United States 

Department of 

Agriculture 

Forest Service 

Northeastern Forest 

Experiment Station 

Research Paper NE-637 

Regionally Averaged Diameter 

Growth in New England Forests 

Robert B. Smith 

James W. Hornbeck 

C. Anthony Federer 

Paul J. Krusic, Jr. 
Abstract 

A regional sample of tree-ring measurements was used to determine average 

annual growth in trees of 10 major species in New England. There have been 

extended periods of decreasing growth rates in red spruce since about 1960 and 

in balsam fir since about 1965. The other eight species, which included sugar 

maple and white pine, showed constant or increasing growth rates through 1980. 

The decreases in growth rate in sampled red spruce and balsam fir were 

independent of physical site characteristics, elevation, and geographic location, 

indicating that regional factors are involved. Weather parameters and indexes 

were not closely correlated with growth rates, and the best predictive equation 

explained only 33 percent of annual variation. Due to past harvests and epidemics 

of the spruce budworm, much of the red spruce-balsam fir forest below 1,000 m 

in elevation can be considered to be functioning as even-aged. Historical growth 

information suggests that these trees should have reached maximum growth 

around 1960, and that decreasing growth rates since then are the result of normal 

aging. 

The Authors 

ROBERT 8. SMITH, JAMES W. HORNBECK, C. ANTHONY FEDERER, and 

PAUL J. KRUSIC, JR., are with the Northeastern Forest Experiment Station's 

Forest Sciences Laboratory at Durham, New Hampshire. 

Manuscript received for publication 16 October 1989 

Cover Cross section from a representative New England red spruce. The center 

ring was formed in 1906. This tree probably germinated after overstory trees were 

felled for lumber or pulpwood. Such harvesting was widespread in the spruce-fir 

forests of New England around the turn of the century. Historical growth data 

suggest that the narrowing rings spanning the most recent 25 years are the result 

of normal aging. 

Northeastern Forest Experiment Station 

5 Radnor Corporate Center, Suite 200 

100 Matsonford Road, Radnor, PA 19087 

April 1990 
Introduction 

Forest health has become a widespread concern in recent 

years in Europe, the United States, and Canada as 

scientists and others have noticed unusual foliage loss, 

narrowing ring widths, and increasing mortality. In the 

Eastern United States and Southeastern Canada, mortality 

and dieback of red spruce seem to have been increasing 

since the late 1960's and early 1970's. Concerns over red 

spruce have led to the closer inspection of other species 

such as sugar maple, balsam fir, eastern white pine, and 

white ash. Maple syrup producers are particularly 

concerned with recent foliar symptoms and diebacks of 

sugar maple (McLaughlin et al. 1985; Mcllveen et al. 1986). 

Some of the earliest reports of declining health were from 

studies of high-elevation red spruce forests in the Northeast 

(Johnson and Siccama 1983, 1984). These sites receive 

acidic precipitation and considerable fog and cloud 

moisture, which is even more acidic than rain and snow 

(Lovett et al. 1982). This has led to the suspicion that 

atmospheric deposition is an important influence on the 

health of high-elevation forests. 

In the early 1980's, the Northeastern Forest Experiment 

Station was in the midst of a 10-year inventory of forest 

resources in New England.' More than 6,000 randomly 

located plots were surveyed for vegetation data and 

physical site characteristics. To determine stand age, one 

increment core was collected from each of four dominant or 

codominant trees adjacent to each plot. More than 20,000 

cores were collected. 

Ten commercially important tree species were well 

represented in this collection, providing a readily available 

source of information for assessing the growth and health of 

New England's forests. We used these increment cores to 

focus on four questions: 1. Did growth rates for any of the 

10 species decrease recently for extended periods? 2. Is 

there a consistent pattern in the timing of any growth 

decreases? 3. Is there a consistent elevational or 

geographic pattern to any decreases? 4. Can growth 

patterns and trends be related to atmospheric deposition or 

other factors? We have attempted to answer these 

questions within the framework of the National Forest 

Response Program, which was established to address 

concerns about impacts of air pollution on tree health 

(Schroeder and Kiester 1989). 

Field Sampling 

The USDA Forest Service inventories each state at intervals 

of 10 to 15 years. Photo interpreters systematically locate 

thousands of points on aerial photographs. Ground plots are 

'Forest Service resource inventory: an overview. 1985. 

USDA Forest Service, Forest Economics Research Staff, 

Washington, DC. 

determined from a stratified random subsample of these 

points. Single increment cores are obtained from each of 

four healthy dominant or codominant trees representing the 

major species on each ground plot. Cored trees are just 

outside the actual plot to prevent possible damage to trees 

on the permanent plot. Trees are cored parallel to the slope 

contour at breast height (1.37 m above ground). The 

recorded data for each tree include species, diameter at 

breast height (d.b.h.), tree height, sample date, and breast 

height age. Each core was stored in a straw that was 

labeled with the state and county codes, and plot and tree 

numbers. Stored cores were allowed to air dry within the 

partially sealed straws. 

Core Preparation 

Increment cores were mounted, with vessels or tracheids 

oriented vertically, in a shallow lengthwise cut in a block of 

kiln-dried softwood. Visibility of annual rings was enhanced 

by mechanically sanding or planing a radial surface of the 

core (Krusic et al. 1987). Annual rings in coniferous species 

have well-defined boundaries that are exposed by 

successive sandings of 220-, 400-, and 600-grit sandpaper 

followed by polishing with a wool buffing pad. Reflected 

light provided adequate illumination for measurement of all 

conifers. 

Ring-porous hardwoods had to be planed because sanding 

occluded vessels and made the rings indistinct. Reflected 

light also is used when measuring these cores. Diffuseporous hardwoods have poorly defined rings, especially in 

sapwood portions, and must be prepared carefully. We 

embedded the cores within a groove in a wood block and 

alternately planed both sides until the core was about 1.5 

mm thick (Krusic et al. 1987). Transmitted light from a 

source beneath the core then makes the ring boundary 

appear more distinct. 

Core Measurement 

A digital micrometer accurate to 0.01 mm was used to 

measure annual rings. An attached microscope equipped 

with video camera and monitor magnified the core image so 

that annual rings could be discerned. Bundled fiber optics 

acted as the light source for both reflected and transmitted 

readings. The micrometer was interfaced with a 

microcomputer where software collected data and checked 

for operator input errors. 

Cores were measured from the bark toward the pith. If a 

tree was cored before September 1 of the year of collection, 

the last annual ring was considered incomplete and was not 

used in subsequent data analyses. Some cores did not 

strike the pith. If only one or two annual rings were missed, 

the widths were estimated. The geometric center of the tree 

was located by making the arc of the boundary for the last 

visible ring congruent with a circle of known radius on a 

template (Liu 1986). The corresponding circle radius was 

entered into the data file along with the number of 

estimated years to the geometric center. This last 

measurement, which was useful for determining subsequent 

annual basal-area calculations, was excluded from our 
computations of mean annual basal-area increments by 

flagging the tree with an indicator variable. 

