width of the rings. Growth rate can be determined by the width of the rings and number of rings in the outside inch of the tree.
It is also very interesting to look at ages of trees in stands as we thin them. Some trees are three to six inches in diameter with very little crown or top and some are twenty inches in diameter. Both are the same age. Growth rings on the smaller, stunted trees are so close together you can hardly count them. That is clear indication to harvest them for they are not growing, are competing for nutrients from dominant trees and are nothing but clutter in your stand. Management requires the less desirable trees be harvested and the healthy trees with wide growth ring, (dominant and co-dominant trees) be saved for maximum return in investment.
Using Core Sample to Determine Site Index
Site index (SI) is also determined by age of tree. Site index is a measure of soil quality for timber. A site index curve is utilized to determine the site quality based on an age of 50 years and the height of the tree. You determine the age of the tree from the rings and the average height of the dominant and co-dominant trees. Once you have this data, you can plot the soil quality or site index on the site index curve. There are site index tables to help you understand how this applies to your land and timber. Basically, SI 70 is average and SI 80, and above is good. This data will provide you some indication of your Return on Investment of your timber investment.
As you can see, growth rings provide quite a bit of information. When we are working with clients and we bore their trees, they are often surprised at the results. The Increment Bore is a very helpful and meaningful management tool, providing a very tangible example of the stand health and stand potential. Some trees growth rings are 20 rings per outside inch of tree. This means the tree has very slow growth and needs some management decision made. Some trees have 10 or less rings per outside inch. This means they are very healthy and fast growing, indicating a younger pine plantation in excellent soils with excellent management.
Green Hill Land & Timber understands all these factors, tools and management prescriptions. We utilize these tools to help our clients get the best outcome for their management objectives and goals. Let us know if we can meet and share options that would help you with your timber in investment.