United States

Department of

Agriculture

Forest Service

Northeastern

Research Station

Research Paper NE-710

Understory Tree Characteristics

and Disturbance History of a

Central Appalachian Forest

Prior to Old-Growth Harvesting

Thomas M. Schuler

Mary Ann Fajvan
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Abstract

To better understand the dynamics of red oak regeneration, we evaluated the

composition of understory woody species and recruitment characteristics of a

mixed mesophytic forest in the central Appalachian region at the time of old-growth

logging. We also evaluated canopy disturbance history during both the old-growth

and second-growth periods. Three possible modes of oak recruitment are

proposed: isolated, episodic, and continuous. Patterns of stemwood radial growth

were used to evaluate the frequency of disturbance. Levels of change in red oak

radial growth were greatest from 1906 to 1911, an indication of major disturbance.

Oak regeneration in all sampled areas that developed into second-growth forest

was dominated by seedling-size individuals recruited from 1902 to 1910. However,

there also was evidence that red oak, white ash, and bitternut hickory were

developing into larger size classes before 1900, and that recruitment and

development was related to periodic canopy disturbance. The stand-wide median

canopy disturbance interval was 30.83 years between 1797 and 1983. Secondgrowth oak forests on mesic sites may represent the reproductive potential of an

abundance of existing seedlings in the understory prior to harvesting rather than

older and larger advanced regeneration.

The Authors

THOMAS M. SCHULER, research forester, received a B.S. degree in forest

management from Purdue University, an M.S. degree in silviculture from Colorado

State University, and a Ph.D. degree in forest biology from Purdue University. He is

currently engaged in forest management research with the Northeastern Research

Station’s Timber and Watershed Laboratory at Parsons, West Virginia.

MARY ANN FAJVAN, associate professor of silviculture, received a B.S. degree in

forest management from Rutgers University, an M.F.S. degree in silviculture from

the Yale School of Forestry and Environmental Studies, and a Ph.D. degree in

quantitative silviculture from the University of Maine. She is a member of the Forest

Resources Management faculty at West Virginia University, Morgantown, West

Virginia.

Manuscript received for publication 19 April 1999
1

Introduction

Pollen evidence has established the importance of oak as a

major forest constituent for thousands of years during the

Holocene in the central Appalachians and elsewhere in the

eastern hardwood region (Kapp and Gooding 1964; Watts

1979; Larabee 1986; Delcourt and Delcourt 1987). However,

for the past 40 years, most efforts to regenerate oaks on

mesic sites have been unsuccessful (Weitzman and Trimble

1957; Carvell and Tryon 1961; McGee 1975; Lorimer 1984;

Schuler and Miller 1995). Yet logging of old-growth forests

often resulted in the retention and possibly the enhancement

of the oak component in the newly established stands

(Potzger and Friesner 1934).

Research has shown that successful regeneration of

northern red oak (Quercus rubra L.) on mesic sites is

enhanced by the establishment of oak seedlings of sufficient

size and number before overstory removal (Carvell and

Tryon 1961; Sander and others 1976). Loftis (1990) found

that large oak seedlings have a greater probability of

survival than smaller seedlings following overstory removal.

However, it is not known whether second-growth oak forests

are the result of the reproductive potential of abundant small

seedlings, fewer larger individuals, or both. Delineating the

size and age-class structure of understory oak just before

old-growth harvesting provides insight into this question and

helps define prior disturbance regimes that potentially led to

this condition.

Three possible modes of oak recruitment are proposed:

isolated, episodic, and continuous. A short period of

recruitment that results in a single cohort with a narrow age

distribution suggests that conditions suitable for the

establishment and development of oak seedlings were

isolated. Such periods of recruitment may have been related

to unusual disturbance events. A longer period of

recruitment (50 to 100 years) that results in an all-age

understory suggests that conditions for oak regeneration

were relatively continuous. These conditions would require

lower levels of stocking, perhaps more frequent disturbances

to maintain such levels, and perhaps regular acorn crops.

Episodic recruitment that results in two or more distinct oak

cohorts suggests that conditions for regeneration were

discrete periods with a favorable environment. This also

suggests a disturbance history of multiple events with a

relatively rapid recovery to a predisturbance state.

