United States

Department of

Agriculture

Forest

Service

Northern

Research Station

Research Paper

NRS-13

SEVENTY-YEAR RECORD OF CHANGES

IN THE COMPOSITION OF OVERSTORY

SPECIES BY ELEVATION ON THE

BARTLETT EXPERIMENTAL FOREST

William B. Leak and Mariko Yamasaki
Abstract

Remeasurements over a 70-year period (1931-1932 to 2002-2003) on 404 cruise 

plots on the Bartlett Experimental Forest in New Hampshire provided a record 

of landscape-level changes in the composition of overstory species over time 

by elevation and d.b.h. (diameter at breast height) classes. Typically, early to 

mid-successional species declined while late successional species, especially 

hemlock, increased. The exception was at upper elevations (2,000 feet and 

higher), where natural wind disturbance maintained a variable component of 

paper and yellow birch. There is no evidence of species decline or migration 

that is inconsistent with natural succession or natural disturbance.

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USDA FOREST SERVICE USDA Forest Service

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Delaware, OH 43015-8640

September 2010 Fax: 740-368-0152

The Authors

WILLIAM B. LEAK is a research forester, and MARIKO YAMASAKI is a research 

wildlife biologist, with the USDA Forest Service’s Northern Research Station at 

Durham, New Hampshire.

Manuscript received for publication April 2010

Cover Photo

Upper, Middle, and Lower Haystack Mountains on the Bartlett Experimental 

Forest. Photo by U.S. Forest Service.
Page 1

INTRODUCTION

Over the past several centuries, the forests of New 

England have been subjected to many threats and 

disturbances including heavy timber harvesting and 

fi res coupled with possible environmental threats such 

as acid rain, climate change, and nutrient depletion 

(Leak 2009). Long-term information on the forest 

resource can be used to evaluate these disturbances. 

In 1931-1932, a systematic series of about 500 cruise 

plots (mostly 1⁄4-acre) was established on the Bartlett 

Experimental Forest in central New Hampshire 

(Fig. 1). Elevations on these plots ranged from about 

600 to 2,700 feet. All trees 1.5 inches in diameter 

breast height (d.b.h.) and larger were tallied by 

species. Remeasurements were made in 1939, 

1991-1992, and 2002-2003, and subsets of the 

plots were measured in the 1950s and 1960s.

The Bartlett Experimental Forest, an area of 2,600 

acres when the cruise plots were established, 

consists of three elevation zones that vary in history, 

management activity, and site conditions. Most of 

the lowest zone, about 600 to 1,100 feet, was cleared 

around 1890 for railroad fuel and limited agriculture; 

some softwood stands were left intact. The soils 

consist of water-worked granitic material supporting 

red maple/beech types along with imperfectly drained 

basal till supporting softwoods (hemlock, red spruce, 

and some balsam fi r1

). This lower zone has received 

partial harvests associated with a study of growth 

related to stand density as well as some group/patch 

harvests and one shelterwood cut (these heavier 

cutover areas were eliminated from this analysis).

Figure 1.—Location and compartments. Original compartments are in blue; managed expansion area 

compartments are in pale yellow.

1

 Common and scientifi c names of all trees listed in this 

report can be found in the Appendix on page 12.
Page 2

The middle zone, ranging in elevation from about 

1,100 to 1,800 feet, may have received light partial 

harvests for the best softwoods before 1900, but this 

area never was cleared. Much of the middle zone 

was harvested by single-tree selection one to three 

times between the 1950s and early 1990s. The soils 

are mostly fi ne tills supporting typical mature/oldgrowth northern hardwoods. Some areas of softwood 

(hemlock with some spruce) are associated with 

heavily washed materials along the drainages. 

Clearcuts and shelterwoods since the 1980s were 

omitted from this analysis. 

The upper zone, 1,900 to 2,900 feet (available cruise 

plots up to 2,700 feet), is unmanaged except for some 

light harvests at the lower extremes. Some of the best 

softwoods might have been removed before 1900. 

Much of this area is shallow to bedrock supporting 

spruce with some fi r and very few hemlock, though 

there are pockets of fi ne till with a stronger hardwood 

component. A few small areas of shallow bedrock, 

facing southerly, support some red oak and white pine. 

