Secondary Succession in a Mosaic of Unmanaged Conifer Plantations and
Former Old Fields
Abstract of
a thesis presented to the Faculty
of the University at Albany, State University of New York
in partial fulfillment of the requirements
for the degree of
Master of Science
College of Arts & Sciences
Department of Biological Sciences
Program in Biodiversity, Conservation & Policy
Emily Theressa Starr
2010
Abstract
Much of the land in the northeastern United States, previously cleared for
agriculture, has become a mosaic of regenerating forests. Fields and pastures were
abandoned a different times, providing varied lengths of time since secondary succession
began. Some areas were replanted with exotic conifers, adding single-species stands to
the mosaic, and disturbances like tree pests and increasing deer populations have
contributed to the patchiness of the landscape. Based on successional theory, the region
will eventually become a more uniform forest, dominated by eastern hemlock (Tsuga
canadensis) and northern hardwoods. This prediction is well-supported by studies in old
field succession, but there has been relatively little study of succession in unmanaged
plantations. This study investigated whether a mosaic of abandoned fields and conifer
plantations in central New York is reverting to contiguous native forest, and it re-sampled
a forested nature preserve that has vegetation surveys dating back to 1939. The present
study was modeled after a study from ten years ago, using the same approximate transect
locations in regenerating native forests and unmanaged conifer plantations. Over the last
ten years, in the secondary forests, the densities of eastern hemlock (15.0%) and
American beech (Fagus grandifolia) (9.3%) trees over 10 cm dbh have remained the
same, but sugar maple (Acer saccharum) increased to 40.6%. Sugar maple is by far the
most dominant species at the preserve, in terms of both density and frequency. Former
old fields are now late-successional secondary forests, but the plantations are still
dominated by the original conifers. Sugar maple and white ash (Fraxinus americana) are
the most common hardwoods in the plantations. Since 1999, the community composition
of hardwoods in the plantations has become more similar to that of the secondary forests,
ii
and hardwood diversity has increased in the plantations. Because the planted species are
not regenerating, they will eventually disappear from the preserve. For now, the planted
areas of the preserve can still be more accurately described as plantations than as natural
secondary forest, and they remain distinct from the later stage hemlock-northern
hardwood forest that characterizes most of the native stands. However, at broader scales
the hemlock-northern hardwood forest is challenged by a number of anthropogenic
disturbances, including exotic tree diseases and insects that specialize on ash, beech,
maple, and hemlock. Unmanaged plantations may be among the most affected, if their
diversity remains limited to declining conifers and a few susceptible native tree species.
iii
Secondary Succession in a Mosaic of Unmanaged Conifer Plantations and
Former Old Fields
A thesis presented to the Faculty
of the University at Albany, State University of New York
in partial fulfillment of the requirements
for the degree of
Master of Science
College of Arts & Sciences
Department of Biological Sciences
Program in Biodiversity, Conservation & Policy
Emily Theressa Starr
2010
Acknowledgments
This project would not have been possible without the guidance of my thesis advisor,
George Robinson; William Pfitsch and Thomas Caraco served on my committee and
provided valuable feedback. I would like to thank my field assistants for their work,
particularly Patrick Cooke, as well as Lilly Schelling, Jared Handel, Catherine Gilb,
Robert Wysocki, Evan Downey, Holly Read, and Anthony Champion. Thanks also to the
staff at the Edmund Niles Huyck Preserve, especially Chad Jemison and Audrey Kropp,
for their support of the project.
v
Table of Contents
Introduction………………………………………………………………….. 1
Methods……………………………………………………………………… 5
Study site……………………………………………………………… 5
Forest survey methods………………………………………………… 6
Analytical methods…………………………………………………… 7
Results ………………………………………………………………………... 9
Secondary forests……………………………………………………... 9
Plantation trees………………………………………………………... 16
Invasions into Plantations …………………………………………… 17
Diversity and similarity indices………………………………………. 25
Discussion…………………………………………………………………….. 27
Forest composition over time…………………………………………. 27
Long-term changes in forest composition ……………………………. 29
Trends in old-growth species ………………………………………… 32
Predicted future trends…………………………………………………33
Persistence of plantation trees………………………………………… 37
Conservation implications……………………………………………. 44
Conclusions …………………………………………………........................... 45
References…………………………………………………………………….. 46
vi
List of Tables
TABLE I. Tree species encountered in surveys of secondary forests, 1999 and 2009 … 12
TABLE II. Comparison of primary species in former old fields, 1999 and 2009……… 13
TABLE III. Dominant-species demographics in secondary forests……………………. 15
Table IV. Demographics of planted conifer species……………………………………. 18
Table V. Tree species encountered in the 1999 and 2009 surveys in red pine
and white spruce plantations……………………………………………………. 19
Table VI. Frequency and relative density of main species in the pine plantations…… 23
Table VII. Frequency and relative density of main species in the spruce plantations….. 24
Table VIII. Shannon diversity index for different forest types, 1999 and 2009……….. 25
Table IX. Jaccard index of similarity between forest types, 1999 and 2009…………… 26
vii
List of Figures
Figure 1. Dominant species in secondary forests, 1999 and 2009……………………… 11
Figure 2. Size-class distribution of the dominant species in the secondary forest……… 14
Figure 3. Dominant hardwoods in pine and spruce plantations………………………… 20
Figure 4. Size-class distributions of plantation species…………………………………. 21
Figure 5. Box plot diagrams of plantation conifer sizes (dbh) versus
condition in 1999 and 2009.
22
Figure 6. Odum’s (1943) diagram of predicted successional pathways
at the preserve…………………………………………………………………… 28
Figure 7. Timeline of hardwood invasions into red pine and
white spruce plantations………………………………………………………… 42
viii
INTRODUCTION
The rise and fall of agriculture has shaped the structure and composition of forests
in the Northeastern United States (Smith et al., 1993; Fuller et al., 1998; McLachlan et
al., 2000; Russell & Davis, 2001; Hall et al., 2002). Across the region, European settlers
cleared most of the land for agriculture in the 1800s, only to abandon a significant
proportion of it in the 1900s (Smith et al., 1993; Russell & Davis, 2001; Hall et al.,
2002). In New York, for example, farmland decreased by over 2 million ha (five million
acres) between 1880 and 1930 (Odum, 1943). Abandoned farmland that was not
developed has since reforested through the process of old field succession (Barnes et al.,
1998; Smith et al., 1993; Russell & Davis, 2001). The forests in the region can now be
characterized as mosaics of stands that have reached different stages of secondary
succession (Foster, 1988; Niering, 1998).
Although most of the forests in the Northeast are undergoing natural succession, a
significant amount of abandoned agricultural land was reforested as single or mixedspecies conifer plantations. In the early 1900s, plantations were common in Europe, and
they were recommended in the United States to produce timber “on idle lands so badly
depleted that natural reforestation is slow in starting” (Odum, 1943). The Civilian
Conservation Corps (CCC), part of Franklin Roosevelt’s New Deal policy, planted 2.3
billion trees on over a million ha (2.5 million acres) of degraded land across the country
(Maher, 2008). Over 20,000 ha of pine plantations were planted in New York State, but
few were ever harvested (Tobiessen & Werner, 1980). Thus, plantations remain an
important part of the post-agricultural landscape.
1
The general pattern of species replacements over time in old-field succession is
predictable in terms of life-history strategies (Bazzaz, 1968; Odum, 1969; McCook,
1994). Herbaceous species are the first to invade, with annuals most common at first,
which are then replaced by perennials. Shrubs and pioneer trees (fast-growing, shade
intolerant woody species) then become dominant. The late stages of succession are
characterized by a community of long-lived, shade-tolerant species (Bard, 1952; Bazzaz,
1968; Foster & Tilman, 2000; Odum, 1943). Which species represent the different life
histories depends on the region (Bard, 1952; Odum, 1969), as does the timeframe of
successive invasions (Wright & Fridley, 2010). Given enough time, patches of forest in
different successional stages should converge as they arrive at the late-stage community,
but disturbances can interrupt succession and maintain earlier-successional species
(Fuller et al., 1998; Woods, 2000b). After disturbances pass, the native late-successional
community will often return (Connell & Slatyer, 1977; Foster & Zybryk, 1993). The
late-successional community in central New York is expected to be a hemlock-northern
hardwood forest, dominated by eastern hemlock (Tsuga canadensis), American beech
(Fagus grandifolia), and sugar maple (Acer saccharum), in that order (McIntosh, 1962;
Russell, 1968).
