United States Department of Agriculture

Forest 

Service

Research Note 

NRS-201

Northern 

Research Station September 2015

Dominant-Tree Thinning in 

New England Northern 

Hardwoods—a Second Look

William B. Leak
Visit our homepage at: http://www.nrs.fs.fed.us/

Published by: For additional copies:

U.S. FOREST SERVICE U.S. Forest Service

11 CAMPUS BLVD SUITE 200 Publications Distribution

NEWTOWN SQUARE PA 19073 359 Main Road

Delaware, OH 43015-8640

Fax: (740)368-0152

September 2015 Email: nrspubs@fs.fed.us

Manuscript received for publication 15 July 2015

Abstract

A dominant-tree thinning was conducted in 2003 in a 69-year-old even-aged northern 

hardwood stand, clearcut in about 1935, where a precommercial thinning study had been 

conducted in 1959. The 2003 commercial thinning concentrated on the removal of the 

early maturing, short-lived paper birch and aspen, the largest-diameter trees in the stand 

(hence the term “dominant-tree thinning”). Diameter growth rates after thinning, up to 

about 6 years per inch over the following 12 years, were acceptable although not greatly 

different from the unthinned plots. Basal area growth response was highly acceptable after 

thinning: about 2.3 ft2 per acre per year. Annual basal area growth was about negative 

0.9 ft2 per acre on the unthinned plots. Understory development of beech and shrub 

species was dense under the thinned plots, and will require treatment/removal during the 

regeneration phase.

The Author

WILLIAM B. LEAK is a research forester with the Northern Research Station of the U.S. 

Forest Service in Durham, NH.

Cover Photo

Uncut portion of Compartment 22, Bartlett Experimental Forest, in 2003 (69 years old). 

Photo by M. Yamasaki, U.S. Forest Service.
1

INTRODUCTION

Commercial thinning in mixed northern hardwoods in 

New England presents unique problems. The stands 

commonly contain species that differ in longevity 

and commercial maturity. Species such as paper 

birch (Betula papyrifera) and bigtooth and trembling 

aspen (Populus grandidentata and P. tremuloides) 

mature much earlier (at roughly 50-70 years of age) 

than longer lived species such as sugar maple (Acer 

saccharum) and beech (Fagus grandifolia) that reach 

maturity at 120-140 years. Other species such as 

white ash (Fraxinus americana) and red maple (Acer 

rubrum) are moderate in maturity/longevity. Typical 

approaches to thinning such as crop-tree thinning or 

thinning from below would not be efficient due to 

impending mortality of the short-lived species. The 

natural approach would be to concentrate the removal 

on the short-lived species, which commonly are the 

larger, dominant stems, hence the term “dominant-tree 

thinning.” This might be considered a form of crown 

thinning (Nyland 2002, Smith et al. 1997), except for 

the emphasis on removal of early maturing species 

rather than release of better residuals. The approach 

would not be applicable where stand composition was 

dominated by long-lived species.

A dominant-tree thinning was conducted in 2003 

in a stand on the Bartlett Experimental Forest, New 

Hampshire. Preliminary (4-year) results from this 

thinning have been previously described (Leak 2007). 

This note describes responses after 12 years.

METHODS

The stand developed from a clearcut in about 1935, 

which had been experimentally precommercially 

thinned in 1959 (four treatments and twenty 1⁄4-acre 

plots with 1-chain buffers between plots). Responses 

from the precommercial work were appreciable and 

have been well described (Marquis 1969). But the 

impacts from this early work were not readily evident 

before the dominant-tree thinning (Leak and Smith 

1997), so the 2003 thinning was applied to plots 

irrespective of the earlier precommercial work.

The guidelines for the dominant-tree thinning were 

to remove paper birch and aspen as well as obviously 

declining stems but to maintain at least 50 ft2

 basal 

area per acre in the 4-inch (diameter at breast height, 

4.5 ft above ground [d.b.h.]) class and larger. To meet 

these guidelines, a small proportion of paper birch was 

retained (about 6.7 percent of the residual basal area). 

The objective of the thinning was to salvage mortality 

of the short-lived species while maintaining stocking/

growth of the residual stand. The paper birch and 

aspen averaged 10-14 inches d.b.h.; the other species 

averaged 5-9 inches d.b.h. (and white ash averaged 

about 12 inches), so this was truly a thinning from 

above. Five plots were left as unthinned controls. The 

thinning also was applied to the buffer strips (1 chain 

wide) between treated plots. Residual basal areas 

ranged from about 134-148 ft2

 per acre on the five 

unthinned plots to 54-123 ft2

 per acre on the thinned 

plots. A high white ash component accounted for the 

largest values of residual basal area on the treated 

plots. This level of variability is common on small, 

northern hardwood plots in the region.

