THE BENEFITS OF MARKING THE FIRST PINE THINNING
By Bob Daniels, PhD and Tom Ebner
The Mississippi Extension Publication 2260 by Tim Traugott entitled “Are My Pine Trees Ready to Thin” (1) gave private forestland owners some guidelines for determining when to thin their plantations. It also defined the goal of thinning “To reduce stand density by removing the slow growing, lower quality trees, thus maintaining rapid growth on the straight, healthy, vigorous, and evenly spaced crop trees.”
While Traugott established the “why” for thinning pine plantations he did not address the “how.” To phrase it differently, “What is the best way to thin a pine plantation in need of thinning?” His publication did not get into such questions as “what tree per acre level to thin to,” or “is there a financial penalty for delaying the thinning if pulpwood prices are low,” nor “should the stand be marked for thinning.” Economics can help answer theses questions and guide landowner decisions. In this article we address whether “operator select” or “marked” thinning is best.
We were interested in these questions and started installing permanent growth plots in thinned pine plantations in 1998. By the end of year 2005, plots were installed in approximately 100 different stands, 30 of which were fertilized. In this study, we focused on the 70 unfertilized stands. About half of these stands were thinned by the logging contractor (termed an “operator select thinning”). The other half of stands had every 5th row harvested. Then leave trees in residual rows were marked and all but marked trees were cut (termed a “marked thinning”). Some of the marked stands were marked by registered foresters, some by the timberland owner, and some by contract timber markers. These plots are located in east central Mississippi and west central Alabama, the area bounded by Pickens county, AL and Clay county, MS to Newton county, MS and Greene county, AL.
The age of the first thinning on these plots ranged from age 10 to age 23. The trees remaining after thinning ranged from100 trees/acre to 350 trees/acre. The marked thinnings had the leave trees marked.
To make a judgment which thinning method is preferred it’s necessary to know pre-thinning conditions in each stand so “before and after” comparisons can be made. The pre-thin stand conditions were very close to the same for both the operator select thinning and for the marked thinning. The stump diameters were measured on the thinned trees to determine the pre-thinning stand conditions. On average, the stands remaining after marked thinning had a 0.99 inch diameter gain. The operator select thinnings had a 0.67 inch diameter gain. The diameter gain from thinning is determined by comparing the average stand diameter before thinning with the average stand diameter after thinning. We call this after thinning diameter gain “diameter lift.” In 70 thinned stands, marked stands had an average .32 inches higher diameter lift over operator select stands. However the average marked stand had 34 fewer trees/acre after thinning and 8.6 square feet less basal area. Leaving fewer trees per acre would allow some additional gain in diameter lift.
The amount of “diameter lift” obtainable in the first thinning can be affected by a number of factors. The age when thinned has a lot to do with the amount of possible diameter lift. As you walk through an older stand, say 16 or older, you will see more variation in tree diameter than in a 10 or12-year-old stand. By age 16, many of the smaller, slower-growing trees will have lost most of their crowns as they have been overtopped by the more rapidly growing trees. This makes marking easier.
The quality of the trees in the stand can also affect the amount of potential diameter lift. The tree quality among stands does vary considerably due to the genetic quality of the original planting stock. Second generation genetic planting stock generally has better and more consistent tree form than the first generation which is normally an improvement over non-genetically improved planting stock.
What about growth after the thinning? On average the marked stands had an average annual diameter growth of 0.484 inches while the operator select stands had a 0.381 average annual diameter growth in stands first thinned between 10 and 19. The average age of the first thinning on the marked stands was 14.9 years while on the operator select stands it was 15.1 years. The average site index (base 25) was 71.5 for the marked stands and 71.9 for the operator select stands.
The amount of “diameter lift” from thinning is important to growth. Since in a plantation the trees are all the same age, the largest trees are the fastest growing trees. If these trees were the fastest growing trees before thinning, it is reasonable to assume that they would also be the fastest growing trees after thinning. Therefore, by retaining more of these larger trees in the thinning the average stand diameter growth should be increased. The marked stands in our sample had an average of 27% greater diameter growth per year than did the operator select stands.
