Effects of Prescribed Fire on the Buried Seed Bank in
Mixed-Hardwood Forests of the Southern Appalachian
Tara L. Keyser, Tracy Roof, Jacquelyne L. Adams, Dean Simon, and Gordon Warburton
Southeastern Naturalist, Volume 11, Issue 4 (2012): 669–688
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2012 SOUTHEASTERN NATURALIST 11(4):669–688
Effects of Prescribed Fire on the Buried Seed Bank in
Mixed-Hardwood Forests of the Southern Appalachian
Tara L. Keyser1,*, Tracy Roof 1, Jacquelyne L. Adams1, Dean Simon2,
and Gordon Warburton3
Abstract - This study characterizes the seed bank prior to and immediately following
dormant-season prescribed fire in mature, mixed-Quercus spp. (oak) forests in the southern
Appalachian Mountains. Thirty samples from the litter/duff (LD) and the top 5 cm of
the mineral soil (MS) were collected from five 5-ha burn units (6 plots per experimental
unit) before and immediately after low-intensity prescribed fires, where maximum fire
temperatures varied from <79 to 316 °C. A split-plot ANOVA and multi-response permutation
procedures (MRBP) were utilized to assess the effects of burn treatment (pre- or
post-fire) and seed bank layer (LD and MS) on the diversity and density of the buried seed
bank. An average of 471 emergents/m2 was observed in the buried seed bank comprising
133 identifiable taxa. No differences in total seed-bank density, Shannon-Weiner’s
diversity index (H′), or overall species composition between pre- and post-fire sampling
or between the LD and MS layers were observed. Species richness (S) of the seed bank,
however, was slightly greater pre-fire than post-fire, regardless of layer. Similarity, as
defined by Sørenson’s index, of species common to the seed bank and aboveground forest
understory was low, with a slight increase in Sørenson’s index observed during post-fire
sampling of the seed bank and aboveground vegetation. Although we observed only negligible
effects of a once-applied, low-intensity prescribed fire on the buried seed bank, the
effects of a low-intensity prescribed fire management regime—one that involves repeated
low intensity burns—on the buried seed bank are unknown and should be a focus of future
studies across mixed-oak forests in the eastern US.
The composition and contribution of the buried seed bank to post-disturbance
species composition of the arborescent and herbaceous vegetation layers in
mixed-Quercus spp. (oak) forests in the eastern US has been little studied. Results
from the few studies to quantify and describe the seed bank of mixed-oak
forests suggest the density and composition of the seed bank is spatially and
temporally variable. For example, a depauperate seed bank containing an average
of only 0.4 seeds/m2 was found by Schiffman and Johnson (1992) in mature,
ridge-top forests of the Ridge and Valley physiographic province of the southern
Appalachians, while Schuler et al. (2010) observed a density of 248 arborescent
emergents/m2 in the seed bank of a second-growth mixed-oak forest in the central
1USDA Forest Service, Southern Research Station, Bent Creek Experimental Forest,
1577 Brevard Road, Asheville, NC 28806. 2North Carolina Wildlife Resources Commission,
8676 Will Hudson Road, Lawndale, NC 28090. 3North Carolina Wildlife Resources
Commission, 783 Deep Woods Drive, Marion, NC 28752. *Corresponding author -
670 Southeastern Naturalist Vol. 11, No. 4
Appalachians. Although across-site differences in the density of the seed bank
are common, within-site differences in the density and composition of the seed
bank have also been observed across topographic positions and areas of varying
site quality within a given forest stand, further emphasizing the heterogeneity
inherent to the buried seed bank (Ashton et al. 1998, Leckie et al. 2000, Singhakumara
et al. 2000, Small and McCarthy 2010).
Time since disturbance or the stage of stand development (Oliver and Larson
1996) has been shown to affect the characteristics and potential contribution of the
buried seed bank to the structure and composition of the forest understory (Graber
and Thompson 1978, Grandin 2001, Plue et al. 2010). For example, in a chronosequence
of old-field to old-growth Acer-Fagus (maple-beech) stands in Ohio,
Roberts and Vankat (1991) found that richness, diversity, and density of the seed
bank decreased as time since disturbance increased, as did the similarity between
the composition of the seed bank and aboveground vegetation. Factors associated
with changes in seed-bank characteristics over time include (1) changes in life-history
types in aboveground vegetation (e.g., change from shade-intolerant annual/
biennial species early in stand development to shade-tolerant perennial species
during later stages of stand development) (Bossuyt and Hermy 2001, Brown and
Oosterhuis 1981, Warr et al. 1994); (2) decreased seed viability after prolonged
periods without disturbance (Bossuyt and Hermy 2001, Warr et al. 1994); and
(3) decreased input to the seed bank from aboveground vegetation (Plue et al.
2010). As such, while aboveground vegetation in mature second-growth forests
may consist primarily of shade-tolerant species, the buried seed bank is generally
dominated by highly persistent shade-intolerant annual and biennials species common
to recently disturbed forest conditions (e.g., young-forest habitats; Korb et
al. 2005, Thompson et al. 1998), which under the more conducive environmental
conditions (e.g., high light) may germinate and contribute to the development and
composition of the post-disturbance community.
The paradigm that the buried seed bank of mature, second-growth forests is
dominated by shade-intolerant species characteristic of the early stages of stand
development (e.g., Grandin and Rydin 1998, Korb et al. 2005) has implications
regarding the restoration of oak ecosystems in the southern Appalachians. Several
researchers have suggested a change in the disturbance regime (e.g., cessation
of anthropogenic burning) has promoted the conversion of mixed-oak forests to
forests dominated by shade-tolerant species, such as Acer rubrum (Red Maple)
(e.g., Abrams 1992, Brose et al. 2001, Orwig and Abrams 1994), while even-aged
forest management practices have resulted in a conversion of oak-dominated
forests to stands dominated by shade-intolerant species, such as Liriodendron
tulipifera (Yellow-Poplar) (e.g., Beck and Hooper 1986, Loftis 1983). Despite
evidence suggesting that seed banking of arborescent species is of only a minor
importance in the regeneration of temperate forests (Bossuyt et al. 2002, Meadows
et al. 2006), in high-quality, mixed-oak forests, mesophytic tree species that
often interfere with oak regeneration (e.g., Yellow-Poplar, Betula lenta [Sweet
Birch], and Red Maple), are capable of regenerating from seed stored in the longterm
(e.g., Yellow-Poplar) or transient (e.g., Sweet Birch and Red Maple) seed
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 671
bank following disturbance (Clark and Boyce 1964, Hille Ris Lambers and Clark
2005, Sander and Clark 1971, Sullivan and Ellison 2006).