While the general pattern of species replacements in old-field succession is
understood, the process in unmanaged plantations is ill-defined; the timing, order, and
predictability of invading species is yet unknown, and there have been few published
studies on the subject (Russell, 1968; Goldblum, 1998). Several of the published studies
of succession in North American plantations have been conducted in central New York at
2
the Edmund Niles Huyck Preserve, where both red pine (Pinus resinosa) and white
spruce (Picea glauca) plantations were planted in the late 1920s and early 1930s.
Odum (1943) believed that the plantations represented “an early seral stage
which, if there is no further interference, will eventually be replaced by the native climax,
provided of course that native climax species are not exterminated.” The term “climax
community” refers to the characteristic late-successional forest type of a region, such as a
hemlock-northern hardwood forest. In a later study at the preserve, Russell (1968)
compared the progress of old field succession to that of succession in the plantations and
concluded that the plantations had “actually speeded up natural succession instead of
hindering it” and believed that the plantations would become a late-successional
community more quickly than the abandoned fields.
In a later study at the same site, Goldblum (1998) found that red pine and white
spruce were not regenerating, and he predicted an eventual return to a natural forest type.
In order to reach a natural state, he described “an advanced form of old-field succession”
that would skip the early stages, including the monocots and herbs, and possibly fastgrowing, shade intolerant trees. Odum, Russell, and Goldblum all conceptualized
succession in a plantation as a stage of old-field succession, with presumably the same
endpoint of a native old growth community. Most plantations in NY State are not old
enough yet to confirm this expectation, but approximately 80 years of the process have
now played out, and current progress is worth investigating.
The persistence of the hemlock-northern hardwood forest is challenged by a
number of current and future environmental factors. First, each of the three expected
dominant species is affected or threatened by an introduced tree pest. The hemlock
3
wooly adelgid (Adelges tsugae) is eliminating hemlocks in central Atlantic and New
England forests (Small et al., 2005), altering biogeochemical processes and species
composition (Stadler et al. 2005). Beech bark disease, a syndrome involving the beech
scale insect (Cryptococcus fagisuga) and a fungus (Nectria spp.), has reduced beech
populations in the Northeast and subsequently changed forest structure (Forrester et al.,
2003). The Asian longhorn beetle (Anoplophora glabripennis) represents a serious threat
to maple species and could potentially spread to much of the eastern United States if
eradication efforts fail (Bancroft et al., 2002; Peterson et al., 2004). Other ecological
changes that could affect community composition are increased populations of whitetailed deer (Horsley et al., 2003) and climate change, which is expected to alter the
composition of species in many forests (Iverson & Prasad 1998, 2001).
This study considered secondary succession in a typical post-agricultural mosaic
in central New York. It surveyed former old fields, as well as pine and spruce plantations
that were planted on former agricultural fields in the 1920s and 1930s. The main
research questions addressed two types of secondary succession: old field succession and
succession in unmanaged conifer plantations. The general research questions were:
1. Has forest community composition changed over the last ten years?
2. Is the forest becoming a hemlock-northern hardwood forest as expected?
3. How does secondary succession in conifer plantations compare to old field
succession, in terms of timeframe and the succession of species invasions?
4
METHODS
Study Site
Fieldwork was conducted at the Edmund Niles Huyck Preserve in Rensselaerville,
New York (42° 31’ N, 74° 09’ W), where the elevation ranges from 360 to 650 meters
(Robinson, 2003). In the 19th and early 20th centuries, most of the land in the area was
used for agriculture; in 1889, it was mostly cleared hay fields. Russell (1958) wrote that
most of the land was undisturbed since about 1900, but there were some fields still being
hayed in the late 1950s. Others were left to recover and underwent old field succession.
Additionally, in the 1920s and early 1930s, some of the fields were planted with
spruce or pine plantations, which were never managed or harvested (Russell, 1968). The
exact years of planting have been reported differently; either it occurred from 1927-1930
(Odum, 1943) or from 1924 to 1930 (Russell, 1968). In either case, the Huyck preserve
was established at the end of the plantings, in 1931. The original preserve protected
about 200 ha of land and has been expanded several times, now covering approximately
800 ha.
There is little or no virgin forest at the preserve or in the area (Odum, 1943), but
by the 1950s, the native forests of the area were dominated by hemlock-hardwood
forests. Russell (1968) wrote that “plant succession in this region tends to restore these
forests.” Presently, the preserve is a mosaic of regenerating old fields and abandoned
conifer plantations, both of which can be considered secondary forests. Conifer
plantations cover a significant portion of the preserve, with red pine plantations
occupying 6.4% and white spruce plantations covering 2.3% (Goldblum, 1998). In the
5
late 1990s, Goldblum described 68.0% of the preserve as mixed northern hardwoodhemlock forests, and the remaining 23.1% as regenerating old fields. The land that was
not converted to plantations represents secondary forests that have reached different
stages of succession following agricultural abandonment. This study only sampled in
areas that contained woody species over 10 cm diameter at breast height. For clarity in
this paper, the former old fields will be referred to as the “secondary forests,” even
though the plantations are also a type of secondary forest. Plantations will simply be
called plantations.
Forest Survey Methods
Fieldwork was conducted during the summer of 2009, when trees 10 cm in
diameter at breast height (DBH) and larger were sampled along transects across the
preserve. Former old fields, now secondary forests, red pine plantations, and white
spruce plantations were sampled along 99 transects, including a total of 1,946 trees.
Sample methods and transect locations were based on Robinson (2003). His
transects were located in a stratified random distribution across the preserve. Transects
for this study were placed in the same approximate locations as Robinson’s, based on
marked paper maps and written descriptions of the locations. For this survey, transect
locations were recorded with GPS coordinates so that they could be relocated more
accurately in the future.
The majority of transects were 100 meters long, but some were shorter because
they ran into preserve boundaries or roads. Each transect was divided into 20-meter
stratified segments, and a random sample point was selected in each segment. The area
6
around the sample point was divided into quadrants, and the second-closest tree to the
center point in each quadrant was sampled (following recommendations of Engeman &
Sugihara, 1998). The size of the quadrants was therefore determined by the relative
density of trees over 10 cm DBH in the area, which varied. Full-length transects sampled
20 trees. Each tree’s DBH and species was recorded. Whether or not the tree reached the
canopy was determined, and its condition was categorized as healthy, not healthy (either
diseased or damaged), or dead. Dead trees that could be identified were included in the
sample; otherwise, the next closest tree was used.
Analytical Methods
For analysis, the dataset was separated into secondary forests (former old fields)
pine plantations, and spruce plantations, and individual trees were classified by the type
of forest they occupied. Trees were considered within a plantation if at least one tree in
its quadrant was a plantation species (red pine or white spruce), or if trees on both sides
of the quadrant were considered in a plantation because they had at least one plantation
tree. The remaining trees were considered to be in secondary forest. Thus, some
transects had quadrants in both a plantation and secondary forest. A few stands of oldgrowth hemlocks near Lincoln Pond were included in the secondary forest data. Some of
those trees most likely regenerated following a clear-cut in about 1800 (Runkle, 1990).
Direct comparisons between the 1999 and 2009 datasets were made possible by
limiting the earlier data to the trees 10 cm DBH or larger, which also made the sample
sizes of the two surveys more comparable. To asses changes in community composition,
species’ relative densities and frequencies were considered. A species’ relative density is
7
its percentage of all trees sampled. Its frequency is the percentage of all transects in
which the species was sampled. Relative densities and frequencies were compared using
a Z test for the equality of two proportions. Mean diameters were compared using twosample t-tests; all statistical analyses were done in MYSTAT 12.
