United States 

Department of An Old-Growth Definition for 

Agriculture 

Forest Sewice Western and Mixed Mesophytic 

Forests 

Southern Cathryn H. Greenberg, Donald E. McLeod, and 

Research Station David L. Loftis 

General Technical 

A Section sf the Old-Growth Definition Series 
The Authors: 

Cathryn H. Greenberg, Research Ecologist, and David L. Loftis, Project 

Leader, Southern Research Station, U.S. Dep ent of Agriculture, 

Forest Service, Asheville, NC 28806; Donald E. McLeod, Retired Professor, 

Mars Hill College, Mars Hill, NC 28754. 

Preface 

Old growth is widely acknowledged today as an essential part of managed forests, particularly on public lands. However, this 

concept is relatively new, evolving since the 1970's when a grassroots movement in the Pacific Northwest began in earnest to 

define old growth. In response to changes in public attitude, the U.S. Department of Agriculture, Forest Service, began 

reevaluating its policy regarding old-growth forests in the 1980's. Indeed, the ecological significance of old growth and its 

contribution to biodiversity were apparent. It was also evident that definitions were needed to adequately assess and manage the 

old-growth resource. However, definitions of old growth varied widely among scientists. To address this discrepancy and other 

old-growth issues, the National Old-Growth Task Group was formed in 1988. At the recommendation of this cornmiltee, old 

growth was officially recognized as a distinct resource by the Forest Service, greatly enhancing its status in forest management 

planning. The committee devised "The Generic Definition and Description of Old-Growth Forests" to serve as a basis for 

further work and to ensure uniformity among Forest Service Stations and Regions. Emphasis was placed on the quantification 

of old-growth attributes. 

At the urging of the Chief of the Forest Service, all Forest Service Stations and Regions began developing old-growth 

definitions for specific forest types. Because the Southern and Eastern Regions share many forest commrmnities (together they 

encompass the entire Eastern United States), their efforts were combined, and a cooperative agreement was established with 

The Nature Conservancy for technical support. The resulting project represents the first large-scale effort to defme old growth 

for all forests in the Eastern United States. This project helped bring the old-growth issue to public attention in the East. 

Definitions will first be developed for broad forest types and based mainly on published infomation and so must be viewed 

accordingly. Refinements will be made by the Forest Service as new information becomes available. This document represents 

1 of 35 forest types for which old-growth definitions will be drafted. 

In preparing individual old-growth definitions, authors followed National Old-Growth Task Group guidelines, which differ 

fiom the standard General Technical Report format in two ways-the abstract (missing in this repoa) and the literaare 

citations (listed in Southern Journal of Applied Forestry style). Allowing for these deviations will ensure consistency across 

organizational and geographic boundaries. 

September 1997 

Southern Research Station 

P.O. Box 2680 

Asheville, NC 28802 
An Old-Gro Definition for Westem 

and Mixed Mesophytic Forests 

Cathryn H. Greenberg, Donald E. McLeod, and 

David I,. Loftis 

Introduction 

Mesophytic forests can be segregated into two subgroups 

based on species richness and composition-western and 

mixed mesophytic forests. Western mesophytic forests 

occur primarily in the Interior Low Plateau, southern 

Central Lowland, Ozark Plateaus and Ouachita 

physiographic provinces, and the northern Coastal Plain 

along the Mississippi River. Typically oak (Quercus spp.)- 

dominated, this type occurs in a wide range of topographic 

positions, including drier sites than the more mesic, mixed 

mesophytic forests. 

Mixed mesophytic forests occur in the Appalachian Plateau, 

Ridge and Valley, and Blue Ridge physiographic provinces. 

In the mountains, this forest type occurs on lower northand east-facing slopes and mesic coves up to about 5,000 

feet 11524 meters (m)] in elevation (McLeod 1988). In less 

mountainous terrain, mixed mesophytic forest may cover 

the entire landscape where conditions are suitable. 

Mixed mesophytic forest types are among the most 

biologically diverse ecosystems of the United States and 

perhaps of temperate regions worldwide (I-linkle et al. 

1993). The most common of the 25 to 30 characteristic tree 

species are sugar maple (Acer saccharum Marsh.), beech 

(Fagus grandfolia Ehrh.), hemlock [Tsuga canadensis (L.) 

Carr.], silverbell (Halesia carolina L.), yellow-poplar 

(Liriodendron tulipifera L.), red maple (A. rubrum L.), 

white ash (Frainus atnericana L.), white oak (Q. alba L.), 

northern red oak (Q. rubra L.) and yellow birch (Betula 

alleghaniensis Britton), yellow buckeye (Aesculus octandra 

Marsh.) and basswood (Tilia heterophylla Vent.) (Braun 

1935, 1938, 1940, 1942, 1950; WiMaker 1956; Core 1966; 

Quarteman st al. 1972; Winstead and Nicely 1976; 

Dickison 1950) (appendix A). The latter two are indicator 

species for the mixed mesophytic forest type but are absent 

from western mesophytic forests (Braun 193 8). 

associated differences in soils, moisture, insolation, and 

microclimate contribute to subcommunity distributions 

within the mixed mesophytic forest (Caplenor 1965, Martin 

1975, Dickison 1980, Muller 1982, Crownover 1988, 

McLeod 1988, Hinkle 1989). Many of the characteristic 

mixed mesophytic forest tree species are associated with 

high pH, and with cation exchange capacity, percent base 

saturation, and some nutrient contents (Muller 1982, 

McLeod 1988). Depth of organic soil averages 3.0 f 0.4 

inches [7.5 + 1.1 centimeters (cm)]' in nonrocky areas. 