Because of our study objectives and the need to measure a 

large number of increment cores in a short time, 

crossdating was done carefully, but not rigorously. There 

may be occasional errors due to missing rings, so our 

individual core data is not ideally suited for uses such as 

response analysis. Crossdating errors on our earliest 

analyzed red spruce increment cores were minimized by 

comparison with Marchand's high-elevation red spruce 

chronology (Marchand 1984). Marchand identified 1977, 

1960, 1956, and 1948 as benchmark years for narrow 

annual rings. Our own red spruce chronology was 

developed after measuring approximately 1,000 cores. In 

addition to the years identified by Marchand, narrow rings 

were found in 1966, 1925, 1923, and 1921 while 1924 

represented a large ring. The years 1966, 1956, and 1948 

remained important for other species. 

Our data files are available to the public. A description and 

examples of the files are given in the Appendix. 

Data Analysis 

Study regions were delineated by state boundaries except 

for Maine where the five northernmost counties, which had 

recent defoliation by spruce budworm, were separated from 

Table 1 .-Distribution of sample by species and age class 

the remaining 11 counties. Our first goal was to 

characterize growth trends for all the species in these 

regions. We chose to convert radial-increment 

measurements to basal-area increments (BAI), which 

represents the cross-sectional area of wood formed for a 

given period at breast height. Basal area is a commonly 

used measurement of both stand and individual tree 

development. Since ring widths tend to decrease in older 

and larger trees, BAl is a better indication of whether growth 

rates are decreasing (Phipps 1984). The annual BAl of the 

nth ring was calculated by: 

where R is the tree radius obtained by summing ring widths. 

Mean annual BAl for each species was calculated by 

averaging over all trees with measured diameter growth for 

that year. 

We usually present our results for the period 1900-80. Prior 

to 1900, with the exception of red spruce, there were too 

few trees from which to construct meaningful regional 

curves (Table I). Red spruce is the only species with 

appreciable numbers before 1900 but many of these trees 

were suppressed. Their growth rates never were higher 

than the 1-2 cm2 yr-' around 1900, as shown in Figure 1. In 

addition, our geographic regions were sampled from 1980 

through 1983 and took 1 to 2 years to sample. In many 

Age class (years) 

1- 21- 41- 61- 81- 101- 121- 141- 161- 181- 

Species 20 40 60 80 100 120 140 160 180 200 >200 Total Percent 

Red spruce 

Sugar maple 

Red maple 

White ash 

Yellow birch 

American beech 

Red oak 

Hemlock 

Balsam fir 

White pine 
I 1 BALSAM FIR - N 

*.-.-. NEW HAMPSHIRE . . . . . . . NEW HAMPSHIRE 

-NEW YORK 

I 

EASTERN HEMLOCK 

...... NEW HAMPSHIRE 

- CONNECTICUT AND RHODE ISLAND 66 

--- EASTERN WHITE PINE - N 

852 

-CONNECTICUT AND RHODE ISLAND 89 

lure 1 .-Regional mean annual BAl (cm2) for red spruce, balsam fir, eastern 

mlock, and eastern white pine. 
instances, the last year of sampling in a region included too 

many trees with incomplete annual rings. The drop in the 

number of trees at the end of the regional curves gave a 

spurious fluctuation which was omitted by truncating the 

curves in 1980. 

We also generalize about growth trends using polynomial 

regression equations for the period 1950-80, including only 

trees that were at least 50 years old at breast height in 1980 

(Hornbeck et al. 1988). This period coincides with 

increasing exposure to atmospheric deposition and ensures 

a sample not biased toward very old or young trees. Annual 

BAl for each tree was normalized by dividing by the tree's 

average annual BAl over the period. The normalized BAl for 

each tree was then regressed against time to obtain linear 

(1st order) and curvature (2nd order) coefficients using the 

polynomial model: 

where biy is the annual BAI for tree i and year y, bi is the 

mean increment from 1950-80, and ty is (year - 1965). The 

value of 80 is the mean of ty2 over the 31 years. The ai and 

pi coefficients were averaged over all trees within the 

species to generate a growth curve for that species. Mean 

annual BAI and the regression coefficients were tested 

between species by one-way ANOVA. Differences among 

species were tested with the Student-Neuman-Keuls test. 

Table 2.-Distribution of individuals by diameter class 

Seventy percent of the 9,588 increment cores used for 

analysis were from softwoods (red spruce, eastern white 

pine, balsam fir, and hemlock) and 30 percent were from six 

hardwood species (Table 1). Thirty-one percent of the total 

cores were red spruce. The age structure of the sample 

reflects extensive harvesting in New England around the 

turn of the century. At the time of sampling, 80 percent of 

the trees were less than 80 years old at breast height and 

60 percent were less than 60 years old. The age range of 

red spruce, with many trees over 200 years old, was the 

widest of any species. Sixty-five percent of the trees had 

inside bark diameters of 15 to 25 cm (Table 2). Ten percent 

of the sample, mostly red spruce and eastern white pine, 

had diameters in excess of 30 cm. Eastern white pine had 

more individuals over 30 cm in diameter than red spruce 

even though 95 percent of the white pine were less than 80 

years old (compared to 60 percent for red spruce). The 

study sample generally is from low elevations; 70 percent of 

the trees were from elevations less than 400 m (Table 3). 

Six percent of the sample was from elevations above 700 m; 

most of these were red spruce. 

Growth Patterns 

Red spruce (Picea rubens Sarg.). Annual BAI of sampled 

red spruce increased from 1900 until about 1960 (Fig. 1). 

Diameter class (cm) 

.l- 5.1- 10.1- 15.1- 20.1- 25.1- 30.1- 35.1- 40.1- 45.1- 

Species 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 50+ 

Red spruce 

Sugar maple 

Red maple 

White ash 

Yellow birch 

American beech 

Red oak 

Hemlock 

Balsam fir 

White pine 
Table 3.-Distribution of individuals by elevation class 

Elevation class (m) 

0- 101- 201- 301- 401- 501- 601- 701- 801- 901- 1001- 

Species 100 200 300 400 500 600 700 800 900 1000 1100 r1101+ 

Red spruce 

Sugar maple 

Red maple 

White ash 

Yellow birch 

American beech 

Red oak 

Hemlock 

Balsam fir 

White pine 

....................................................................... Number .............................. ........................................ 

386 395 321 454 428 373 235 158 95 63 28 19 

26 19 21 78 114 112 83 51 16 0 0 0 

181 137 79 83 92 31 34 35 5 4 0 0 

5 1 67 67 46 44 38 15 2 0 0 0 0 

16 22 10 22 40 60 43 39 15 7 3 0 

13 31 44 45 36 10 18 4 2 0 2 0 

156 195 168 105 65 18 5 4 1 0 0 0 

163 197 99 77 51 11 1 0 0 0 0 0 

196 168 219 229 216 109 44 23 27 21 8 22 

656 651 267 186 91 45 4 0 0 0 0 0 

The average for northern and southern Maine and Vermont 

rose to 9 to 10 cm2 yr-' by 1960, while the average for New 

York and New Hampshire reached 12 cm2 yr-' at the same 

time. After 1960, BAl decreased in the early 1960's, showed 

a slight recovery in all regions in the late 19601s, then 

continued to decrease until 1980. The overall decrease in 

BAl from the peak values around 1960 until 1980 ranged 

from 13 to 40 percent with the largest decreases found in 

New Hampshire and New York. 

