The
Connecticut
Agricultural
Experiment
Station,
New Haven
Stand Dynamics
in Connecticut
Forests: The
New Series Plots
(1959-2000)
BY JEFFREY S. WARD
s
Bulletin 995
June 2005
Stand Dynamics in Connecticut Forests:
The New-Series Plots (1959-2000)
JEFFREY S. WARD
Most of Connecticut appears as a sea of hills swathed
with trees when viewed from a high overlook. This
seemingly never-changing cloak of trees is, in fact, a
constantly changing assemblage of individual trees. Most
of our forest, including the tracts discussed in this bulletin,
have arisen after harvesting or farm abandonment in the
1800's (Ward and Barsky 2000). The young saplings which
grew on those cutover and abandoned lands are now the
large, upper canopy trees in our forests today.
Because forest growth and development are long-term
processes, patterns of forest development have been largely
derived using indirect methods such as stand reconstruction
and comparing stands of different ages. Indirect methods
have outlined the general framework of forest stand
dynamics. However, they are of limited utility in providing
a specific prediction on the future development of an
individual stand of trees with its unique initial composition
and disturbance history.
Ultimately, forest stand development is the aggregate of
the growth, or demise, of many individual trees.
Understanding the causal factors that affect the future
growth and survival of individual trees will lead to better
comprehension of how these factors influence forest
succession. This requires a large long-term database with
detailed information on individual trees. Fortunately, four
large, permanent tracts, the Old-Series plots, were
established in young forests (~25-years-old) in central
Connecticut in 1926-27. These tracts were reexamined in
1937, 1957, 1967, 1977, 1987, and 1997. These tracts are
invaluable because of the length (since 1926-27), depth
(43,357 trees, 41 species), and breadth of information
(species, dbh, crown class, spatial location, etc.). In
addition, their continuity and replication on four sites make
these tracts unique.
Earlier reports (Stephens and Waggoner 1980, Ward et
al. 1999) have described changes occurring during seventy
years on the Old-Series plots. Changes in growth, mortality
and ingrowth were related to soil moisture and defoliation.
These data have also been used to examine the long-term
effects of wildfire (Ward and Stephens 1989), gypsy moth
defoliation (Stephens 1971), and individual tree
development (Ward and Stephens 1994, 1996, 1997).
However, all four tracts lie relatively close to one another.
contain few conifers, and have an uneven distribution
among soil moisture classes.
Therefore, four additional tracts, the New-Series plots,
were established in 1959-1960. These tracts were
established on sites with either dry or moist soil moisture
classes. Data from these plots were used to determine the
relationship between defoliation levels and subsequent
mortality (Stephens 1971, 1981). These four tracts represent
a wider geographical distribution, a more even distribution
among soil moisture classes, and a greater differences in
age of trees. Two of the tracts contained abundant conifers:
eastern hemlock and eastern white pine (scientific names of
woody plants are in Appendix I). A survey of the
permanent tracts in 2000 documented forty years of
dynamic change in forest composition. These changes in
forest composition will affect the quality and variety of
forest resources that are available to future generations and
wildlife. Therefore, it is prudent from both ecological and
economic perspectives to understand these changes and
their possible consequences.
TRACT LOCATIONS AND HISTORY
Because the initial report of these tracts (Stephens and
Hill 1971) is out of print, descriptions of the forests are
repeated here. The four tracts all lie in the upland region of
metamorphic rocks and glaciated soils. The Eastern tracts,
Gay City and Natchaug, are relatively younger hardwood
forests. The Western tracts, Catlin Woods and Norfolk, are
older and have a significant conifer component. The tracts
vary in soil, climate, and history.
The Gay City tract, mostly in the Meshomasic State
Forest near Gay City State Park, is a mixed hardwood
woodland with few conifers. One portion occupies the crest
of a north-south ridge at an elevation of about 850 feet. The
abundance of rocks, the presence of old charcoal hearths
and stone walls and the absence of a plow layer suggest that
the land was cleared, but never tilled. In 1980, dominant
trees on the somewhat excessively drained ridgetop were
found to have originated between 1905-1910 and the
smaller trees, between 1910-1920. Scattered dominants
originated before 1900 on the moister sites and around
1880 on the poorly drained site. The remaining smaller
canopy trees on these sites originated around 1910. This
tract lies closest, about 10 miles northeast, to three of the
stand Dynamics in Connecticut Forests New Series
Old-Series plots reported in an earlier bulletin (Ward et al.
1999).
The Natchaug tract is a stand of mixed hardwood in the
Natchaug State Forest in Eastford, about 25 miles northeast
of Gay City. Its gently rolling topography ranges in
elevation from 700 to 750 feet and its north-facing slope
varies from one to seven percent. Stone walls indicate that
the land was once cleared, but abundant rocks and absence
of a plow layer suggest it was never tilled. In 1980, the
larger scattered dominants were found to have originated
between 1890-1900, while smaller canopy trees originated
between 1910-1920.
Catlin Wood is a stand of hemlock, white pine, and
transition hardwoods on a nearly flat plain at about 900 feet
elevation in the White Memorial Foundation in Litchfield.
Slope ranges from one to four percent. Catlin Wood is the
oldest of the four tracts in the New Series. This stand was
established around 1795. Its origin is obscure, but since
early 19th century the main disturbance has been cutting or
windthrow (Smith 1956). Removal or death of chestnut
permitted a second age group of mixed hardwoods and
hemlock, originating around 1910-1920, to develop.
The Norfolk tract in the privately owned Great
Mountain Forest, lies about 18 miles north of Catlin Wood
in a region of rugged terrain in the lower Berkshire Hills.
Its east-facing slope varies from one to fifteen percent and
lies between 1400 and 1500 feet elevadon. In 1980 the
larger white ash and red oak were found to have originated
between 1880-1890. The presence of sprout clumps and
charcoal hearths suggest the area was heavily cut around
1 880. Smaller and younger beech, yellow birch and black
cherry about 90 years old suggest a second disturbance in
1910. Hemlock was not used for charcoal, but it may have
been removed at a later date. Persistent stumps reveal that
chestnut was also present earlier. The absence of fire scars
suggests that this tract was not burned.
Site Characteristics
On the Gay City tract, soils have formed on friable
glacial till derived chiefly from Bolton schist. The
somewhat excessively drained, shallow Hollis soil
predominates. The remainder of the tract lies about 0.6
miles east at 500 to 550 feet elevation on an east-facing
slope of 4 to 1 1 percent. The well drained Charlton soil
occupies the upper slopes, the moderately well drained
Sutton occupies the lower slopes, and the poorly drained
Leicester occupies the drainage swales.
On the Natchaug tract, soils have formed on compact
glacial till derived from Eastford granitic gneiss. Hardpan
is present throughout the area sampled. The well drained
c
o
100
80
60
■■S 40
a
20
West (conifer)
'East (hardwood)
A
I960 1970 1980
Year
1990
Figure 1. Estimated canopy defoliation (%) on New-
Series plots between 1960-1990. There were no
observed defoliation episodes after 1989.
Woodbridge soil on the upper slope gives way to the poorly
drained Ridgebury soil on the lower slope.
At Catlin Woods, the underlying bedrock is mostly
Brookfield diorite gneiss. The soils developed on glacio-
lacustrine sands which thinly mantle the underlying glacial
till. On the lower slopes, the glacial till forms a weakly
developed hardpan at depths of 20 to 30 inches. On the
upper slopes, the well drained Agawam and the moderately
well drained Sudbury soil formed in sand and gravel. The
poorly drained Walpole soil occupies a broad drainage
swale at the base of the terrace.
On the Norfolk tract, soils are formed on compact
glacial till derived principally from Canaan Mountain
schist. Hardpan is present at depths of 20 to 30 inches,
restricting downward drainage and creating seepage areas
near the base of the slope. Well drained Paxton soil occurs
on the upper slopes, moderately well drained Woodbridge
on the lower slopes, and the poorly drained Ridgebury soil
occurs at the base of the slope.