Society of American Foresters forest cover types included 

within the definition sf mixed mesophytic and western 

mesophytic forests are 

25-sugar maple-beech-yellow birch (in part) 

27-sugar maple 

52-white oak-black oak-northern red oak 

57-yellow-poplar-eastern hemlock 

59-yellow-poplar-white oak-northern red oak 

Human influence on eastern forests has a long history 

(Guffey 1977). Native Americans cleared large areas of 

forest and commonly set fire to woodlands to increase game 

populations (Eller 1982). Later, European settlers 

accelerated the clearing of forests for farmland. Woodlands 

were often heavily grazed by free-ranging hogs and 

livestock (Eller 1982). With the development of a logging 

industry capable of cutting and milling large volumes of 

timber, coupled with newly completed railroad access, 

eastern forests were extensively logged around the turn of 

the century (Shands 1992). Mixed mesophytic forests were 

clearcut or high-graded with little thought for hhxre land 

condition. By the late 19th and early 20th centuries, all but 

the most inaccessible stands of old-growth forests were 

eliminated (Buthrick 1923, Westveld 1933). 

Species dominance patterns, or "association-segregates," 

may vary with geographic or physiographic region and site 

conditions (Braun 1950). Topographic features, including 

slope, aspect, elevation, and geomorphic form, and 

' McLeod, Donald E. December 3, 1996. Unpublished raw data. On file 

with: U.S. Department of Agriculture, Forest Service, Southern Research 

Station, Bent Creek Research and Demonstration Forest, 1577 Brevard 

Road, Asheville, NC 28806. 
Introduction of exotic plants, animals, and pathogens has 

also dramatically affected forest dynamics. The American 

chesaut blight (Cvphonectria parasitica), introduced in 

the early 20th century, caused widespread death of this 

previously dominant tree species by 1930 and greatly 

changed forest species composition and regeneration 

patterns (Ashe 191 1, Woods and Shanks 1959). Similarly, 

Dutch elin disease (Ceratoeystis ulmi) dramatically affected 

forest dynamics and species composition where Dutch elm 

was dominant (Boggess and Bailey 1964). Introductions of 

the European wild hog (Sus scrofa), dogwood anthracnose 

(Discuta destructiva), and gypsy moth (Porthetria dispar) 

have also significantly altered forest dynamics. 

Structure and Composition of Old-Growth 

Forests 

Government surveyors described the coves below Mount 

Mitchell, near Asheville, North Carolina, as "a forest of 

oaks, hickories, maples, (American) chestnuts [(Castanea 

dentata (Marsh.) Borkh.)], and tulip poplars, some of them 

large enough to be suggestive of the giant trees on the 

Pacific Coast."' 

While no single attribute defines old-growth forests, a 

combination of several factors may serve as important 

indicators. Pertinent structural attributes of the living 

component of old-growth forests include species 

composition, richness and diversity of canopy, and 

understory and herbaceous strata; plant and animal species 

potentially dependent upon old growth (Martin 1992); age, 

diameter, density, and basal area of canopy trees; vertical 

stand structure; and stand age and size structure including 

apportionment of small and large stems (Schmelz and 

Lindsey 1965, Weaver and Ashby 197 1, Martin 1992). 

Important nonliving shuctural features include the volume 

and distribution of coarse woody debris (CW) and 

standing snags and their apportionment among size and 

decay classes; tree-fall gaps of various size and age; 

undisturbed soil and soil macropores; and little evidence of 

disturbance by humans (Martin 1992). Below, we discuss 

specific characteristics of stnrctured categories that m;ly 

assist in defining and identifying old-growth western and 

mixed mesophytic forests. 

Southern Alppalachim Center, Mars Hill College. 1979. A socioeconomic 

ovemiew of western Carolina for Nmb&ala-Pisgah Forests. 73 p. 

Unpublished report. On file with: Mars Hill College, College tibrq, 

Southern Appalachian Room, Mars HiII, NC 28754. 

Vertical Structure 

Nurnerous factors contribute to a complex vertical struckre 

in old-growth, mixed mesophytic forests. Different size and 

age distributions of canopy tree species create a wide spread 

in heights. Understory trees, shrubs, and herb layers fom 

distinct forest strata. Continual creation and closure of gaps 

create a temporally and spatially "shifting mosaic" of age 

and size-class patches. 

Canopy height of eastem old-growth forests ranges from 

98.4 to 13 1.2 feet (30 to 40 m) (Whittaker 1966, McLeod 

1988). Clebsch and Busing (1989) described old-grod 

canopy as having overlapping and spreading crowns. Such 

canopy structure allows only 0.3 to 2 percent of hcident 

light penetration to the herb stratum (Whittaker 1966, 

Canham 1989). The subcanopy and shrub layer tend to be 

sparse (5 to 30 percent cover) where they are deciduous 

(McLeod 1988) but can be thick where dominated by 

ericaceous shrubs. Likewise, a multistructural herbaceous 

layer may be present under a deciduous canopy but sparse 

to nonexistent beneath dense evergreen shrubs or in 

excessive shade (Caplenos 1965, McLeod 1988). McLeod 

(1988) reported a thick (about 100 percent cover), speciesrich herbaceous cover in old-growth stands of the Black and 

Craggy Mountains of North Carolina. 

Whittaker (1966) estimated aboveground biomass of 223 to 

272 tons per acre [500 to 6 10 metric tons per hectare (ha)] 

and net productions of 3.3 to 3.9 ounces per square foot 

[I000 to 1200 grams per square meter (grams per m2)] 

annually in mature climax mesic forests. Of total 

aboveground production, about 95.8 percent were trees, 0.1 

percent shrubs, 3.4 percent summer herbs, and 0.7 percent 

vernal herbs. 

Many old, living trees are hollow or severely decayed. 

McLeod (see foobote 1) found an average of 4.9 k 2.4 

decadent trees per acre (12 k 6 decadent trees per ha), or 3 

percent of living trees in six old-growth stands in the 

Southern Appalachians (table 1). Of decadent trees, 2 1 

percent were Florida dogwood and 26 percent were beech. 