Balsam fir (Abies balsamea (L.) Mill.). BAl of sampled trees 

in all four regions steadily increased in all regions until 

between 1965-70 (Fig. 1). In 1970, the average BAl for all 

regions was 9 to 10 cm2 yr-' except Vermont, where BAI 

was approximately 14 cm2 yr'. After 1970, growth rates 

remained fairly stable or decreased. The particularly sharp 

decrease in northern Maine in 1975-77 was the result of an 

outbreak of spruce budworm (Choristoneura fumiferana). 

Eastern hemlock (Tsuga canadensis (L.) Carr.). In all 

regions, BAl increased steadily to 11 to 13 cm2 yr-' during 

the late 1970's (Fig. 1). New Hampshire and the combined 

region of Rhode Island and Connecticut had slower growth 

rates than the other regions after 1950, reaching 10 to 11 

cm2 yr-' by the mid-1970's. 

Eastern white pine (Pinus strobus L.). Eastern white pine 

obtained by far the highest BAl's for any species that we 

studied (Fig. 1). Growth rates steadily increased through the 

late 1970's and ranged from 17 to 22 cm2 yr-I. 

Northern red oak (Quercus rubra L.). Growth rates in this 

species increased to 10 to 13 cm2 yr-' by 1980 (Fig. 2). 

Rhode Island and Connecticut showed a growth decrease 

from the early 1950's to the early 1970's that has been 

attributed to drought and insect defoliation (Stephens and 

Hill 1971). In 1980, single-year growth decreases of as 

much as 37 percent occurred in Connecticut, Rhode Island, 

Massachusetts, and Vermont due to an epidemic of the 

gypsy moth (Lymantria dispar). 

White ash (Fraxinus americana L.). Growth rates in sampled 

white ash increased slowly from 1900 to 1940, averaging 3 

to 4 cm2 yr-I (Fig. 2). Growth rates accelerated in all regions 

after 1940 and reached maximums of 11 to 13 cm2 yr-' by 

the late 1970's. Trees in Vermont and Massachusetts 

outgrew those in other regions during this period. Growth 

reductions in several regions from 1978-80 are unexplained. 

Red maple (Acer rubrum L.). Red maple growth rates 

steadily increased to 9 to 11 cm2 yr-' by 1980 (Fig. 2). All 

regions apparently were affected by a drought in the early 

1960's. Connecticut and Rhode Island did not show a 

substantial growth recovery until the mid 1970's compared 

to a recovery in the mid to late 1960's for the other regions. 

New Hampshire growth rates dipped the most due to the 
NORTHERN RED OAK N 

NEW HAMPSHIRE 

MASSACHUSETTS 

'---. CONNECTICUT AND RHODE ISLAND 201 

WHITE ASH 

- MAINE 

..... . NEW HAMPSHIRE 

-- VERMONT 

12 -4 --- - MASSACHUSETTS 43 j y, - CONNECTICUT AND RHODE ISLAND 66 

10 

- SUGAR MAPLE - N 

155 14- - MAINE 135 

.-.... HEW HAMPSHIRE 115 NEW HAMPSHIRE 85 - 

158 - - VERMONT 301 

132 12 - 

-CONNECTICUT AND RHODE ISLAND 127 - 

10 - 

- 

8 - 

- 

6 - 

- 

4 - 

- 

Figure 2.-Regional mean annual BAl (cm2) for northern red oak, white ash, red maple, 

and sugar maple. 
1960's drought, but this region had a faster growth rate for 

the 10 years preceding the drought. 

Sugar maple (Acer saccharum Marsh.). Growth rates 

steadily increased in all regions to 10 to 11 cm2 yr-' by 

1980 (Fig. 2). Decreases in growth during the early 1980's 

in Vermont and New Hampshire can be attributed to 

defoliation by gypsy moth, forest tent caterpillar 

(Malacosoma disstria), and the saddled prominent 

(Heterocampa guttivitta.) 

Yellow birch (Betula alleghaniensis Britt.). Vermont, New 

Hampshire, and Maine were the only states containing 

sufficient quantities of yellow birch for analysis. Growth 

rates reached levels of 11 to 12 cm2 yr-' by the early 

197OYs, and then leveled off through the early 1980's (Fig. 3). 

American beech (Fagus grandifolia Ehrh.). Growth rates 

were uniform at 1 to 2 cm2 yr-' from 1900 until the late 

1930's (Fig. 3), then increased steadily from 1940 and 

attained rates of 9 to 10 cm2 yr-' by 1980. All regions 

showed a slight growth depression from 1960 through 1965. 

All species. Figures 1-3 suggest that often there are 

simultaneous increases or decreases in annual growth over 

several or all regions. Common influences such as weather, 

forest aging, insect attacks, or other forest perturbations 

may be responsible for these synchronized growth events. 

An exception to this regional synchronicity occurred in the 

Rhode Island-Connecticut species. From 1950 to 1970, 

species in this region showed fairly constant growth as 

opposed to generally increasing trends in other regions. 

YELLOWBIRCH 

- MAINE 70 ---- NEW HAMPSHIRE 55 

-.-.-. VERNONT 154 

Graphs of BAI for all 10 species indicate that red spruce has 

been undergoing a growth decrease since 1960; that 

balsam fir shows a similar decrease after the middle to late 

196OYs, and that the other species show no obvious longterm decreases in annual BAl (Figs. 1-3). A further analysis 

of differences between species for the period 1950-80 

substantiates these findings (Fig. 4, Table 4). These years 

span the period of concern over impacts of atmospheric 

deposition. We chose trees that were at least 50 years old 

at breast height in 1980 so that some growth would have 

occurred prior to the era of increasing atmospheric 

deposition levels after 1950. 

Eight of the 10 species had positive linear coefficients that 

measured the rate of change in growth (Table 4). Growth 

was increasing most rapidly in Americen beech. White pine, 

yellow birch, sugar maple, red oak, eastern hemlock, and 

white ash had positive linear coefficients that were 

significantly greater than zero but were not significantly 

different from each other. Balsam fir and red spruce had 

negative linear coefficients, indicating a downward growth 

trend, though balsam fir's was not significantly different 

from zero. 

The curvature coefficient represents the change in the rate 

of change of growth. American beech, white ash, red 

maple, white pine, red oak, and sugar maple had positive 

coefficients, though only beech and white ash had 

coefficients significantly greater than zero, indicating that 

growth rates of these two species were increasing the 

fastest. Hemlock, yellow birch, red spruce, and balsam fir 

had negative coefficients. Balsam fir and red spruce were 

AMERICAN BEECH 

-MAINE 

---- NEW HAMPSHIRE 

-.-.-, VERNONT 

Figure 3.-Regional mean annual BAl (cm2) for yellow birch and American beech. 
HEMLOCK 

- 

- 

.___..._..._..-.--------a BALSAM FIR 

Figure 4.-Regional growth curves for major species in New England forests, 1950-80. 

the only species with curvature coefficients significantly less 

than zero. Balsam fir growth was decreasing more rapidly. 

