United States

Department of Incidence and Impact

Agriculture of Oak Decline

Forest Service

0

CG

in Western Virginia, 1986

Southeastern Forest

Experiment Station Steven W. Oak

Resource Bulletin Cindy M. Huber

SE-1 23 Raymond M. Sheffield
THE AUTHORS

Steven W. Oak and Cindy M. Huber are

plant pathologist and supervisory entomologist,

respectively, Southern Region, Forest Pest

Management, Asheville, NC; and Raymond M.

Sheffield is a resource analyst with the Forest

Inventory and Analysis Work Unit, Southeastern

Forest Experiment Station, Asheville, NC.

November 1991

Southeastern Forest Experiment Station

P.O. Box 2680

Asheville, North Carolina 26802
Incidence and Impact of Oak

Decline in Western Virginia, 1986

Abstract

Oak decline incidence, distribution, and losses in the Northern

Piedmont and Mountain Survey Units of Virginia were estimated

from data collected during a 1986 inventory of Virginia’s forests.

Oak decline occurred on 1.1 million acres, and it was estimated

to cause an annual mortality between 7.4 and 13.8 million cubic

feet since the previous survey in 1977. Incidence and mortalit,y

volume were greatest, in the Northern Mountain Unit. Oak

decline affected about one-fourth of t.he oak stands on National

Forests. Incidence was lower on other ownerships. Analyses

of associations of species composition, site quality, age, and

physiograply with oak decline indicate that hazard rating may

be possible. Highest incidence was associated with average to

poor site quality, advanced stand age, xeric landforms, and

stands with a high percentage of oak. Volume losses were

greatest on high-quality sites and mesic landforms. The site

index/age ratio appears valuable as a measure of physiological

age and may be a better oak decline predictor than either site

index or age alone. Reduced cut,ting, lengthened rotations, and

problems with regenerating oaks are causes for concern, especially

on public land, over whether oaks will be a major component of

new stands on affected areas.

Keywords: Quercus, mortality, volume loss, forest management,

tree age, stand condition, decline.

Introduction

Oak decline is a complex disease involving interactions

between environmental and biological stresses and

subsequent attacks by secondary pests. It causes crown

dieback, reduces radial growth, and kills trees. Species

in the red oak group are damaged more than those in

the white oak group, and black and scarlet oak are most

prone to mortality (Starkey and others 1989).

Since the early 1980’s, reports of oak decline from

Arkansas to Virginia have been increasing (Starkey and

others 1989). Wide distribution, high timber value, and

contributions to wildlife habitat make the oaks the most

important group of upland hardwood tree species in the

Southern United States. More than 65 million acres

of southern timberland (35 percent of the total) are

occupied by upland hardwood forest types in which oak

species predominate (USDA Forest Service 1988). Oak

decline is currently the most widespread disease problem

in southern oak forests, but its distribution and the

timber losses it causes have not been well documented.

The fifth forest inventory of Virginia was conducted

by the Southeastern Forest Experiment Station’s

Forest Inventory and Analysis Work Unit (FIA) in

1986. This inventory provided an opportunity to

estimate oak decline incidence and losses over a wide

geographic area. The objectives of the analyses were:

(1) to determine the geographic distribution of oak

decline in three Survey Units in western Virginia, (2) to

estimate the acreage affected and the volume of timber

killed, and (3) to examine relationships between disease

severity and stand age, sit,e quality, and physiography.

One underlying purpose of the third objective was to

identify promising factors for classifying vulnerability

and risk in oak stands.

Description of Oak Decline

The disease generally progresses slowly over several

years. It begins with a long-term predisposing stress

such as prolonged drought or adva.nced age. Stressed

trees are often subsequently damaged by short-term

inciting factors such as insect defoliation, spring frosts,

or acute drought. In their weakened condition, the t,rees

may be attacked by insects and diseases that normally

do not invade healthy trees (Ma.nion 1981). At this

point, classic decline symptoms appear. The most

visible symptom of decline-affected trees is progressive

dying back from the ends of branches, beginning at the

top and outside of the crown and proceeding downward

and inward. Less noticeable is a reduction, in radial.

growth that may precede crown symptoms by years

or even decades (Tainter and others 1990). Dieback

may continue for several years and often terminates in

mortality of affected trees. Local physiography and

tree species composition may influence the patterns

of damage in affected areas. The most important

underlying factor when resource damage is severe may

be a tree population dominated by senescent overstory

oaks lacking in vigor (Mueller-Dombois and others

1983).

Oak decline can be distinguished from other diseases

by: (1) relatively slow but progressive terminal branch

dieback; (2) branch and bole sprouts and stagheaded

crowns; (3) patterns of mortality related to site features,

tree stress, and attacks of secondary insects and

diseases; and (4) tree mortality usually peaking 2 to

5 years after stress (Wargo and others 1983). These

characteristics were used by FIA crews to identify oak

decline. Only dominant and codominant trees were

considered in order to eliminate symptoms resembling

decline but caused by suppression.
Met hods

FIA crews routinely collect damage data on live trees

and determine cause of mortality for dead trees. The

standard FIA damage code that correlates closest with

oak decline is dieback when it occurs in dominant and

codominant oak (USDA Forest Service 1985). Pest

management specialists provided supplemental training

to field crews to ensure proper and consistent diagnosis.