Most decadent trees (59 percent) were small fK'7.9 inches 

(20 em) in diameter at breast height (d.b.h.11 or midsize 126 

percent were from 7.9 to 15.4 inches (20 to 39 cm)]. Only 

15 percent were larger than 15.7 inches (40 em) d.b.h. Hardt 

and Swank (in press) found 5.1 and 8.7 decadent trees 

r 1 1.8 inches d.b.h, per acre (1 2.5 and 2 1.5 decadent trees 

230 em d.b.h. per ha) in %Mi0 old-growth Southern 

Appalachian stands, respectively. mey suggest that species 

composition has an impostant influence oar tree decadence, 

since some species (such as red maple, beech, and 
Table 1 (IEngtish unitsvtandardkd tabie of old-growth anributes for western and mixed mesophytic forests 

Quantifiable 

attribute 

Value Number 

Range Mean of stands References 

Stand density (no.iacre) 

-trees 24 in. d.b.h. 68-184 130k34 

Stand basal area (ftyacre) 

-trees r4 in. d.b.h. 

Age of large trees (yrs) (maximum) 

Liriodendron tulipifera L. 

Tilia heterophylla Vent. 

Acer saccharum Marsh. 

Aesculus octandra Marsh. 

Fagus grandifolia Ehrh. 

Tsuga canadensis (L.) Carr. 

Number of 4-in size classes 

-trees 24 in. d.b.h. 

Maximum d.b.h. (in) 

L. tulipifera L. 

Tilia heterophylla Vent. 

Acer saccharum Marsh. 

Aesculus octandra Marsh. 

F. grandifolia Ehrh. 

Tsuga canadensis (L.) Carr. 

Standing snags (no./acre) 

-snags 24 in. d.b.h. 

Downed logs (ft3/acre) 

Decadent trees (no./acre) 

-trees 24 in. d.b.h. 2-8 5k2 

Percent of canopy in gaps 3-24 9.5 

14 Bryant 1987 

Muller 1982 

Palmer 1 98'7" 

Mc~eod~ 

Bryant 1987 

Muller 1982 

Palmer 1 987" 

kfcLeodb 

in Runkle 1982 

in Runkle 1982 

Tubbs 1977 

in Runkle 1982 

Morey 1936 

Morey 1936 

McComb and Muller 1983 

Muller 1982" 

kfc~eod~ 

Muller and Liu 199 ld 

McLeodb 

Hardt and Swank, in press 

14 Runkle 1982 

" See also Whittaker 1966, Weaver and Ashby 1971, Martin 1975, Winstead and Nicely 1976, Dickison 1980, McGee 1984, Lorimer 1985, and 

CIebsch and Busing 1989. 

McLeod, Donald E. December 3, 1996. Unpublished raw data. On file with: U.S. Department of Agriculture, Forest Service, Southern Research 

Station, Bent Creek Research and Demonstration Forest, 1577 Brevard Road, Asheville, NC 28806. 

" See also Schmelz and Lindsey 1965, McGee 1984, Rosenberg et al. 1988, Poulson and Platt 1989, and Martin 1992. 

"see also Thompson 1980; and MacMillan 1981, 1988. 

See also Hardt and Swank, in press. 
Table 1 (metric unitswtandardized table of old-growth attributes for western and mixed mesophytic forests 

Quantifiable 

attribute 

Value Number 

Range Mean of stands References 

Stand density (no.lha) 168-455 322a85 

-trees 2 10 cm d.b.h, 

Stand basal area (m2fha) 

-trees 2 10 cm d.b.h. 

Age of large trees (yrs) (maximum) 

Liriodendron tulipifera L. 

Tilia heterophylla Vent. 

Acer saccharum Marsh. 

Aesculus octandra Marsh. 

Fagus grandifolia Ehrh. 

Tsuga canadensis (L.) Carr. 

Number of 10-cm size classes 

-trees 2 10 cm d.b.h. 

Maximum d.b.h. (cm) 

L, tulipifera L. 

Tilia heterophylla Vent. 

Acer saccharum Marsh. 

Aesculus octandra Marsh. 

F. grandifolia Ehrh. 

Tsuga canadensis (L.) Carr. 

Standing snags (no.fha) 

-snags 2 10 cm d.b.h. 

Downed logs (m3ha) 

Decadent trees (noha) 

-trees 10 em d.b.h. 

14 Bryant 1987 

Muller 1982 

Palmer 1987" 

~c~eod~ 

14 Bryant 1987 

Muller 1982 

Palmer 1 987" 

~c~eod~ 

in Runkle 1982 

in Runkle 1982 

Tubbs 1977 

in Runkle 1982 

Morey 1936 

Morey 1936 

McComb and Muller 1983 

Muller 1982" 

McLeodb 

Muller and Liu 199 1 

Mc~eod' 

Hardt and Swank, in press 

Percent of canopy in gaps 3-24 9.5 14 Runkle 1982 

a See also Whittaker 1966, Weaver and Ashby 1971, Martin 1975, Winstead and Nicely 1976, Dickison 1980, McGee 1984, Lorimer 1985, and 

CIebsch and Busing 1989. 

McLeod, Donald E. December 3, 1996. Unpublished raw data. On file with: U.S. Department of Agriculture, Forest Service, Southern Research 

Station, Bent Creek Research and Demonstration Forest, 1577 Brevard Road, Asheville, NC 28806. 

See also Schrnelz and Lindsey 1965, McGee 1984, Rosenberg et al. 1988, Poulson and PIatt 1989, and Martin 1992. ' See also Thompson 1980; and MacMillan 198 1, 1988. 

See also Hardt and Swank, in press. 
basswood) are more susceptible to heart rot and cavity 

fornation. Stillwell (1955) reported that 67 percent of old 

yellow birch were highly decayed. Williams (1936) reported 

that nearly all large beech trees in an Ohio climax forest 

were hollow, at least at the base, because of various fungal 

infections. Norden (1954) found that 91 percent of old 

sugar maples were highly decayed. 

Diversity 

Old-growth forests tend to have fewer tree species overall, 

but they have more canopy species than younger stands 

(~63 years) (Clebsch and Busing 1989). Gap-phase 

regeneration permits regeneration of both tolerant and 

intolerant species, which contributes to the maintenance of 

great canopy-species diversity in old growth. Conversely, 

younger stands may be dominated by yellow-poplar and 

other less shade-tolerant species (Clebsch and Busing 1989; 

Wardt and Swank, in press). Martin (1 992) reported 43 tree 

species in 7 mixed mesophytic communities within the 

Lilley Cornett Woods in Kentucky. Appendix A presents 

tree species characteristic of old-growth, mixed mesophytic 

forests. 