The species curves (Fig. 4) confirm that red spruce and 

balsam fir are the only sampled species in New England 

showing extended periods of decreasing growth in recent 

years. Growth of red spruce has been decreasing since 

about 1960 while growth of balsam fir generally began 

decreasing slightly later. American beech and white ash 

have the fastest accelerating growth rates toward the end of 

the 1950-80 period. The remaining species tend to have a 

constant positive rate of change over the study period. 

Detailed Analysis of Red Spruce 

The growth decreases evident in the regional BAI curves of 

red spruce warranted a more detailed analysis of this 

species since our findings agree with earlier studies 

pointing to slowing growth starting around 1960. The timing 

and spatial dimension of the growth decrease relates 

circumstantially with atmospheric deposition which has 

increased regionally since the late 1940's. However, 

detailed records of regional atmospheric deposition over 

this fimespan are not available, so direct analysis of impacts 

on annual growth rates are not possible. Other possible 

causes of the decrease must be ruled out before 

atmospheric deposition can be assumed as the cause. Thus 

we concentrated on investigating other possible 

explanations for the growth trends. 

Age and Size Classes 

The regional curves were recalculated by age and size 

classes to determine if certain ages or sizes of trees were 

causing the mean annual BAI to decrease after 1960. The 

sample from northern Maine, which is representative of the 

trends in the other recalculated regional curves, was divided 

into four age classes as of 1980: 50 years or less, 51 to 70 

years, 71 to 90 years, and 91 + years. All four age classes 

had similar patterns after 1960, showing growth decreases 

until the mid-1960's, recoveries to pre-1960's levels by 

1970, and then further growth decreases after 1970 (Fig. 5). 

This later growth decrease coincides at least partly with a 

spruce budworm epidemic that began in 1975. 

These same trees also were assigned to three size classes 

based on diameter in 1980: less than 20 cm d.b.h., 20 to 30 

cm d.b.h., and 31+ cm d.b.h. Although larger diameter 

classes grew at higher absolute rates than smaller diameter 

classes, the timing and direction of growth fluctuations after 

1958 coincided for all three diameter classes (Fig. 6). The 

data suggest that growth decreases after 1960 are 

independent of tree size and age. 
Table 4.-Mean annual BAI, mean regression coefficients and standard deviations for 

the period 1950-80; vertical lines connect species that are not significantly different 

by the Student-Neuman-Keuls test; range test on mean annual increment carried out 

on log-transformed values to homogenize the variance; =is defined in [I] 

- Species Mean s n w 

White pine 

Hemlock 

Yellow birch 

Red spruce 

Red oak 

Sugar maple 

Mean Annual BAl 

~aisam fir 7.7 

White ash 7.6 

American beech 6.7 

Red maple 6.7 

American beech 

White pine 

Yellow birch 

Sugar maple 

Red oak 

Hemlock 

White ash 

Red maple 

Balsam fir 

Red spruce 

American beech 

White ash 

Red maple 

White pine 

Red oak 

Sugar maple 

Hemlock 

Yellow birch 

Red spruce 

Balsam fir 

Linear Coefficient x lo3 

[I] Mean growth curve for each species: 

by =6 + tyT/W + (ty2 - 80) /W 

w = (I In) 2 (1 lbi) 

Curvature Coefficient x 1 o3 

Elevation 

0.64 

0.59 

0.33 

0.28 

0.19 

0.14 

Earlier reports of decline symptoms and mortality of red 

spruce in the Northeast were limited to sites with elevations 

ranging from 800 to 1,100 m (Johnson and Siccama 1984; 

McLaughlin et al. 1987). These elevations are higher than 

those associated with the commercial spruce-fir forests of 

the region and are subjected to different environmental 

impacts. Ninety-three percent of our red spruce sample 

spanned elevations from near sea level to 800 m, and nearly 

2.87 

1.75 

2.16 

2.59 

1.46 

2.47 

100 percent were from elevations less than 1,000 m (Table 3). 

This provided a means to determine if declining growth in 

commercial forests is associated with increasing elevation. 

A linear regression equation was fit to each tree's annual 

BAI measurements from 1960 through the last complete 

annual ring. The majority of trees had negative regression 

coefficients and scatter plots, indicating that declining 

growth is independent of elevation. Figure 7 illustrates this 

point for New Hampshire, which had the widest elevation 

range of any of our study regions. 

-0.07 2.24 

-0.27 2.39 

-0.93 1.93 

-1.72 1.94 
Figure 5.-Red spruce mean annual BAl for four age classes in northern Maine. 

Factors Affecting Growth 

Several factors or combinations of factors may be involved 

in the decreasing growth rates of red spruce that have 

occurred since 1960. These include acid deposition, insects 

and diseases, regional weather events, and the normal 

process of tree maturation. The data base on acid 

deposition is temporally and spatially weak, making it 

difficult to develop regional relationships between growth 

patterns and deposition. Insects and diseases, at least 

those known to be important in the past, do not seem major 

factors in the decline. The spruce budworm has been active 

at times since 1960, the last example being a sharp 

decrease in growth from 1975-77 in the northern Maine 

sample (Fig. 5). However, overall activity of the budworm 

does not coincide with the start of the decrease in growth 

rates around 1960 (Hardy et al. 1986). In addition, the 

regional curves for southern Maine, Vermont, and New 

York, areas free of recent budworm activity, are similar 

during the decline period to those for northern Maine and 

New Hampshire, which have a history of budworm activity 

(Fig. 1). Armillaria root disease also has been ruled out as a 

major factor (Carey et al. 1984). We have studied the role of 

the remaining two factors, regional weather and tree 

maturation. We also have attempted to determine if growth 

rates are related to some of the site variables measured on 

each inventory plot. 

Maturation. The red spruce forests in this region were 

heavily logged around the turn of the century and also 

subjected to severe attacks by spruce budworm from 

1912-20 (Seymour 1985). In northern Maine, southern 

Maine, and Vermont, 57 to 68 percent of our sample trees 

are in the 41- to 80-year age classes and 79 percent are 

between 41 and 100 (Table 5). New York trees have a much 

broader age distribution, with New Hampshire intermediate. 

In terms of size, 66 to 73 percent of the trees in Maine and 

Vermont were 15 to 25 cm in diameter, with lower 

percentages in New Hampshire and New York (Table 6). 

The changing diameter distribution of the northern Maine 

trees over time verifies the even-aged, even-sized nature of 

the Maine forest as described by Seymour (1985) (Fig. 8). 

Red spruce's ability to survive long periods of suppression 

and to respond when released suggests that some of the 

remaining 20 percent of our age sample, trees that are older 

than 100 years, are growing like younger trees after being 
Figure 6.-Red spruce mean annual BAl for three diameter classes in northern Maine. 

released by logging or widespread mortality of overstory 

trees due to the 1912-20 budworm epidemic. Physiological 

age may differ considerably from chronological age in red 

spruce. 