Diversity comparisons among the secondary forest and plantation types were
made using the Shannon diversity index (Magurran, 2004), and comparisons between
1999 and 2009 were made as well. Planted conifers were excluded from the index, and
only trees less than 20 cm DBH were used. The Shannon index was calculated as
follows:
s
H = ∑ - (Pi * ln Pi)
i=1
where H is the Shannon diversity index
Pi = the fraction of the entire population that species i represents
S = total number of species
∑ = sum of species from 1 to S encountered
The similarity of species composition among secondary forests, pine and spruce
plantations was compared using the Jaccard index; comparisons were also made between
the 1999 and 2009 data (Magurran, 2004). The same subset of data was used for these
comparisons as in the Shannon index. The Jaccard index was calculated as follows:
J = __A___
A+B+C
where J is the Jaccard similarity index
A = the number of species shared between two sites
B = the number of species unique to the first site
C = the number of species unique to the second site
8
RESULTS
Secondary Forests
The secondary forest can be described as a late-successional community
dominated by hemlock, beech, and sugar maple, with a shift in community composition
that includes fewer early and mid-successional species than it did a decade ago. Table 1
shows all of the species that were sampled in 1999 or 2009, some of which were only
represented by one or a small number of individuals. Species that were at least greater
than 1% of the total sample are considered in more detail.
Species’ dominance can be measured by its frequency, relative density, and/or
relative basal area. Sugar maple was the most dominant species by any measure in 2009
(Figure 1 & Table II). Hemlock and beech decreased in frequency over the ten-year
period, and the dominant species’ rank in terms of frequency changed (Table II). In both
surveys, sugar maple, hemlock, beech, and white ash were among the top four mostfrequent species, but sugar maple was number one in both relative density and frequency
in 2009 (Table II). The densities of hemlock and beech did not change significantly, but
the relative density of sugar maple increased (Table II).
The percentage of trees contributing to the canopy increased for all three
dominant species, and the mean DBH increased for all of them, but only significantly for
sugar maple (Table III). The health of the dominant species showed some changes
between 1999 and 2009. The percentage of hemlocks that were unhealthy or dead
increased, while the percentages of unhealthy and dead beech decreased. The percentage
of diseased or damaged sugar maples increased tenfold, but the percentage of dead trees
9
did not change (Table IV). Size-class distributions are approximately reverse-J shaped
for hemlock and sugar maple, but beech had few remaining large individuals (Figure 2).
After the three most common species, white ash (Fraxinus americana) was the
next most dense tree, followed by white pine (Pinus strobus), ironwood (Carpinus
caroliniana), red maple (Acer rubrum), and northern red oak (Quercus rubra). Since
1999, white ash, ironwood, trembling aspen (Populus tremuloides), yellow birch (Betula
allegheniensis) and black cherry (Prunus serotina) decreased significantly in relative
density, and eastern hop hornbeam (Ostrya virginiana) showed a significant increase in
relative density (Table II). Eastern hop hornbeam increased in frequency as well,
whereas a number of species decreased in frequency, some of which had corresponding
decreases in relative density (Table II).
10
Dominant Speices in Secondary Forests, 1999
Dominant Species in Secondary Forests, 2009
50
40
sugar maple
45
sugar maple
35
40
30
Relative basal area
35
Relative bassal area
25
hemlock
20
15
30
25
20
15
10
10
white pine
white ash
white ash
ironwood
5
11
white pine
5
beech
hemlock
beech
0
ironwood
0
5
10
15
20
25
30
35
40
45
0
0
5
10
15
20
25
30
35
40
Relative density
Relative density
Figure 1. Dominant species in secondary forests, 1999 and 2009. Shows the relationship between species’ relative density (% of
total trees) and relative basal area (% of total basal area) in former old fields at the Edmund Niles Huyck Preserve in central New
York.
TABLE I. Tree species encountered in surveys of secondary forests, 1999 and 2009. Complete species
list of trees 10 cm DBH or larger in secondary forests at the Edmund Niles Huyck Preserve. The total
sample size in 1999 was 2,367; in 2009, it was 1,946. Xs indicate presence. Some of the species were
represented by only a few individuals; statistically significant differences are shown in later tables.
Species
Abies balsamea
Acer pensylvanicum
Acer rubrum
Acer saccharum
Amalanchior arborea
Amelanchior laevis
Betula allegheniensis
Betula papyrifera
Betula populifolia
Carpinus caroliniana
Carya laciniosa
Carya ovate
Carya tomentosa
Fagus grandifolia
Fraxinus americana
Fraxinus nigra
Fraxinus pennsylvanica
Hamamelis virginiana
Juniperus virginiana
Larix decidua
Malus sp.
Ostrya virginiana
Picea glauca
Pinus resinosa
Picea rubens
Pinus strobus
Pinus sylvestris
Populus grandidentata
Populus nigra
Populus tremuloides
Prunus pensylvanica
Prunus serotina
Prunus virginiana
Pseudotsuga menziesii
Pyrus coronaria
Quercus rubra
Rhus glabra
Rhus typhina
Robinia pseudo-acacia
Thuja occidentalis
Tilia americana
Tsuga canadensis
Ulmus rubra
Viburnum lentago
Viburnum nudum
Common name
Balsm fir
Striped maple
Red maple
Sugar maple
Allegheney serviceberry
Downey serviceberry
Yellow birch
Paper birch
Gray birch
Ironwood
Shellback hickory
Shagbark hickory
Mockernut hickory
American beech
White ash
Black ash
Green ash
Witch hazel
Eastern red cedar
European larch
Apple species
Eastern hop hornbeam
White spruce
Red pine
Red spruce
White pine
Scots pine
Big-tooth aspen
Black poplar
Trembling aspen
Pin cherry
Black cherry
Choke cherry
Douglas fir
American crabapple
Northern red oak
Smooth sumac
Staghorn sumac
Black locust
White cedar
Basswood
Eastern hemlock
Slippery elm
Nannyberry
Viburnum
12
1999
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
-
2009
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
TABLE II. Comparison of primary species in former old fields, 1999 and 2009. Trees 10 cm DBH or larger were surveyed in 1999 and 2009
in upstate New York. Relative density (% of all trees encountered) and frequency (% of transects the species was found in) are shown. Significant
differences between the 1999 and 2009 datasets are marked as * to signify p <0.05; ** to signify p<0.01, or *** for p<0.001. P-values were
obtained using a Z-test for the equality of two proportions. Classifications of species as early, mid, or late-successional were based on descriptions
in the US Forest Service database (USFS, 2010).
Change in
Species
Count
Transects
Relative Density(%) Frequency (%)
Density
Frequency
Early Successional
1999
2009
1999
2009
1999
2009
1999
2009
White ash
229
129
54
38
10.9
7.9
52.9
38.4
White pine
84
73
24
26
4.0
4.5
23.5
26.3
Paper birch
52
28
18
16
2.5
1.7
17.6
16.2
Trembling aspen
30
7
15
4
1.4
0.4
14.7
4.0
Red maple
49
35
28
24
2.3
2.1
27.5
24.2
Northern red oak
58
35
92
18
2.8
2.1
92.2
18.2
Black cherry
32
5
18
6
1.5
0.9
17.6
6.1
Ironwood
89
37
35
19
4.2
2.3
34.3
19.2
Basswood
35
17
19
12
1.7
1.0
18.6
12.1
Sugar maple
782
666
84
81
37.3
40.6
82.4
81.2
Hemlock
335
246
95
47
16.0
15.0
93.1
46.5
decrease***
Beech
208
152
96
43
9.9
9.3
94.1
43.4
decrease***
Yellow birch
31
8
25
6
1.5
0.5
24.5
6.1
decrease**
decrease***
Eastern hop hornbeam
11
29
6
18
0.5
1.8
5.9
18.2
increase***
increase**
2096
1640
102
99
decrease**
decrease*
decrease**
decrease*
Mid Successional
decrease **
decrease*
decrease**
Late Successional
Total
increase*
13
decrease***
American beech
Eastern hemlock
100
100
50
2009
1999
40
40
60
60
30
30
Count
80
Count
80
Count
Count
50
2009
1999
40
40
20
20
20
20
10
10
0
0
50
100
150
0
0
50
100
0
0
150
10
20
30
40
50
0
0
10
20
30
40
50
DBH (cm)
DBH (cm)
Sugar maple
200
200
1999
150
Count
Count
150
100
50
0
0
14
2009
100
50
40
80
120
0
0
40
80
120
DBH (cm)
Figure 2. Size-class distribution of the dominant species in the secondary forest. Shows size-class distributions of secondaryforest trees at the Edmund Niles Huyck Preserve in central New York from 1999 and 2009 surveys. Trees smaller than 10 cm DBH
were not sampled.