Insects and Disease
Annual defoliation maps prepared from aerial
reconnaissance by the State Entomologist were used to
estimate defoliafion on the tracts. The eastern hardwoods
tracts were defoliated more frequently, and more severely,
than the western conifer tracts (Fig. 1). The eastern tracts
had partial defoliation by gypsy moth (Lymantria dispar)
and canker worm {Paleacrita vernatd) during 1962 and
1967. Severe multi-year defoliation episodes were noted
during 1971-73 (gypsy moth and elm spanworm {Ennomos
Connecticut Agricultural Experiment Station
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
Figure 2. Mean growing season temperature and lowest Palmer drought severity index values during the growing season
(April-September) between 1960-2000. Running three year averages are shown.
subsignarius), and 1980-1983 (gypsy moth). In contrast,
defoliation was noted in the western tracts only in 1972,
1981, and 1989. The 1989 defoliation was controlled by
the gypsy moth fungus {Entomophaga maimaigd). Gypsy
moth populations in Connecticut have continued to be
controlled by the fungus.
Introduced diseases have also influenced the
composition of these forests. American chestnut have been
recorded on ail the tracts. However, chestnut blight fungus
{Cryphonectria parasitica) has largely relegated this
formerly regal species the status of an understory shrub.
Dutch elm disease {Ceratocystis ulmi) reached the Gay City
tract (the only one with elm) before the first survey in 1959.
Because elms were never abundant in these forests, the
disease had less impact than chestnut blight.
Beech bark disease, a complex of beech scale
{Cryptococcus fagisuga) and a fungus {Nectria coccinea
var.faginaia), was found on 14% of American beech.
Beech bark disease weakens, and may kill trees, by both
feeding on sugars flowing through the branches and trunk,
and by killing tissues that feed and produce the bark. A
native canker, Nectria canker {Nectria galligena), was also
present. It was found on nearly 4% of black birch in these
tracts, about half the rate of 8% observed in the Old-Series
tracts (Ward et al. 1999). Although it rarely kills trees,
Nectria canker can weaken trees and cause considerable
loss of commercial wood production.
Weather
Climate varies somewhat among tracts because of their
distribution over the state. In general, the western conifer
tracts in the Litchfield Hills are cooler and moister than the
eastern hardwood tracts. Climatic data used here are from
Bradley Airport in Windsor Locks, Connecticut. Gay City
is approximately 20 miles southeast of the airport. Catlin
Woods, Norfolk, and Natchaug are slightly more than 30
miles from the airport and lay southwest, west, and east,
respectively. The area is in the northern temperate climate
zone. Mean monthly temperature ranges from 25''F in
January to 73°F in July. There are an average of 176 frost
free days per year. Average annual precipitation is 44.4 in
per year, evenly distributed over all months.
Soil moisture is replenished during winter months
because trees do not remove water via transpiration.
Adequate rainfall during the growing season is crucial if
trees are to maximize growth. A wet August or September
can mask the presence of a drought during the early
summer. Therefore, we determined the lowest (most
severe) Palmer drought index value during the entire
growing season (April-September) for a given year. The
lowest Palmer drought severity index values, along with the
mean temperature during growing season, are presented for
the period between 1960-2000 (Fig. 2). Three year
averages are shown to emphasize trends by smoothing the
often dramatic year-to-year fluctuations. Climate values
Stand Dynamics in Connecticut Forests New Series
were obtained from the National Oceanic and Atmospheric
Administration (NOAA 2004).
The climate in northern Connecticut has oscillated
between wet and dry during the past forty years. The first
decade (1959-1970) was the coldest and driest period. The
following decade (1970-1980) was the wettest period and
had average temperatures. Temperatures between 1980-
2000 were slightly elevated from the previous twenty years
and had average to slightly moister than average conditions.
It should be noted that there were years within each 10-year
period when drought severity differed significantly from the
average for the decade.
FIELD METHODS
In each tract a base line was established generally
perpendicular to the contour and across a series of drainage
classes. Along the base line, soils were identified according
to profile morphology and slope position. Drainage classes
were identified according to the Soil Survey Manual (Anon.
1951). Within each drainage class, transects were
established parallel to the contour on one or both sides of
the base line. The transects were 16.5 feet wide (5 m) and
66 feet (20 m) to 394 feet (120 m) long. The end of each
transect segment was permanently marked with an iron t-bar
and rock cairn at 66-feet intervals. Where possible,
approximately equal areas were sampled in each drainage
class (Table I). The drainage classes were grouped into
three sites: moist, containing the very poorly drained,
poorly drained and somewhat poorly drained soils; medium
moist, containing the moderately well drained and well
drained soils; and dry, containing the somewhat excessively
drained and excessively drained soils.
Along the transects, each stem with a diameter of at
least 0.5 inches at 4.5 feet above ground, was plotted on a
map, identified, and described. The 1959-60 tree
descriptions included species, dbh, crown class, and
whether the stem was part of a sprout clump. Diameters
were measured to the nearest 0.1 inch. The Norfolk, Gay
City, and Catlin Woods tracts were established in 1959. The
Natchaug study area was established in 1960.
Crown class is a qualitative measure of a tree's position
in the canopy relative to its neighbors (Smith 1962). The
upper canopy of a forest is comprised of dominant and
codominant trees (Fig. 3). Upper canopy trees have well-
developed crowns that receive direct sunlight from above
and partly on the side. Intermediate and suppressed trees
form the lower canopy. Intermediate trees only receive
direct sunlight from above. Suppressed trees are found
under the other crown classes and receive no direct
sunlight, except for occasional sunflecks.
"9. S
m^ i
CSCSDSC 1 SC
Figure 3. Schematic drawing of crown classes. D-dominant,
C-codominant, I-intermediate, S-suppressed.
Individual trees were relocated using maps from the
previous survey for the surveys in 1970, 1980, 1990, and
2000. A total of 2831 stems were included in these surveys.
Mortality of previously counted stems and ingrowth (stems
that had grown to at least the minimum dbh since previous
survey) were also recorded. Total height of all dominant
trees and every tenth other tree was measured to the nearest
foot in 1980. Trees measured for height were also
examined for stem and crown defects. The defects were of
form and symmetry and external injury to crown and stem.
Internal defects such as heartrot were not included.
Beginning with the 1980 survey, the perpendicular distance
of each stem from the centerline of the transect was
measured and recorded. Stems were measured using the
metric system during the 1990 and 2000 inventories.
Diameters were measured to the nearest 0. 1 cm and the
minimum diameter was slightly decreased to 1.2 cm (0.47
inches).
Regeneration (stems < 0.5 inches dbh) was first
inventoried in 1980 using 1/300 acre circular plots. The
center of each regeneration plot was located halfway, or 33
feet, between the cairns with stakes. A slightly smaller 1/
1000 hectare (1/405 acre) circular plot was used for the
1990 and 2000 inventories. Stems were tallied by species
in one-foot height classes (< 1 , 1 - 1 .9, 2-2.9, . . . , > 9 ft tal 1).
For this Bulletin, regeneration was categorized as either
seedlings (< 4 feet tall) or saplings (> 4 ft tall and < 0.5
inches dbh).
Species groups
There were 26 major tree species represented, 7 minor
species, and 13 shrub species which included small
understory trees, chestnut sprouts and large shrubs. Species
are categorized into similar groups to simplify the
discussion. As before, extensive tables with summaries by
Connecticut Agricultural Experiment Station
500
1^400 j
Total density
Oak - - ^>- - • Vlaple
■ Conifer —•<<■— Birch
■ Other —->.-— Beech
1959 1970 1980 1990
Eastern tracts
2000
1959 1970 1980 1990 2000
Western tracts
Figure 4. Total stand density (stems/acre) by species group and survey year for New-Series plots.
individual species are provided. These are found at the end
of the Bulletin. Preceding these tables is a species list with
their common and scientific names.
The OAK group included northern red, black, scarlet,
white, and chestnut oak. The BIRCH group includes black,
yellow, and paper birch. The MAPLE group includes red
and sugar maple. American beech is the sole species in the
BEECH group. The CONIFER group includes eastern
white pine and eastern hemlock. The OTHER group
includes those species that can form part of the upper
canopy in a mature forest, but were found at low densities
on these tracts. To fit the individual species tables on a
page the following species were combined: green and white
ash, slippery and American elm, the various species of
shadbush.