The plot information has been analyzed for various 

purposes (Jensen 1941a; Filip et al. 1960; Leak 1961a, 

b; Leak and Smith 1997) including estimates of growth 

rates and changes in species composition. Understory 

changes (trees 1.5 to 4.5 inches in d.b.h.) between 

1931-1932 and 2002-2003 were analyzed to determine 

whether there were measurable effects of climate 

change. Results showed that understory hemlock, a 

climatically limited species, was not replacing red 

spruce at upper elevations (1,900+ feet) (Leak 2009). 

These two species occupy similar sites apart from the 

elevation difference. The conclusion was that climate 

change was having no effect on species distribution in 

the Bartlett Experimental Forest or adjacent regions.

This analysis addresses spatial and temporal changes 

in overstory species composition by elevation class. 

It shows which species/size classes are increasing 

or declining, and suggests reasons for these changes 

based on numerous research studies on the Forest. 

Comparisons are at the landscape scale and include 

unmanaged and lightly managed stands, except at 

upper elevations, i.e., the upper unmanaged zone.

METHODS

The cruise plots were laid out in 1931-1932 on a 

regular grid of 5 by 10 chains. Nearly all were square 

1⁄4-acre plots with a very few of 1/10-acre. All trees 

1.5 inches and larger in d.b.h. were tallied by species 

and 1-inch d.b.h classes. All remeasurements followed 

the same procedure. The most recent complete 

remeasurement (2002-2003) included marking dead 

trees with three axe marks. This allows recognition of 

new dead trees during each ensuing remeasurement as 

well as an estimation of periodic mortality.

The number of trees per plot by species and 1-inch 

d.b.h. classes was recorded from the original tally 

sheets; live trees tabulated as defective were included. 

The original tally sheets were faded but mostly 

legible. The trees per plot then were tallied from 

the electronic records available from the 2002-2003 

survey. Plot records from recently regenerated areas 

and records that seemed fl awed (no understory, excess 

numbers of trees, etc) were eliminated, leaving 404 

plots comprising 47.3, 37.0, and 16.0 acres in the 

low, middle, and upper elevation zones, respectively. 

Elevation per plot (100-foot classes) was determined 

from a base map showing both contours and the plot 

grid. Numbers of trees by 100-foot interval were 

summarized by species and d.b.h. groups: 5 to 10 

inches, 11 to 16 inches, and 17+ inches. Species 

composition (percent of trees) was calculated by d.b.h 

group, 100-foot elevation class, and year (designated 

1932 and 2003). Species composition in Figs. 2-27 is 

based on number of trees by d.b.h. group and elevation 

class. For example, in Figure 2, 37 percent beech in 

the 5- to 10-inch d.b.h. class at an elevation of 1,150 

feet in 2003 means that beech comprises 37 percent of 

the stems in that size class relative to the stems of all 

other species. Note that the vertical scale varies among 

the fi gures. 
Page 3

RESULTS AND DISCUSSION

Beech

Over the 70-year period, beech poletimber (5 to 10 

inches, Fig. 2) increased or maintained its composition 

at all elevations but was most predominant between 

about 1,200 to 2,000 feet where it attains a maximum 

composition of nearly 40 percent. Above that point, 

spruce-fi r becomes the predominant type. Below 

1,200 feet (in the low elevation zone) species such 

as eastern hemlock, eastern white pine, red maple, 

and paper birch predominate. These areas, underlain 

with water-worked soils and compact till, are less 

suitable for northern hardwoods. This trend with 

elevation is similar in the larger d.b.h. classes (Figs. 

3 and 4). The 11- to 16-inch stems maintained an 

essentially constant composition over time, while 

the larger stems generally declined, no doubt due 

to the combined effects of the beech scale-Nectria 

disease and the timber-sale marking of defective/risky 

beech. However, 17+-inch beech increased somewhat 

at 2,000+ elevations where there was little or no 

management. Composition of the larger beech at 

mid-elevations maintained at about 30 to 40 percent. 

Long-term results on one managed compartment, 

harvested three times beginning in 1952, showed 

a minor decline in the proportion of beech from 

53 percent basal area in 1952 to 49 percent in 

2000. But there were increases in the proportion 

of sawtimber-size trees and signifi cant increases in 

quality, indicating that management can produce a 

healthy, productive component of beech despite the 

beech-bark disease (Leak and Sendak 2002).

