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Snag Density and Utilization by Wildlife In the Upper
Piedmont of South Carolina 1
D. Breck Carmichael, Jr. and David C. Guynn, Jr. 2
Abstract.--Snag densities were estimated for major forest
types on the Clemson Experimental Forest, in the upper Piedmont
of South Carolina. Two-hundred 0.1-ha plots were established
in various aged stands of cove hardwood, upland hardwood,
pine-hardwood, and pine plantations. Climbable snags containing
cavities were inspected to determine use by wildlife during warm
months (May-September) and again during cold months (NovemberMarch). Mean snag densities were 50.3 snags per ha for upland
hardwoods, 37.3 snags per ha for cove hardwoods, 31.2 snags per
ha for pine-hardwoods, and 21.3 snags per ha for pine plantations. Cavities occurred in only 8.8% of all snags tallied.
Preliminary results indicate that more than 35% of snags with
cavities were utilized by southern flying squirrels (Glaucomys
volans).
INTRODUCTION
In most natural communities, nongame species
constitute the greatest portion of vertebrate
species and biomass; furthermore, they are critical
to the functioning of the ecosystem (Bury et al.
1980). Wildlife researchers and managers are now
aware of the importance of standing dead trees, or
snags, as habitats for many of these species.
Activities such as bird watching and wildlife
photography have become popular (More 1979), with
annual expenditures totalling in the millions of
dollars in the United States (DeGraaf and.Payne
1975). Also, many species of snag-dependent wildlife are insectivorous and help prevent insect
populations from reaching epidemic levels (Beebe
1974).
Information on snags and snag-dependent
species is lacking in the Southeast. Extensive
studies have been carried out on the endangered
red-cockaded woodpecker (Picoides borealis), but
this species requires live southern pines (Pinus
spp.) f~r cavity construction. All other southern
woodpeckers utilize snags for cavity construction,
1Paper presented at the Snag Habitat Management Symposium. Northern Arizona University,
Flagstaff, June 7-9, 1983.
2
D. Breck Carmichael Jr. and David C.
Guynn, Jr. are, respectively, Graduate Research
Assistant and Associate Professor, Department of
Forestry, Clemson University, Clemson, S.C.
and a large number of secondary cavity-nesters use
these cavities. Some 38 species of birds that
breed and/or winter in upper South Carolina are
known to utilize snags (Legrand and Hamel 1980).
Several mammalian species nest, feed, or hibernate
in snags; and amphibians and reptiles may even use
snags (McComb and Noble 1981). We initiated a
study in 1981 to estimate snag densities in
4 major forest types in the upper Piedmont of
South Carolina and to determine the diversity of
wildlife species utilizing snags within these
forest types.
STUDY AREA
The study was conducted on the 7,024 ha
Clemson University Experimental Forest, in the
upper Piedmont of South Carolina. The tract was
obtained between 1934 and 1939 from private
owners by the U. S. Department of Agriculture.
More than 100 years of clearing, burning, row
cropping and abandonment had turned the area into
severely eroded red clay hills and gullies. The
scattered woodlands present were mostly rough
pines and low quality hardwoods. Federal work
programs helped initiate the reforestation of the
area, and in 1954 the land was deeded to Clemson
University. An intensive forest management
program has restored the Clemson Forest to a
productive state (Warner et al. 1973).
All study plots were established on the
"North Forest," maintained prilllllrily for research,
teaching, and recreation. The terrain is slightly
107
Table 1.--Mean snag densities on the Clemson
Experimental Forest ("North Forest") in
the Piedmont of South Carolina, 1982.
rolling to hilly, typical of the upper Piedmont.
Stands ranged in size from less than 0.5 ha to
greater than 10 ha, and all ages from seedlings
to mature sawtimber were present.
Stand Type
METHODS
Upland hardwood
Cove hardwood
Pine hardwood
Pine plantation
Four stands in each of the 10 following
forest types were located on the study area:
pine-hardwood - 20 to 30 years, pine-hardwood 30 to 50 years, pine-hardwood - over 50 years,
pine plantation - 1 to 9 years, pine plantation 20 to 40 years, pine plantation - over 40 years,
cove-hardwood - 40 to 60 years, cove-hardwood over 60 years, upland hardwood - 40 to 60 years,
and upland hardwood - over 60 years. Within each
of the 40 stands, five 0.1 ha (20m x 50 m) study
plots were randomly located and a 100% tally of
all snags was made. A snag was defined as any
dead or mostly dead standing tree at least 10.2 em
(4 in) dbh and 1.8 m (6 ft) tall. Total height
and dbh were measured, and each snag was numbered
at breast height with CFI paint and at stump
height with an aluminum tag. Climbable snags
containing cavities were inspected to determine
use by wildlife during warm months (May-September)
and again during cool months (November-March).