MINOR species are those species that do not grow large
at maturity and generally do not appear in the canopy
except in very young stands. This group includes intolerant
pioneer species (e.g. gray birch) and species that can grow
and develop in the understory (e.g., flowering dogwood,
blue-beech, shadbush, and hophombeam). American
chestnut is also included in the MINOR species category
because chestnut blight kills stems before they grow large
enough to enter the upper canopy. Species that do not grow
tall enough to form part of the upper canopy (e.g.
witchhazel and highbush blueberry, and spicebush) were
included in the SHRUB category.
COMBINED CROWN CLASSES
Density
For the reader's convenience, all tables are at the end of
this Bulletin. To simplify the analysis presented in this
Bulletin, the similar eastern hardwood tracts (Natchaug and
Gay City) were combined, as were the similar western tracts
(Catlin Woods and Norfolk) that had a significant conifer
component. Total tree density is the mean density (stems/
acre) of the combined species over all moisture classes.
In 1959 the number of stems per acre varied among
tracts and sites. The relatively younger eastern tracts had
higher densities than the older western tracts. This
difference has largely disappeared over the past forty years.
These tracts are increasingly dominated by late-seral or
"climax" species. Between 1959-2000, Maple/Birch/Beech
have increased from 44% to 59% of stems in the eastern
tracts. In the western tracts over the same time period, the
proportion of Maple/Beech/Conifer increased from 70% to
90%.
Species that require more sunlight to reach the forest
understory for their seedlings to grow, and depend on more
severe disturbances to increase the sunlight, have been
declining in numbers over the past forty years. This group
includes the oaks, ashes, aspens, and black cherry. It is
likely these species will continue to decline in numbers until
there in a major disturbance event such as a hurricane or
intense wildfire.
The decline in oak and other more shade intolerant (sun
loving) species is not unique to this study, other unmanaged
forests (Christensen 1977, Nigh et al. 1985, Barton and
Schmelz 1987, Ward and Parker 1989, Ward and Stephens
1993) or forests that are partially harvested (Heiligmann et
al. 1985, Jokela and Sawtelle 1985, Smith and Miller 1987,
Abrams and Scott 1989, Abrams and Nowacki 1992). This
will lead to large scale changes in the landscape from even-
aged to uneven-aged forests, and may accelerate the shift in
dominance from midtolerant to tolerant species. Stand
growth rates may slow when stands become dominated by
Stand Dynamics in Connecticut Forests New Series
-S? 1200
■a
000
B
B 200
800
600 i
400
0
SJ3
S
a
U -400
-200
S Initial
■ Ingrowth
n Persistence
■ Mortality
Initial
1959- 1970- 1980- 1990- Initial 1959- 1970- 1980-
1970 1980 1990 2000 1970 1980 1990
Eastern tracts Western tracts
Figure 5. Components of total population dynamics by sur\'ey year for New-Series plots.
1990-
2000
more tolerant species (Lamson and Smith 1991). These
changes will affect not only the quality and makeup of
forest products available to future generations, but will also
affect the quality and variety of wildlife habitats (Scanlon
1992).
Total tree density decreased on the eastern tracts
between 1959-70, rose between 1970-80, and has steadily
decreased between 1980-2000 (Table 2, Fig. 4). This
pattern is similar to that noted for the Old-Series tracts and
was attributed to a lag response to the period of drought and
defoliation during the early 1960's (Ward et al. 1999) that
killed many of the upper canopy trees. Death of the upper
canopy trees allowed increased sunlight to reach the forest
floor - this resulted in an increase in regeneration.
Increased populations of black birch and spicebush
accounted for most of the increased density.
Density on the western tracts, in contrast, rose steadily
from 1959-1990. These tracts experienced only minor
defoliation over the past forty years. Eastern hemlock and
American beech accounted for all of the increase. Density
of every other species, except striped maple and elderberry,
decreased during this period. The decrease of all species
between 1990-2000 was probably due to self-thinning of
the very dense stands, and not to an introduced insect.
Hemlock woolly adelgid (Adelges tsugae) and elongate
hemlock scale (Fiorinia externa) were observed in the
western tracts in 2000, but had not caused any appreciable
damage or mortality.
Minor species density peaked in 1980. American
chestnut was the predominant Minor species in the eastern
tracts, and striped maple in the western tracts. The most
numerous Shrub species in both the eastern and western
tracts was witchhazel. There was also a significant
component of spicebush and elderberry in the eastern and
western tracts, respectively.
Components of change
We examined the net changes in stem density from
decade to decade in the preceding section. Decade-to-
decade changes can be separated into three components
(persistence, mortality, and ingrowth) to better understand
the underlying dynamics affecting our forests (Fig. 5).
Persistence is the number of stems that survive during a
given time period. Persistence is important because it
conveys a sense of the population stability. Mortality is the
number of stems that die, and ingrowth is the number of
new stems during a given period. Mortality measures
disappearance from the forest. The net change in the
population is determined by the balance between mortality
and ingrowth. Population density can be stable under
scenarios where mortality and ingrowth are both low, or
where mortality and ingrowth are both high.
Persistence
The small decadal changes in density can be related to
the high persistence of most species groups between the
surveys (Fig. 6). Persistence peaked between 1970-1990 on
the eastern tracts and between 1980-1990 on the western
tracts. Persistence was similar on all tracts (~ 630 stems/
acre) between the most recent surveys, 1990-2000. The
number of stems that persisted exceeded the combined total
of mortality and ingrowth for a given period.
There were differences in persistence among species
groups. On the eastern tracts, Birch and Maple exhibited
•a
350
a
300
^z
ci
250
u
s
?00
r-
S
150
100
w
s
50
■4^
0
L.
U
Pn
Connecticut Agricultural Experiment Station
M-
Persistence
M-
M-
_:-^^
B ff-
-K— Oak
■M' " ■ Maple
-C— Conifer
- B - Birch
-♦ — Otiier
- b - Beech
"IW-
R-
IM-
TVl
B R
1959- 1970- 1980- 1990-
1970 1980 1990 2000
Eastern tracts
1959- 1970- 1980- 1990-
1970 1980 1990 2000
Western tracts
Figure 6. Persistence (stems/acre/decade) by species group and survey years for New-Series plots. Persistence includes
stems that survived from one survey to the next.
higher persistence than Oak. Birch persistence increased
from 1959-2000, while Maple persistence slightly
decreased over the same period. Different patterns of
persistence were noted for the western tracts. Conifer and
Beech persistence dramatically increased from 1959-1990,
while Maple and Birch persistence decreased steadily. It
will take another 10-20 years to know if the drop in Conifer
and Beech persistence between 1990-2000 is part of a long-
term trend.
Mortality
As noted above, mortality is the loss of stems present at
one inventory and absent on a subsequent inventory. The
causes of mortality are varied. Large canopy trees usually
die as a result of storm damage, disease, or declining vigor.
As trees become larger and larger, more and more of the
sugars produced by the tree are utilized to keep alive the
massive support structure (trunk and branches) that lift the
leaves above competing trees. Therefore, less energy can
be allocated to defense against insect and disease attacks.
Thus, as an aging tree becomes larger, it becomes more
likely to succumb to an infestation. Competition for light,
water and nutrients eliminates stems from the lower canopy
and understory. Attack by insects and disease eliminates
stems from all canopy strata. Some trees are broken by
snow or ice, severe storms or other falling trees. Mortality
can also occur on areas flooded by beaver impoundment.
For any given ten-year period, mortality varied from
238-385 stems/acre in the eastern tracts and 110-296 stems/
acre in the western tracts (Table 3). Mortality generally
increased over time for species groups with large numbers
of stems in the subcanopy (e.g., Shrubs, Conifer, Beech).
Species that were primarily in the upper canopy, such as
Oak and Other, demonstrated a pattern of decreasing
mortality over time. The mortality for a given decade was
highly correlated (r^ = 82%) with the density at the
beginning of the period (Fig. 7). This was expected, given
that trees are competing for limited resources (light,
moisture, nutrients). More trees on a given acre means
there are fewer resources per tree. For some trees this
means death from competition.