Composition (%)

Elevation (feet)

Figure 2.—Percent composition of 5- to 10-inch beech 

in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 3.—Percent composition of 11- to 16-inch 

beech in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 4.—Percent composition of 17+-inch beech in 

1932 and 2003 by elevation.
Page 4

Yellow Birch

Composition of 5- to 10-inch yellow birch declined 

appreciably over time at and slightly above midelevations (1,000-2,000 feet) from about 25 percent 

to about 10 percent (Fig. 5). Smaller stems of this 

mid-successional species are beginning to decline due 

to a lack of regeneration openings. Yellow birch will 

be reduced to a minor component without regeneration 

openings provided by timber harvests or intense 

natural disturbance. However, at elevations above 

2,000 feet, pole-size yellow birch is maintaining its 

composition (though in variable fashion) due to the 

heavy natural disturbance that characterizes these 

shallow-bedrock, higher elevation sites (see Jensen 

1941b for details on the 1938 hurricane). Apparently, 

yellow birch, and paper birch in some areas, can be 

considered components of the upper elevation, late 

successional forest due to their continued maintenance 

by natural disturbance (Leak 1975). Larger stems have 

maintained at 10 to 20 percent or slightly declined 

in composition at mid-elevations (Figs. 6 and 7). 

However, the composition of these larger stems will 

decline over time due to lack of ingrowth from smaller 

trees. Again, note the positive effects of natural 

disturbance on 11- to 16-inch stems coupled with a 

loss in the 17+-inch class at upper elevations.

Figure 5.—Percent composition of 5- to 10-inch yellow 

birch in 1932 and 2003 by elevation.

Elevation (feet)

Composition (%)

Figure 6.—Percent composition of 11- to 16-inch 

yellow birch in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 7.—Percent composition of 17+-inch yellow 

birch in 1932 and 2003 by elevation. 
Page 5

Sugar Maple

Somewhat similar to yellow birch, sugar maple shows 

a decline in 5- to 10-inch composition (down to 

about 5 percent) over much of the midrange (Fig. 8). 

Although a tolerant, late successional species, there 

is some evidence that regeneration of sugar maple in 

this region is aided by disturbance (Leak 2005). This 

may be true especially on poorer soils derived from 

low-nutrient, granitic bedrock. An earlier study based 

on 101 cruise plots in mid-elevation compartments 

treated with single-tree selection showed a decline 

(about 50%) in sugar maple understories (2-, 3-, and 

4-inch trees) between 1931-1932 and 1991-1992 

in compartments harvested once, but only a minor 

decline in compartments harvested twice; increases 

in beech understories were moderate to slight, 

respectively. There were major increases in hemlock 

and especially in striped maple (Leak 2006). 

The 11- to 16-inch sugar maple stems, though variable 

in percent composition, appear to maintain at about 

15 percent. The 17+-inch stems show increases over 

time, some to nearly 50 percent, apparently replacing 

the larger beech (Figs. 9 and 10). However, stems in 

both of these larger classes decreased at the highest 

elevations due to intense natural disturbance. There 

seems no evidence of the decline in maple that has 

been of concern farther west (Horsley et al. 2002). 

However, regeneration and continued ingrowth of 

sugar maple is the primary concern in maintaining 

this species.

Figure 8.—Percent composition of 5- to 10-inch sugar 

maple in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 9.—Percent composition of 11- to 16-inch 

sugar maple in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 10.—Percent composition of 17+-inch sugar 

maple in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)
Page 6

Red Maple

Apparent increases in red maple in the eastern United 

States have caused concern (Alderman et al. 2005), 

though this species is much more marketable in 

recent years. Red maple of all sizes at the Bartlett 

Forest maintains a composition of about 30 percent 

at elevations below about 1,000 feet (Figs. 11-13). 

Some of the heavily water-worked or compact soils 

are conducive to softwood species, and red maple 

is a common associate in softwood types. At the 

middle and upper elevations, this species maintains 

a moderate composition (about 10 percent). Moderate 

proportions of 5- to 10-inch stems at these elevations 

indicate that red maple probably will not increase 

appreciably in the future. 

Figure 11.—Percent composition of 5- to 10-inch red 

maple in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 12.—Percent composition of 11- to 16-inch red 

maple in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 13.—Percent composition of 17+-inch red 

maple in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

rmaple 1932

rmaple 2003
Page 7

Paper Birch 

An early-successional species, paper birch declined to 

less than 5 percent in all size classes at mid-elevations. 

There was less decline in trees larger than 5 to 10 

inches in d.b.h. at elevations below about 1,000 feet,

where there are younger stands; and there was 

appreciably less decline on sites at upper elevations 

due to continued natural wind disturbance (Figs. 

14-16). Similar to yellow birch, paper birch remains a 

component of upper elevation spruce-fi r stands (Leak 

1975). Over time and without management, only 

areas at these upper elevations will have a signifi cant 

component of paper birch. 