Normal damage coding procedures were followed, and

dieback was not given priority over other concurrent

damages. Determining the primary cause of mortality

was often difficult in trees that had other damage in

addition to dieback. If trees surrounding a dead oak

displayed decline symptoms, the mortality was coded as

dieback-associated.

The geographic scope of this analysis was limited to the

Northern Mountain, Southern Mountain, and Northern

Piedmont Survey Units. Although a complete statewide

evaluation would have been desirable, the remaining

Coastal Plain and Southern Piedmont Survey Units were

omitted because they were surveyed during the dormant

season, when identification of dieback is putatively less

reliable. Nevertheless, most of Virginia’s hardwood

forest is found in the study area. Sixty percent of the

State’s merchantable hardwood volume grows there.

Softwood volume comprises only one-sixth of the total

inventory in the study area, compared with one-half of

the total in the Southern Piedmont and Coastal Plain

Units (Bechtold and others 1987).

After data collection, plots with forest types dominated

by oaks were segregated from the overall data base. The

type groups of interest were oak-hickory and oak-pine.

The specific types included white oak-red oak-hickory,

chestnut oak, yellow-poplar-white oak-northern red

oak, shortleaf pine-oak, Virginia pine-southern red

oak, white pine-northern red oak-white ash, and

mixed hardwoods. Forest types dominated by pines

and northern hardwoods, such as white pine, shortleaf

pine, and maple-beech-birch, may also contain oaks

subject to decline. These types were excluded from the

analyses because of their relatively small proportions of

oak. From the designated types, plots with damage

and mortality codes attributable to oak decline were

isolated. Decline symptoms were found on 273 plots.

Symptoms ranged from very light (one oak on the plot

with dieback) to very severe (high incidence of mortality

and advanced crown decline). Decline incidence was

used to determine distribution, while the volume loss

associated with oak mortality was used to assess relative

severity. Since subjective evaluation of dieback wan

considered the greatest potential source of error, Forest

Pest Management specialists field-checked 10 percent

of the plots with decline taken by each field crew. This

field check revealed that the crews were proficient

in identifying decline areas; 92 percent of the plots

diagnosed as decline-affected were correctly classified.

2

Results

Estimates of oak decline impacts throughout Virginia

would have been desirable, but our methods do not

permit such estimates. Damage is reported here

only for forested land in the Northern Piedmont,

Northern Mountain, and Southern Mountain Survey

Units of Virginia. Live-tree volume, as used in this

discussion, includes the volume from a l-foot stump to a

4-inch-diameter top (outside bark) for all living trees 5

inches d.b.h. and larger.

Distribution, Incidence, and Volume Losses

Oak forest types were widely distributed across the

study area. Overall, 85 percent of the forested land

was in oak forest types. The Nort,hern Piedmont Unit

had the lowest percentage of oak types (77 percent).

The two Mountain Units had approximately equal

proportions (89 percent in the Northern Mountains; 87

percent in the Southern Mountains). Overall, there were

6.7 million acres of oak forest types in the three Survey

Units.

Oak decline occurred on an estimated 1 .l million acres

in the study area, but it was not uniformally distributed

(fig. 1). More than half of the plots with oak decline

were in the Northern Mountains. Over 650,000 acres, or

30 percent of the area in oak forest types in this Survey

Unit, had decline symptoms. The Southern Mountains

had only 9 percent incidence, despite having a greater

acreage of oak forest. The Northern Piedmont had the

smallest oak forest area (1.8 million acres) and a

decline incidence similar to the Southern Mountains

(11 percent).

Annual mortality in oak forests was high for counties

with concentrations of decline (fig. 2). Oak stands in

Shenandoah County in the Northern Mountain Unit

sustained an average annual loss of 24.9 cubic feet per

acre from 1977 to 1986, the highest in the study area.

Oak stands in the surrounding counties of Frederick,

Warren, Page, and Rockingham had annual volume

losses between 14 and 19 cubic feet per acre (fig. 2).

The only county outside the Northern Mountain Unit

with a similar level of mortality was Montgomery

County in the Southern Mountain Unit. Mortality

volume was low in oak stands in most of the Northern

Piedmont Unit. Only four counties there had annual

mortality volume greater than 3 cubic feet per acre, and

they were all clustered in the northeastern portion of

this Unit.

Affected areas differed from unaffected areas in several

attributes (table 1). They had higher basal area and

volume, were composed of a higher percentage of oak,

and had nearly twice the annual mortality of unaffected

areas. These differences were expected. High basal area

and high volume in affected areas could be caused by
NORTHERN PIEDMONT

Oak Forest = 1,848,903 Acres

Decline Affected = 204,740 Acres

Incidence = 11.1 Percent

NORTHERN MOUNTAINS

Oak Forest = 2,217,285 Acres

Decline Affected = 657,852 Acres

Incidence = 29.7 Percent

SOUTHERN MOUNTAINS

Oak Forest = 2,646,852 Acres

Decline Affected = 241,079 Acres

Incidence = 9.1 Percent

Figure l-Distribution and incidence of oak decline in the Mountain

and Northern Piedmont Survey Units of Virginia, 1986.

