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Indices to Potential Tree-Cavity-Nesting Wildlife Habitat

See the overlapping and related unit.

Wildlife trees are " standing live or dead tree with special characteristics that suggest a strong potential role for the tree in providing food or shelter to wild animals" (cf BC Ministry of Forestry 1995). The cavities in such trees are emphasized below. The tree on the ground is also emphasized elsewhere. On the ground, the interest is in decomposition and mineral cycling as well as in the production of vertebrate and invertebrate forage for some animal species. These things are clearly important but it is important to weight them properly in the needs for information, the costs of surveys, and the actual use to which the detailed information will be put. For most areas, using three classes of snag quality will suffice and all snags seen in a viewed strip (say 40-50 feet on each side of the observer) x the estimated distance walked during a field-day on the site will produce useful numbers. Dead and down wood will correlate well with the standing snags.

Possible contributions of the dead and down tree to desired volumes of coarse woody debris in streams may be considered (Hagan, J.M. and S.L. Grove. 1999. Coarse woody debris. J. Forestry 97(1):6-11).

Snags have recently been called "legacy trees". The number of snags desired has been hotly debated. Whether any should be present is very much related to the silvicultural system selected. In New Hampshire sustainable forest initiatives, 6 snags per acre is the recommended number with other criteria, namely at least one exceeding 18 inches dbh and 3 exceeding 12 inches dbh. In even age work, one patch of uncut trees per 10 acres is suggested, or about 5 percent of the landscape in large hardwoods that may become snags.

The Trevey provides one of the few analyses available of the quality of trees for cavity formation. Cavities are one of the most profound faunal space requirements -- often more important than food for many life groups. Where intensive faunal resource management is to be conducted and one or more cavity-nesting species is the objective, than at least one cavity tree per acre is needed. One superior tree per three acres is a minimum standard. When there is 1 per 3 then managers can expect to pace-off about 40 yards between such trees on average.

There is evidently a strong relationship between snags and dead and down wood in the forest. Fauna relate by life groups to the conditions that these provide. The snag becomes the down log at a predictable rate, related to site conditions (of the alpha unit). Similarly, rates of decomposition are largely site specific. The woodpeckers apply early mechanical destruction. The importance of the several species of termites in the forest need emphasis.

Artificial nesting structures may be used to replace, add to, or simulate old-growth conditions in young stands for woodducks, bluebirds, chickadees, woodpeckers, and squirrels. Some hawks and owls will use them. Only rough lumber is needed. They make excellent local handicraft projects and may be a source of local income within an enterprise.

Cavities are built by birds in advanced-decay wood (stippled area) and in some cases sound wood. The sill beneath the hole may be very thin.

Cavities in trees are widely used by birds, mammals, and insects. They are used for incubation and feeding sites, as well as hibernacula, resting areas, escape from predators, and winter storm protection. For some species they are believed to be an essential component of their habitat. A spate of reports have recently been issued on studies of cavities such as the symposium on "The ecology and management of the red-cockaded woodpecker" Thompson (ed.) (l971), Conner et. al. (1975), McClelland and Frissell (1975), Bull and Meslow (1977), Evans and Conner (1979), Cunningham et al. (1980), and Carey and Sanderson (1981). See also notes on dead and down wood.

Absence of cavities nay prevent species occurrence. For others they represent alternatives, i.e. a leaf nest will replace a tree-stem cavity nest. In most cases they are better than alternatives, but in the case of large mammals, ground dens or caves nay be superior. The criteria for superiority have not been developed but probably are best seen as being population-related and will include the major role of cavities in thermoregulation (Moen 1973), their permanence, and their defendability or inaccessibility to predators, hunters, or disturbance. Margalef (1968) provided the profound insight that a nest, like a trail, is an energy resource; it is environmental information. An animal having a calorie-saving nest may not need equivalent food calories. A cavity may be expressed in terms of the net energetics of the population. It is equivalent to stored food, foregone energy loss to convection, energy not spent in escape behavior, energy not needed in order to assemble young for feeding.

In order to measure habitat suitability for a species or species group, to characterize habitats, to provide statistical control over forest parameters, to estimate future forest productivity of wildlife, or to estimate the impact on populations from certain silvicultural practices, a knowledge of potential cavities is believed to be useful.