Gross mortality numbers only tell how many stems have
died, not how fast the stems are dying. For example, let us
500
t 400
I 300
in
.•§■ 200
s 100
^
w
%
\Wv
w
0 400 800 1200
Initial density (stem.s/acre)
Figure 7. Relationship between initial density and mortality
during the following decade for New Series plots.
E - eastern tracts, W - western tracts.
Stand Dynamics in Connecticut Forests New Series
50
« 40
u
o
3 30
■^20 -
10
— K— Oak
- -M' • ■ Maple
— C — Conifer
- B - Birch
•--^1
^«
^x^
- b - Beech
Total mortality
1959-
1970- 1980-
1990-
1970
1980 1990
Eastern tracts
2000
959-
1970- 1980-
1990-
1970
1980 1990
Western tracts
2000
Figure 8. Mortality rate (%/decade) by species group and survey years for New-Series plots. Mortality rate is percent of
stems that died between surveys.
imagine that the mortality of two species groups, A and B,
was both 50 stems/acre/decade. If at the beginning of the
period species group A had 100 stems and species group B
had 1000 stems, then species group A would have a higher
mortality rate (50%) than species group B (5%). These
mortality rates (%/decade) are presented in Figure 8.
The mortality rate varied from decade-to-decade in both
the eastern and western tracts. In all periods except 1990-
2000, the mortality rate was higher in the eastern hardwood
tracts, 29-36%, than in the western conifer tracts, 18-32%
(Table 3). As noted above, much of this variation can be
explained by the correlation with initial density and
subsequent mortality.
Distinct patterns were noted for the different species
groups. The mortality rate for Oak decreased over time on
all tracts from a high of 48% between 1959-1970 to a low
of 11% between 1990-2000. In contrast to the declining
mortality rate exhibited by Oak over the past foity years.
Maple mortality increased from 16% to 23%, and Conifer
mortality increased from 2% to 31%. It is surprising that
Beech mortality has increased only slightly over past forty
years because 18% of trees were infected with beech bark
disease (Sirococcus clavigignenli-Juglandacearum I Nectria
coccinea var. faginata or N. galligend). This disease
complex has resulted in severe mortality (>50%) of upper
canopy trees in other regions (Houston 1999).
160
1l40
i •-^
I 100
o
en
80
60
40
20 ^
0
Ingrowth
^.,.,..|r-r.:.:^..
-K — Oak - nV|- ■ ■ Maple
-C — Conifer - B - Birch
-• — Other - b- - Beech
M-
B-
■-»-
1959- 1970- 1980- 1990-
1970 1980 1990 2000
Eastern tracts
1959- 1970- 1980-
1970 1980 1990
Western tracts
— « —
1990-
2000
Figure 9. Ingrowth (stems/acre/decade) by species group and survey years for New-Series plots. Ingrowth includes steins
that grew to threshold diameter between sui-veys.
10
Connecticut Agricultural Experiment Station
400
-i 300
200
3 100
0
Subcanopy
— K— Oak - -M- - • Maple
— C— Conifer - B - Birch
— • — Other - b- - Beech
^■^.rrrr^
^--■^^^■^ I
1959
2000
1970 1980 1990 2000 1959 1970 1980 1990
Eastern tracts Western tracts
Figure 10. Subcanopy density (stems/acre) by species group and survey year for New-Series plots. Subcanopy includes
trees in intermediate and suppressed classes.
Some species, such as gray birch and bigtooth aspen, are
pioneer species that colonize recently disturbed areas, grow
quickly, and die at a relatively young age (for trees). These
species had very high mortality rates and have disappeared
from these undisturbed forests. Mortality rates of Minor
and Shrub species were generally higher, often much higher,
than mortality rates for the other species rates.
Ingrowth
The growing space (and associated limited resources)
that had been utilized by a tree becomes available when that
tree dies. Some of the growing space is captured by the
expanding root and crown systems of neighboring trees.
Some of the growing space is colonized by new seedlings
that may then grow large enough (0.5 inches dbh) to be
included in our surveys. These new trees (ingrowth) are the
pool of individuals that will form the future forest. Some of
the ingrowth will survive and grow into the upper canopy
with the passage of time. Examining the composition of the
ingrowth provides us with clues as to the makeup of our
future forests.
Ingrowth peaked between 1970-1980 in both the eastern
and western tracts with 383 and 297 stems/acre,
respectively (Table 4). This was probably a lag response to
the periods of defoliations of the 1960's and 1970's. It can
take 10-20 years for a seedling to grow large enough to be
included in our surveys. Ingrowth densities decreased in
each of the following decades with the absence of any
addition disturbance.
Although a wide diversity of species was found on these
tracts, almost all of the ingrowth was limited to several
species. These species differed between the eastern and
western tracts. There has been no oak or hickory ingrowth
observed on these tracts since 1980. Among the species
capable of growing into the upper canopy in these mature
forests. Maple and Birch accounted for 83-95% of ingrowth
on the eastern tracts (Fig. 9). On the western tracts, Beech
and Conifer accounted for 94-99% of ingrowth.
Striking differences between the eastern and western
tracts were also observed in the composition and density of
Minor and Shrub ingrowth. Between 1980-2000, there
were fewer than six stems/acre of Minor ingrowth in the
western tracts, compared with 44 stems/acre in the eastern
tracts. Most of this ingrowth was American chestnut and
the deer resistant striped maple. Shrub ingrowth has been
minimal on the western tracts, especially since 1980. In
contrast. Shrub and Minor species have accounted for 49-
65% of all ingrowth stems in the eastern tracts. American
chestnut was the most common species, with some
bluebeech and hophombeam in recent years. Witchhazel
and spicebush have been the dominant Shrub species.
SUBCANOPY TREES
In an unmanaged forest with a disturbance regime of
single-tree or small group mortality, ingrowth trees
(discussed above) form part of the subcanopy. Subcanopy
trees are in the intermediate and suppressed crown classes
under the upper canopy (Fig. 3). The more numerous
suppressed trees live completely in the shade of lower trees,
while intermediate trees receive sunlight on the top of their
crowns. The subcanopy forms the pool of trees from which
future upper canopy trees will emerge in a mature forest
without major disturbance, such as the New-Series tract.
However, most subcanopy trees grow and die before a
stand Dynamics in Connecticut Forests New Series
11
100
2 75
50
^ 25
Subcanopy mortality
■Oai< --M-- Maple
C — Conifer - B — Birch
* — Otiier -b-Beecii
:":u^
-b-=^
1959-
1970
1970- 1980- 1990- 1959- 1970- J980-
1980 1990 2000 1970 1980 1990
Eastern tracts Western tracts
Figure 11. Subcanopy mortality (stems/acre/decade) by species group and survey year for New-Series plots.
1990-
2000
canopy opening is created by the death of an adjacent upper
canopy tree.
This environment where subcanopy trees grow is quite
distinct from that of the upper canopy trees. Surviving and
growing in this environment requires a different set of
attributes from those best suited for growing in an open
field, a recent clearcut, or a hurricane blowdown.
Understory trees need to be able to produce sugars
(photosynthesize) to survive and grow, albeit slowly, at low
light levels. Light levels can be reduced by 90% or more,
and the light that does get through is of a lower quality.
One adaptation is that subcanopy trees often leaf out before
the overstory trees. Some evergreen species have another
adaptation. The maximum rates of photosynthate storage
for hemlock occur on mild days during the winter and early
spring before hardwood trees have formed new leaves
(Hadley and Schedlbauer 2002).
Nutrient availability is also low in mature forests.
Subcanopy trees have to be efficient scavengers of scarce
mineral nutrients such as nitrogen, phosphorus, and iron.
Humidity is generally higher, but obtaining soil moisture is
constrained by the well established root systems of larger
trees. Browse damage can be high, especially for the
smaller saplings. Small trees can be crushed or damaged by
falling branches and storm damaged trees.
Subcanopy trees have important ecological functions.
Small mammals and birds consume the fruit of many
subcanopy species such as spicebush, winterberry, and
arrowwood. The preferred nesting site for some birds are
the low branches of subcanopy trees. Subcanopy trees also
provide cover for other animals. By filling the root gaps of
larger trees, and by being efficient scavengers of nutrients,
subcanopy trees recover nutrients that otherwise would be
lost to natural leaching. This helps maintain site
productivity and reduce mineral loss to adjacent wetlands
and streams.
