What's a Tree Worth?
Goals of the Lesson
- The students should recognize and be able to use Biltmore tree scale stick (international quarter-scale rule) FC.78
- The students should know how lumber is sold and what a board foot is.
- The students should understand the difference between a log and a bolt.
- The students should be able to estimate the number of board feet expected from a tree.
- 100-inch tape measure
- paper and pencil
- one Biltmore stick for every three students FC.78
- several 66-foot pieces of mason twine with a 6-penny nail tied to the end.
- From the Woods: Incredible Wood and From the Woods: Hardwood Lumber booklets (one per student)
State Standards Addressed: Grade 10 & 12: Humans and The Environment (4.8); Grade 12: Agriculture and Society (4.4)
Subjects Covered: math, using a Biltmore stick, social issues, marketing, tree identification
Topics Covered: estimating distance, using Biltmore stick, estimated usable or marketable lumber, board footage, log lengths and bolts
"Trees are worth varying amounts to different people. A 2,000-year-old redwood tree as seen by a visitor to a national park is priceless. A large shade tree in our yard is greatly valued in summer when it's 100 degrees Fahrenheit and the sun is directly over our heads, but it seems to lessen in value as we toil in the fall to rake up its leaves and clean our gutters. A large red oak in our back yard has a different value than the same tree on a mountain being viewed by a forester. Today we're going to look at trees from a forester's viewpoint and be able to determine their volume in boards and also their value as they stand in the woods. "
Introduce students to some terms that you'll be using:
- DBH: "Diameter Breast High"; distance 4.5 feet above the ground where a tree's diameter is measured
- Biltmore Stick: A tree scale instrument that, when used correctly, will give the number of logs (16 feet) in a tree, the tree's diameter, and a table with expected board feet of yield in that tree
- Logs: 16 feet of log greater than 8 inches on its smallest end
- Bolts: 8-foot long log lengths
- Board Foot: The way finished lumber (once log is cut up into boards) is measured; one board foot equals 12 inches by 12 inches by 1 inch
- Merritt Hypsometer: A scale that when held 25 inches in front of your eye at a distance of 66 feet from the base of a tree can be used to calculate many logs are in that tree
- The students will move to a level soil or turf area (macadam can be used with 100-inch tape or chalk lines). The 66-foot pieces of mason line should be fastened to the soil at one end with the 6-penny nail and stretched to its 66-foot length and held by a student. Each student should then, at their normal pace, count how many paces they would need to cover 66 feet. This can be checked by removing the tight string and having them pace 66 feet off from the nail and then recheck. Once their paces are fairly accurate, write it on a piece of paper. My pace is 3 feet or 22 paces per 66 feet. Students having trouble may take the nail and string on to the next station.
The students will now move to a light standard or telephone pole to determine the number of logs in that upright using the Biltmore stick.
- Each student should pace off 66 feet from the base of the upright, then turn and face it.
- Now turning the Biltmore stick on edge, the student should see Merritt Hypsometer along the edge and number one to five spaces from bottom to top with one being on bottom.
- The student should grasp the stick at the bottom so that they can see from the bottom edge up to the top. Now, holding the stick directly in front of their eyes at an approximate distance of 25 inches, they should sight the tree with the stick's lower edge corresponding to the trees' base parallel with the trunk or pole.
- At a place where the students see a major defect or a "Y" or a diameter less than 8 inches on the pole or trunk, they should read the scale, which is in 16-foot log lengths. They should give it to nearest half-log length. For example, a two-log tree would be 2 on the scale and be actually 32 feet from ground to that point where log is no longer of commercial values.
- Each student should write down how many logs are in this sample, and the instructor should circulate and check their results.
The student group is now ready to move to a larger tree or group of trees.
- Once in the proper location, the students will each pace off their 66-foot length from the selected trees base.
- The student should be looking across the slope, not up or down, and should be using their knowledge and the Biltmore stick to determine the number of logs in the tree or trees to be scaled. The number of logs should be written as well as the name of the tree species being scaled.
- The student is now ready to determine the diameter and the board footage in that log. Each student should now walk to the tree and with the Biltmore stick held at arm's length and at breast height, they should turn the wide side of the stick toward them that says "Tree Scale Stick." With the stick held as above, they should sight so that it is directly in front of them and the left edge is aligned with the left side of the trunk. They should now move their eyes till the right side of the trunk corresponds to the scale along the top edge that reads "Diameter of Tree (inches)." If the trunk aligns with 24, it's a 24-inch diameter tree.
- Now the student should look to the left of the scale under "Diameter of Tree" at the one- to five-log length columns. They should then follow the column to the right and stop under the trunk diameter of that tree. If the tree was 24 inches in diameter and had two logs, it would have 441 board feet of finished lumber in it. If the tree has one-half or three-quarters of a log like such as 1.5 or 1.75, you may estimate or calculate the difference between the two log lengths as shown on the scale. A 1.5-log tree with a diameter of 24 inches falls between 251 board feet and 441 board feet. Subtract 251 from 441 and the difference is 190 board feet. Divide 190 by 2 for 95 extra board feet and add that to the original 251 board feet for a total of 346 board feet in the 1.5-log tree with a 24-inch diameter at breast height.
- The students should do several trees in addition to the original class tree to get a feel for using the stick. Each student could do their own tree if they are available.
- The instructor should now give the students the current market value on the stump that is being paid for that particular species and the board footage it contains. For example, a two-log red oak with a 24-inch diameter has 441 board feet. If a mill is paying $0.55 per board foot, then the tree is worth $241.55. Prices can be obtained by calling a local mill; this mill could also serve as a possible field trip.
- The students should then be taken to another site with a marked tree and instructed to calculate the board footage of that tree. These papers should be collected and the students evaluated on their comprehension of this task.
- The student should be given time to read From the Woods: Incredible Wood and From the Woods: Hardwood Lumber --two booklets dealing with lumber and wood in Pennsylvania.
A simple quiz can be given that would cover vocabulary as presented and materials found in the two Penn State pamphlets, with the quiz accounting for 50 percent and the evaluation tree accounting for the other 50 percent. Each student should achieve a score of 80 percent or better.
Hansen, Robert S., and James C. Finley (1996). Trees + Me = Forestry. University Park, Pa.: The Pennsylvania State University.
Smith, Sanford S., and Lee R. Stover (2002). From the Woods: Incredible Wood. University Park, Pa.: The Pennsylvania State University.
Smith, Sanford S., Roy Adams, and Anni Davenport (2000). From the Woods: Hardwood Lumber. University Park, Pa.: The Pennsylvania State University.
Ronald Fite, Dauphin County Technical School, Horticulture Dept., Grades 9-12