Figure 14.—Percent composition of 5- to 10-inch 

paper birch by in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 15.—Percent composition of 11- to 16-inch 

paper birch by elevation in 1932 and 2003. Composition (%)

Elevation (feet)

Figure 16.—Percent composition of 17+-inch paper 

birch in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)
Page 8

Aspen

Aspen once accounted for as much as 30 percent of 

the 5- to 10-inch class at low elevations and about 9 

percent of the 11- to 16-inch class (Figs. 17 and 18). 

By 2003, aspen was virtually absent from the lightly 

managed or unmanaged areas except for an ephemeral 

component of 11- to 16-inch trees at low elevations. 

Unlike the birches, aspen is not a component of the 

naturally-disturbed stands at upper elevations.

Red Spruce and Eastern Hemlock

Except for an increase in the 5- to 10-inch trees on 

softwood sites at low elevations, the upper elevations 

remain a stronghold for red spruce where it accounts 

for more than 50 percent in all sizes despite variability 

due to natural disturbance (Figs. 19-21). Eastern 

hemlock, which grows on similar soils as red spruce 

(e.g., shallow bedrock) is increasing rapidly at lower 

elevations, but is nearly absent in the small and 

medium classes at elevations above 2,000 feet 

(Figs. 22 and 23). The small component of larger 

hemlock above 2,000 feet apparently is not being 

replaced (Fig. 24).

Figure 17.—Percent composition of 5- to 10-inch 

aspen in 1932 and 2003 by elevation.

Figure 18.—Percent composition of 11- to 16-inch 

aspen in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)
Page 9

Figure 19.—Percent composition of 5- to 10-inch red 

spruce in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 20.—Percent composition of 11- to 16-inch red 

spruce in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 21.—Percent composition of 17+-inch red 

spruce in 1932 and 2003 by elevation.

Figure 22.—Percent composition of 5- to 10-inch 

hemlock in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

hem 2003

Figure 23.—Percent composition of 11- to 16-inch 

hemlock in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 24.—Percent composition of 17+-inch hemlock 

in 1932 and 2003 by elevation.
Page 10

Eastern White Pine and Northern Red Oak

Eastern white pine remains a major component of 

the 17+-inch stems at the lowest elevations (Fig. 27), 

but there have been moderate to substantial declines 

in smaller trees over time (Figs. 25 and 26). Early 

clearing and perhaps agriculture, are responsible for 

the presence of white pine. Without such disturbances, 

this species should decline over time and be replaced 

by hemlock and some spruce on softwood sites, and 

by red maple/beech on sandy tills. Of interest is the 

continued presence of a small component of white 

pine, especially in the 17+-inch class, at higher 

elevations along with a small amount of northern red 

oak. These species are common in small numbers on 

shallow bedrock, often on slightly southerly/westerlyfacing slopes. Regeneration is minimal. It may be that 

historical fi res are responsible for their presence.

Figure 25.—Percent composition of 5- to 10-inch 

white pine in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 26.—Percent composition of 11- to 16-inch 

white pine in 1932 and 2003 by elevation. Composition (%)

Elevation (feet)

Figure 27.—Percent composition of 17+-inch white 

pine in 1932 and 2003 by elevation.
Page 11

CONCLUSION

This 70-year analysis of changes in species 

composition over time by elevation class reveals fairly 

typical changes due to natural selection and natural 

disturbance. Generally, early to mid-successional 

species declined while late successional species, 

such as hemlock, increased. However, there were 

exceptions: 1) at elevations above about 2,000 feet, 

paper and yellow birch are maintained by natural wind 

disturbance; 2) hemlock, a rapidly increasing species 

at low to mid-elevations, did not materially invade 

elevations above 2,000 feet, where red spruce remains 

as the dominant softwood; i.e., there is no evidence 

of elevational redistribution due to climate change. 

This conclusion was reinforced by an earlier analysis 

of understory species composition (Leak 2009); 

3) although beech remains as a common, aggressive 

species, there is some indication of a decline in large 

beech at midslope due to the beech bark disease and 

subsequent timber marking of defective, risky trees. 

There is no evidence of decline in sugar maple, red 

spruce or other species except for changes due to 

natural succession. However, without management 

disturbance, the proportion of sugar maple poletimber 

(5 to 10 percent) seems inadequate to maintain current 

levels of sawtimber-sized stems (15 to 30 percent or 

more) at mid-elevations on the Bartlett Experimental 

Forest. 