Diversity [Shannon-Weiner Index (H')] based on tree 

density is more variable in old-growth forests than in 

younger tracts. However, H' based on biomass tends to be 

higher in older stands than in younger stands because 

biomass is more evenly distributed among canopy species. 

High species diversity, richness and equitability, and low 

dominance of canopy tree species appear to characterize 

old-growth, mixed mesophytic forests (Martin 1992). 

Martin (1 992) suggests quantitative criteria for defining the 

canopy community composition of old-growth, mixed 

mesophytic forests: (1) 220 species, (2) H' >3.0, (3) 

evenness >O.50, and (4) Simpson's dominance values c0.30. 

Shrub, tree seedling, and herbaceous species richness also 

tends to be high. McLeod (1988) reported an average of 

5 1.1 vascular plant species per 0.25 acre (0.1 ha), with 

herbs contributing 72.2 percent of the total flora. Species 

richness generally increases with soil pH (McLeod 1988). 

Seedling density is significantly lower under ericaceous 

shrubs, suggesting that such shrubs may prevent seedlings 

from becoming established. This could be due to soil 

acidification, other chemical modifications, or decreased 

moisture or light levels beneath heath (Palmer 1987). 

Candidate species include Fraser's sedge [Cymophyllus 

fraseri (Andr.) Mackenzie] and spotted mandarh 

[Disporum maculatum (Buckley) Britt.] (Martin 1992). It is 

likely that if old-growth-dependent plants exist, myconhim1 

fungus species limit their distribution (Martin 1992). 

Mixed mesophytic forests support rich mammalian, 

avifaunal, and herpetofaunal communities, several of which 

are rarely found in other forest types (appendix B) (Hinkle 

et al. 1993). No species is known to be restricted to oldgrowth forests, but several require the structural features 

(Hardt and Swank, in press) and microclimate of mature 

mesophytic forests (Haney and Schaadt 1996, Meier et al. 

1996, Pelton 1996). Hence, moisture gradients affect the 

distribution of several species within the mixed rnesophytic 

forest type (Hudson 1972, Hinkle et al. 1993). 

Basal Area and Density 

Basal area of old-growth, mixed mesophytic forest trees 

- >3.9 inches (10 cm) d.b.h. ranges from 1 13.0 to 296.0 

square feet per acre (26 to 68 m2 per ha) (table 1). Clebsch 

and Busing (1989) found that basal area in second-growth 

forests approached that of old growth by age 63, but species 

composition differed. Muller (1982) reported that basal area 

did not significantly differ between an old-growth stand and 

an adjacent 35-year-old, second-growth stand in 

southeastern Kentucky [average 126.3 square feet per acre 

(29 rn2 per ha)]. However, fewer large diameter individuals 

comprised more basal area in old growth, while more 

smaller diameter individuals were present in younger 

growth. 

Canopy trees are usually widely spaced. Reported numbers 

range from 68.0 to 349.0 stems per acre (168 to 863 stems 

per ha), but values depend on count method (table I). 

Martin (1 992) suggests that an average of 10 1.1 trees per 

acre (250 trees per ha) 23.9 inches (10 cm) d.b.h. may be an 

indicator, although not a defining attribute, of old-growth, 

mixed mesophytic forests. 

Density of large trees may be more useful in defining oidgrowth mesic forests. Density of trees 229.5 inches (75 cm) 

ranged from 3.4 to 17.9 per acre (8.5 to 44.3 per ha) and 

averaged 1 1.3 (It 4.9) per acre (27.8 It 12.0 per ha) in five 

old-growth mixed mesophytic stands in the Southern 

Appalachians (see foomote 1). Martin (1992) suggests at 

least 2.8 trees per acre (7 trees per ha) 229.5 inches (75 cm) 

d.b.h. indicate old growth. 

Although several plants are associated with old growth, no 

plant species is currently known to be restricted to oldgrowth, mixed mesophytic forests (Meier et al. 1996). 
Species composition, site factors, such as soil type and 

moisare, and dishrrbance history, affect tree density 

(Martin 1992). 

Snags 

Sanding dead trees, or snags, are important foraging and 

nesting resources for many cavity-nesting birds (Runkle 

199 1, Haney and Schaadt 1996). Numerous other animal 

species use standing snags for cover, denning, and foraging 

(Cmichael and Guynn 1983, Pelton 1996). Animal use 

may depend on the stage of decomposition (Cline and 

Phillips 1983). The number of snags depend on their 

formation rate and longevity, which vary by size, species, 

and cause of death (Bull 1983, McComb and Muller 1983, 

Raphael 1983, MacMillan 1988). 

Annual snag formation rates vary from 0.7 to 9.3 per acre 

(1.6 to 23 per ha) (Lindsey and Schmelz 1965, Runkle 

199 1). Density estimates of snags 23.9 inches (1 0 cm) in 

old-growth, mixed mesophytic forests range from 4.0 to 

28.3 per acre (10 to 70 per ha) [McComb and Muller 1983, 

Martin 1992, McLeod (see footnote l)] (table 1). McComb 

and Muller (1983) reported that snag densities were the 

same or greater in a 35-year-old forest than in an oldgrowth, mixed mesophytic forest for all size classes. The 

younger forests had more than twice as many small snags 

than the older forests [l.O to 3.9 inches (2.5 to 9.9 cm) 

d.b.h.1; both stands had 0.8 large snags 9.8 to 35.4 inches 

d.b.h. per acre 11.9 large snags (25 to 90 cm) d.b.h. per ha]. 