Cubic Feet Per Acre

pJ l-3

m 3.1-10

10.1-20

Greater than 20

Not Surveyed

Figure Z-Annual oak decline mortality volume per acre on oak forest types, by county,

for the Mountain and Northern Piedmont Survey Units of Virginia, 1977-1986.

3
age or stand density, or both. Oak decline is more

common in mature overstory trees (usually larger)

than in immature trees (usually smaller), and affected

stands generally are older and have higher volume than

unaffected stands. Basal area and volume differences

could reflect an association between oak decline and

stand density. Decline is stress-mediated and trees in

stands with high basal area and volume may endure

more intense competition for resources during times of

stress. Effects of age, stand density, site quality, and

physiography on decline incidence and severity will be

more fully explored later in this paper.

Oak composition and total annual mortality volume

were closely linked. Nearly all the difference in annual

mortality between affected and unaffected areas was

accounted for by higher oak mortality. Similar amounts

of mortality among non-oak species occurred in affected

and unaffected areas (7.6 and 8.5 cubic feet per acre per

year, respectively), while oak mortality volume was three

times as high in affected as in unaffected areas. Non-oak

species were not dying at higher rates in affected areas

like oak species were.

Large volume losses were associated with oak decline

in the Mountains and Northern Piedmont of Virginia

between 1977 and 1986. The total volume loss in

affected areas was over 29 million cubic feet in the

three Survey Units, with oaks accounting for 20.6

million cubic feet. However, not all of this total can

be attributed to oak decline. The loss caused by oak

decline can be estimated by deducting the oak mortality

volume expected if decline had not occurred. The

difficulty, of course, is that we do not know how much

oak mortality would have occurred in the absence of

oak decline. One estimate of this figure is the oak

mortality volume in unaffected areas. If one assumes

that oak mortality volume per acre in affected areas

would have been the same as in unaffected areas, the

annual loss caused by oak decline in the Mountain and

Northern Piedmont Survey Units during the survey

interval was 13.8 million cubic feet. This assumption,

however, ignores the large difference in initial oak

inventory between affected and unaffected areas. If one

assumes that the percentage loss of oak volume in the

absence of oak decline would have been the same in

affected and unaffected areas, annual decline loss was

7.4 million cubic feet. This estimate does not account

for differences between affected and unaffected areas in

age and site quality that could influence mortality rates.

The actual oak decline loss was probably somewhere

between 7.4 and 13.8 million cubic feet per year.

There were clear differences in oak decline incidence

among land ownership classes. Most of the 1.1 million

acres of decline-affected oak forest was privately owned,

but the incidence of decline was much higher on

National Forests than on other ownerships (table 2).

About one-fourth of the oak stands on National Forest

land had decline damage. Incidence in other public and

private oak stands was 16 and 14 percent, respectively.

The severity of oak decline was also greatest on National

Forest land (table 3). Annual oak mortality on National

Forests in affected areas was 26.9 cubic feet per acre.

This was three-fourths of the total annual mortality

volume on affected National Forest land. Other public

and private ownerships had much lower total annual

mortality than did National Forests, and only two-thirds

of it was oak. Thus, a disproportionately large amount

of the oak mortality in the study area occurred on

National Forests. Forty-two percent of the annual

oak mortality (8.7 million cubic feet) came from the

29 percent of decline-affected acres that occurred on

National Forest land. The variation among ownerships

in the percentage of annual gross growth (annual

mortality volume + net annual volume growth) lost in

decline-affected areas was large. National Forests lost

44 percent of gross growth, and other public ownerships

lost 24 percent. In contrast, the percentage of gross

growth lost in unaffected areas varied little among

ownerships.

Predicting Oak Decline

Six factors that show promise for predicting oak decline

are species composition, site quality, age, site index/age,

physiography, and stand density. In prediction, two

factors must be accounted for: vulnerability and risk of

loss. Vulnerability is the probability of occurrence in a

given stand. The incidence of oak decline by category

provides a measure of relative vulnerability. Risk is

the probability of volume loss if oak decline occurs.

Mortality volume by category provides a measure of

relative risk. We have not attempted to merge these two

components into an oak decline rating system, but we

believe that additional research could lead to such a

system.

Species composition-Individual oak species vary in

their susceptibility to decline. Therefore, it is reasonable

to assume that species composition affects vulnerability

and risk. For analysis, oak forest types were placed in

three type groups: oak-pine, oak-hickory, and chestnut

oak.

In terms of total acreage, most of the oak decline

occurred in the oak-hickory forest type group because

it was by far the most prevalent type group in the
Thousand Acres Percent Incidence

surveyed units (table 4). The chestnut oak type group,

however, was clearly the most vulnerable. Decline

occurred in 28 percent of chestnut oak stands, compared

with only 16 percent of oak-hickory sta.nds. Oak-pine

types had the lowest incidence. Low vulneriibility in

oak-pine types was somewhat unexpected because

oak decline is common under the relatively harsh site

conditions (Starkey and others 1989) typical of oa,k-pine

stands. The amount of oak within forest type groups

influenced vulnerability. The percentage of volume made

up by oaks was consistently higher in affected than in

unaffected stands (table 5).