Data collected by Meyer (1929) were used to determine if 

our regional curves from 1900 through 1980 were as 

expected for an even-aged red-spruce forest (Hornbeck et 

al. 1986). Meyer collected data in the 1920's from 201 

second-growth even-aged stands that had colonized 

abandoned fields in Maine, New Hampshire, and Vermont. 

His data for mean stand diameter in 10-year intervals were 

converted into annual BAI after fitting the data by Weibull 

functions (Federer and Hornbeck 1987). Meyer stated that 

red spruce seedlings reach breast height in about 15 years 

and adjusted his age data for this. The past insect attack 

and cutting histories indicate that many of our sample trees 

probably originated from suppressed advance reproduction 

and seed during this period, and may have reached breast 

height between 1905 and 1925. Shifting the curve derived 

from Meyer's data to start at breast height in 1915 and 

superimposing it over our mean annual basal-area curves 

provides a close match (Fig. 9). Meyer's stand basal-area 

and density estimates approach asymptotes after stand 

ages of 80 to 100 years, indicating that mean tree BAI 

curves must reach a maximum and then decline (Federer 

and Hornbeck 1987). This is exactly what our regional 

annual BAl curves show. Meyer's data also predict a 

constant radial increment initially, followed by a decrease, 

just as our trees do (Fig. 9). 

Although Meyer's data were obtained for old-field 

successions, they have been and still are used successfully 

to predict tree growth in all spruce-fir forests in northern 

New England. The excellent agreement of our BAI and 

radial increments with Meyer's data and the 1915 initiation 

date cannot be coincidental. The northeastern red spruce 

forest as a whole is growing as if it were an even-aged 

stand that reached breast height around 1915. 

On the other hand, the New York red spruce and, to some 

extent, New Hampshire red spruce are not even-sized or 

even-aged. This may explain why they have the highest 

average BAI values. The fact that they also reached a peak 

BAl around 1960 argues that factors other than maturation 

are involved in the regional synchrony of the growth 
- I .5 -1.0 -0.5 0.0 0.5 I .O I .5 

SLOPE 

Figure 7.-Slope of BAI 1960-82 vs. elevation for New Hampshire red spruce. 

decrease. Regional weather events might have induced this 

synchrony. 

Regional weather. The similar timing of many increases or 

decreases in annual BAI among the regions indicated that 

weather might be an important factor in determining 

interannual variation of BAl. Standard dendroclimate work 

on red spruce has related monthly precipitation and 

temperature to detrended ring width series by use of 

multiple regression. Cook et al. (1987) and Conkey (1979) 

found that diameter growth in red spruce was positively 

correlated with the current growing season's May and 

September temperatures as well as early winter 

temperatures of the previous year. They found negative 

correlations between diameter growth and the previous 

year's July, August, and October temperatures. The 

previous year's July or August precipitation was weakly 

correlated with diameter growth while the current year's 

precipitation had no effect. These studies accounted for 

less than 30 percent of the variance in diameter growth. 

To increase the variance explained by multiple regressions 
of weather data on diameter growth, Federer et al. (1989) 

used daily temperature and precipitation to construct more 

complicated variables based on physiological growth 

responses and on soil-water deficits derived from the 

BROOK model (Federer and Lash 1978). The National 

Climatic Data Center provided daily precipitation and daily 

maximum and minimum temperatures for 1926 through 

1980 from 14 weather stations in northern New England and 

northeastern New York. The stations were grouped into 

three regions: Maine, New Hampshire and Vermont, and 

the Adirondack Mountains of New York. Within each region 

daily values were averaged. A detrended time series for 

each region was derived by fitting a cubic smoothing spline 

(Cook and Peters 1981) with a period of 50 to the mean 

annual BAI measurements for each region (Fig. 10). These 

indexed series were standardized by taking the ratio of the 

actual mean annual BAl to the fitted cubic-spline value. 

Autocorrelation was removed from each regional series by 

fitting with an AR(1) model (Cryer 1986). 

Three multiple regression models were tested using the 

detrended and delagged BAl time series: I: a standard 

dendroclimate model based on daily weather values; II: a 

model using variables based on seasonal temperature and 

soii-water deficit; Ill: a model with seasonal estimates of 

photosynthesis and respiration based on temperature and 

water deficit. If one of the variables used in any of the 

models was significant in one of the regions, it was entered 

Table 5.-Distribution of red spruce ages by geographic area and percentage of sample 

Age (years) 

1 - 21- 41- 61- 81- 101- 121- 141- 161- 181- 

Location 20 40 60 80 100 120 140 160 180 200 >200 Total 

So. Maine 1 10 32 33 14 5 3 1 1 0 0 402 

New Hampshire 0 4 17 23 20 12 9 7 2 2 4 391 

Vermont 1 14 35 33 11 3 2 1 0 0 0 303 

New York 0 0 8 14 9 11 13 9 8 7 21 224 

Table 6.-Distribution of red spruce diameters by geographic area and percentage of sample 

Diameter class (cm) 

0.1- 5.1- 10.1- 15.1- 20.1- 25.1- 30.1- 35.1- 40.1- 45.1- 

Location 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 51+ 

No. Maine 0 0 7 38 35 15 4 1 0 0 0 

So. Maine 0 0 9 38 31 14 5 2 1 0 0 

New Hampshire 0 1 4 20 28 20 11 6 3 4 3 

Vermont 0 0 7 32 34 19 5 3 0 0 0 

New York 0 0 2 10 23 24 2 1 13 6 1 0 
into the regressions for the other two regions so that the 

results were comparable. 

In Model I, the previous July-August temperature, winter 

temperature, and the September temperature were 

significant in at least one of the regional series (Table 7), in 

agreement with other dendroclimate studies of red spruce 

(Conkey 1979; Cook et al. 1987; McLaughlin et al. 1987; 

Kimball and Kiefer 1988). Diameter growth is negatively 

correlated with the previous year's JuneJuly temperature 

and positively correlated with winter temperature and 

September temperature. 

Model II included six variables: early season degree days, 

late season degree days, previous late season degree days, 

early season soil-water deficit, late season soil-water deficit, 

and previous late season soil-water deficit. The previous late 

season degree days was the only variable of any predictive 

significance in this model and it was negatively correlated 

with growth (Table 7). 

Model Ill was based on seasonal estimates of photosynthesis 

and respiration using the same season lengths as in Model 

II. Daily photosynthesis was reduced by the daily ratio of 

actual to potential evapotranspiration as simulated by the 

BROOK model. Seven variables were constructed from this 

data: early season photosynthesis, late season photosynthesis, 

previous late season photosynthesis, early season respiration, 

late season respiration, previous late season respiration, 

and winter respiration. The previous year's late growing 

season respiration and winter respiration were the only 

significant variables in this model (Table 7). Winter respiration 

was positively correlated with growth while the late season 

respiration was negatively correlated with growth. 

The physiologically based models II and Ill were 

outperformed by the standard dendroclimate Model I 

(Federer et al. 1989). The dendroclimate model explained 

from 18 to 33 percent of the variation for the three regions 

(Table 7), which is typical of other dendroclimate models. 