Sample size fluctuated due to snags falling
between successive cavity inspection periods.
For purposes of the determination of wildlife
use, new cavity trees were continually added to
the sample whenever found, so that some cavity
trees were inspected as many as 3 times and some
only once. Snag densities by forest type were
compared by analysis of variance (Sokal and Rohlf
1973). The number of snags required for nesting
by indigenous avian cavity nesters was estimated
as discussed by Harlow and Guynn (1983) and compared with the number of snags found on the study
area.
Snags 2er hectare
SE
X
50.3**
37.3
31.2
21.3
6.27
4.56
2.86
2.96
** p < 0.01
FMNF. The hilly terrain on the Clemson Forest
makes some areas inaccessible for salvage whereas
a number of private salvage operators eagerly
compete for dead and dying timber on the more
accessible FMNF. Forests of the Coastal Plain
also have a smaller hardwood component than those
of the Piedmont, and the ~mF is open to public
firewood cutting. Firewood cutting is strictly
prohibited on the Clemson Forest, except in designated areas which were not part of the study area.
Prescribed fire is used more frequently in pine
stands of the FMNF than those of the Clemson
Forest. Additionally, one of the major management
practices in hardwood stands of the Clemson Forest
has been to girdle or chemically inject undesirable
stems.
RESULTS AND DISCUSSION
Differences in biotic and abiotic factors in
the Coastal Plain and the Piedmont may also explain
differences in snag densities. There are probably
a greater variety of diseases operating as tree
mortality factors in the Piedmont. For example,
littleleaf disease (Phyto2hthora cinnamomi) is
frequent on the Clemson Forest due to the prevalance of red clay soils but is mostly absent from
the sandy soils of the Coastal Plain. Climatic
factors such as ice storms are more frequent and
severe in the Piedmont than in the Coastal Plain.
Upland hardwood stands contained significantly (P < 0.01) greater numbers of snags than
other stand types (Table 1). Forest management
practices on the Clemson Forest have resulted
in a large number of snags in all stand types
c~mpared to some other southern forests.
McComb
and Muller (1983) reported high snag densities
in eastern Kentucky, but their study areas had
received no management for 40 years or more.
Snag densities on the Francis Marion National
Forest (FMNF), in the Coastal Plain of South
Carolina were found to be much lower than those
in the present study (Harlow and Guynn 1983).
Pine stands on FMNF contained approximately
84% fewer snags than hardwood and mixed
pine-hardwood stands of the Clemson Forest,
mostly because lightning struck and beetle
(Dendroctonus frontalis and 1£! spp.) killed
trees are removed from the FMNF soon after
detection. Snags are generally not removed
from the Clemson Forest. Beetle kills are
sometimes salvaged, but not as often as on the
Snag densities on the Clemson Forest were
much greater in the 10.1-25.0 em diameter class
than in the larger diameter classes (Table 2).
Sixteen snags were in such an advanced stage of
decomposition that an accurate dbh measurement
was impossible. These snags were included in
the calculation of density by forest type but
were excluded from density by diameter class
and forest type. Estimates of optimum snag size
and densities required to support selected
cavity-nesting birds at various population levels
are presented in Table 3. These requirements
should be considered minimum because no reserve
snags were included in the estimates. Bull and
Meslow (1977) and Thomas et al. (1979) recommended
16 and Evans and Conner (1979) 10 reserve snags for
each snag utilized; but at this time, there is no
biological basis for reserve snag estimates (Harlow
and Guynn 1983). Cavity-nesters that require snags
in the 10.1-25.0 em dbh range, such as the downy
woodpecker (Picoides 2ubescens), Carolina
chickadee (Parus carolinensis), and eastern
108
(N = 654). Seasonal cavity inspections are still
underway, but preliminary results (N = 107)
indicate a high rate of utilization by southern
flying squirrels (Glaucomys volans) (Table 4).
Few inspections have taken place during the peak
nesting season for most avian cavity-nesters, and
it is expected that the rate of utilization by
birds will increase as the study continues.
Undoubtedly, some snags for which wildlife use
could not be determined were being used by birds
as roosting sites. On several occasions, cavities
initially occupied by downy woodpeckers and even
the large pileated woodpecker, were occupied by
flying squirrels at the next inspection period.
In a study on interspecific competition for
red-cockaded woodpecker cavities on the FMNF,
Harlow and Lennartz (In Press) found that flying
squirrels used 32% of the cavities inspected.
