United States Department of Agriculture

Forest Service Northern Research Station Research Paper NRS-31 June 2018

Characterizing Effects of Prescribed 

Fire on Forest Canopy Cover in the 

George Washington and Jefferson 

National Forests

Jean Lorber, Melissa Thomas-Van Gundy, and Steve Croy
Published by

U.S. FOREST SERVICE

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June 2018

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Manuscript received for publication 16 March 2018

Abstract

On the George Washington and Jefferson National Forests, managers have used prescribed fire 

to create and maintain early-successional and open forest conditions across large areas. We 

used a landscape-scale and image-based approach to assess the extent that prescribed fires, 

including repeated fires, have created these forest conditions and put the results in context 

of the new George Washington National Forest management plan. At the landscape level, 

early-successional forest made up an average of 5 percent of burn unit area after one burn, 9 

percent after two fires, 17 percent after three fires, and 14 percent after four fires. On average 

across all burn unit acreage, open forest made up 5 percent of the area after one burn, 7 percent 

after two burns, 9 percent after three, and 8 percent after four fires. The forest plan desired 

condition of 12 percent of the area in early-successional forest was met after three or four 

fires and was exceeded in some individual burn units. It is harder to achieve open-forest than 

early-successional conditions using prescribed fire alone. We also examined possible drivers of 

canopy gap creation in these forests. Vegetation type and heat load index, a topographic-based 

measure of solar radiation received by a site, were important predictors of where canopy gaps 

formed after prescribed fire.

The Authors

JEAN LORBER is a conservation scientist with the Virginia Chapter of The Nature Conservancy, 

Charlottesville, VA

MELISSA THOMAS-VAN GUNDY is a research forester with USDA Forest Service, Northern 

Research Station in Parsons, WV.

STEVE CROY is a retired ecologist from the USDA Forest Service, George Washington and 

Jefferson National Forests, Roanoke, VA.

Quality Assurance

This publication conforms to the Northern Research Station’s Quality Assurance Implementation 

Plan which requires technical and policy review for all scientific publications produced or funded 

by the Station. The process included blind technical reviews by reviewers who were selected 

by the Assistant Director for Research and unknown to the author. This review policy promotes 

the Forest Service guiding principles of using the best scientific knowledge, striving for quality 

and excellence, maintaining high ethical and professional standards, and being responsible and 

accountable for what we do.

Cover Photo

View of aerial ignition of the Middle Mountain burn unit in 2010. This unit was included the 

analysis reported here, with 7 percent of the area becoming early successional habitat and 2 

percent becoming open forest after one burn. Photo by Sam Lindblom, The Nature Conservancy, 

used with permission.
1

INTRODUCTION

Fire has a long history in the eastern United States, particularly in oak and oak-pine forests 

(Lafon et al. 2017, Patterson 2006). A recent synthesis of the state-of-knowledge on fire in 

the Appalachians describes the fire history as one of frequent burns and spatially extensive in 

areas supporting oak (Quercus) and pine (Pinus) forests (Lafon et al. 2017). Reconstructing 

fire regimes and even basic fire return intervals in the central Appalachian forests is 

substantially hampered by Euro-American settlement and land use. As settlers moved 

west, Native American populations were disrupted by disease, conflict, and displacement 

(Mann 2005, Ruffner and Abrams 2002). As technologies improved, forest harvesting for 

timber, charcoal, and other products accelerated from the colonial era to the 1900s, with 

mountainous areas generally the last to be cleared during this industrial logging period 

(Lewis 1998). These actions largely removed Native Americans, who used fire for a variety 

of reasons, while eliminating much of the fire history recorded by trees. However, isolated 

stands of old, remnant trees still exist in the Appalachian Mountains (Nowacki and Trianosky 

1993), allowing a glimpse of past fire regimes captured in fire scars. For instance, a tree-ring 

study estimated fire-return intervals of about 3 to 15 years in pine-dominated stands in 

Virginia until 1930 (Aldrich et al. 2010). Historically in this area, most fires occurred in the 

dormant season and fire scars across multiple stands demonstrated that area-wide fires spread 

among the pine-dominated ridges (Aldrich et al. 2010). Even shorter return intervals were 

seen in the tree-ring record at another ridge and valley site in Virginia. With a fire chronology 

beginning in 1794, the mean composite fire interval recorded in pines was 2.2 years, mostly 

during the dormant season with larger fires occurring every 12–13 years (Hoss et al. 2008). 

Similarly, at a ridge and valley forest in western Maryland, white (Quercus alba) and chestnut 

oaks (Q. montana) recorded a modal fire interval of about 8 years over a 400-year period, 

with most of those fires in the dormant season (Shumway et al. 2001).

Other less direct evidence exists for fire in the central Appalachians (Lafon et al. 2017). 

Dating of soil charcoal has shown fire to be a driver of vegetation for 4,000 years and that fire 

was not confined to dry oak-pine ridges (Fesenmyer and Christensen 2010). The presence of 

fire-dependent and fire-adapted species is indirect evidence of fire in these forests. Species 

with obvious fire-dependent traits such as serotinous cones (Table Mountain pine [Pinus 

pungens] and pitch pine [P. rigida] in some areas) are found in the central and southern 

Appalachians, including the forests of western Virginia (Della-Bianca 1990, Little and Garrett 

1990). Pitch pine is also one of the few pines that resprout from basal buds after fire. Oak 

species found in the mountain forests of Virginia exhibit many fire-adapted traits (Abrams 

1992). With adaptations to disturbance and water stress, oaks possess traits that enhance 

survival following repeated fire. In general, mature oaks have thick bark (Harmon 1984) 

and deep root systems (Hinckley et al. 1981), and they have the ability to compartmentalize 

stem injury and resist rotting (see Abrams 1990, 1992; and Lorimer 1985 for reviews). Also, 

seedlings can resprout from root collar buds after topkill (Huddle and Pallardy 1999, Peterson 

and Reich 2001, Waldrop and Lloyd 1991) forming advanced regeneration. The presence of 

fire-adapted species in early land surveys has been used to infer the spatial extent of fire as a 

disturbance regime in West Virginia (Thomas-Van Gundy and Nowacki 2013).

The loss of fire as a disturbance agent through deliberate suppression since the 1930s and 

a cultural shift in the importance of fire in hardwood forests have resulted in observable 

change. Eastern forests are shifting in species composition (Dyer 2006, Fei et al. 2011, 
2

Nowacki and Abrams 2015), most noticeably in the understory where shade tolerant and/or 

fire-sensitive species, such as red maple (Acer rubrum), sugar maple (Acer saccharum), and 

blackgum (Nyssa sylvatica), have generally increased in abundance (Steiner et al. 2008). On 

more mesic sites, and some dry sites, shade intolerant, rapidly growing species such as yellowpoplar (Liriodendron tulipifera) and black birch (Betula lenta) often outcompete oaks after 

timber harvest or other canopy disturbance. Where pine species are a component of eastern 

forests, declines in pine regeneration and species composition changes are also occurring, 

particularly in the yellow pines (P. rigida, P. virginiana, P. echinata, and P. pungens) (Harrod 

et al. 1998). In ridgetop pine communities, the Appalachian endemic Table Mountain pine is 

not regenerating in the absence of periodic fire (Williams and Johnson 1990).

The reduction in the fire frequency of eastern oak forests over the past 80 years has meant 

that many of the fire-adapted advantages of oak and pine species are not realized. This is 

essentially the underlying cause driving the “mesophication” of eastern forests (Nowacki and 

Abrams 2008). The result is a positive feedback cycle in which the removal of fire has resulted 

in a landscape that is increasingly fire-proof and less amenable to either the restoration of the 

historic fire regime or the maintenance of oak-dominated forests.

Managers of National Forest System lands in the East are increasing their use of prescribed 

fire to return this historically important disturbance to oak and oak-pine forests (Brose et al. 

2001). Much of this increase is due to information generated from research supported by the 

Joint Fire Science Program and Landscape Fire and Resource Management Planning Tools 

(LANDFIRE) initiated as part of the National Fire Plan after the 2000 fire season. The George 

Washington (GWNF) and Jefferson National Forests (JNF) have a history of prescribed 

fire, with treatment acres expanding annually since 1998. The GWNF Revised Land and 

Resource Management Plan (GWNF Plan) (USDA Forest Service 2014) recognizes the need 

for fire in the restoration and maintenance of oak, oak-pine, and pine forests and woodlands. 