To assess the results of the thinning, complete tallies 

(4-inch class and larger) were made on the twenty 

1⁄4-acre plots in late summer of 2014, for comparison 

with the initial 2003 tallies. This included the 

remeasurement of more than 80 sample trees of the 

six most common species to assess diameter growth. 

In addition, understory stems (4.5 ft tall to 3.5 inches 

d.b.h.) were counted by tree/shrub species on 5 

milacres per plot.

RESULTS

Species composition after the thinning clearly showed 

the effects of the thinning (Table 1). The unthinned 

plots had 49.0 and 6.8 percent of the basal area in 

paper birch and aspen, whereas the thinned plots 

averaged 6.7 and 0.0 percent in the respective species 

(Table 1). Residual basal areas averaged 140.9 and 

74.4 ft2

 per acre, respectively.

Annual diameter growth was substantially higher for 

yellow birch (Betula alleghaniensis) on the thinned vs. 

unthinned plots (0.13 vs. 0.07 inches), and moderately 
2

higher for sugar maple (0.18 vs. 0.14 inches) (Table 2). 

Paper birch grew slowly (annual rate of 0.07 inches 

on thinned plots vs. 0.08 inches on unthinned plots), 

which reflects its maturity. The growth rates are similar 

to the 4-year growth rates reported earlier (Leak 

2007), and also similar to or slightly better than those 

reported for a comparable early thinning study laid out 

in 1936 and remeasured in 1941–1951 (Wilson 1953). 

Apparently environmental concerns (e.g., acid rain/

nutrient depletion, climate change) since this early 

period have had no noticeable effects on tree growth.

The primary effect of the dominant-tree thinning 

was on stand growth. Annual basal area growth 

(production) averaged negative (-) 0.92 ft2

 per acre on 

the unthinned plots and positive (+) 2.29 ft2

 per acre 

on the thinned plots. The average deviation in basal 

area growth among these small thinned plots was ± 0.5 

ft2

 per acre. The rates after thinning are comparable 

to or better than the rates reported for long-term 

growth studies on the Bartlett Experimental Forest for 

equivalent residual basal areas (Leak and Gove 2008).

Large numbers of understory stems were developing in 

the thinned plots—more than five times the number as 

on the unthinned plots (Table 3). Beech, striped maple 

(Acer pensylvanicum), and hobblebush (Viburnum 

alnifolia) are the most numerous. These will need to 

be dealt with during the regeneration of this stand, 

probably through group/patch selection or clearcutting 

with sufficient ground disturbance to remove this 

understory. Any type of thinning to this low level 

of stocking would have produced this understory 

response.

Table 1.—Basal area (4-inch class and larger) and percent basal area by species in 5 unthinned plots and 

15 thinned plots (treatment in 2003), Bartlett Experimental Forest, New Hampshire, 2014

Treatment

Basal area/

acre Beech

Yellow 

birch

Sugar 

maple

Red 

maple

Paper 

birch

White 

ash Aspen Other

(ft2/ac) -----------------------------------------------percent-------------------------------------------------

Unthinned 140.9 4.3 3.6 18.8 10.4 49.0 7.1 6.8 --

Thinned 74.4 13.2 18.5 20.4 14.8 6.7 24.8 0.0 1.6

Table 2.—Annual d.b.h. growth, 2003 through 2014, in unthinned and thinned plots for six species of 

sample trees, Bartlett Experimental Forest, New Hampshire

Treatment Beech

Yellow 

birch

Sugar 

maple

Red 

maple

Paper 

birch 

White 

ash

--------------------------------------------------------inches --------------------------------------------------------

Unthinned 0.16 0.07 0.14 0.20 0.08 0.15

Thinned 0.16 0.13 0.18 0.18 0.07 0.17

Table 3.—Understory stems (number per acre) between 4.5 ft tall and 3.5 inches d.b.h. by species and 

thinning treatment (2003), based on 5 milacres per plot, Bartlett Experimental Forest, New Hampshire, 2014

Treatment Beech

Yellow 

birch

Sugar 

maple

White 

ash

Striped 

maplea Hobblebush

Pin 

cherrya Aspen All

(number of stems/ac)

Unthinned 200 40 80 -- 320 -- -- -- 640

Thinned 1,013 107 200 80 1,293 587 13 13 3,306

a Striped maple (Acer pensylvanicum), pin cherry (Prunus pensylvanica).
3

CONCLUSIONS

The dominant-tree thinning reported here produced 

good results over a 12-year period in both stand 

growth and tree diameter growth. Also on the plus 

side, the thinning presalvaged large volumes of paper 

birch and aspen (about 15-20 cords per acre) that 

otherwise would have been lost to mortality after 

standard and less aggressive forms of thinning. When 

the white ash and red maple reach optimum size, it is 

possible that a comparable thinning will be feasible 

for targeting these two species as well as low-quality 

and low-vigor sugar maple, beech, and yellow birch. 

