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The Long-Term Effect of Timber Stand Improvement
on Snag and Cavity Densities In the
Central Appalachlans1
John J. Moriarty and William C. McComb 2
Abstract.--Snag and cavity densities were measured on
two watersheds in a mixed mesophytic forest in eastern Kentucky. One watershed received timber stand improvement
(TSI) by girdling 20-30 y~rs prior to measurement and one
did not receive TSI. There were more snags on the TSI
watershed than on the non-TSI watershed. Total cavity density was similar between watersheds, but the TSI watershed
had a higher density of animal cavities while the non-TSI
watershed had a higher natural cavity density. Management
recommendations include selected TSI of heart-rotted trees
on 10- to 15-year intervals to provide snags.
INTRODUCTION
The effects of tree girdling as a silvicultural
method of timber stand improvement (TSI) on change
in vegetation and wildlife habitat have been well
studied (Murphy and Ehrenreich 1965, Metzger and
Schultz 1981), but most studies have been shortterm. There is a dearth of information on the
long-term effects of tree girdling on wildlife habitat, especially on snag and cavity densities.
Need for this information in the central Appalachians is increasing due to growing use of intensive forest management practices and loss of forest
habitat through surface mining for coal.
Recommendations for management of snag-dependent
wildlife species include long rotations of forest
stands, retaining snags during harvest, injecting
trees with a heart-rot fungus, and providing herbicide-killed trees (McClelland and Frissell 1975,
Hardin and Evans 1977, Jackson et al. 1976, Conner
1978, and Evans and Conner 1979). Conner et al.
(1981) and McComb and Rumsey (1983) reported the
potential value of herbicide-killed trees for woodpeckers' habitat: spraying and injection of herbicides did not appear to adversely affect the tree
as a foraging or nesting site. Girdling of trees
may provide foraging or nesting substrate for some
species or may adversely affect cavity-dependent
wildlife by killing cull trees with natural cavities
(Miller and Miller 1980). Hence, this practice may
actually limit the number of cavities available to
species of cavity-dependent wildlife that require
cavities in living trees. Girdling may result in
snag characteristics different from those of natural snags, because of the rate and type of fungal
decay in the tree (Conner et al. 1981). Normally,
girdled trees do not remain standing as long as a
natural cavity-tree or snag would stand (Miller and
Miller 1980).
This study was undertaken to provide information on snag and cavity densities in TSI and nonTSI stands in a mixed mesophytic forest. The objectives were to quantify the long-term effects of
girdling trees on snag and cavity densities and to
determine the density of potentially usable snags
and cavities per tree species.
STUDY AREA
The study was established in 2 watersheds on
the University of Kentucky's Robinson Forest, located in Breathitt, Perry, and Knott Counties, Kentucky. Robinson Forest is a mixed mesophytic forest in the Cumberland Plateau region of Kentucky
(Braun 1950). Xeric sites are dominated by scarlet
oak (Quercus coccinea), black oak (Quercus
velutina), chestnut oak (Quercus prinus), white oak
(Quercus alba), red maple (Acer rubrum) and sourwood (Oxydendrum arboreum). Mesic sites are dominated by eastern hemlock (Tsuga ranadensis), American beech (Fagus grandifolia), northern red oak
(Quercus rubra) and yellow-poplar (Liriodendron
tulipifera). It is a second-growth forest which
was heavily cut prior to 1920. Davenport (1958)
reported that extensive TSI, including the girdling
1
This paper was presented at the Snag Habitat Management symposium, Northern Arizona State
University, Flagstaff, Arizona 7-9 June 1983. The
information reported in the paper (83-8-66) is in
connection with Project No. 624 of the Kentucky
Agricultural Experiment Station and is published
with the approval of the Director.
2
John J. Moriarty is presently stewardship
biologist for the Kentucky Chapter of the Nature
Conservancy, Lexington, Kentucky; William C.
McComb is assistant professor of forestry and wildlife management at the University of Kentucky,
Lexington, Kentucky.