The purpose of this paper is to develop a rationale for cavity formation, to compute an index to relative abundance of cavities, and to show how cavity potentials can be mapped. Such maps are believed to have utility in planning coordinated timber-wildlife management (Giles 1962); explaining population change over time, use with other habitat-factor maps to describe area suitability for species over time, and to determine where management is most needed and where resources should be allocated (e.g., creating cavities, placing of nest boxes, exercising den-tree saving policy) to cause desired change in wildlife populations Giles 1978).

A tree cavity is not a tree "defect" or merely a hole or space in a tree. Herein, a cavity is defined as any space in a tree branch, stem, or bole with an opening large enough to admit a bird or mammal and large enough to contain that animal for one or more natural activities. Wildlife, as frequently as possible species-specific, as we1welltree species should be specified.

A Rationale for Natural Tree-Cavity Formation

Tree bark openings or injuries, like plant communities from non-vegetative soil, have patterns of succession. An opening in tree bark, from whatever cause, can be analyzed identically to an open field. There are primary invaders, complex species-substrate interactions, and eventually a cavity, then stem or bole break up and deterioration with cavity loss. Cavities are thus an advanced seral stage of the tree ecosystem, but not its last sere.

The causes of bark openings nay be natural pruning of branches. Host causes of openings are not intrinsic to the growth process or stages of a tree, but are extrinsic. We call these initiators (Table 1).

Table 1. Factors Initiating Tree Cavities

Initiators	Comment*	Special References
INTRINSIC
Limb and branch scars	(3) Caused by shading of lower       branches	Baumgartner 1939, Gysel 1961
PARENT STUMP	(4) Growth from a stump; basal       rot
EXTRINSIC
Fire	(1)
Insects	(2) Live tree attacks	Headstrom 1970
Wind Storms	(5)
Lightning strikes	(5)	Gysel 1961
Ice storms
Frost cracks		Gysel 1961
Disease	Rust and galls, weakened branches
Room damage	(6) Many of the other causes
Mechanical stem wounds	(7) Equipment, axe
Wildlife	(8) Woodpeckers, bears	Jackson et al., 1979

*Numbers in parentheses show the order of importance (1 being the highest) of each initiator found by Berry (1969, 1977).

The predominant initiators are of significance in forest management, particularly to students of protection, but at present ranking them does not seem useful. The literature (e.g., Shigo and Larson 1969, Berry 1977, Loewus and Runeckles 1977) is most expressive of wood decay and wood loss. The data, while instructive, were not very helpful inmakingq the analyses herein.

Cavity Succession

The general pattern of succession of events from the initiation is shown in Figure 1. (Typical pattern of cavity formation in a tree, evidencing community succession.) The figure is generalized from Boyce (1948) , Shigo and Larson (1969), Verrall (1970) , Conner et al. (1976), and Shigo and Shortle (1979).

Conner et al. (1975) observed that woodpeckers excavate the softened wood resulting from fungal growth. Insects such as the carpenter worm Prionoxystus robiniae (Peck), and some borers, Saperda, bore into the sap wood and heartwood of living trees and weaken it, also carrying bacteria and fungi into the tree thus hastening cavityformationn (Headstrom 1970).

Berry (1969) observed that of the 22 species of wood-decaying fungi found in association with oaks, four species, Polyporus compactus (Overh.), Stereum frustulatum (pers. ex fr.) Fckl, Poria Cocos (Schw.) Wolf, and Stereum gausapatum (Fr.) Pr., accounted for over 50% of the 183 identified infections.

The heart rots seem to be the most significant factor in the cavity-formation process. Like Berry (1969), Verrall (1970) found Polyporus and Poria the most important fungi associated with heart rot, but added Fomes and Hydnum as important contributors. He noted that the vegetative structure of these fungi is the destructive part, for in this stage its hyphae secrete enzymes which dissolve the wood constituents. Verrall (1970, appendix III:129) gave a thorough list of tree diseases and their pathogens.