Specifically, fire is to be “used in a controlled, well-planned manner to manage vegetation, 

restore fire-dependent ecosystems and species, create desired wildlife habitat conditions, and 

modify uncharacteristic fuel conditions resulting from extended absence of fire and/or tree 

mortality from nonnative insects and disease” (USDA Forest Service 2014). As stated in the 

GWNF Plan, a fire-return interval of 5 to15 years is desired in oak systems for creating open 

canopy structure and maintaining historic species composition. For pine-dominated systems, 

a target fire-return interval of 3 to 9 years is desired.

In the JNF forest plan (JNF Plan) (USDA Forest Service 2004), forest-wide direction includes 

restoring fire regimes to forests and grasslands within or near the historical range for the 

restoration and maintenance of fire-adapted ecosystems. Objectives for dry and xeric oak 

forests, woodlands, savannas, and xeric pine and pine-oak forests and woodlands call for 

maintaining a prescribed fire cycle of 4 to 12 years (USDA Forest Service 2004). In dry-mesic 

oak forest and dry and dry-mesic oak-pine forest communities, the JNF plan objectives are 

for a burn cycle of 8 to 20 years (USDA Forest Service 2004). Prescribed fires can be used in 

either the growing season or dormant season on both the GWNF and JNF.

The wildlife habitat conditions created through the use of prescribed fire include patches 

of early-successional forest to benefit a variety of animal species. In general, fire increases 

sources of food for browsers and frequent fires favor herbaceous plants over woody ones 

(Van Lear and Harlow 2002). However, burning “for wildlife” is an unclear objective as some 

species do benefit (for example, turkey [Meleagris gallopavo silvestris], white-tailed deer 

[Odocoileus virginianus], reptiles) while others experience negative effects (for example, 

ground nesting birds and salamanders) depending on season of burn and fire intensity 
3

(Harper et al. 2016). In the GWNF and JNF Plans, the goal of creating open canopy structure 

through the use of prescribed fire suggests management for a certain suite of wildlife species. 

For example, these open canopy conditions should benefit songbirds including loggerheaded 

shrike (Lanius ludovicianus), eastern bluebird (Sialia sialis), prairie warbler (Setophaga 

discolor), and various sparrows (Harper et al. 2016). In a study in the mountains of North 

Carolina, researchers found that on sites with high severity fire and mechanical treatments 

of the subcanopy, breeding bird species richness and density were higher compared to other 

treatments, though the treatments may have temporarily reduced habitat for ground nesting 

birds (Greenberg et al. 2013). For wildlife that benefit from fire, which includes many game and 

nongame species, the lack of fire in the forests of the central hardwoods and Appalachians is a 

greater limiting factor than applying fire without knowing the exact fire frequency, severity, or 

seasonality to benefit any given species (Harper et al. 2016).

Along with creating and maintaining an open canopy, returning fire to these forests also 

results in changes to the understory and herbaceous layer. The herbaceous layer is broadly 

defined as the stratum composed of all vascular species that are less than 3 feet in height, 

including tree regeneration, shrubs, graminoids (grasses and sedges), and forbs (Gilliam 

2007). Most of the plant diversity in a forest is found in the herbaceous layer. Since litter from 

herbaceous species often decays faster than tree litter, the herbaceous layer is important in 

nutrient cycling (Gilliam 2007). Creating an open canopy structure through a prescribed fire 

increases the amount of light reaching the forest floor, resulting in changes to the herbaceous 

layer beyond the immediate fire effects to the canopy and subcanopy.

Even a single fire can cause grass species cover to increase depending on landscape position 

(Elliott et al. 1999, Glasgow and Matlack 2007); however, multiple fires are usually needed to 

sustain this change, otherwise the grass-cover increase may disappear within a decade (Elliott 

et al. 2009). Fire generally increases plant species diversity and richness in forests across the 

eastern United States (Bowles et al. 2007; Elliott et al. 1999, 2009; Holzmueller et al. 2009; 

Hutchinson et al. 2005a). Due to their early spring emergence, the abundance or cover of 

spring ephemerals are not significantly impacted by dormant-season prescribed fire (Bowles 

et al. 2007, Kem 2013).

Along with a general increase in grasses, others have found tick-trefoil (Desmodium spp.), 

goldenrod (Solidago spp.), and blueberry (Vaccinium spp.) to be significantly associated 

with sites where multiple prescribed fires have occurred (Holzmueller et al. 2009). In 

addition, others have found sedges (Carex spp.), bearded shorthusk (Brachyelytrum erectum), 

American burnweed (Erechites hieraciifolius), woodland sunflower (Helianthus divaricatus), 

and panic grasses (Panicum boscii, P. commutatum, P. dichotomum) to be associated with sites 

with multiple burns (Hutchinson et al. 2005a). These species, along with species like little 

bluestem (Schizachyrium scoparium), big bluestem (Andropogon gerardii), and Indian grass 

(Sorghastrum nutans) could be used as indicators of success in creating woodland conditions. 

During a field review of some recent prescribed fire units on the GWNF, many savanna or 

woodland-indicator species were noted in the herbaceous layer that had established naturally 

in the areas of multiple prescribed fires. These species included anisescented goldenrod (S. 

odora), roundleaf throughwort (Eupatorium rotundifolium), horseflyweed (Baptisia tinctoria) 

and a hoarypea (Tephrosia spp).1

1 Cecil Frost, Blue Star Consulting, Rougemont, NC; personal communication.
4

Objectives of this Work

Land managers and national forest stakeholders may benefit from knowing how prescribed 

fire on the GWNF and JNF has impacted forest structure and if progress is being made 

toward meeting GWNF forest plan goals. Determining the landscape-scale effects of 

prescribed fire or wildfire can be done through remotely sensed data. One method is the 

calculation of a normalized burn ratio from Landsat imagery taken before and after a fire 

(Key and Benson 2006, Miller and Thode 2007, Wimberly and Reilly 2007). We chose a more 

direct method of determining initial fire effects through the use of digital aerial photography 

to map the creation of canopy gaps (overstory tree mortality) after prescribed fire. In this 

analysis, we document changes in forest structure from prescribed fires and examine these 

changes to determine if structure goals are being achieved. Given the history of prescribed 

fire on the two national forests, we were able to describe the canopy conditions resulting from 

a single prescribed fire, two fires, and three or more fires in the same management unit. In 

this report, we display and discuss: 1) the results of mapping canopy gaps after prescribed fire 

from aerial photography, 2) descriptions of forest structure after prescribed fire from on-theground plot data, and 3) an analysis of factors associated with canopy gap creation.

Canopy mortality pattern resulting from the Falling Rock wildfire in the James River Face Wilderness in 

April of 2010. The photo was taken about 3 months after the fire. The reference conditions and goals for the 

prescribed fire program on the two national forests are based on recreating these patterns. Photo by Steve 

Croy, retired, USDA Forest Service.
5

METHODS

Study Area

All examined burns units were located in the GWNF and JNF, in Virginia, West Virginia, 

and Kentucky (Fig. 1). The GWNF covers 1.1 million acres and is primarily located in the 

Northern Ridge and Valley physiographic section with its eastern portion located in the 

Blue Ridge Mountains section. The Northern Ridge and Valley section is characterized by 

long, parallel ridges of sandstone parent materials, interspersed with valleys of limestone 

parent materials (Cleland et al. 2007). The JNF covers 0.8 million acres and is primarily 

located in the Northern Ridge and Valley section, with portions in the Northern Cumberland 

Mountains in the west. Over the last 25 years, the region around the GWNF and JNF 

averaged around 40 inches of precipitation annually, spread relatively evenly throughout the 

year. The frost-free period is typically mid-April to mid-October (NOAA 2016).

Seventy-five burn units were examined, covering over 85,000 acres (see appendix 1 for 

details about individual burn units used in this analysis). These 75 units experienced a total 

of 117 burn events, primarily from the late 1990s through 2014. None of these units showed 

evidence of widespread tree mortality or disturbance prior to known burn event(s) based 

on review of preburn aerial photography. Only burn units over 250 acres were included in 

our examination, as larger-scale burns allow for a greater possible expression of landscapemediated fire effects; the median unit size was 743 acres.

Figure 1.—Location of the George Washington and Jefferson National Forests in relation to physiographic provinces. 

