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In frequently burned ecosystems, many plants persist by repeated resprouting from basal or belowground buds. This strategy requires that plants reach a balance between biomass loss and recovery, which depends on the shape of the relationship between pre- and post-fire size. Previous analyses of this relationship, however, have focused on the size of the largest stem, which ignores the importance of the multi-stem growth habit that is common in pyrogenic ecosystems. We hypothesized that the presence of multiple stems causes a substantial shift in the relationship between pre- and post-fire size and in the relationship between pre-fire size and size recovery. We measured the height and basal diameter, then calculated volume and biomass, of all stems of six tree species before and nine months after complete removal of aboveground biomass via coppicing. The number of resprouts was correlated with the original number of stems for four species. For all species, the relationship between pre-coppicing and resprout size fit a positive curvilinear function, and the shape of this curve did not differ for maximum and total stem size. Smaller individuals recovered a larger proportion of their pre-coppicing size than larger individuals, but the shape of the size recovery curves were the same regardless of whether the analysis was performed with all stems or only the largest stem. Our results indicate that measuring only the largest stem of multi-stemmed individuals is sufficient to assess the ability of individuals to recover after complete loss of aboveground biomass and persist under frequent burning.
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Size Dependency of Post-Disturbance Recovery of Multi-
Stemmed Resprouting Trees
Jennifer L. Schafer*
, Michael G. Just
Department of Plant and Microbial Biology, North Carolina State University, Raleigh, North Carolina, United States of America
In frequently burned ecosystems, many plants persist by repeated resprouting from basal or belowground buds. This
strategy requires that plants reach a balance between biomass loss and recovery, which depends on the shape of the
relationship between pre- and post-fire size. Previous analyses of this relationship, however, have focused on the size of the
largest stem, which ignores the importance of the multi-stem growth habit that is common in pyrogenic ecosystems. We
hypothesized that the presence of multiple stems causes a substantial shift in the relationship between pre- and post-fire
size and in the relationship between pre-fire size and size recovery. We measured the height and basal diameter, then
calculated volume and biomass, of all stems of six tree species before and nine months after complete removal of
aboveground biomass via coppicing. The number of resprouts was correlated with the original number of stems for four
species. For all species, the relationship between pre-coppicing and resprout size fit a positive curvilinear function, and the
shape of this curve did not differ for maximum and total stem size. Smaller individuals recovered a larger proportion of their
pre-coppicing size than larger individuals, but the shape of the size recovery curves were the same regardless of whether
the analysis was performed with all stems or only the largest stem. Our results indicate that measuring only the largest stem
of multi-stemmed individuals is sufficient to assess the ability of individuals to recover after complete loss of aboveground
biomass and persist under frequent burning.
Citation: Schafer JL, Just MG (2014) Size Dependency of Post-Disturbance Recovery of Multi-Stemmed Resprouting Trees. PLoS ONE 9(8): e105600. doi:10.1371/
Editor: Christopher Carcaillet, Ecole Pratique des Hautes Etudes, France
Received May 4, 2014; Accepted July 25, 2014; Published August 21, 2014
Copyright: ß2014 Schafer, Just. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Data Availability: The authors confirm that all data underlying the findings are fully available without restriction. All relevant data are within the paper and its
Supporting Information files.
Funding: This research was supported by a cooperative agreement between the US Army Engineer Research and Development Center and North Carolina State
University (W9132T-11-2-0007 to W. Hoffmann). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the
Competing Interests: The authors have declared that no competing interests exist.
* Email:
¤ Current address: Department of Biology, William Jewell College, Liberty, Missouri, United States of America
Resprouting provides resilience to fire and allows plants to
persist in pyrogenic ecosystems. When aboveground stems are
killed by fire (i.e., topkilled), species that are able to resprout
generate new biomass from plant parts that survive fire [1,2] such
as basal buds, lignotubers, rhizomes, or the root collar [3,4].
Resprouting ability and resprout biomass [5–7] are influenced by
the size of the belowground bud bank [8], the pool of belowground
resources (e.g., carbohydrates and nutrients [9–14]), and pre-fire
plant size [15,16].
In frequently burned ecosystems, resprouting species are
subjected to repeated cycles of topkill and resprouting [17], so
persistence depends on the ability of plants to recover their pre-fire
size to maintain a balance between biomass loss and recovery
[13,18]. Resprout height and diameter are positively correlated
with pre-fire stem height and diameter [16,19,20], with the
relationship between pre- and post-fire size fitting a curvilinear
scaling function [18]. This ‘‘resprout curve’’ illustrates the balance
between biomass loss and recovery and determines the equilibrium
size (i.e., where pre-fire and post-fire size are equal) upon which
plants will converge over multiple fire cycles ([18]; Figure 1A).
Although resprout size is correlated with pre-fire size [16,19,20],
large plants often recover their pre-fire size more slowly than small
plants [18,21]. This ‘‘recovery curve’’ is a negative curvilinear
relationship between pre-fire size and the ratio of post- to pre-fire
size (Figure 1B).
Studies on the relationship between pre- and post-fire size and
the size dependency of post-fire recovery, however, often focus
only on the largest pre-fire stem and largest resprout [16,18,19]
even though many resprouting species are multi-stemmed before
and/or after fire (e.g., [22–24]). In fact, the number of resprouts is
correlated with the number of stems pre-fire [20,25,26]. Allocation
of biomass to multiple stems, rather than one stem, may be
beneficial due to limitations on maximum stem height and growth
rates [27–29] and the improvement in competitive success
conferred by a large crown volume [30]. If the curvilinear nature
of resprout and recovery curves is a consequence of limitations on
maximum stem growth rates [28,31], then this limitation could be
overcome by producing multiple stems.
Accounting for all stems of multi-stemmed resprouting species,
therefore, may cause an upward shift in resprout (Figure 1A) and
recovery (Figure 1B) curves. An upward shift in the resprout curve
would indicate that individual plants are able to maintain a greater
biomass (i.e., a greater equilibrium plant size) with frequent
burning. Consequently, larger individuals would be able to recover
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their pre-fire size. In this case, production of multiple stems could
increase the ability of plants to escape a suppressed state of
repeated topkill and resprouting [17,32,33] during a longer fire
free interval. Alternatively, accounting for all stems could lead to a
change from a curvilinear to linear relationship between pre- and
post-fire size and size recovery, indicating that curvilinearity is not
a fundamental property of resprouting. Regardless, understanding
the impact of multiple stems on resprout and recovery curves is
important because the ability of individual plants to recover
biomass lost during fire allows for persistence with repeated
burning [13].
We assessed resprouting success and the size dependency of
volume and biomass recovery after complete loss of aboveground
biomass. Specifically, we coppiced aboveground stems – as has
been done in other studies to simulate fire-induced topkill
[6,14,34,35] – of six tree species that occur in the pyrogenic
longleaf pine savannas and adjacent stream-head pocosins of the
southeastern United States [36,37]. To test the hypothesis that
accounting for all stems of multi-stemmed resprouting species
causes a shift in resprout and recovery curves, we measured all
stems pre-coppicing and all resprouts. We assessed possible shifts
in resprout and recovery curves by testing for differences in the
slopes and y-intercepts of the log-transformed relationships
between pre-coppicing and resprout size (i.e., volume and biomass)
of the largest stem (maximum size) and all stems (total size;
Figures 1C and 1D).
Materials and Methods
Ethics Statement
We obtained approval for data collection from the Endangered
Species Branch at Fort Bragg Military Installation. Data was
collected on publicly owned land. No protected species were used
in this study.
Study site and species
We conducted our study at Fort Bragg, which is located in the
Sandhills region of North Carolina (35u079N, 79u109W).