Whether there is direct aggressive conflict
between flying squirrels and other species is not
known. Silver-haired bats (Lasionycteris
noctivigans) were found roosting behind the
loose bark of snags and are, therefore, not
dependent on the presence of cavities. A number
of herptofauna were observed during cavity inspections, but no attempt was made to enumerate or
identify these species.
Table 2.--Mean snag densities by diameter class
on the Clemson Experimental Forest ("North
Forest") in the Piedmont of South Carolina,
1982.
Dbh Class
(em)
10.1-25.0
25.1-40.0
40.1-55.0
> 55.0
Total
1UHW
41.8
6.3
0.8
0.5
49.3
2CHW
28.8
4.8
1.5
0.3
35.3
Snass Eer hectare
3PHW
4pp
Overall
23.8
14.7
27.3
6.3
5.8
5.8
0.8
0.2
0.8
o.o 0.0
0.2
20.7
34.1
31.0
1
2Upland hardwood
cove hardwood
3
4Pine hardwood
Pine plantation
Table 3.--0ptimum snag size and minimum snag
densities for selected cavity-nesting birds
in the Southeastern United States.
SEecies
Pileated woodpecker
Red-bellied
woodpecker
Downy woodpecker
Barred owl
Wood duck
White-breasted
nuthatch
Tufted titmouse
Eastern bluebird
Carolina chickadee
Total
1
Dbh of
cavity
tree
(em)
2Snags/ha required
to support various
population levels
60%
20%
100%
45.7-66.0
35.6-53.5
0.15
0.52
0.10
0.32
0.02
0.10
15.2-25.4
50.8+
50.8+
30.5+
0.32
0.10
0.30
0.35
0.20
0.05
0.17
0.20
0.07
0.02
0.05
0.07
30.5+
20.3+
15.2+
0.90
0.25
0.69
3.58
0.54
0.15
0.54
2.27
0.17
0.05
0.15
0.70
Table 4.--Utilization of snags as cavity sites
by various wildlife species on the Clemson
Experimental Forest ("North Area") in the
Piedmont of South Carolina, 1982-83.
SEecies
Southern flying
squirrel
Gray squirrel
Downy woodpecker
Pi lea ted
woodpecker
Red-bellied
woodpecker
Red-headed
woodpecker
Brown-headed
nuthatch
Common flicker
Silver-haired bat
Undetermined
1
Adapted from Evans and Conner (1979)
2Adapted from Harlow and Guynn (1983)
bluebird (Sialia sialis) probably can find
sufficient snags to support 100% maximum population levels on the Clemson Forest (Tables 2 and 3).
Avian species that utilize snags in the 25.140.0 em dbh range can also find favorable habitats
in terms of the density of suitable-sized snags.
This group includes species such as the tufted
titmouse (Parus bicolor) and the white-breasted
nuthatch (Sitta carolinensis). The Clemson Forest
does not contain adequate numbers of suitable
snags for species that require larger snags
(dbh 40.1-55 em and greater) such as the pileated
woodpecker (Dryocopus pileatus), red-bellied
woodpecker (Melanerpes carolinus), barred owl
(Strix varia), and wood duck (Aix sponsa).
Percent of caviti inspections
1
3PHW
4pp Overall
cHW 2UHW
23.8
35.7
36.4
43.6
36.4
14.3
4.8
7.1
9.1
3.0
2.6
2.6
10.3
7.5
2.8
3.7
2.6
0.9
2.6
0.9
2.6
0.9
2.6
30.8
0.9
1.9
43.0
7.1
57.1
50.0
3.0
45.4
1cove hardwood
2upland hardwood
3Pine hardwood
4Pine plantation
CONCLUSIONS
Management practices that favor the creation
and retention of snags have resulted in high snag
densities on the Clemson Forest compared to other
managed southern forests. Snag densities are
Snags containing cavities made up only 8.8%
of all snags tallied in the original survey
109
! and M. R. Lennartz. In Press. Inter_____s_p_e_cr.[fic competition for red-cockaded woodpec~1er cavities during the nesting season in
South Carolina. Proc. Red-cockaded Woodpecker
Symp. II. Panama City, FL.
probably adequate for cavity-nesting species
that can utilize snags 40 em dbh or less but may
be limiting for species that require larger snags.
A large percentage of snags with cavities are
utilizea-oy-soutbelfn-flylrig squirrels. Where
flying squirrels are abundant, competition
between other cavity-dependent wildlife species
and squirrels may be serious.
LeGrand, H. E., Jr. and P. B. Hamel. 1980.
Bird-habitat associations on southeastern
forest lands. Dept. of Zoology, Clemson
Univ., Clemson, S.C. 276 pp.
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110