Underplanting for Oak/ Black Walnut Regeneration in a Southern Dry-Mesic Oak Forest NPC on the Buelow Unit (MN DNR)

State or Province
Minnesota
Nearest city or town
La Crescent
Describe the location
The site is in Winona County, in the Buelow Unit of the Richard J. Dorer Memorial Hardwood Forest (RJDMHF).
Landowner
Minnesota DNR
Cover type
MN ECS
Plant community detail and growth stage
NPC: Southern Dry-Mesic Oak Forest (MHs37), with some inclusions of Southern Dry-Mesic Oak Hickory Woodland (FDs38) Growth stage: Young forest
Forest health threats
Adaptive silviculture options
Silviculture system
Estimated year of stand origin
2007
Additional information about stand origin
This stand originated from natural and underplanted artificial regeneration and a clearcut with reserves harvest in 2007.
Site index
60 feet
for species
northern red oak
Brief silvicultural objective
Regenerate a mature oak stand to a young stand of similar composition.
Site preparation method
Soil texture
Soil details
Elbaville-Seaton silt loams, 30 to 45 percent slopes; Lacrescent silt loam, rocky, 45 to 70 percent slopes; Brodale-Bellechester complex, 30 to 60 percent slopes, rocky; Rollingstone silt loam, 3 to 20 percent slopes
Stand area
27 acres
Treatment area
27 acres

43.859526, -91.467463

Overview

In Minnesota DNR’s Lewiston forestry administrative area, a common prescription for regeneration of mature oak stands includes underplanting oak seedlings before a regeneration timber harvest. We wanted to do an assessment of how well the practice had met oak regeneration objectives by gathering current data on several sites that had been underplanted with oak. This study is an assessment of oak regeneration and overall stand condition in 2021 (14 years after planting and harvest) for one of those sites. 

Background on typical oak regeneration through pre-harvest underplanting prescription: 

Seedlings have been planted prior to harvest (instead of after) because: 

  • They become established for a year or two, helping them be better able to grow and compete with other vegetation after exposure to full sunlight post-harvest. 
  • It is extremely difficult and expensive to plant seedlings after a harvest, with heavy amounts of slash on the ground.     
  • Non-oak species such as black walnut are mixed into plantings as appropriate for the site. 
  • Most often, the harvest prescription has been a clearcut with reserves, although there have also been some shelterwood harvests. 
  • Damage to underplanted seedlings during harvesting activity is usually modest. The young stems are pretty flexible and most often survive being run over by a skidder by bending but not breaking. Those that do break off generally resprout and exhibit the rapid juvenile growth associated with sprout origin stems.
  • Crop tree release of desirable young regeneration, along with thinning of oak stump sprout clumps has typically been accomplished 8 to 15 years after the harvest.

Silviculture Objectives

  1. Regenerate a mature oak stand to a young stand of similar composition. 
  2. Maintain acreage of oak forest type.
  3. Maintain and improve wildlife habitat with a strong component of oak trees in the new stand. Oak forests provide habitat for numerous wildlife species. One of oaks’ most important contributions to wildlife is mast, or acorns which can be an important seasonal food source for many species.
  4. Improve timber quality and value. A good component of healthy, well-formed oaks and other fine hardwoods will help ensure high timber value at harvest time. 

Pre-treatment stand description and condition

Stand establishment and management history

Most of the mature oak stands in southeastern Minnesota at the time of project initiation in 2007 originated after control of regular fires after European settlement. 

The stand was part of a privately owned farmstead until the state obtained it in 1979, so it probably had a history of use as a woodlot and wooded pasture prior to state ownership. 

Pre-treatment species composition

The pre-treatment stand was dominated by oak, including black, northern red, white and bur oak. Modest volumes of a mixture of other central hardwood species common to the plant community were present, including basswood, elm, hackberry, black cherry, shagbark and bitternut hickory, and a very small amount of sugar maple. See Table 1.