To assess modes of oak recruitment, we evaluated the age,

size-class structure, and species composition of an oldgrowth forest understory (around 1900) using the overstory

of a contemporary second-growth forest that was initially

logged around the turn of the century. Stand reconstruction

required establishing the date of old-growth harvesting by

dendroecological analysis and then using the year of

harvesting to reconstruct the age and size-class structure of

the understory at that time. It was anticipated that the oak

component would predate a new cohort of shade-intolerant

species established after initial logging. New oak seedlings

that germinate at the time an older stand is clearcut often fail

to compete with sprouts and faster growing species such as

yellow-poplar (Liriodendron tulipifera L.) (Beck 1970; Sander

and Clark 1971). Oaks rely on advance reproduction and

dominance probability increases with initial stem size (Loftis

1990). The characteristics of a preharvest oak component

prior to initial logging provides insight into the size and

abundance of advanced oak regeneration that are required

to compete with other species following a major disturbance,

and tests the three possible modes of oak recruitment

described. We also investigated the history of canopy

disturbance using older understory components in the oldgrowth forest that survived initial logging. The objective was

to gain insight into the disturbance pattern prior to oldgrowth harvesting and how that might have influenced oak

recruitment.

Methods

Study Area

This study was conducted on the 1,900-ha Fernow

Experimental Forest (39.030 N, 79.670

 W) within the

Monongahela National Forest in north-central West Virginia.

The ecological landtype of the Fernow, which is

administered by the USDA Forest Service’s Northeastern

Research Station, is referred to as the Allegheny Mountains

of the Central Appalachian Broadleaf Forest (McNab and

Avers 1994). The draft landtype association is the Allegheny

Front Sideslopes (DeMeo and others 1995) and is

representative of more than 40,000 ha on the Monongahela

National Forest alone. The vegetation of the Fernow ranges

from mixed mesophytic to northern hardwoods at higher

elevations (Braun 1950). Mesic site overstories often include

northern red oak, yellow-poplar, black cherry (Prunus

serotina Ehrh.), sugar maple (Acer saccharum Marsh.),

white ash (Fraxinus americana L.), and basswood (Tilia

americana L.). Shade-tolerant understories often consist of

American beech (Fagus grandifolia Ehrh.), sugar maple,

striped maple (Acer pensylvanica L.), and serviceberry

(Amelanchier arborea (Michx. f.) Fern.). The topography of

the surrounding area is mountainous with elevations on the

Fernow ranging from about 530 to 1,115 m above sea level.

Mean annual precipitation is about 143 cm and is distributed

evenly throughout the year (Pan and others 1997). The

average growing season is 145 days (May to October).

The Elklick watershed (which later became the Fernow) was

initially logged between 1903 and 1911 (Trimble 1977)

during the railroad logging era (Fansler 1962). Skidding was

done with horses and log slides to a temporary standardgauge railroad. During this period of forest exploitation,

many trees were left due to insufficient size or poor form, or

because the species was considered undesirable (e.g.,

sugar maple and American beech).

Field Data

In 1994, as part of a long-term silvicultural study on the

Fernow, 18 openings (0.162 ha each) were created by

harvesting all merchantable stems within these openings in

a 28-ha research unit known as Compartment 18A&B. At the

same time, three openings were selected for
2

dendroecological analysis. These openings were distributed

from the lower (793 m) to the upper boundary of

Compartment 18B (915 m) and are referred to as plots 37,

51, and 55, respectively. Sample units were selected based

on the abundance of oak coupled with the presence of what

appeared to be old-growth residual sugar maples. Sample

selection was based on our desire to investigate the

possibility of a correlation between disturbance, as indicated

by patterns of stemwood radial growth of existing trees and

oak recruitment. The analysis reflects only a portion of the

heterogeneity of the stand, but it was the intent of this study

to examine the developmental history of the portions of the

stand that led to oak dominance. Individual-tree

measurements including species and diameter were

recorded for all stems larger than 12.7 cm in diameter at

breast height (d.b.h.) in each opening. The NED/SIPS

computer program was used to summarize the data

(Simpson and others 1995), including a measure of relative

density (Stout and others 1987).

Disks for dendroecological analysis were cut from each tree

at stump height, approximately 10 cm above the ground line

on the uphill side of the tree, and labeled by opening and

species. Minimum tree size for collection and analysis was

12.7 cm d.b.h. On the basis of field inspection, it was

determined that smaller stems were too young to explain the

dominance of overstory oak. The number of stems per

opening used for analysis was 47, 81, and 42 for plots 37,

51, and 55, respectively. All disks were prepared for ringwidth measurements by sanding the surface of the disk with

up to 800-grit sandpaper so that the rings could be seen

under magnification. Ring width was measured with a

Velmex measuring stage calibrated to 0.01 mm in

conjunction with PJK6DOS® software to record tree-ring

measurement files. Measurement direction was from the

bark to the pith using a cross-slope radius to avoid tension

wood characteristics often found on the uphill side of

angiosperms. Most oaks were measured along two radii;

other species generally were measured along one. Following

crossdating of tree-ring measurements using marker years

based on consistently narrow years (e.g., 1988), a program

called COFECHA® (Grissino-Mayer and others 1997) was

used to statistically validate the crossdating of ringmeasurement series for individual species.