Burn units that were examined are shown in red. 
6

All burns were conducted during the end of the dormant season or early in the growing 

season, typically during April and May. Smaller units (<500 acres) were typically handignited. Larger units were hand-ignited along the perimeter, followed by aerial ignition of the 

interior. Ignition was usually finished in 1 day, although several of the largest units (>2,000 

acres) continued to burn for several days after ignition.

Ecological communities within the burn units represented the full range of the Appalachian 

forest. The primary matrix-forming forest was dry to dry-mesic mixed oak stands, composed 

of chestnut oak, northern red oak (Q. rubra), scarlet oak (Q. coccinea), and white oak. On 

more xeric ridgetops or southwestern slopes, large patches of pitch pine and Table Mountain 

pine were found. The most common community on the GWNF is oak forest and woodlands, 

comprising 756,000 acres or 64 percent of total area (USDA Forest Service 2014, see Table 

2-3).

GIS Canopy Cover Assessment

We defined three levels of live canopy cover using thresholds adapted from the GWNF Plan 

representing the desired canopy structures (Table 1): EARLY, OPEN, and CLOSED. We made 

adjustments to the categories of EARLY and OPEN since they overlapped as described in 

the GWNF Plan. We defined the minimum basal area for OPEN as 30 ft2/acre, more in the 

range of residual basal area for a two-aged stand (Miller et al. 2006). This minimum basal area 

translates to a minimum canopy closure of 39 percent (using Buckley et al. 1999), which we 

rounded up to 40 percent. The maximum canopy closure for OPEN was left unchanged at 60 

percent.

The next adjustment was to transform the canopy closure into canopy cover, as the latter most 

accurately describes the metric obtained when using overhead imagery (Korhonnen et al. 

2006). Using Fiala et al. 2006, we adjusted canopy closure values for OPEN downward by a 

conservative 10 percentage points for a final range of 30–50 percent canopy cover. We defined 

canopy closure for EARLY as less than 30 percent cover.

Using these categories, author Lorber examined leaf-on imagery from 2003 to 2016 (Farm 

Services Agency 2013 through 2016); imagery covered both preburn and post-burn time 

periods for each burn. Using ArcMap 10.2 (ESRI 2013), all imagery was examined at a 

Table 1.—Canopy cover thresholds and desired conditions, adapted from Table 2-4 of the 

George Washington National Forest’s 2014 Revised Land and Resource Management Plan 

(USDA Forest Service 2014). Landscape targets apply to oak-dominated community types.

Defined 

thresholds

Forest canopy 

condition Description

Desired portion 

of landscape

EARLY

Adjusted canopy 

cover of <30%

Early successional or 

regenerating forest

Stands developing after a major 

disturbance or timber harvest, 

generally less than 11 years in age in 

the most common systems, but can 

be up to 35 years

12%

OPEN

Adjusted canopy 

cover of 30–50%

Mid- or latesuccessional open 

canopy forest

Stands beyond regeneration that 

stay in a relatively open canopy 

(canopy closure of 25–60%)

67%

CLOSED

Adjusted canopy 

cover >50%

Mid- or latesuccessional closed 

canopy forest

Stands...with a largely closed canopy 

(all layers) greater than 60%, includes 

natural canopy gaps

21%
7

scale of 1:5000; any visually distinct area showing canopy mortality was hand-digitized and 

classified as EARLY or OPEN (Figs. 2 and 3). The remainder of the burn unit was considered 

CLOSED. For most burn events, several years of post-burn imagery were assessed to 

account for delayed tree mortality (Yaussy and Waldrop 2010). Patches of canopy mortality, 

or canopy gaps, smaller than 0.25 acres were not readily detectible, making this size the 

default threshold for gap detection. Areas of EARLY or OPEN conditions existing in preburn 

imagery, typically rock outcrops or barrens, were ignored for this analysis. Young forest 

was considered EARLY only if it was clear that fire killed the canopy, thus creating new 

EARLY forest. To minimize variability, one person digitized all gaps and relied on cover class 

estimation guides for calibration (NWCG 2017).

Units with multiple known burns predating the imagery were still included; however, canopy 

gaps could not be attributed to a specific burn. Therefore, the record of canopy gap formation 

was left incomplete (e.g., no first burn results), beginning only with the first prescribed burn 

that occurred when imagery was available.

Multiple sources of information about biotic and abiotic conditions within the burn units 

were compiled in ArcMap 10.2 (ESRI 2013) to describe the types of forests in which the 

EARLY and OPEN conditions were created. Current vegetation and stand age were obtained 

from the Field Sampled Vegetation (FSVeg) database, the stand-level database maintained 

by the Forest Service (https://www.fs.fed.us/nrm/). For the potential vegetation types, the 

ecological zones (ecozones) models developed for the GWNF (Simon 2011) and the JNF 

(Simon 2013) were used. These models integrated a suite of abiotic and biotic factors to 

predict the potential vegetation types at a 10-m pixel scale. For our analysis, the FSVeg forest 

type categories and ecozones were grouped along a gradient of site productivity and moisture 

(appendixes 2 and 3).

Heat load index (HLI) (Evans 2014) was calculated for the study area from a 30-m digital 

elevation model. This index incorporates latitude, slope, and aspect to estimate annual solar 

radiation at a given point. HLI has been shown to be related to fire effects and fire severity 

(Arkle et al. 2012, Holden et al. 2009) and was used to describe patterns of canopy creation.

Plot Data

On-the-ground data from within the burn units were used to validate the results of the 

GIS-based canopy classification. Data were obtained from a vegetation monitoring dataset 

maintained by the Central Appalachian Fire Learning Network (FLN; https://www.

conservationgateway.org/ConservationPractices/FireLandscapes/FireLearningNetwork/

RegionalNetworks/Pages/CentralApps.aspx). The FLN has been monitoring over 300 plots 

since 2008, sampling several layers of vegetation at each plot both before and after prescribed 

burn treatments. Plots were established in burn units on both George Washington and 

Jefferson National Forests, located randomly in ArcGIS using Hawth’s tools (Beyer 2004). 

Plots were established at least 100 feet from a road or trail and 100 feet apart to avoid 

duplicate sampling. Plot centers were georeferenced in the field with a handheld global 

positioning system unit and marked with steel rebar. The 80 plots that were examined in this 

study included all plots that had been burned once and that had both preburn and post-burn 

data.

The plots had a nested design with subsampling to capture the condition of the overstory, 

midstory and understory. The overstory was sampled using a variable-radius BAF 10 prism 

at the nested plot center to determine the basal area of live and dead trees >5 inches diameter 

at breast height (d.b.h.). The midstory was sampled using a 0.01-acre circular plot (radius 
8

Figure 2.—Example of canopy 

gap delineation using post-burn, 

leaf-on imagery from the National 

Agricultural Imagery Program (A). 

Gap boundaries are superimposed 

on preburn imagery (B).

Figure 3.—Example of burn unit canopy 

assessment showing the three mapped 

canopy conditions.
9

of 11.8 feet), in which all woody tree and shrub stems >3.3 feet tall were counted and their 

d.b.h. recorded in two size classes: <1 inch and 1-4 inches. Canopy cover was also estimated 

from this plot center: the presence or absence of overhead cover (>5 feet tall) was determined 

at five points along each of four transects (20 points total) located in the cardinal directions 

from each plot center using a sighting tube (densitometer). Canopy cover was then calculated 

as the percentage of the 20 points where overhead cover was present. The understory was 

sampled within four, 10.75-square feet subplots located 11.8 feet from plot center in four 

cardinal directions. For analysis purposes, data from the four subsamples were averaged for 

a single plot value. In these quadrats, all woody stems 0.5 to 3.3 feet in height were counted 

and the percentage spatial cover (above ground, not basal) of graminoids, forbs, woody trees/

shrubs, woody vines, and nonnative invasive species was estimated using seven cover classes 

(0–1 percent, 1–5 percent, 5–25 percent, 25–50 percent, 50–75 percent, 75–95 percent, 

95–100 percent) and then converted to the midpoint of each class.

The plots were assigned to one of the three canopy conditions—EARLY, OPEN, or CLOSED 

—after examination of leaf-on imagery as described above. Photo-point monitoring of the 

FLN plots provides examples of these three canopy conditions and the pre-burn condition. 