Table 1: 2007 Timber sale appraisal of volume of non-reserved merchantable trees with stems greater than 12 inches DBH 

Species

Volume (Board Feet)

Black Oak

47,500

Red Oak             

33,500

White Oak         

19,000

Central Hardwoods

9,000

Bur Oak        

2,700

Total:           

111,700

Landowner objectives/situation 

While specific objectives vary from parcel to parcel, lands under the administration of DNR-Forestry are managed in alignment with Section Forest Resource Management Plans (SFRMP) to ensure that state forest management activities meet statewide goals for ecological protection, timber production, wildlife habitat and cultural/recreational values. The DNR assembles teams from the Divisions of Forestry, Fish & Wildlife, and Ecological & Water Resources who work with partners and the public to develop SFRMPs. 

The Minnesota DNR goal for oak forest acreage at the time of project initiation was to maintain as much of it as possible through regeneration of mature stands. 

Silviculture prescription

The following series of treatments were implemented:

Treatment

Date

Description

Acres Treated

Silvicultural assessment and timber sale appraisal

2006 and 2007

Timber was appraised for sale, data was obtained on stems of existing regeneration, and the stand was assessed to determine a silvicultural strategy. 

26

Underplanting

Spring 2007

Bare root seedlings were hand underplanted prior to anticipated harvest at approximately 8’ x 8’ spacing. Target density was approximately 750 stems/ acre. 

Records do not indicate whether the species mix was totally random across the site, or whether species were somewhat targeted for certain portions of the site.

Species:

  • Red Oak: 350 stems/acre
  • White Oak: 200 stems/acre
  • Black Walnut: 200 stems/acre

26

Clearcut with reserves harvest

2007

Trees greater than 12 inches DBH were harvested in a commercial clearcut with reserves harvest.

Scattered trees of larger bur, white, red and black oak were reserved for mast production as a seasonal wildlife food source, to provide den and roost trees, and also as a seed source for regeneration. 

26

Post-sale killing of undesirable competing trees

Fall, 2009

Stems of undesirable competing trees (boxelder, elm and ironwood) were killed by girdling with a chainsaw, and applying Tordon herbicide to the girdle wound.

26

Crop tree release and oak sprout clump thinning

December

2018

Crop tree release: Release from competing woody vegetation up to 150 well-formed, desirable hardwood crop trees (3’ and taller)/acre. 

In order of crop tree preference, desirable species of the following released: Walnut, Oak,

Shagbark Hickory, Bitternut Hickory, healthy Butternut, Cherry, Hackberry, Sugar Maple, Silver Maple, Kentucky Coffeetree, Basswood, Cottonwood, Paper Birch and Aspen. Mast producing species take priority over non mast trees.

Sprout thin: Mechanically cut stump sprout(s) of Crop Trees to the one best formed sprout near the base of the stump.

26

Invasive species control

2018

Treat the following invasive exotics/non-desirable species with herbicide: all buckthorn, black locust, honey locust, multiflora rose, amur maple

(ginnala) and non-native honeysuckles taller than 3’ tall, barberry taller than 2’, Oriental bittersweet and grape vines 1” diameter and larger.

26

 

Color infrared aerial photograph of study site (heavy black outline) and surrounding area

Figure 1: Color infrared aerial photograph of study site (heavy black outline) and surrounding area

What actually happened during the treatment

As far as we can tell now from existing records, everything went largely as planned per the prescription.

Post-treatment assessment

Regeneration

The silvicultural prescription of pre-harvest underplanting, a clearcut with reserves harvest, and crop-tree release 11 years after harvest has resulted in a young stand consisting of mixed hardwood regeneration as of 2021

14 years after initial treatment, there was a mixture of desirable hardwood regeneration (Table 2). A fair number of these seedling and sapling stems are above deer browse, with many clearly at “free to grow” status.

Desirable hardwood species regeneration includes red oak, black cherry, basswood, hackberry, black walnut, shagbark hickory, and (on a small portion of the site) sugar maple. Other species present include elm, bitternut hickory, ash, trembling aspen, paper birch, black locust and butternut. 

 

Michelle Martin among mixed hardwood regeneration in fall 2021. Note the black walnut stem behind her.

Figure 2: Michelle Martin among mixed hardwood regeneration in fall 2021. Note the black walnut stem behind her.