In the southern Appalachian Mountains, prescribed fire is increasingly used by
land managers to promote the regeneration of ecologically valuable oak species
by controlling competition from both shade-tolerant (Abrams 1992, Orwing and
Abrams 1994) and shade-intolerant (Brose et al. 2001) arborescent species, decrease
hazardous fuel loadings, enhance wildlife habitat, and increase understory
species diversity and structural heterogeneity (Vose 2000). Upland hardwood
forests of the southern Appalachian Mountains possess some of the highest levels
of tree and understory vegetation diversity in the US. The role of the buried
seed bank is often overlooked despite the known contribution the seed bank has
in shaping post-disturbance ecosystem structure and composition (Leck et al.
1989). The density of composition of viable seed remaining in the seed bank
following prescribed fire can affect post-disturbance community dynamics (Auld
and Denham 2006). In this study, we (1) quantify and describe the buried seed
bank on intermediate to high-quality mixed-hardwood forests in the southern Appalachian
Mountains, (2) examine the effects of prescribed fire on the density and
composition of the buried seed bank, and (3) identify the relationship between
aboveground species composition and that of the buried seed bank prior to and
following prescribed fire.
Field site description
This study was conducted on the North Carolina Wildlife Resource Commission’s
Cold Mountain Game Lands (CMGL) in Haywood County in western
North Carolina. The CMGL encompass 1333 ha and are located on the Blue
Ridge physiographic province of the southern Appalachian Mountains. Past land
use consisted primarily of exploitive logging (e.g., widespread clearcutting) during
the mid-20th century, making age of the stands within CMGL approximately
80 years. Terrain is mountainous with steep slopes. Slopes of areas used in this
study range from approximately 35 to 55 percent. Elevations within the study
area range from 975 m to 1280 m. Average annual temperature ranges from 3
°C in January to 24 °C in July (McNab and Avers 1994). Average precipitation
approximates 1200 mm annually and is evenly distributed throughout the year
(McNab and Avers 1994). Vegetation on CMGL consists of mature, secondgrowth,
upland mixed-hardwood forests. Oak and Carya spp. (hickory) species
along with Yellow-Poplar are the predominant overstory trees, while the midstory
consists primarily of shade-tolerant species, including Oxydendrum arboreum
(Sourwood), Cornus florida L. (Flowering Dogwood), Nyssa sylvatica Marsh.
(Blackgum), Halesia tetraptera Ellis (Silverbell), and Red Maple (Schafale and
During the summer of 2008, five 5-ha replicate units (approximately 225 x
225 m) were located throughout the CMGL. Each replicate consisted of fully
672 Southeastern Naturalist Vol. 11, No. 4
stocked stands of mixed-species composition. Within each of the 5 replicates,
2 transects were established. Transects were parallel to and >30 m from a unit
boundary, and positioned across a slope gradient. The first transect was located by
picking a random distance along the boundary line from the farthest downslope
corner of each burn unit.
Along each of the 2 transects per experimental unit, three 0.05-ha permanent
circular plots (12.6-m radius) were established at 50 m, 112 m, and 175 m
(Fig. 1). Within each 0.05-ha permanent plot, all overstory trees ≥25 cm diameter
at breast height (dbh) were inventoried and tagged. Midstory trees ≥5 cm and
<25 cm dbh were inventoried and tagged within a 0.01-ha (5.6-m radius) subplot
concentrically nested within each plot. For all tagged trees, species, dbh, and
crown class was recorded. Tree regeneration was sampled using two 0.004-ha
circular regeneration subplots originating 8 m from plot center at bearings of
Figure. 1. Conceptual diagram portraying plot and subplot locations within each
of the five 5-ha replicates. Replicates contained 2 parallel transects approximately
225 m in length along which plots were established. Transects within replicates
were separated by ≥30 m. Vegetation plots were located at approximately 50 m,
112 m, and 175 m along each transect.
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 673
45° and 225°. In the regeneration subplots, advance reproduction (arborescent
species <3.8 cm dbh) was enumerated by species in 5 height/diameter classes:
(1) <0.3 m tall; (2) ≥0.3 m to <0.6 m tall; (3) ≥0.6 m to <0.9 m tall; (4) ≥0.9 m to
<1.2 m tall; and (5) ≥1.2 m tall to <3.8 cm dbh. Information on forest understory
vegetation, including species presence/absence, and percent cover was collected
using four 1-m2 subplots located 12 m from plot center in the north, south, east,
and west directions (Fig. 1). Percent cover by species was determined via ocular
estimation. Collection of forest understory vegetation data occurred in 2008,
prior to the fire and again during the first growing season post- fire.
Seed-bank samples were collected at 5 m north and 5 m south of the regeneration
subplot located at the 225° azimuth in each of the 5 replicates prior to the fire
and again at 5 m east and 5 m west of the tree regeneration subplot immediately
following the fire (Fig. 1). Samples of the seed bank from the litter and duff (Oi +
Oe + Oa) and mineral soil to a depth of 5 cm were collected separately using a
25-cm by 25-cm (0.0625-m2) sampling frame. The litter and duff layer was easily
distinguishable from the mineral soil layer. During each pre- and post-fire
sampling period, the 2 litter/duff (LD) seed-bank subsamples collected from each
0.05-ha plot were combined. Similarly, during each pre- and post-fire sampling
period, the 2 mineral soil (MS) seed-bank subsamples collected from each 0.05-
ha plot were combined. Pooling resulted in a total of 30 subsamples from each
pre- and post-fire LD layer (6 LD subsamples per replicate and sampling period)
and 30 subsamples from each pre- and post-fire MS layer (6 MS subsamples per
replicate and sampling period). The 6 subsamples per replicate, seed-bank layer
(LD and MS), and sampling period (pre- and post-fire) combination were averaged
for all analyses (n = 5), making the 5-ha replicate the experimental unit.