Martin (1 992) reported 21.2 snags per acre (3 snags per ha) 

- 323.6 inches (60 cm) d.b.h. Hardt and Swank (in press) 

found about 6.9 snags 29.8 inches d.b.h. per acre (17.0 

snags 225 cm d.b.h. per ha) in two old-growth stands in the 

Southern Appalachians. They suggest that because species 

differ in their modes of mortality and decay rates, species 

composition influences snag density in old-growth stands. 

Muller and Liu (1 99 1) reported that snags made up 24 

percent of total CW mass and 18 percent of total CW 

volume in an old-growth forest in Kentucky. 

Coarse Woody Debris 

Coarse woody debris provides important microhabitat and 

"safe sites" for bryophytes, livenvorts, fungi, and tree 

seedlings (Martin 1992). Many animal species use CW for 

hiding, egg-laying and development, foraging for 

arthropods, and other functions. Thompson (1 980) reported 

that fallen logs and pits created by tip-up mounds were 

important colonimtion sites for numerous herbaceous 

species. Coarse woody debris is also an important nutrient 

reserve, slowly releasing them as the wood decays. 

Gap-phase disturbance (Barden 1980, Runkle 198 1, Romme 

and Martin 1982) creates an uneven distribution of downed, 

dead logs in mixed mesophpic forests. Mufler and Liu 

(1991) reported that 39.2 percent of CWD >7.9 inches (20 

em) d.b.h. occurred in only 12.5 percent of plots, prhaily 

because of recent tree falls or standing snags. Estimates of 

the number of logs range from 7.7 to 6 1.1 logs r 7.9 inches 

d.b.h. per acre (1 9.0 to 1 5 1.0 logs 220 cm d.b. h. per ha). 

Because log accumulations vary widely depending on 

disturbance type and history, and past and present species 

composition, they are poor indicators of the old-grovvth 

condition (nompson 1980; MacMillan 198 1 ; Martin 1992; 

Hardt and Swank, in press). Muller and Liu (1991) found 

only a weak inverse relationship between plot basal area 

and CW. Species composition of CWD is largely dictated 

by forest species composition (Muller and Liu 1991). 

Estimates of CWZ) volume range from 943.1 to 5,858.9 

cubic feet per acre (66 to 4 10 rn3 per ha) [average 2,2 15.0 * 

1,6 15.0 cubic feet per acre (1 55.0 * 1 13 m3 per ha)] [Muller 

and Liu 199 1 ; McLeod (see footnote 1); Hardt and Swank, 

in press] (table 1). Although McLeod (see footnote 1) 

recorded 98 percent of the total volume of CWD as 

moderately to highly decayed, Muller and Liu (199 1) 

reported only 49 percent as moderately to highly decayed. 

Hardt and Swank (in press) found logs in two old-growth 

stands to be well distributed among decay classes, 

suggesting regular inputs to the forest floor. 

Site conditions influence CW volume because 

decomposition rates increase with increasing temperature 

and moisture. Hence, dry, exposed sites tend to have more 

CW than moist, protected sites (Muller and Liu 199 1). For 

similar reasons, more CW occurs in cool deciduous 

forests than in warm temperate deciduous forests (Muller 

and Liu 1991). 

Wood-decomposition rate varies among species. MacMilIan 

(1988) reported that maple decays faster than beech, which 

decays faster than oak and hickory (Carya spp.). 

Fragmentation of CW and subsequent accelerated decay 

varies among species. Beech, oak, and hickory Eragrnent 

rapidly (MacMillan 1988). Muller and Liu (1 99 1) reported 

that although American chestnut has not reached tree size 

[>3.9 inches (10 cm) d.b.h.1 since the mid-1940's because of 

the chestnut blight, it contributed 1 1 percent to the total 

CW mass in their 1991 study. MacMillan (1988) found 

that the diameter of CW affects decay rate only slightly, 

with large-diameter wood decaying somewhat faster than 

smaller-diameter debris. Such differences may affect sizeclass distribution of CW. 
Silsbee and Larson (1983) found 4 times more woody 

debris volume and 10 times more material in debris dams in 

streams of watersheds that were never logged than in those 

that were logged 45 years ago. Large, rotten wood was more 

than four times more common in streams of unlogged 

watersheds than of logged watersheds. Most of the woody 

debris in never-logged streams was concentrated in debris 

dams* 

Soil 

Soils of undisturbed forest stands have well developed 

organic horizons with no compaction (Martin 1992). 

Constant plant turnover maintains a thick, nutrient-rich 0 

and A horizon that retains moisture. Old root channels and 

animal burrows create soil macropores in sites with 

undisturbed soils. These macropores may influence water 

availability, soil mixing, root distribution (Martin 1992), 

and underground use by animals. 

Old-Growth Dynamics 

Disturbance 

Lorimer (1980) suggests that climax forests be defined as 

"those capable of self-perpetuation in the absence of severe 

disturbance." For forest types not mediated by high intensity 

disturbance, this definition may be suitable. Although the 

perpetuation of climax, mixed mesophytic forests may not 

depend on severe disturbance, several types of disturbance 

act at variable scales and frequencies to influence forest 

dynamics. 

Wind damage, including windthrow (Lorimer 1980), 

tornadoes (Runkle 1982), hurricanes, and microbursts may 

create forest openings of various sizes (Greenberg and 

McNab, in press; Martin 1992). Ice storms, insect damage, 

and fungal infections, floods, and landslides (Runkle 1982, 

Shands 1992) are other disturbances that variously 

influence forest structure and composition. 

The existence of association segregates dominated by 

shade-intolerant species, such as yellow-poplar, suggests 

that large-scale disturbance influences tree regeneration and 

species composition. Lorimer (I 980) suggested that a heavy 

wind created the old-growth poplar cove at Joyce Kilmer 

Memorial Forest near Robbinsville, NC, over 300 years 

ago. McGee (1984) reported heavy mortality of old trees at 

Dick Cove, apparently from a combination of drought, heat, 

and defoliation by insects. Approximately 17 percent of 

northern red oak, 13 percent of white oak, and 19 percent of 

hickories died within a 3-yea period. 

The prevalence of mixed mesophytic forest across its 

geographic range, and the susceptibiliv of species to fieinduced damage or death suggest that large-scale, high 

intensity fire was infrequent (Hamon et al. 1983). 