TABLE III. Dominant-species demographics in secondary forests. The mean DBH (standard deviation), percentage of trees
classified as diseased or damaged, percentage of dead trees, and percentage of trees that occupied the canopy are shown. Data was
collected on trees over 10 cm dbh. Significant differences between the 1999 and 2009 data sets are marked as * to signify p <0.05; as
** to signify p<0.01, or *** for p<0.001. P-values were obtained using a Z test for the equality of two proportions.
Mean DBH (cm)
% Diseased/Damaged
% Standing dead
2009
3.7***
% in canopy
Hemlock
1999
23.0 (15.7)
2009
24.7 (12.0)
1999
0.90
2009
7.3***
1999
7.2
1999
34.0
2009
4.2***
Beech
19.8 (7.7)
24.7 (8.4)
81.2
69.1**
11.5
5.3*
51.0
78.9***
Sugar maple
22.6 (10.5)
26.5 (13.7)*** 1.3
12.9***
2.0
2.1
78.8
88.4***
15
Species
Plantation Trees
Both red pine and white spruce increased in mean DBH and percentage of canopy
occupancy over the last decade (Table IV). Comparing the size-class distributions of
plantation trees at different points in time show that the plantation species are not
regenerating. Goldblum (1998) presented size-class distributions for white spruce in1954
and 1993. Between those dates, the size-class distribution of white spruce had flattened
and widened, with no trees less than 8 cm DBH and gaining larger individuals. A similar
pattern in the shape of the curves was observed for red pine, which lost all individuals
under 12 cm DBH by 1993. Between 1999 and 2009, red pine and white spruce sizeclass distributions also seem to be collapsing around the mean DBH (Figure 4), with no
evidence of regeneration. Both species appear to be in the process of continuous selfthinning, with larger stems persisting and smaller stems dropping out (Figure 5).
Goldblum (1998) concluded that neither white spruce nor white pine had
regenerated in the plantations at the Huyck Preserve. Although this study focused on
larger trees, no evidence of successful regeneration was observed. Not only have red pine
and white spruce failed to reproduce, a high percentage of them had died by 2009. The
percentages of dead trees increased to 9.2% for red pine and to 29.2% for white spruce,
almost double the percentage of 1999.
Native hardwood trees have established in the plantations (Table V), but the
plantations are still dominated by planted conifers (Tables VI and VII). Although the
main plantation species were white spruce and red pine, a few other conifer species were
mixed in that were probably included in the original plantations. Red pine plantations
had some Scots pine (Pinus sylvestris) and a few European larch (Larix decidua). The
16
white spruce plantations included a number of balsam fir (Abies balsamea) and a few red
spruce (Picea rubens) trees.
Invasions into Plantations
No significant changes were found in the frequency or relative density of invading
species or of the total planted conifers between 1999 and 2009. In both plantation types
in 2009, sugar maple was the most common hardwood, with both the highest relative
density and frequency (Figure 4). White ash was the second-most dense invading
species, and it had a high frequency in both types of plantations. Other invaders included
black ash (Fraxinus nigra), white pine, trembling aspen, and northern red oak (Tables VI
and VII). Of the three dominant species expected to occupy late successional forests in
the region, only sugar maple has successfully invaded the plantations to date; not one
hemlock was found in a plantation, and only one beech tree was sampled.
The native hardwood species invading the plantations had similar species
composition between the pine and spruce plantations. There was only one significant
difference in the relative density of a hardwood species in pine and spruce plantations in
1999; paper birch had invaded the spruce plantations, but not the pine plantations. There
were no significant differences in invading species’ densities between the pine and spruce
plantations in 2009, nor was there a significant difference in the proportions of planted
conifers versus native hardwoods in the plantation types.
17
Table IV. Demographics of planted conifer species. Shows the mean DBH (standard deviation), the percentages of trees that were
diseased or damaged, dead, and that occupied the canopy. Significant differences between the 1999 and 2009 datasets are marked as *
to signify p <0.05; ** to signify p<0.01, or *** for p<0.001. P-values were obtained with a Z test for the equality of two proportions.
Mean DBH (cm)
1999
2009
% Diseased/Damaged
% Standing dead
% in canopy
1999
2009
1999
2009
1999
Red pine
21.8 (6.8)
24.8 (7.9)**
13.8
4.1*
9.2
17.3*
74.
White spruce
19.8 (7.7)
25.2 (9.1)***
6.9
5.615.1
29.2*
57.3
78.9**
2009
91.8**
18
Species
Table V. Tree species encountered in the 1999 and 2009 surveys in red pine and white spruce
plantations. Trees 10 cm DBH or larger were sampled in 1999 and 2009. Sample size in 1999 was 139
and 99 for pine and spruce plantations, respectively. Sample sizes in 2009 were 148 in the
pine plantations and 122 in the spruce plantations. Xs indicate presence.
Species
Common name Red Pine Plantation
White Spruce Plantation
1999
2009
1999
2009
Abies balsamea
Balsm fir
-
-
-
x
Acer pensylvanicum
Striped maple
x
x
-
-
Acer saccharum
Sugar maple
x
x
x
x
Amalanchior arborea
Allegheny serviceberry
-
-
-
x
Betula allegheniensis
Yellow birch
x
-
-
-
Betula papyrifera
Paper birch
-
x
x
x
Betula populifolia
Gray birch
-
-
-
x
Carpinus caroliniana
Ironwood
-
x
-
x
Fraxinus americana
White ash
x
x
x
x
Fraxinus nigra
Black ash
-
x
-
x
Fraxinus pennsylvanica
Green ash
-
x
-
-
Larix decidua
European larch
-
x
-
-
Malus sp.
Apple species
-
-
-
x
Ostrya virginiana
Eastern hop hornbeam
-
x
-
x
Picea glauca
White spruce
-
-
x
x
Pinus resinosa
Red pine
-
x
-
x
Picea rubens
Red spruce
-
-
-
x
Pinus strobus
White pine
-
x
x
-
Pinus sylvestris
Scots pine
x
x
-
-
Populus grandidentata
Big-tooth aspen
-
x
-
-
Populus nigra
Black poplar
-
x
-
-
Populus tremuloides
Trembling aspen
x
x
x
-
Prunus serotina
Black cherry
-
-
x
-
Quercus rubra
Northern red oak
-
-
-
x
Tilia americana
Basswood
x
-
-
-
Tsuga canadensis
Eastern hemlock
-
-
-
x
19
Dominant Hardwood Speices in Pine Plantations, 2009
Dominant Hardwood Speices in Pine Plantations, 1999
8
14
7
12
sugar maple
6
Relative basal area
Relative basal area
10
5
4
3
8
6
white pine
4
2
white ash
trembling
aspen
1
2
trembling aspen
striped maple
0
0
0
0
1
2
3
4
5
6
Relative density
7
8
9
2
4
6
10
8
10
12
14
16
Relative density
Dominant Hardwood Speices in Spruce Plantations, 1999
Dominant Hardwood Species in Spruce Plantations, 2009
18
8
white ash
sugar maple
16
7
14
12
sugar maple
5
10
4
8
paper birch
3
6
2
trembling aspen
1
black cherry
0
0
2
black ash
4
4
6
8
10
12
14
Relative Density
Relative basal area
Relative Basal Area
6
white ash
2 paper birch
northern red oak
0
0
2
4
6
8
10
12
Relative density
Figure 3. Dominant hardwoods in spruce and pine plantations, 1999 and 2009.
Shows the relationship between species’ relative density (% of total trees) and relative
basal area (% of total basal area) in former old fields at the Edmund Niles Huyck
Preserve in central New York.
20
14
White spruce
30
Red pine
30
30
1999
20
20
30
40
50
0
0
Coun
t
10
10
10
20
Count
Coun
t
Count
20
10
2009
1999
2009
20
0
0
30
10
20
30
40
DBH (cm)
50
0
0
10
10
20
30
40
50
0
0
10
20
30
40
50
DBH (cm)
surveys in central New York. Pine and spruce plantations were planted in the late 1920s to early 1930s. Only trees 10 cm DBH or
larger were sampled, so the smallest size classes are not shown.