Density
As with total density (Table 2), subcanopy density
decreased on the eastern tracts between 1959-70, rose
between 1970-80, and has steadily decreased between
1980-2000 (Table 5, Fig. 10). Most of the increased
density in the eastern tracts can be attributed to black birch
and spicebush. As noted above, this pattern is similar to that
noted for the Old-Series tracts and was probably a lag
response to the period of defoliation during the 1960's and
1970's that caused high mortality of established trees. This
mortality spike allowed increased sunlight to reach small
seedlings and saplings.
Density on the western tracts rose steadily from 1959-
1990 before decreasing by 23% between 1990-2000.
Eastern hemlock and American beech accounted for nearly
all of the increase. Density of every other species, except
striped maple and elderberry, decreased during this period.
This decrease was probably due to self-thinning of the very
dense subcanopy stratum.
The density of most species groups has fallen during the
past forty years. Between 1950-2000, the subcanopy
density of Oak, Other, and Maple species decreased by
97%, 70%, and 39%, respectively. Oak has not been found
in the subcanopy on the western tracts since 1960 and has
virtually disappeared from eastern tracts by 2000. Some of
the more shade intolerant species such as scarlet oak and
black oak are no longer found in the subcanopy. While
Birch declined by 73% on the western tracts to only 17
stems/acre, it increased by 26% to 200 stems per acre on
12
Connecticut Agricultural Experiment Station
the eastern tracts. The subcanopy density of the most shade
tolerant species have exhibited an increase over the past
forty years. Increases of eastern hemlock and American
beech have been 190% and 39%, respectively.
Mortality
Trees in the subcanopy grow in a restricted resources
environment with low light levels, low nutrient availability,
limited available root space, etc. Small trees store the
starch reserves needed to replace leaves or other parts
destroyed by insects, disease, or browsing in these
suboptimal conditions. Without these starch reserves, trees
may be unable to recover from multiple episodes of damage
and consequently, die. Subcanopy trees that develop in
canopy gaps often decline and die when the gap is closed by
lateral branch extension of surviving upper canopy trees.
These scenarios and others (e.g., competition) contribute to
the high levels of subcanopy mortality.
Subcanopy mortality, expressed as stems/acre/decade (S"
'^■°), has fluctuated between 228-376 S'^^ since 1959 on the
eastern hardwood tracts (Table 6). Except for the period
between 1959-70 when Oak mortality was high. Minor and
Shrub species accounted for the largest share of mortality
on the eastern hardwood tracts. Shrub species accounted
nearly half of the mortality since 1980. The decrease in
Oak mortality from a high of 83 8*° between 1959-1970 to
only 4 S'*" between 1990-2000 was related to a decrease in
the number of subcanopy oaks, and not to increased
survivorship as will be shown below.
In contrast, subcanopy mortality has steadily increased
over time on the western conifer tracts, from 107 8'*°
between 1959-1970 to 229 8"^° between 1990-2000.
Subcanopy mortality for all species groups were relatively
lower on the western conifer tracts until the 1990-2000
period. Eastern hemlock mortality increased from 2 8''^°
between 1980-90 to 128 S'"-" between 1990-2000. It is
unclear whether this increased mortality is related to
competition or to an alien insect (e.g., elongate hemlock
scale). An analysis of mortality rates (i.e., the percent of
stems that died on a per decade basis) reveals temporal
patterns that were obscured by differences in initial
densities (Fig. 11). Although the number of Oak subcanopy
trees dying has steadily decreased since 1959-1970, the
mortality rate has remained above 50% for the entire period
between 1959-2000. The high mortality rate of this species
group, coupled with the lack of ingrowth since 1980 (Table
4), suggests that Oak may not be present in the subcanopy
within twenty years. This is important because in the
absence of major disturbance, such as a hurricane, only
trees in the subcanopy are able to grow into the upper
Upper canopy ingrowth
(ascension from snhcanopy>
Figure 12. Schematic drawing showing upper canopy
regression and ingrowth (ascension). Regression includes
those trees that failed to grow fast enough to stay in the
upper canopy (i.e., the tree had slower height growth than
its neighbors). Upper canopy ingrowth (ascension) includes
trees in the intermediate crown class that grew tall enough
to form part of the upper canopy.
canopy. We may be witnessing the beginning of the loss of
Oak from these stands.
Not only has absolute mortality increased on the western
conifer tracts, as noted above, but the mortality rate has also
increased - from 20% between 1959-70 to 32% between
1990-2000. Mortality rates on the western tracts have
increased to levels higher than those observed on the
eastern tracts. The mortality rate has increased for every
species group, but most dramatically for Birch and Conifer.
Comparing the 1959-1970 to 1990-2000 periods. Birch
mortality has nearly doubled and Conifer mortality has
increased 15-fold.
SUBCANOPY / UPPER CANOPY DYNAMICS
While most of the changes in subcanopy density can be
explained by mortality and ingrowth (i.e., small trees
growing large enough to be measured), there are other
pathways, albeit smaller in scale. Subcanopy density is
decreased by some trees growing into the upper canopy, and
subcanopy density is increased by some canopy trees
regressing into the subcanopy.
Occasionally, canopy gaps are large enough to allow a
tree in the intermediate crown class to move into the upper
stand Dynamics in Connecticut Forests New Series
13
canopy (Fig. 12). Tiiis is ascension, or ingrowth into the
upper canopy from the subcanopy. Canopy gaps in
unmanaged stands are commonly created in one of two
ways: gradual tree mortality or severe weather.
Trees are not immortal. A healthy tree has one year's
worth of starch reserves stored in the roots and above
ground woody tissues. This reserve is used by the tree to
recuperate from injuries caused by weather (broken
branches, late spring freezes, drought), insects (gypsy moth,
bronze birch borer), disease (anthracnose, Nectria canker),
and fire. However, as trees become larger, more and more
of the sugars produced by photosynthesis are used to feed
the existing trunk, branch, and root systems. This leaves
fewer sugars available to maintain the starch reserves and to
produce the defensive compounds that protect a tree from
injurious insects and disease. When a tree has low starch
reserves, any moderate damage can cause the tree to enter a
decline spiral and die - creating a canopy gap. Severe
weather can also remove a tree from the upper canopy by
causing massive damage to the uppermost branches, or in
extreme cases, uprooting the tree or snapping off the trunk.
The reverse of ascension is regression. Regression in
the movement of trees from an upper canopy position to the
subcanopy. There are three common ways this can happen.
First, a storm can break off the uppermost branches of a
tree. Second, mortality of upper branches (dieback) may to
sufficient that the tree is no longer in an upper canopy
position. This may happen when the root system is
damaged or reduced by competition. Lastly, regression
includes those trees that failed to grow fast enough to
remain in the upper canopy, i.e., the tree had slower height
growth than its neighbors. For example, a 40-year-old
upper canopy maple is 50 feet tall and surrounded by 50
foot tall oaks. Over the next 25 years the maple only grew
nine feet taller, while the surrounding oaks grew 20 feet.
Although the maple has increased its height, it has regressed
into a lower canopy position because it was overtopped by
the faster-growing neighboring oaks. Earlier studies have
found that most of the larger maples and birch that are
found under the upper canopy oaks are not younger than the
oaks, just slower growing (Oliver 1978, Ward et al. 1999).
Upgrowth (Ascension)
Upgrowth, or upper canopy ascension, was much a more
important process than regression between 1959-1970 (Fig
13). High upper canopy mortality during 1959-1970
increased the amount of growing space (light, nutrients, and
moisture) available for lower canopy trees. This allowed
some of them to grow sufficiently to move into the upper
canopy (Table 7). Upgrowth on the eastern tracts averaged
3 1 stems/acre between 1959-60, and 42 stems/acre on the
western tracts during the same period. This influx of new
upper canopy trees precluded other lower canopy trees from
ascending to a higher position in later years. Thus,
upgrowth declined precipitously after 1980 to an average of
only three stems/acre/decade. Because there were few, if
any oaks in the subcanopy, most of the new upper canopy
trees were species typical of the northern hardwood forest.