 

Michelle Martin measures a regenerated black cherry stem among other regeneration in fall 2021

Figure 3: Michelle Martin measures a regenerated black cherry stem among other regeneration in fall 2021

 

Abundant stems of mixed species regeneration in the fall of 2021

Figure 4: Abundant stems of mixed species regeneration in the fall of 2021

 

While there is an oak component in portions of the stand, it is not as abundant or well-distributed as we would like

It is important to note that while this is now well on its way to becoming a healthy mixed central hardwoods stand, the oak component is considerably less than we were hoping for. And we also need to note that the majority of the larger stems of oak regeneration present are of coppice, not planting origin. This is in spite of early post-planting regeneration data in 2009 showing the presence of good numbers and distribution of red oak saplings (Table 3). The oak mortality between the years 2009 and 2021 indicates clearly that additional release from understory competition in the early years after planting (and probably also deer browse protection, typically annual bud capping) would have been necessary for more oaks to recruit into larger size classes.

We want to note that the crop tree release work 10 years after harvest was important for allowing oaks and other desirable shade-intolerant species to survive and thrive. However, an earlier release would have been better.

Foresters will continue to monitor and assess the site over time. They should have options to adjust species mix as desired through future crop tree release/thinning treatments.

 

Table 2: Regeneration Summary: Trees/Acre and Plot Frequency by Species and Size Class

Size Class

< 1’ tall

≥1’ tall and 

< 1” DBH

1” to 3” DBH

3” to 5” DBH

Species

Stems/ Acre

Freq

Stems/ Acre

Freq

Stems/ Acre

Freq

Stems/ Acre

Freq

Ash

129

12.9%

484

29.0%

48

9.7%

23

19.4%

Aspen

0

0.0%

0

0.0%

16

3.2%

10

6.5%

Basswood

32

3.2%

129

6.5%

16

3.2%

12

12.9%

Bitternut Hickory

0

0.0%

32

3.2%

16

3.2%

19

12.9%

Black Cherry

32

3.2%

226

16.1%

32

6.5%

35

29.0%

Black Locust

0

0.0%

0

0.0%

48

6.5%

3

3.2%

Black Walnut

32

3.2%

32

3.2%

16

3.2%

10

6.5%

Boxelder

0

0.0%

32

3.2%

48

9.7%

26

9.7%

Butternut

0

0.0%

0

0.0%

32

3.2%

3

3.2%

Elm

194

12.9%

581

19.4%

194

29%

55

32.3%

Hackberry

65

6.5%

97

6.5%

48

6.5%

3

3.2%

Ironwood

0

0.0%

97

3.2%

16

3.2%

3

3.2%

Paper Birch

0

0.0%

0

0.0%

0

0.0%

10

6.5%

Red Oak (Seedling)

129

9.7%

32

3.2%

16

3.2%

3

3.2%

Red Oak (Sprout)

0

0.0%

32

3.2%

16

3.2%

13

12.9%

Shagbark Hickory

0

0.0%

0

0.0%

32

6.5%

3

3.2%

Sugar Maple

129

9.7%

65

6.5%

0

0.0%

3

3.2%

Total Stems/Acre

742

 

1,839

 

594

 

234

 

 

Table 3: Fall 2009 regeneration check stems/acre by species and size class, 3 growing seasons after initial treatment

Species

Size Class 0”-.9” DBH

Size Class 1”-2.9” DBH

Size Class 

3”-4.9” DBH

Total

Distribution

Aspen

33

0

0

33

Well distributed

Black Cherry

33

0

0

33

Well distributed

Elm

33

66

0

99

Well distributed

Red Oak

0

200*

0

200

Well distributed

Shagbark Hickory

33

33

33

99

Well distributed

Total

132

299

33

464

 

*Note: We think there was probably an error recording red oak size class in 2009. It is likely that most of the red oak should have been listed in the 0” to .9” DBH size class. This is because any red oak seedlings and even sprouts in 2009 would have been less than 1” DBH. 

Residual overstory trees

We were most interested in regeneration for this study, so residual overstory trees are not a major part of the story here. However, we want to include data on residual overstory trees to give a full picture of site conditions. The data in Table 4 below shows basal area of residual tree stems in the study area.