21
Figure 4. Size-class distributions of plantation species. Shows size-class distributions of plantation species in 1999 and 2009
40
40
30
20
30
20
Healthy Damaged
Dead
50
40
40
30
20
10
10
10
50
Diameter (cm)
50
Diameter (cm)
50
Healthy Damaged
White spruce 2009
White spruce 1999
Red pine 2009
Diameter (cm)
Diameter (cm)
Red pine 1999
Dead
30
20
10
Healthy Damaged
Dead
Healthy Damaged
Dead
22
Figure 5. Box plot diagrams of plantation conifer sizes (dbh) versus condition in 1999 and 2009. Center bars are arithmetic
medians, box lengths are interquartile ranges, and asterisks are individual outliers. For both species across both surveys, trees scored
as healthy were larger on average. ANOVA tests: Red pine 1999 F2,105 = 12.75, p < .001: red pine 2009 F2,95 = 5.37, p = .006: white
spruce 1999 F2,79 = 11.89, p < .001: white spruce 2009 F2,68 = 9.95, p < .00
Table VI. Frequency and relative density of main species in the pine plantations. Shows the main species of trees 10 cm DBH or
larger found in red pine plantations. Thee was no significant (p < 0.5) difference in any species’ density or frequency between 1999
and 2009. Significant differences between the 1999 and 2009 data sets are marked as * to signify p <0.05; as ** to signify p<0.01, or
*** for p<0.001. P-values were obtained using a Z test for the equality of two proportions.
Transects
1999
2009
Relative Density
1999
2009
Frequency
1999
2009
Canopy Occupancy (%)
1999
2009
0
109
2
111
2
98
10
8
0
8
0
8
1
8
1
8
0.0
78.4
1.4
79.8
1.4
66.2
6.8
74.4
0.0
100.0
0.0
-
12.5
100.0
12.5
-
75.2
100.0
75.7
100.0
91.8*
100.0
92.0***
0
1
9
0
1
2
5
3
0
1
3
1
1
2
2
2
0.0
0.7
6.5
0.0
0.7
1.4
3.4
2.0
0.0
12.5
37.5
12.5
12.5
25.0
25.0
25.0
100.0
33.3
-
100.0
100.0
100.0
66.7
0
0
2
0
2
1
0
1
0
1
0
0
1
0
2
1
0
1
0
1
0.0
0.0
1.4
0.0
1.4
0.7
0.0
0.7
0.0
0.7
0.0
0.0
12.5
0.0
25.0
12.5
0.0
12.5
0.0
12.5
50.0
0.0
100.0
100.0
100.0
12
139
20
148
4
8
6
8
8.6
-
13.5
-
50.0
-
75.0
-
66.7
-
95.0
-
23
Planted species
European larch
Red pine
Scots pine
Conifers total
Early successional
Paper birch
Trembling aspen
White ash
White pine
Mid-successional
Black ash
Black cherry
Ironwood
Northern red oak
Striped maple
Late Successional
Sugar maple
Total
Count
1999
2009
Table VII. Frequency and relative density of main species in the spruce plantations. Shows the main species of trees 10 cm DBH
or larger in white spruce plantations. Thee was no significant (p < 0.5) difference in any species’ relative density or frequency
between 1999 and 2009. Significant differences between the 1999 and 2009 data sets are marked with a* to signify p <0.05.
Count
Frequency
1999
2009
Percent in Canopy
1999
2009
9.8
1.6
1.6
0.0
58.2
71.2
0.0
20.0
0.0
0.0
100.0
-
14.3
14.3
14.3
0.0
100.0
-
100.0
57.5
74.7
75.0
100.0
50.0
78.9*
78.3
3.0
1.0
12.1
1.0
0.8
0.0
6.6
0.0
40.0
20.0
80.0
20.0
14.3
0.0
42.9
0.0
66.7
100.0
33.3
0.0
100.0
100.0
-
1
0
0
2
0
0.0
2.0
0.0
0.0
0.0
2.5
0.0
0.0
1.6
0.0
0.0
40.0
0.0
0.0
0.0
14.3
0.0
0.0
28.6
0.0
0.0
-
100.0
100.0
-
7
7
12.3
-
76.1
-
60.0
-
100.0
-
100.0
-
80.0
-
2009
Relative Density
1999
2009
2009
0
1
0
0
73
74
12
2
2
0
71
87
0
1
0
0
5
5
1
1
1
0
7
7
0.0
1.0
0.0
0.0
73.7
74.7
3
1
12
1
1
0
8
0
2
1
4
1
1
0
3
0
0
2
0
0
0
3
0
0
2
0
0
2
0
0
0
6
99
15
122
3
5
24
Planted species
Balsam fir
Red pine
Red spruce
Scots pine
White spruce
Conifers total
Early successional
Paper birch
Trembling aspen
White ash
White pine
Mid-successional
Black ash
Black cherry
Ironwood
Northern red oak
Striped maple
Late successional
Sugar maple
Total
Transects
1999
1999
Diversity and Similarity Indices
Diversity among small stems (10-20cm) of hardwood species did not change in
the secondary forest between 1999 and 2009, but hardwood diversity increased in both
the red pine and white spruce plantations (Table VIII). In both surveys, diversity was
highest in the secondary forest and lowest in the spruce plantations.
Table VIII. Shannon diversity index for different forest types, 1999 and 2009. Gives
the Shannon diversity index (H) for secondary forests, red pine plantations, and white
spruce plantations in 2999 and 2009 surveys in central New York. The data used to
calculate the Shannon index excluded the plantation species and only included stems 1020 cm DBH. Higher values of H represent higher diversity.
Secondary forest
H
Red pine plantations White spruce plantations
1999
2009
1999
2009
1999
2009
2.18
2.17
1.49
1.70
1.29
1.51
The Jaccard index showed low similarities between the secondary forest and the
spruce plantations, which did not change appreciably between 1999 and 2009 (Table IX).
There was low similarity between the secondary forest and pine plantations in 1999, but
they had become substantially more similar by 2009. The pine and spruce plantations
also became more similar to each other by 2009, which was the comparison with the
highest similarity. Sugar maple and white ash were common to and important in all three
forest types. If the plantation trees were included in this analysis, the similarities between
the plantations and native forest would have been reduced substantially.
25
Table IX. Jaccard index of similarity between forest types, 1999 and 2009. Values
of the Jaccard similarity index (J) in comparisons between secondary forests, red pine
plantations, and white spruce plantations from 1999 and 2009 surveys in central New
York. The data used to calculate J excluded plantation species and only included stems
10-20 cm DBH. Higher values of J indicate a more similar species composition.
Comparison
1999 J
2009 J
Secondary forest
and spruce plantations
0.20
0.22
0.17
0.31
0.22
0.36
Secondary forest
and pine plantations
Pine plantations
and spruce plantations
26
DISCUSSION
The secondary forest at the Edmund Niles Huyck preserve can currently be
characterized as a late-successional community dominated by hemlock, beech, and sugar
maple, with a shift in community composition that includes fewer early and midsuccessional species than it did a decade ago. Sugar maple has remained the most
frequently-encountered species, and its relative density rose to 40.6%. This is much
higher than the second-most common species, hemlock, at 15%. In addition to the top
three species, white ash has a relative density almost as high as that of beech, although
white ash had significantly decreased in frequency over the ten-year period analyzed.
The three dominant species are shade-tolerant climax species, whereas white ash is a
pioneer species, so the decrease in white ash is consistent with successional theory.
Forest Composition over Time
Forest composition at the preserve, like other forests in the Northeastern United
States, has been influenced by centuries of human disturbance. Even the few remaining
stands in the region that have never been cut have been altered indirectly by human
activity (Russell et al., 1993; McLachlan et al., 2000), so the “natural” late-successional
community type is not known (Russell et al., 1993). People used to expect forests to
restore themselves to pre-settlement conditions, the natural state of an earlier time
(Odum, 1943; McIntosh, 1962).
Once the Huyck Preserve was established in 1931, the land was left to recover
from agricultural use. Old field succession began in former hay fields, and the
plantations were never thinned or harvested (Russell, 1968). In the 1940s, Odum (1943)
27
described 26 different plant communities at the preserve, which was only about 200 ha at
the time. Based on the historical dominance of hemlock and the dominance of hemlock
in the oldest undisturbed section of the preserve, Odum predicted that the climax
community would be a hemlock consociation or a beech-hemlock association, or a
mixture of the two (Figure 6). Odum expected the patchy landscape to eventually
coalesce into one or two climax communities. He did not include the plantations as part
of succession, unless he expected them to be logged and follow the middle pathway.
Predicted succession (Odum, 1941)
Approx. time (yr)
200
150
50
Hemlock - Beech
Hemlock - Birch Red Maple
?
Hemlock
Hemlock - White Pine
Beech - Sugar Maple
Hemlock - Birch
Hornbeam - Ash - Alder Maple Beech -Maple
Basswood
Ash - Sugar
Maple
Aspen - Birch
Willow - Alder
Hydric soils
?