The maximum variance explained for the other two models 

was 17 percent. Neither physiologically based model was 

able to explain any significant variance in Maine. The 

previous late season degree days of Model II and the 

previous late season respiration from Model Ill are 

alternative expressions of the previous late season 

temperature used in Model I. Detrending and delagging of 

the annual BAI time series removed any association of the 

current and previous year's growth controlled by the 

previous season's weather. The effects of the previous 

year's late season temperature on current growth are 

additional effects not related to the previous years growth 

(Federer et al. 1989), and may reflect reductions in the 

stored carbohydrate pool due to higher respiration. The 

positive correlation between winter temperature and the 

current year's growth in Model I also may reflect the amount 

of metabolic products produced for hardening physiology. 

The association of current year's growth and September 

temperature may be a spurious correlation in our data due 

to the warm September in 1961 (Federer et al. 1989). 

Relationships to site variables. We investigated whether site 

characteristics were related to the declining growth of red 

spruce. Principal components analysis (PCA) and factor 

analysis (FA) were used to group correlated variables so 

that hypotheses could be generated about relationships 

between constructed growth variables and site variables. 

After screening potential variables, four related to growth 

and seven related to site were chosen for analysis. The 

constructed growth variables included the linear and 

curvature growth coefficients of individual trees derived 

from 1950-80 as well as the mean BAl and the basal area at 

the midpoint of this same period for individual trees. The 

linear and curvature coefficients were used as indicators of 

tree decline. Some site variables had too few categories to 

be used in either PCA or FA and had to be converted into 

two-level variables. The converted variables were recent 

harvestlnon-harvest, shallow rooted (0- to 10-inch 

depth)/non-shallow rooted, sandy soil/non-sandy soil, and 

drylnon-dry sites. Other site variables were elevation, 

organic depth, and total-plot basal area. 

The four growth indices and seven site variables were 

analyzed by PCA to determine how many of the 11 possible 

factors would be retained in subsequent FA. Factors 

containing large amounts of variance from the correlation 

matrix usually are retained (Tabachnick and Fidell 1983) 

while those factors accounting for little variance are 

discarded from later FA. The PCA indicated that five factors 

should be used in the FA. 

Of the five factors generated in the FA, two or three 

variables usually defined each factor (Table 8). The most 

important factors lead to conclusions that are expected. The 

first factor was dominated by the mean BAI value for the 

period and the basal area at the midpoint of the period; 

large trees tend to have a higher mean BAI compared to 

smaller trees. The second factor indicated that unharvested 

plots had higher basal areas. The third factor states that dry 

sites, which have shallow organic horizons, tend to have 

deeper rooted trees growing on them. The fourth factor 

loaded heavily on the linear regression term and marginally 

on the midpoint basal area and mean annual BAl for the 

period. This factor was associated with small basal-area 

trees that were in the ascending portion of their growth 

curve. The last and least important factor had marginal 

loadings on elevation, sandy soil, and the curvature 

coefficient. Although our work and that of others have 

shown that declining growth rates are independent of 

elevation, increasing elevation was weakly associated with 

the fastest decreasing growth rates and with less sandy 

soils. 

The least important factor was the only one that included a 

relationship between a growth variable and a site variable. 

The lack of strong relationships between the two types of 

variables may mean that we constructed the wrong growth 

indicators, that the two-level variable categories were too 

broad, or that there is no link between constructed growth 

indicators and the available site variables. 
1 5 9 13 17 2 1 25 29 33 37 

DIAMETER CLASS (em) 

Figure 8.-Diameter distributions for northern Maine red spruce at 20-year intervals, 

1875-1 975. 

Growth Patterns During Senescing Years site at an elevation of 800 m on Mt. Washington in New 

Hampshire. Disks that contained large amounts of decay 

Although red spruce mortality has been studied from a were impregnated with a wood glue to preserve their 

stand perspective (Weiss et al. 1985), individual-tree growth 

patterns preceding death have not been examined. We 

conducted two separate studies of dead trees to determine 

if growth information could be recovered from trees in varying 

stages of decay, and to see if there were common growth 

patterns preceding death in trees that died years apart. 

The first study took place in the fall of 1986. We took disks 

from 15 standing and fallen dead trees from an east-facing 

physical structure before being banded and b~ffed.~ Four 

radii from each disk were crossdated and subsequently 

measured on the digital micrometer. A mean radius for the 

tree was constructed by averaging the two longest radii. 

Krusic, P. J.; Hornbeck, J. W. 1989. Preserving decayed 

wood samples for tree-ring measurement. Submitted to 

Tree-Ring Bulletin. 
Figure 9.-Radial increment and BAI derived from data in Meyer (1929) compared with 

present-day values for red spruce in five regions. 
1930 1940 1958 19 60 1970 1988 

YEAR 

Figure 10.-Time series of BAl for red spruce in three regions. (top) raw series and 

cubic smoothing spline, (middle) detrended series of raw vaiuelsplined value, (bottom) 

delagged, detrended series, or residuals of AR (1) model fitted to the detrended series. 
Table 7.-Results of multiple regression analyses by region using independent variables 

defined below, with detrended, delagged, regional mean BAl as the dependent variable, 

1927-81 (n = 55); these final models include those variables that were significant in 

one or more regions; F-values are in parentheses; values greater than 4.0 indicate 

significance at the 95-percent level 

Region r2 Intercept Coefficient and variable 

Percent 

18 

29 

33 

1 

7 

14 

3 

14 

17 

MODEL l 

-0.004 pJAT 

(0.1 3) 

-0.029 pJAT 

(1 1.55) 

-0.047 pJAT 

(17.63) 

MODEL ll 

-0.007 pLDD 

(0.25) 

-0.027 pLDD 

(3.96) 

-0.049 pLDD 

(8.87) 

MODEL Ill 

-0.002 pLRs 

(0.14) 

-0.009 PLRS 

(3.29) 

-0.020 PLRS 

(9.15) 

+0.011 WRs 

(1.70) 

+0.013 WRS 

(5.32) 

+0.008 WRs 

(1 .l4) 

pJAT = previous July-August temperature; WT = previous Nov-Dec-Jan temperature; 

ST = September temperature; pLDD = previous late season degree days; pLRs = previous 

late season respiration; WRs = winter respiration. 

Of the 15 trees sampled, 1 tree died in the 1950's, 2 died in 

the 1960's, 6 died in the 19701s, and 6 died in the 1980's 

(Table 9). The breast-height age of these trees ranged from 

133 to 321 years and diameters ranged from 18 to 52 cm. 

On the basis of tree ages and diameters, the stand appears 

to be old-growth, not subjected to prior harvest. Annual BAI 

growth in these trees fell roughly into three categories 

(Fig. 11). Eight trees had slow growth rates that were less 

than 5 cm2 yri since 1850. Three trees grew at 

intermediate rates and had extended periods of growth of 5 

to 10 cm2 yr-l since 1850. The four fast-growing trees had 

growth rates as high as 35 cm2 yrl. The fast-growth trees 

had an average diameter of 44 cm compared to 33 and 24 

cm for intermediate and slow-growth trees, respectively. 