Longleaf pine (Pinus palustris Mill.) savanna (e.g., upland pine/
scrub oak sandhill sensu [36]) is the most widespread vegetation
type on the installation. Pine needles and wiregrass (Aristida stricta
Michx.) accumulate quickly and facilitate frequent fire; the
average historical fire return interval is approximately 2 years
[38]. For the lowland stream-head pocosins (i.e., wetlands)
Figure 1. Hypothesized shifts in resprout and recovery curves resulting from inclusion of all stems. (A) Differences in resprout curves
that could arise from inclusion of all stems of multi-stemmed trees. Stars indicate the equilibrium size that develops over multiple fire cycles that
corresponds to the point at which biomass loss is equal to biomass recovery (i.e., intersects with the 1:1 line; following [18]). (B) Recovery curves that
correspond with resprout curves. (C) Illustration of the transformation of resprout curves to a logarithmic scale. (D) Illustration of the transformation
of recovery curves to a logarithmic scale. We assessed shifts in resprout and recovery curves by testing for differences in the slopes and y-intercepts
of the log
-transformed relationships between maximum and total size and size recovery.
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embedded within the savanna matrix [37], higher moisture
content and differences in species composition contribute to a
longer fire return interval of 7–50 years [39]. Soil moisture
increases along the gradient from upland savanna to lowland
pocosin, and soils are classified as entisols, inceptosols, or ultisols
[40]. Mean annual precipitation is 1275 mm, and summer is the
wettest season [37]. Fort Bragg is divided into discrete landscape
units locally referred to as burn blocks, within which prescribed
fire is applied approximately every 3 years [41]. Prescribed fires at
Fort Bragg are conducted during the dormant season (December–
March) and the growing season (April–July) [42]. Lightning
Table 1. General characteristics of individuals included in the study.
#of Stems Pre-
Coppicing #of Resprouts
Maximum Stem
Height (cm)
Maximum Basal
Diameter (mm)
Quercus laevis 29 26 1–6 0–8 60–330 6.99–61.18
Diospyros virginiana 26 26 1–2 1–5 58–285 7.74–40.01
Liquidambar styraciflua 32 31 1–5 0–17 12–399 2.38–41.20
Liriodendron tulipifera 29 27 1–8 0–37 37–610 5.12–56.92
Persea palustris 31 31 1–4 1–7 53–289 5.46–34.33
Acer rubrum 30 28 1–6 0–9 38–382 4.27–30.13
Species are listed in order of their position along the savanna-to-pocosin gradient.
Does not include individuals burned in the June 2013 wildfire.
For stems pre-coppicing.
Figure 2. Ratio of resprout stem number to pre-coppicing stem number. In the boxplots, the solid and dotted bars represent the median
and mean, respectively; the lower and upper bars represent the 25
and 75
percentiles, respectively. The lower and upper ‘‘whiskers’’ show the
largest and smallest values that are not outliers and the lower and upper dots show the 5
and 95
percentiles. Kruskal-Wallis
= 20.03, P= 0.001;
different letters indicate significant differences among species. The dashed line indicates where the number of resprouts equals the number of stems
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ignited fires in the southeastern US typically occur during the
spring and summer (April–September) [43,44].
We selected six focal species that differ in their distribution
along the savanna-to-pocosin gradient: Quercus laevis Walter
(turkey oak), Diospyros virginiana L. (persimmon), Liquidambar
styraciflua L. (sweetgum), Liriodendron tulipifera L. (tulip poplar),
Persea palustris (Raf.) Sarg. (swamp bay), and Acer rubrum L. (red
maple; Table 1; nomenclature follows The PLANTS Database
(US Department of Agriculture, Natural Resources Conservation
Service; Quercus laevis is a savan-
na species, and D. virginiana occurs in the savanna and the
ecotone between savanna and pocosin. Liquidambar styraciflua is
most common in the ecotone, and L. tulipifera,P. palustris, and
A. rubrum are restricted to the pocosin and ecotone. All study
species typically resprout from basal or belowground buds after
topkill via fire or other damage.
Figure 3. Curvilinear relationships between total pre-coppicing stem volume and total resprout stem volume.
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Figure 4. Curvilinear relationships between total pre-coppicing stem biomass and total resprout biomass.
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Field measurements and calculations
In October 2012, we selected 30–32 individuals of each species
that spanned a range of maximum stem heights and diameters
(Table 1); even the largest individuals were considered saplings.
Individuals were found throughout their distribution along the
savanna-to-pocosin gradient in multiple burn blocks (n = 6) that
were burned 3–4 years previously. We measured the height and
basal diameter (within 2 cm of ground level) of all stems of each
individual and then, to simulate topkill, coppiced all stems at
,2 cm above ground level. Stems were coppiced in October, at
the beginning of the dormant season and after the typical wildfire
season [43,44]. Coppicing is commonly used as a surrogate for
disturbance-induced topkill (e.g., [34,35]), and resprouting success
is similar between burned and coppiced individuals [6,15,45]. A
wildfire in June 2013 burned a small section of one of our study
sites, which reduced our sample size of all species except L.
styraciflua (Table 1). In July 2013, 9 months after coppicing and
near the end of the growing season, we measured the height and
basal diameter of all resprouts of each individual.
For individuals that resprouted, we calculated the conical
volume of each stem from measurements of stem height and
diameter. We determined the maximum stem volume (i.e., volume
of the largest stem) and total stem volume (i.e., the sum of volumes
of all stems) of each individual pre-coppicing and after resprouting.
For three species – Q. laevis,D. virginiana, and L. styraciflua –we
used allometric equations from Robertson and Ostertag [46] to
calculate maximum and total stem biomass of each individual pre-
coppicing and after resprouting. Except for large pre-coppiced Q.
laevis and small L. styraciflua resprouts, the majority of our stems
were within the range of diameters used to develop the allometric
equations [46].
Statistical analyses
For each species, we analyzed the relationship between pre-
coppicing stem number and the number of resprouts using
Kendall’s tau. To analyze differences among species in resprouting
success (i.e., production of resprouts), we calculated the ratio of
resprouts to pre-coppicing stems for all individuals and used a
Kruskal-Wallis test, with post-hoc pair-wise significance tests
Figure 5. Relationships between pre-coppicing stem volume and resprout stem volume on a logarithmic scale. Total stem volume is
denoted with filled symbols and dashed lines. Maximum stem volume is denoted with open symbols and solid lines. ** P,0.01, *** P,0.001 for
regressions. Pvalues for differences in slopes and intercepts between maximum and total volume are given.
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adjusted for multiple comparisons. To determine if there was a
significant curvilinear relationship between total resprout size and
total pre-coppicing size, we used the curve estimation function in
SPSS version 19.0 (IBM Corporation, Armonk, NY, USA).
Specifically, we fit power functions to the relationships between
total pre-coppicing stem volume and total resprout stem volume
(for all species) and total pre-coppicing stem biomass and total
resprout biomass (for Q. laevis,D. virginiana, and L. styraciflua).
We used a regression model with log
resprout size (i.e., volume
or biomass) as the dependent variable and log
pre-coppicing size
(i.e., volume or biomass), data type (i.e., maximum or total size,
coded as 1 and 0, respectively), and an interaction term (log
coppicing size * data type) as independent variables entered into
the model to determine if there was a significant difference
between the slopes and y-intercepts of the relationships between:
(1) pre-coppicing and resprout maximum and total stem size
(Figure 1C) and (2) pre-coppicing size and recovery of maximum
and total stem size (Figure 1D) for each species.
