United States

Department of 

Agriculture

Forest Service

Northern 

Research Station

Research Paper NRS-19

Tree Species 

Migration Studies in 

the White Mountains of 

New Hampshire

William B. Leak

Mariko Yamasaki
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Abstract

The movement of tree species in either latitude or elevation has attracted increased recent 

attention due to growing national/international concerns over climate change. However, 

studies on tree species movements began in the early 1970s in the White Mountains of New 

Hampshire, mostly due to ecological interests in the episodic behavior of upper-elevation 

tree species on some of the most scenic mountains. Observations taken while making 

elevational transects appeared to indicate that regeneration of some species was advancing 

or retreating in relation to the main stand of mature trees. This process was formalized into a 

graphical model that would predict rates of movement which was then tested on the Bartlett 

Experimental Forest located in the White Mountain National Forest. This paper describes the 

several types of migrational models that were developed as well as long-term remeasured 

plot evidence against signifi cant recent changes in the species distributions.

Manuscript received for publication 3 October 2011

Cover Photo

Bartlett Experimental Forest, White Mountain National Forest. Photo by Ken Dudzik, U.S. 

Forest Service.
1

INTRODUCTION

Change in the distribution of tree species has been a subject of 

considerable interest in New England. One line of research focused on 

prehistoric species distributions as evidenced through pollen analysis 

(e.g., Gajewski 1987, Spear et al. 1994) in relation to early trends in 

climatic regimes. For example, at Mirror Lake in New Hampshire, near 

the Hubbard Brook Experimental Forest, pollen diagrams have traced 

the overwhelming changes from spruce-birch-pine dominance 10,000 

to12,000 years ago through pine-oak during the period from 6,000 to 

10,000 years ago to beech-hemlock-birch from 6 thousand years ago to 

the present (Spear et al. 1994).

More recently, in response to concerns over climate change, computer 

models have projected major changes in species distributions based 

primarily on projected changes in temperature/precipitation regimes 

from available global circulation models coupled with covariates related 

to soils, elevation, and landscape variables (e.g., Iverson and Prasad 

1998, Iverson et al. 2011). Related analyses (Woodall et al. 2009) of 

the latitudinal peaks in tree biomass versus seedling abundance have 

provided broad-scale snapshots of species migrational tendencies in 

eastern United States.

In the 1970s, prior to the research dominated by climate-change 

hypotheses, research in the White Mountains of New Hampshire 

attempted to describe the observable elevational characteristics of 

tree species and, as followup, to examine the evidence for tree species 

migration, especially at the upper limits of their elevational ranges. 

Th e purpose of this paper is to describe the elevational transects, the 

fi eld-based models derived from this work, and documented changes in 

species distributions provided by long-term remeasurements.

Th e Authors

WILLIAM B. LEAK and 

MARIKO YAMASAKI are a 

research forester and research 

wildlife biologist, respectively, 

with the U.S. Forest Service’s 

Northern Research Station in 

Durham, New Hampshire.
2

ELEVATION TRANSECTS

In the early 1970s, transects were run up the sides of Mt. 

Washington (elevation 6,290 feet,) and Mt. Whiteface 

(elevation 4,020 feet) with the purpose of describing 

the species and size/age development of the vegetation 

in relation to elevation (Leak and Graber 1974a). Th e 

disturbance histories varied: Mt. Washington had been 

logged up to about 3,000 feet elevation in the 1800s 

primarily for softwood. Mt. Whiteface had never been 

logged.

On Mt. Washington, diameters were measured on all 

stems taller than 4.5 feet on plots located at every 33-foot 

rise in elevation. Th e largest and smallest stems by species 

were aged by increment cores, sectioning, or counting 

terminal bud scars.