Trees in the fast growth-rate class exhibited two periods 

when slowing growth was followed by a 30- to 40-year period 

of higher relatively constant growth (Fig. 12). A 66 percent 

drop in growth from 1870 to 1872 was followed by a long 

period of relatively constant growth that was higher than 

pre-1870 levels. A second decrease around 1920 was 

followed by subsequent growth rates that fluctuated at a 

higher level until 1958. Growth rates in all four trees fell an 

average of 47 percent from 1958 to 1960. The largest tree, 

52 cm d.b.h., had a steep linear decrease in growth from 

1960 until 1984 when it died. Two other trees had steep 

linear growth decreases for 10 years from 1960 to 1970 and 

then 9 to 11 years of less steeply decreasing growth rates 

until their deaths. The remaining tree had a steep linear 
Table 8.-Rotated factor pattern from factor analysis 

Variable Factor 1 Factor 2 Factor 3 Factor 4 Factor 5 

MEANBAI 

BA-MID 

PLOT-BA 

HARVEST 

DRY 

DEPTH 

SHAL-ROOT 

LINEAR 

ELEVATION 

SAND 

CURVATURE 

growth decline from 1971 to 1982. 

The period of decreasing growth preceding the death of 

individuals in the slow- and intermediate-growth classes is 

approximately half of the 20-year period for the high-growth 

trees (Fig. 11). The 1958-60 growth decrease signaled the 

start of the decline in the fast-growing trees. Intermediategrowth trees were able to maintain pre-1958 rates through 

the 1960's even though they had a similar percentage 

decrease in growth as the fast-growth trees for the 1958-60 

period. The slow-growth trees had a 62 percent decrease for 

this period. Four of the eight trees in this class had a marked 

decrease in 1958-60 while three other trees had minimal 

growth for 10 to 15 years preceding this period. Graphing 

individual trees indicated that most trees in the two slower 

growth classes experienced similar declines earlier in their 

lives from which they were able to recover. These earlier 

events, including the growth decreases occurring around 

1870, probably included the death of competitors. Weiss et 

al. (1985) reported that numerous red spruce in northern 

New England and the Adirondacks were killed by the spruce 

beetle (Dendroctonus rufipennis Kirby) during the 1870's. 

The beetles may have been responding to conditions similar 

to those leading to the current rates of mortality. 

The second study entailed collecting increment cores at 

breast height from trees that died between 1986 and 1987 

surveys of permanent plots located in three states. The 

sample consisted of 16 dominant trees, 54 to 128 years 

old, growing at elevations of 700 to 1,000 m. Diameters 

ranged from 10 to 27 cm. The dead trees represented an 

average of 3 percent of the total trees on a plot. The 

general growth patterns discussed for the Mt. Washington 

sample are repeated for trees located in New Hampshire, 

New York, and Vermont (Fig. 13). Faster growing trees 

have the longest and steepest changes in growth compared 

to slower growing trees, which tend to grow at steadier 

rates. 

In the early to mid-1960's, growth rates began to decrease 

from an average of 5 cm2 yrl for trees in New Hampshire 

and New York. The faster growing trees had nearly linear 

declines lasting 10 to 15 years while slower growing trees 

had steep growth drops occurring over 3 to 4 years followed 

by constant growth at a lower plateau. Sample trees from 

Vermontwith growth rates of 1 to 2 cm2 yr-1 tended to grow 

slower than trees from the other states, and showed a 

reduction in growth from 1969 to 1974. Growth was 

relatively stable at these lower rates until death. The 

timespan covered by decreasing growth increment for most 

of these dead trees indicates that processes affecting 

mortality are accumulated over 2 to 3 decades. 
Discussion 

Our study was conducted as part of the Forest Response 

Program, a national research effort for addressing concerns 

about impacts of atmospheric pollutants on forest health 

(Schroeder and Kiester 1989). The Program includes six 

cooperatives that have been assigned research questions 

focusing on three policy issues. The first of these issues, of 

most concern to our study, asks: Is there a significant 

problem of forest damage in North America which might be 

caused by acid rain, its precursors, and associated 

pollutants? Regarding this issue, the National Vegetation 

Survey Cooperative, which has funded our research, has 

been asked to answer two scientific questions: 

1. Are changes over time in the condition of forests 

greater than can be attributed to typical trends and levels of 

natural variability? 

2. What spatial pattern or patterns, if any, exist in forest 

condition, and how do such patterns relate to spatial 

patterns of pollutant exposure? 

Regarding Question 1, our study suggests that changes in 

annuai growth rates in portions of New England forests 

represented by our sample are not greater than expected 

natural variability. Most species grew at constant or 

increasing rates through the 1970's, with year-to-year 

variation explainable by weather variation and insect 

outbreaks. Only in red spruce and balsam fir has there been 

a generally decreasing growth rate of trees throughout the 

region. This decrease began around 1960 and coincides 

with expectations for an even-aged forest regenerated in the 

early part of the century. 

We stress that most of our sampled red spruce were 

growing at elevations below 1,000 m, in what is commonly 

called the commercial spruce-fir forest. The age of this 

forest has been strongly structured by past cutting and 

budworm outbreaks, adding plausibility to the theory of 

common maturation. The picture is less clear for red spruce 

at higher elevations, and in New York, where ages are more 

variable and generally older. Our sample chronologies from 

individual dead trees on Mt. Washington indicate that 

previous periods of decreasing growth rates, similar to the 

1958-60 decrease that led to the death of these trees, have 

occurred in the past and are not unusual in high-elevation, 

old-growth forests. Van Deusen (1987) suggests that oldgrowth red spruce at higher elevations do not show a 

consistent decrease in growth rates compared with our 

second-growth low-elevation red spruce. However, others 

including Cook et al. (1987), McLaughlin et al. (1987), and 

Johnson and Siccama (1984) suggest that growth rates at 

high elevations (more than 1,000 m) have been decreasing 

since around 1960 in combination with unusual foliar 

symptoms and increased mortality. 

We have argued that the growth decrease at low elevations 

and the mortality at high elevations could have two separate 

causes. But the synchrony of maximum growth around 1960 

followed by a decrease in growth or mortality in both low 

and high-elevation trees throughout the Northeast, suggest 

that a common cause is possible. A series of abnormal 

weather periods has been suggested as that cause 

(McLaughlin et al. 1987). Loss of foliage from winter injury 

and lack of carbohydrate storage over winter have been 

suggested. However, such weather-induced effects have 

been neither well quantified regionally nor explained 

physiologically. There is considerable unexplained state-tostate covariance in ring widths, so undescribed regional 

weather effects do exist. Such effects could both have 

induced a 20-year slide into mortality of old, high-elevation 

trees, and have synchronized the years of maximum growth 

in a generally even-aged low-elevation population. 

The often stated argument that high-elevation mortality is 

related to high levels of air pollution does not explain the 

1960 synchrony at low and high elevations. Shortle and 

Smith (1988) suggest that a possible explanation for growth 

Table 9.-Characteristics of dead trees from Mt. 