For all species, at least 90% of individuals resprouted after
coppicing (Table 1). The number of resprouts was positively
correlated with the number of coppiced stems for Q. laevis
(t= 0.339, P= 0.025), L. styraciflua (t= 0.296, P= 0.042), P.
palustris (t= 0.296, P= 0.058), and A. rubrum (t= 0.491,
P= 0.001). The number of resprouts of D. virginiana (t= 0.251,
P= 0.239) and L. tulipifera (t= 0.224, P= 0.139) was not
correlated with the number of coppiced stems. The number of
Figure 6. Relationships between pre-coppicing stem biomass and resprout stem biomass on a logarithmic scale. Total stem biomass is
denoted with filled symbols and dashed lines. Maximum stem biomass is denoted with open symbols and solid lines. ** P,0.01, *** P,0.001 for
regressions. Pvalues for differences in slopes and intercepts between maximum and total biomass are given.
Figure 7. Relationships between pre-coppicing stem volume and the ratio of resprout volume to pre-coppicing volume. Data is
shown on a logarithmic scale. Total stem volume is denoted with filled symbols and dashed lines. Maximum stem volume is denoted with open
symbols and solid lines. * P,0.05, ** P,0.01, *** P,0.001 for regressions; NS indicates not significant. Pvalues for differences in slopes and intercepts
between maximum and total volume are given.
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resprouts of all species tended to be equal to or greater than the
number of coppiced stems (Figure 2); 73% of individuals that
resprouted had more resprouts than coppiced stems.
There was a positive curvilinear relationship between total
resprout and pre-coppicing stem volume (Figure 3) and biomass
(Figure 4) for all species studied. There was no difference between
the slopes or intercepts of the relationships between pre-coppicing
and resprout maximum and total volume (Figure 5) and pre-
coppicing and resprout maximum and total biomass (Figure 6). In
other words, for all species, resprout curves were similar for
maximum and total size.
Recovery of volume and biomass was negatively correlated with
pre-coppicing volume and biomass, regardless of whether all stems
were included in the analysis. For all species, there was no
difference between the slopes or intercepts of the relationships
between recovery of maximum and total volume (Figure 7) and
recovery of maximum and total biomass (Figure 8). Most
individuals recovered less than 55% of their maximum stem
The ability of plants to resprout after topkill contributes to their
persistence in pyrogenic ecosystems. Across species in our study,
95% of individuals resprouted after complete removal of
aboveground biomass (Table 1). Resprout number has been
found to be positively correlated with the number of stems present
before fire [20]; this was the case for four of our six study species.
Individuals with more stems pre-fire may have larger storage
organs, which translate to larger pools of carbohydrates and buds
to support resprouting [7,47,48]. For the two species in our study
for which resprout number was not positively correlated with pre-
coppicing stem number, D. virginiana and L. tulipifera,
individuals with only one stem pre-coppicing produced 1 to 5
and 1 to 14 resprouts, respectively. Factors such as bud activation
and proximity of buds to the soil surface [49], as well as pre-fire
stem size [15,16], may have affected resprout number.
We found that total resprout size was positively correlated with
pre-coppicing total size and fit a curvilinear function (Figures 3
and 4). Although maximum resprout size may be limited by
growth rates [28,31], the ability to increase mechanical strength to
support height growth [50], or physiological changes that alter
allocation of photosynthates [51], we found no difference in the
resprout curves for maximum and total size (Figures 5 and 6;
determined by analyzing log
-transformed data). Accounting for
all stems did not cause a significant shift in the resprout curves, and
thus, production of multiple stems does not change the size at
which individuals persist in frequently burned ecosystems. One
explanation for the lack of upward shift in resprout curves could be
related to the concomitant increase in resprout and pre-coppicing
volume and/or biomass – individuals in our study had up to eight
stems pre-coppicing – such that inclusion of all stems of multi-
stemmed individuals affected the location of an individual on the
curve rather than the shape of the curve. In addition, intraspecific
variation in pre- and post-fire sizes could be related to resource
availability because plants in high-resource environments are
larger after fire than plants of the same initial size in low-resource
environments [18].
Similar to Grady and Hoffmann [18], when we accounted for
only the largest stem, larger individuals recovered a smaller
fraction of their pre-coppicing size than smaller individuals.
Contrary to our hypothesis, there was no difference in the shape of
the recovery curves of maximum and total size (Figures 7 and 8;
determined by analyzing log
-transformed data). Accounting for
all stems, rather than only the largest stem, does not affect which
individuals, in terms of pre-coppicing size, are able to recover all
biomass lost during fire. Although 73% of the resprouting
individuals in our study experienced an increase in stem number
after complete removal of aboveground biomass (Figure 2), our
results suggest that the potential benefits of producing multiple
stems do not extend to post-disturbance biomass recovery.
The shape of resprout and recovery curves may be influenced
by resprout age. Historically, the fire return interval in longleaf
pine savannas ranged from 0.5 to 12 years [38], and savannas at
our study site are currently burned every 3 years, on average, with
stream-head pocosins generally burning less frequently [39]. The
number of resprouts per clump is higher in more recently burned
sites than longer unburned sites [52,53], suggesting that self-
thinning of resprouts can occur over time such that total size may
converge on maximum size as the number of stems decreases.
Furthermore, large individuals recovered a lower proportion of
their size regardless of whether resprouts were 9 months (Figures 7
and 8) or 3 years old [18].
The shape of resprout and recovery curves may also be
influenced by fire season. In the southeastern US, plants burned
during the dormant season have greater post-fire stem densities
[4,54] and aboveground biomass [55] than plants burned during
the growing season. Differences in resprout number should have
little or no effect on the persistence equilibrium since there is no
difference between resprout and recovery curves of maximum and
total stem size (Figures 5-8). Greater biomass [55] and a larger
increase in growth rates [56] after dormant season fires suggests
that resprout curves of plants burned during the dormant season
could be shifted upward from plants burned during the growing
season. Nonetheless, any effects of fire season on resprout and
recovery curves should be consistent for maximum and total stem
Our study assessed the importance of considering all stems, not
just the largest stems, when assessing size recovery after complete
removal of aboveground biomass. The ability of plants to produce
multiple resprouts did not allow individuals to reach a larger
equilibrium size or recover a greater proportion of their pre-
coppicing size. Production of multiple stems, therefore, does not
appear to affect persistence in frequently burned ecosystems in
regard to the balance between biomass loss and recovery. Our
study species are all trees that resprouted from the root crown; it is
not clear how differences in allometric constraints on resprout
allocation (e.g., shrubs vs. trees; [57]) or the belowground structure
from which resprouts are produced (e.g., lignotubers or rhizomes;
[3]) influence relationships between maximum and total stem size.
Nevertheless, accounting for only the largest pre-fire stem and
largest resprout appears to be an adequate predictor of species’
equilibrium size and their ability to recovery their pre-fire size and
Figure 8. Relationships between pre-coppicing stem biomass and the ratio of resprout biomass to pre-coppicing biomass. Data is
shown on a logarithmic scale. Total stem biomass is denoted with filled symbols and dashed lines. Maximum stem biomass is denoted with open
symbols and solid lines. ** P,0.01, *** P,0.001 for regressions. Pvalues for differences in slopes and intercepts between maximum and total biomass
are given.
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should not lead to misinterpretation of persistence ability over
multiple fire cycles.
Supporting Information
Dataset S1 Pre-coppicing and resprout stem volume
and biomass.
We thank Alicia Ballard, Spencer Bell, Bradley Breslow, and Ashley
McGuigan for help in the field. Alice Broadhead, Rene´e Marchin,
Matthew Hohmann, and William Hoffmann provided helpful comments
on the manuscript.
Author Contributions
Conceived and designed the experiments: JLS MGJ. Performed the
experiments: JLS MGJ. Analyzed the data: JLS MGJ. Contributed to the
writing of the manuscript: JLS MGJ.