On 25 February 2009, the North Carolina Wildlife Resources Commission
implemented a prescribed burn on 2 of the 5 replicate units. Because these 2
replicates were located in close proximity to one another, the burn was conducted
as a single prescribed fire. However, because of the buffers (≥50 m)
between replicate units, we considered these units to be two independent
replicates. Due to poor burning conditions, the remaining 3 replicates were left
unburned until 1 April 2010. In the 2010 burns, 2 of the 3 replicates were
burned by a single prescribed fire due to the proximity of the replicates, while
the last replicate was burned during a separate fire on the same day. Because
of buffers (≥50 m), we consider all replicate units to be independent. The prescribed
fires were cool, backing fires ignited with short, strip lighting and/or
flanking strip lighting. Ten-hour fuel moisture on the burn days ranged from
9 to 11%, and relative humidity was between 20 and 40%, with wind speeds
<12 km/hr. Maximum temperature at surface level was quantified at the regeneration
subplot closest to seed-bank sampling using Tempilaq® temperature
sensitive paints (Tempil, Inc., South Plainfield, NJ).
In the case of the 2009 prescribed fire in which only 2 of the 5 replicates
were burned, pre-fire seed-bank samples were collected during the first 2
674 Southeastern Naturalist Vol. 11, No. 4
weeks of December, 2008. Post-fire seed-bank samples were collected on 25
February and 26 February 2009. For these 2 replicates, pre-fire seed-bank
samples were collected prior to completion of the cold-stratification period
characteristic of the study area. Consequently, pre-fire seed-bank samples for
these 2 replicates were cold stratified at 4 °C for an additional 60 days prior
to further processing and germination. Post-fire seed-bank samples for these
2 replicates were cold stratified along with the pre-fire seed-bank samples.
In the case of the 2010 prescribed fires, pre- and post-fire seed-bank samples
were collected on 1 April and 5 April 2010, respectively, after completion
of the normal cold-stratification period. Consequently, samples from these 3
replicates received no further cold stratification. Although collection of seedbank
samples from the 3 replicates burned in 2010 were collected later in the
year than the 2009 samples, no seedling germination was observe d in the field
prior to collection. An unseasonably cold winter with considerable snow cover
late into 2010 likely delayed the start of the growing season. Consequently,
the timing of collection as well as differences in cold-stratification periods
likely had little effect on the results presented here.
In the greenhouse, seed-bank samples were sieved through a 6-mm-mesh
screen. This removed vegetative material (e.g., roots, rhizomes, tubers, etc.)
that could have added to the germination potential of the samples. When large
seeds (>6 mm diameter) were encountered (e.g., acorns, Hickory nuts, etc.), we
manually placed them into the sieved sample. Once sieved, we placed the seedbank
samples into 28- x 53-cm flats in combination with soil medium (Premier
Pro-mix Bx). Flats were placed in the greenhouse and watered 3 to 4 days per
week. The seed bank was identified by using the seedling germination technique
(Brown 1991). We checked for new germinants 3 days per week over a 6-month
period. Control trays containing only soil medium were placed in the greenhouse
to check for contamination.
The similarity between species observed in aboveground understory sampling
and the LD and MS seed-bank layers was assessed using Sørenson’s
similarity index. Using presence or absence of species, Sørenson’s index was
calculated as: 2w / (A + B), where A = the number of species in aboveground
vegetation, B = the number of species in the seed bank, and w = the number
of shared species in common in above- and belowground samples. Sørenson’s
index ranges from 0 to 1, with 0 indicating a lack of similarity between species
present aboveground versus the seed bank and 1 indicating complete agreement
between aboveground and seed-bank species. Pre-fire Sørenson similarity
index values were calculated using pre-fire aboveground vegetation and prefire
seed-bank data. Post-fire Sørenson similarity index values were calculated
using the post-fire aboveground vegetation and post-fire seed-bank data. Sørenson’s
index was calculated separately for each of the 0.05-ha plots and averaged
by replicate. Sørenson’s similarity index was used because of its widespread
use in the seed-bank literature (e.g., Hopfensperger 2007).
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 675
Differences in total seed-bank density (determined by the number of individuals
that germinated), seed-bank density by lifeform (i.e., forb, graminoid,
shrub, arborescent, vine), species richness (S), Shannon-Weiner’s diversity index
(H′), and Sørenson’s index between the LD and MS layers and burn treatment
(pre- and post-fire) were analyzed using a mixed-effects split-plot analysis of
variance (ANOVA), where seed-bank layer (LD and MS) was the main-plot factor
and burn treatment (pre- and post-fire) was the split-plot factor. In addition
to the main effects, the interaction between seed-bank layer and burn treatment
was included in the ANOVA. Seed-bank layer and burn treatment were fixed effects
and replicate and replicate*seed-bank layer were random effects. Because
the primary objective of the prescribed burns was to control competition from
some of oaks’ main competitors, we performed a similar ANOVA on seed-bank
density of species known to interfere with oak regeneration, including Yellow-
Poplar, Sweet Birch, and Red Maple, on mid- to high-quality sites. Seed-bank
collections were equally correlated (i.e., only one repeated measurement).
Therefore, the split-plot design rather than a repeated-measures design was employed
as suggested by Littell et al. 1998. Following significant F-tests in the
split-plot ANOVA, pairwise comparisons of least-square means were performed
using Tukey’s honestly significant test. Some density data were square-root or
loge(y + 1) transformed to achieve normality and homoscedasticity. Analyses of
seed-bank density, diversity, and similarity were conducted using the Proc Mixed
procedure in SAS (SAS Institute, Inc.).
We used blocked multi-response permutation procedures (MRBP) on
presence/absence data to test for differences in species composition using
PC-ORD v. 5.0 (McCune and Grace 2002). Permutation procedures were used
to test the null hypothesis that there were no significant differences in species
composition among defined groups (McCune and Grace 2002). Because
MRBP can only accommodate relatively simple experimental designs, the
data were sliced (McCune and Grace 2002) to test the following hypotheses:
(1) there is no difference between pre- and post-fire species composition in
the LD layer, (2) there is no difference between pre- and post-fire species
composition in the MS layer, and (3) there is no difference in species composition
between the LD and MS seed-bank layers. For all analyses, an alpha =
0.05 was used to assess significance.