Steirly (1951) found red-cockaded woodpeckers used trees with red-ring rot (Trametes pini [Thore]) for excavating cavities. Some woodpeckers start cavities, and others, following advanced decomposition of the site, may further excavate them (e.g. squirrels, other woodpeckers). Miller et al. (1979) working in the northwestern United States concluded that woodpeckers, except the pileated, prefer to excavate cavities in decayed wood. In some cases, sound wood was excavated to achieve a sufficiently large cavity. There may be a faunal sequence in cavity development to animal use, which is related to the size of the cavity and the energy required in its excavation. A cavity used and excavated by a downy woodpecker (Picoides pubescens) one year, with increased decomposition and further excavation and cleaning, nay be used by a fox squirrel (Sciurus niger) the following year.

Allen (1943:195) observed that fox squirrels, manage tree cavity entrances by chewing on the edges and keeping open the holes that may otherwise close.

Dead punky wood is removed by woodpeckers or the squirrels themselves as decay penetrates into the tree trunk. Squirrels habitually gnaw the entrances to their dens, as well as branches and twigs in the vicinity. When the entrance hole heals to an opening about three and one-half inches in diameter, the animals maintain it at that size by gnawing back each season's growth. It is a curious fact that squirrels will gnaw the edges of tree wounds after they are healed past all possibility of the animal entering.

Allen (1943:200) noted that tree cavities do have certain disadvantages not found in leaf nests. They cannot be "built at will," they are sites for ectoparasites, and sanitation (death of a young) is a problem though "they may rear their young on top of a putrid carcass oblivious to the stench."

Cavities and their associated decay are evidently the bane of foresters. They are said to claim 2 to 12 percent of volume in some forests. Similarly they are sites for certain mosquitoes when water collects. The tree-hole mosquitoes are quite specific for the chemical makeup of the water contained in the tree hole (Peterson and Willis (1971). Four species of mosquitoes commonly found breeding in cavities in southwestern Louisiana can also be found in Virginia. These include Aedes triseriatus, Anopheles barber, Orthopedemyia signitera, and Toxorhyochites rutilus septentrionalis. Table 2 presents a representative list of insects found breeding in tree cavities in Virginia, along with diseases for which they are vectors.

Table 2. Some Insects Found Breeding in Tree Cavities in Virginia

Species
Common Name	Scientific Name	Comments	Special References
Ants
Black-carpenter ant	Camponotus pennsylvanicus	Can be destructive to buildings
Shed building ant	Cremastogaster lineolata		Headstrom 1970
Beetles    Ambrosia beetle	Platypus flavicornis	This group of beetles bores into the sapwood and/or heartwood, serving as entrance courts for decay	Headstrom 1970
Columbian timber beetle	Corthylus columbianus
Cotton wood borer	Plectrodera scalator
Hickory bark beetle	Scolytus quadrispinosus
Red oak borer	Monochamus spp.
Southern pine sawyers	Goes tigrinus
White oak borer
Gnats    See Table 3			Battle and Turner 1971. Fallis and Bennett 1961
Mosquitos      Yellow fever mosquito	Aedes aegypti	Disease vector for yellow fever	Gladney and Turner 1969
	Aedes thibaulti
	Aedes triseriatus	Excellent vector potential for eastern and western encephalitis
	Anopheles barberi	Rare in Virginia
	Culex salinarius	Female is very troublesome biter
	Toxorhynchites rutilus	Nectar feeders - possiblebeneficiall species as pollinators
	Orthopodomyia alba	Rare in Virginia; not believed to feed on blood
	Orthopodomyia signifera	Rare in Virginia
Moths       Carpenter worm	Prionoxystus robiniae	Larval stage bores into wood	Headstrom 1970
Looper	Phigala titea	Larval stage bores into wood
Wasps      Giant hornet	Vespa crabro		Spradberry 1973
	Paravespula vulgaris
Other Insects      Common termite	Reticulitermes flavipes	Can be destructive to buildings	Headstrom 1970
Honey bee	Apis mellifica	Beneficial as pollinator

The only disease for which tree-hole gnats or sedges (Culicoides) may be vectors is eastern encephalitis. Table 3, lists these gnats or midges and the animals upon which each feeds.

