Shelterwood and slash walls to regenerate northern red oak and eastern hemlock (USFS)

Overview

A site has been identified in the Cadillac/Manistee Ranger District as an excellent candidate for construction of a slash wall to exclude deer and promote desired tree regeneration. Slash walls were pioneered at Cornell University as a cost-effective means of reducing deer herbivory and there is interest in utilizing slash walls in Michigan forests. Deer browsing has been suspected as a significant contributing factor to limited regeneration of northern red oak and eastern hemlock on the Huron-Manistee National Forest. Compartment 28 Stand 72 (Stand 28/72) has both northern red oak and eastern hemlock in the overstory, yet pre-treatment advanced regeneration is dominated by American beech and ironwood. In addition, adjacent forest management actions over the last 25 years aimed to regenerate oak and hemlock have also resulted in regeneration dominated by American beech and ironwood.

The proposal was to implement construction of a slash wall in combination with a shelterwood with reserves regeneration harvest. The revenue from a portion of the sawtimber sized trees will be used to cover the cost of wall construction. Reserve trees would include northern red oak and eastern hemlock at approximately 20-40 ft2/ac basal area. Activities would occur during the snow free period (ideally early fall) to help scarify the seed bed and kill existing undesirable advanced regeneration. Advanced regeneration would also be treated mechanically during harvest. Some sawtimber, all sub-merchantable sized material, all cull material, and all top-wood material would be used to construct a slash wall that is 20 feet wide, 10 feet tall, and sufficiently dense to exclude deer. Stand boundaries may be modified slightly to improve slash wall construction efficiency. The site is also adjacent to a planned aspen regeneration harvest that could be a potential source for additional wall material if needed. 

Harvest and slash wall construction occurred concurrently over a two-week period in late October and early November of 2024. There was a moderate acorn crop and no snow cover during this time. Slash wall construction went smoothly, and no additional wall material was needed from outside of the stand. All advanced regeneration (exclusively American beech) was mechanically felled during harvest operations. Monitoring began following implementation and included immediate post-harvest stand inventory (December 2024), end of one growing season stand inventory (October 2025), and winter track surveys (2024-2025). Operational specifics, photos, and monitoring results are reported below.

Silviculture Objectives

The short term objectives for this project are to create conditions favorable for desirable regeneration of northern red oak and eastern hemlock as well as install a slash wall via a stewardship project. Long term objectives include:

1. Establish a new cohort of desired northern red oak, eastern hemlock, and mixed northern hardwoods. 

2. Evaluate the slashwall for cost-effectiveness and exclusion of deer and associated herbivory, as well as assessing the natural regeneration success of desired species. 

3. Improve age class, species composition, and habitat distribution within the stand and local landscape. 

Desired Condition: Forest Plan direction for MA 2.1: Management activities provide high volumes of quality hardwood timber products and firewood with special consideration for enhancing wildlife habitats. Emphasis is given to managing grouse, deer and wildlife emphasis areas, and fish habitat. A broad variety of recreational opportunities is available and visual diversity is high.

Stand Condition: Fully stocked, two-aged, two-storied stand of northern red oak, eastern hemlock, and mixed northern hardwoods

Pre-treatment stand description and condition

Stand establishment and management history

This stand has not been managed since its establishment, however adjacent stands surrounding this stand have been previously managed (see Figures 2 and 3).

Pre-treatment species composition

Table 1: Stocking table for the treatment area. 

Figure 1: Pre-treatment stand condition illustrating oak overstory and American beech understory. 

Figure 2: Adjacent Stand 28/70 where shelterwood establishment (2013) resulted in beech/ironwood

Figure 3: Map of adjacent stands and management history, as well as the proposed treatment in stand 28/72.

The following are relevant attributes of Stand 28/72:

Table 2: Stand characteristics for the treatment area. 

Pre-treatment forest health issues 

Oak decline is an issue in adjacent stands, but not an issue in the current stand. Spongy moth has defoliated the stand at least twice, peaking in 2021/2022. In the long term, hemlock health will be a consideration due to the relatively close proximity of hemlock wooly adelgid (HWA). So far, it's been found in the southwest portion of the ranger district about 30 miles away from the current stand.

Silviculture prescription

Shelterwood Establishment Cut with Leave Trees Marking Guidelines:

• Retain northern red oak, eastern hemlock, and yellow birch at 40 ft2/ac on average across stand.
  • Retain all hemlock and yellow birch regardless of BA (this will result in some areas above 40 BA due to pockets of hemlock)
  • Minimize retention of other species and do not retain any beech, red maple, or aspen.
  • When designating northern red oak for removal (some expected), remove/retain a mix of sized trees
• Retain all existing snags
• Within 33 feet of the unit boundary do not retain any trees as this will be a high traffic area during slash wall construction and the primary wall supply zone.  May need to consider this when marking the boundary to avoid reserve trees (e.g. hemlock).

Timing Restrictions:

• Conduct cutting of hardwood trees >3" DBH outside of the May 1 - August 31 time period to avoid effects to roosting bats.
• Activities will occur during the snow free period (ideally early fall) to help scarify
  the seed bed and damage/kill existing undesirable advanced regeneration.
• To reduce the impacts of oak wilt activities would not occur from April 15 to July 15 where oak trees greater than 2” diameter at breast height may be wounded or cut through management activities (e.g. harvesting, road/landing construction, site preparation, slash wall construction, etc.).

Site Preparation for Natural Regeneration:

• Fell all live stems of any species, except hemlock, that are greater than 0.5 inches in diameter at ground line and less than 5 inches DBH. Maximum stump height shall not exceed 4 inches above the ground, except where forking or obstructions prevent cutting at this height.  Mechanical felling using masticator or hot saw is preferred and activity can occur pre-, during, or post-harvest.