40
of residual trees, was done from 1955-1960 on an
area of the forest which included Falling Rock
watershed (TSI treatment in this study) but not
Bucklick Hollow (control in this study). Both
watersheds encompass a drainage of approximately
80 ha and the altitude is from 300-412 m. Slopes
are steep (20 to 100 percent) and characterized by
short intermittent streams (Carpenter and Rumsey
1976).
200
METHODS
Study Design
Two 20-ha study areas were established, one in
the Bucklick (control) watershed and the other in
the Falling Rock (TSI) watershed. Each study area
consisted of about 50 percent north slopes and 50
percent south slopes. A 50-point grid was established on an 80 x 50 m spacing and a 0.05-ha circular plot was established at each point.
DBB CLASS(cm)
Figure 1.--Tree distribution by diameter class on
TSI'ed (cross-hatched) and non-TSI'ed (open
bars) watersheds, Breathitt County, Kentucky
1981, 20 years post-treatment.
Girdled trees, snags, and cavities were counted on each plot during the winter so that foliage
would not obscure any cavity entrances. Cavitytrees and snags were identified to species whenever possible.
Table 1.--Cavity and snag densities per hectare for
two watersheds in Robinson Forest, Breathitt
County, Kentucky, 1981.
Vegetation over 10 em dbh was tallied on each
plot by species and diameter was measured to the
nearest 0.1 em. Basal area and density of each
species were summed by plot. Relative dominance
was calculated for each species on each watershed.
Student's t-test was used to compare stand structural characteristics between watersheds. Linear
correlation was used to investigate associations
between various combinations of structural attributes on the study areas.
Cavity Type
Cavities
Animal
Natural
Basal
Total
Snags
Girdled 1
RESULTS AND DISCUSSION
*P<O.Ol
Overs tory
1
There were more trees (P<0.05) on Falling Rock
(TSI) (958 stems/ha} than Bucklick (non-TSI) (563
stems/ha). This was reflected in a higher average
basal area estimate on Falling Rock (46.1 m2/ha)
than on Bucklick (34.2 m2/ha}. Differences between
watersheds were probably due to the TSI practices
on Falling Rock in the 1950's. There were more
trees greater than 20 em on Bucklick than on Falling Rock (fig. 1). Release of suppressed individuals following TSI allowed increased growth and
higher stand density.
Watershed
Falling Rock (N=50)
Bucklick (N=50)
(TSI)
(Control)
Mean
S.E.
Mean
S.E.
15.6
6.0
8.8
30.4
18.0
8.4
0.51
0.34
0.34
1.19
0.41
0.37
*
*
*
*
*
10.4
12.8
7.2
30.4
14.8
o.o
0.46
0.39
0.30
1.15
0.40
0
Included within snag densities; 20 years posttreatment.
of girdled trees on Falling Rock was correlated with
natural snag density (rc+0.55, P<O.Ol) and total snag
density (girdled trees and snags) was weakly correlated with the number of animal cavities (r=+0.27,
P<O.Ol). Snags provide primary excavators a soft
substrate to excavate for nesting, gnd they provide
a foraging substrate. Additional foraging substrate was available on Falling Rock in the form
of snags 2.5 to 10 em dbh. More of these small
snags were found on Falling Rock (X=46.4 stems/ha)
than on Bucklick (X=20.4 stems/ha) probably as a
result of natural mortality in the TSI released
stems. Large residual girdled trees provided more
potential nest sites and feeding substrate for
large cavity-nesters, such as pileated woodpeckers
(Dryocopus pileatus), without adversely affecting
availability of nest sites for small cavity-nesters
(fig. 2). It should be noted however, that not all
of the nest sites available would meet the requirements of large primary cavity-nesters due to a
Tree species composition was similar between
watersheds. There were 33 species on the Falling
Rock watershed and 32 species on the Bucklick
watershed; 30 species were common to both areas.
Snag and Cavity Densities
We found no girdled trees on Bucklick, but an
average of 8.4 girdled trees per ha remained standing on Falling Rock (table 1). Snags were more
evenly distributed among diameter classes on Falling Rock than on Bucklick (fig. 2). The density
41
spongy outer layer of the girdled snag. Pileated
woodpecker nest holes were observed in several residual girdled trees on Falling Rock. Girdled
trees infected with heart-rot prior to girdling may
provide suitable nest sites.