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Recovery of Multi-Stemmed Resprouting Trees
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Recovery of Multi-Stemmed Resprouting Trees
PLOS ONE | 12 August 2014 | Volume 9 | Issue 8 | e105600
... The larger the size of the tree prior to topkill, the greater the potential access to resources to drive resprouting and stem growth. It has in fact been well established that growth following resprouting is positively correlated with pre-disturbance stem size (Grady & Hoffmann, 2012;Holdo, 2006b;Schafer & Just, 2014) and that this relationship can hold vegetation in a persistent, stable fire trap (Grady & Hoffman, 2012). It is unclear, however, how post-disturbance growth rates and their dependence on pre-disturbance size vary across species and the consequences of this interspecific variation for escape. ...
... We show that there is considerable variation in growth following resprouting: our estimates project an almost five-fold difference in the expected time needed to recover pre-disturbance size (starting from a pre-disturbance basal area of 20 cm 2 ) between the slowest and fastest grower. Supporting previous work (Bonfil et al. 2004;Grady & Hoffmann, 2012;Schafer & Just, 2014), we found a strong dependence of post-disturbance growth on pre-disturbance size (even two years after the original disturbance event), but there was no evidence for variation in the magnitude of this dependence across species. Fast-growing species might be expected to exhibit a stronger relationship with predisturbance size than slow-growing species, for example, assuming that fast-growing species are more likely to invest in growth and escape from future disturbances rather than in storage and the ability to tolerate disturbance. ...
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Vegetation states in savannas are highly sensitive to tree growth rates, which determine whether individual trees can “escape” periodic disturbances. Resprouting trees have lopsided shoot:root ratios and are often multi‐stemmed, and these variables can modify post‐disturbance growth rates and therefore the probability of escape. To date, few studies have systematically examined the implications of interspecific variation in these factors for escape. We conducted a two‐year field experiment across 16 tree species in a South African lowveld savanna to quantify growth metrics following topkill. We examined the dependence of growth on pre‐disturbance stem size and the relationship between growth rate and the tendency of trees to produce a few large vs. many small resprouts following disturbance. We found that resprout growth was strongly influenced by pre‐disturbance size, but the strength of this relationship did not vary across species. In contrast, our results showed that fast‐growing species tended to allocate resources toward a few dominant stems, while slow‐growing species allocated new biomass towards many smaller stems. Tree species that produced a few large stems also tended to produce individual stems that were tall and thin, further suggesting that the “few large vs. many small” axis is linked to intrinsic species attributes. These findings have implications for understanding how interspecific variation in savanna tree communities may influence their ability to escape disturbance traps.
... For each of the 290 located individuals, we recorded the sex and maximum stem height (cm). We did not include number of stems in the current analyses as maximum stem height has been shown to be sufficient for characterizing growth in this system (Schafer and Just 2014). As L. subcoriacea exhibits limited clonality, we defined an individual as all stems separated by \ 0.5 m. ...
... A previous study of resprouting shrubs across wetland ecotones on Fort Bragg indicated that small-sized individuals recovered most or all of their pre-burn size 1-year post-fire (Grady and Hoffmann 2012), but the pre-burn measurement collection in that study differed from our collection methods. A separate study of resprouting found that none of the six tree species investigated recovered their aboveground biomass 1 year after physical removal of stems (Schafer and Just 2014). While we did not measure stems of other species surrounding L. subcoriacea individuals, our anecdotal observations of the response of those species suggested that their post-fire recovery was similar to L. subcoriacea, with neighboring species not outcompeting or overtopping regenerating L. subcoriacea individuals. ...
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Understanding demographic vital rates and the factors that affect those rates are key components of successful conservation strategies for many threatened and endangered rare plant species. Lindera subcoriacea is a rare dioecious shrub that occupies isolated wetland habitats in a small number of locations in the southeastern United States. The species faces a number of threats to its continued persistence, including habitat destruction, invasive species, and population isolation. From 2011 to 2019, we collected demographic information from 290 L. subcoriacea individuals within 28 populations on Fort Bragg, North Carolina and used the data to estimate demographic vital rates in unburned populations and after being exposed to prescribed fire. We then constructed population matrices and estimated population growth rates under a 3-, 5-, and 10-year return interval. Results indicated that L. subcoriacea individuals have high survivorship in both burned and unburned populations, seed production was reduced 1- and 2-year post-fire, seed production was highly uneven across individuals, seedling recruitment was extremely low, and simulated population growth rates were only above 1.0 under the 10-year fire return interval. Taken together, these results indicate that (1) L. subcoriacea populations are persisting with population growth rates close to one, (2) the short-term impacts of fire on the overall population growth rate of L. subcoriacea, while only 2–3% may determine long-term population viability, and (3) extremely uneven seed production and limited recruitment of seedlings into larger size classes make L. subcoriacea populations vulnerable to stochastic demographic processes.
... Because the resprout category also includes surviving trees, many resprouts were large in diameter. Resprouting from roots or stems is a survival tactic that allows a tree to persist after disturbance (Clarke et al., 2013;Schafer and Just, 2014). Resprouting trees can survive even severe damage (Schafer and Just, 2014). ...
... Resprouting from roots or stems is a survival tactic that allows a tree to persist after disturbance (Clarke et al., 2013;Schafer and Just, 2014). Resprouting trees can survive even severe damage (Schafer and Just, 2014). In the present study, some trees were cut down to stumps during the flood debris removal process and were still able to resprout. ...
... Key factors at larger scales are historical disturbance regimes, disturbance type and severity, and environmental characteristics, among others (Kruger et al., 1997;Bellingham and Sparrow, 2000;Del Tredici, 2001;Bond and Midgley, 2001;Bond and Midgley, 2003;Pausas and Keeley, 2014). At a smaller scale, growth form Vesk, 2006;Zizka et al., 2014) and individual plant size (Burrows, 1985;Hodgkinson, 1998;Keeley, 2006;Schafer and Just, 2014) are also key to explain plant response to disturbance, mainly because there is a trade-off between reserve storage and the production of new tissues (Bond and Midgley, 2001;Schwilk and Ackerly, 2005;Vesk, 2006). For example, it's been reported that shrubs in semiarid environments tend to produce a greater number of thinner resprouts than trees, and a greater total volume of resprouts per unit area, so their canopies can rapidly achieve the reproductive size; whereas trees allocate reserves to a smaller number of thicker resprouts to grow tall and escape the flame zone (Hoffmann and Solbrig, 2003;Zizka et al., 2014). ...
... Further measurements will help confirm the performance of the proposed RCIs for said species. Our results indicate that despite the variability in the number and diameter of resprouts and trunks between and within species, the allometric relationship between their respective estimated composite diameters (ECRD and ECTD) is closely linked to the relationship between the diameter of the main resprout and the main trunk, as has been shown for a limited number of tree species by Schafer and Just (2014). ...
Qualitative measures of resprouting capacity often fail to capture inter-and intra-species variation, whereas available quantitative methods can be complex and time-consuming, hindering broad-scale comparative studies. Here, we propose two quantitative indices that can be applied in a standard way in different regions. We sampled 1046 plants of 20 dominant species (6 shrubs, 7 trees and 7 tree/shrubs) from the seasonally dry forests of the arid Chaco, central-western Argentina. Sampling was conducted in burned field sites one growing season after fire. For each sampled plant we measured the diameter of the main burned trunk (MTD) and main resprout (MRD), and the number of burned trunks (TN) and resprouts (RN); we then built estimated composite diameters for trunks and resprouts (ECTD and ECRD) and we calculated two alternative Resprouting Capacity Indices: RCI 1 (ECRD/ECTD); and RCI 2 (MRD/MTD). The indices were validated against a measure of Resprouting Vigour (RV) that included detailed measurement of all trunks and resprouts for a subset of sampled plants. In all cases, variables indicative of fire severity were measured and included in the analyses. The RCIs and RV were highly related, both at the species and growth form levels. Fire severity had no significant effect on these relationships, but growth form affected RCI 2. All species were capable of resprouting, showing considerable inter-species variation for the two proposed RCIs. Species rank differed considerably between RCIs and survival-only estimations. RCI 1 was higher in tree/shrubs (i.e. species regarded as trees or shrubs) and trees than in shrubs. All species showed decreasing resprouting capacity with increasing ECTD. Our results support the use of the proposed RCIs as a robust tool to assess resprouting capacity, providing more details than survival-based assessments. Choosing one or the other implies a trade-off between accuracy and simplicity, and may depend on the scale and objective of the study, and resprouting patterns of studied species. Species, growth form and individual plant size are relevant in explaining post-fire resprouting capacity and survival.