Figure 4 shows an example of a plot that transitioned from a CLOSED-canopy before a 

prescribed fire to an EARLY-successional forest. Figure 5 shows a plot that transitioned from 

a CLOSED-canopy before a prescribed fire to an OPEN-canopy. Figure 6 shows an example 

of a plot that remained in CLOSED canopy conditions after fire.

Figure 4.—Photo of a CLOSED canopy plot (A) that became 

EARLY successional after one burn (B) (North Fork Pound, 

plot 1-6). Note the overhead canopy gap photo inset in B.

Figure 5.—Example of a CLOSED canopy plot (A) that 

became OPEN canopy after one burn (B) (North Fork Pound, 

plot 1-4). Note the overhead canopy gap photo inset in B.
10

Analysis

To determine whether repeated burning had an effect on forest structure, we first calculated 

the percentage of the unit that was in an EARLY or OPEN condition after each successive 

burn. These percentages were averaged by burn history category (e.g., one burn, two burns, 

etc.), with each burn unit serving as an equally-weighted sample. We also calculated the mean 

and median gap size for EARLY and OPEN conditions by burn history category. All summary 

statistics and comparative tests were conducted using JMP® software (SAS 2013).

We conducted a means-separation test for percentage EARLY and percentage OPEN for all 

pairwise comparisons of burn history categories (e.g., one burn versus two burns). Due to 

unequal sample sizes among the categories, we used Tukey’s Honestly Significant Different 

(HSD) test, which is a conservative test of means separation in this circumstance. Tukey’s 

HSD test assumes a comparison of independent datasets, which is not completely accurate in 

this case; some burn units are found in several burn history categories (see Table 2).

In addition, we conducted a matched-pairs analysis, using only those burn units common to 

multiple burn history categories (Table 2). The inferential power of this approach is superior 

as it focuses on the same set of burn units, before and after a specific burn. We used a paired 

t-test to determine whether the post-burn percentages of EARLY and OPEN were different 

from pre-burn amounts.

Figure 6.—Example of a CLOSED canopy plot (A) that 

remained CLOSED after one burn (B) (North Fork Pound, plot 

2-2). Note the overhead canopy gap photo inset in B.
11

To determine whether the GIS-mapped canopy condition represented different on-theground conditions after one burn, we grouped the 80 FLN plots based on the three GISmapped conditions (EARLY, OPEN, or CLOSED) at plot center. We then calculated mean 

values for several common metrics of forest structure and conducted a means-separation test 

of all three canopy conditions. Due to unequal sample sizes among the categories, we used 

Tukey’s HSD test.

To identify possible drivers of EARLY and OPEN creation after a first burn, we examined the 

effects of HLI, FSVeg forest type, and ecozone type on the amount of gap (EARLY or OPEN) 

formation. For the seven ecozones and six FSVeg forest type categories, we calculated the 

percentage of area in each unit that became EARLY and OPEN. Categories with less than 10 

acres in a burn unit were omitted from the analysis.

For HLI, we conducted a simple polynomial regression of HLI and percentage of area in gaps 

(EARLY and OPEN combined) for units in the Northern Ridge and Valley section, testing 

for model significance and fit-of-model (SAS 2013). For FSVeg forest type and ecozones , we 

conducted an overall test for significance using a one-way ANOVA of the mean percentages 

of post-burn EARLY, OPEN, and EARLY+OPEN (SAS 2013). We also conducted a meansseparation test on the categories of each variable using Tukey’s HSD test.

RESULTS

Creation of Canopy Gaps

After a single burn, an average of 5 percent of the burn area was classified as EARLY and an 

average of 5 percent was classified as OPEN. There was large variability among burn units, 

ranging from 0 to 40 percent in EARLY and 0 to 34 percent in OPEN (Table 3 and Fig. 7). 

The maximum amount of combined EARLY and OPEN in an individual burn unit was 54 

percent of the unit area. Mean gap size after one fire was 7 acres for EARLY and 5 acres for 

OPEN (Table 4). There was great variation in gap size for both canopy conditions although 

median gap sizes were the same at 3 acres for both EARLY and OPEN conditions. However, 

91 percent of the area in EARLY gaps and 85 percent of the area in OPEN gaps occurred in 

gaps that were greater than or equal to their respective median gap size.

After two fires, an average of 9 percent of the burn area was classified as EARLY and 7 percent 

was classified as OPEN (Table 3, Fig. 7). Here again there was large variability among burn 

units, with the portion of EARLY conditions ranging from 0 to 52 percent, and a range of 

0 to 24 classified as OPEN. The maximum amount of combined EARLY and OPEN in an 

individual unit was 64 percent of unit area. The mean size of gaps was 7 acres (EARLY) and 4 

acres (OPEN) (Table 4). The median EARLY gap size was 2 acres with 92 percent of the gap 

acreage occurring in gaps greater than or equal to 2 acres and the median OPEN gap size was 

also 2 acres with 84 percent of gap area occurring in gaps greater than or equal to this.

Table 2.—Burn units used in canopy gap analysis, categorized by burn history

Burn history 

category

Number 

of units

Area 

(acres)

Units in 

common with 

1 burn

Units in 

common with 2 

burns

Units in 

common with 

3 burns

Units in 

common with 

4 burns

1 burn 58 69,707 all 24 6 1

2 burns 36 33,946 all 10 4

3 burns 15 14,204 all 7

4 burns 7 4,566 all
12

Table 4.—Attributes of EARLY canopy gaps and OPEN canopy gaps, by burn history category

Burn history 

category

EARLY OPEN

Mean 

gap size 

(acres)

Median 

gap size 

(acres)

Percentage of gap 

acreage ≥ median 

gap size

Mean 

gap size 

(acres)

Median 

gap size 

(acres)

Percentage of gap 

acreage ≥ median 

gap size

1 burn 7 3 91 5 3 85

2 burns 7 2 92 4 2 84

3 burns 14 3 95 5 3 86

4 burns 8 2 94 5 3 84

Table 3.—Mean percentage (± one standard error) of burn unit area 

classified as EARLY canopy gaps, OPEN canopy gaps, and combined gaps, 

by burn history category. Means in a column followed by the same letter 

are not statistically different (Tukey’s HSD, p=0.05).

Burn history 

category

Mean percentage 

EARLY ± SE

(range)

Mean percentage 

OPEN ± SE

(range)

Mean percentage 

ALL GAPS ± SE

(range)

1 burn 5 ± 1 a 

(0–40) 

5 ± 1 a

(0–34)

11 ± 2 a

(0–54)

2 burns 9 ± 2 ab

(0–52)

7 ± 1 a

(0–24)

16 ± 3 ab

(0–64) 

3 burns 17 ± 5 b

(0–54)

9 ± 1 a

(1–16)

26 ± 6 b

(2–64)

4 burns 14 ± 7 ab

(1–54)

8 ± 2 a

(1–14)

22 ± 8 ab

(8–64)

Figure 7.—Percentage of burn area 

in EARLY or OPEN gap formation 

after prescribed burning, by burn 

history category. The mean value 

of each burn/canopy combination 

is denoted by a red line, the black 

line is the median. The 90th and 

10th percentiles are defined by the 

bars and dots represent outliers.

1 burn 2 burns 3 burns 4 burns
13

For units in the three-burn category, a mean of 17 percent of the area was classified as EARLY, 

with a range of 0 to 54 percent. Nine percent was categorized as OPEN conditions with a 

range of 1 to 16 percent (Table 3 and Fig. 7). The maximum amount of combined EARLY and 

OPEN in an individual unit was 64 percent of unit area. Mean gap size in EARLY was 14 acres 

and OPEN was 5 acres (Table 4). Median gap sizes in these units were 3 acres for EARLY and 

3 acres for OPEN conditions, with 95 percent and 86 percent of gap acreage occurring in gaps 

greater than or equal to these respective medians (Table 4).

For the units in the four-burn category, the mean percentage of area in EARLY conditions 

was 14 percent with a range of 1 to 54 percent—similar to units in the three-burn category. 

An average of 8 percent of the area was classified as OPEN conditions, with a range of 1 to 14 

percent, also similar to the three-burn category (Table 3 and Fig. 7). The maximum amount 

of combined EARLY and OPEN in an individual unit was 64 percent of unit acreage. Mean 

canopy gap sizes were smaller than the three-burn category for both EARLY (8 acres) and 

OPEN (5 acres) conditions (Table 4), although the means were not compared statistically 

due to the low number of units. Median gap size was similar to all burn classes at 2 acres for 

EARLY and 3 acres for OPEN, with 94 percent and 84 percent of the acreage within gaps 

greater than or equal to the respective medians (Table 4).