Table 3. Tree-hole Gnats or Midges of PotentialSignificancee as Disease Vectors for Eastern Encephalitis

Gnats or Midges	Hosts (feed on or bite)
	Human	Avian	Livestock and Other Mammals
Culicoides arburicolr	X	mainly X
Culicoides beckae		X
Culicoides debilipalpis		X	X
Culicoides flukei	unknown
Culicoides footei	unknown
Culicoides guttipennis	mainly X	X
Culicoides hinmani	X
Culicoides nanus	unknown
Culicoides ousairani		X
Culicoides paraensis	X
Culicoides snowi	X
Culicoides stellifer	X		X
Culicoides villosipennis		X

Species Proclivity to Decay

Although difficult to quantify, it seems clear from field observations that some tree species never seem to have cavities and others frequently do. Some seem to have cavities well-suited to wildlife, others are of almost no value, on the average. We have attempted to review the scant literature on the subject and to formulate the beginning of an index to the proclivity of trees forming usable cavities. There are numerous problems with the approach but a first approximation seems needed and perhaps will encourage later work. The uses of this index will be discussed later.

We compared studies of the cavity prevalence within tree species made by Baumgartner (1939), Gysel (1961), Shigo and Larson (1969), Affelbranger (1971), and Conner et. al. (1975), and learned that species proclivity to cavities varied widely among studies. An hypothesis was tested that these studies would show a general gross relation between cavities, wood density and specific gravity. The hypothesis was rejected, there being such great variability in all aspects of the site-tree-wood-cavity formation system. It seems likely that an improved index of tree species proclivity to cavities (P) can result from studies of:

P = f (species, age, site index, soils, slope, elevation, temperature, moisture, and growth form)

Luxford and Trayer (1935) found that rate of decay in cut timber varies greatly with temperature, moisture, and altitudinal changes.

Moisture and temperature, which vary greatly with local conditions, are the principal factors affecting the rate of decay. When exposed to conditions that favor decay, wood in warm, humid areas of the U.S. deteriorates sore rapidly than that in cool or dry areas. High altitudes, as a rule, are less favorable to decay than are low altitudes because the average temperatures are lower and the growing seasons for fungi, which cause decay, are shorter.

This same principal should apply to standing timber, as well.

Similarly, as temperature is a necessary condition, so is the site itself. Rapid grown trees have less dense heartwood and thus are more susceptible to decay, once the succession is initiated. Similarly, rapid growth can heal a wound quickly preventing initiation.

Since species can be weighted in terms of their relative cavity potentials (no matter how crudely at this time), then different forest stands composed of different species may and are likely to have different amounts of cavities over time. Given that large tracts (wildlife refuges, public and private forests) must be evaluated for many reasons, and given that cover type maps are frequently available or can be made, it nay be possible to create an index to cavities over time in each type.

We created a FORTRAN program that accepts the SAP forest type number (Society of American Foresters 1967) for an area, reads from a matrix developed from the text the species present, reads their relative proportion in the named type, weights each by the proclivity index- determined above, and prints a map (Fig. 2 -- under development) of the area showing in gray tones the relative goodness of the area for abundant cavities over time. Later refinements can be made based on mean monthly moisture and temperature indices, aspect, and tree vigor.

Stand Age-Related Phenomena

To aid in planning and estimating impacts of forest changes, curves were needed, expressive of potential cavity usefulness for animals. Table 4 shows all birds that use cavities in Virginia. The table was compiled from Bailey (1913), Shomon (1951), Reilley and Pettingill (1968), Bull and Farrand (1977), and Scott et al. (1977). Table 5 shows all mammals that use cavities. The table vas compiled from Handley (1947), Burt and Grossenheider (1964), Headstrom (1970), and Thomas (1979). By evaluating stand type and size changes over time, it is possible to evaluate the dynamics of the quality of a stand for cavity-using animals. We attempted to do this for each animal species, but the information was not available. We developed a series of 6 general curves (Table 6, Fig. 3) for the birds and mammals of Virginia. Table 6 was compiled from Hardin and Evans (1976), Conner (1978), Evans and Conner (1979), and Thomas et al. (1979). Thus, it is now possible to make stand- specific, species-specific analyses of probable, long-term cavity dynamics in many types of forests. By studying Table 6 it can be seen that when a stand reaches a certain size (correlated well with age and site) it will meet the cavity requirements of a different faunal complex. Also, when a stand reaches a certain critical size, it will not only meet the cavity requirements of that particular faunal complex but those of the preceding ones as well (e.g., at 30 cm. dbh cavity requirements are set for group IV and also groups II and III). By studying forest changes with computer simulations or optimization progress, it will be possible to explain or predict changes in species diversity and richness over time as these erg influenced by cavities.

