United States 

Department of 

Agriculture

Forest Service

Northern 

Research Station

Research Note

NRS-170

Effects of Low-Density Thinning 

in a Declining White Pine Stand 

in Maine

William B. Leak

Mariko Yamasaki

Abstract:

Low-density (32 ft2/acre residual basal area) and 

medium-low density (60 ft2

/acre residual basal area) 

thinnings were studied over a 4-year period in 

a declining white pine stand on the Massabesic 

Experimental Forest in southern Maine. Gross basal 

area growth at 60 ft2

 was about three-fourths the rate of 

the control and more than twice as much as the 32 ft2

thinning, while diameter growth at 60 ft2 was twice that 

of the control and about the same as the low-density 

treatment. Regeneration under the thinning treatments 

was abundant. Declining white pine stands apparently 

respond quickly to low-density thinnings and the 

optimum level, among the treatments studied, is 

about 60 ft2

 residual basal area. 

Citation: Leak, William B.; Yamasaki, Mariko. 2013. 

Effects of low-density thinning in a declining white 

pine stand in Maine. Res. Note NRS-170. Newtown 

Square, PA: U.S. Department of Agriculture, Forest 

Service, Northern Research Station. 6 p.

KEY WORDS: low-density thinning, white pine, 

 decline

WILLIAM B. LEAK, Research Forester, and 

MARIKO YAMASAKI, Research Wildlife Biologist. 

U.S. Forest Service, Northern Research Station, 

Durham, New Hampshire 03824

Introduction

Low-density thinning of white pine (Pinus strobus) 

stands is a system based on wide spacing between trees 

(low stand density) to encourage rapid growth and early 

returns from harvesting. The system usually includes 

some level of pruning to provide clean boles with 

minimal dead limbs (black knots). The system has been 

applied successfully since the early 1960s (Guiterman 

et al. 2011, Hunt and Mader 1970, Seymour and Smith 

1987, Seymour 2007). In addition to rapid growth 

rates of the individual trees, the Hunt and Mader study 

showed increased soil water availability due to reduced 

area-wide transpiration.

In 2008, numerous white pine stands on the Massabesic 

Experimental Forest in Lyman, Maine showed signs 

of severe decline including dead tops and widespread 

mortality. These stands, now about 65 years old, 
developed naturally, or were planted, following the 

severe fires in October 1947. The decline symptoms 

were similar to those described by Livingston (2005), 

who attributed the decline to moisture stress, coupled 

with secondary pests and pathogens, from several years 

of drought on soils with a shallow, firm plow layer 

(compacted by early agricultural activity), which limited 

root development. Although the Massabesic stands did 

not have an obvious plow layer, it seemed quite possible 

that moisture stress could be a contributing factor to the 

decline. So, a large-scale thinning study was established 

to see if this approach would mitigate the decline 

symptoms. 

Methods

In a ~90 acre stand, two thinning treatments were 

applied in the growing season of 2008: a low-density 

treatment resulting in 32 ft2

/acre residual basal area 

(Fig. 1) and a medium-low density treatment resulting 

in 60 ft2

/acre residual basal area (Fig. 2). Due to the 

advanced decline, it was difficult for the marking crew 

to find sufficient well-spaced residual trees. 

In a portion of an adjacent stand, which exhibited 

moderate decline (Fig. 3), a control was established with 

a residual of 148 ft2 (trees 4.5 inches diameter at breast 

height (d.b.h.) and larger). In each treatment, the effects 

were monitored in five prism plots (10-factor in the 

thinnings, 20-factor in the control), coupled with four 

sample trees for d.b.h. and crown-width measurements. 

Basal-area growth was estimated by projecting tree 

diameters in the prism-plot tallies using d.b.h. growth 

measurements from the sample trees. Four-year results 

are reported here; because of concerns over the decline, 

early responses to the treatments were of particular 

interest.

Figure 1.—Low density thinning after four growing seasons, Massabesic Experimental Forest, Maine. Note the extensive white 

pine regeneration. Photo by Mariko Yamasaki, U.S. Forest Service.
Figure 2.—Medium-low density thinning after four growing seasons, Massabesic Experimental Forest, Maine. Note the 

extensive white pine regeneration. Photo by Mariko Yamasaki, U.S. Forest Service.

Figure 3.—Control area, Massabesic Experimental Forest, Maine. Photo by Mariko Yamasaki, U.S. Forest Service.
For comparison with the latest stocking charts for 

white pine (Leak and Lamson 1999), basal areas of the 

thinning treatments were below the managed B-line 

basal area of about 100 ft2/acre and managed C-line of 

about 75 ft2

, based on the mean diameters in Table 1. 

The control was below the A-line of about 200 ft2. 

Results

Estimated gross annual basal area growth per acre was 

1.08, 2.74, and 3.49 ft2/acre for the low, mediumlow, and control treatments, respectively, and the 

corresponding d.b.h. growth rates were 0.21, 0.25, and 

0.10 inches per year (Table 1). Similar to other lowdensity studies, the treatments produced a significant 

increase in diameter growth but a decline, especially 

under the 32-ft2

 treatment, in basal area growth per acre 

due to the understocking. Accurate mortality estimates 

are not yet available, but appear to be insignificant in the 

thinned areas. 