Although chestnut oak stands were the most vulnerable,

they did not carry the highest risk of loss when decline

occurred (table 5). The oak-hickory type group had

the highest annual oak mortality overall. Further, oak

mortality volume was not much greater in affected

than in unaffected chestnut oak stands. Oak mortality

volume was much larger in affected than in unaffected

oak-hickory stands. Oak-pine types had the lowest

overall loss for affected areas. These results a.re in

general agreement with those of Stringer and others

(1989) and Starkey and others (1989), who reported low

mortality in oak-pine and chestnut oak st,ands, and

greatest losses in red oak-white oak and oak-hickory

stands.

Site quality-oak decline is usually more prevalent

on somewhat dry upland sites, which have relatively

low site indices. This relationship was confirmed by

the analysis of decline incidence by site index (SI)

class, which showed that oak decline vulnerability was

inversely related to SI (fig. 3). Below-average site

qualities (SI < 70 feet) were twice as likely as average

and better sites to be affected (23 vs. 10 percent

incidence). Over one-third of poor-quality sites (SI < 50

feet) had decline.

Despite low vulnerability, high-quality sites had the

highest risk of loss when decline did occur (table 6).

Annual oak mortality on SI > 90 land with decline

was over 30 cubic feet per acre. This loss was over 2

percent of the total 1977 oak volume, and almost 10

times as high as the annual oak mortality on unaffected

high-quality sites. Average and better sites (SI >

70 feet) accounted for about 36 percent of the oak

mortality in affected areas and 33 percent of the affected

acreage.

Age-The incidence of decline increased as age class

increased (fig. 4). Dec ine was present in only 3 percent 1

of the stands < 40 years old, but was in 29 percent

of the stands > 80 years. The average stand age in

unaffected areas was 54 years, while that in affected

areas was 70 years.

3000

2500

2000

1500

1000

500

0

50-69 70-89

Site Index

> 89

25

20

1 5

1 0

5

0

Figure ~-ACES and percentage of oak decline incidence by site

index class in the Mountain and Northern Piedmont Survey

Units of Virginia, 1986.

Thousand ‘Acres Percent Incidence

1800

1600

1400

1200

1000

800

600

400

200

0

m Acres m Incidence

-

< 4 1 41-50 51-60 61-70 71-80 > 80

Age Class

3 5

3 0

2 5

2 0

15

1 0

5

9

Figure d--Acres and percentage of oak decline incidence by

age class in the Mountain and Northern Piedmont Survey Units

of Virginia, 1986.
Decline was observed in 4 percent of the area in the Oto lo-year age class (grouped with other young stands in

fig. 4). Trees of this age are not affected by oak decline,

but stands in this age class often contain some large

trees remaining from the previous mature stand. Decline

symptoms presumably occurred in the scattered old

individuals left after an earlier harvest. This condition

was confirmed by comparing initial (1977) total volume

and initial (1977) basal area for the youngest age

classes. For affected areas, initial volume per acre and

initial basal area per acre in the 0- to lo-year age class

were 431 cubic feet and 52 square feet, respectively. In

the ll- to 20-year age class, both total volume and basal

area per acre were lower (106 cubic feet and 20 square

feet), reflecting the loss of large residual overstory trees.

Old stands carried the highest risk for annual oak

mortality, but the connection between increasing age

and increasing risk did not appear to be as strong as

it was for vulnerability (table 7). Volume losses were

unexpectedly high in the < 40-year age class (again

due to mortality of scattered old residuals), but they

were also higher for the 5I- to 60-year age class than

for either the 61- to 70-year or the 71- to 80-year

classes. Chronological age may not accurately reflect the

physiological condition of trees that are prone to decline

(Manion 1981).

Site Index/Age-Hyink and Zedaker (1987)

characterized senescence as the result of changes in

the efficiencies of water transport and translocation,

hormone balances, and the balance between

photosynthesis and respiration. They described

physiological age as the progression toward critical levels

of these relationships. They detailed the limitations

of chronological age for characterizing senescence and

suggested that a measure of physiological age would be

of greater biological significance than chronological age.

We created an index of physiological age by dividing SI

(an indirect measure of moisture availability and stress

in southern upland hardwood stands) by chronological

age. Thus, 50-year-old oaks growing on poor SI 50 land

(SI/age = 1.0) would be more mature physiologically

than 80-year-old oaks growing on productive SI 90 land

(SI/age = l.l), despite having a lower chronological age.

The distributions of acres by SI/age classes were very

different for affected and unaffected areas (fig. 5).

Unaffected areas were nearly equally partitioned among

the four classes, whereas affected areas were much more

likely to have relatively low ratios. Nearly 60 percent

of the affected acres had a ratio less than 1.0, and 84

percent had ratios less than 1.4.