In the creation of EARLY canopy gaps, significantly more area was created with three burns 

than with a single burn; this was the only significant pairwise comparison (p=0.012). Mean 

EARLY gap size was also greatest in the three-burn category. There were no statistically 

significant differences for the creation of OPEN canopy gaps across burn categories, when 

examined as a percentage of the burn units (Table 3).

Changes in the area of EARLY and OPEN forest were sometimes seen between preburn 

and post-burn in units that were burned multiple times (matched pairs tracked through 

time) (Table 5). Following 23 burn units from post-first burn to post-second burn, the 

area of EARLY forest increased significantly (6 percent versus 10 percent of unit acreage, 

respectively), but the area of OPEN forest did not increase significantly (5 percent versus 

6 percent of unit acreage, respectively). For the 10 burn units where conditions from postsecond burn to post-third burn were compared, EARLY forest area increased significantly (17 

percent versus 18 percent of unit acreage, respectively), but OPEN forest did not increase. No 

differences in EARLY or OPEN were seen for the six burn units from post-first burn to postthird burn. In this case, we think the small sample size and large variability overwhelmed any 

actual changes that occurred (Table 5).

Table 5.—Matched-pairs analysis of canopy gap formation within the 

same burn units. In each pairwise comparison, means (± one standard 

error) in a column followed by the same letter are not statistically 

different (paired t-test, p=0.05).

Burn history 

category

Total area 

(acres)

Mean percentage 

EARLY ± SE

Mean percentage 

OPEN ± SE

1 burn (n=24)

24,810

5 ± 2 a 5 ± 1 a

2 burns (n=24) 10 ± 3 b 6 ± 1 a

2 burns (n=10)

8,360

17 ± 6 a 8 ± 1 a

3 burns (n=10) 18 ± 6 b 9 ± 1 a

1 burn (n=6) 5,35615 ± 7 a 10 ± 5 a

3 burns (n=6) 25 ± 10 a 9 ± 2 a
14

Field Verification of Canopy Gap Structure

Field data collected 1 year after a burn verified the accuracy of GIS-mapped canopy 

conditions; mean forest structure metrics differed among plots considered EARLY, OPEN and 

CLOSED (Table 6). Basal area in EARLY plots averaged 18 ft2/acre, OPEN plots averaged 56 

ft2/acre, and CLOSED plots averaged 83 ft2/acre of basal area. Similarly, there are fewer stems 

per acre in the mid-story of the EARLY and OPEN plots than the CLOSED plots, with OPEN 

plots differing significantly from CLOSED (Table 6). However, because of high variability 

among burn units, differences between OPEN and EARLY were not statistically significant. 

Large numbers of live stems 0.5 to 3.3 feet tall were found in the understory of EARLY and 

OPEN plots, with more than three times the number of stems per acre of CLOSED plots 

(Table 6). The numbers of taller understory stems (less than 1 inch d.b.h.) were similar for 

all canopy conditions, but greater numbers were found in OPEN plots. Nonwoody vegetative 

cover did not vary by canopy condition, with values ranging from 1 to 9 percent.

Drivers of EARLY and OPEN Conditions

The creation of EARLY and OPEN canopy conditions described above pertains to all ecozone 

and FSVeg forest types combined. To begin determining drivers of canopy mortality from 

prescribed fire, we compared the creation of EARLY and OPEN canopy conditions by 

ecozone (Table 7 and Fig. 8) and by current FSVeg forest type (Table 8 and Fig. 9). Ecozone 

was statistically related to the area of combined EARLY and OPEN conditions (canopy gaps) 

found after the first prescribed burn in a burn unit (p<0.0001). The overall trend was greater 

area of canopy gaps created in more xeric ecozones (Table 7, Fig. 8). For instance, 22 percent 

of the dry pine/oak ecozone area was converted to a canopy gap (percentage of all gaps), 

while only 3 percent of cove area experienced sufficient canopy mortality to create canopy 

gaps. The percentage of canopy gaps in the dry pine/oak was statistically greater than all other 

categories except barrens (13 percent). When EARLY and OPEN conditions were considered 

Table 6.—Forest structure attributes 1 year after the first prescribed burn, by postburn canopy condition, as determined using GIS methodology. Means (± one standard 

error) in the same row that are followed by the same letter are not statistically different 

(Tukey’s HSD, p=0.05).

Sampling 

strata Attribute

Canopy condition

EARLY (n=10) OPEN (n=10) CLOSED (n=60)

Overstory

Live basal area 

(ft2/acre)

18 ± 6 a 56 ± 9 b 83±4 c

Canopy cover (%) 26 ± 8 a 68± 7 b 87± 3 c

Mid-story

Live woody stems/acre 

(1–4 inch d.b.h.)

11 ± 11 ab 0 a 214± 37 b

Understory

Live woody stems/acre 

(<1 inch d.b.h. and >3.3 

ft tall) 

1,800 ± 392 a 2,180± 630 a 1,136± 243a

Live woody stems/acre 

(0.5–3.3 ft tall)

170,758 ± 

36,720 a

150,141 ± 

35,749 a

47,535 ± 

5,787 b

Nonwoody vegetative 

cover (%) (<3.3 ft)

7 ± 3 a 1 ± 0.3 a 9 ± 3 a
15

individually, the trends are similar for the combined gaps, although fewer of the means 

separation tests are significant.

FSVeg forest type was statistically related to the area of combined EARLY and OPEN 

conditions found after the first prescribed burn (p< 0.0001). Like the ecozones, greater areas 

of canopy gaps were created in the more xeric forest types (Table 8, Fig. 9). For instance, 22 

percent of dry pine/oak acreage became a canopy gap, while only 5 percent of cove acreage 

became a canopy gap. The percentage of canopy gaps in dry pine/oak was statistically greater 

than all other categories except dry oak heath (14 percent). When EARLY and OPEN 

conditions were considered individually, these trends basically are the same, although fewer 

of the means separation tests are significant.

The topographic variable HLI was a strong predictor of the area of combined EARLY 

and OPEN conditions (canopy gaps) found after the first prescribed burn (Fig. 10). The 

percentage of area in canopy gaps increased with increasing HLI, best described by a 

quadratic model, which was significant and had an adjusted R-squared value of 0.939.

Table 7.—Mean percentage of area in EARLY and OPEN forest after one 

prescribed burn by ecozone. Means in the same column that are followed by the 

same letter are not statistically different (Tukey’s HSD, p=0.05). Any ecozone 

group with <10 acres in a burn unit was omitted from the dataset.

Ecozone group

Mean percentage 

EARLY

Mean percentage 

OPEN

Mean percentage 

ALL GAPS

Barrens (n=15) 7 ab 6 abc 13 abc

Dry pine/oak (n=38) 14 b 9 c 22 c

Dry oak heath (n=59) 7 a 7 bc 14 b

Dry-mesic oak (n=57) 4 a 5 abc 9 ab

Mesic oak (n=48) 4 a 4 ab 8 ab

Cove (n=55) 2 a 1 a 3 a

Floodplains (n=18) 0 a 0 a 0 a

Figure 8.—Percentage of 

EARLY and OPEN canopy after 

one prescribed burn (n=59), 

by ecozone group. The 

mean value of each ecozone 

group/canopy combination 

is denoted by a red line, the 

black line is the median. The 

90th and 10th percentiles are 

defined by the bars and dots 

represent outliers. 
16

Table 8.—Mean percentage of total area in EARLY and OPEN forest after one 

prescribed burn by current FSVeg forest type. Means in the same column that are 

followed by the same letter are not statistically different (Tukey’s HSD, p=0.05).

FSVeg forest type 

Mean percentage 

EARLY

Mean percentage 

OPEN

Mean percentage 

ALL GAPS

Barrens (n=7) 0 b 1 ab 1 a

Dry pine/oak (n=31) 12 a 10 a 22 b

Dry oak heath (n=46) 9 ab 6 ab 14 ab

Dry-mesic oak (n=35) 4 b 5 ab 9 a

Mesic oak (n=57) 3 b 4 b 7 a

Cove (n=20) 2 b 3b 5 a

Figure 9. Percentage of EARLY 

and OPEN canopy forest in 

units after one prescribed burn 

(n=59), by FSVeg forest type 

(FSVeg group). The mean value 

of each FSVeg group/canopy 

combination is denoted by a red 

line, the black line is the median. 