One of the objectives of thinning identified in the Traugott article was to remove the lower quality trees. From a timber management perspective, the “lower quality” or “poor quality” trees are trees which will remain pulpwood quality regardless of size or age. Therefore, they should be removed as soon as possible. “Poor quality” trees were graded as trees with a fork in the first sixteen feet and trees with excessive sweep or crook. In the marked stands, 5.2% of the remaining trees after the first thinning were poor quality trees. In the operator select thinnings, 14.2% of the remaining trees after the first thinning were poor quality trees.
The skill of the operator or the marker also plays a part in determining what diameter lift you can achieve in the first thinning. For example, if you have 600 trees per acre before thinning and you remove 400 trees per acre you create the opportunity for more diameter lift than if you only remove 200 trees per acre. In the marked stands thinned at age 16, the diameter lift from the thinning varied from 1.30 inches to 0.05 inches. For a first thinning at age 16 in an average site 70 stand (base age 25) the Present Value of an inch of diameter lift in the thinning is approximately $100/acre. This suggests that an incentive clause in the thinning contract which relates to diameter lift and the residual tree quality would help the landowner to insure the quality of the thinning job.
First thinning marking costs in MS are approximately $40-50 dollars per acre. (2) Therefore, if you can gain 0.50 inches of diameter lift by marking, you can offset the marking cost.
The financial return from a first thinning at age 10 through age 19 was tested at different stocking levels after the first thinning (using a proprietary growth model) which ranged from 275 trees per acre to 100 trees per acre. These stands were then grown to the age of the second thinning. The Present Value of the stand at the second thinning plus the value of the thinning removals at the first thinning were then discounted to age 10 at a 10% and 6% discount rate. When all these factors (better growth, larger diameter lift, and better tree quality) are put together for an average stand, the best thinning combination (highest present value at age 10) was an age 13 thinning leaving 200 trees per acre for a marked thinning. For an operator select thinning the best combination was an age 12 thinning leaving 225 trees per acre.
For the marked thinning at age 13 and then grown to age 22, the stumpage value of the stand prior to the second thinning was $2570/acre. For the operator select thinning the stumpage value at age 22 was $2105/acre or $465/acre less.
If the marking cost was $50/acre, the return on investment for the additional cost of marking is 28% for an average quality marking.
In the above example, the modeled stand was thinned at age 13 and the value comparisons were made at age 22 when the marked stand would be ready for the second thinning. In this projection the marked stand would have grown from a basal area after thinning of 61.0 to a basal area of 132.2 at age 22. The operator select stand would have grown from a basal area of 61.1 to a basal area of 118.4.
The better diameter growth after thinning in the average marked stand increased the basal area growth over the operator select thinning by 13.9 square feet over this nine-year period between thinnings. By age 22, the marked thinning has an average diameter of 11.44 inches while the operator select stand has an average diameter of 11.04 inches.
These findings suggest that landowners can greatly improve their timber investments by using marked thinnings. Marked thinning results in higher quality residual stands, increased diameter growth and higher stand present value prior to the second thinning than in operator select thinning. Costs for marking are easily justified by increased stand value.
Few timberland owners have an average stand. In order to determine the quality of the thinning or the quality of the marking, the owner must know some basic facts about the condition of his stand before thinning. The owner should know the average number of trees per acre and average diameter as discussed in the Traugott publication. The owner should also know the percent of sawtimber quality trees in his stand.
These variables are relatively easy to determine as described in the Traugott publication. The only addition is to determine the tree quality in the stand. Trees with a fork in the first sixteen feet were called “poor quality” trees as well as trees with excessive sweep or crook.
Bob Daniels is a Realtor and Timberland Investment Specialist with Century 21 in Starkville, MS. He recently retired as Extension Forestry Professor at Mississippi State University. He can be reached at firstname.lastname@example.org.
Tom Ebner is a Forestry Consultant in Columbus, MS. He is retired from Weyerhaeuser Company and co-author of the book Timberland Investments published in 1992 by Timber Press in Portland, Oregon. He can be reached at email@example.com.
The complete study from which this paper was developed is approximately 35 pages. If you would like a copy please send a $5 check for copying and mailing to: Mr. Tom Ebner, Consulting Forester 468 Petersburg Drive, Columbus, MS 39702.
1. Traugott, Timothy A. 2000. Are My Pine Trees Ready To Thin?. Mississippi State Extension Service. Publication No. 2260. 7 pp.
2. Consultation with several practicing foresters in the area.