Low SI/age ratios were associated not only with high

vulnerability but also with high risk of mortality. Where

ratios were < 1.4, annual oa.k mortality volume was

much higher in affected than in unaffected areas (table

8). However, the greatest difference in oak mortality

volume between affected and unaffected areas occurred

where ratios were 1.4 - 2.0. For that SI/age class,

mortality volume was 3.5 times greater in affected than

in unaffected areas.

There was evidence that the low incidence of decline in

the high-ratio classes was due more to young age than

to high SI. Initial basal area and volume were lower

for areas with ratios > 2.0 than for areas with lower

ratios, especially in unaffected areas. If high site quality

was the predominant influence, somewhat higher initial

volumes would have been expected (see table 6).

Physiography-As expected, dry sites had higher

incidence and vulnerability than did more moist sites

(table 9). Forty-four percent of all decline-affected acres

were classed as xeric, though these areas comprised only

30 percent of the area. Mesic landforms had about half

the incidence rate of xeric sites. Mesic sites include

moist mountaintops and slopes (usually coves with

north-to-east aspects and relatively deep, fertile soils),

floodplains, natural stream levees, and valley bottoms.

Percentage of Acres

70

60

50

4 0

3 0

20

1 0

0

r

Oak Decline Status

m Not Affected m Affected

< 1.0 1.0 to 1.3 1.4 to 2.0 > 2.0

Site Index/Age Ratio

Figure 5-Percentage distribution of acres, by site index/age

ratio, for oak decline-affected and-unaffected areas in the

Mountain and Northern Piedmont Survey Units of Virginia,

1986.
Physiography did not appear to have a great influence

on mortality risk, but the difference in annual oak

mortality volume between affected and unaffected areas

was greatest on mesic landforms (table 10). As with the

analyses of losses by forest type, SI, and SI/age, oak

decline losses were greatest when they occurred on more

favorable sites (more mesic landforms).

No decline was detected on hydric landforms, and only a

small amount of oak forest type was found there. Oak

mortality was high on unaffected hydric sites, but dead

trees did not display evidence of prolonged dieback.

Density-Decline is a stress-mediated condition. If

intertree competition is an important contributor to

decline etiology, one would expect affected areas to have

higher initial (1977) basal area and total volume than

unaffected areas. In general, basal area and volume were

higher on affected than on unaffected areas (table 1).

However, prediction of decline incidence and severity

from basal area or volume has limited value because

these stand characteristics depend on many factors,

including stand age, site quality, and previous treatment.

An association between decline vulnerability and stand

density might be indirectly revealed by examining

density characteristics within age and SI categories. Of

the factors included in this work, age class would be

expected to have the greatest effect on density (table 7).

In most age classes, there were only slight differences

in initial basal area and total volume between affected

and unaffected areas. The differences were substantial

only for the < 40-year age class. This result is probably

attributable to decline occurring in a residual overstory

component from an older age class. While intertree

competition may well contribute to occurrence of decline

in individual trees, we conclude from these data that

stand basal area is not a useful predictor of where

decline will occur. However, stand density cannot be

dismissed as a factor until its influence has been isolated

from those of other closely associated variables.

Conclusion

In the Mountain and Northern Piedmont Survey

Units in Virginia, oak decline was the leading cause of

mortality between 1977 and 1986. Our best estimate is

that annual losses due to oak decline averaged between

7.4 and 13.8 million cubic feet during the period.

Bechtold and others (1987) reported that hardwood

mortality increased in Virginia as a whole by 59 percent

since the previous statewide inventory, and that

two-thirds of that increase occurred in the Mountain

Units. Our results show that oak decline is a primary

cause for that increase.

There seems little doubt that drought in the early and

middle 1980’s predisposed the oaks to decline. In the

last few years, rainfall has been adequate, and that

is comforting. We believe, however, that it would be

foolish for forest managers and forest policymakers to

ignore the implications of these findings. There have

been droughts in the past in western Virginia, and there

will be droughts in the future. When they occur, heavy

losses of maturing oaks can be anticipated.

Oak stands on National Forests were particularly prone

to damage, probably because stands there are older,

overall, than other publicly and privately owned stands.

Bechtold and others (1987) reported that public lands

supported a large proportion of the upland hardwood

stands where growth is slow and risk of mortality is

high. The present management direction for National

Forests in the South appears to be toward longer

rotations and less frequent timber harvests. While

this direction may be reasonable given recent public

comment on National Forest Land Management Plans, it

should be recognized that it will lead to very large losses

of oak timber in the long run.

Since this inventory, gypsy moths have overspread most

of the Northern Mountain and Northern Piedmont

Survey Units in Virginia. Area of defoliation has

increased more than a hundredfold from 5,200 acres in

1985 (USDA Forest Service 1986) to 594,000 acres in

1990 (USDA Forest Service, In press). Gypsy moths

attack oaks preferentially (McManus and others 1989),

and defoliation predisposes oaks to decline. The

probability of mortality is especially high for oaks that

are defoliated after decline has begun (Herrick and

Gansner 1987). Thus, losses of oaks in the study area

are likely to continue and even increase.