Using the measured crown widths, and assuming 

round crowns, the estimated percent crown coverage 

for the low and medium-low thinnings were 27 and 

56 percent, respectively. Changes in crown width 

were not evident; however, crown density and vigor 

(unmeasured) appeared better after the thinnings.

Table 1.—Annual basal area and d.b.h. growth over 4 years and initial crown widths by thinning treatment.

Post-cut Annual gross Annual Initial

basal area Initial basal area average average

Thinning Treatment per acre mean d.b.h. growth/acre d.b.h. growth crown width

ft2 in	 ft2 in	 ft

Low 32 12.7 1.08 0.21 20.4

Medium-Low 60 11.1 2.74 0.25 18.7

Control 148 7.7 3.49 0.10 18.8

Diameter growth was not well related to tree d.b.h. 

in the thinning treatments (Fig. 4A and 4B) but were 

related slightly better to d.b.h. in the control, due mostly 

to low growth rates of the smaller trees (Fig. 4C). In 

calculating basal area growth rates, the average d.b.h. 

growth rates were used, applied to the trees per acre 

calculated from the prism cruises. 

During the last (fourth) year, the average d.b.h. growth 

rates were 0.36 inches for the low and medium-low 

thinnings, and 0.1 inches for the control. Apparently, the 

residual trees in the thinnings continued to respond with 

increasing rates of growth. 

As an aside, the low and medium-low thinnings acted 

as shelterwood harvests. Regeneration of white pine, 

oak (Quercus spp.), and other species, sometimes 

under short-lived grey birch (Betula populifolia), was 

visibly very abundant. A small sample of 20 milacres 

in the medium-low thinning, assessed by recording the 

dominant stem and dominant commercial stem, showed 

40 percent oak or pine, 20 percent grey birch over oak or 

pine, 25 percent other species (red maple [Acer rubrum], 

balsam fir [Abies balsamea], aspen [Populus spp.]), and 

15 percent (nonstocked or no commercial species). This 

influx of regeneration was the result of a good white 

pine seed year, a heavy harvest to thoroughly scarify the 

seedbed, and wildlife activity to plant acorns under the 

overhead white pine cover. 
Figure 4.—Annual d.b.h. growth over the 4-year period for 

the A) low density, B) medium-low density, and C) control 

plots.

Discussion

This short-term study showed a rapid response of 

declining white pine to low and medium-low density 

thinning. Diameter growth in both treatments was twice 

that of the control. Based on the last year’s rate, the 

trees are growing at about 1 inch in diameter in 3 years. 

At this rate, the trees will grow about 10 inches in 30 

years, and will average over 20 inches in d.b.h. Similar 

to other studies, basal area growth was about one-third 

(low density) to three-fourths (medium-low) of that in 

the control. However, over time, as the crowns close, 

the per-acre growth will approach that of a fully stocked 

stand—especially under the medium-low thinning. 

Considering both diameter growth and basal area growth 

per acre, the 60-ft2

 treatment (medium-low) was better 

than the low-density thinning. Low-density management 

is best applied with repeated pruning of the lower dead 

branches, beginning when the stand is of poletimber size. 

Without pruning, as in this study, a longer time period 

will be needed to develop large trees with a component 

of quality sawtimber. 

One common concern over low-density thinning is the 

abundant understory development, which could limit 

desirable regeneration or require substantial investments 

during the regeneration phase. However, this study 

shows that with preparation and foresight, a low-density 

thinning can be the start of an effective shelterwood 

harvest.

Literature Cited

Guiterman, C.H.; Weiskittel, A.R.; Seymour, R.S. 

2011. Influences of conventional and low-density 

thinning on the lower bole taper and volume 

growth of eastern white pine. Northern Journal 

of Applied Forestry. 28: 123-128.

Hunt, F.M.; Mader, D.L. 1970. Low-density 

management-a means to increase timber yields 

while using less soil moisture. Bull. No. 588. 

Amherst, MA: Massachusetts Agricultural 

Experiment Station. 24 p.

A

B

C

D.b.h. (in)

D.b.h. (in)

D.b.h. (in)

Annual d.b.h. growth Annual d.b.h. growth Annual d.b.h. growth

Low Density

Medium-low Density

Control
Leak, W.B.; Lamson, N.I. 1999. Revised white pine 

stocking guide for managed stands. NA-TP-01-99. 

Radnor, PA: U.S. Forest Service, Northeastern Area 

State and Private Forestry. 2 p.

Livingston, W.H.; Granger, G.; Fries, M.; Granger, 

C.; Trial, H.; Struble, D.; Steinman, J.; Howell, S. 

2005. White pine decline in Maine. Powerpoint 

document at: https://extension.unh.edu/resources/

files/Resource001710_Rep2384.pdf. (Accessed 

November 19, 2012).

Seymour, R.S. 2007. Low-density management of 

white pine crop trees: a primer and early research 

results. Northern Journal of Applied Forestry. 24: 

301-306.

Seymour, R.S.; Smith, D.M. 1987. A new stocking 

guide formulation applied to eastern white pine.

Forest Science. 33: 469-484.

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