... Escape height has been reported for tree populations in several mesic savannas (e.g. Bond et al., 2012;Freeman et al., 2017;Nguyen et al., 2019;Pilon & Durigan, 2017;Prior et al., 2010;Schafer & Just, 2014;Werner, 2012;Werner & Franklin, 2010). The term 'resistance height' used in this paper is equivalent to the term 'escape height' used in some papers (Balfour & Midgley, 2006;Bond et al., 2012). ...
1. In mesic savannas worldwide, trees experience frequent fires, almost all set by humans. Management fires are set to reduce or enhance tree cover. Success depends greatly on responses of sub‐adult trees to such fires. To date, the number of successive years that sub‐adult trees can resprout nor the number of years that they must resist being top‐killed by successive fires, nor the requisite height, have been reported. 2. In a six‐year experimental field study in Guinean savannas of West Africa, we monitored annually the heights and responses of 1,765 permanently tagged sub‐adult trees under annual fires set in three different periods of the long dry season: early‐dry season (EDS), mid‐dry season (MDS) and late‐dry season (LDS). Annual MDS fires are the common local management protocols of Guinean savannas, although EDS fires are common in some of the savannas. 3. Results showed that overall, the proportion of sub‐adults that resisted being top‐killed differed across fire seasons. Further, resisting one fire gave a better chance of resisting the next. Only sub‐adults that were able to resist direct damage for three successive EDS and MDS fires reached sufficient height to be recruited to the adult stage. Resistance height (avoiding topkill) was ∼1 m for EDS and ∼2 m for both MDS and LDS fires. Recruitment height (threshold for transition to adult stage) was ∼3 m for EDS and ∼ 3.3 m for MDS fires. No height was great enough for sub‐adult trees to be recruited to adult stages in LDS fire. Synthesis and applications: The results of this novel field study showed clearly that successive early‐ and mi‐dry season fires can enhance tree density and that successive late‐dry season fires alone reduce tree density in Guinean savannas due to the effects of successive fires on sub‐adult trees. The results suggest that a planned regime of these seasons of fire could be used to maintain the desired tree density in Guinean savannas and may inform fire management in other mesic savannas where goals are to increase or decrease tree densities. It also provides relevant information for comparative studies on the mechanisms of recruitment of sub‐adult trees to an adult stage in all mesic savannas, a process that ultimately determines savanna physiognomy.
... Plant cover (%) was measured every late spring, using the same sampling quadrats of the seeder species. Finally, three individuals per species and plot were selected to regularly measure plant vigour (cm), for which purpose the maximum length reached by any resprout of a given plant was measured (Schafer & Just 2014). ...
La disponibilidad hídrica se considera como el factor más limitante en el crecimiento y la distribución de las especies vegetales presentes en los ecosistemas mediterráneos, donde los rigores del clima imponen una doble adversidad a los sistemas biológicos: la escasez de precipitaciones y la irregularidad de las mismas. Por su parte, el fuego ha sido una perturbación recurrente en los ecosistemas mediterráneos durante los últimos miles de años, modelando su paisaje y las formaciones vegetales presentes en los mismos. Sin embargo, se espera que las condiciones en ambos factores varíen en el futuro, ya que con el cambio climático se proyecta un aumento en la frecuencia e intensidad de los periodos de sequía, lo cual unido a la elevación de las temperaturas provocará un aumento en el riesgo de incendios y en la ocurrencia de los mismos. En la presente tesis doctoral se muestran los resultados obtenidos a partir de un experimento de manipulación del régimen de precipitaciones llevado a cabo durante cinco años en un matorral mediterráneo del centro de la Península Ibérica. Para ello se instaló en campo un sistema de riego y cubiertas de exclusión de lluvia automatizadas, con las que se simularon varios tratamientos de sequía antes y después de llevar a cabo una quema experimental. El objetivo principal de este trabajo ha sido estudiar y entender mejor la respuesta frente a la sequía de la vegetación presente en estos ecosistemas de matorral, tanto en su estado maduro (antes del fuego) como en su fase juvenil (después del fuego). El estudio se ha realizado desde una perspectiva de grupos funcionales, intentando discernir si la respuesta frente a la sequía es diferente o no en especies con distinta estrategia de regeneración (especies semilladoras frente a rebrotadoras). Así mismo, el desarrollo del trabajo se ha realizado de una forma integral, estudiando desde la ecofisiología y la respuesta funcional a nivel de planta hasta la estructura y composición de la comunidad vegetal en su conjunto, pasando por la dinámica de las distintas poblaciones de plantas. La tesis doctoral se ha estructurado en cuatro capítulos en formato de artículos científicos: En el capítulo 1, “Modificación de los patrones de lluvia en un matorral mediterráneo: diseño del sistema, respuestas de las plantas y quema experimental”, se describe el diseño y la implantación del experimento de manipulación del régimen de precipitaciones. Los objetivos de este capítulo fueron evaluar el efecto de estas manipulaciones sobre la humedad del suelo y el microambiente de las parcelas, analizar las primeras respuestas de las plantas frente a la sequía antes de la quema experimental y reportar las características del fuego registradas en dicha quema. En el capítulo 2, “Diferencias en los rasgos morfo-fisiológicos de la hoja reflejan la respuesta del crecimiento frente a la sequía en una especie mediterránea semilladora pero no en una rebrotadora”, se presenta la respuesta de dos especies con diferentes características foliares y estrategias de regeneración (la semilladora Cistus ladanifer y la rebrotadora Erica arborea) frente a la sequía durante una estación de crecimiento antes del fuego. Los objetivos de este trabajo fueron entender mejor los mecanismos funcionales que las plantas utilizan para hacer frente a la sequía y determinar los principales rasgos morfo-fisiológicos de la hoja relacionados con el crecimiento de la planta. Una vez realizada la quema experimental de las parcelas de estudio, en el capítulo 3, “Los ambientes post-fuego son favorables para el funcionamiento de los arbustos mediterráneos semilladores y rebrotadores, incluso bajo sequía”, se describe la respuesta ecofisiológica frente a la sequía en las principales especies leñosas de la comunidad (Cistus ladanifer, Erica arborea, Erica scoparia y Phillyrea angustifolia) durante los tres primeros años después del fuego. Los objetivos de este capítulo fueron comparar la respuesta funcional de las plántulas y rebrotes respeto a las plantas adultas (es decir, quemado frente a no quemado), estudiar el efecto de la sequía post-incendio en estas respuestas e intentar discernir si existía o no una sensibilidad diferente entre especies con distinta estrategia de regeneración (semilladoras frente a rebrotadoras). Finalmente, en el capítulo 4, “Dinámicas post-incendio a corto plazo en un matorral mediterráneo sometido a una sequía experimental”, se muestra la dinámica de regeneración de la comunidad vegetal presente en la zona de estudio durante los cuatro primeros años después del fuego. En este caso, el objetivo del estudio fue evaluar el efecto de la sequía post-incendio en la dinámica poblacional de las principales especies leñosas semilladoras (Cistus ladanifer, Rosmarinus officinalis y Genista hirsuta) y rebrotadoras (Erica arborea, Erica scoparia y Phillyrea angustifolia), averiguar si la estrategia de regeneración (semilladoras frente a rebrotadoras) jugaba un papel clave en la recuperación de las especies y evaluar si los cambios a nivel poblacional, en caso de producirse, afectaban finalmente a la configuración de la comunidad en su conjunto. En resumen, los resultados obtenidos en la presente tesis doctoral nos muestran que el matorral mediterráneo presenta una alta resiliencia frente a la sequía, tanto antes como después del fuego, aunque algunas especies (especialmente las semilladoras) pueden verse afectadas negativamente por dicho factor. De hecho, hemos visto que los cambios que las plantas sufren a nivel funcional, pueden traducirse posteriormente a nivel poblacional y terminar afectando significativamente a la comunidad en su conjunto. Por ello, creemos que experimentos como el realizado en esta tesis, aun siendo complejos, son claves para estudiar y entender de una manera global el papel de la sequía y el fuego en los ecosistemas mediterráneos, ya que nos permiten abordar la respuesta de las plantas desde distintos niveles de análisis y a lo largo de diferentes momentos en su ciclo vital. Además, ahondar en nuestro conocimiento acerca de los efectos de la sequía y el fuego sobre la vegetación puede ser clave para entender y prever los efectos del cambio climático en los ecosistemas mediterráneos, puesto que las proyecciones nos indican que ambos factores jugarán un papel determinante en la futura composición, estructura y funcionamiento de muchos ecosistemas en dichas regiones del globo.