Maple and Birch accounted for 73% of all upgrowth on the
eastern tracts over the past forty years. Conifer (37%),
Maple (28%), and Beech (21%) were the predominate
species moving into the upper canopy on the western tracts.
Regression
For most periods examined, very few upper canopy
trees regressed into the lower canopy (Fig 12). Regression
Q Initial
Dl Upgrowth
n Persistence
S Regression
■ Mortality
1959
1959- 1970- 1980- 1990- 1959 1959- 1970- 1980-
1970 1980 1990 2000 1970 1980 1990
Eastern ti-acts Western tracts
Figure 13. Components of upper canopy population dynamics by survey year for New-Series plots.
1990-
2000
14
Connecticut Agricultural Experiment Station
60
CI
50
u
u
~5i
40
B
s
30
>^
C/}
20
O
Q
10
Upper canopy
K ft
K— Oak - -M- - ■ Maple
€ — Conifer — B - Birch
-• — Other - b - Beech
1959 1970 1980 1990
Eastern tracts
2000
1959 1970 1980 1990
Western tracts
2000
Figure 14. Upper canopy density (stems/acre) by species group and survey year for New-Series plots. Upper canopy
includes trees in dominant and codoniinant crown classes.
averaged slightly less than three stems/acre (~ 3% of upper
canopy stems) on the eastern hardwood tracts for all
periods, except 1980-90 when over 17 stems/acre regressed
into the lower canopy. Maple and Birch accounted for 68%
of all regression. Regression on the western conifer tracts
was also highest between 1980-90 when nearly 18 stems/
acre moved from the upper to lower canopy stratum.
Conifer (37%) and Maple (37%) accounted for most the
regression on the western tracts over the past forty years.
UPPER CANOPY TREES
From a distance the impression of a forest is gained only
from those tree crowns that form the main canopy, the
dominant and codominant trees. Trees and shrubs
submerged in the lower canopy or in the understory remain
unseen. As mentioned in the Methods section, upper
canopy (or overstory) trees are those trees that have well
developed crowns and receive direct sunlight from above
and partly on the side. Forests are often typed, especially
by the casual observer, by the composition of the upper
canopy. Midslope forests with a northern red oak overstory,
red maple subcanopy, and a mountain laurel shrub layer are
most commonly categorized as red oak forests.
The composition of the upper canopy is important for
several reasons. The composition of the upper canopy has a
direct impact on seed production because there is a
correlation between the amount of sunlight a tree receives
and the amount of seeds produced. Thus, upper canopy
composition affects both the makeup of the seedling strata
and the wildlife species that live in the forest. Turkey,
eastern white-tailed deer, and chipmunks are more common
in oak forests, grouse in young aspen stands, and red
squirrels in conifer forests.
Although 24 major, 7 minor, and 8 shrub species have
been observed on these tracts, only 16 species appeared as
dominant or codominant stems in the canopy during 1959-
2000 (Table 8). Upper canopy stems were only a small
fraction of all stems — 10% and 13% on the eastern
hardwood and western conifer tracts, respectively. Only
four species accounted for the majority of upper canopy in
both the east and west. Eastern tracts were dominated by
northern red oak, black birch, red maple, and scarlet oak.
Western tracts were dominated by red maple, eastern
hemlock, northern red oak, and sugar maple.
We commonly think of the forest as unchanging,
especially for the large trees. The upper canopy is, in fact
quite dynamic at time scales that span decades (Fig. 14).
Nearly half of the original upper canopy trees found in 1959
had either died or regressed into the lower canopy by 2000.
Indeed, a careful analysis (the details of which are beyond
the scope of this bulletin) shows that the average sojourn of
Oak in the upper canopy was 89 years, compared with only
65 years for Maple and 42 years for Birch.
As noted above, the Oaks are gradually being replaced
by species typically found in the northern hardwood forests
of central New England. Maple, Birch, and Beech have
increased from one-third to more than one-half of the upper
canopy trees on the eastern tracts over the past forty years.
Over the same time period, the proportion of the upper
canopy on the western tracts that is comprised of Conifer,
Maple, and Beech has increased from 54% to 66%. Thus,
in the absence of a major change in climate or disturbance,
our children and grandchildren will know a very different
Stand Dynamics in Connecticut Forests New Series
15
forest than that which we are familiar with today - as we
know a very different forest than our ancestors icnew 100
years ago.
BASAL AREA
A decreasing number of trees is not necessarily
indicative of a declining forest; but is usually a consequence
of trees growing larger. Large trees need more resources
(light, moisture, nutrients) than small trees. One or more
resources becomes limiting as individual trees grow and
utilize more and more resources. Mortality can be
especially high for smaller trees growing under their larger
neighbors. Because these smaller trees are more numerous,
total forest density will decrease as part of natural stand
development.
Another gauge of forest development and change is
basal area. If you were to cut a tree at 4.5 feet aboveground
and calculate the surface area of the cut, you would have
determined the value that foresters refer to as the basal area
of that tree. The basal area of a stand is simply the sum of
the basal area value of all trees in that stand.
Basal area is an important measure as it is closely
correlated with the bulk, or volume, of the forest. Because
basal area is proportional to diameter squared it is easily
seen that the basal area of many small trees is not great
whereas the basal area of only a few trees of large diameter
can be considerable. For example, 196 1-inch diameter
trees have the same basal area as one 14-inch diameter tree.
In general, basal area tends to increase with increasing
stand age even though population decreases.
Unlike density, basal area has steadily increased over
the past forty years, except between 1990-2000 on the
western tracts (Table 9). The average annual basal area
increase has been 1.1% and 0.5% on the eastern and
western tracts, respectively. This indicates that although
density has been generally declining since 1980 (Table 2),
the forest is healthy and increasingly comprised of larger
trees. Since 1959, the number of sawtimber trees (diameter
> 10.5 inches) has more than doubled on the eastern tracts
and increased by 19% on the western tracts (Table 10). It is
especially striking the density of trees with diameters larger
than 20 inches has nearly tripled over the past forty years.
Basal area has also increased for most species groups
over the past forty years (Fig. 15). Oak basal area
increased on both the western and eastern tracts. It has
remained near 25% of all basal area over the past forty
years even as Oak density decreased from 12% to only 3%
of stems. Beech increased on both the eastern and western
tracts. Maple and Birch basal area increased on the eastern
tracts, while declining on the western tracts. Conifer basal
area increased by over 70% on the western tracts between
1959-1990 and then fell slightly in the following ten years.
SEEDLINGS AND SAPLINGS
Every tree species is adapted to thrive in a specific,
optimal range of soil moisture, fertility, and climate; after
all, oranges don't grow in New England. A large
determinant of which species will be found in the seedling
and sapling layer of unmanaged stands, such as those in this
study, is the suite of adaptations that allow a seedling to
grow in the shade of established trees and to exploit
ephemeral canopy gaps created by dying trees. Species
with these adaptations, such as American beech, eastern
hemlock, sugar maple, and black birch, are flourishing in
90
<-N
80
o
70
ss
'i; 60
w
50
40
u
es
^0
20
ca
10
0
Total basal area
— K— Oak - -M - ■ Maple
— C^ — Conifer — B — Birch
— • — Other - b— Beech
Bj;--^^^"*^
.-^--»^
^-^
-e — : — e — — <g- ■ ■ - ■ ir • ~ c
1959 1970 1980 1990 2000
Eastern tracts
1959 1970 1980 1990
Western tracts
2000
Figure 15. Stand basal area (ftVacre) by species group and survey year for New-Series plots.
16
Connecticut Agricultural Experiment Station
the New-Series stands. Witiiout a change in the disturbance
type or climate, it is likely that they will continue to
increase and eventually dominate these stands. Species such
as oak and aspen that require periodic disturbances (e.g.,
drought, fire) are slowly declining in these forests.
Seedlings populations are highly variable and can
change rapidly over a period of several years. Seed
production of different species is not synchronized. Beech,
hemlock, birch, and maple produce some seed every year,
with heavy production every several years. Other species
including oak and hickory have large seed crops at longer
intervals. Thus, in a given year, several species have high
seed production, several species have intermediate
production, and most species have very low seed
production.