Table 4. Cavity Nesting Birds of Virginia

Common Name	Scientific Name
Wood duck	Aix sponsa
Common Golden-eye	Bucephala clangula
Buffle-head	Bucephala albeola
Hooded merganser	Lophodytes cucullatus
Common merganser	Mergus merganser
Turkey vulture	Cathartes aura
Black vulture	Coragyps atratus
Peregrine falcon	Falco peregrinus
Merlin	Falco columbarius
American kestrel	Falco sparverius
Barn owl	Tyto alba
Screech owl	Otus asio
Barred owl	Strix varia
Saw-whet owl	Aegolius acadicus
Chimney swift	Chaetura pelagica
Common flicker	Colaptes auratus
Pileated woodpecker	Dryocopus sileatus
Red-bellied woodpecker	Melanerpes carolinus
Red-headed woodpecker	Melanerpes erythrocephalus
Yellow-bellied sapsucker	Sphyrapicus varius
Hairy woodpecker	Picoides villosus
Downy woodpecker	Picoides pubescens
Red-cockaded woodpecker	Picoides borealis
Great-crested flycatcher	Myiarchus crinitus
Tree swallow	Iridoproene bicolor
Purple martin	Progne subis
Black-capped chickadee	Parus atricapillus
Carolina chickadee	Parus carolinensis
Tufted titmouse	Parus bicolor
White-breasted nuthatch	Sitta carolinensis
Red-breasted nuthatch	Sitta canadensis
Brown-headed nuthatch	Sitta pusilla
Brown creeper	Certhia familiaris
House wren	Troglodytes aedon
Winter wren	Troglodytes troglodytes
Bewick's wren	Thryomanes bewickii
Carolina wren	Thryothorus ludovicianus
Eastern bluebird	Sialia sialis
Starling	Sturnus vulgaris
Prothonotary warbler	Protonotaria citrea
House sparrow	Passer domesticus
Common grackle	Quiscalus quiscula
Brown-headed cowbird*	Molothrus ater

*Although the cowbird does not nest, it parasitizes those species that do nest in cavities.

In the future it may be possible to produce a species probability curve for heart rot or a species-specific cavity curve, then to aggregate species within a stand or forest (Giles 1978), however, the information is not available for doing this. An effort is made to determine a first approximation, general curve for cavity usefulness (Fig. 4), and to weight tree species, on a gross scale of 0 to 4 to express their relative proclivity to cavity formation (Table 7).

Table 7. Select Tree Species (Virginia) Grouped by Estimated Decay Resistance of the Heartwood

Class 4	Class 3	Class 2	Class 1	Class 0
Baldcypress Black locust Easter red-cedar Northern white-     cedar	Atlantic white-     cedar Black cherry Chestnut oak Honey-locust Loblolly pine Longleaf pine Post oak Sassafras Shortleaf pine White oak White pine	Dogwood spp. Pitch pine Pond pine Sugar maple Table-mountain     pine	Bear oak Beech (american) Bitternut hickory Black ash Blackjack oak Butternut Carolina ash Chinkapin     (Allegheny) Chinkapin oak Dwarf chinkapin     oak Green ash Hemlock (Eastern) Laurel oak Live oak Mockernut hickory Mountain ash Overcup oak Pignut hickory Pumpkin ash Red spruce Scarlet oak Shagbark hickory Shellbark hickory Shingle oak Shumard oak Swamp chestnut     oak Sweetgum Turkey oak Virginia Pine Water oak White ash	American elm Balsam fir Basswood Bigtooth aspen Blackgum Black oak Black willow Cottonwood     (eastern) Fraser fir Gray birch Northern red oak Quaking apsen Red maple River birch Rock elm Sandbar willow Silver maple Slippery elm Southern red oak Swamp     cottonwood Sweet birch Water hickory Willow oak Winged elm Yellow birch Yellow poplar

Class 4: Heartwood very resistant to decay.
Class 3: Heartwood resistant but less than Class 4.
Class 2: Heartwood of intermediate resistance.
Class 1: Heartwood resistance intermediate between Class 2 and 0.
Class 0: Heartwood of low resistance.