White Pine
Mixed shrubs
Post-logging
Old fields
Figure 6. Odum’s (1943) diagram of predicted successional pathways at the preserve.
The timeline on the left has been added to the original diagram.
About a decade later, Russell (1955) analyzed eleven forest stands in the preserve.
Across the preserve, the most dominant species were hemlock, sugar maple, beech, and
white ash, in that order. He found that the composition varied on a stand scale. He
28
believed the differences were due to varying local conditions and species availability for
recruitment, and he doubted that a “regional climax” community would emerge. Both
Odum (1943) and Russell described the preserve as a mosaic of forest types. The forest
at the preserve is still clearly fragmented by plantations, and some heterogeneity in
forests can be expected. For example, McLachlan et al. (2000) found that pre-settlement
forests could be described as patches of forest types, with early and mid-successional
species coexisting in a landscape; disturbance can maintain populations of less shadetolerant species.
Long-Term Changes in Forest Composition
Odum believed that the forest at the preserve, once sheltered from direct
disturbance, would return to its pre-settlement state. Knowing the state of pre-settlement
forests is somewhat challenging, due to a lack of scientific surveys. Historical records,
primarily surveyor’s records, are often the most comprehensive descriptions of forests
available. McIntosh (1962) used this type of data to characterize pre-settlement forests in
the Catskill Mountains. Although the Huyck preserve is not in the Catskills, it is in the
same region, and McIntosh’s descriptions are for the same elevation. Therefore, the
following is not a direct comparison of a location’s forest, but it can approximate regional
changes in forest composition.
McIntosh’s study shows that during pre-settlement times, beech, hemlock, and
sugar maple dominated pre-settlement forests, with densities of 49%, 20%, and 13%,
respectively. Birch species were the next most common and accounted for 7% of the
trees (McIntosh, 1962). In 2009, beech in the former old fields only had a relative
29
density of 9.3%, a more than five-fold decease in abundance since pre-settlement times.
This is lower than the abundance of beech found recently in the Catskills; Griffin et al.
(2003) reported a beech relative density of 17.0%. Both current figures, however,
represent a substantial decrease in abundance since pre-settlement times. Beech
populations were declining slowly even before Europeans arrived (Fuller et al., 1998),
and beech bark disease has furthered its decline (Lovett et al., 2004).
The percentage of hemlock at the preserve is also lower than the historical condition, and
it too was declining prior to European settlement (Fuller et al., 1998).
Human activity has certainly accelerated or renewed hemlock’s decline, however.
By the late 19th century, almost all the hemlock in the area had been cut for use in tanning
(Odum, 1943), and the large-scale clearing for agriculture reduced its relative density as
well (Russell et al., 1993). Historically, hemlock has recovered following declines, and
northern hardwood species, including sugar maple, beech, birch, elm, and ash tend to
recover along with hemlock (Foster & Zybryk, 1993). Hemlocks’ return to dominance
may require between 600 and 1,000 years (Woods, 2000b), leaving time for its recovery
to be hindered by disturbances like the hemlock wooly adeglid and deer over-browsing
(Weckel et al., 2006). The effect of the hemlock wooly adelgid alone could cause an
unprecedented loss of hemlock in the Northeast (Orwig et al. 2002).
Sugar maple has increased in abundance to more than triple its pre-settlement
proportion of the forest community (McIntosh, 1962). This is despite the phenomena of
sugar maple decline, a general reduction in the health of sugar maples in the Northeast
linked to a number of stressors, particularly changes in soil chemistry (reviewed in St.
Claire et al., 2008).
30
In 2009, birch species had a combined relative density of 3%, less than half of
what records indicate used to be in the forest, and white ash has become as common as
birch used to be. In both pre-settlement and current times, the top three species have
been late-successional, but early or mid-successional species have also been common.
Different species of birch have different successional statuses, but only yellow birch is
considered late-successional (USFW, 2010). Generally speaking, birch species have
become less common in the area.
Overall, the three most common species from the 17th century have regained their
dominance following post-agricultural abandonment, but their proportions have changed
considerably. Numerous other studies have shown that regenerated Northeastern forests
are dissimilar to historical forests (Foster & Zybryk, 1993; Russell et al., 1993; Rooney &
Dress, 1997; Fuller et al., 1998; Bürgi et al. 2000; McLachlan et al., 2000; Russell &
Davis, 2001; Singleton et al., 2001). A study in Massachusetts found that compared to
Colonial forests, maple, birch, and cherry had generally increased, and beech, hemlock,
and chestnut had declined (Bürgi et al., 2000). The decline in hemlock and beech and
rise in sugar maple abundance at the preserve is consistent with the Massachusetts data.
In a much shorter timeframe, over the last ten years, forests have continued to
change at the preserve, with shifts in species’ frequencies and densities. Compared to
both pre-settlement times and ten years ago, sugar maple has become even more
dominant. Over the last decade, white ash, trembling aspen, northern red oak, black
cherry, ironwood, hemlock, beech, yellow birch, and yellow birch have decreased in
abundance, and sugar maple and eastern hop hornbeam have increased. These changes
are consistent with successional theory, as early and mid-successional species are
31
decreasing, and some of the late-successional species are increasing. Hemlock and
beech, however, have decreased in frequency, but had not changed in relative density,
becoming patchier in distribution. Beech bark diseases and hemlock wooly adelgid could
lead to future declines for these species (Orwig et al., 2002; Lovett et al., 2004).
Trends in Old-Growth Species
A closer look at the three dominant old-growth species shows changes in their
canopy occupancy, size, and general health. Sugar maple, beech, and hemlock all
became more likely to occupy the canopy, another indication of their dominance. Mean
DBH increased for all three species, but only significantly for sugar maple.
All three species had changes in general health, but the meaning of the changes is
difficult to interpret with the data from this study. Sugar maple and hemlock increased in
the percentage of trees classified as unhealthy, mostly because they had broken limbs or
stems. The observed changes could be a result of wind or ice storms during the time
between surveys (NOAA, 2010). Older and larger trees are also more susceptible to
damage, but a comparison of size versus damage did not show a relationship between
size and damage. The differences in the damaged category could also be a result of the
2009 survey using a lower threshold for “damaged” than the 1999 survey.
The health of the beech population showed improvements in both the percentage
of dead and diseased trees, almost all of which were classified as diseased/damaged for
showing signs of beech bark disease. Although the majority of beech trees at the
preserve are diseased, the percentage decreased from 81.2% to 69.1%. More detailed
analyses would be needed to assess the health of the beech population, but some healthy
trees remain. The size-class distribution of beech shows that there are few large
32
individuals and relatively high numbers of small stems, consistent with the pattern of
beech bark disease, to which larger trees are more susceptible (Forrester et al., 2003).
Predicting Future Trends
To approximate natural late stage communities, people often look to the oldest
stands in an area (Millar et al., 2007; Odum, 1943; Runkle, 1999). At the Huyck
Preserve, there is a particularly old stand dominated by hemlocks, part of which regrew
after a clearcutting around the year 1800 (Runkle, 1990). Data collected in 2002 show
that hemlock was almost 2/3 of the total relative density and basal area in the stand;
hemlock was clearly the dominant species. However, community composition had
changed over the period from 1978 to 2002; northern red oak and yellow birch had
increased since 1978, while white ash, beech, and bigtooth aspen (Populus
grandidentata) decreased significantly, either in relative density, relative basal area, or
both measures (Runkle, 2005).
The community in the rest of the preserve may not ever resemble the old-growth
hemlock stands, and Runkle’s data suggest that the “old growth” community composition
may be a moving target. Old-growth forests that are several hundred years old in general
may not have a stable composition (Woods, 2000a). The average lifespan for trees in
hemlock-hardwood forests is on the order of centuries, with the average age of death 216
years for sugar maple and 301 years for hemlock, so mature forests probably cannot be
classified as old-growth until they are about 180-250 years old (Lorimer et al., 2001).
Only the oldest hemlock stand at the preserve is within this range.