On Mt. Whiteface, basal areas were measured by species 

with a 10-factor prism at every 50- foot rise in elevation 

and the largest and smallest stems in the prism count, 

or 3.3- by 33-foot subplot, were measured for diameter 

and age. Th ese transects provided an elevational sequence 

showing species occurrence, abundance, and sizes 

between around 2,000 to 3,900 feet (Mt. Whiteface ) or 

4,500 feet (Mt. Washington) above sea level (Fig. 1). In 

general, softwoods were more abundant at elevations of 

2,625 to 2,950 feet and above, while hardwoods (except 

paper birch) were most abundant below that level. Most 

of the high-elevation paper birch was mountain paper 

birch (Betula papyrifera var. cordifolia).

During the intensive fi eld work required for these 

transects, R.E. Graber, research ecologist, noted that many 

species showed elevational trends in size distributions: 

in some cases, small (apparently young) trees occurred 

far upslope or downslope of the body of mature trees; in 

other areas, large and small trees were together. Graphical 

analysis of maximum and minimum age in relation to 

elevation showed, in some cases, the trends illustrated 

in Figures 2, 3, and 4 where species such as yellow birch 

(Betula alleghaniensis) and paper birch appeared to have 

an upward-moving elevational front (young trees out in 

front of older trees) while other species, such as beech 

(Fagus grandifolia), showed a stationary front. Based on 

these preliminary observations, a graphical model of tree 

species movements was developed as well as a description 

of several types of migrational fronts.

Figure 1.—Elevational ranges of woody species on Mt. Whiteface and Mt. Washington, 

based on occurrence of stems over 1 year old. Transects began around 2,000 and 

2,100 feet above sea level and ended around 3,900 and 4,500 feet, respectively (Leak 

and Graber 1974a).
3

Figure 2.—Maximum and minimum age for beech over 

elevation on Mt. Whiteface, showing approximate shape of 

migrational fronts (Leak and Graber 1974a).

Figure 3.—Maximum and minimum age for yellow birch over 

elevation on Mt. Whiteface, showing approximate shape of 

migrational fronts (Leak and Graber 1974a).

Figure 4.—Maximum and minimum age for paper birch over 

elevation on Mt. Whiteface, showing approximate shape 

of migrational fronts. In this case, the curves are drawn as 

envelope curves, ignoring some of the irregularities in plotted 

points (Leak and Graber 1974a).
4

MIGRATIONAL MODELS

Assuming that tree species move at a fairly constant rate 

(a simplifi cation), the relationship of age over distance or 

elevation would appear like Figure 5 (Leak and Graber 

1974 b). Th e rate of movement would simply be the 

inverse of the slope of the relationship of maximum 

age plotted/regressed over distance. Figure 5 shows this 

relationship even if the trend is discontinuous due to 

missing data. A stationary front is represented by trees 

of maximum age and minimum age occurring at the 

same location. A retreating front shows a reverse slope. 

Obviously, this approach is viable where the movement 

is gradual and continuous, without discontinuous 

breaks as might occur with dispersal by birds or human 

transportation. It is most applicable to shade-tolerant 

species, which gradually invade the understory, but also 

should apply to less tolerant species at high elevations 

where natural wind disturbance is frequently severe. 

Heavy disturbances from land-use changes or heavy 

harvesting, for example, would disrupt the understory 

and midstory development and age relationships. Figure 

5 also illustrates age-distance relationships where there 

is no movement (stationary) or a retreating front. Th is 

model is similar to the approach applied by Woodall 

et al. (2009) at a broader regional scale based on the 

latitudinal distribution of biomass versus seedling counts; 

however, the White Mountain approach provides an 

estimated time-scale.