Table 7 was compiled from Luxford and Trayer (1935), Brown et al. (1949), Cartwright and Findlay (1950), U.S. Department of Agriculture (1974), and Shigo (1980). Appendix A lists the scientific names for the tree species used in Table 7. The weight can probably be made more precise (using a scale of at least 0 to 10), that site factors can be included, that effects of uses like grazing can be expressed, and that fundamental relations within trees (e.g. cell structure, chemical properties) may eventually be quantified to enable an equation to be formed of the proclivity of trees in a region to have high quality cavities, K, as:

K = f (species, age, site index, soils, slope, aspect, activities within the forest, forest fire probability, lightning probability, precipitation, summer temperature, days when temperature is below X⁰C)

However the information is not available from the literature, and will require expert professional teams in future work.

Discussion and Conclusion

Given an index of tree species proclivity to fore cavities, and the ability to produce a map of cavity potentials within a stand, anything from a woodlot to an entire forest may be more effectively managed. Those areas of high cavity potential for any animal species of interest nay be specially treated and surrounding timber used for other purposes. This "cavity island". will be influenced by silvicultural practices in surrounding stands. This type of system could be extremely useful in creating suitable habitat for endangered species or for creating communities where bird species richness is maximized for observers. Comparison of areas, especially of the relative cavity-nesting species abundance, is a conspicuous use.

Snag management has become a common and wide-spread investment in forest-wildlife management. Snags may become a modifier or enhancing factor within a stand, the cavity index of which is determined largely from the SAF type. Where natural conditions or prior decisions make snag management impossible, then alternative strategies can be employed such as installing wooden next boxes (Gary and Morris 1980). The system now operational can explain population changes within a forest, describe forest area suitability for a species of interest, and guide the path of management toward more suitable habitats.

The approach to predicting cavity potentials is structured so improvement can readily be made. More research is needed on a micro, rather than the macro-level presented herein. This approach may be extremely useful in managing cavities as a part of the complex task of managing forest wildlife over large areas.

Table 5. Cavity Nesting Mammals of Virginia

Common Name	Scientific Name
Eastern harvest mouse	Reithrodontomys humulis
Opossum	Didelphis marsupialis
Marten	Martes americana
Fisher	Martes pennanti
Red squirrel	Tamiasciurus hudsonicus
Eastern gray squirrel	Sciurus carolinensis
Eastern fox squirrel	Sciurus niger
Southern flying squirrel	Glaucomys volans
Northern flying squirrel	Glaucomys sabrinus
White-footed mouse	Peromyscus leucopus
Black bear	Ursus americanus
Raccoon	Procyon lotor
Deer mouse	Peromyscus maniculatus
Cotton mouse	Peromyscus gossypinus
Porcupine	Erethizon dorsatum
Little brown bat (myotis)	Myotis lucifugus
Silver-haired bat	Lasionycteris noctivagans
Big-brown bat	Eptesicus fescus
Longtail weasel	Mustela frenata
Spotted skunk	Spilogale putorius
IN A HOLLOW STUMP OR STUB
Mink	Mustela vison
Red-backed vole	Clethrionomys gapperi
Masked shrew	Sorex cinereus
Smoky shrew	Sorex fumeus
Eastern woodrat	Neotoma floridana
Shorttail weasel	Mustela erminea
Least shrew	Cryptotis parva
Shorttail shrew	Blarina brevicauda

Table 6a. Minimum Tree Size for Cavity Use by Cavity Nesting Birds (Virginia)

