Variable Density Thinning in Red Pine (Carlton County)

State or Province
Nearest city or town
Describe the location
Eastern Carlton County near Minnesota-Wisconsin border
Carlton County
Cover type
Plant community detail and growth stage
Forest health threats
Adaptive silviculture options
Silviculture system
Estimated year of stand origin
Site index
65 feet
for species
Red pine
Brief silvicultural objective
Develop a more structurally diverse red pine stand while increasing opportunities for natural regeneration while maintaining an economically feasible timber harvest
Site preparation method
Soil texture
Soil details
Omega loamy sand
Stand area
56 acres
Treatment area
56 acres

46.442952, -92.437795


The Carlton County Land Department manages tax-forfeited lands under Minnesota Statute 282.  Our objective is to maximize revenue from the lands while managing to diversify our forests and forest assets while supporting the local economy.  The lands we manage are also third party certified by the Sustainable Forestry Initiative (SFI) and the Forest Stewardship Council (FSC).

This silvicultural prescription was designed for a previously managed red pine stand on newly acquired land with the objective to utilize natural pine (white and red) regeneration in gaps and more heavily thinned blocks, while generating a normal income flow as compared to a comparable stand.

Figure 1: Planned residual basal area map

Silviculture Objective(s)

The silvicultural objective for this stand was to use an economically viable timber harvest to vary the residual basal area across the sale area.  Thirty-five, approximately one-acre blocks were marked with the objective of leaving five different residual basal areas (0, 50, 100, 120, 150).  The clearcut blocks were placed adjacent to residual white pine and red oak with the objective to increase the species diversity within the stand through natural seeding.   Another key objective was to maintain the economic viability of the harvest.  Approximately 14 cords/acre was removed which is similar to the volume that would be removed per acre for a traditional thinning harvest in this growth stage of red pine. 

Another objective of this harvest is to create spatial and vertical diversity that will benefit game and non-game wildlife species alike.  For example, wild turkey poults utilize the thick, brushy early successional habitat of the clearcut gaps for cover and foraging throughout their early lives.  Also, all wild turkey utilize the thermal cover provided by the reserve blocks in the winter while also foraging through the entire stand as conifer stands typically have less snow underneath them than stands dominated by deciduous species.  The varying treatment blocks will harbor different understory herbs and woody stems that will create varying browsing oppurtunities. 

Pre-treatment stand description and condition

Stand establishment and management history: 

Area the stand occupies has a history of fire as the area was burned in 1939.  Fire was thought to have been started by the adjacent railroad line bordering the northern edge of the stand.  Area was occupied by mainly grass and forbs until 1965 when it was planted with red pine stock whose origins are unknown.  Stand was then row-thinned in approximately 1980 and then thinned again in 1990.  Variable density thinning was then implemented in 2019 with the intention to reduce the overall average basal area to 90-100 square feet while greatly diversifying the stand structure to meet our other listed silvicultural objectives.    

Pre-treatment species composition: 

At the time of the treatment, the stand basal area was 150 square feet which was almost entirely made up of 12” DBH red pine (49 cords/acre) with a small amount of northern red oak (1 cord/acre) with scattered, large white pine on the edges of the stand (didn’t show up in cruise but they are present) at the rate of approximately 1-2 an acre.

Pre-treatment forest health issues: 

In the Lake States region, red pine often are exposed to Diplodia and/or Sirococcus shoot blights.  While the overstory in this treatment block shows no evidence of decline due to either of these diseases, it is also fair to say that the disease is present.  Our objective is to emulate what we are seeing naturally happen in this management area where gaps are filled over the course of 10-15 years with natural conifer regeneration.  Some regeneration may be lost to the previously mentioned diseases, but from what is naturally occurring, enough recruitment will be present to fully regenerate the treatment created gaps.

Landowner objectives/situation: 

The Carlton County Land Management Plan outlines goals and objectives for the management of species under the Carlton County Land Department's management.  This treatment aligns with the goals and objectives stated in the plan.  These goals and objectives balance ecological protection with wildlife, timber production, recreational, and cultural values.

Figure 2: 2019 Pre-harvest Photograph

Silviculture Prescription

The prescription was a marked, variable density thinning with standard, shelterwood, regeneration, and legacy blocks created to provide varying stand conditions to recruit natural conifer regeneration representative of what historically occurred in this area.  Non-frozen ground harvest occurred with full-tree skidding that created a fair amount of soil scarification.  Skidding was encouraged through the regeneration gaps to scarify those gaps as much as possible for regeneration of seeded species. 

What actually happened during the treatment

Harvest was performed in August of 2019 by a conventional logging system that also chipped the woody biomass.  The harvest removed 795 cords of red pine (14 cords/acre) along with 10 cords of northern hardwoods (small paper birch, aspen, northern red oak around landing areas).  Slash and tops were utilized and main skid trails were placed through the clearcut blocks to encourage more soil scarification. 

Figure 3: Red pine seedling in clearcut block

Post-treatment assessment

Regeneration was assessed in the spring of 2022 in the clearcut gaps.  Northern red oak and white pine were represented at the rates of 611 seedlings/acre and 167 seedlings/acre respectively.  The white pine are believed to be of seed origin due to their small size (<5” in height).  The northern red oak seedlings had an average size of 6” in height leading us to believe that they are of seed origin as well.  Red maple was also present at a rate of 778 seedlings/acre.  In the absence of fire, traditional logging practices don’t seem to deter this species much.  Red pine seedlings were seen in very low numbers across the gaps but these few seedlings did not end up being tallied on any regeneration plots.

The harvest blocks where we retained a basal area of 50 square feet will be assessed in the fall of 2024 for regeneration under this treatment.  The clearcut gaps will also be assessed at this time for an update on the regeneration status.

Figure 4: 2021 Post Harvest Photograph

Plans for future treatments

The stand will be monitored for regeneration and basal area and harvested according to departmental plans.

Costs and economic considerations

The Carlton County Land Department is tasked with returning value from the lands they manage to their local trust.  That being said, this timber harvest generated $48.00 per cord for red pine which was within the range expected when this timber sale was auctioned in 2017.  

Other notes

This case study was developed with support from the United States Department of Agriculture's National Institute for Food and Agriculture, Renewable Resources Extension Act. Project #2021-46401-35956, principal investigator Eli Sagor, University of Minnesota.

Climate Adaptation Considerations

Red and white pine are both species that are thought to be more competitive if our climate gets drier.  Northern red oak is predicted to do better if the climate gets warmer and drier.

Summary / lessons learned / additional thoughts

A variable density thinning is a tool that aligns with Carlton County’s management objectives when applied to larger red pine stands that are present within larger blocks of lands Carlton County manages.  The ability to repeat this treatment in adjacent stands will aid in overall pine management while increasing the area where we can diversify not only our habitat for wildlife but diversify our tree species in these stands for future management options.  At this time, future entries will involve removing more volume from the three higher residual basal area blocks while we build regeneration in the shelterwood (BA 50) and clearcut blocks. 

Going forward, management like this will require the forester to keep descriptive records of the treatment in a form that is easily passed on to future foresters to make it easier to continue this management.  With the ability to use tablets armed with GIS derived information, this style of management is easy and economical to implement in the field and will be another tool in our tool box for future harvests.