6
10-14.9
15-24.9
25-34.9
3!-44.9
45-54.9
There were more natural snags (3/ha) in northern red oak than in any other species (table 2).
The highest density of girdled trees was found in
American Beech; 83 percent of the beech snags had
been girdled. Scarlet oaks and chestnut oaks were
also girdled as cull trees on Falling Rock. Gustafon (1946) reported that red maple and American
beech were not normally cut during the logging of
the early 1900's and residual stems were heavily
scarred by poor logging practices.
55-64.9
DBB CLASS(cm)
NeM Site AvailablU'J'
_ _ _ _ _ _ _ _ _ _ _ _......,._
Carolina
chlckadee·~Ba_,l..,r"l
Standing snags in 1981 may have been different
from what was created in the late 1950's because
different species have different decay rates (Harmon
1982). Oaks are fast decayers (X=lO%/yr), while
sourwood and pines (Pinus spp.) are slow decayers
(X=3.8%/yr) (Harmon 1982). The slow-decaying species favor the development of a greater number of
animal cavities than fast-decaying species because
they remain standing longer (Thomas 1979). Thinbarked, noncommercial species such as American beech,
red maple, and sourwood, tended to have more natural
wooc!peclr.er------------e-.
Bec!-bellled
woodpeclr.er--------PUeatec!
woodpeclr.e·------
Figure 2.--Distribution of snags by diameter class
on TSI'ed (cross-hatched) and non-TSI'ed (open
bars) watersheds, Breathitt County, Kentucky,
1981, 20 years post-treatment. Nest site
availability is also depicted for four common
primary cavity-nesters.
Table 2.--The density/10 ha of snags and cavities by tree species for two watersheds in Robinson Forest,
Breathitt County, Kentucky, 1981.1
Snags
Tree Species
NonTSI
TSI
American beech
(Fagus grandifolia)
sourwood
(Oxydendrum arboreum)
unknown3
red maple
(Acer rubrum)
white oak
(Quercus alba)
blackgum
(Nyssa sylvatica)
scarlet oak
(Quercus coccinea)
yellow-poplar
(Liriodendron tulipifera)
black oak
(Quercus velutina)
northern red oak
(Quercus rubra)
chestnut oak
(Quercus prlnus)
post oak
(Quercus stellata)
others4
TOTAL
48(40)
·4
2
0
8
44(36)
0
0
0
Cavities
Natural
Basal
NonNonTSI
TSI
TSI
TSI
8(8)
16
40
32
52 (20)
8
Total
TSI
Non
TSI
16
104(64)
76
24
24(0)
76
0
28(20)
40(0)
40
16
4
0
4
4(4)
0
4
12
12(4)
8
12
0
0
0
24(4)
8
0
12
0
0
8
4
4
16(0)
12
20(12)
8
0
4
4
8
4
4
8(0)
16
12
4
8
4
0
4
8
0
16(0)
8
12
8
4
16
0
0
0
0
4(0)
16
16
12
0
12
0
4
0
0
0(0)
16
12
4(4)
0
0
4
4(4)
0
12(12)
0
0
0
0
8
0
8
8
20
132
16(4)
0
12(4)
4
8(4)
0
28(12)
176(76)
20
Animal
NonTSI
TSI
0
20(12)
32
8
4
64
148
16
140(60)
40
20
104
4(4)
56(12)
0
88(28)
4
72
0
24(0)
300(100)
16
44
308
~ata presented are based on 50 0.05-ha samples per watershed.
2
Total wit~ value f~r girdled trees that remained standing after 30 years indicated parenthetically.
3
Snags that could not be identified to genus.
4
Taxa with 22 cavities per 2. 5 ha: Betula lenta, Carya glabra, Carya spp., Cornua florida, Magnolia trip!itala,
Pinus spp., Quercus spp., Robinia pseudoacacia, Tilia spp. and Ulmus rubra.
42
and basal cavities (table 2) caused by logging and
fire injuries, which allow decaying agents to enter
the tree and form cavities.