Data Analysis

Patterns of stemwood radial growth were used to evaluate

the frequency of disturbance (Lorimer and Frelich 1989).

Distinguishing releases from climatic effects was based on

the period of release. Drought effects in eastern mesic

forests have been shown to last only for several years

(McIntyre and Schnur 1936; Cook and Jacoby 1977).

Release events were defined as changes in growth with

respect to subsequent 10-year growth periods (McCarthy

and Bailey 1996; Nowacki and Abrams 1997), and were

calculated using established methodology (Eqn. 1):

where %GC is percent growth change from preceding to

superseding 10-year radial means, M1

 is the preceding 10-

year mean radial growth (exclusive of the current year), and

M2

 is the superseding 10-year mean radial growth (inclusive

of the current year).

Established criteria regarding magnitude of %GC were used

to further screen out undesired responses such as droughts

or other climatic factors (Lorimer and Frelich 1989; Abrams

and others 1995; McCarthy and Bailey 1996). A major

release was defined as an increase in growth greater than

99 percent. A moderate release was an increase in growth of

50 to 99 percent. Duration of release was also variable and

an important consideration in the analysis, but specific

temporal criteria were not employed to classify responses

into discrete categories. Rather, duration of response was

used graphically to determine the response characteristics

of known disturbances, which was then used as a guide to

evaluate the character of unknown disturbances.

Minor releases were also used and were defined as

changes in growth rate greater than 25 percent but less than

50 percent that displayed graphical peaks in %GC. Nowacki

and Abrams (1997) found that a change in percent growth of

about 25 percent was useful in central Pennsylvania to

demarcate significant growth changes of overstory trees

because of their inability to respond as robustly as

understory trees following a disturbance. Mean northern red

oak %GC was used in part to identify the date of old-growth

logging. Red oak was used for this purpose because of its

abundance throughout the stand and because it is notably

responsive to disturbance (Minckler 1957; Kurtz and others

1981; Orwig and Abrams 1995).

Disks also were inspected for evidence of fire or any other

distinguishing characteristics that might provide insight into

the past disturbance history. Recruitment dates for all

individuals and species groups were evaluated as potential

indicators of past disturbances (McClaran and Bartolome

1989). Although historical documentation provides dates of

initial timber harvests for the watershed as a whole, the year

of harvesting at the spatial scale of the individual plots was

of interest. The time of old-growth harvesting was

established from shade-intolerant species establishment

dates, significant and sustained differences in %GC, logging

damage to residual trees, and historical documentation.

Disturbance frequency was evaluated graphically and

statistically using the distribution of moderate or greater

%GC’s. Distributions of this nature often are positively

skewed and overestimate the interval length assuming a

normal distribution (Baker 1992) and are more appropriately

described by measures of central tendency such as the

Weibull distribution (Sutherland 1997). Central tendencies of

the Weibull are expressed as exceedance probabilities (i.e.,

the 0.5 exceedance probability is the 50th percentile of the

distribution). The FHX2® program was designed in part to

evaluate goodness of fit between fire interval data and

normal and Weibull distributions using the one-sample

Kolmogorov-Smirnov (K-S) test (Grissino-Mayer 1995). Here

it was used to evaluate the distribution of disturbance
3

intervals. It may be that disturbances are serially correlated

within a stand. Such correlations, if they exist, might produce

p-values that are too low, and underestimate interval length.

As a result, the associated p-values from the K-S test should

be interpreted as relative measures rather than absolute

values.

Stand-wide disturbance frequency was modeled and defined

as concurrent moderate or greater %GC’s on two or more

trees. The disturbance caused by chestnut decline was

detected but we chose not to use it to calculate stand-wide

disturbance frequency because of its unique character,

which is more dispersed in time. Chestnut blight, first noted

in West Virginia as early as 1909 (Brooks 1911), resulted in

a 25-percent reduction in the volume of standing timber on

the Fernow during the 1930’s (Weitzman 1949). Thus, our

standwide disturbance frequencies are more representative

of canopy gap characteristics created by storm damage or

logging operations rather than disease outbreaks.

