This case study looks at the response of a red pine plantation after a thinning. Some field foresters suggested that this stand has not responded to the thinning very well and wanted to know why.
Determine the cause of slowed growth following thinning and how to restore the productivity of the site.
Pre-treatment stand description and condition
Stand establishment and management history:
This site appeared to be a field/pasture in 1939 aerial photos. In 1947 aerial photos, it appeared to have been furrowed or plowed and possibly planted with trees. Unfortunately I could not find any planting or stocking records for this stand. According to the state forest inventory, this stand was planted in 1964.
Pre-treatment species composition:
2002 average BA in sq. ft. per acre:
- Red pine- 82
- Jack pine-32
- Aspen- 3.25
- Paper birch- 2
- White spruce- 0.48
- Bur oak- 0.48
- White pine- 0.08
- Northern red oak- 0.24
- Overall Basal area- 120.53
Pre-treatment forest health issues:
When cruised for the timber sale in 2002, the jack pine was of poor health or dead. No cause was specified.
A logger-select thinning in 2004 removed all merchantable jack pine and aspen from the stand and thinned the red pine to a residual basal area of 90 or 100 sq. ft. per acre, taking the red pine of poor quality first. A cut-to-length system processed trees at the stump. Spruce, oak, white pine, paper birch, and balsam fir were reserved. The goal of the project was increase growth of residual trees and reduce the fuel load within the stand to permit the use of prescribed burning.
What actually happened during the treatment
Red pine basal area was less than 90 in places, and the logger occasionally removed fewer trees than directed, so the result was a variable density stand with the highest basal area around 100 ft²/acre. Harvesting occurred during June and November, 2004.
The average diameter increment over the 11-year period before the thinning (from 1993 to 2004) was 23.95mm. In the 10-year period after the thinning (from 2005-2015), average diameter increment declined to only 17.53mm. In other words, mean annual increment actually declined by 19.8%, from 2.18mm to 1.75mm after the thinning.
Figure 1: 2015 stand picture
Species richness is similar to a natural origin stand in the same Native Plant Community (FDc24). Possible reasons for the decline of the red pine include armillaria, bark beetles, and weather factors. Pockets of dead trees could also suggest red pine pocket mortality. Red pine pocket mortality is pockets of dead trees that develop within a 30-45 year old red pine plantation after thinning. It usually starts with a few dead trees and then expands. The Wisconsin DNR and the USFS2 research center are trying to figure out why plantations are suffering from this. The Wisconsin DNR website1 suggests red turpentine beetles that transport Leptographium (Blue/black wood discoloration) disease are a factor. When working in the stand, Mike Parisio (MNDNR Forest Health Specialist) and I found armillaria rhizomorphs beneath the bark of dead trees and a red turpentine beetle, but no evidence of Leptographium disease. However, I consider red pine pocket disease is still a possibility in the decline of this stand.
Figure 2: Dead tree pocket within stand
Figure 3: Pockets of 3 dead trees or more
Figure 4: Armillaria sign on tree
Figure 5: Armillaria on tree
Figure 6: Bug damage on tree
Figure 7: Sap from turpentine beetle entrance
Plans for future treatments
We have several options:
1. Clear cut and regenerate red pine. This is the simplest and quickest way to handle the stand. This option would not alleviate the armillaria problem, and it would abruptly and dramatically change the appearance of a prominent landscape feature. Armillaria infection might be expected in half of the planted seedlings. Removal of stumps and roots might reduce infection of planted seedlings. (http://www.apsnet.org/edcenter/intropp/lessons/fungi/basidiomycetes/page...)
2. Cut gaps and allow for natural regeneration. Remove unhealthy trees as they become noticeable. Bur oak is the most abundant advance regeneration species at 1,787 stems/acre. The second most abundant is northern red oak at 433 stems/acre. The third most abundant is red maple at 270 stems/acre. This will promote a two-aged stand. Armillaria will likely persist in the stand which will affect the naturally regenerating red pine and oak within the stand along with the possibility of shoot blight diseases in regenerating pines. A percentage of existing oaks may be grubs, small trees with multiple stems. Grubs are conditioned from a long history of being top-killed by fires, so are unlikely to ever develop a merchantable form (conversation with Dr. John Almendinger, MNDNR Ecological Classification System consultant).
3. Cut gaps where armillaria is present and plant a variety of native tree species suited to the site to study armillaria resistance. I suggest this because I could not find any studies on armillaria resistance that had taken place in the Great Lakes region. A paper from the west3 suggests that Scots pine and Norway spruce species may be resistant and a website from the Pacific Northwest4 suggests that larch and birch are resistant. The MNDNR tree suitability table rates the following species as suitable for FDc24: (1) jack pine (2) quaking aspen (3) red pine (4) bur oak (5)paper birch (6) northern red oak.
4. If red pine pocket disease is proven to exist on this site, use this stand to study it and the effect of alternative treatments recommended by Wisconsin DNR.
Leaving the stand intact for a study could result in more tree mortality and financial loss.
I favor options 3 and 4, because studying stands like this now can help improve future management and minimize the damage caused by these diseases.
Summary / lessons learned / additional thoughts
This stand has been declining. While some possible reasons seem evident, I suggest conducting a long-term study to verify suspected causes or determine additional causes and identify effective treatment options.
Harvey was a staff forester at the MNDNR Northwest Region headquarters in Bemidji, MN. His primary focus was Ecological Land Classification and applications in silviculture. Prior to 2008, he was primarily involved in the timber program. He worked for the Minnesota DNR since he graduated from the University of Minnesota in 1978. Harvey passed away in July of 2022.