Minimum fire-return interval was greater than a canopy 

generation (Runkle 1990). Fires within the mixed 

mesophytic region were probably small andlor restricted to 

specific topographic positions, such as xeric ridges 

(Harmon et al. 1983). Infrequent fire may have been the 

primary large-scale disturbance type, but frequency has 

decreased even further since fire suppression was begun by 

State and Federal agencies in the 1930's (Eller 1982, Runkle 

1985, McLeod 1988). 

Gap Dynamics 

The creation of small canopy gaps by the death of a portion, 

entire, or group of trees accounts for the nearly constant tree 

turnover and species composition of old-growth, mixed 

mesophytic forests (Runkle and Yetter 1987, Barden 1989). 

Actual gap size may range from 10.8 to 16,032.4 square feet 

(1 to 1490 m2) but commonly does not exceed 4,304.0 

square feet (400 m2) (Barden 1980; Lorimer 1980, 1989; 

Runkle 198 1, 1982, 1985; Romrne and Martin 1982; Runkle 

and Yetter 1987; Clebsch and Busing 1989). However, 

"expanded" or effective gaps, where more light reaches the 

forest floor, may exceed 2 1,520.0 square feet (2000 m2). 

Estimates of background tree mortality for all species range 

from 5 to 10 percent per decade in old-growth, mixed 

mesophytic forests (Christensen 1977; Lorimer 1980, 1989; 

Buchman 1983; Smith and Shifley 1984; Runkle 199 1). 

Estimates of canopy turnover rates vary from <0.4 percent 

to 1 percent annually (Runkle 1982, 1985; Barden 1989). 

Caps may close from above by lateral-branch extension of 

surrounding canopy trees or infill from below by sapling 

growth (Runkle 1982, 1990). The proportion of land area in 

gaps ranges from 3.2 to 24.2 percent (average 9.5 percent) 

(Runkle 1982) (table 1). The size and orientation of gaps 

may influence canopy recruitment patterns. For example, 

Poulson and Platt (1989) report more light in small, northsouth gaps than in east-west gaps. Time required for lateral 

gap infilling also is greater for north-south than east-westoriented gaps. 

Tree Regeneration and Canopy Recruitment 

Many characteristic, mixed mesophytic forest canopy tree 

species are shade tolerant; their seeds are able to geminate 
and persist for years as saplings beneath a tree canopy. 

Because light beneath a closed canopy forest can be as little 

as 0.3 to 2 percent, even small gaps can more than double 

understory radiation (Wittaker f 966, Canham 1989). 

Wile shade-tolerant species, such as beech and sugar 

maple may be released by small gaps (Canham 1988), 

shade-intolerant species may require larger gaps that permit 

more light, longer daily periods of light, and greater gap 

longevity (the length of time for the canopy to close 

laterally before saplings reach canopy height). Species also 

vary in importance as a firnction of gap size and age 

(Runkle and Yetter 1987, Runkle 1990). Runkle (1990) 

reported that sugar maple was most important in small gaps 

of all ages; beech in all sizes of old gaps; white ash in large, 

young gaps; and yellow-poplar in large gaps of all ages. 

Barden (1 98 1) reported that shade-tolerant species replaced 

most single- and multiple-tree gaps in the Great Smoky 

Mountains, but four species of low shade tolerance (yellowpoplar, black cherry (Prunus serotina Ehrhart), American 

ash, and northern red oak) maintained their presence in 3 

percent of the canopy by infrequent captures of multipletree gaps. 

Recruitment patterns and old-growth stand dynamics 

affecting future stand composition depend upon a 

combination of disturbance type and pattern, current species 

composition, and regeneration mode (Forcier 1975). For 

example, sugar maple produces many seeds with good 

dispersal ability (Fowells 1965). Hence, abundant, shadetolerant seedlings can exploit canopy gaps as they occur 

(Dickison 1980). Conversely, beech seeds have poor 

dispersal ability (Fowells 1965). Hence, its distribution 

depends upon advance regeneration in gaps fomed by or 

near parent trees or by root suckers (Williams 1936, 

Dickison 1980). Buckeye also has poorly dispersed seeds 

and low seed production (Fowells 1965). Basswood is 

highly clonal, so it recollonizes gaps rapidly if present 

(Dickison 1980, Barden 198 1, Runkle 1989). Dickison 

(1980) reported that intolerant and two tolerant species 

(basswood and buckeye) regenerated periodically, while 

shade-tolerant species, including sugar maple, beech, and 

bophombeam [Ostrya virginiana (Mill.) K. Koeh] 

regenerated continuousIy in Walker Cove. 

Interspecific differences in seed gemination and seedIing 

and sapling survival (competitive ability) also affect forest 

dynamics. Williams (1936) noted poorer survival of beech 

than sugar maple seedlings but a high mortality of sugar 

maple saplings. Red maple produced abundant seed, but 

gemination was low and young trees were poor competitors 

with forest dominants. Variation in moisture and climate 

may affect gemination and survival differently from year to 

year (Schmelz et al. 1975). 

Age Structure and Diameter Distributions 

Old-growth, mixed mesophy-tic forests are broadly unevenaged or all aged (Lorimer 1980). The diameter distribution 

of uneven-aged forests is commonly negatively exponential, 

with many more small- than large-diameter trees (Lorimer 

1980, 1985; Palmer 1987). Old-growth stands differ Grom 

younger, uneven-aged forests in having greater range of tree 

sizes, maximum tree age, and more large-diameter trees 

(table 1). Hardt and Swank (in press) reported an average of 

2.4 and 2.5 trees 230.0 inches per acre (5.9 and 6.3 trees 

2 75.0 cm d.b.h. per ha) in two old-growth stands in the 

Southern Appalachians. Longevity varies with species 

(Morey 1936, Tubbs 1977, Runkle 1982). However, few 

studies cite age exceeding 250 years for trees in old-growth, 

mixed mesophytic forests, although occasional trees much 

older than 250 years have been reported (table 1). 