Results

The second-growth forest patches selected for analysis had

a total density of 425 stems ha-1 and a basal area of 47.98

m2

 ha-1 for stems larger than 12.7 cm d.b.h. following the

1994 growing season. Northern red oak, sugar maple, black

cherry, and basswood accounted for 86 percent of the basal

area (Table 1). Relative stand density calculated as a

percentage of full site occupancy was 153 percent of the

average maximum stocking expected in undisturbed stands

of similar size and species composition. The medial d.b.h.

was 59.4 cm for northern red oak, 41.9 cm for sugar maple,

52.1 cm for black cherry, and 33.5 cm for basswood. The

aggregate diameter distribution approximated a reverse J

shape, though the shape of the distribution was heavily

dependent on abundant sugar maple in the smaller size

classes (Fig. 1). Moreover, in contrast to the reverse J shape

of the overall sample, the northern red oak population

displayed a unimodal size-class distribution typical of evenaged cohorts (Fig. 1).

Figure 1.—Diameter-class

distribution in 1994 by d.b.h. midpoint

interval in a second-growth forest,

Compartment 18A/B, Fernow

Diameter Class Midpoint (cm) Experimental Forest, West Virginia.

Stems per Hectare

Table 1.—Total basal area (m2ha-1), percent species composition (based on total basal area), and tree density (ha-1) in

sampled forest areas used for dendroecological analysis after the 1994 growing season (d.b.h. > 12.7 cm)

Item All species Red oak Sugar maple Black cherry Basswood Yellow-poplar Red maple Other

Basal area 48.01 21.40 9.74 5.56 4.55 2.14 1.72 2.92

Species 100 44.6 20.3 11.6 9.5 4.5 3.6 5.9

 composition

Tree density 425 91 168 30 69 7 17 42
4

Date of Old-Growth Logging

The mean ring-width chronology for northern red oak

included 41 trees and 70 ring-width series (29 red oaks were

measured along two radii) totaling 6,471 rings. During the

157 years evaluated for red oak (1838 to 1994), the highest

%GC was recorded from 1906 to 1911, exceeding 100

percent for the 6-year period (Fig. 2). In 1908, %GC peaked

at more than 121 percent, though the mean red oak ring

width in 1907 was slightly greater. Growth releases of this

nature are indicative of major canopy disturbances.

Additional evidence of a disturbance during the period

identified by %GC analysis was obtained from a white ash

sapling (55fr03). In 1906, the tree was 9 cm in d.i.b.

(diameter inside bark at stump height, about 10 cm above

the ground line). About one-fourth of the xylem tissue formed

during that year was damaged. The outer cellular structure

of the remaining xylem tissue was rough and appeared to be

the result of a mechanical abrasion after the onset of

seasonal xylem formation. Scar tissue that formed during

the 1907 growing season was intact, as was the xylem

tissue formed in 1905. Thus, the tree was damaged during

the period bounded by the summer of 1906 and the onset of

growth in 1907.

Black cherry and yellow-poplar were the only shadeintolerant species in the three openings selected for

dendroecological analysis. The emergence of yellow-poplar

was first noted in 1908 in plot 37 with subsequent

recruitment from 1910 to 1912 (Fig. 3a). Black cherry

recruitment ranged from 1905 to 1916 on plot 37 (Fig. 3a),

but only became evident in 1908 on plots 51 and 55 (Fig.

3b,c). Black cherry was the only shade-intolerant species in

these two plots.

We concluded that old-growth harvesting at the sample

locations likely occurred between the middle of the 1906

growing season and the onset of growth in 1907. Using this

period, it was possible to quantify the age and size-class

structure of the surviving understory of the old-growth forest

at that time.

Size and Age of Oak Regeneration

Oak regeneration in all sampled areas (n = 41) that

developed into the second-growth forest overstory was

dominated (90.2 percent) by seedling-size individuals

recruited from 1902 to 1910 (recruitment peaked in 1906,

Fig. 3d). The mean d.i.b. of oak stems present following the

1906 growing season was 0.7 cm and the distribution of

sizes did not deviate from normality (p = 0.3995) when

excluding four significantly older and larger stems

established before 1900 (Fig. 4). The even-age structure of

oak suggested by the overstory size-class distribution (Fig.