The 90th and 10th percentiles 

are defined by the bars and dots 

represent outliers. 

Figure 10.—The percentage of 

area in canopy gaps (dots) by heat 

load index (HLI), fit to a quadratic 

model (solid line). The relationship 

between the amounts of area in 

canopy gaps created after one 

burn across HLI, a measure of 

a sites’ exposure, is linear to an 

inflection point and then stabilizes. 

The relationship was significant 

and had an adjusted R-squared 

value of 0.939.
17

DISCUSSION

Our primary goal was to quantify the scale of change displayed over many large prescribed 

burns that represent the modern burning program on the two national forests. This new 

landscape-scale dataset can inform monitoring and research on vegetation and wildlife in 

EARLY and OPEN habitat areas created by prescribed fire. In addition, this dataset is unique 

for the eastern oak and oak-pine forests and could be a source of information for other 

assessments and research into fire effects.

On average, these burn units have been moderately affected by fire, becoming more 

heterogeneous in terms of forest structure and age. Depending on the number of burns, 

an average 11 percent (1 burn category) to 26 percent (3 burns category) of the burn unit 

became newly-created EARLY and OPEN forest (Table 3). These new canopy gaps were also 

created at a biologically-meaningful scale: most gap acreage occurred in patches greater 

than 2 acres (Table 4). In these larger canopy gaps, the increase in light reaching the forest 

floor should create a mix of grasses, forbs, and shrubs, helping achieve ecosystem restoration 

and wildlife habitat goals, including early-successional habitat for many bird species 

(Harper et al. 2016). These gaps also appear suitable for regeneration of shade intolerant 

and intermediate tolerant species such as oaks. Silvicultural guidelines for group selection 

methods give a minimum size range for gaps as 0.1 to 0.6 acres, and caution that smaller gaps 

likely close quicker depending on site quality (Johnson et al. 2009). It should be noted that 

the range of results from individual burns was quite variable (see Figs. 8 and 9) and likely 

related to site-level factors such as fuel, weather, and ignition patterns. For example, the first 

burn of the Grindstone unit (in 2006) resulted in no visible canopy gaps, while the first burn 

of the nearby Hone Quarry unit (in 1999) resulted in 40 percent of its acreage becoming 

EARLY.

Our analysis also showed that repeated burning did not necessarily result in increasing 

amounts of canopy gaps. Considering only those units that could be tracked over multiple 

burns (Table 5), the area of OPEN forest did not increase after any additional burns. The 

amount of EARLY forest did increase from one to two burns and from two to three burns, 

but only slightly. Considering both canopy gap categories together (Table 3), units with one 

burn had a statistically equal percentage of area in canopy gaps compared to units with two 

or four burns (11 percent versus 16 and 22 percent, respectively). Comparing these results to 

the existing body of prescribed fire research is difficult, due to methodological differences. 

Our use of a landscape-scale assessment is quite different from the plot-based research being 

conducted in the region. Our approach was less quantitative, but more spatially extensive; we 

broadly categorized post-burn structure, but assessed over 85,000 acres.

Methodology aside, our results agree with much of the stand-level or plot-based assessments. 

The fire effects documented here can be characterized as low to mixed severity. A fire is 

considered to be low severity if less than 25 percent of the dominant vegetation is consumed 

or killed directly by fire; mixed severity fire effects are defined as 25–75 percent mortality of 

dominant vegetation (Hann et al. 2008). In Ohio, multiple prescribed fires had little effect 

on the density and basal area of larger trees (Hutchinson et al. 2005b), and similar results 

occurred after two prescribed fires in West Virginia (Schuler et al. 2013). In other stand-level 

assessments, prescribed fire had little impact of first-year survival however, delayed mortality 

of overstory trees was documented for 4 to 5 years after the prescribed fire or fires (Waldrop 

et al 2008, Yaussy and Waldrop 2010). Predictably, mortality was related d.b.h and bark 

thickness and trees with low vigor preburn were more likely to die within the 4 year study 

period (Yaussy and Waldrop 2010). Note that when making these comparisons the purposes 
18

of the prescribed fires and the burn unit sizes in our analysis were much different than most 

of the plot-level/stand-level studies. Much of the current research is on prescribed fire as a 

silvicultural tool to promote oak regeneration with fire intensities intentionally restrained 

(when possible) to minimize overstory mortality to retain timber value. Since the primary 

objectives here were to open the canopy, enhance light penetration, and increase ground flora 

cover and diversity, a greater range of fire intensities and effects was expected and encouraged 

because high-value timber products were not the objective.

Where gaps occurred, we saw clear relationships that made ecological sense: canopy 

gaps were created on hotter and drier sites more frequently than on cooler, wetter sites. 

Individually, three different variables that describe site characteristics (potential vegetation, 

current vegetation, and annual solar radiation [estimated by HLI]) were all significant in 

explaining patterns of canopy gap formation. However, the low incidence of gap formation 

in barrens (Figs. 5 and 6) is somewhat puzzling. One explanation is that barrens sites are so 

xeric that they have relatively low fuel loading and therefore fire intensity is lower than in the 

heath-dominated understory of the next-driest type of dry pine/oak. The topographic-based 

HLI metric had a strong correlation with the variation of canopy gap formation; when HLI 

was higher, so was the percentage of canopy gap creation.

Other researchers have found a similar association of increased HLI with an increase in fire 

severity (Arkle et al. 2012, Flatley et al. 2011, Holden et al. 2009, Wimberley and Reilly 2007). 

HLI as a measure of solar radiation a site receives has a known impact of species composition 

(Martin et al. 2011), likely impacts biomass and therefore fuels available, and fuel moisture 

content, influencing fire severity. HLI was found to be an important predictor of increased 

fire severity in models for the pinyon-juniper-oak community after a wildfire (Holden et 

al. 2009). In that semi-arid landscape, moisture controls the productivity of vegetation, 

influences forest composition, and fire severity (Holden et al. 2009). While our study area is 

broadly described as temperate and not semi-arid, very dry microsite conditions do occur on 

some landforms.

The relationship between HLI and fire severity does not explain all of the observed variability 

found in our study area. Some units have no canopy gaps despite having plentiful hot, dry 

microsites. More research into the multiple drivers of canopy gap formation after prescribed 

fire is needed. It is likely that human decisions about burning operations, such as ignition 

types and patterns, and fire weather conditions coupled with phenological stage of vegetation 

will be important variables. Also, extended drought cycles can influence how a forest 

responds to prescribed fire (Littell et al. 2016). We know that some first prescribed fire entries 

occurred either during or at the tail end of the drought cycle of the late 1990s or early 2000s.

Management Implications for GWNF and JNF

Even though these burns were mostly conducted under past forest plans, it is still useful 

to compare their impacts using metrics and goals from the revised GWNF Plan, as it 

incorporated the most current ideas on using prescribed fire in the Appalachians. The 2014 

GWNF Plan describes several desired conditions based on forest structure and age and sets 

goals for each condition, measured as a percentage of the overall landscape. In reviewing our 

results, we asked a simple question: “Are prescribed fires creating the desired conditions in 

the same percentages as given in the forest plan goal?”

Our analysis shows that burning one to four times resulted in on average 5 to 17 percent of a 

burn unit becoming EARLY forest, which is comparable to the GWNF Plan goal (12 percent). 

A few individual units far exceeded the EARLY acreage goal, with a maximum observed 
19

value of 54 percent of unit area. Since the Plan goals apply at the landscape level and not at 

the individual burn unit, instances where EARLY habitat created in an individual unit were 

greater than the target should not be viewed as detrimental to achieving overall forest plan 

goals.

Prescribed fire has not yet created OPEN forest at target amounts sought by the GWNF Plan. 

Our results show that single prescribed fires did not create large amounts of OPEN forest (5 

percent) and even four burns (8 percent) resulted in a landscape short of the GWNF Plan 

goal of 67 percent. The maximum observed value for OPEN forest was 34 percent of unit 

acreage.

While large amounts of OPEN forest were not detected after one to four burns, we urge 

caution in interpreting these results. Creating open-canopy forests through burning could be 

a more gradual process than creating early-successional habitat patches. Delayed post-burn 

mortality documented in the Appalachians shows fire’s ability to influence overstory canopy 

over time (Waldrop et al. 2008), which could eventually result in open-canopy woodlands.