Stands used in this study were mature, fully stocked, second-growth stands.
Mean (SE) basal area (m2/ha) and stems per hectare prior to burning was 36.2
(4.2) and 719 (27), respectively, with 60% of the pre-fire basal area (m2/ha) comprised
of oak and hickory species. The first growing season post-fire, mean (SE)
basal area and stems per hectare was 35.6 (4.2) and 702 (28), r espectively.
The seed bank within the fully stocked mixed-hardwood stands was abundant
and diverse. At the end of the study, 7058 germinants from the LD and MS layers
comprising 133 identifiable taxa were observed. In order of relative abundance,
the LD layer was dominated by forb, arborescent, shrub, graminoid, and vine
676 Southeastern Naturalist Vol. 11, No. 4
species, while the MS layer was dominated by the seeds of forb, shrub, graminoid,
arborescent, and vine species. In the combined LD and MS layers from both the
pre- and post-fire sampling periods, we observed 70 forb species (15 annuals/
biennials, 43 perennials, and 15 identified to only the genus level), 22 graminoid
species (19 perennials and 3 identified to only the genus level), 12 shrub species, 5
vine species, 24 arborescent species, and 1 group of unknown species.
Of the 133 identifiable species, approximately 30 were categorized as ruderal
species. Some of the more frequently observed ruderal species included Rubus
spp. (brambles) (average 192 emergents/m2), Phytolacca americana (Pokeweed)
(average 9 emergents/m2), Oxalis spp. (Wood Sorrel) (average 52 emergents/m2),
and Erechtites hieraciifolia (Fireweed) (average 3 emergents/m2) (Table 1). Of
the species that could be categorized, annual and perennial species possessed average
(SE) densities of 5.7 (1.1) and 361.5 (27.1) emergents/m2, respectively. The
only non-native species encountered in the seed bank was Paulownia tomentosa
(Thunb.) Siebold & Zucc. Ex Steud. (Princess Tree) (average 0.3 emergents/m2),
which occurred on only 7% of sampling locations pre-fire. Most species were
not uniformly distributed across the study area, with only 51 species observed on
≥10% of the sample locations (Table 1).
The prescribed fires conducted in this study were of low intensity. Maximum
temperature at the litter surface 5 m from where pre- and post-fire seed-bank subsamples
were collected ranged from <79 to 316 °C. Average (SE) scorch height
on overstory and midstory trees was 0.3 m (0.1). Litter consumption reflected the
low fire intensity, with litter depth (cm) averaging (SE) 5.1 (0.6) cm prior to the
fire and 2.7 (0.5) cm post-fire.
Results of the split-plot ANOVA revealed no statistical difference in total
seed-bank density or Shannon-Weiner’s diversity index (H′) between the LD
and MS layers or between pre- and post-burn sampling periods (P > 0.05). There
was, however, a significant effect of burn treatment on species richness (S), with
slightly greater richness pre-fire than post-fire (F = 11.68; df = 1,4; P = 0.0091).
Overall, seed-bank density was highly variable, with density averaged across
replicates ranging from 144 to 1274 seeds/m 2 (Table 2).
At the lifeform level, the split-plot ANOVA revealed a significant effect of
seed-bank layer on the density of arborescent species (F = 15.8; df = 1,4; P =
0.0165). The seed bank of arborescent species was characterized by significantly
greater density in the LD than MS layer, with mean densities (SE) of 139 (28.1)
and 43 (10.4) emergents/m2 in the LD and MS layers, respectively. No significant
effect of seed-bank layer or burn treatment was observed for forbs, graminoids,
shrubs, and vines (P > 0.05). Similarly, no significant effect of seed-bank layer
or burn treatment was observed for the arborescent species of interest, including
Yellow-Poplar, Sweet Birch, and Red Maple (P > 0.05).
After averaging data across groups defined by the specific hypotheses, results
from the MRBP analyses revealed no significant differences in species composition
between pre- and post-fire sampling periods for the LD and MS layers, nor
did we observed any significant differences in species composition between the
LD and MS layers (Table 3).
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 677
Table 1. Frequency of occurrence (%) and average density (emergents/m2) observed in the buried seed bank. Frequency relates to 0.05-ha plots nested within
replicates (n = 30). Only species occurring on ≥10% of the plots are listed. For lifeform: F = forb, T = arborescent, S = shrub, G = graminoid, and V = vine.
For life history: A = annual, P = perennial, and B = biennial. Lifeform and life history were determined in accordance with the USDA Plants Database (USDA,
NRCS 2011). Species listed as annual/biennial by were classified as annu als.
