Many factors go into measuring trees' value
Sometimes people will ask, “What’s an acre of trees worth?” Obviously, a regular reader of Forest & People magazine would know that to answer that question, we need more information, which would be obtained on site.
Inputs like tree size, vigor, form, number of trees per acre is information that is generally collected with a timber cruise. Now is a good time to go over some of the basics of forest measurement.
To count, measure and value trees, we need some sort of inventory. We get this with a timber cruise. A timber cruise involves sampling a stand (or several stands) of trees to get good and statistically accurate information. To set up a timber cruise it is helpful for the landowner to begin with the end in mind.
It could be for management, a timber sale, damages, a right-of-way or estate planning. It could even be a single high value tree such as a residential or an historic tree. But that is a different type of appraisal.
For the manager, the diameter distribution, rate of growth, volume, etc., are important to make management decisions, both for now and for the future.
A timber buyer typically has a higher time preference. Assessing what is to be sold, he will be concerned about the accuracy of the estimate, including number of trees in the different diameter classes, species, overall quality of the trees, distance from the mills, fuel costs and market conditions.
Wildlife folks might be looking at habitat management.
For an estate, the value and basis as of a certain date are important.
For rights-of-way, well pads and access roads to them, the price for the timber contribution is usually negotiable, and is often more than the value estimated by cruise. However, it is good to go into negotiations knowing what you have. The negotiation is different when dealing with an entity with eminent domain and quick take authority, meaning that they will take it when they are ready and you can argue the value in the future.
As you can see, there is no simple answer to the original question. However, the basic process of obtaining the required information for most applications is similar. Here are several methods for cruising timber.
Plot Method
A grid pattern is set up based on the plot size and the cruiser will measure all the trees within a specific area. For example, for a 10 percent cruise, the cruiser may use one 1/10-acre plot per acre. After collecting all the field data, he will then use an expansion factor of 10 to get his estimate for the total volume.
Strip Method
Similar to plot in that a fixed area is cruised, say 10 percent, and then expanded to get the per acre estimate of the species mix, volume and value. Lines are established at prescribed intervals and widths, but no plots are set up. The cruise is continuous. This method works best with large, well-spaced trees on flat frequently prescribed burned ground. This allows the cruiser to drive between the trees and cruise from his air-conditioned truck (just kidding), although I have known individuals to cruise from horseback.
Point Method
The point cruise also uses a grid, but instead of the cruiser at the center of a plot, the individual tree is the center of its own “plot.” The bigger the tree, the bigger the plot. The cruiser sets a point at a predetermined location (the grid) and counts each tree that falls within a calculated distance based on the diameter of the tree. Rather than measure each distance, most cruisers will use a wedge prism or an angle gauge. This allows the cruiser to determine which trees are “in” or “out” without having to physically measure the distance to the tree.
However, use of the prism or angle gauge requires an unobstructed view of the tree to be tallied, which is a problem with thick underbrush. An additional benefit of using the prism or angle gauge is that a person can get an immediate idea of the Basal Area (BA) per acre at a given point. The BA is a measure of the stocking density and is estimated by the factor built into the prism or gauge.
Ideally, trees are well spaced within the stand. An old rule of thumb is the “D+6” method. Take the diameter in inches and add 6 feet to estimate the desired spacing for a tree of a given diameter. For example, the spacing on the 14-inch tree would be 20 feet. While not perfect, it does provide quick and useful information.
Tools used by cruisers include diameter tape, logging tape, compass, GPS, aerial photographs, hypsometer (height measurement), calipers, prism, angle gauge, range finder, snake gaiters, insect repellent and a tally book.
People selling timber on a pay-as-cut basis often ask how the mill calculates payment to the landowner. While it begins with a negotiated unit price of each product, it can get confusing with talk of board feet, form class, log scales, Doyle scale, weight conversation, defects, etc.
However, with few exceptions, incoming log loads are weighed. Then several variables such as the number of stems, diameter, length, quality, visible defects, etc., are applied to determine the volume to which the unit value is applied.
If you want to know more about this fascinating topic, keep reading your Forest & People magazine, visit the Louisiana Forestry Association website and peruse the Internet.
(David Lassiter is a consulting Forester from Mansfield. He can be reached at davidlassiter55@gmail.com.)