These findings should not be seen as a failure of prescribed fire to meet goals and objectives, 

but perhaps as a lesson in goal setting. The 67-percent goal for OPEN forest landscape may 

be too specific and unnecessarily ambitious (Hiers et al. 2016) for the intent of the prescribed 

fire program, which includes increasing light to the forest floor and subsequent changes in 

plant communities. Given the long-term absence of fire in these forests, this goal may take 

much longer to reach, perhaps as many years as the area has gone without fire.

We found that the footprint of EARLY and OPEN patches resulting from the first burn 

did not tend to expand greatly after subsequent burns. If more gaps did develop, they were 

EARLY, not OPEN (Table 5). The lack of new gaps in subsequent burns is perhaps due to 

a uniformity in how a unit was burned. Managers may be executing multiple burns on the 

same unit with the same ignition pattern or burn prescription. In units where the initial 

fire had only minimal effects to the canopy (but canopy effects were desired), it might be 

beneficial to consider a different prescription, including changing season of the burn, for 

subsequent burns.

The potential for undesired effects from prescribed fire in non-fire-adapted communities 

seems to be limited. Very little EARLY or OPEN forest was created after one prescribed fire 

in mesic oak, cove, and floodplain communities (Tables 7 and 8). Even though no measures 

were taken to exclude these communities from burning, fire severity was seemingly held 

in check by the sites’ mesic conditions. Based on these results, expecting topography to 

moderate severe fire effects in these possibly sensitive areas would seem valid.

CONCLUSIONS

After examining almost every large-scale prescribed burn conducted on George Washington 

and Jefferson National Forests over the past two decades, we determined that prescribed 

burning consistently created the desirable conditions of OPEN and EARLY forest. However, 

multiple burns did not always result in increased amounts of these conditions and the 

creation of OPEN forest was less than the landscape-level goal in the GWNF Plan. The 

GIS-based methodology used here was validated by field data. Forest patches delineated as 

EARLY, OPEN, or CLOSED canopy were found to have very different structural attributes, at 

both the canopy and understory levels.
20

This difficulty in creating open-canopy conditions through prescribed fire alone has also 

been seen in other eastern oak-dominated forests where prescribed fire was used to promote 

oak reproduction (Brose et al. 2013; Holzmueller et al. 2014; Hutchinson et al. 2012a, 2012b; 

Iverson et al. 2008). This may mean that commercial or noncommercial thinning may 

be needed to meet the goals for open-canopy conditions (Waldrop et al. 2016). However, 

timber harvesting is not an option on 60 percent of GWNF and JNF acreage due to either 

management designations or unsuitable conditions (e.g., erodible soils, steep slopes). In 

many remote areas, prescribed fire may be the only tool available to land managers, so more 

information is needed on burning techniques that have a high probability for creating opencanopy conditions.

This analysis sheds light on the heterogeneous nature of the effects of large-scale prescribed 

fire in the central Appalachian oak and oak-pine forests. Further research is needed to 

determine the drivers of canopy gap formation and understand why fire severity patterns 

for individual burn units differ so greatly. While the likelihood of a wildfire starting at any 

given place or time is controlled largely by fuel characteristics (Falk et al. 2011), fire severity 

or intensity is controlled by topography (Falk et al. 2007) and the interactions of topography 

and vegetation (Birch et al. 2015). We expect that identifying the variables that control fire 

severity for prescribed fires on the GWNF and JNF will help land managers predict the 

impacts of prescribed fires and will aid in tactical decisions about burning individual units.

ACKNOWLEDGMENTS

The authors would like to thank Megan Sebasky of LANDFIRE and Lindsey Curtin and 

Karen Stevens of the USDA Forest Service for their help in developing an initial dataset. 

Additional thanks to the Central Appalachian Fire Learning Network’s monitoring group 

who collected the vegetation data used in this report. Many others played key roles in 

highlighting the need for this information, both from a fire effects monitoring perspective, a 

forest planning perspective, and a “so what” perspective. These include: Marek Smith, Nikole 

Simmons, and Sam Lindblom, The Nature Conservancy; Carol Croy, Russ MacFarlane, and 

Beth Buchanan, USDA Forest Service; Ken Landgraf, retired, USDA Forest Service; and the 

Central Appalachians Fire Learning Network.

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27

APPENDIX 1

Canopy Gap Results for Burn Units

Table 9.—After one prescribed burn, burn units and canopy gap results, by area and as 

percentage of total area.

Unit Name

Area (acres) Percentage of Burn Unit

EARLY OPEN CLOSED Total EARLY OPEN All GAPS

Back Valley 7 29 305 341 2 8 11

Big Branch 104 76 545 724 14 10 25

Big Cobbler 2 0 443 445 0 0 0

Big Wilson C 715 258 1,968 2,942 24 9 33

Big Wilson N 95 109 1,234 1,438 7 8 14

Big Wilson S 293 45 1,085 1,423 21 3 24

Brush Mtn 58 34 553 645 9 5 14

Brushy Ridge 50 63 608 721 7 9 16

Burns Creek 1 20 425 446 0 4 5

Cane Patch 0 0 743 743 0 0 0

Cole Mtn 0 1 1,052 1,053 0 0 0

Cub Run 356 246 2,784 3,385 11 7 18

Cubville 32 132 748 912 3 14 18

Dunkle Knob 15 20 663 698 2 3 5

Elkhorn 3 5 1,005 1,013 0 0 1

Ewing Mtn 35 45 612 692 5 7 12

Fenwick Mines 286 187 699 1,172 24 16 40

Flatwoods 57 146 1,307 1,511 4 10 13

Gauley Ridge 6 63 1,206 1,275 0 5 5

Glade Mtn 203 233 2,378 2,815 7 8 16

Glades 0 5 824 829 0 1 1

Grindstone 2 6 841 849 0 1 1

Gum Lick 37 60 622 718 5 8 13

Hall Spring 5 26 2,071 2,101 0 1 1

Heavener 12 29 983 1,024 1 3 4

Hone Qrry Spruc 0 23 1,426 1,449 0 2 2

Hone Qrry W 541 37 783 1,361 40 3 42

Jackson River 105 89 2,057 2,251 5 4 9

Lake Keokee 1 4 374 379 0 1 1

Little Fork 10 52 1,889 1,951 0 3 3

Little Neal 18 56 1,267 1,341 1 4 6

Little Schloss 191 316 1,050 1,557 12 20 33

Low Place 0 1 590 591 0 0 0

Mare Run 73 67 736 876 8 8 16

Middle Mtn 62 16 843 921 7 2 8

Mill Creek S 60 103 136 300 20 34 54

Mill Mountain 70 24 451 545 13 4 17

Mills Creek 16 41 319 377 4 11 15

Moody 1 1 255 257 0 0 1

Morris Hill 0 12 481 492 0 2 2

Neal Run 260 350 1,681 2,291 11 15 27

New Road Run 21 28 533 582 4 5 8

continued
28

Unit Name

Area (acres) Percentage of Burn Unit

EARLY OPEN CLOSED Total EARLY OPEN All GAPS

North Fork Pound 188 208 3,085 3,481 5 6 11

North New Road 41 47 4,274 4,362 1 1 2

North River 21 23 1,197 1,241 2 2 4

North Short Mtn 141 101 1,998 2,240 6 4 11

Patterson 14 20 2,216 2,250 1 1 2

Piney Mtn 90 95 985 1,170 8 8 16

Rocky Mtn 15 54 1,108 1,176 1 5 6

Round Mtn 3 9 1,442 1,454 0 1 1

Skegg Branch 42 39 731 811 5 5 10

Snake Den 64 25 606 696 9 4 13

Straight Fork 5 10 916 931 1 1 2

Tar Run 2 9 344 355 1 3 3

Tucker Gap 0 6 386 393 0 2 2

Upper Craig A 4 24 553 581 1 4 5

Upper Craig B 0 0 390 391 0 0 0

Wells Branch 31 18 692 741 4 2 7

Table 10.—After two prescribed burns, burn units and canopy gap results by area and as 

percentage of total area.