Our results give no clear indication of how forest

managers should respond to oak decline. Certainly,

oaks are valuable for timber, and they may be even

more valuable for wildlife. Specific research should be

conducted to determine whether oak regeneration occurs

beneath declining trees. We do know, however, that

decline can cause major reductions in the quantity and

quality of acorns produced by affected trees (Gysel

1957; Oak and others 1989). We also know that

reproducing red oaks on good sites requires considerable

care and skill (Loftis 1990). In the absence of specific

information, it may be reasonable to assume that

without management intervention, oak decline and gypsy

moth defoliation will reduce the proportion of oak in the

hardwood stands of western Virginia. We think that

forest managers should address that probability.

7
Our analyses indicate that a system can be developed

for identifying stands that are vulnerable to oak decline.

Factors that create high vulnerability include: (1) a

high proportion of oak in the stand, (2) xeric landforms

and accompanying low SI, and (3) physiological maturity

as expressed by SI/age ratio. In our study, 80 percent of

the declining stands had an %/age ratio lower than 1.4.

While identification of vulnerable stands appears

possible, devising a biologically and socially acceptable

way of treating them will be difficult. Introducing age

diversity would seem prudent. Uneven-aged management

systems are currently favored by most of the vocal

publics, but limited observations of some partial cuts in

vulnerable or damaged stands have revealed continued

or even accelerated decline. When adequate advance oak

reproduction is already present, clearcutting results in a

high proportion of oaks in the new stand (Loftis 1990).

Clearcutting is rejected by many as a management

option, however, particularly on public land. Studies

monitoring the effects of management practices on

decline and oak regeneration are needed.

Literature Cited

Bechtold, William A.; Brown, Mark J.; Tansey, John B.

1987. Virginia’s forests. Resour. Bull. SE95. Asheville,

NC: U.S. Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station. 89 pp.

Gysel, Leslie W. 1957. Acorn production on good, medium,

and poor oak sites in southern Michigan. Journal of

Forestry. 55: 570-574.

Herrick, Gwen W.; Gansner, David A. 1987. Mortality risks

for forest trees threatened with gypsy moth infestation.

Northeastern Forest Experiment Station, RN-338. Broomall,

PA: U.S. Department of Agriculture, Forest Service. 4 pp.

Hyink, D.M.; Zedaker, S.M. 1987. Stand dynamics and the

evaluation of forest decline. Tree Physiology. 3: 17-26.

Loftis, David L. 1990. A shelterwood method for regenerating

red oak in the Southern Appalachians. Forest Science. 36(4):

917-929.

McManus, M.; Schneeberger N.; Reardon, R.; Mason,

G. 1989. Gypsy moth. For. Insect and Dis. Leaf. 162.

Washington, DC: U.S. Department of Agriculture, Forest

Service. 13 pp.

Manion, Paul D. 1981. Tree disease concepts. Englewood Cliffs,

NJ: Prentice-Hall. 399 pp.

Mueller-Dombois, Dieter; Canfield, Joan E.; Hold, R.

Alan; Buelow, Gary P. 1983. Tree group death in North

American and Hawaiian forests: a pathological problem or a

new problem for vegetation ecology? Phytocoenologia. 11:

117-137.

Oak, Steven W.; Starkey, Dale A.; Dabney, Joseph M.

Oak decline alters habitat in southern upland forests.

Proceedings of the annual conference of the Southeast

Association of the Fish and Wildlife Agencies; 1988

November 7-10; Hilton Head, SC. 42: 491-501.

Starkey, Dale A.; Oak, Steven W.; Ryan, George; [and

others]. 1989. Evaluation of oak decline in the South.

Prot. Rep. R8-PR 17. Atlanta, GA: U.S. Department of

Agriculture, Forest Service, Southern Region. 39 pp.

Stringer, Jeffrey W.; Kimmerer, Thomas W.; Overstreet,

John C.; Dunn, James P. 1989. Oak mortality in eastern

Kentucky. Southern Journal of Applied Forestry. 13: 86-91.

Tainter, F.H.; Retzlaff, W.A.; Starkey, D.A.; Oak, S.W.

1990. Decline of radial growth in red oaks is associated with

short-term changes in climate. European Journal of Forest

Pathology. 20: 95-105.

U.S. Department of Agriculture, Forest Service. 1985.

Field instructions for the Southeast. [Unnumbered].

Asheville, NC: U.S. Department of Agriculture, Forest

Service, Southeastern Forest Experiment Station, Forest

Inventory and Analysis Work Unit. 165 pp.

U.S. Department of Agriculture, Forest Service. 1986.

Forest insect and disease conditions in the United States,

1985. [Unnumbered]. Washington, DC: U.S. Department of

Agriculture. 112 pp.

U.S. Department of Agriculture, Forest Service. 1988.

The South’s fourth forest: alternatiws for the future. For.

Resour. Rep. 24. Washington, DC: U.S. Department of

Agriculture. 512 pp.

U.S. Department of Agriculture, Forest Service. [In press].

Forest insect and disease conditions in the United States,

1990. [Unnumbered]. Washington, DC: U.S. Department of

Agriculture.