... Deforestation and changes in land use intensity are common activities that could negatively impact native forest biota [3][4][5][6]. New seed input [7], buried seeds in the soil [8,9], resprouting [10], and seedling survival rates determine the development of subsequent vegetation after disturbances [11]. Thus, in pristine natural forests, continuous seed input and storage could ensure plant community regeneration following a disturbance [12]. ...
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Human activity negatively affects the sustainability of forest ecosystems globally. Disturbed forests may or may not recover by themselves in a certain period of time. However, it is still unclear as to what parameters can be used to reasonably predict the potential for self-recovery of human-disturbed forests. Here, we combined seed rain, soil seed bank, and seed emergence experiments to evaluate the potential for self-recovery of a highly disturbed, tropical, mixed deciduous forest in northeastern Thailand. Our results show a limited potential for self-recovery of this forest due to low seedling input and storage and an extremely high mortality rate during the drought period. There were 15 tree species of seedlings present during the regeneration period in comparison with a total number of 56 tree species in current standing vegetation. During the dry season, only four tree seedling species survived, and the highest mortality rate reached 83.87%. We also found that the correspondence between the combined number of species and composition of plant communities obtained from seed rain, soil seed bank, and seedling emergence experiments and the standing vegetation was poor. We clearly show the temporal dynamics of the seed rain and seedling communities, which are driven by different plant reproductive phenology and dispersal mechanisms, and drought coupled with mortality. We conclude that this highly disturbed forest needs a management plan and could not recover by itself in a short period of time. We recommend the use of external seed and seedling supplies and the maintenance of soil water content (i.e., shading) during periods of drought in order to help increase seedling abundances and species richness, and to reduce the mortality rate.
... Experiments on the effects of disturbances on resprouting commonly include clipping aboveground plant parts (e.g., Cruz et al. 2003;Schafer and Just 2014;Martinez-Vilalta et al. 2016). If the main effect of repeated loss of aboveground biomass is carbohydrate starvation, then clipping and burning should have similar effects on resprouting (Hmielowski et al. 2014;Michielsen et al. 2017). ...
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Background Resprouting is an effective strategy for persistence of perennial plants after disturbances such as fire. However, can disturbances be so frequent that they limit resprouting? We examined the effects of fire and mowing frequency on eight species of resprouting shrubs in Florida scrub, USA, using a factorial field experiment. We burned or mowed plots at four disturbance return intervals (DRI): either annually, biennially, every three years, or once in six years (with all plots being treated in the sixth year to control for time since disturbance). We analyzed plant growth responses (height, aboveground biomass, number of stems) based on sampling pre treatment, and six months, one year, two years, and four years post-treatment. We also measured non-structural carbohydrates (NSC) and soil properties to evaluate these factors as potential drivers of resprouting responses. Results Fire temperatures were hot (mean maxima 414 to 698 °C among burn days), typical of larger fires in Florida scrub. Plant biomass and heights were affected by DRI (being suppressed by frequent disturbance, especially initially) and varied among species with palmettos recovering biomass faster, and species within the same genus generally showing similar responses. Biomass recovery in mown versus burned treatments showed comparable effects of DRI and similar trajectories over time. Numbers of stems were affected by DRI, disturbance type, and species, and increased after disturbances, especially with less frequent disturbances and mowing, and subsequently declined over time. NSC concentrations varied among species and over time and were positively related to biomass. One year post disturbance, soil moisture and organic matter content were higher in mown plots, while pH was higher in burned plots. Given the slightly lower elevation of the mown plots, we interpreted these differences as site effects. Soil properties were not affected by DRI and did not affect biomass responses. Conclusions Although very frequent disturbances reduced shrub growth responses, the magnitude of plant responses was modest and the effects temporary. Because resprouting shrubs in Florida scrub appear resilient to a range of disturbance return intervals, frequent fire or mowing can be used effectively in restorations.
... In this approach, the occurrence of fire is therefore uninfluenced by time since last fire, which is possible only if flammability is regained quickly after fire, owing to the rapid accumulation of fine fuels. This is commonly true in longleaf pine savannas because they regain flammability quickly after fire and can burn annually (Stambaugh et al. 2011, Schafer andJust 2014). However, a constant probability of burning is nevertheless an oversimplification because of changing fuel loads with increasing time since fire. ...
Fire controls tree cover in many savannas by suppressing saplings through repeated topkill and resprouting, causing a demographic bottleneck. Tree cover can increase dramatically if even a small fraction of saplings escape this fire trap, so modelling and management of savanna vegetation should account for occasional individuals that escape the fire trap because they are “better” (i.e. they grow faster than average) or because they are “lucky” (they experience an occasional longer‐than‐average interval without fire or a below‐average fire severity). We quantified variation in growth rates and topkill probability in Quercus laevis (turkey oak) in longleaf pine savanna to estimate the percentage of stems expected to escape the fire trap due to variability in 1) growth rate, 2) fire severity, and 3) fire interval. For trees growing at the mean rate and exposed to the mean fire severity and the mean fire interval, no saplings are expected to become adults under typical fire frequencies. Introducing variability in any of these factors, however, allows some individuals to escape the fire trap. A variable fire interval had the greatest influence, allowing 8% of stems to become adults within a century. In contrast, introducing variation in fire severity and growth rate should allow 2.8% and 0.3% of stems to become adults, respectively. Thus, most trees that escape the fire trap do so because of luck. By chance, they experience long fire‐free intervals and/or a low‐severity fire when they are not yet large enough to resist an average fire. Fewer stems escape the fire trap by being unusually fast‐growing individuals. It is important to quantify these sources of variation and their consequences to improve understanding, prediction, and management of vegetation dynamics of fire‐maintained savannas. Here we also present a new approach to quantifying variation in fire severity utilizing a latent‐variable model of logistic regression.
... Survival of these trees was generally consistent with those from an earlier study where 58 permanently marked sub-adult eucalypts were followed for six years . Where a resprouting sub-adult tree initially produced multiple stems after the complete loss of above ground biomass, the maximum height of those stems was sufficient to accurately assess recovery and persistence of the individual (Werner and Franklin 2010, P. A. Werner, unpublished data), as was the case in a study of six woody species in a pine savanna in North Carolina (Schafer and Just 2014). ...