1) was reflected by the unimodal age-class (Fig. 3d) and

size-class distributions of the sampled trees (Fig. 4).

The three sampled plots were similar in that the dominant

age class of all species was a cohort established from 1900

to 1909 (Fig. 3a,b,c). This cohort included as many as 10

different species, though it was dominated by northern red

oak. Sugar maple was the principal shade-tolerant species

in all three areas and was established in conjunction with

shade-intolerant species following the 1906-07 logging date.

However, unlike the shade-intolerant species, recruitment of

sugar maple, basswood, and other shade-tolerant species

continued for several more decades, and presumably

continued in the smaller size classes until the 1994 harvest.

Sugar maple and American basswood have accounted for

more than 80 percent (based on number of stems) of all new

recruitment since 1920.

Disturbance History

The second objective of this study was to use the old-growth

understory to evaluate disturbance history using age

cohorting and frequency of moderate or greater %GC’s.

Calendar Year

Ring Width (mm)

Percent Growth Change

Figure 2.—Radial ring width (solid

line) and percent growth change

(dashed line) chronologies of 70

northern red oak series from

Compartment 18A/B, Fernow

Experimental Forest, WV.
5

Figure 3.—Recruitment characteristics

from 1901 to 1925 in Compartment 18A/

B, Fernow Experimental Forest, a: foot

slope, b: lower-middle slope, c: uppermiddle slope, d: combined red oak ageclass distribution.

Figure 4.—Northern red oak

seedling diameter-class distribution

by d.i.b. midpoint interval after the

1906 growing season (n = 23). Red

oak stems established before 1900

(n = 4) and after 1906 (n = 14) are

not represented.
6

Older understory northern red oak (i.e., established

before 1900) were recruited in 1838, 1858, 1876, and

1890 and were 23.3, 22.0, 8.8, and 2.1 cm in d.i.b.,

respectively, at the time of old-growth logging.

Development of these individuals followed the same

general pattern characterized by initial slow radial

growth (i.e., < 2.0 mm yr-1) for 10 to 20 years after

recruitment followed by a rapid increase in growth

that eventually declined before the dramatic growth

increase in 1906 (Fig. 5). The oldest individual tree of

this group (55qu04) demonstrated two distinct periods

of release before old-growth logging; the youngest

(51qu14) was released for the first time by the

disturbance caused by logging. All of the older

advanced oak regeneration established before 1900

responded to old-growth logging with unprecedented

increases in radial growth (Fig. 5).

White ash and bitternut hickory also were in the oldgrowth understory for at least 5 decades before initial

logging. In plot 55, white ash was recruited in 1861

and 1875 and was 10.9 and 9.3 cm d.i.b. following the

1906 growing season. This size indicates that both

individuals were larger sapling-size trees prior to

harvesting. Reflecting understory oak dynamics,

white ash recruitment dates coincided closely with

oak recruitment years and both individuals (55fr03

and 55fr02) were released between 1884 and 1885

(Fig. 6). The timing of understory white ash release on

plot 55 corresponded closely with understory oak

release in the same location (Fig. 2).

Of the limited number of hickories sampled (n = 6),

those established before 1900 (n = 3) had periods of

extremely slow growth (i.e., <0.5 mm yr-1). They

produced indistinct ring structures that made crossdating difficult. Moreover, due to the presence of

heartwood decay, it was not possible to establish the

recruitment date of two of the three hickories

recruited before 1900 (51ca01 and 51ca02). However,

it was clear that this species was developing in the

understory prior to old-growth harvesting (Fig. 7).

Understory hickory on plot 51 was 8.1, 8.0, and 2.9

cm in d.i.b. following the 1906 growing season (d.i.b.

was established at 2.4 m above the ground line for

51ca01 and 51ca02 due to heart rot). Major %GC’s

for 51ca01 and 51ca02 were evident in conjunction

with old-growth logging (i.e., 1906-07), though distinct

release events prior to that time were not apparent

(Fig. 7).

Throughout the sampled area, the oldest remaining

trees were sugar maples that ranged in d.i.b. from 5.7

to 37.3 cm following the 1906 growing season (Fig. 8).

Establishment dates ranged from 1728 to 1787,

making these trees about 120 to 179 years old in

1906. Sugar maple chronologies demonstrated

extended periods of slow radial growth (<1.0 mm yr-1).

This is best illustrated by 51ac02, which was recruited

in 1772. It experienced three moderate or greater

%GC’s during the 19th century, though radial growth

Figure 5.—Red oak radial increment (solid line) and percent

growth change (dashed line) with establishment dates before

1900 in a second-growth forest initially logged in 1906-07.