Pre-fire Post-fire Life- Life
Species Litter/duff Mineral soil Litter/duff Mineral soil form history
Acer rubrum L. (Red Maple) 40 (22.0/m2) 3 (0.7/m2) 23 (4.7/m2) 3 (1.3/m2) T P
Ageratina altissima (L.) King & H. Rob. (White Snakeroot) 10 (2.7/m2) 10 (2.0/m2) 17 (3.3/m2) 23 (9.3/m2) F P
Aruncus dioicus (Waleter) Fernald (Bride’s Feathers) 7 (2.0/m2) 10 (4.0/m2) 13 (3.3/m2) 7 (3.3/m2) F P
Aristolochia macrophylla Lam. (Pipevine) 13 (4.0/m2) 3 (0.7/m2) 13 (3.3/m2) 7 (1.3/m2) V P
Arisaema triphyllum (L.) Schott (Jack In The Pulpit) 7 (1.3/m2) 0 (0.0/m2) 13 (3.3/m2) 7 (2.0/m2) F P
Betula lenta L. (Sweet Birch) 73 (245.3/m2) 63 (57.3/m2) 73 (160.0/m2) 67 (49.3/m2) T P
Campanula divaricata Michx. (Small Bonny Bellflower) 10 (2.0/m2) 17 (4.0/m2) 0 (0.0/m2) 7 (2.0/m2) F P
Carex digitalis Willd. (Slender Woodland Sedge) 7 (3.0/m2) 17 (4.0/m2) 13 (6.0/m2) 3 (0.7/m2) G P
Carex spp. (sedge) 17 (3.0/m2) 13 (5.3/m2) 33 (19.3/m2) 30 (28.0/m2) G P
Carex virescens Muhl. Ex Willd. (Ribbed Sedge) 17 (7.3/m2) 27 (14.7/m2) 23 (10.0/m2) 20 (30.7/m2) G P
Conyza Canadensis (L.) Cronquist (Canadian Horseweed) 1 (5.3/m2) 7 (1.3/m2) 27 (8.7/m2) 20 (14.0/m2) F A
Dichanthelium boscii (Poir.) Gould & C.A. Clark (Bosc’s Panicgrass) 0 (0.0/m2) 7 (6.7/m2) 7 (2.0/m2) 17 (5.3/m2) G P
Dichanthelium spp. (rosette grass) 27 (12.7/m2) 17 (8.0/m2) 7 (3.3/m2) 3 (1.3/m2) F -
Dichanthelium commutatum (Schult..) Gould (Variable Panicgrass) 40 (46.7/m2) 43 (70.7/m2) 37 (26.0/m2) 37 (64.7/m2) G P
Dichanthelium dichotomum (L.) Gould (Cyoress Panicgrass) 10 (2.7/m2) 23 (37.3/m2) 20 (24.0/m2) 23 (22.0/m2) F P
Erechtites hieraciifolia (L.) Raf. ex DC. (American Burnweed) 30 (6.0/m2) 7 (1.3/m2) 13 (2.7/m2) 3 (0.7/m2) F A
Eupatorium purpureum L. (Sweetscented Joe Pye Weed) 20 (6.0/m2) 10 (5.3/m2) 7 (2.0/m2) 10 (2.0/m2) F P
Fraxinus americana L. (White Ash) 3 (0.7/m2) 0 (0.0/m2) 17 (3.3/m2) 0 (0.0/m2) T P
Gnaphalium obtusifolium L. (Rabbit-Tobacco) 13 (6.7/m2) 7 (1.3/m2) 0 (0.0/m2) 3 (0.7/m2) F A
Hieracium spp. (hawkweed) 10 (6.0/m2) 7 (4.0/m2) 7 (1.3/m2) 0 (0.0/m2) F -
Hieracium paniculatum L. (Allegheny Hawkweed) 3 (2.0/m2) 7 (2.0/m2) 7 (2.0/m2) 17 (9.3/m2) F P
Houstonia purpurea L. var. purpurea (Venus’ Pride) 17 (23.3/m2) 17 (14.7/m2) 27 (12.0/m2) 40 (26.7/m2) F P
Hydrangea arborescens L. (Wild Hydrangea) 43 (81.3/m2) 43 (60.0/m2) 23 (36.0/m2) 40 (68.7/m2) S P
Juncus spp. (rush) 17 (3.3/m2) 3 (0.7/m2) 13 (3.3/m2) 20 (4.0/m2) G -
678 Southeastern Naturalist Vol. 11, No. 4
Table 1, continued.
Pre-fire Post-fire Life- Life
Species Litter/duff Mineral soil Litter/duff Mineral soil form history
Juncus tenuis Willd. (Poverty Rush) 10 (2.7/m2) 10 (10.0/m2) 7 (2.0/m2) 13 (3.3/m2) G P
Liriodendron tulipifera L. (Yellow-Poplar) 57 (41.3/m2) 47 (28.0/m2) 40 (58.7/m2) 37 (19.3/m2) T P
Lobelia inflata L. (Indian-Tobacco) 3 (0.7/m2) 10 (2.7/m2) 13 (8.0/m2) 17 (11.3/m2) F A
Lysimachia quadrifolia L.(Whorled Yellow Loosestrife) 3 (0.7/m2) 13 (7.3/m2) 3 (1.3/m2) 7 (4.7/m2) F P
Melampyrum lineare Desr. (Narrowleaf Cowwheat) 10 (2.0/m2) 7 (2.0/m2) 0 (0.0/m2) 3 (0.7/m2) F A
Oxalis stricta L. (Common Yellow Oxalis) 17 (88.7/m2) 7 (1.3/m2) 27 (7.3/m2) 13 (4.7/m2) F P
Oxydendrum arboreum (L.) DC. (Sourwood) 40 (87.3/m2) 27 (20.0/m2) 20 (6.0/m2) 10 (2.0/m2) T P
Phytolacca americana L. (Pokeweed) 17 (3.3/m2) 33 (14.7/m2) 17 (10.7/m2) 23 (7.3/m2) F P
Potentilla canadensis L. (Dwarf Cinquefoil) 7 (2.0/m2) 27 (14.7/m2) 13 (7.3/m2) 23 (26.7/m2) F P
Prenanthes altissima L. (Tall Rattlesnakeroot) 3 (0.7/m2) 7 (1.3/m2) 10 (3.3/m2) 0 (0.0/m2) F P
Pycnanthemum montanum Michx. (Thinleaf Mountainmint) 10 (3.3/m2) 17 (5.3/m2) 10 (4.0/m2) 13 (10.7/m2) F P
Robinia pseudoacacia L. (Black Locust) 30 (10.0/m2) 37 (14.0/m2) 40 (10.7/m2) 40 (13.3/m2) T P
Rubus allegheniensis Porter (Allegheny Blackberry) 57 (184.7/m2) 57 (253.3/m2) 63 (103.3/m2) 70 (205.3/m2) S P
Rubus odoratus L. (Purpleflowering Raspberry) 0 (0.0/m2) 3 (0.0/m2) 20 (8.7/m2) 10 (0.7/m2) S P
Salix nigra Marsh. (Black Willow) 30 (11.3/m2) 10 (2.0/m2) 7 (0.9/m2) 7 (0.9/m2) T P