Density of snags >10 em (including girdled
trees) was significantly higher (P<0.05) on Falling
Rock (18.0 snags/ha) than on Bucklick (14.8 snags/
ha) (table 1). These densities are lower than the
densities found by McComb and Muller (1983) for a
30-year-old second-growth forest (85.6 snags/ha) in
southeastern Kentucky. A managed forest in Connecticut had a density of 14.8 snags/ha (McComb and
Noble 1980). McComb and Muller (1983) found a density of 44.2 snags/ha for an old-growth forest in
southeastern Kentucky. The variation in snag densities between old-growth and second-growth forests
can be explained by stand histories. The high snag
density reported by McComb and Muller (1983) may be
due to rapid regrowth with minimal site disturbance
after cutting and subsequently greater annual mortality in the 30-year-old stand than in uncut stands.
Robinson Forest was subjected to frequent fires
immediately following cutting, and this disturbance
probably resulted in slow regrowth and low annual
mortality after 50 years.
Total cavity density for Falling Rock and Bucklick averaged 30.4 cavities/ha, but types of cavities differed between watersheds (table 1). Falling
Rock had more (P<0.05) animal cavities (15.6/ha)
than Bucklick (l0.4/ha) possibly because snags were
more abundant on Falling Rock than Bucklick. Carolina chickadees (Parus carolinensis) frequently used
the soft, remaining girdled snags but cavities created by chickadees may not be used by many other
cavity-nesting species because of the small cavity
size (Thomas 1979). Natural cavities were significantly (P<O.Ol) more abundant on Bucklick (12.8/ha)
than Falling Rock (6.0/ha). The girdling of the
large hollow trees would accelerate falling due to
lack of internal support. McComb and Rumsey (1983)
reported similar reducation in natural cavity density following forest herbicide application at Robinson Forest. The recommended cavity density for
maintaining viable populations of cavity-dependent
species in the oak-hickory forest is 10 cavities/ha
(Hardin and Evans 1977); lower than the cavity densities found on Falling Rock and Bucklick. Cavity
densities on Falling Rock or Bucklick were higher
than reported in other studies (McComb and Noble
1980, Carey and Healy 1981), but this may be due to
differences in species composition, logging practices, or climatic conditions, all of which affect
the suitability of a tree or snag for cavity formation.
Girdling of trees, particularly those which contain heart-rot, would be of benefit to some primary
cavity-nesters and secondary cavity-nesters that prefer animal cavities. Release of suppressed trees by
girdling large (>40 em dbh) unmerchantable trees,
particularly those with heart-rot, 'results in additional potential nesting sites for primary nesters,
and long-term availability of feeding substrate due
to natural mortality in the released trees. To sup~
ply a sustained yield of snags for cavity-nesters in
5Q-year-old second-growth central Appalachian stands
we suggest girdling 1 or 2 heart-rot infected trees
> 40 em dbh per hectare on lQ- to 15-year intervals.
Natural mortality of TSI released stemS will provide
small and medium sized snags. At least 2 large,
natural cavity-bearing trees per hectare should be
left untouched to provide nesting sites for species
preferring natural tree cavities. In the long run,
this should provide a more equitable distribution of
small, medium, and large diameter snags while still
maintaining natural cavity density.
ACKNOWLEDGEMENTS
We thank T.K. Sheehan, C.L. Chambers, D. Roberts,
J.W. Moriarty for assistance with field work; M.
Noble, A.B. Marshall and the Robinson Forest staff
for technical support; and C. Rowell, C.J. Liu, and
R.N. Muller for assistance with data analysis; and
B.A. Thielg~s, R.N. Muller, G.A. McPeek, and D.B. Hill
for reviewing an early draft of the manuscript.
LITERATURE CITED
Braun, E.L. 1950. Deciduous forests of eastern
North America. Blakiston Co. Philadelphia.
596 pp.
Carey, A.B. and W.M. Healey. 1981. Cavities in
trees around spring seeps in the maple-beechbirch forest type. U.S. Dep. Agric. For. Serv.
Res. Paper NE-480. 7 pp.
Carpenter, S.B. and R.L. Rumsey. 1976. Trees and
shrubs of Robinson Forest, Breathitt County,
Kentucky. Castanea 41:277-282.