Figure 6.—White ash radial increment (solid line) and

percent growth change (dashed line) established before

1900 in a second-growth forest initially logged in 1906-07.
7

did not exceed 2.0 mm yr-1 until after 1906 (Fig. 8).

Consequently, even though this individual tree was

approximately 135 years old at the time of initial

logging, it was only 5.7 cm in d.i.b. The remaining three

sugar maples with establishment dates before 1800

experienced a series of moderate or greater %GC’s that

resulted in sustained growth rates greater than 2.0 mm

yr-1 prior to old-growth logging (Fig. 8).

There was considerable dendroecological evidence of

stand-wide disturbances during both the old-growth and

second-growth periods. Most recently, a stand-wide

disturbance pattern was graphically evident in

association with a stand-wide light thinning conducted

between October 1952 and July 1953 (Figs. 2 and 9).

Harvesting activities in October 1984 also were

reflected by growth increases in plots 51 and 55. In

1984, plot 55 was adjacent to a 0.162-ha harvest

opening and plot 51 was bisected by a skid road. The

disturbance pattern is characterized by periods of

increased growth rates and close association of peaks

in those changes (Fig. 9). The indirect effects of

American chestnut decline in the 1920’s and 1930’s

also were detected. The growth response varied more

temporally compared to the thinning response (Fig. 9).

Throughout the 3 centuries sampled, old-growth logging

was the most prominent and defined disturbance (Figs.

2 and 9).

These disturbance signatures from known events make

the interpretation of unknown disturbances more

plausible. For instance, the peak of the response does

not always correlate among trees given a common

disturbance event such as occurred in 1906 and 1952.

However, the broad band of increased growth rates (i.e.,

Figure 8.—Sugar maple radial increment (solid line) and percent

growth change (dashed line) with establishment dates before

1800 in a second-growth forest initially logged in 1906-07.

Figure 7.—Bitternut hickory radial increment

(solid line) and percent growth change (dashed

line) with establishment dates before 1900 in a

second-growth forest initially logged in 1906-07.
8

> 50 percent) do correlate. Prior to old-growth harvesting,

such stand-wide disturbance signals were identified in 1797,

1837, 1849, and 1885 (Fig. 9). Individual-tree growth peaks

(Fig. 9) and peaks in %GC analysis for combined red oak

(Fig. 2) correspond closely for disturbances in 1849, 1885,

1906, 1952, and 1984.

The distribution of stand-wide disturbance intervals using

both the Weibull function (K-S d = 0.139, p = 0.9998) and a

normal distribution (K-S d = 0.301, p = 0.6469) described

the data adequately. The median Weibull disturbance

interval for stand-wide events was 30.83 years from 1797 to

1983. Stand-wide disturbance intervals less than 18 years

and more than about 44 years were unusual based on

threshold level exceedance probabilities (Table 2). There

was no statistical evidence of temporal changes with respect

to whole-stand disturbances (K-S d = 0.500, p = 0.925)

when old-growth and second-growth periods were compared

with this technique.

Figure 9.—Disturbance chronologies from Compartment 18A/B, Fernow Experimental Forest, West Virginia. Each

horizontal line represents the disturbance history of one tree (qu = red oak, fr = white ash, ca = bitternut hickory, ac

= sugar maple). Stand-wide canopy gap disturbances are identified graphically in 1983, 1954, 1907, 1885, 1849,

1837, and 1797 as indicated by vertical lines that span multiple chronologies. Gray zone indicates %GC > 50

percent, black zone indicates %GC > 25 percent, short vertical line in %GC indicates peak year of response.

Table 2.—Disturbance intervals (years) as measured by %GC on the Fernow

Experimental Forest, Compartment 18A/B from 1728 to 1994 (<< = significantly

short interval, >> = significantly long interval)

Exceedance probability Stand-wide disturbance intervala

0.875 17.94<<

0.750 23.09

0.500b 30.83

0.250 38.73

0.125 44.25>>

 Mean interval 31.00

 Total intervals 6

a

p > di = exp(-(di/34.78)**3.04), where di = disturbance interval.

b

Weibull median.
9

Discussion

The results suggested two modes of oak recruitment into the

canopy layer. First, the second-growth oak component was

predominantly the result of an isolated period of recruitment

that arose from the disturbance associated with logging of

the old-growth forest in 1906-07. The above-ground ageclass structure of this oak cohort was unimodal and

reflected the diameter-class structure of the second-growth

oak overstory. There was little evidence that the oak

component of the second-growth forest was dependent on

the presence of sapling-size or larger advanced

regeneration at the time of initial logging. Peak recruitment

coincided with logging activities in 1906. Seedlings of

preharvest origin contributed somewhat more than

postharvest origin seedlings to the newly established oak

cohort, though not significantly so. However, estimates of the

age and density of advanced regeneration based on

recruitment date alone may be conservative. Oaks recruited

after 1906 may have been of sprout origin from existing

seedlings or stumps or had not yet reached sample height.