Min. dbh. of nest tree (cm.)	10	15	25	30	38	50+
Group	I	II	III	IV	V	VI
Species
Wood duck						X
Common golden-eye						X
Buffle-head					X
Hooded merganser					X
Common merganser						X
Turkey vulture						X
Black vulture						X
Peregrine falcon						X
Merlin						X
American kestrel				X
Barn owl						X
Screech owl				X
Barred owl						X
Saw-whet owl				X
Chimney swift						X
Common flicker				X
Pileated woodpecker						X
Red-bellied woodpecker				X
Red-headed woodpecker				X
Yellow-bellied sapsucker			X
Hairy woodpecker			X
Downy woodpecker		X
Red-cockaded woodpecker
Great-crested flycatcher				X
Tree swallow			X
Purple martin				X
Black-capped chickadee	X
Carolina chickadee	X
Tufted titmouse				X
White-breasted nuthatch				X
Red-breasted nuthatch				X
Brown-headed nuthatch				X
Brown creeper			X
House wren			X
Winter wren			X
Bewick’s wren			X
Carolina wren			X
Eastern bluebird			X
Starling			X
Prothonotary warbler			X
House sparrow			X
Common grackle	unknown
Brown-headed cowbird	unknown

  Table 6b. Minimum Tree Size for Cavity Use by Cavity Nesting Mammals (Virginia)  

Min. dbh. of nest tree (cm.)	10	15	25	30	38	50+
Group	I	II	III	IV	V	VI
Species
Eastern harvest mouse	unknown
Opossum						X
Marten					X
Fisher						X
Red squirrel				X
Eastern gray squirrel	unknown
Eastern fox squirrel					X
Southern flying squirrel				X
Northern flying squirrel				X
White-footed mouse	unknown
Black bear	unknown
Raccoon						X
Deer mouse			X
Cotton mouse	unknown
Porcupine						X
Little brown bat (myotis)				X
Silver-haired bat				X
Big brown bat				X
Longtail weasel				X
Spotted skunk						X
Mink	unknown
Red-backed mouse	unknown
Masked shrew	unknown
Smoky shrew	unknown
Eastern woodrat				X
Shorttail weasel			X
Least weasel	unknown
Shorttail shrew	unknown

Literature Cited

Affelbranger, C. 1971. The red heart disease of southern pines. pp.96-99. In. Thompson R.L. (ed.) The ecology and management of the red-cockaded woodpecker: A symposium. Bur. Sport Fish. and Wildl. U.S.D.I. and Tall Timbers Res. Stn., Tallahasse, FL. 188 pp.

Allen, D.L. 1943. Michigan fox squirrel management. Michigan Dept. Cons., Game Div. Publ. 100. 404 pp.

Bailey, H.H. 1913. The birds of Virginia. J.P. Bell Co., Inc., Lynchburg, VA. 326 pp.

Battle, P.V. and E.C. Turner. 1971. The insects of Virginia: no. 3. A Systematic review of the genus Culicoides (Diptera:Ceratopogonidae) in Virginia, with a geographic catalog of the species occuring in the eastern U.S., north of Florida. Res. Div. Bull. 44. Virginia Tech, Blacksburg, VA. 129 pp.

Baumgartner, L.L. 1939. Fox squirrel dens. J. Mamm. 20(4):456-465.

Berry, F .H. 1969. Decay in the upland oak stands in Kentucky. U.S.D.A. Forest Service, Res. Paper NE-126, Northeastern Forest Exp. Sta., Upper Darby, PA. 16 pp.

Berry, F.H. 1977. Decay in yellow-poplar, maple, black gum, and ash in the central hardwood region. U.S.D.A., Forest Service, Res. Note NE-242, Northeastern Forest Exp. Sta., Upper Darby, PA. 4 pp.

Boyce ,J.S. 1948. Forest pathology (second ed.). McGraw-Hill Book Co., Inc., New York, NY 550 pp.

Brockman, C.F. 1968. Trees of north America. A field guide to the major native and introduced species north of Mexico. Western Publishing Co., Inc., Racine, WI. 280 pp.

Brown, H.D., A.J. Panshin, and C.C. Porsaith. 1949. Textbook of wood technology. v.1. McGraw-Hill Book Co., Inc., New York, NY. 652 pp.