Slash Wall Specifics:

Construct a wall of trees/wood around the perimeter of the unit with the following specifications: 

• Construct a relatively solid base of wood that is sufficiently dense to prevent deer passage to a height of ~5-6’ and then pile coarse slash and tops on the wall such that the height-to-highest 2” branch is 10’.  Slash walls at this height will likely have a width of ~ 20’.
• Avoid placing porous material (e.g stiff branched tops) at the base of the wall that may inadvertently create tunnels for deer.
• All small stems (<5” DBH), pulpwood, tipwood (branches/tops), and beech/aspen sawlog material within the unit will be available for wall construction. If needed additional material may be available in adjacent aspen clearcut in stand 28/9.
• Install a gate in the wall along FSR 7570 that prohibits deer access but allows machine/vehicle access into the unit.

Stocking Surveys:

• Monitor natural regeneration success through stocking surveys beginning after site preparation. Conduct multiple exams (Years 1, 3, and 5) as required/needed to certify that unit is stocked with oak/hemlock/other desired species at 700 TPA.  Minimum acceptable stocking is 60% or 400 TPA of desirable species

Tree Release and Weeding:

• Once regeneration is established (est. 5-10 yrs post-harvest), release desired species from beech, ironwood, and by thinning stump sprouts.
   

What actually happened during the treatment 

Sale preparation followed the prescription with minimal issues.  Additional cruising was necessary to ensure that enough biomass was available for wall construction and to determine what could be sold commercially. Contract specifications were prepared and advertised. Multiple bids were received, and the sale was awarded based on price and best value criteria. A separate contact inspector was designated to oversee wall construction. Contractors developed a plan to fell, process, yard, and sort trees destined for the wall or for removal. Five pieces of equipment were used: wheeled feller-buncher to cut and sort trees; rubber-tired skidder to position wall material; excavator to construct the wall; processor and forwarder were used for trees being commercially removed. One modification to the boundary was made during the harvest to improve wall construction efficiency.

Figure 4: Excavator constructing the slash wall.

Figure 5: Author next to the slash wall for scale.

Figure 6: Forwarding processed logs to the landing. 

Figure 7: UAS imagery of the project area.

Post-treatment assessment

Monitoring has included stand inventory immediately following harvest, stocking surveys at the end of the first growing season post-harvest, and winter track surveys. Post harvest stand inventory confirmed a residual basal area of 34 sqft/ac and limited trees less than 5” DBH (see Table 3 below). Stocking surveys suggest increased species diversity, reduction in undesirable species, and an increase of desired species (Table 3). Winter track surveys and game cameras confirmed the slash wall was effectively excluding deer.

Table 3: Stand stocking table immediately following harvest (December 2024).

Figure 8: Pre- and post-treatment sapling (<2" DBH) TPA. 

Figure 9: Conducting regeneration monitoring at the end of the first growing season post-harvest. 

Plans for future treatments 

There are no plans to remove the northern red oak and eastern hemlock overwood in this stand with regards to the shelterwood system. This will create a two-aged stand condition. We anticipate timber stand improvement to occur within 5-10 years of harvest in 2029-2034 and will include the release of desired species and stump thinning.

Costs and economic considerations 

This is, in part, a demonstration project to assess the feasibility and effectiveness of slash walls to control deer herbivory and establish desired tree regeneration at one location in Michigan. Although this represents only one data point, slash wall construction costs exceed initial estimates suggesting that slash walls may not be locally economically viable and may be more costly than other options. Local updated costs were not calculated for alternative approaches such as individual tree protection or area fencing. Factors contributing to the increased cost may include...

• The fact that this is a locally novel technique

• The size and shape of this slash wall

• The presence of a local pulp market and other timber market factors at the time of offer

• Local equipment availability

• The opportunity costs of wall construction vs production logging

• Current inflation

• Recent workforce/market increases

• Forest Service stewardship contract bidding design 

It is recommended that those interested in utilizing slash walls should consider local economic factors up front.

Climate adaptation considerations

Climate adaptation is a consideration underlying all of the management practices as this project focuses on diversity and diversifying the age class of oaks across the landscape to promote resilience. With the projection of increased deer herbivory in the light of climate change as well as the potential for lower snowpack, the slash wall will be an important tool for protection. Overall, there is a positive potential for oak communities in northern Michigan associated with climate change. Oak dominated forests are relatively drought tolerant and increased drought stress might reduce competition from other species. Oak dominated forests may increase in abundance and range in light of warmer/drier conditions and more frequent fire. Slash walls may represent a novel management opportunity for some landowners.

Other notes 

This is an ideal location for this project due to the surrounding stand management and those results. As mentioned in the stand establishment and stand history section, two adjacent stands (28/29 and 28/70) received shelterwood harvests to regenerate oak in 1995 and 2013 respectively.  Regeneration surveys in both stands indicated the harvests resulted in regeneration dominated by American beech with little to no oak establishment. As a result, this 10-acre shelterwood harvest incorporated a slash wall to explore if deer exclusion has a positive effect on oak and hemlock regeneration success. 

Summary

This project provides a locally novel approach of utilizing a slash wall to exclude deer and influence the species composition of regeneration following a shelterwood harvest. Initial monitoring suggests the slash wall is effectively excluding deer and regeneration data indicates increased species diversity including northern red oak. Monitoring will continue to track if desired species persist and recruit to the overstory. Careful economic consideration will be necessary prior to implementing future slash walls.