Seeds have innumerable hurdles to surpass in the
process of germinating, surviving, and growing into the
sapling size class. Most do not. Before a seed germinates,
it must escape detection by a host of predators (weevils,
mice, deer, etc.) that consume nearly every seed. For the
few seeds that successfully escape detection and are able to
germinate, most will begin life where chances of survival
are minimal because of inadequate growing space (high
competition), unfavorable soil/moisture environment, or
recurring damage by deer browsing. Considering the host
of tribulations that beset a seed before it can develop into a
sapling, the natural regeneration of a forest is a remarkable
process.
Seedlings
Seedling (<4 feet tall) densities were much higher than
the combined density of saplings, subcanopy and upper
canopy trees (Table 11). In 1980 there were nearly 12,000
seedlings/acre on the eastern tracts and over 8,600
seedlings/acre on the western tracts. There were a few
trends for seedlings on the western tracts. Seedling
densities increased for sugar maple, red maple, white ash,
black oak, sassafras, and shadbush. Seedling density
decreased for black birch, yellow birch, American beech,
flowering dogwood, and bluebeech. Although yellow birch
had the highest density in the sapling size class in 2000; red
maple, white oak, white ash, and shadbush had higher
seedling densities. Whether this is a harbinger of future
changes in the composition of the sapling size class, or
reflects the competitive superiority of yellow birch to
develop into saplings, will require us to revisit these stands
in future decades.
A different pattern was noted on the western conifer
tracts where seedling density in 1990 was twice that of
1980, and triple that of 2000. The bulge of seedling density
was largely explained by an increase of over 8000 stems/
acre of eastern hemlock. Fewer than 700 of these seedlings
were still alive ten years later. Seedling densities of two
species, American beech and striped maple, increased
between 1980 and 2000. Over the same time period,
seedling densities of red maple, northern red oak, yellow
birch, and shadbush declined. Interestingly, while eastern
hemlock and American beech accounted for 87% of
saplings on the western tracts in 2000; only 27% of the
seedling population was comprised of these two species.
Although nearly 40% of seedlings were red maple, no red
maple saplings were found.
Saplings
For this section, saplings are defined as trees at least
four feet tall with diameters less than one half inch. There
is intense competition among the thousands of seedlings
and fewer than ten percent grow large enough to become a
sapling (Table 12). Sapling density doubled between 1980-
2000 on the eastern hardwood tracts (Fig. 25). This
increase was largely driven by an dramatic increases of
highbush blueberry (1280%) and yellow birch (450%).
Oak sapling density was relatively stable, while Maple
sapling density actually declined. The complete loss of
dogwood saplings after 1980 was probably related to
dogwood anthracnose that was widespread in the region
(Anagnostakis and Ward 1996).
In contrast, sapling density declined on the western
conifer tracts between 1980-2000. Most of this decline was
related to a decrease in eastern hemlock sapling density
from 200 to 45 stems/acre. Many of the hemlock saplings
were in "dog-hair" patches in canopy gaps created by the
mortality of an upper canopy oak. The decrease in hemlock
density was somewhat counterbalanced by an increase in
American beech from 192 to 247 stems/acre. It is worth
noting that two aforementioned species were the only tree
species present in the sapling size class. This would
suggest that these forests may be become less diverse with
the passage of time.
stand Dynamics in Connecticut Forests New Series 17
THE FUTURE FOREST
Forty years of the research have shown that even our
older forests are not static dioramas, but rather that they are
dynamic and constantly changing as trees grow, die, and are
replaced. Change will continue to be a characteristic of
these and all of our forests. The research reported in this
Bulletin suggests that two very different forests are
developing.
On the wanner and drier tracts, oaks are not reproducing
and are gradually being replaced by maple and birch. If this
trend of the last forty years were to continue, scarcely ten
percent of upper canopy trees will be oak in 100 years. The
future is uncertain because of the potential effects of
climate change, an alien insect that prefers maple (Asian
longhorned beetle, Anoplohora g/abripennis), and the
potential reintroduction of blight resistant American
chestnut (Anagnostakis 2001).
The cooler and moist tracts in western Connecticut have
become increasingly dominated by northern hardwood
species and eastern hemlock. The latest survey in 2000
found that nearly 90% of subcanopy trees were either
eastern hemlock or American beech. However the fate of
those species is uncertain because of the alien pests
hemlock woolly adelgid and beech bark disease.
We will continue to monitor these tracts to more
completely understand the processes that shape our forests.
This will also allow us to gauge the any future impact to the
forest caused by hurricanes, alien pests that are already in
Connecticut (e.g., beech bark disease, hemlock woolly
adelgid), and alien pests that may arrive within the next
decade (e.g., Asian longhorned beetle, emerald ash borer
(Agrilus planipennisj). The one lesson that we can take
from this study of forest dynamics, and the history of the
Connecticut forest, is that our forests are resilient and with
careful conservation will continue to cloak our sea of hills
with an ever changing kaleidoscope of species.
18 Connecticut Agricultural Experiment Station
ACKNOWLEDGMENTS
As with all long-term studies, a debt of gratitude is owed to the generations of scientists and field technicians who
preceded us. I wish to thank D.E. Hill, S. Collins, and A.R. Olson for participating in the establishment and original
inventory of these tracts in 1959; D.B. Downs and L.E. Gray for assisting in 1970; W. Holbrook for assisting in 1990; and
J. P. Barsky, A. Shutts, J. Rawson for completing the 2000 survey. I gratefully acknowledge the support of Division of
Forestry, Connecticut Department of Environmental Protection, White Memorial Foundation, and Great Mountain Forest for
preserving the study areas. Lastly, I would like to extend a special thanks to G.R. Stephens who helped with the original
establishment of these tracts and was the lead scientist responsible for the monitoring through 1990. We would also like
thank Gypsy Moth survey crew. This research was partly fijnded by Mclntire-Stennis Project CONH-558.
stand Dynamics in Connecticut Forests New Series 19
REFERENCES
Abrams, M.D., and G.J. Nowacki. 1992. Historical variation in fire, oak recruitment, post-logging accelerated succession in
central Pennsylvania. Bulletin of the Torrey Botanical Club 119: 19-28.
Abrams, M.D., and M.L. Scott. 1989. Disturbance-mediated accelerated succession in two Michigan forest types. Forest
Science 35: 42-49.
Anagnostakis, S.L., and J.S. Ward. 1996. The status of flowering dogwood in five long-term plots in Connecticut. Plant
Disease 80: 1403-1405.
Anagnostakis, S. L. 2001. The effect of multiple importations of pests and pathogens on a native tree. Biological Invasions
3: 245-254.
Anonymous. 1951. Soil Survey Manual. USDA Agricultural Handbook 18. 503p.
Barton, J.D., and D.V. Schmelz. 1987. Thirty years of growth records in Donaldson's Woods. Proceedings Indiana Academy
ofScience 96: 209-214.
Christensen, N.L. 1977. Changes in structure, pattern, and diversity associated with climax forest maturation in Piedmont,
North Carolina. American Midland Naturalist 97: 176-188.
Hadley, J.L., and J.L. Schedlbauer. 2002. Carbon exchange of an old-growth eastern hemlock {Tsuga canadensis) forest in
central New England. Tree Physiology 22: 1079-1092.
Heiligmann, R.B., E.R. Norland, and D.E. Hilt. 1985. 28-year reproduction on five cutting practices in upland oak. Northern
Journal of Applied Forestry 2: 17-22.
Houston, D.R. 1999. Beech bark disease. P. 35 in Proceedings, U.S. Department of Agriculture interagency research forum
on gypsy moth and other invasive species: 1999, (S.L.C. Fosbroke and K.W. Gottschalk, ed.). USDA Forest Service General
Technical Report NE-266. 82p.
Jokela, J.J., and R.A. Sawtelle. 1985. Origin of oak stands on the Springfield plain: a lesson on oak regeneration. P.181-188
in Proceedings Fifth Central Hardwood Forestry Conference, (J. Dawson and K.A. Majerus, ed.). University of Illinois,
Urbana-Champaign, IL.
Lamson, N.I., and H.C. Smith. 1991. Stand development and yields of Appalachian hardwood stands managed with single-
tree selection for at least 30 years. USDA Forest Service Research Paper NE-655.