To test the validity of this model and to further examine 

the preliminary graphics from Mts. Washington and 

Whiteface, another study was conducted in the 1990s on 

Upper Haystack Mountain (2,995 feet elevation) on the 

Bartlett Experimental Forest in central New Hampshire 

(Solomon and Leak 1994). Fixed plots along the contour 

coupled with prism plots were taken at every 100 feet 

horizontal distance up to an elevation of 2,420 feet, and 

then every 50 feet to an elevation of 2,700 feet. Th e site 

was classifi ed at each point to aid in the interpretation 

of species occurrences (Leak 1982). Elevations were then 

developed from contour maps. Ages were taken on four 

species: beech, sugar maple (Acer saccharum), red spruce 

(Picea rubens), and eastern hemlock (Tsuga canadensis). 

Age/diameter at breast height (d.b.h.) regressions were 

developed to predict tree ages throughout the range in 

tree size; R2 values ranged from 0.40 (red spruce) to 0.95 

(sugar maple).

Although variability was high, several consistent 

migrational patterns emerged (Fig. 6). Red spruce and 

beech showed stationary fronts, i.e., no indication of 

migrational change in elevation. Red spruce showed a 

double, stationary front due to the species absence on 

the fi ne till soils better suited to deciduous species (Leak 

1982). Sugar maple showed a retreating/collapsing front 

at its upper elevational limit (about 2,400 feet); there were 

small seedlings, but no trees of intermediate age apparently 

due to competition from an aggressive beech understory. 

Hemlock showed an advancing front; the inverse of the 

slope of a linear regression of age over distance provided 

an estimated migration rate of about 2 feet per year 

(horizontal distance)—very slow but measurable.

Based on the Haystack study (Solomon and Leak 1994), 

a series of hypothetical advancing-front scenarios were 

developed ranging from constantly advancing fronts, 

accelerating or decelerating, to incipient, catastrophic, 

and stationary fronts (Fig. 7). As yet, all of these 

possibilities have not been fi eld-detected. “Incipient” 

means the apparent beginning of an advancing front not 

yet fully developed. “Catastrophic” (or collapsing) means 

the disappearance of entire age classes.

LONG-TERM MIGRATION RECORDS

Although the models developed for the White Mountain 

region reveal migrational tendencies, confi rmation 

of species’ changes in elevation comes only from 

long-term remeasurements. Fortunately, such longterm confi rmation is available from the cruise plots 

on the Bartlett Experimental Forest. A network of 

about 450-500 plots, mostly quarter-acre in size, were 

established in 1931-32 covering a range in elevation 

from about 700 feet above sea level to over 2,900 feet 

near the top of Upper Haystack Mountain. Complete 

remeasurements in 1931-32, 1991-92, and 2002-

03 of all trees in the 2-inch class (1.5 to 2.5 inches 

d.b.h.) and larger, and some partial remeasurements 

in intervening years, provided a detailed account of 

successional trends and changes in species abundance 

by elevation classes. In examining species’ movements, 
5

it is important to recognize that species’ occurrences are 

limited by site conditions (Demers et al. 1998) (see also 

Fig. 6). Hemlock is the ideal indicator species since it is 

climatically limited, found at mid- to lower elevations in 

the White Mountains, but also adapted to the shallowbedrock sites found at higher elevations. Additionally, 

hemlock is a very tolerant and aggressive species on 

suitable sites. More demanding species such as sugar maple 

and ash are very uncommon on such sites, especially on 

low-nutrient bedrock types such as granite.

Analyses of these cruise plot records up through 1984 

(partial remeasurement) (Leak 1987) and 1991-92 (Leak 

and Smith 1996) showed little indication that hemlock 

was invading stands above about 2,000 feet elevation. A 

detailed analysis of changes in seedling/sapling understory 

trees (1.5 to 4.5 in. d.b.h.) based on the 2002-03 

remeasurement (Table 1) again showed little evidence 

that hemlock was invading the upper elevations 

dominated by red spruce and miscellaneous hardwoods 

(Leak 2009). An overstory analysis gave similar fi ndings 

(Leak and Yamasaki 2010) showing that the percent 

composition of hemlock at mid-elevations roughly 

doubled but remained near zero above about 2,100 

feet except for a few large trees (17 inches d.b.h. and 

larger). Th e upper-elevation numbers are variable due 

to the heavy natural wind disturbances that occur on 

these shallow-bedrock sites where hardwoods (especially 

yellow birch and beech) are aggressive open-canopy 

invaders. Th e Haystack transect (Fig. 6) indicated that 

hemlock was moving at about 2 feet in horizontal 

distance per year. Over 70 years (the cruise-plot record), 

Figure 5.—Hypothetical relationships of maximum and 

minimum age related to elevation for a species that is A. 