Scirpus cyperinus (L.) Kunth (Woolgrass) 13 (2.7/m2) 3 (0.7/m2) 7 (2.0/m2) 3 (0.7/m2) G P
Smilax rotundifolia L. (Roundleaf Greenbrier) 7 (1.3/m2) 10 (6.0/m2) 3 (0.7/m2) 0 (0.0/m2) V P
Solidago curtisii Torr. & A. Gray (Mountain Decumbent Goldenrod) 17 (4.7/m2) 17 (3.3/m2) 27 (8.7/m2) 13 (4.0/m2) F P
Solidago puberula Nutt. (Downy Goldenrod) 17 (6.0/m2) 7 (2.7/m2) 7 (2.0/m2) 10 (2.0/m2) F P
Sonchus asper (L.) Hill (Spiny Sowthistle) 13 (4.7/m2) 0 (0.7/m2) 0 (0.0/m2) 0 (0.0/m2) F A
Unknown 47 (48.0/m2) 50 (27.3/m2) 47 (16.0/m2) 40 (18.0/m2) N/A -
Viola spp. (Violet) 23 (8.0/m2) 17 (4.7/m2) 23 (13.3/m2) 27 (15.3/m2) F -
Viola blanda Willd. (Sweet White Violet) 27 (79.3/m2) 17 (39.3/m2) 27 (56.0/m2) 17 (41.3/m2) F P
Viola rotundifolia Michx. (Roundleaf Yellow Violet) 37 (84.0/m2) 33 (30.7/m2) 33 (58.7/m2) 30 (39.3/m2) F P
Viola sororia Willd. (Common Blue Violet) 60 (72.0/m2) 83 (96.0/m2) 80 (78.0/m2) 87 (99.3/m2) F A
Vitis aestivalis Michx. (Summer Grape) 67 (76.7/m2) 63 (46.7/m2) 67 (56.0/m2) 53 (38.0/m2) V P
Zizia trifoliata (Michx.) Fernald (Meadow Alexanders) 10 (6.7/m2) 10 (3.3/m2) 7 (2.0/m2) 7 (1.3/m2) F P
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 679
We observed 147 and 143 species during the sampling of aboveground
forest understory vegetation pre- and post-fire, respectively. Perennial forbs
dominated the forest understory vegetation. The split-plot ANOVA revealed
slightly greater similarity between species common to the aboveground vegetation
and post-fire seed bank than species common to the aboveground
vegetation and pre-fire seed bank, regardless of the seed-bank layer sampled
(F = 14.6; df = 1,8; P = 0.0051). Despite the significant effect of the prescribed
fire, similarity between the species observed in the aboveground
vegetation and the buried seed bank was low. Sørenson values ranged from
0.12 to 0.28 (mean = 0.16) prior to the fire and 0.16 to 0.34 (mean = 0.25)
post-fire. Pre-fire, the number of species common to the seed bank and
aboveground vegetation was 29 and 25 for the LD and MS layers, respectively
(Table 4). Post-fire, the number of species represented in both the seed bank
and aboveground vegetation was 34 and 31 for the LD and MS layers, respectively
(Table 4). Most of the species responsible for the increase in similarity
between the buried seed bank and aboveground understory vegetation were
perennial forbs and perennial graminoids (Table 4).
Table 3. Test statistics related to the multi-response permutation procedure (MRBP) for seed-bank
species composition. dobserved and dpredicted = observed and expected weighted mean within-group
distance, respectively, A = chance-corrected within-group homogeneity, and P = the probability of
observing a smaller or equal d observed .
MRBP analysis dobserved dexpected A P
1. Test for differences between pre- and post-fire species 3.7058 3.7843 0.0207 0.1011
composition in the litter/duff layer
2. Test for differences between pre- and post-fire species 3.5638 3.5525 -0.0032 0.5896
composition in the mineral soil layer
3. Test for differences between species composition in 3.6409 3.7196 0.0212 0.0926
the litter/duff and mineral soil seed bank layers
Table 2. Summary statistics for seed-bank propagule density (emergents/m2), species richness (S),
and Shannon-Weiner’s diversity index (H′) pre- and post-fire for the litter/duff (LD) and mineral soil
(MS) layers averaged across replicates (n = 5). Data presented are from raw, untransformed data.
LD (n = 5) MS (n = 5)
Mean SD Min Max Mean SD Min Max
Pre-fire 603 417 299 1274 435 124 304 585
Post-fire 424 248 144 692 419 137 272 573
Species richness (S)
Pre-fire 12.3 1.6 10.0 14.3 12.1 1.1 11.0 14.0
Post-fire 11.3 1.5 9.2 13.2 11.0 1.2 10.0 12.8
Weiner’s diversity index (H′)
Pre-fire 1.9 0.1 1.8 2.0 2.1 0.1 1.9 2.1
Post-fire 1.9 0.2 1.6 2.1 1.9 0.1 1.7 2.0
680 Southeastern Naturalist Vol. 11, No. 4
Table 4. Species common to the buried seed bank and aboveground vegetation for the litter/duff
(LD) and mineral soil (MS) seed-bank layers, pre- and post-fire. L = litter/duff, M = mineral soil.
P = present, A = absent.