Irregular age distributions are common in old-growth stands 

and reflect severe natural disturbance or irregularities in 

seed production (Lorimer 1980). Breaks in slope or peaks in 

curves may indicate disturbance as it affects recruitment and 

mortality (Schmelz and Lindsey 1965, Schmelz et al. 1975, 

Lorimer 1980). Estimates of background tree mortality for 

all species range from 5 to 10 percent per decade in oldgrowth, mixed mesophytic forests. An additional 6 to 8 

percent mortality caused by disturbance within a given 

decade is sufficient to create peaks in diameter distributions 

as more seedlings and saplings survive and grow into the 

canopy stratum (Lorimer 1980). 

The diameter distributions of species within stands probably 

reflect their frequency of recruitment into the canopy 

(Palmer 1987). Palmer (1 987) noted that Fraser's magnolia 

(Magnoliafiaseri Walt.), a prolific basal sprouter, had a 

negatively exponential diameter distribution, whereas two 

other species that reproduce by seed did not. 

Old-Growth Forests and Change 

Clearly, old-growth forests are not stalic in, species 

composition or structural attributes. Increases in basal area 

and density, and shifts in species composition have been 

reported for numerous old-gowth stands (Weaver and 

Ashby 197 1, Schmelz et al. 1975, MacMillan 198 1, Busing 

1989). Sap-model projections by Clebsch and Busing 

(1989) predicted a shift in species composition from 

yellow-poplar to sugar maple over 250 years, aPZer which 

changes would stabilize, with some increase in biomass sf 
several subdominant species. Williams (1936) noted more 

red oak swmps than live red oaks in a beech-maple climax 

in Ohio. The elimination of canopy-sized American 

chestnut by the chestnut blight dramatically altered canopyspecies composition of old-growth stands. 

%ittaker (1966) reported basal-area growth of 1.3 to 2.6 

square feet per acre per year (0.3 to 0.6 m2 per ha per year) 

in mature climax mesic forests of the Great Smoky 

Mountains. Busing (1989) reported a 52-year increase in 

basal area from 173.7 to 195.5 square feet per acre (39.9 to 

44.9 m2 per ha) and from 1 18.0 to 167.7 square feet per acre 

(27.1 to 38.5 m2 per ha) in two old-growth stands in the 

Great Smoky Mountains National Park (Busing 1989). 

Increases were mainly in sugar maple and hemlock or 

silverbell, primarily in response to American chestnut 

mortality. 

Conelusion 

Defining old growth is enigaradic and problematic. The 

assignment of specific values to a host of attributes 

disregards the tremendous variability among and 

combination of features exhibited in old-growth forests. 

Viewed as the sum of a series of rigid criteria, a given stand 

may not "add up," whereas in fact, viewed as a whole it is 

indeed old growth. The species composition and structural 

attributes of old-growth western and mixed mesophytic 

forest stands are widely variable and depend upon the 

history of the specific stand. Species composition depends 

upon stand origin. An old-growth forest may be dominated 

by "pioneer" species, such as yellow-poplar, if the stand 

originated following a catastrophic disturbance (such as the 

Joyce Kilrner Memorial Forest), or of shade-tolerant species 

if gap dynamics has been the dominant process driving 

regeneration for several tree generations. Similarly, the 

number of snags, decadent trees, and logs depends upon 

tree mortality rates and mode, which in turn, depend upon 

disturbance history (including less dramatic diswrbance 

such as drought), species composition and specific 

vulnerabiliy to disease, heart rot, and blow down. Even-age 

and diameter distribution depend upon stand histow and, if 

too rigidly defined, may exclude some stands that would 

othervvise be recognized as old growth. Nonetheless, 

assimilation of studies in which old-growth characteristics 

have been studied, and the drafting of general guidelines 

provide a starting point in defining and identieing old 

growth. Furlher work is needed to distinguish features that 

are unique lo old growth. 

Acknowledgments 

We thank C. Ross Hinkle, Chief Scientist, Dynamac 

Corporation, Kennedy Space Center, FL; Paul Schmalzer, 

Senior Field Ecologist, Dynamac Corporation, Kennedy 

Space Center, FL; and Chris Ulrey, doctoral student, North 

Carolina State University, Raleigh, NC, for reviewing an 

earlier version of this manuscript. 

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Appendix A 

Tree, shrub, and select vascular herbaceous species that are characteristic of mature western mixed mesophytic forests:" 

Canopy and understory trees 

A cer pensylvanicum L. 

A. rubrum L. 

A. saccharum Marsh. 

Aescml?~sJlma Solander 

Amelanchier arborea (Michx. f.) Fern. 

Betula lenta L. 

B. alleghaniensis Britt. 

Carpinus caroliniana Walt. 

Carya cordformis (Wang.) K. Koch 

C. glabra (Mill.) 

C. ovata (Mill.) I(. Koch 

C. tomentosa (Poir.) Nutt. 

Cercis canadensis L. 

Cladrastis kentukea (Durn.-Cours.) Rudd 

Cornus florida L. 

Fagus grandifolia Ehrh. 

Fraxinus americana L. 

Halesia carolina L. 

Ilex opaca Ait. 

Juglans nigra L. 

J. cinerea L. 

Liquidambar styraclflua L. 

Liriodendron tulipifera L. 

Magnolia acuminata L. 

M. fraseri Walt. 

M. macrophylla Michx. 

M tripetela L. 

Morus rubra L. 

Nyssa sylvatica Marsh. 

Ostrya virginiana (Mill.) K. Koch 

Oxydendrum arboreum (L.) DC. 

Pinus echinata Mill. 

P. rigida Mill. 

P. virgiana Mill. 

Prunus serotina Ehrhart 

Quercus alba L. 

Q. coccinea Muenchh. 

Q. muhlenbergii Engelm. 

Q. montana Willd. 

Q. rubra L. 

Q. vefutina Lam. 

Robinia pseudoacacia L. 

Sassafras albidum (Nutt.) Nees 

Tilia heterophylla Vent. 