Many oak seedlings are damaged during logging and form a

new terminal shoot. In the southern Appalachians, about half

of the existing understory oak seedlings resprouted following

a clearcut (Loftis 1990). Therefore, our finding that 38

percent of the oak stems reached sample height after 1906

are consistent with results observed more recently and

simply may account for stems of sprout origin.

In reconstructing past understory dynamics, it is helpful to

understand whether oak regeneration originated from

abundant small seedlings or less abundant, larger

individuals. Our results suggest that both abundance and

size were more favorable in 1906 than conditions typically

found today. We estimate there were about 9,000 seedlings

ha-1 in 1906 to achieve the survivorship observed in 1994

(Appendix). This estimate was partially based on a mean

d.i.b. of 0.7 cm and the associated dominance probability 20

years after clearcutting (Loftis 1990). The estimate also

incorporates the survival rate of northern red oak in a 20-

year-old stand projected 70 years using NED/SIPS and NETWIGS (Simpson and others 1995). Oak seedling density

seldom exceeds 2,400 stems ha-1 in the understory of

present day mesic forests and often is substantially less

(Schuler and Miller 1995; Clatterbuck and others 1999).

Contributing factors to modern understory oak

characteristics are high deer herbivory of acorns and young

seedlings (Steiner and Joyce 1999) and the presence of

dense understories of shade-tolerant species, which may be

limiting both oak longevity and development in the

understory (Lorimer and others 1994). Control of shadetolerant understories is feasible and increases both

understory oak survival and seedling growth (Loftis 1988;

Lorimer and others 1994). However, herbivory of acorns may

be limiting initial oak seedling densities today compared to

past conditions, increasing the importance of silvicultural

intervention to sustain oak’s presence in the understory.

However, reliance on fewer but larger seedlings to achieve

oak regeneration goals requires longer planning horizons

and is difficult to implement on mesic sites.

In contrast to the predominant mode of recruitment of the

second-growth forest, the red oak established before 1900

appeared to result from periodic recruitment. Although the

data were limited, red oak establishment prior to 1900

occurred under less than free-to-grow conditions based on

initial radial growth rates of less than 2 mm yr-1. Following

establishment, red oak persistence in the understory and

midstory appeared to be functionally related to periodic

canopy disturbance. A pattern of periodic recruitment and

release could have led to an uneven age-class structure of

red oak in the overstory before 1906. The correlation

between age and size of red oak established before 1900

suggests that upper canopy recruitment was occurring during

the 19th century even in the absence of major disturbances.

The stand-wide disturbance interval of about 31 years with

even greater frequency of smaller events indicates the

potential for developing an uneven-age stand structure and

is consistent with the distribution of understory red oak,

white ash, and hickory before 1900 and the continued

recruitment of shade-tolerant species in the 20th century. Our

estimate of a stand-wide disturbance frequency generally

reflects previous estimates of partial canopy disturbance

frequencies in the central Appalachians (Lorimer 1980;

Nowacki and Abrams 1997; Ruffner and Abrams 1998).

Such disturbances frequently influenced oak recruitment in

both mesic (McCarthy and Bailey 1996) and more xeric

(Ruffner and Abrams 1998) oak-dominated old-growth

forests. However, the effect of such disturbances no longer

facilitates oak establishment or development and it is widely

recognized that eastern hardwood forests are increasingly

dominated by shade-tolerant species (Carvell and Tryon

1961; Parker and others 1985; Smith and Miller 1987) and

that the rate of change is increased by small-scale canopy

disturbances (Schuler 1998). Our findings do not isolate a

limiting factor related to poor oak competitiveness following

overstory removal, but they do suggest that oak recruitment

is not limited by the frequency of canopy gaps.

The apparent ability of oak to regenerate in small gaps

before1900 in this case study has implications for

silvicultural attempts to regenerate mesic site oak forests.