Species L M L M
Acer rubrum (Red Maple) P P P P
Amphicarpaea bracteata L. Fernald (American Hogpeanut) A A A P
Aristolochia macrophylla (Pipevine) P P P P
Arisaema triphyllum (Jack In The Pulpit) P A P P
Betula lenta (Sweet Birch) P P P P
Campanula divaricata (Small Bonny Bellflower) A A A P
Carex spp. (sedges) P P P P
Carex digitalis (Slender Woodland Sedge) A A P P
Carya glabra (Mill.) Sweet (Pignut Hickory) P A A P
Chelone lyonii Pursh (Pink Turtlehead) A P P A
Circaea lutetiana L. (Broadleaf Enchanter’s Nightshade) P P A A
Dichanthelium spp. (rosette grass) P P P A
Dichanthelium boscii (Bosc’s Panicgrass) A A P P
Dichanthelium commutatum (Variable Panicgrass) A A P P
Dichanthelium dichotomum (Cypress Panicgrass) A A P P
Eupatorium purpureum (Sweetscented Joe Pye Weed) P P P P
Fraxinum americana (White Ash) P A P A
Galium triflorum Michx. (Gragrant Bedstraw) A A P A
Hieracium paniculatum (Allegheny Hawkweed) P P P P
Houstonia purpurea var. purpurea (Venus’ Pride) A A P P
Hydrangea arborescens (Wild Hydrangea) A A P P
Kalmia latifolia L. (Mountain Laurel) P A A A
Laportea canadensis (L.) Weddell (Canadian Woodnettle) A A P A
Liriodendron tulipifera (Yellow-Poplar) P P P P
Lysimachia quadrifolia (Whorled Yellow Loosestrife) A P A P
Melampyrum lineare (Narrlowleaf Cowwheat) A A A P
Oxydendrum arboreum (Sourwood) P P A P
Potentilla canadensis (Dward Cinquefoil) P P P P
Prenanthes altissima (Tall Rattlesnakeroot) A A P A
Prunus serotina Ehrh. (Black Cherry) P A P P
Pycnanthemum montanum (Thinleaf Mountainmint) A P A A
Robinia pseudoacacia (Black Locust) P P P P
Rubus allegheniensis (Allegheny Blackberry) A A P P
Sassafras albidum (Nutt.) Nees (Sassafras) P A A A
Sambucus nigra L. ssp. canadensis ) (L.) R. Bolli (American Elderberry) P P A A
Sanguinaria canadensis L. (Bloodroot) A A P A
Sanicula spp. (sanicle) A A P A
Smilax glauca Walter (Cat Greenbrier) A P A A
Solidago curtisii Torr. & A. Gray (Mountain Decumbent Goldenrod) P P P P
Thalictrum dioicum L. (Early Meadow-Rue) P A P P
Vaccinium pallidum Aiton (Blue Ridge Blueberry) A P A A
Vitis aestivalis Michx. (Summer Grape) A P P P
Viola blanda (Sweet White Violet) P P P P
Vicia caroliniana Walter (Carolina Vetch) A A A P
Viola rotundifolia (Roundleaf Yellow Violet) P P P P
Viola sororia (Common Blue Violet) P P P P
Zizia trifoliata (Meadow Alexanders) P P P P
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 681
Despite the abundance of information characterizing the distribution and
diversity of species across the landscape and the effects of forest management
on understory community composition, little is known about the diversity and
density of the buried seed bank in the southern Appalachians. Outside of studies
that describe the importance of the seed bank for a limited number of shrub and
arborescent species (e.g., Hille Ris Lambers and Clark 2005, Hille Ris Lambers
et al. 2005), this study was the first to our knowledge to describe and quantify
both the woody and non-woody buried seed bank in the Blue Ridge Province
of the southern Appalachian Mountains, an area possessing the highest levels
of diversity of arborescent and herbaceous vegetation in the US. We found the
forest floor (LD) and the upper portions of the mineral soil (MS) contained, on
average, 514 and 427 seeds/m2, respectively, representing 133 identifiable taxa.
Although the density of the seed bank in this study substantially exceeds that in
xeric ridge-top oak forests of the southern Appalachians (Schiffman and Johnson
1992), the density of the seed bank is less than that reported in other mixed-oak
and mixed-mesophytic eastern hardwood forests (Ashton et al. 1998). Species
richness of the buried seed bank in this study, however, was far greater than
reported for other temperate hardwood forests (Schelling and McCarthy 2007,
Small and McCarthy 2010), likely reflecting the diversity inhere nt to productive
southern Appalachian forests.
The overall experimental design used in this study was not specifically
developed to address the effects of controlled burns on the seed bank. Rather,
the experimental design, including the location of plots within experimental
units as well as the vegetation sampling within the experimental units, was
designed to address a larger question of how vegetation (both arborescent and
understory vegetation), as opposed to strictly the buried seed bank, responds
to 3 recommended oak-regeneration treatments, one of which included the
prescribed burn treatments conducted in this seed-bank study. The clustering
of seed-bank sampling around a single regeneration subplot nested within the
larger 0.05-ha plot (Fig. 1) was performed because (1) of the proximity to a
location where fire intensity was set to be recorded, and (2) to avoid disturbing
areas within the permanent plot where other vegetation and fuels data were
being collected. In regards to both the density and diversity of the buried seed
bank reported in this study, the clustering of seed-bank sampling around one
tree-regeneration subplot, as opposed to sampling being conducted throughout
the entire 0.05-ha plot, may have affected our estimates of seed-bank diversity
and/or density (Bigwood and Inouye 1988, Csontos 2007). Had the sampling
been more widely distributed, it is possible the number of parent plants contributing
to the seed-bank subplots would have increased, thereby potentially
increasing seed-bank density and/or diversity. With that caveat in mind, this
study does provide new and detailed information that not only characterizes
the seed bank in productive forests of the southern Appalachians, but also provides
information as to the potential effects of prescribed fire on the density
and diversity of the seed bank.
682 Southeastern Naturalist Vol. 11, No. 4
The composition of the soil seed bank in previously disturbed systems is often
dominated by non-native, shade-intolerant annual, and/or ruderal species (Korb
et al. 2005, Pickett and McDonnell 1989), which can dominate the early stages of
stand development following disturbance. Species frequently observed following
substantial canopy-reducing disturbances, including brambles, Pokeweed, and
other shade-intolerant annual forbs (e.g., Fireweed) were present in the buried
seed bank both pre- and post-fire. However, unlike the seed bank of other temperate
forests (e.g., Bossuyt and Hermy 2001, Bossuyt and Honnay 2008, Halpern
et al. 1999), the seed bank of the mixed-oak stands sampled in this study also
contained numerous perennial species. This finding supports Leckie et al. (2000)
who report the seed bank of a temperate deciduous forest in Québec, Canada contained
a high proportion of both annual and shade-tolerant perennial species. This
study confirms that ruderal and/or annual species can form a persistent seed bank
(Korb et al. 2005, Tsuyuzaki and Kanda 1996, Whitney 1986), but questions the
generalization that the seed bank of mature, closed-canopied forests is dominated
by “early-successional” species.
With the exception of the arborescent seed bank, where emergent density was
≈225% greater in the LD than MS layer, we found no effect of seed-bank layer,
which is a proxy for soil depth, on the overall density and species composition
of the buried seed bank. Many studies document a reduction in the density of the
buried seed bank with increased soil depth (Blodgett et al. 2000, McGee and Feller
1993, Pratt et al. 1984, Qi and Scarratt 1998) as well as varying composition
between upper and lower seed-bank depths (Halpern et al. 1999, Rydgren and
Hestmark 1997). Shade-intolerant perennial and annual species characteristic of
the early stages of stand development are often located lower in the forest floor
profile suggesting a more persistent seed bank (Pratt et al. 1984, Qi and Scarratt
1998), while shade-tolerant perennial forest species are predominantly located in
the upper portions of the seed bank and represent more of a transient seed bank
(Bossuyt et al. 2002). The fact that this study found no significant difference in
the density or composition of the LD and MS layers could imply that even with
increased fire intensity and increased duff consumption, the contribution of the
seed bank to the aboveground vegetation may not change, as the LD and MS layers
were similar in density and composition.