Conner, R.N. 1978. Snag management for cavitynesting birds.
pp. 120-128. In: Proceedings
of the workshop management of southern forests
for nongame birds, DeGraaf, R.M. (ed.). U.S.
Dep. Agric. For. Serv. Gen. Tech. Rep. SE-14.
• J.G. Dickson and B.A. Locke. 1981.
___H
__e_r...,.b_,i-cide-killed trees infected by fungi:
Potential cavity sites for woodpeckers. Wildl.
Soc. Bull. 9:308-310.
MANAGEMENT IMPLICATIONS
Timber stand improvement by girdling provided
additional feeding substrate and some nesting sites
for primary cavity-nesters 20-30 years after treatment. Tree girdling reduced natural cavity abundance but increased animal cavity density. Secondary cavity users, such as barred owls (Strix varia),
Virginia opossums (Didelphis virginiana), and gray
squirrels (Sciurus carolinensis), which prefer natural tree cavities to animal-made cavities, may not
benefit from TSI unless provisions are made to leave
an adequate number of natural-cavity trees for these
species.
43
Crawford, H.S. 1971. Wildlife habitat changes
after intermediate cutting for even-aged oak
management. J. Wildl. Manage. 35:275-286.
Davenport, O.M. 1958. Timber management and research. p. 75. In: Results of research in
1957. Ky. Agric.JExper. Stn. Ann. Rep. 90 pp.
Evans, K.E and R.N. Conner. 1979. Snag Management.
pp. 2 4-225. In: Proceedings of the workshop
1
of management of northcentral and nort heastern
forests for nongame birds. DeGraaf, R.M. and
K. E. Evans (eds.). U.S. Dep. Agric. For. Serv.
Gen. Tech. Rep. NC-51 . 268 pp.
------~
7 , and R.E. Noble. 1980. Effects of
single-tree selection cutting upon snag and
natural cavity characteristics in Connecticut.
Trans . Northeast Sec. Wild!. Soc. 37:50-57.
Gustafon, R.O. 1946. Forest fires, basal wounds,
and resulting damages to timber in an eastern
Kentucky area. Ky. Agric. Exper. Stn . Bull.
493. 15 pp.
----------' and R.L. Rumsey. 1983. Characteristics and cavity-nesting bird use of picloramcrea ted snags in the central Appalachians.
So. J. Appl. For . 7:34-37 .
Hardin , K.I. and K.E. Evans. 1977. Cavity nesting
birds in the oak-hickory forest .. . a review.
U.S. Dep. Agric . For. Serv. Gen. Tech. Rep.
NC- 30 . 23 pp.
Metzger, R. and J. Schultz. 1981. Spring ground
layer vegetation 50 years after harvesting in
northern hardwood forests . Am . M.idl. Nat.
105:44-50.
Harmon, H.F. 1982. Decomposition of standing dead
trees in the southern Appalachian mountains.
Oecologia 52:214-215.
Hiller, E. and D.R. Miller. 1980. Snag use by
birds. pp. 337-356. In: Workshop proceedings:
Management of western forests and grasslands
for nongame birds. R. M. DeGraaf (ed.), U.S.
Dep. Agric. For . Serv. Gen. Tech. Rep . INT- 86.
535 pp.
Jackson, J.A., R. Weeks and R. Shindala. 1976.
The present status and future of red-cockaded
woodpeckers in Kentucky. Ky. l~arbler 52 :7580.
Murphy, D.A. and J.A. Ehrenreich. 1965 . Effects
of timber harvest and stand improvement of
forage production. J. Wild!. Manage. 29:
734-739.
McClelland, B.R. and S. Frissell . 1975. Identifying forest snags useful for hole-nesting
birds. J . For. 73:414- 417.
Thomas, J.W. (ed.). 1979. Wildlife habitats in
managed forests, the Blue Mountains of Oregon
and Washington. U.S. Dep. Agric. Handb. 553.
512 pp .
McComb, W.C. and R.N. ~luller . 1983. Snag densities in old-growth and second-growth Appalachian forests . J . Wild!. Manage. 47:376-382.
44