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Fire is a major disturbance driving the dynamics of the world's savannas. Almost all fires are set by humans who are increasingly altering fire timing and frequency on every continent. The world's largest protected areas of savannas are found in monsoonal northern Australia. These include relatively intact, tall, open forests where traditional indigenous fire regimes have been largely replaced in the past half century by contemporary patterns with trees experiencing fire as often as three out of five years. Eucalypt canopy trees form the basic structure of these savannas and changes to the canopy due to fire regimes cascade to affect other plants and animals. In this study, we used data from nearly three decades of field studies on the effects of fire on individual trees to define eight life‐history stages and to calculate transition rates among stages. We developed a stage‐based matrix population model that explicitly considers how fire season and understory influence growth, survival, and recruitment for each life‐history stage. Long‐term population growth rates and transient population dynamics were calculated under five different fire regimes, each in two understory types, using both deterministic and stochastic simulations of seasonal timing of fires. We found that fire was necessary for long‐term persistence of eucalypt canopy tree populations but, under annual fires, most populations did not survive. Population persistence was highly dependent on fire regime (fire season and frequency) and understory type. A stochastic model tended to yield higher population growth rates than the deterministic model with regular, periodic fires, even under the same long‐term frequency of fires. Transient population dynamics over 100 yr also depended on fire regime and understory, with implications for savanna physiognomy and management. Model predictions were tested in an independent data set from a 21‐yr longitudinal field study in Kakadu National Park. This study is a novel and integrative contribution to our understanding of fire in savanna biomes regarding the potential for long‐term persistence and transient dynamics of savanna canopy tree populations. The model is relatively simple, generalizable, and adaptable for further investigations of the population dynamics of savanna trees under fire.
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Although resprouting is recognized as a key post-disturbance response for plants, few studies have closely examined post-fire growth responses of resprouting species. Following a prescribed burn in Florida scrub, we compared intraspecific and interspecific growth patterns of 16 resprouting shrub species. We then examined how resprouting growth is related to species life history strategies to understand how the resprouting response could contribute to niche differentiation and species coexistence. We defined growth by calculating relative growth rates based on height, crown area, and crown volume of resprouts. In addition, we measured the number, diameter, and height of all resprouting stems. The number and diameter of all stems present before fire were also estimated. The number of resprouting stems after the fire was higher than the number of stems present before the fire for all species. As expected, species varied significantly in their post-fire growth rates, especially between those with differing recovery modes. Resprouting shrubs that are also post-fire seeders had the lowest growth rates compared to those that resprout and grow clonally, those that only resprout, and palmettos. We also found differences in post-fire growth among species with different growth forms, with palmettos having the fastest growth, followed by shrubs, and then by sub-shrubs. Within species, tradeoffs were found between height and the density of new stems, but not between height and diameter of resprouting stems. Overall, Florida scrub species exhibit a continuum of post-fire growth rates, suggesting the coexistence of a number of successful strategies for post-fire resprouting rather than a single optimal recovery strategy.
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Restoration of the Pinus palustris (longleaf pine)-wiregrass ecosystem of the southeastern United States requires information on reference conditions such as the historical fire regime. Aristida beyrichiana (wiregrass), a keystone perennial bunchgrass, was historically widespread throughout the southeast, but its dependence upon growing season fires for sexual reproduction hastened its decline in the face of decades of human fire suppression. The reproductive response of wiregrass is described by patterns of meristem allocation between competing life history strategies (i.e., vegetative growth vs. sexual reproduction). The temporal link between fire and flowering indicates this allocation was optimized to the historical fire regime through selection. In this study, we used the observed allocation of wiregrass reproductive effort to sexual reproduction as the response variable to examine reproductive response to fire season, using plant size as a covariate. Sexual reproduction was positively associated with plant size. Plants burned during early summer (May–June) produced a greater proportion of inflorescences than did those burned in early spring (March–April) or in late summer (August). Using state records of natural (lightningignited) and anthropogenic (human-ignited) fires from historical (1933–1946) and contemporary (1998– 2010) periods we found that the distribution of maximum wiregrass reproductive output most closely reflected the distribution of historical fires with natural ignition sources. Moreover, while the monthly distributions of historical and contemporary fires were different for anthropogenic ignitions, they did not differ for fires with natural ignitions. Our predictions of peak allocation based upon the biology of wiregrass provide strong support for the use of wiregrass as an indicator of the historical fire season (early summer). Efforts to restore the longleaf pine ecosystem should therefore consider the biological response of wiregrass in planning prescribed fires.
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The resprouting ability of woody plants in frequently burned ecosystems may be influenced by the season and method of topkill. We conducted an experiment to test for the effects of season and method of topkill on aboveground biomass, belowground biomass, and mortality of hardwoods found in a southeastern U.S. pine-grassland. We predicted that topkill occurring during the growing season and topkill by fire would have greater negative impacts on resprouting and root growth and result in greater mortality. We conducted a shadehouse experiment in north Florida in which we applied topkill treatments (burn, clip, and no-topkill) in three seasons (dormant, early growing, and mid growing) to Quercus nigra (water oak) saplings. Plants were destructively sampled 12 months post-treatment to measure aboveground and belowground biomass. Saplings topkilled in the early and mid growing seasons had reduced growth and greater mortality one-year post-treatment compared to plants topkilled in the dormant season. While there was no difference in one-year post-treatment biomass or mortality of saplings between the two methods of topkill, clipped plants had more stems and shorter average stem height than plants topkilled by fire. Root growth continued despite topkilling for all seasons and was greatest for no-topkill plants. These results suggest that while topkill reduces biomass, hardwoods have evolved to maintain belowground biomass reserves, enabling genets to resprout following subsequent topkilling and to persist through frequent disturbances.
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We studied the source of the nitrogen used for the growth and resprouting of holm-oak (Quercus ilex L.), and the contribution of nitrogen and carbohydrate root reserves to these processes. Three-year-old plants were grown in a greenhouse with either a sufficient or restricted nitrogen supply for one year. Half the individuals were subjected to shoot excision to provoke resprouting, and a 15N solution was given to these plants and to controls for two months. Nitrogen, Total Non-structural Carbohydrate (TNC), Total Soluble Protein content, and 15N and 13C composition were determined, and histological analyses of woody tissue were performed. Our results show that N-deprived plants used nitrogen from root reserves to support a growth rate similar to that of non-deprived plants. However, deprived plants lost their resprouting capacity in spite of the high TNC accumulation and nitrogen resupply to the soil. After the supply of nitrogen was restored to N-deprived plants, this nutrient mainly accumulated in under-ground organs, which limited the above-ground growth. Resprouting plants first remobilized the nitrogen stored in roots, and thereafter took it up from the solution. The root-crown region did not behave as a specialised reserve organ in three-year-old Quercus ilex L. plants.