Tsuga canadensis L. (Carr.) 

7: caroliniana Engelm. 

lllmus americana L. 

U, alata Michx. 

Shrubs 

Aralia spinosa L. 

Asimina triloba (L.) Dunal 

Clethra acuminata Michx. 

Cornus alternifi>fia L. f. 

Euonymus americanus L. 

E. atropurpureus Jacq. 

Hamamelis virginiana L. 

Hydrangea arborescens L. 

Kalmia Eatifofia L. 

Lindera benzoin (L.) Blume 

Pyrularia pubera Michx. 

Rhododendron maximum L. 

Ribes cynosbati L. 

Sambucus canademis L. 

Stavartia ovata (Cav.) Weatherby 

Viburnum acerifolium L. 

Woody vines 

Aristolochia macrophylla Lam. 

Bignonia capreolata L. 

Celastrus scandens L. 

Parthenocissus quinquefolia (L.) Planch. 

Smilax tamnoides L. 

vitus spp. 

Herbaceous species 

Anemone fancifolia Pursh 

A. quinquefolia L. 

Thalictrum thalictroides (L.) Eames & Boivin 

Actaea pachypoda Ell. 

Aster spp. 

Caulophyllum thalictroides (L.) Michx. 

Claytonia caroliniana Michx. 

C. virginica L. 

Cyprkedium calceolus L. 

Delphinium tricorne Michx. 

Dicentra canadensis (Goldie) Walp. 

D. cucullaria (L.) Bernh. 

Dioscorea villosa L. 

Disporum lanuginosum (Michx.) Nicholson 

Erythronium americanum Ker-Caw 1. 

Eupatorium rugosum HouMryn 

Hydrophyllum spp. 

Phlox divaricata L. 

Sanguinaria canademis L. 

Sedum ternatum Michx. 

Solidago spp. 

Stylophorum diphyllum (Michx.) Nutt. 

Synandra hispidula (Michx.) Baill. 

Tiarella cordifolia L. 
Appendix A (continued) 

Herbaceous species (continued) 

Trillium grand~florum (Michx.) Salisb. 

7: erecturn L. 

Viola spp. 

Ferns 

Adiantzlm pedatum L. 

Ath~rizrm filix-femina (L.) Roth 

Dvopteris cmthusiana (Villars) H.P. Fuchs 

D. goldiana (Hooker) A. Gray 

Osmunda claytoniana L. 

Thehpieris hexagonoptera (Michx.) Weath. 

Polystichum acrostichaides (Michx.) Schott 

a Nomenclature from Wofford 1989. 

Compiled from Braun 1938, McLeod 1988, and Hinkle et al. 1993. 
Appendix B 

Common birds, mammals, and hewetofauna of mature mixed mesophytic forest:" 

Birds 

Cerulean warbler (Dendoica cerulea) 

Black-throated green wmbler (D, virens) 

Acadian flycatcher (Empidona virescem) 

Black-and-white warbler (Mniotilta varia) 

Kentucky warbler (Oporornisformosus) 

Parula warber (Parula americana) 

Summer tanager (Piranga rubra) 

Ovenbird (Seiurus aurocapillus) 

Yellow-throated vireo (VireoJlavifrons) 

Mammals 

Short-tailed shrew (Blarina brevicauda) 

Opossum (Didelphis virginiana) 

Big brown bat (Eptisicus fwcus) 

Southern flying squirrel (Glaucomys volans) 

Red bat (Lasiurus borealis) 

Striped skunk (Mephitis mephitis) 

Little brown bat (motis lucifugus) 

Eastern woodrat (Neotomafloridana) 

White-tailed deer (Odocoileus virginianus) 

Hairy-tailed mole (Parascalops breweri) 

White-footed mouse (Peromyscus leucopus) 

Eastern pipistrelle (Pipistrellus subffavus) 

Raccoon (Procyon lotor) 

Gray squirrel (Sciurus niger) 

Smoky shrew (Sorex fumeus) 

Eastern chipmunk (Tamias striatus) 

Gray fox (Urocyon cinereoargenteus) 

Black bear (Ursus americanus) 

Herpetofauna 

Copperhead (Agkistrodon contortrk) 

Green salamander (Aneides aeneus) 

American toad (Bufo americanus) 

Fowler's toad (B, woodhousei) 

Black racer (Coluber consfrictor) 

Worm snake (Corphophis amoenus) 

Mountain salamander (Desmognathus monticola) 

Ring-necked snake(Diad0phis punctatus) 

Black rat snake (Elaphe obsoleta) 

Coal skink (Eumeces anthracinus) 

Five-lined skink (Eumeces fasciatus) 

Cave salamander (Eurycea lucifuga) 

Spring peeper (Hyla crucger) 

Gray treefrog (2 versicolor) 

Red-spotted newt (Notophthalmus viridescens) 

Slimy salamander (Plethodon glutinosus) 

Mountain chorus frog (Pseudacris brachyphona) 

Eastern box turtle (Terrapene carolina) 

Garter snake (Thamnophis sirtalis) 

Wood frog (Rana sylvatica) 

" Adapted from Hinkle et al. 1993. 
Greenberg, Cathryn H.; McLeod, Donald E.; Loftis, David L. 1997. An 

old-growth definition for western and mixed mesophytic forests. Gen. Tech. 

Rep. SRS- 16. Asheville, NC: U.S. Department of Agriculture, Forest 

Service, Southern Research Station. 14 p. 

Old-growth mixed and western rnesophytic forest characteristics may include 

high canopy species diversity; uneven-age and size distribution, including 

several old, decadent, large-diameter trees per hectare; low density and high 

basal area of canopy trees; and multiple vegetation strata. Additional indicators 

include the presence of snags and logs in several size and decomposition 

classes; undisturbed soil with no compaction, well-developed organic layer and 

soil macropores; and tree-fall gaps of various sizes and ages. 

Keywords: Forest dynamics, forest structure, mixed mesophytic forests, old 

growth, western mesophytic forests. 
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use management of the Nation" forest resources 

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