advancing; B. static or stationary; or C. retreating (Leak and 

Graber 1974b).

Elevation Year Red Spruce Hemlock

(ft) (%) (%)

1500-1600 1931-32 9 22

2002-03 10 25

1600-1700 1931-32 8 13

2002-03 8 16

1700-1800 1931-32 22 10

2002-03 11 8

1800-1900 1931-32 9 9

2002-03 9 15

1900-2000 1931-32 36 7

2002-03 21 4

2000-2100 1931-32 50 2

2002-03 22 2

2100-2200 1931-32 55 2

2002-03 44 1

2200-2300 1931-32 53 -

2002-03 30 4

2300-2400 1931-32 47 1

2002-03 33 -

2400-2700 1931-32 29 -

2002-03 32 -

Table 1.—Percent seedlings/saplings (1.5 to 4.5 inches 

d.b.h.) of red spruce and hemlock by year and elevation 

on the Bartlett Experimental Forest (Leak 2009).
6

Figure 6.—Predicted maximum and minimum ages (stems more than 3.28 feet tall) over 

horizontal distance for the major species on Haystack Mountain (Solomon and Leak 1994).

this would amount to about 140 feet horizontal distance. 

At 25-50 percent slope, this horizontal movement would 

amount to about 35-70 feet elevation, not a large change 

but perhaps somewhat more than shown by the cruiseplot record. However, Fig. 6 represents long-term past 

movement along a single transect, possibly infl uenced by 

early harvesting activity.

As a supplement to the White Mountain studies, species 

changes were analyzed on more than 500 U.S. Forest 

Service Inventory and Analysis (FIA) plots throughout 

Maine during the period from 1950-60 to the early 

1980s, an average period of 24 years (Solomon and Leak 

1994). Th e basic approach was to compare the latitudes, 

longitudes, and elevations initially occupied by major 
7

Figure 7.—Schematic examples of types of fronts: advancing (A-C); retreating (D-F); incipient (G); 

catastrophic (H); stationary (I) (Solomon and Leak 1994).

species with those newly occupied at the end of the 24-

year period. Results indicated that white pine and balsam 

fi r had moved slightly (but signifi cantly) lower in both 

elevation (50 and 23 feet, respectively) and latitude (2.1 

and 0.85 miles, respectively). Very likely, these changes 

were due to land-use impacts (primarily cessation of 

agriculture), which are very diffi cult to assess and often 

very confusing in developing regional evaluations.

SUMMARY AND CONCLUSIONS

Transects of tree species and ages on Mts. Whiteface, 

Washington, and Haystack in the White Mountains 

of New Hampshire were utilized in developing a series 

of geometrical models showing migrational patterns of 

tree species in either elevation or distance. Th ese studies 

were followed by examination of changes in species 
8

occurrences on U.S. Forest Service Forest Inventory plots 

in Maine and longterm, remeasured cruise plots, over a 

range of elevations, on the Bartlett Experimental Forest 

in New Hampshire.

Despite national/international concerns over the purported 

impacts of climate change on forest conditions, this 

series of studies in New England’s White Mountains and 

adjacent Maine showed no consistent patterns of climaterelated species’ movements in either elevation or latitude. 

Th e primary agent of change in species composition of 

the northern hardwood-hemlock and spruce-fi r types in 

this region continues to be natural succession.