In the southern Appalachians, prescribed fire is utilized to restore structure
and composition, reduce hazardous fuel loadings, promote the regeneration of
desirable tree species, and increase understory production and diversity (Vose
2000). We found no significant effect of a single prescribed burn on the density,
composition, and relative abundance of life forms within the buried seed bank.
This finding is in contrast to studies reporting both increased (Allen et al. 2008,
Schuler and Liechty 2008) and decreased (Blodgett et al. 2000, Clark and Wilson
1994, Schuler et al. 2010) seed-bank emergence following fire and/or experimental
heating. The fires conducted in this study were of low intensity, which
is characteristic of winter burns in eastern US oak forests (e.g., Glasgow and
Matlack 2007; Hutchinson et al. 2005a, b). Heat transfer through the soil profile
decreases with increasing depth (Steuter and McPherson 1995). Consequently,
2012 T.L. Keyser, T. Roof, J.L. Adams, D. Simon, and G. Warburton 683
incomplete consumption of the litter layer coupled with insulation of seeds stored
in the duff and mineral soil likely inhibited seed mortality during the fire (Cain
and Shelton 1998, Greenberg et al. 2012).
In general, low-intensity prescribed fires in mixed-oak forests of the eastern
US have little to no effect on aboveground species composition (e.g., Elliott and
Vose 2005, 2010; Elliott et al. 1999; Hutchinson et al. 2005a). The lack of similarity
between species composition in the seed bank and aboveground vegetation
is well documented (e.g., Grandin 2001, Hopfensperger 2007, Plue et al. 2010,
Roberts and Vankat 1991). In this study, the small, but significant increase in
similarity between the seed bank and aboveground vegetation following a onetime
low intensity burn suggests the seed bank has a limited role in contributing
to community dynamics in mixed-oak forests following typical dormant-season
prescribed fires. Our results confirm studies that document little to no change
in the seed-bank composition following both intermediate silvicultural treatments
(e.g., forest thinning; Korb et al. 2005) and prescribed fire (Schelling and
McCarthy 2007). However, evidence suggests that prescribed fires of greater
intensity or multiple fires may affect not only the density of the buried seed bank,
but also alter the composition by consuming seeds directly or exhausting the seed
bank through increased post-fire germination (Allen et al. 2008, Schuler et al.
2010). It is within the immediate years following more intense, canopy-reducing
disturbances, where environmental conditions may be more conducive to the germination
and establishment of individuals from the seed bank (i.e., ruderal and
other shade-intolerant species), when similarity between aboveground vegetation
and the buried seed bank increases (Bossuyt et al. 2002).
In the context of oak restoration, the lack of an overall effect of prescribed fire
on the density of the seed bank of known oak competitors, including Sweet Birch
and Yellow-Poplar is informative. Studies in other mixed-oak forests have suggested
the use of prescribed fire to reduce the abundance of oak competitors in
the seed bank and thus improve oak regeneration success (e.g., Hutchinson et al.
2005b, Schuler et al. 2010). Either the prescribed fires in this study were not of
high enough intensity to initiate mortality in the Sweet Birch or Yellow-Poplar
seed banks, or these species are fairly resistant to the effects of low-intensity fire.
Results from Schuler et al. (2010) suggest that either multiple burns are required to
deplete the seed bank of these mesophytic species and/or that prescribed fires must
be of greater intensity than the ones implemented in this study. The concentration
of the arborescent seed bank in the LD layer suggests the seed bank of these species
is especially susceptible to fire-induced mortality (Auld and Denham 2006,
Tozer 1998). However, prescribed burns aimed at promoting oak regeneration are
generally conducted with low intensity, and generally consume only a proportion
of the leaf-litter layer and aboveground biomass (e.g., Glasgow and Matlock 2007,
Hutchinson et al. 2005b). Therefore, seed stored in the duff, which was included
in the LD layer in this study, may be protected from mortality during these lowintensity
fires (Greenberg et al. 2012). Yellow-Poplar, which is a particularly aggressive
competitor with oak on moderate- to high-quality sites (Beck and Della-
Bianca 1981), can remain viable up to 8 years in the seed bank (Clark and Boyce
684 Southeastern Naturalist Vol. 11, No. 4
1964, Sander and Clark 1971), and is a prolific seed producer on an almost annual
basis (Beck and Della-Bianca 1981). Consequently, if restoration goals include reducing
the seed source of Yellow-Poplar from mixed-oak stands in order to reduce
competitive pressures during the oak-regeneration process, removal of nearby
seed-producing individuals coupled with repeated, higher-intensity prescribed
burns that consume the litter and duff layers as well as heat the mineral soil may
play a role in reducing competition from Yellow-Poplar seedlings. Although we
observed only negligible effects of a once-applied, low-intensity prescribed fire
on the buried seed bank, the effects of a low-intensity prescribed fire management
regime—one that involves repeated low-intensity burns for the purposes of
promoting oak regeneration (e.g., Brose et al. 2001)—on the buried seed bank are
unknown and should be a focus of future studies across mixed-oak forests in the
This is a contribution of the Regional Oak Study (ROS). This research was initiated
by the Forest Service, USDA, Southern Research Station, Upland Hardwood Ecology and
Management Research Work Unit (RWU-4157) in partnership with the USDA Northern
Research Station, the North Carolina Wildlife Resources Commission, the Stevenson
Land Company, and the Mark Twain National Forest. The authors express their gratitude
to Mark Williams and other members of the North Carolina Wildlife Resources Commission
for preparing and implementing the prescribed burns. In addition, the authors thank
Kenny Frick for assistance in collecting seed-bank samples as well as assisting on the
prescribed burn; Alisha Goodman and Andrea Hinek for assistance in sample collection,
processing, and data collection; Josh Bronson from the USDA Forest Service for providing
greenhouse space and equipment; Dave Dannelly for assistance in identification; and
Beverly Collins from Western Carolina University for providing details regarding seedbank
sampling protocols. Comments from Stan Zarnoch, Dan Dey, Tom Schuler, and two
anonymous reviewers greatly improved this manuscript.
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