Table 4: Basal area (ft2/ac.) of trees > 5” DBH by species and diameter class

 

Diameter Class

 

Species

5-10” DBH

10-15” DBH

15-20” DBH

>20” DBH

Total 

Ash

0.0

0.6

0.0

0.0

0.6

Basswood

1.9

0.0

0.0

0.0

1.9

Bitternut Hickory

0.6

0.0

0.0

0.0

0.6

Black Cherry

1.3

1.0

0.0

0.0

2.3

Black Locust

1.0

0.0

0.0

0.0

1.0

Black Walnut

0.3

0.0

0.0

0.0

0.3

Bur Oak

0.0

0.6

0.0

0.0

0.6

Butternut

1.3

0.0

0.0

0.0

1.3

Elm

0.3

0.0

0.0

0.0

0.3

Hackberry

2.6

0.3

0.0

0.0

2.9

Red Oak 

1.3

4.2

10.0

1.6

17.1

Shagbark Hickory

1.3

1.9

0.6

0.0

3.8

Sugar Maple

0.0

0.0

0.3

0.0

0.3

White Oak

1.0

1.3

1.6

0.0

3.9

Total

12.9

9.9

12.5

1.6

36.9

 

Invasive Species

Black locust: in spite of past control efforts, we found one patch of black locust regeneration in the stand as of 2021. 

Buckthorn: in spite of past control efforts, we found some buckthorn on 29% of our sample plots as of 2021. See Table 5.

Table 5: Buckthorn stems/acre and plot frequency by size class in 2021

Size Class

< 1’ tall

 

≥1’ tall and < 1” DBH

 

1” to 3” DBH

 

3” to 5” DBH

Species

Stems/ Acre

Freq

Stems/ Acre

Freq

Stems/ Acre

Freq

Stems/ Acre

Freq

Buckthorn

355

12.9%

581

19.4%

97

9.7%

0

0.0%

We will continue to monitor invasives and treat again if necessary.

Plans for Future Treatments

Monitor the stand through periodic inventory surveys. Harvest and regenerate the stand when it is selected in the forest planning process. 

Costs and economic considerations

Costs 

2007 underplanting:                                                $9,083.30 total          $  363.33/acre

2009 post-sale kill competing trees:         $5,200.00 total          $  200.00/acre

2018 crop tree release, sprout clump

Thin and invasive species control:           $8,670.00 total          $ 333.46/acre           

Total costs:                                                                                      $  896.79/acre

 

Revenue

2007 timber sale:                                          $22,247.50                $ 855.67/acre

Total revenue:                                             $22,247.50                $ 855.67/acre                                       

Other notes

We had review and editing help from MNDNR Silviculture Program Consultant Mike Reinikainen.

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.

Summary

The silvicultural prescription of pre-harvest underplanting, a clearcut with reserves harvest, and crop-tree release 10 years after harvest has resulted in a young stand consisting of mixed hardwood regeneration as of 2021

In 2021, 14 years after initial treatment, there was a mixture of desirable hardwood regeneration including red oak, black cherry, basswood, hackberry, black walnut, shagbark hickory, and (on a small portion of the site) sugar maple. Other species present include elm, bitternut hickory, ash, trembling aspen, paper birch, black locust and butternut. 

Foresters will continue to monitor and assess the site over time. They should have options to adjust species mix as desired through future crop tree release/thinning treatments.

While there is an oak component in portions of the stand, it is not as abundant or well-distributed as we would like

While this is well on its way to becoming a healthy central hardwoods stand, the oak component is considerably less than we were hoping for. This is in spite of adequate early post-planting and harvest oak regeneration. The oak mortality between the years 2009 and 2021 indicates that additional release from understory competition in the early years after planting (and probably also deer browse protection) would have been necessary for more oaks to recruit into larger size classes.

The crop tree release work 10 years after harvest was important for allowing oaks and other desirable shade-intolerant species to survive and thrive. However, an earlier release would have been better since it would have enabled far greater numbers of these species to survive and recruit.

Supplemental content

2007 timber sale permit

Supplemental figure 1: 2007 timber sale permit