LITERATURE CITED

Demers, J.D.; Lee, T.D.; Barrett, J.P. 1998. Substrate 

type and the distribution of sugar maple at its 

elevational limit in the White Mountains, New 

Hampshire. Canadian Journal of Forest Research. 28 

494-498.

Gajewski, K. 1987. Climatic impacts on the vegetation 

of eastern North America during the past 2000 

years. Vegetatio. 68: 179-190.

Iverson, L.R.; Prasad, A.M. 1998. Predicting abundance 

of 80 tree species following climate change in the 

eastern United States. Ecological Monographs. 68: 

465-485.

Iverson, L.R.; Prasad, A.M.; Mathews, S.N.; Peters, M.P. 

2011. Lessons learned while integrating habitat, 

dispersal, disturbance, and life-history traits into 

species habitat models under climate change.

Ecosystems. 4: 105-1020.

Leak, W.B. 1982. Habitat mapping and interpretation 

in New England. Res. Pap. NE-496. Broomall, 

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

Northeastern Forest Experiment Station. 28 p.

Leak, W.B. 1987. Fifty years of compositional change in 

deciduous and coniferous types in New Hampshire.

Canadian Journal of Forest Research. 17: 388-393.

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

development by elevation class in a New 

Hampshire mixed forest: management 

implications. Northern Journal of Applied Forestry. 

11: 164-166.

Leak, W.B.; Graber, R.E. 1974a. Forest vegetation 

related to elevation in the White Mountains of 

New Hampshire. Res. Pap. NE-299. Upper Darby, 

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

Northeastern Forest Experiment Station. 7 p.

Leak, W.B.; Graber, R.E. 1974b. A method for 

detecting migration of forest vegetation. Ecology. 

55: 1425-1427.

Leak, W.B.; Smith, M.L. 1995. Sixty years of 

management and natural disturbance in a New 

England forested landscape. Forest Ecology and 

Management. 81: 63-73.

Leak, W.B.; Yamasaki, M. 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.

Solomon, D.S.; Leak, W.B. 1994. Migration of tree 

species in New England based on elevational and 

regional analyses. Res. Pap. NE-688. Radnor, PA: 

U.S. Department of Agriculture, Forest Service, 

Northeastern Forest Experiment Station. 9 p.

Spear, R.W.; Davis, M.B.; Shane, L.C.K. 1994. Late 

quaternary history of low- and mid-elevation 

vegetation in the White Mountains of New 

Hampshire. Ecological Monographs. 64: 85-109.

Woodall, C.W.; Oswalt, C.M.; Westfall, J.A.; Parry, 

C.H.; Nelson,M.D.; Finley, A.O. 2009. An indicator 

of tree migration in forests of the eastern United 

States. Forest Ecology and Management. 257: 1434-

1444.
Printed on Recycled Paper

Leak, William B.; Yamasaki, Mariko. 2012. Tree species migration studies in the 

White Mountains of New Hampshire. Res. Pap. NRS-19. Newtown Square, PA: 

U.S. Department of Agriculture, Forest Service, Northern Research Station. 8 p.

The movement of tree species in either latitude or elevation has attracted increased 

recent attention due to growing national/international concerns over climate change. 

However, studies on tree species movements began in the early 1970s in the White 

Mountains of New Hampshire, mostly due to ecological interests in the episodic 

behavior of upper-elevation tree species on some of the most scenic mountains. 

Observations taken while making elevational transects appeared to indicate that 

regeneration of some species was advancing or retreating in relation to the main 

stand of mature trees. This process was formalized into a graphical model that would 

predict rates of movement which was then tested on the Bartlett Experimental Forest 

located in the White Mountain National Forest. This paper describes the several types 

of migrational models that were developed as well as long-term remeasured plot 

evidence against signifi cant recent changes in the species distributions.

KEY WORDS: tree species migration, tree species elevation ranges, New England, 

forest climate-change impacts, mountain ecology, tree migration models

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