LITERATURE CITED

Alderman, D.R.; Bumgardner, M.S.; Baumgras, J.E. 

2005. An assessment of the red maple resource 

in the Northeastern United States. Northern 

Journal of Applied Forestry. 22(3):181-189.

Filip, S.M.; Marquis, D.A.; Leak, W.B. 1960. 

Development of old-growth northern 

hardwoods on the Bartlett Experimental 

Forest—a 22-year record. Stn. Pap. 135. 

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

Forest Service, Northeastern Forest Experiment 

Station. 7 p. 

Horsley, S.B.; Long, R.P.; Bailey, S.W.; Hallett, R.A.; 

Wargo, P.M. 2002. Health of eastern North 

American sugar maple forests and factors 

affecting decline. Northern Journal of Applied 

Forestry. 19(1):34-44.

Jensen, V.S. 1941a. Eight year’s growth in hardwood 

stands on the Bartlett Experimental Forest.

Stn. Tech. Note 43. Upper Darby, PA: U.S. 

Department of Agriculture, Forest Service, 

Northeastern Forest Experiment Station. 4 p.

Jensen, V.S. 1941b. Hurricane damage on the 

Bartlett Experimental Forest. Offi ce Report. 

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

Forest Service, Northeastern Forest Experiment 

Station. 15 p. [Report on fi le at the U.S. Forest 

Service, Northern Research Station, offi ce in 

Durham, N.H.]

Leak, W.B. 1975. Age distribution in virgin red 

spruce and northern hardwoods. Ecology. 

56:1451-1454.

Leak, W.B. 1961a. Development of secondgrowth northern hardwoods on the Bartlett 

Experimental Forest—a 25-year record.

Stn. Pap. 155. Upper Darby, PA: U.S. Department 

of Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 8 p. 
Page 12

Leak, W.B. 1961b. Yellow birch grows better in 

mixedwood stands than in northern hardwood 

old-growth stands. Res. Note 122. Upper Darby, 

PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 

4 p.

Leak, W.B. 2005. Effects of small patch cutting on 

sugar maple regeneration in New Hampshire 

northern hardwoods. Northern Journal of 

Applied Forestry. 22(1):68-70.

Leak, W.B.; Sendak, P.E. 2002. Changes in species, 

grade, and structure over 48 years in a 

managed New England northern hardwood 

stand. Northern Journal of Applied Forestry. 

19(1):25-27.

Leak, W.B.; Smith, M.L. 1997. Sixty years of 

management and natural disturbance in a New 

England forested landscape. Forest Ecology and 

Management. 81:63-73.

Leak, W.B. 2006. Sixty years of change in the 

sapling understories of northern hardwood 

selection stands in New Hampshire. Northern 

Journal of Applied Forestry. 23:301-303.

Leak, W.B. 2009. 70 years of understory 

development by elevation class in a New 

Hampshire mixed forest: management 

implications. Northern Journal of Applied 

Forestry. 26:164-166.

APPENDIX

Common and scientifi c names of tree species referred 

to in this report.

Common Name Genus Species

American beech Fagus grandifolia

Yellow birch Betula alleghaniensis

Sugar maple Acer saccharum

Red maple Acer rubrum

Paper birch Betula papyrifera

White ash Fraxinus americana

Red spruce Picea rubens

Eastern hemlock Tsuga canadensis

Balsam fi r Abies balsamea

White pine Pinus strobus

Northern red oak Quercus rubra
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Printed on recycled paper

Leak, William B.; Mariko Yamasaki. 2010. Seventy-year record of changes in the 

composition of overstory species by elevation on the Bartlett Experimental 

Forest. Res. Pap. NRS-13. Newtown Square, PA: U.S. Department of Agriculture, 

Forest Service, Northern Research Station. 12 p.

Remeasurements over a 70-year period (1931-1932 to 2002-2003) on 404 cruise 

plots on the Bartlett Experimental Forest in New Hampshire provided a record 

of landscape-level changes in the composition of overstory species over time by 

elevation and d.b.h. (diameter at breast height) classes. Typically, early to midsuccessional species declined while late successional species, especially hemlock, 

increased. The exception was at upper elevations (2,000 feet and higher), where 

natural wind disturbance maintained a variable component of paper and yellow 

birch. There is no evidence of species decline or migration that is inconsistent with 

natural succession or natural disturbance.

KEY WORDS: northern hardwoods, hemlock, spruce, natural succession, elevation, 

 tree species migration. 
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