Washington 

Last year of Age at last Diameter Growth 

growth at BH year of growth rate 

Years 

160 

133 

32 1 

31 2 

248 

159 

21 2 

I56 

208 

222 

292 

162 

161 

253 

233 

slow 

slow 

slow 

slow 

intermediate 

slow 

slow 

slow 

fast 

fast 

intermediate 

slow 

intermediate 

fast 

fast 
ANNUAL BASAL-AREA INCREMENT (cm2) 

d 4 r0 0uraurcn~8 

ANNUAL BASAL-AREA 

d 

a 

cn o 
NEW HAMPSHIRE 

14 

12 

Figure 13.-BAI for individual dead red spruce trees that 

grew in New Hampshire, New York, and Vermont. 

decreases and mortality of red spruce at high elevations is 

that acid precipitation on shallow, unfertile soils disrupts the 

balance between soluble calcium and aluminum. An 

increase in aluminum is then thought to inhibit uptake of 

calcium, resulting in reduced crown and declining vigor. 

However, this and other arguments for high-elevation 

pollution do not explain the synchrony with low-elevation 

growth patterns. 

Balsam fir was the only other species showing a recent, 

extended period of decreasing growth rates. It has not 

suffered the same high-elevation mortality as red spruce. 

Maturation of the low-elevation forest may be an adequate 

explanation (Hornbeck et al. 1986). The other eight 

species we studied, which together with red spruce and 

balsam fir make up 86 percent of New England forests, 

showed either level or increasing growth rates since 1950 

(Fig. 4). The species included sugar maple, which did not 

show any indication of the decline that is of present 

concern in the province of Quebec (McLaughlin et al. 1985), 

and white pine, which is particularly susceptible to air 

pollution (Gerhold 1977). In short, none of the 10 major 

species examined showed trends or levels of growth that 

appear to be outside ranges explainable by natural 

variation. 

With regard to Question 2 about spatial patterns, there is a 

pronounced gradient in acid deposition across New 

England, with heaviest levels in western and southern 

sections, gradually decreasing when progressing to the 

north and east (Nat. Atmos. Deposition Prog. 1988). The 

growth data we developed from tree rings did not show a 

relationship with this gradient. Growth patterns for individual 

species were consistent regardless of location. 

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Appendix 

Description of Data Files 

Individual-tree ages ranged from less than 20 to more than 

300 years. Early growth data from the very old trees was not 

critical to our analysis of growth of present-day forests. 

Thus, data storage requirements were reduced by storing 

only the measurements from 1850, termed "1850" files, 

after the data were converted from raw ring widths to 

annual BAI. Measurements predating 1850 were retained in 

the original files generated by the measuring device. 

The 1850 files consisted of alternating decades of annual 

BAl and raw ring widths from 1850 through 1985 for each 

tree (Table lo), along with a header record containing a 

tree's plot number, tree number, species code, county, 

state, age, estimated years to pith, measurer's initials, 

measurement date, file type, bark thickness, d.b.h. inside 

bark, d.b.h. in 1850, and a variable indicating whether or 

not the core struck the pith. 

A record for each tree was entered into a separate plot-level 

file containing physical site characteristics and growth 

indices (Table 11). Plot files and 1850 files were linked by 

plot number, tree number, county number, and state code. 

Important plot characteristics selected for this file included 

harvest history, elevation, depth of organic layer, rooting 

depth, soil texture, parent material, moisture class, soil 

series, and total-plot basal area. Individual-tree growth 

indicators could be added to the plot-level files at any time, 

allowing the exploration of relationships between growth 

and site characteristics. Both the 1850 and pbt-level files 

are available to the public. 
Table 10.-Example of an 1850 file that stores both radial and BAI from individual trees within the same file 

MCK 82984 AC 5.19 20.63 0.00 1 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.12 0.69 0.81 

0.00 0.00 0.00 1.96 3.12 2.10 

2.01 1.61 1.69 2.02 2.44 2.45 

1.94 1.41 1.38 1.53 1.72 1.61 

2.66 2.96 3.18 3.59 3.03 3.68 

1.33 1.42 1.46 1.58 1.28 1.50 

6.60 4.74 5.28 6.20 7.02 7.30 

2.15 1.49 1.61 1.83 2.00 2.01 

6.76 7.92 5.95 6.88 7.21 8.08 

1.61 1.84 1.35 1.53 1.57 1.72 

12.07 15.99 12.29 9.86 8.09 12.41 

2.19 2.82 2.11 1.66 1.34 2.02 

0.00 0.00 0.00 0.00 

0.00 0.00 0.00 0.00 

MCK 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

0.00 

DECADE OF BAl (SQ. CM) 

DECADE OF RADIAL INCREMENTS (MM) 

DECADE OF BAl 

DECADE OF RADIAL INCREMENTS 

* * * 

BAI VALUES THROUGH 1985 

RADIAL INCREMENTS THROUGH 1985 
10 

rn Table 1 I .-Example of a plot-level file linking individual-tree measurements with site information 
Smith, Robert B.; Hornbeck, James W.; Federer, C. Anthony; Krusic, Paul J., Jr. 

1990. Regionally averaged diameter growth in New England forests. 

Res. Pap. NE-637. Radnor, PA: US. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 26 p. 

A regional sample of tree-ring measurements was used to determine average 

annual growth in trees of 10 major species in New England. There have been 

extended periods of decreasing growth rates in red spruce since about 1960 

and in balsam fir since about 1965. The other eight species, which included 

sugar maple and white pine, showed constant or increasing growth rates 

through 1980. The decreases in growth rate in sampled red spruce and 

balsam fir were independent of physical site characteristics, elevation, and 

geographic location, indicating that regional factors are involved. Weather 

parameters were not closely correlated with growth rates, and the best 

predictive equation explained only 33 percent of annual variation. 

ODC: 181.65 (74) 

Keywords: growth decline; growth patterns; red spruce; annual basal-area 

increment; increment cores; forest maturation; air pollution; regional weather 

*U. S. GOVERNMENT PRINTING OFFICE: 19901748-070100021 
Headquarters of the Northeastern Forest Experiment Station is in Radnor, Pennsylvania. Field laboratories are maintained at: 

Amherst, Massachusetts, in cooperation with the University of Massachusetts 

Berea, Kentucky, in cooperation with Berea College 

Burlington, Vermont, in cooperation with the University of Vermont 

Delaware, Ohio 

Durham, New Hampshire, in cooperation with the University of New Hampshire 

Hamden, Connecticut, in cooperation with Yale University 

Morgantown, West Virginia, in cooperation with West Virginia University 

Orono, Maine, in cooperation with the University of Maine 

Parsons, West Virginia 

Princeton, West Virginia 

Syracuse, New York, in cooperation with the State University of New York, College of Environmental Sciences and Forestry at Syracuse University 

University Park, Pennsylvania, in cooperation with The Pennsylvania State University 

Warren, Pennsylvania 

Persons of any race, color, national origin, sex, age, religion, or with any handicapping condition are welcome to use and enjoy all facilities, programs, and services of 

the USDA. Discrimination in any form is strictly against agency policy, and should be 

reported to the Secretary of Agriculture, Washington, DC 20250.