National Oceanic and Atmospheric Administration. 2004. Web page, http://wwwl.ncdc.noaa.gov/pub/data/cirs/
Nigh, T.A., S.G Pallardy, and H.E. Garrett. 1985. Changes in upland oak-hickory forests of central Missouri: 1968-1982.
P. 170- 180 in Proceedings Fifth Central Hardwood Forestry Conference, (J. Dawson and K.A. Majerus, ed.). University of
Illinois, Urbana-Champaign, IL.
Oliver, CD. 1978. The development of northern red oak in mixed stands in central New England. Yale University School of
Forestry and Environmental Studies. Bulletin 91. 63p.
Scanlon, J.J. 1992. Managing forests to enhance wildlife diversity in Massachusetts. Northeast Wildlife 49: 1-9.
Smith, D.M. 1962. The practice of silviculture. 7th ed. Wiley & Sons, New York, NY.
Smith, D.M. 1956. Catlin Wood. P. 19-24 in Six points of special interest in Connecticut. Connecticut Arboretum,
Connecticut College, New London. Bulletin No. 9. 32p.
Smith, H.C, and GW. Miller. 1987. Managing Appalachian hardwood stands using four regeneration practices — 34-year
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Stephens, G.R., and D.E. Hill. 1971. Drainage, drought, defoliation, and death in unmanaged Connecticut forests.
Connecticut Agricultural Experiment Station Bulletin 728. 50p.
Stephens, G.R., and P.E. Waggoner. 1980. A half century of natural transitions in mixed hardwood forests. Connecticut
Agricultural Experiment Station Bulletin 783. 44p.
20 Connecticut Agricultural Experiment Station
Stephens, G.R. 1971. The relation of insect defoliation to mortality in Connecticut forests. Connecticut Agricultural
Experiment Station Bulletin 723. 16p.
Stephens, G.R. 1981. Defoliation and mortality in Connecticut forests. Connecticut Agricultural Experiment Station Bulletin
796. 13p.
Ward, J.S., S.L. Anagnostakis, and F.J. Ferrandino. 1999. Seventy years of stand dynamics in Connecticut hardwood forests -
the Old-Series plots (1927-1997). The Connecticut Experiment Station Bulletin 959. 68p.
Ward, J.S., and J.P. Barsky. 2000. Connecticut's Changing Forest. Connecticut Woodlands 65(3): 9-13.
Ward, J.S., and G.R. Parker. 1989. Spatial dispersion of woody regeneration in an old-growth forest, Indiana, USA. Ecology.
70: 1279-1285.
Ward, J.S., and G.R. Stephens. 1989. Long-term effects of a 1932 surface fire on stand structure in a Connecticut mixed-
hardwood forest. P.267-273 in Proceedings Central Hardwood Forestry Conference VII, (G Rink and C.A. Budelsky, ed.).
Southern Illinois University, Carbondale, IL.
Ward, J.S., and GR. Stephens. 1993. Influence of crown class and shade tolerance on individual tree development during
deciduous forest succession in Connecticut, USA. Forest Ecology and Management 60: 207-236.
Ward, J.S., and G.R. Stephens. 1994. Crown class transition rates of maturing northern red oak {Quercus rubra L.). Forest
Science 40: 221-227.
Ward, J.S., and G.R. Stephens. 1996. Influence of crown class on survival and development ofBetula lenta in Connecticut,
USA. Canadian Journal of Forest Research 26: 277-288.
Ward, J.S., and G.R. Stephens. 1997. Survival and growth of yellow birch {Betula alleghaniensis Britton) in southern New
England. Canadian Journal of Forest Research 27: 156-165.
Stand Dynamics in Connecticut Forests New Series 21
22
Connecticut Agricultural Experiment Station
APPENDIX I
Common and scientific names of trees and shrubs mentioned in this Bulletin
Oak
White oak
Scarlet oak
Northern red oak
Black oak
Quercus alba
Quercus coccinea
Quercus rubra
Quercus velutina
Conifer
Eastern white pine
Eastern hemlock
Pinus strobus
Tsuga canadensis
Maple
Other
Red maple
Sugar maple
Birch
Yellow birch
Black birch
Beecli
American beech
Acer rubrum
Acer saccharum
Betula alleghaniensis
Betula lenta
Fagus grandifolia
Pignut hickory
Shagbark hickory
Mockemut hickory
White ash
Black ash
Tupelo
Bigtooth aspen
Black cherry
Black locust
Sassafras
Basswood
American elm
Slippery elm '^
Carya glabra
Carya ovata
Carya tomentosa
Fraxinus americana
Fraxinus nigra
Nyssa sylvatica
Populus grandidentata
Prunus serotina
Robinia pseudoacacia
Sassafras albidum
Tilia americana
Ulmus americana
Ulmus rubra
Minor
Shrubs
Shadbush
Gray birch
Bluebeech
American chestnut
Flowering dogwood
Hophombeam
Striped maple
Amelanchier arborea
Betula populifrjlia
Carpinus caroliniana
Castanea dentata
Cornus florida
Ostrya virginiana
Acer pensylvanicum
Witchhazel
Winterberry
Spicebush
Highbush blueberry
Hobblebush
Arrowwood
Northern wild raisin
Elderberry
Maleberry ^
Hamamelis virginiana
Ilex verticillata
Lindera benzoin
Vaccinium corymbosum
Viburnum alnifr>lium
Viburnum dentatum
Viburnum cassinoides
Sambucus canadensis
Lyonia ligustrina
'^combined with American elm for analysis
^combined with highbush blueberry for analysis
stand Dynamics in Connecticut Forests New Series 23
LIST OF TABLES
Table 1. Distribution of area (acres) by tract and soil moisture class of New-Series research plots.
Table 2. Stand density (stems/acre) during 1959-2000.
Table 3. Periodic mortality (stems/acre/decade) during 1959-2000.
Table 4. Periodic ingrowth (stems/acre/decade) during 1959-2000.
Table 5. Stand density (stems/acre) of subcanopy trees during 1959-2000.
Table 6. Periodic mortality (stems/acre/decade) of subcanopy trees during 1959-2000.
Table 7. Periodic ascension (stems/acre/decade) of trees that moved from lower to upper canopy position during 1959-2000.
"n" indicates that subcanopy trees were present, but none moved into the upper canopy.
Table 8. Stand density (stems/acre) of upper canopy trees during 1959-2000.
Table 9. Stand basal area (feetVacre) during 1959-2000.
Table 10. Diameter distribution (stems/acre) during 1959-2000.
Table 11. Stand density (stems/acre) of seedlings (< 4 feet tall) during 1980-2000.
Table 12. Stand density (stems/acre) of saplings (> 4 feet tall and < 0.5 inches dbh) during 1980-2000.
24 Conneclicul Agricultural Experiment Station
Table 1. Distribution of area (acres) by tract and soil moisture class of New-Series research plots.
E
ast
West
Combine
East
■d_
plots
West
Gay
City
Natchau
g
Catlin
Woods
N
orfolk
Total
Wet
Medium
Dry
0.10
0.10
0.25
0.10
0.20
0.00
0.10
0.23
0.13
0.15
0.15
0.15
0.20
0.30
0.25
0.25
0.38
0.28
0.45
0.68
0.53
Total
0.45
0.30
0.45
0.45
0.75
0.90
1.65
Stand Dynamics in Connecticut Forests New Series
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The Connecticut Agricultural Experiment Station (CAES) prohibits discrimination in all of its programs and activities on the
basis of race, color, ancestiy, national origin, sex, religious creed, age, political beliefs, sexual orientation, criminal conviction
record, genetic information, learning disability, present or past history of mental disorder, mental retardation or physical disability
including but not limited to blindness, or marital or family status. To file a complaint of discrimination, write Director, The
Connecticut Agricultural Experiment Station, P.O. Box 1106, New Haven, CT 06504 or call (203) 974-8440. CAES is an equal
opportunity provider and employer. Persons with disabilities who require alternate means of communication of program information
should contact the Chief of Services at (203) 974-8442 (voice); (203) 974-8502 (FAX); or Michael.Last@.po.state.ct.us (E-
mail).
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