Wargo, Philip M.; Houston, David R.; LaMadeliene,

Leon A. 1983. Oak decline. For. Insect and Dis. Leaf. 165.

Washington, DC: U.S. Department of Agriculture, Forest

Service. 8 pp.
Table l--Basal area, volume, and annual mortality per acre, by oak decline

status, in the Mountain and Northern Piedmont Survey Units of Virginia

Stand condition

Unaffected Affected

areas areas

All oak

forests

Initial (1977) basal area

Initial (1977) total volume

Initial (1977) oak volume

Total annual mortality

Oak annual mortality

Oak mortality (percent)a

7 3 ft2

1,399 ft3

657 ft3

14.7 ft3

6.2 ft3

.94

90 ft2

1,735 ft3

1,271 ft3

26.3 ft3

la.7 ft3

1.47

76 ft2

1,455 ft3

759 ft3

16.6 ft3

a.2 ft3

1.08

a(Oak annual mortality/Initial oak volume) x 100.

Table 2--Acres in the Mountain and Northern Piedmont Survey Units of Virginia with

oak decline, by ownership

Ownership

Total Oak forest Area affected Oak decline

(all forest types) typesa by oak decline incidence

- - - - - - - - Thousand acres - - - - - - - - Percent

National Forest 1,468.5 1,342.6 323.6 2 4

Other publicb 229.0 199.8 31.2 1 6

PrivateC 6.180.8 59165.8 748.9 1 4

All ownerships 7378.3 6.708.2 19103.7 1 6

aIncludes oak-pine, oak-hickory, and chestnut oak forest types.

b

Small sample size.

'Includes forest industry.
Table s--Initial (1977) volume per acre and annual mortality per acre for oak

decline affected and unaffected areas in the Mountain and Northern Piedmont Survey

Units of Virginia, by ownership

Decline

status Ownership

Initial

basal

area

Initial Annual

volume mortality

Total Oak Total Oak

Square feet - - - - - - Cubic feet - - - - - - - - - -

Unaffected National Forest 7 7 1,434 972 16.4 (28) 10.4

Other public 7 9 1,441 722 13.3 (21) 5.0

Private 7 2 1,389 583 14.4 (22) 5.2

All ownerships 7 3 1,399 657 14.7 (23) 6.2

Affected National Forest 89 1.675 1.313 35.1 (44) 26.9

Other public 98 1,741 1,265 10.6 (24) 6.1

Private 90 1,760 1,254 22.9 (30) 15.5

All ownerships 90 1,735 1,271 26.3 (34) 18.7

Numbers in parentheses are percentage of annual volume of gross growth lost to

mortality.
Table &-Acres in the Mountain and Northern Piedmont Survey Units of

Virginia with oak decline, by forest type group

Forest type

group

Oak forest

types

Acres affected Oak decline

by oak decline incidence

Oak-pine

Oak-hickory

- - - - Thousand acres - - - Percent

677.1 78.4 1 2

51673.7 925.2 1 6

Chestnut oak 357.5 100.1 -28

All types 6.708.3 1,103.7 1 6

Table s--Initial (1977) volume per acre and annual mortality per acre for oak

decline affected and unaffected areas in the Mountain and Northern Piedmont

Survey Units of Virginia, by forest type group

Decline

status

Forest type

group

Initial

basal

area

Initial Annual

volume mortality

Total Oak Total Oak

Unaffected Oak-pine

Oak-hickory

Chestnut oak

All types

- - Square feet - - - - - Cubic feet - - -

7 1 1,319 494 14.4

72 1,394 634 14.6

92 1,673 1,462 18.0

7 3 1,399 657 14.7

- - -

5.1

5.9

12.8

6.2

Affected Oak-pine 7 5 1,326 666 17.5 11.9

Oak-hickory 91 1,780 1,298 27.5 19.5

Chestnut oak 9 4 1,608 1,450 21.3 16.2

All types 90 19735 1,271 26.3 18.7

11
Table 6--Initial (1977) volume per acre and annual mortality per acre for oak

decline affected and unaffected areas in the Mountain and Northern Piedmont

Survey Units of Virginia, by site index

Decline Site

status index

Initial

basal

area

Initial

volume

Total Oak

Annual

mortality

Total Oak

Unaffected < 50

w-69

70-89

L 90

All site indices

Affected < 50

w-69

w-89

-> 90

All site indices

Square feet - -

6 0

69

7 4

86

7 3

8 2

89

- - - - -

~_(___ Cubic feet - - - - -

855 554 7.3 5.2

1.237 763 13.0 7.2

1,466 641 16.1 6.2

1,829 460 18.0 3.5

1,399 657 14.7 6.2

1,355 1,065 21.1 16.7

1,691 1.343 26.0 18.2

1,875 1,224 24.4 18.4

2,428 1,320 54.8 31.1

1,735 1,271 26.3 18.7
Table T--Initial (1977) volume per acre and annual mortality per acre for oak

decline affected and unaffected areas in the Mountain and Northern Piedmont

Survey Units of Virginia, by age class (1986)