Unit Name

Area (acres) Percentage of Burn Unit

EARLY OPEN CLOSED Total EARLY OPEN CLOSED

Beards Mtn 85 70 843 999 9 7 84

Brushy Knob 3 23 329 356 1 7 93

Elkhorn 9 12 992 1,013 1 1 98

Fenwick Mines 405 145 622 1,172 35 12 53

Flatwoods 57 146 1,307 1,511 4 10 87

Fore Mtn 40 242 987 1,268 3 19 78

Gauley ridge 12 78 1,185 1,275 1 6 93

Glades 16 13 799 829 2 2 96

Gum Lick 61 43 615 718 8 6 86

Hone Qrry Spruc 64 53 1,332 1,449 4 4 92

Hone Qrry W 625 92 644 1,361 46 7 47

Horse Heaven E 11 20 483 514 2 4 94

Horse Heaven W 9 29 521 559 2 5 93

Huff Hollow 78 131 1,292 1,502 5 9 86

Lake Keokee 2 7 370 379 1 2 98

Little Fork 91 109 1,751 1,951 5 6 90

Low Place 0 1 590 591 0 0 100

Mill Creek S 156 37 107 300 52 12 36

Mills Creek 91 40 246 377 24 11 65

Morris Hill 72 421 492 0 15 85

New Road Run 45 41 497 582 8 7 85

NFP Cane 3 4 436 444 1 1 98

NFP Laurel 81 117 283 481 17 24 59

NFP Phillips 50 62 382 494 10 13 77

Table 9.—continued

continued
29

Unit Name

Area (acres) Percentage of Burn Unit

EARLY OPEN CLOSED Total EARLY OPEN CLOSED

North River 21 30 1,190 1,241 2 2 96

North Short Mtn 176 235 1,829 2,240 8 10 82

Patterson 20 72 2,160 2,251 1 3 96

Piney Mtn 293 96 781 1,170 25 8 67

Round Mtn 5 14 1,435 1,454 0 1 99

Short Mtn 45 65 1,461 1,571 3 4 93

Straight Fork 58 6 867 931 6 1 93

Tar Jacket 55 29 345 429 13 7 80

Tucker Gap 22 27 344 393 6 7 87

Upper Craig B 9 4 378 391 2 1 97

Walker Mtn 21 48 453 521 4 9 87

Wells Branch 35 19 687 741 5 3 93

Table 11.—After three prescribed burns, burn units and canopy gap results by area and 

as percentage of total area

Unit Name

Area (acres) Percentage of Burn Unit

EARLY OPEN CLOSED Total EARLY OPEN CLOSED

Catback 130 149 1812 2,091 6 7 87

Evick Knob 13 45 277 335 4 13 83

Fenwick Mines 429 139 604 1,172 37 12 52

Hone Qrry Spruc 74 52 1,324 1,449 5 4 91

Hone Qrry W 658 76 627 1,361 48 6 46

Horse Heaven E 25 29 459 514 5 6 89

Horse Heaven W 10 32 517 559 2 6 92

Huff Hollow 78 176 1,248 1,502 5 12 83

Indian Grave 3 5 331 338 1 1 98

Mill Creek S 161 32 107 300 54 11 36

Morris Hill 0 79 413 492 0 16 84

New Road Run 47 38 497 582 8 7 85

Orebank 69 125 1767 1,961 4 6 90

Second Mtn 579 180 361 1,119 52 16 32

Tar Jacket 73 53 302 429 17 12 70

Table 12.—After four prescribed burns, burn units and canopy gap results by area and as 

percentage of total

Unit Name

Area (acres) Percent of Burn Unit

EARLY OPEN CLOSED Total EARLY OPEN CLOSED

Catback Mtn 239 135 1,717 2,091 11 6 82

Evick Knob 15 47 274 335 4 14 82

Indian Grave 3 5 331 338 1 1 98

Mill Creek S 161 32 107 300 54 11 36

Tar Jacket 76 51 301 429 18 12 70

Horse Heaven W 11 37 512 559 2 7 92

Horse Heaven E 32 44 438 514 6 8 85

Table 10.—continued
30

APPENDIX 2

Ecological Zones

Table 13.—Descriptions and area of ecological zones (ecozones) in the George Washington National Forest 

(GWNF) and Jefferson National Forest (JNF) (Simon 2011, 2013)

Group Ecozones (GWNF model) Ecozones (JNF model) Area (acres)

Low Barrens Alkaline woodlands, shale barrens, 

mafic glade and barrens

Shale barrens, pine-oak shale, acid 

glade, limestone-dolomite barrens

1,675

Site Productivity

Site Moisture

Dry pine/oak Low elevation pine, pine-oak heath, 

pine-oak shale woodlands

Shortleaf pine-oak, pine-oak heath 7,326

Dry oak heath Dry oak evergreen heath, dry oak 

deciduous heath

Dry oak evergreen heath, dry oak 

deciduous heath, dry calcareous 

forest

20,266

Dry-mesic oak High-elevation red oak, dry mesic 

oak, dry mesic calcareous forest

High-elevation red oak, dry mesic 

oak, dry mesic calcareous forest

16,460

Mesic oak Colluvial forest, montane oakhickory slope, montane oak-hickory 

cove, montane oak-hickory (rich) 

Colluvial forest, montane oakhickory slope, montane oakhickory cove, montane oak-hickory 

(rich) 

14,605

Cove Northern hardwood slope, 

northern hardwood cove, acidic 

cove, rich cove

Northern hardwood slope, 

northern hardwood cove, acidic 

cove, rich cove , mixed oakrhododendron, rich slope

12,051

High Floodplains Alluvial forest, floodplain forest Alluvial forest, floodplain forest 771

Total 73,154

APPENDIX 3

Field Sampled Vegetation (FSVeg)

Table 14.—Description and area of FSVeg forest types

Group FSVeg forest type Area (acres)

Low Barrens Black locust, brush species 328 Site Productivity Site Moisture

Dry pine/oak Pitch pine-oak, Virginia pine-oak, Table Mountain pine-hardwood, 

shortleaf pine, Virginia pine, pitch pine, Table Mountain pine 6,081

Dry oak heath

Chestnut oak-scarlet oak-yellow pine , white oak-black oak-yellow pine, 

bear oak-southern scrub oak-yellow pine, post oak-black oak, chestnut 

oak, scrub oak, scarlet oak, chestnut oak-scarlet oak 

21,736

Dry-mesic oak

White pine-upland hardwood, upland hardwoods-white pine, northern 

red oak-hickory-yellow pine, white oak, northern red oak, chestnut oakwhite oak-scarlet oak3,900

Mesic oak White oak-northern red oak-hickory, yellow-poplar-white oak-northern 

red oak 32,616

High Cove

White pine-hemlock, hemlock, hemlock-hardwood, white pinecove hardwood, cove hardwoods-white pine-hemlock, bottomland 

hardwood-yellow pine, yellow-poplar, sweetgum-yellow-poplar, sugar 

maple-beech-yellow birch

1,515

Total 66,176
Printed on Recycled Paper

Lorber, Jean; Thomas-Van Gundy, Melissa; Croy, Steve. 2018. Characterizing effects of 

prescribed fire on forest canopy cover in the George Washington and Jefferson National 

Forests. Research Paper NRS-31. Newtown Square, PA: U.S. Department of Agriculture, Forest 

Service, Northern Research Station. 30 p. https://doi.org/10.2737/NRS-RP-31.

On the George Washington and Jefferson National Forests, managers have used prescribed fire 

to create and maintain early-successional and open forest conditions across large areas. We used 

a landscape-scale and image-based approach to assess the extent that prescribed fires, including 

repeated fires, have created these forest conditions and put the results in context of the new 

George Washington National Forest management plan. At the landscape level, early-successional 

forest made up an average of 5 percent of burn unit area after one burn, 9 percent after two 

fires, 17 percent after three fires, and 14 percent after four fires. On average across all burn unit 

acreage, open forest made up 5 percent of the area after one burn, 7 percent after two burns, 9 

percent after three, and 8 percent after four fires. The forest plan desired condition of 12 percent 

of the area in early-successional forest was met after three or four fires and was exceeded in 

some individual burn units. It is harder to achieve open-forest than early-successional conditions 

using prescribed fire alone. We also examined possible drivers of canopy gap creation in these 

forests. Vegetation type and heat load index, a topographic-based measure of solar radiation 

received by a site, were important predictors of where canopy gaps formed after prescribed fire.

KEY WORDS: overstory mortality, fire severity, landscape-scale fire, canopy cover

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