Studies looking back over long periods of time have shown that forest
composition is usually changing (Russell et al., 1993; Fuller et al., 1998; McLachlan et
33
al., 2000; Russell & Davis, 2001), calling the idea of a stable climax community as an
endpoint to succession into question. Even before European settlement, forest
composition was changing in the northeast (Russell et al., 1993; Fuller et al., 1998), with
a slow decline of beech, hemlock, and sugar maple (Fuller et al., 1998). Following
settlement and land clearing for agriculture, hemlock and beech declined, and birch
became more common (Russell et al., 1993). As farmland was abandoned, white pine
and chestnut became more common, and they were later replaced by oaks, red maple, and
birches (Fuller et al., 1998).
Some of the directional changes seen in the forest prior to settlement have
continued, but they are likely also influenced by human disturbance. Russell & Davis
(2001) found that the decline in beech has continued its pre-settlement trend, but they
conclude that the increases in birch and decrease in hemlock are new and probably a
result of anthropogenic disturbance (Russell & Davis, 2001). The abundances of birch
and oak may be reverting to pre-colonial status, but hemlock and beech have not
recovered (Russell & Davis, 2001).
In the long term, forests will be influenced by human disturbances and
environmental change (McLachlan et al., 2000). Beech bark disease has already created
a disturbance in almost all northern hardwood forests (Forrester et al., 2003), including
the forests at the preserve (Runkle, 2005). The main effect of beech bark disease is a
shift in age and size-class structure to smaller individuals (Lovett et al., 2006). Changes
in beech populations lead to changes in other populations’ dynamics as well; in the
Catskills, for example, reductions of beech populations have allowed sugar maple
34
populations to increase (Lovett et al., 2004). This may explain part of the increase in
sugar maple seen at the preserve.
The loss of hemlocks due to the hemlock wooly adelgid is expected to
homogenize the landscape as hardwoods replace them (Orwig et al., 2002; Sullivan &
Ellison, 2006). Birch, maple, and oak are likely to take their place (Orwig et al., 2002).
The hemlock pest has not yet arrived at the preserve, but if beech and hemlock
populations are both reduced in the future, sugar maple could become the main canopy
dominant.
On the other hand, maples are also threatened by an introduced insect, the Asian
longhorn beetle (Anoplophora glabripennis). This beetle favors maple species, but elm
and ash are also potential hosts (Bancroft et al., 2002). There have been outbreaks of the
Asian longhorn beetle in New York and Illinois, and the US Forest Service classifies it as
a “very high risk” pest (Cavey, 2010).
The emerald ash borer (Agrilus planipennis), another pest that could cause a
major disturbance in the forest, has just recently been discovered in several New York
counties (NYSDEC, 2010) and just south of the Huyck preserve. The ash borer is lethal
to white ash and green ash, which together account for 9.4% of the trees in the secondary
forest at the preserve. Together, beech bark disease, the emerald ash borer, the Asian
longhorn beetle, and the hemlock wooly adeglid threaten 80.4% of the trees at the Huyck
Preserve. In a review of exotic pests’ influence on ecosystems, Lovett et al. (2006)
concluded that pests and pathogens could be the most important factor driving ecosystem
change in eastern forests over the next several decades.
35
In addition to exotic insect pests, climate change will be an important disturbance
in Northeastern forests. Climate change has already begun (Arndt et al., 2009), and
species will respond individually (Miyamoto et al., 2010). This is expected to alter
communities as species’ fitness and interactions shift (Miyamoto et al., 2010). For
example, modeling predicts that the maple-beech-birch forests in the Northeast will lose
maples, beech, and yellow birch, and have increases in oak species (Iverson & Prasad,
2001). The exact changes that climate change will bring about at a local scale are hard to
predict, but we can expect forests to be changing in response to climate (Iverson &
Prasad, 1998; Miller et al., 2007). Climate change represents a disturbance and will
therefore affect succession. A warmer climate will not only shift individual species’
ranges (Iverson & Prasad, 1998; Miyamoto et al., 2010), but it could affect rates of
successional change (Wright & Fridley, 2010).
The current forest communities in the Northeast are novel and reflect individual
species’ responses to human disturbances (Russell & Davis, 2001). Multiple disturbances
make the eventual outcome even harder to predict, particularly when different
disturbances predict opposite trends. For example, the hemlock wooly adelgid is
expected to cause increases birches and maples (Orwig et al., 2002), whereas climate
change is expected to reduce their populations (Iverson & Prasad, 2001). On the other
hand, both disturbances are projected to lead to an increase in oak species (Iverson &
Prasad, 2001; Orwig et al., 2002). Furthermore, when disturbances are expected to affect
three or four of the most common species in an area, predicting their full ecological
impact is not straightforward.
36
Persistence of Plantation Trees
The planted species’ continued dominance shows that they have largely inhibited
other trees from invading the plantations. In fact, areas with dense red pine have been
shown to have reduce hardwood seedling survival, but the exact mechanism is unclear
(Tobiessen & Werner, 1980). It is possible that the plantation trees will remain important
on the order of decades, if not for another century. Goldblum predicted that white spruce
and red pine would remain dominant in the plantations for quite some time, based on
their typical lifespans. White spruce usually live 100-250 years in their native boreal
forests, but it is not clear how long they will live in plantations of eastern central New
York and elsewhere (Goldblum, 1998). Red pines in Vermont have a lifespan of 200-300
years, so the pines in New York could be quite long-lived (Goldblum, 1998). Although
there has been recent high mortality among the planted trees, it has mainly been among
the small size classes. This indicates that the forest is self-thinning, and the planted
species are becoming fewer in number, but larger and still the dominant species.
Invasions into Plantations
This study found no differences in the species invading the pine and spruce
plantations, suggesting that succession may proceed similarly, despite the species and
structural differences between the plantations. The pines were planted in rows, whereas
the spruce were planted in a random arrangement, which has led to higher average
understory light levels in the pine plantations (Goldblum, 1998). Goldblum found that
hardwoods had invaded pine plantations more rapidly than the spruce plantations and
thought it was due to higher light levels and more frequent tree-fall gaps. He concluded
37
that because sugar maple and white pine were already regenerating in the pine
plantations, they would reach a species composition closer to the natural forests more
quickly than the spruce plantations.
The Jaccard similarity index comparing hardwood species of 10-20 cm shows that
in 1999, the spruce and pine plantation were nearly equally similar to the secondary
forest. By 2009, however, the pine plantations appear to have a more similar species
composition to the native forest, supporting Goldblum’s hypothesis. The native species
present indicate that the pine plantations will become a more natural forest before the
spruce plantations, but neither type will appear natural until the majority of the plantation
trees are gone. The timeline for either type of plantation returning to a similar
composition to the rest of the secondary forest is not yet known. Whether the plantations
will eventually merge with the rest of the secondary forest also remains to be seen, but
they do seem to be moving in that direction.
Like elsewhere in the preserve, the most common native species invading the
plantations was sugar maple, a shade-tolerant species characteristic of latesuccessional communities. On the other hand, neither hemlock nor beech was wellrepresented in the plantations, as could be expected based on their own shade-tolerance
and high frequencies and densities. This suggests that the combination of shadetolerance and high prevalence is not entirely responsible for sugar maple’s success in the
plantations.
A number of studies at different points in time at the Huyck Preserve can be
pieced together to get a sense of the plantations over time (Figure 7). Plantations were
expected to produce useful timber more quickly than allowing old-field succession to
38
reforest an area, and Odum (1943) mentioned that 15-20 years after planting, plantations
had a higher basal area than old fields. By 1999 and 2009, however the average DBH of
all trees in plantations and all trees in secondary forests were similar.
Russell (1968) compared regenerating old fields and conifer plantations at the
preserve. In the plantations, he described white ash as “easily the most successful
invader.” When the plantation types were combined, white ash had a frequency of 100;
cherry species, 90%; , sugar maple, 70%;, and trembling aspen, 50%. Other invaders
included American elm (Ulmus americana), white pine, staghorn sumac (Rhus typhina),
bigtooth aspen, downy serviceberry (Amelanchior arborea), basswood Tilia americana),
and speckled alder (Alnus rugosa). Russell wrote that the spruce plantations had been
more successfully invaded than the pine plantations, which he explained as resulting from
the slower growth of spruce and effects of the spruce saw-fly.