On the negative side, this approach to thinning may 

lengthen the rotation age of the final crop due to 

the maintenance of the shorter-lived species in the 

overstory until they mature. Another concern is the 

loss of a seed source for the early maturing species; 

such a loss should be averted by maintaining speciesrich no-cut zones. This system appears to work well 

for mixed northern hardwoods with a significant 

component of paper birch and aspen.

LITERATURE CITED

Leak, W.B. 2007. Thinning northern hardwoods in 

New England by dominant-tree removal—early 

results. Northern Journal of Applied Forestry. 24: 

312-313.

Leak, W.B.; Gove, J.H. 2008. Growth of northern 

hardwoods in New England: a 25-year update. 

Northern Journal of Applied Forestry. 25: 103-105.

Leak, W.B.; Smith, M.-L. 1997. Long-term species 

and structural changes after cleaning young evenaged northern hardwoods in New Hampshire.

Forest Ecology and Management. 95: 11-20.

Marquis, D.A. 1969. Thinning in young northern 

hardwoods: 5-year results. Res. Pap. NE-139. 

Upper Darby, PA: U.S. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment 

Station. 22 p.

Nyland, R.D. 2002. Silviculture concepts and 

applications. 2nd ed. Long Grove, IL: Waveland 

Press Inc. 682 p.

Smith, D.M.; Larson, B.C.; Kelty, M.J.; Ashton, P.M.S. 

1997. The practice of silviculture: applied forest 

ecology. 9th ed. New York: John Wiley. 560 p.

Wilson, R.W., Jr. 1953. How second-growth northern 

hardwoods develop after thinning. Stn. Pap. 

NE-62. Upper Darby, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 12 p.
Page intentionally left blank
Printed on Recycled Paper

Leak, William B. 2015. Dominant-tree thinning in New England northern 

hardwoods—a second look. Res. Note NRS-201. Newtown Square, PA: U.S. 

Department of Agriculture, Forest Service, Northern Research Station. 3 p.

A dominant-tree thinning was conducted in 2003 in a 69-year-old even-aged northern 

hardwood stand, clearcut in about 1935, where a precommercial thinning study had 

been conducted in 1959. The 2003 commercial thinning concentrated on the removal 

of the early maturing, short-lived paper birch and aspen, the largest-diameter trees 

in the stand (hence the term “dominant-tree thinning”). Diameter growth rates after 

thinning, up to about 6 years per inch over the following 12 years, were acceptable 

although not greatly different from the unthinned plots. Basal area growth response 

was highly acceptable after thinning: about 2.3 ft2 per acre per year. Annual basal 

area growth was about negative 0.9 ft2 per acre on the unthinned plots. Understory 

development of beech and shrub species was dense under the thinned plots, and will 

require treatment/removal during the regeneration phase.

KEY WORDS: basal area growth, diameter growth, northern hardwoods, thinning

In accordance with Federal civil rights law and U.S. Department of Agriculture (USDA) civil rights 

regulations and policies, the USDA, its Agencies, offices, and employees, and institutions participating in 

or administering USDA programs are prohibited from discriminating based on race, color, national origin, 

religion, sex, gender identity (including gender expression), sexual orientation, disability, age, marital 

status, family/parental status, income derived from a public assistance program, political beliefs, or reprisal 

or retaliation for prior civil rights activity, in any program or activity conducted or funded by USDA (not 

all bases apply to all programs). Remedies and complaint filing deadlines vary by program or incident.

Persons with disabilities who require alternative means of communication for program information (e.g., 

Braille, large print, audiotape, American Sign Language, etc.) should contact the responsible Agency 

or USDA’s TARGET Center at (202) 720-2600 (voice and TTY) or contact USDA through the Federal 

Relay Service at (800) 877-8339. 

To file a program discrimination complaint, complete the USDA Program Discrimination Complaint Form, 

AD-3027, found online at http://www.ascr.usda.gov/complaint_filing_cust.html and at any USDA office 

or write a letter addressed to USDA and provide in the letter all of the information requested in the form. 

To request a copy of the complaint form, call (866) 632-9992. Submit your completed form or letter to 

USDA by: (1) mail: U.S. Department of Agriculture, Office of the Assistant Secretary for Civil Rights, 

1400 Independence Avenue, SW, Washington, D.C. 20250-9410; (2) fax: (202) 690-7442; or (3) email: 

program.intake@usda.gov.
Northern Research Station

www.nrs.fs.fed.us