The even-age condition of most second-growth forests has

been in part the impetus for the use of even-age silviculture

to regenerate oak stands. Yet, the even-aged cohort that

comprised the sampled second-growth forest developed in

the understory of an old-growth, possibly uneven-aged

forest. Apparently, oak can attain upper canopy strata

through the variability associated with past disturbance

patterns once a competitive oak understory is established.

Identifying the factors that lead to a competitive oak

understory is of prime importance. Several aspects of stand

development in the central Appalachians have been altered

significantly in modern forests and include overbrowsing by

white-tailed deer (Marquis 1981; Inouye and others 1994),

changes in fire frequency (Whitney 1987; Crow 1988;

Delcourt and Delcourt 1997; Sutherland 1997), and the

extirpation of American chestnut. A better understanding of

these aspects of forest development may lead to greater

success in maintaining the oak component in both harvested

and unharvested stands.
10

In this study, dendroecological data have been used to

derive past understory tree characteristics in a mixed

mesophytic forest nearly 90 years ago. As is true of all

sources of past ecological information, each has own

limitations and merits (Whitney 1994). Old-growth forests are

particularly suited for retrospective studies because of the

relatively minimal influence of modern anthropogenic

influences on them compared to second-growth forests. The

virtual absence of expansive tracts of old-growth forests in

the eastern United States limits this possibility (Parker

1989), but even if sufficient old-growth forests were available

for study, the factors that favored the current overstory

species composition have been altered significantly (Abrams

1992). However, second-growth forests can be substituted to

determine past old-growth understory characteristics. The

sudden and widespread release of the understory

associated with old-growth logging preserved substantial

information related to species composition, age distribution,

and size-class structure of the understory at the time of the

release. Of course, differential species mortality and the

reduction in stem density by two orders of magnitude make

the interpretation of such data critical. Vertical stem analysis

could be added to the procedures used in this study to

provide additional insight into understory dynamics both

before and after old-growth logging.

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Appendix

Given the following:

Mean diameter inside bark (d.i.b.) of oak stems after

1906 = 0.7 cm,

Dominance probability (D) 20 years after clearcutting for

given mean d.i.b. = 0.02 (Loftis 1990); (d.i.b. not adjusted for

basal diameter, which may inflate estimate of stem density),

Stems/ha recruited from 1902 to 1911 = 75.85

(assumes post-1906 stems were sprout origin and were

present prior to 1907),

Survival rate (S) of oak stems from age 20 to age 90 =

0.42 (from NED/SIPS using NE-TWIGS to make projection;

starting conditions based on 20-year-old oak stand from

Fernow Experimental Forest, Compartment 8A in 1968),

Then oak seedling density can be estimated as the

following:

Oak seedlings present in 1906 = 1/D * 1/S * 75.85 =

9,029/ha.
Printed on Recycled Paper

Schuler, Thomas M.; Fajvan, Mary Ann. 1999. Understory tree characteristics

and disturbance history of a central Appalachian forest prior to old-growth

harvesting. Res. Pap. NE-710. Radnor, PA: U.S. Department of Agriculture,

Forest Service, Northeastern Research Station. 12 p.

To better understand the dynamics of red oak regeneration, we evaluated the

composition of understory woody species and recruitment characteristics of a

mixed mesophytic forest in the central Appalachian region at the time of old-growth

logging. We also evaluated canopy disturbance history during both the old-growth

and second-growth periods. Stemwood radial growth patterns were used to

evaluate the frequency of disturbance. Levels of red oak radial growth change were

greatest from 1906 to 1911, which is indicative of a major disturbance. The oak

regeneration in all sampled areas that developed into the second-growth forest was

dominated by seedling-size individuals that were recruited from 1902 to 1910. The

stand-wide median canopy disturbance interval was 30.83 years between 1797

and 1983.

Keywords: oak regeneration, disturbance, dendroecology, West Virginia
Headquarters of the Northeastern Research Station is in Radnor,

Pennsylvania. Field laboratories are maintained at:

Amherst, Massachusetts, in cooperation with the University of Massachusetts

Burlington, Vermont, in cooperation with the University of Vermont

Delaware, Ohio

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

Hamden, Connecticut, in cooperation with Yale University

Morgantown, West Virginia, in cooperation with West Virginia University

Parsons, West Virginia

Princeton, West Virginia

Syracuse, New York, in cooperation with the State University of New York,

College of Environmental Sciences and Forestry at Syracuse University

Warren, Pennsylvania

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