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Appendix A. Scientific Names of Tree Species from Table 7

Common Name	Scientific Name
American elm	Ulmus americana L.
Atlantic white-cedar	Chamaecyparis Thyoides (L.) B.S.P.
Baldcypress	Taxodium distichum (L.) L.C. Rich.
Balsam fir	Abies balsamae (L.) P. Mill.
Basswood	Tilia spp. L.
Bear oak	Quercus ilicifolia Wang.
Beech (american)	Fagus grandifolia ehrh.
Bigtooth aspen	Populus grandidentata Michx.
Bitternut hickory	Carya cordiformis (Wang.) K. Koch
Black ash	Fraxinus nigra Marsh.
Black cherry	Prunus serotina (ehrh.
Blackgum	Nyssa sylvatica Marsh.
Blackjack oak	Quercus marilandica Muenchh.
Black locust	Robinia pseudoacacia L.
Black oak	Quercus velutina Lam.
Black walnut	Juglans nigra L.
Black willow	Salix nigra Marsh.
Butternut	Juglans cinerae L.
Carolina ash	Fraxinus caroliniana P. Mill.
Chestnut oak	Quercus prinus L.
Chinkapin (allegheny)	Castanea pumila P. Mill.
Chinkapin oak	Quercus muehlenbergii Engelm.
Cottonwood (eastern)	Populus deltoides Bartr. ex Marsh.
Dogwood spp.	Cornus spp. L.
Dwarf chinkapin oak	Quercus prinoides Willid.
Eastern red-cedar	Juniperus virginiana L.
Fraser fir	Abies fraseri (Pursh) Poir.
Gray birch	Betula populifolia Marsh.
Green ash	Fraxinus pennsylvanica Marsh.
Hemlock (eastern)	Tsuga canadensis (L.) Carr.
Honeylocust	Gleditsia triancanthos L.
Laurel oak	Quercus laurifolia Michx.
Live oak	Quercus virginiana P. Mill.
Loblolly pine	Pinus taeda L.
Longleaf pine	Pinus palustris P. Mill.
Mockernut hickory	Carya tomentosa (poir.) Nutt.
Mountain ash (american)	Sorbus americana Marsh.
Northern red oak	Quercus rubra L.
Norhtern white-cedar	Thuja occidentalis L.
Overcup oak	Quercus lyrata Walt.
Pignut hickory	Carya glabra (P. Mill.) Sweet
Pitch pine	Pinus rigida P. Mill
Pond pine	Pinus serotina Dougl.
Post oak	Quercus stellata Wang.
Pumpkin ash	Fraxinus profunda (Bush) Bush
Quaking aspen	Populus tremuloides Michx.
Red maple	Acer rubram L.
Red spruce	Pinea rubens Sarg.
River birch	Betula nigra L.
Rock elm	Ulmus thomasii Sarg.
Sandbar willow	Salix interior Rowlee
Sassafras	Sassafras albidum (Nutt.) Nees
Scarlet oak	Quercus coccinea Muenchh.
Shagbark hickory	Carya ovata (P. Mill.) K. Koch
Shellbark hickory	Carya laciniosa (Michx. f.) Loud.
Shingle oak	Quercus imbricaria Michx.
Shortleaf pine	Pinus echinata P. Mill.
Shumard oak	Quercus shumardii Buckl.
Silver maple	Acer saccharinum L.
Slippery elm	Ulmus rubra Muhl.
Southern red oak	Quercus falcata Michx.
Sugar maple	Acer saccharum Marsh.
Swamp chestnut oak	Quercus michauxii Nutt.
Swamp cottonwood	Populus heterophylla L.
Swamp white oak	Quercus bicolor Willd.
Sweet birch	Betula lenta L.
Sweetgum	Liquidambar styraciflua L.
Table-mountain pine	Pinus pungens Lamb.
Turkey oak	Quercus laevis Walt.
Virginia pine	Pinus virginiana P. Mill.
Water hickory	Carya aquatica (Michx. f.) Nutt.
Water oak	Quercus nigra L.
White ash	Fraxinus americana L.
White oak	Quercus alba L.
White pine (eastern)	Pinus strobus L.
Willow oak	Quercus phellos L.
Winged elm	Ulmus alata Michx.
Yellow birch	Betula alleghaniensis Britt.
Yellow poplar	Liriodendron tulipifera L.

Most of the above text was assembled by Robert H. Giles, Jr., Gregory Knoll, and Donal R. Windon, Jr.,
Dept. of Fisheries and Wildlife Sciences,
Virginia Polytechnic Institute and State University,
Blacksburg, VA 24061 in the 1980's.

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