Russell’s study (1968) also provides a snapshot of old-field succession at the
preserve. At the time, woody species were just beginning to invade old fields, including
(in order of importance): white ash, trembling aspen, sugar maple, and choke cherry
(Prunus virginiana). These species were all found in the conifer plantations at the time
as well. Russell concluded that “the clearing of old fields and planting of red pine and
particularly white spruce has actually speeded up natural succession instead of hindering
it. This may well be because of the amelioration of certain environmental factors, such as
temperature maxima and minima and evaporation rate, by the forest canopy and even
significant extensions of the growing season for native trees” (Russell, 1968). Currently,
however, the former old fields can now be described as late-successional secondary
forests, and the plantations remain essentially plantations. Old-field plantations like
39
those at the preserve are very disturbed sites, as plowing for agriculture followed by
planting is highly disruptive to the soil, topography, and generally destroys the seed bank
(Ramovs & Roberts, 2003). Natural succession has restored a native forest more quickly
than plantations have. The planted trees so far have inhibited the establishment of large
numbers of hardwoods, as demonstrated by the small percentages of native trees
currently found in the plantations at the Huyck Preserve. It is unclear how long this effect
will last.
In 1993, Goldblum (1998) repeated Russell’s survey and used tree cores to
determine the history of hardwood invasions into the plantations. Tree cores showed
some differences between invasions into the pine and spruce plantations. Pine
plantations experienced continuous recruitment of hardwoods over time, and the first
species to invade were black cherry, trembling aspen, and white ash. Paper birch and
white ash had been early invaders in the spruce plantations, and there was recruitment
during the first 25-30 years following planting. Between the 1960s and 1998, however,
there was a break in invasions into the spruce plantations. Goldblum concluded that the
red pine plantations were more susceptible to invasions, the opposite conclusion that
Russell had reached.
Goldblum (1998) described conifer plantations as “an advanced form of old-field
succession” that would skip the monocot and herb stages and perhaps also the shadeintolerant woody species. For every point in time that data are available, white ash has
been an important invader in the plantations, and sugar maple has been important over
the majority of the plantations’ history. The sequence of hardwood species invading
plantations does not follow that of old-field succession, and the coexistence of pioneer,
40
mid-successional, and climax species, along with the planted conifers, cannot be
described as a single stage of old-field succession.
The similarities in hardwood species composition between the pine and spruce
plantations suggest that the conifer species or the physical structure of the plantation does
not affect which species are the most successful at invading plantations. Rather, it seems
that something inherent to sugar maple and white ash make them good at reaching and
persisting in plantations. A study of restoration of pine plantations in Ontario (Parker et
al., 2008) found that with under-plantings of different mid-tolerant species, white ash had
the highest growth and survival, followed by white pine and then northern red oak, which
the authors attributed to white ash’s shade tolerance as a seedling.
The combination of recently-increased, high mortality of red pine and white
spruce, increasing similarity with former old fields, and increasing diversity of hardwood
species in the plantations indicate succession could be at or approaching a tipping point
where community composition will change rapidly. Hardwood seedling survival is
reduced under high densities of live red pines (Tobiessen & Werner, 1980), so as more
pines die, hardwoods could have a higher likelihood of survival and growth. Whether
one type of plantation will decline faster than the other remains to be seen, but if white
spruce continue to have higher mortality rates, the pine plantations could ultimately last
longer.
41
1927-1932
Sugar maple and white pine are
regenerating in the plantations. White
ash is the most common species in
plantations, followed by sugar maple.
1993
Hardwoods invade pine and spruce
plantations. Paper birch and white ash are
early invaders; black cherry invades pine
plantations.
1952-1957
Sugar maple and then white ash
are the most common
hardwoods in the plantations.
1999
White ash, cherry species, sugar
maple, and trembling aspen are the
most frequent hardwoods in
plantations.
1968
Sugar maple is the most common
species; white ash is number two.
Pine and spruce exhibit increased,
high mortality.
2009
Figure 7. Timeline of hardwood invasions into red pine and white spruce plantations. Information used in this timeline is from
the present study, Robinson (2003), Russell (1968), and Goldblum (1998), all of which were done at the Huyck Preserve in central
New York.
42
Planting of pine and
spruce plantations
occurs.
Successional theory and the pattern of species replacements that change a field to
a secondary forest is based on numerous studies. There are so few studies of succession
in unmanaged conifer plantations that it is not yet possible to make fair generalizations
about the process. This study contributes significantly to the body of knowledge about
succession in plantations, especially because it built on previous studies at the same site.
On the other hand, the study is limited by timeframe and by sample size, particularly
because there are still so few hardwood trees in the plantations.
Conservation Implications
Conifer plantations are common in the United States, a direct result of a policy
with both conservation and economic goals. Between 1933 and 1943, the CCC planted
2.3 billion trees on over a million ha of land (2.5 million acres), half of the trees ever
planted in the country (Maher, 2008). Conservationists of the time criticized the use of
plantations for habitat restoration, because monocultures of exotic species bare little
resemblance to natural forests (Maher, 2008). Today, few would argue that plantations
are a good substitute for natural forests in terms of conservation value, but they are
significant globally. In 1999, there were an estimated 60 million ha of plantations
worldwide, with over 13 millions ha in the United States (FAO, 1999), and they are
expected to expand into the future (FAO, 1999; Ramos & Roberts, 2003).
Most plantations are established to produce fiber (Ramovs & Roberts, 2003) and
not for conservation, but plantations can hold conservation value. For example,
afforestation of marginal farmland has been recommended to mitigate climate change
through carbon sequestration, either as pine plantations meant to be harvested (Lee &
43
Dodson 1996) or as native tree plantings (Potter et al., 2007). Different types of
plantations have varied sequestration rates, depending on the species used, harvesting
regimes (Niu & Duiker, 2006), biodiversity and structural heterogeneity (Pacala &
Deutschman, 1995). Even exotic-species plantations can stabilize soils and create
environmental conditions that will allow native species to colonize degraded sites (Lugo,
1997), and plantations can buffer forest edges and connect forest patches (Lacher et al.,
1999). Plantations can also be managed to benefit native wildlife, particularly when
using native tree plantations (Spellerberg & Sawyer, 1996).
Other conservation goals may be accomplished by restoring existing plantations
to expand natural habitat or maintain native species diversity. It seems that the
plantations at the preserve will eventually dissolve, but the process could be accelerated
by under-planting native trees species and thinning of plantation trees, which would
allow an understory of mid-tolerant species to develop (Parker et al., 2008). Increasing
the diversity of the tree species in plantations this way would allow for more diverse
microclimates and forest floor substrates, which would support a higher diversity of
understory species (Ramovs & Roberts, 2003).
In general, the ecological effects of unmanaged plantations of exotic trees are not
well documented, but my results indicate that at least some of these exotic conifers will
die and be replaced with hardwoods. This change would homogenize the landscape in
the same way that losses of hemlock are expected to (Orwig et al., 2002; Sullivan &
Ellison, 2006) and could affect wildlife and ecosystem processes (Lovett et al., 2006).
This may be an important consideration for landscape-level conservation planning in
New York State and elsewhere in the northeastern United States.
44
Conclusions
Forest community composition at the Edmund Niles Huyck Preserve has changed
over the last ten years, with decreases in most early and mid-successional tree species.
Sugar maple increased in relative density since 1999 and is by far the most dominant
species in terms of relative density and frequency. Hemlock and beech decreased in
frequency but not in relative density since 1999, and they retained their status as second
and third most abundant species, respectively. White ash remained the fourth-most
abundant species at the preserve, but it decreased in relative density and frequency over
the last decade. The native forests remain somewhat dynamic, especially due to effects
of the beech bark disease, but can be generally characterized as late-successional
hemlock-northern hardwood stands, although their potential to persist in this state
remains uncertain.
The white pine and red spruce plantations remain dominated by planted conifers,
but hardwoods, most notably sugar maple and white ash, have invaded, with significant
increases in the ten-year interval. Most pioneer trees characteristic of old field succession
have not invaded plantations, so in a sense the pine and spruce plantations are shifting
directly toward later-stage hardwood composition, although missing several late-stage
old-growth native species. Because the planted species are not regenerating, they will
eventually disappear from the preserve, but they are still more accurately described as
plantations, rather than natural secondary forest, and they remain distinct from the later
stage hemlock-northern hardwood forest that characterizes most of the native stands in
the Huyck Preserve. However, at broader scales the hemlock-northern hardwood forest is
45
challenged by a number of anthropogenic disturbances, including exotic tree diseases and
insects that specialize on ash, beech, maple, and hemlock. Unmanaged plantations may
be among the most affected, if their diversity remains limited to declining conifers and a
few susceptible native tree species.
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