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Prescribed fire is increasingly used to inhibit woody encroachment into fire-dependent ecosystems, yet its effects on other processes influencing invasion are poorly understood. We investigated how fire influences exotic woody invasion through its effects on granivore activity, and whether these effects depend on the habitat in which seed predation takes place. We quantified seed removal for four species of exotic woody plants (Albizia julibrissin, Elaeagnus umbellata, Melia azedarach and Triadica sebifera) in 17 sites in longleaf pine savanna that varied in time since fire (one or three growing seasons post-fire) in the sandhills region of North Carolina, USA. Within each site, we established paired plots in upland and upland-wetland ecotone communities and presented seeds in depots that allowed either arthropod, or arthropod and small vertebrate access. We found that differences in seed removal with time since fire were contingent on habitat and granivore community. In ecotones, three of four species had higher proportions of seeds removed from plots that were three growing seasons post-fire than plots one growing season post-fire, whereas only T. sebifera showed this pattern in upland habitat. Allowing vertebrate granivores access to seeds enhanced seed removal, and this effect was strongest in ecotone habitat. While granivores removed seeds of all four plant species, removal of E. umbellata was significantly higher than that of the other species, suggesting that granivores exhibited seed selection. These findings suggest that ecotone habitats in this system experience greater seed removal than upland habitats, particularly as time since fire increases, and differences are mainly due to the activity of vertebrate granivores. Such differences in seed removal, together with seed selection, may contribute to variation in exotic woody invasion of longleaf pine savannas.
(1) Experiments were carried out on Quercus coccifera in southern France to examine the effects of age of stand, fire intensity, fire season, and prefire canopy structure on the vigour of resprouting. Eighteen experimental treatment combinations were tested. Three ages since last fire, three fire intensities, and two seasons were combined. Each treatment combination was repeated six times on plots of 50 × 50 cm. (2) All plant material was clipped, dried, and weighed. Q. coccifera was divided into hierarchical size-classes of basal and branch diameter. The plots were then burned using flame torches. The density and height of each Q. coccifera resprout was recorded through eight weeks following the burn treatments. (3) Significant differences in effect were found between plots of different ages, and between burns of different durations, but season is the dominant variable in all analyses: resprout density and growth are much greater following burning in late May than after burning in early October. Other than season, it is pre-fire canopy structure that most affects resprout vigour. Pre-fire stem density and woody and foliar biomass seem to be important variables, but definitive answers are precluded by high multicollinearity. (4) Path analyses support the hypothesis that resprout density is affected most by pre-fire stem density. This may indicate a reservoir of dormant meristematic tissue. Resprout growth is more strongly affected by pre-fire biomass value, indicative of underground carbohydrate reserves. More vigorous sprouting follows the spring burn, indicating either greater reserves following the flush of spring growth (compared with depleted condition following the dry season) or, more likely, the direct effect of warmer temperatures and increasing sunshine.
Resprouting is advantageous for plants in pyrogenic ecosystems because it allows for quick re-acquisition of space after fire. Resprouting species build multiple stems during their lifetime and have an established root system, which may affect growth and biomass allocation and whether resprouts conform to predicted scaling relationships. We measured height, basal diameter, and biomass of stems of five resprouting shrub species in scrubby flatwoods sites in Florida, varying in time after fire (6 w, 1 y, 8–9 y, 20–21 y). Differences among species in size and allocation ratios tended to be greater in recently burned sites. Six weeks after fire, the dominant species, Quercus inopina, had the highest height:diameter and leaf:stem biomass ratios, which may contribute to the ability of this species to persist over fire cycles. The slope of the relationship between stem height and diameter was higher in recently burned sites than 8 to 21 y after fire, whereas the slope of the relationship between stem height and biomass was higher 8 to 21 y after fire than in recently burned sites. Height and biomass of resprouts generally scaled differently with respect to diameter and height than predicted by allometric theory, but biomass of resprouts, on average, scaled with diameter as predicted. Therefore, resprouted stems were taller for a given diameter and accumulated less biomass with height growth. In pyrogenic ecosystems, it may be more advantageous to grow tall, to maximize light capture, than to invest in strength to avoid damage because fire will eventually remove stems. Our results indicated that current allometric theory does not adequately represent scaling of growth and biomass of resprouting shrubs.
Conference Paper
Background/Question/Methods Nitrogen (N) and phosphorus (P) are essential plant nutrients that limit productivity in most, if not all, terrestrial ecosystems. Due to fundamental differences in the biogeochemistry of N and P, fire has the potential to alter the relative availability of N versus P both immediately following fire and over inter-fire cycles. We investigated the short- and long-term effects of fire on soil and plant nutrients in Florida scrub ecosystems. In addition, we conducted a nutrient addition experiment to test the hypotheses that: (1) plant productivity in recently burned scrubby flatwoods is N-limited; (2) plant productivity in intermediately burned scrubby flatwoods is P-limited; and (3) plant productivity in long unburned scrubby flatwoods is co-limited by N and P. Results/Conclusions In palmetto flatwoods, fire caused a greater increase in phosphate (PO43-) than ammonium (NH4+), resulting in a decrease in the soil available N:P ratio shortly after fire. Similarly, foliar %P of resprouting species increased more than foliar %N, resulting in a decrease in foliar N:P ratios shortly after fire. In scrubby flatwoods, PO43-, but not total inorganic N, varied with time after fire, causing N:P ratios to be greatest at intermediate times after fire and lowest 13 years after fire. In surface soils, soil %C and %N, dissolved organic N, net N mineralization, and microbial N were all highest 13 years after fire. In recently burned scrubby flatwoods, shrubs appear to invest more in aboveground productivity, and Quercus inopina, the dominant oak, responded to P and N + P addition, but Serenoa repens, the dominant palmetto, responded to N addition. At intermediate times after fire, shrubs appear to invest more in belowground than aboveground productivity and show co-limitation by N and P with a stronger P-limitation, while in long unburned sites, scrubby flatwoods shrubs appear to invest in both aboveground and belowground productivity and show co-limitation by N and P. Overall, our research shows that fire affects soil and plant nutrients and limitation of primary productivity, but that reallocation of nutrients from below- to aboveground, fire frequency, species composition, and differences among species may mediate the direct effects of fire on nutrient availability and limitation in Florida scrub.
Resprouting is an efficient means by which woody plants regain biomass lost during disturbance, but there is a life history trade-off that occurs in all disturbance regimes between investment in the current generation through resprouting vs investment in future generations at the same or more distant sites. The relative allocation to resprouting vs seeding in woody plant communities is dictated by the nature of disturbance regimes. Resprouting is the predominant response to the least severe disturbance regimes, but is also a common response in disturbance regimes of high severity, those that destroy most or all above-ground biomass, and which occur at medium to high frequency. The response to disturbance either by resprouting or seeding is dictated by the site's productivity. We present a comprehensive model for relative allocation to resprouting vs seeding across a range of disturbance regimes. Competition between plants that mostly seed vs those that mostly resprout should accentuate differences in allocation along a gradient of disturbance frequency. However the patchy nature of disturbance in time and space, coupled with gene flow among populations undergoing different disturbance regimes, ensures that it is unlikely that either resprouting or seeding will be the sole response in most plant communities at most disturbance frequencies. Additional influences on resprouting in woody plant communities include changes in allocation during the lifespan of individual plants and phylogenetic constraints that are expressed as biogeographic patterns.
Field surveys of lignotuber meristem populations were undertaken in two mallee (Eucalyptus spp.) communities in south-western New South Wales to determine range and variability in the number and density of potential regeneration sites. Lignotuber size ranged from 2.5 to 610 kg in weight and from 2.7 to 495 L in volume while total bud number per lignotuber (92–13300) and bud density (76–450 buds per 100 cm 2 of lignotuber surface area) showed no consistent interrelationships. Eight months after a prescribed fire applied in late spring, total number of buds activated per lignotuber ranged from 14 to 307 but rarely exceeded 100. Most coppices had 5–15 emergent fascicles by this stage, most (80%) of which originated in the surface 8 cm. At this time, an average of only 22.5 ± 1.0% of the total buds activated per lignotuber emerged above the soil surface. Five years after decapitation treatments had been applied, 99% of the variation in coppice biomass could be attributed to the negative relationship between cumulative coppice biomass and the proportion of original fascicles decapitated. All mallee plants died after 100% of fascicles were decapitated in the autumn for two consecutive years following an initial fire.