Decline

status Age class

Initial

basal

area

Initial Annual

volume mortality

Total Oak Total Oak

Unaffected -< 40

41-50

51-60

61-70

71-80

Square feet - - - - -

- - - Cubic feet - - - - - - -

4 1 675 250 6.5 1.8

76 1,375 447 13.0 2.4

8 3 1,607 665 17.3 6.2

8 6 1,681 833 19.0 9.4

8 9 1,785 990 18.4 9.3

> 80 9 2 1,910 1,149 20.8 11.7

All age classes 7 3 1,399 657 14.7 6.2

Affected -< 40 6 2 1,100 752 15.2 11.3

41-50 78 1,431 757 18.7 17.6

51-60 9 1 1,721 1,252 26.3 20.7

61-70 90 1,739 1,306 26.3 15.9

71-80 8 7 1,700 1,156 24.3 13.9

> 80 98 1,950 1,562 31.3 25.2

All age classes 90 1,735 1,271 26.3 18.7

13
Table 8--Initial (1977) volume per acre and annual mortality per acre for

affected and unaffected oak decline areas in the Mountain and Northern

Piedmont Survey Units of Virginia, by SI/age ratio

Decline SI/age

status ratio

Initial

basal

area

Initial

volume

Total Oak

Annual

mortality

Total Oak

Unaffected < 1.0

~-Square feet - - - - - - Cubic feet ___- - - - - -

84 1,600 1,033 17.8 10.5

Affected

1.0-1.3 88 1,742 808 17.5 7.1

1.4-2.0 77 1,487 480 15.8 4.5

> 2.0 43 755 251 7.5 1.9

All classes 73 1.399 657 14.7 6.2

< 1.0 91 1,728 1,362 27.9 20.0

1.0-1.3 92 1,833 1,311 24.4 19.0

1.4-2.0 87 1,691 867 27.3 15.6

> 2.0 65 1,262 967 5.2 4.1

All classes 90 1,735 1,271 26.3 18.7
Table g--Acres in the Mountain and Northern Piedmont Survey Units of

Virginia with oak decline, by physiographic class

Physiographic Oak

class forest type

Acres affected by Oak decline

oak decline incidence

Xerica

Mesicb

HydricC

- - - - Thousand acres - - - - Percent

1.998.6 484.2 24

4.701.8 619.5 13

7.8 0 0

All classes 6,708.2 19103.7 16

aIncludes dry mountain tops and slopes and other xeric.

b

Includes rolling uplands, mesic mountain tops and slopes, narrow flood

plains, and other mesic.

'Includes deep swamps and small drains that are poorly drained except during

periods of extended drought.

15
Table lo--Initial (1977) volume per acre and annual mortality per acre for

affected and unaffected oak decline areas in the Mountain and Northern

Piedmont Survey Units of Virginia, by physiographic class

Decline

status

Physiographic

class

Initial

basal

area

Initial

volume

Total Oak

Annual

mortality

Total Oak

Unaffected Xeric

Mesic

Hydrica

All classes

Affected Xeric

Mesic

Hydricb

All classes

Square feet - - - - - Cubic feet - - - - - - -

71 1,230 837 15.7 9.3

74 1,461 590 14.2 4.9

84 1,616 657 62.9 44.2

73 1,399 657 14.7 6.2

87 1,536

92 1,887

- - --

90 1,735

1,226

1,306

--

1,271

27.6 20.0

25.3 17.6

-- --

26.3 18.7

"Small sample size.

b No decline-affected area in this class.
r----

--_- ---

I Oak, Steven W.; Huber, Cindy M.; Sheffield, Raymond M. I

/

1991. Incidence and impact of oak decline in western Virginia,

1986. Resour. Bull. SE-123. Asheville, NC: U.S. Department I

of Agriculture, Forest Service, Southeastern Forest Experiment I

I Station. 16 pp. I

Data collected in consecutive forest surveys of Virginia show that I

losses to oak decline from 1977-1986 were between 7.4 and 13.5

million cubic feet per year in the Northern Piedmont and Mountain

I

Survey Units. Losses were greatest in the Northern Mountain Unit. I

The ratio of site index/age appears promising as a predictor of I I

I

oak decline occurrence after severe stress caused by factors like

drought.

i

Keywords: Quercus, mortality, volume loss, forest management,

tree age, stand condition, decline. 1

I - -m--w------------- ------------ - t

Oak, Steven W.; Huber, Cindy M.; Sheffield, Raymond M.

1991. Incidence and impact of oak decline in western Virginia,

19S6. Resour. Bull. SE-123. Asheville, NC: U.S. Department

of Agriculture, Forest Service, Southeastern Forest Experiment

Station. 16 pp.

Data collected in consecutive forest surveys of Virginia show that

losses to oak decline from 1977-1986 were between 7.4 and 13.8

million cubic feet per year in the Northern Piedmont. and Mountain

Survey Units. Losses were greatest in the Northern Slountain Unit.

The ratio of site index/age appears promising as a predictor of

oak decline occurrence after severe stress caused by factors like

drought.

Keywords: Quercus, mortality, volume loss, forest management,

tree age, stand condition, decline.