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Propagule quality mediates invasive plant establishment

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Propagule pressure is commonly considered a primary driver of invasive plant establishment and spread. However, the physical size or condition (i.e., quality) of propagules may also affect establishment, particularly under unfavorable habitat conditions such as low light environments. We used an outdoor mesocosm experiment to test the relative contribution of propagule size (number of individuals introduced) and quality (number of rhizome nodes) to the establishment and performance of the highly invasive cogongrass (Imperata cylindrica) under experimental sun and shade treatments. We found that the introduction of higher quality propagules (rhizome segments ≥3 nodes in length) significantly enhanced establishment across both light treatments, and increased final tiller count in the sun treatment. The sun treatment also enhanced rhizome growth, an effect that could increase spread rates and invasion success. Thus, while cogongrass is likely to establish in both sun and shade, introductions of large propagule sizes or large rhizomes in high light environments likely poses the greatest threat to native habitats. Our results demonstrate that propagule quality promoted both establishment and performance of a highly invasive grass species and suggest that propagule quality may play an important but underappreciated role in the invasion process.
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ORIGINAL PAPER
Propagule quality mediates invasive plant establishment
James A. Estrada .Chris H. Wilson .
Julienne E. NeSmith .S. Luke Flory
Received: 7 August 2015 / Accepted: 9 May 2016 / Published online: 18 May 2016
ÓSpringer International Publishing Switzerland 2016
Abstract Propagule pressure is commonly consid-
ered a primary driver of invasive plant establishment
and spread. However, the physical size or condition
(i.e., quality) of propagules may also affect establish-
ment, particularly under unfavorable habitat condi-
tions such as low light environments. We used an
outdoor mesocosm experiment to test the relative
contribution of propagule size (number of individuals
introduced) and quality (number of rhizome nodes) to
the establishment and performance of the highly
invasive cogongrass (Imperata cylindrica) under
experimental sun and shade treatments. We found
that the introduction of higher quality propagules
(rhizome segments C3 nodes in length) significantly
enhanced establishment across both light treatments,
and increased final tiller count in the sun treatment.
The sun treatment also enhanced rhizome growth, an
effect that could increase spread rates and invasion
success. Thus, while cogongrass is likely to establish
in both sun and shade, introductions of large propagule
sizes or large rhizomes in high light environments
likely poses the greatest threat to native habitats. Our
results demonstrate that propagule quality promoted
both establishment and performance of a highly
invasive grass species and suggest that propagule
quality may play an important but underappreciated
role in the invasion process.
Keywords Cogongrass Propagule pressure
Imperata cylindrica Invasion Mechanism
Introduction
Understanding the mechanisms that underlie non-
native plant invasions is essential to predicting
vulnerable habitats and future invaders. However,
identifying factors that are general predictors of
invasion success has proven difficult because the
establishment of invasive plants is unlikely to be
controlled by a single mechanism, but rather complex
interactions among multiple determinants (Gurevitch
et al. 2011; Inderjit et al. 2005; Lau and Schultheis
2015). Nonetheless, propagule pressure has emerged
as a common driver of plant establishment across a
variety of habitats and species (Lockwood et al. 2009;
Simberloff 2009) and is often positively correlated
with invasion success (Blackburn et al. 2009; Lock-
wood et al. 2009; Simberloff 2009; Williamson 1996).
Electronic supplementary material The online version of
this article (doi:10.1007/s10530-016-1163-9) contains supple-
mentary material, which is available to authorized users.
J. A. Estrada (&)S. L. Flory
Agronomy Department, University of Florida,
Gainesville, FL 32611, USA
e-mail: estradaj@ufl.edu
C. H. Wilson J. E. NeSmith
School of Natural Resources and Environment, University
of Florida, Gainesville, FL 32611, USA
123
Biol Invasions (2016) 18:2325–2332
DOI 10.1007/s10530-016-1163-9
Although propagule pressure has been frequently used
to explain the success or failure of past introductions,
studies examining its ability to predict future invasions
remain rare (reviewed in Lockwood et al. 2005).
While the term ‘‘propagule’’ can be defined as
either a group of individuals or reproductive units
(e.g., 100 seeds) or a single individual (a single seed,
piece of stem, or rhizome), the concept of ‘‘propagule
pressure’’ is well defined. It is comprised of two
components: propagule size (number of individuals
introduced) and propagule number (the rate at which
propagules arrive over time; Lockwood et al. 2005;
Simberloff 2009). Thus, propagule pressure represents
the total number of individuals introduced per unit
time. Moreover, both propagule size and number have
been shown to independently increase the likelihood
of establishment (Lockwood et al. 2005; Simberloff
2009).
The mass or physical condition of a propagule
(hereafter referred to as propagule quality) may also
influence the establishment success of invasive plants
(Ruiz et al. 2000; Williamson 1996). For example,
large seed size (i.e., high quality) has been shown to
enhance seed longevity (Moles et al. 2000), germina-
tion (Eisenhauer and Scheu 2008; Moles and Westoby
2004a), and seedling survival (Moles and Westoby
2004b). In particular, large seeds may be beneficial
under adverse conditions or hazards such as shade,
drought, competition, or herbivory (Flory and Clay
2010; Leishman and Westoby 1994; Lonnberg and
Eriksson 2013; Moles and Westoby 2004a), where
stored energy reserves may help to overcome envi-
ronmental stressors and stochasticity. Seed size is
often greater in introduced than native ranges for
invasive plant species, due to enemy release, post-
introduction evolution, or differences in environmen-
tal conditions (Daws et al. 2007). In turn, such
differences in seed size may provide a competitive
advantage for non-native plants in the invasive range.
In contrast, it has also been reported that small seed
size is related to greater invasiveness in some species
(Rejma
´nek and Richardson 1996; Richardson and
Rejmanek 2004), and that small seed mass is corre-
lated with invasion success at larger spatial scales
(Hamilton et al. 2005). Small seed size may be
advantageous because it is often associated with
higher overall seed production (Greene and Johnson
1994; Primack 1978) and enhanced dispersal (Harper
et al. 1970; Van Wilgen and Siegfried 1986). Whether
large or small propagule mass is more advantageous
may be heavily dependent on both species (reproduc-
tive strategy, germination rates, seedling vigor) and
habitat (environmental conditions, disturbance, dis-
persal barriers) characteristics. However, experimen-
tal studies on the role of propagule quality in the
establishment of invasive species are rare (Lockwood
et al. 2005; Simberloff 2009) and limited primarily to
observational investigations or animal studies, such as
ballast introductions (e.g. Ruiz et al. 2000). Further-
more, the likelihood of introducing high quality
propagules is expected to increase with greater
propagule size and number. Thus, studies comparing
the relative influence of propagule quality, size, and
number across environmental conditions are needed.
The effects of propagule quality may be particularly
relevant for plants with vegetative reproduction,
another trait frequently associated with invasion
success (Kolar and Lodge 2001; Lloret et al. 2005;
Quinn and Holt 2009), because the physical size or
condition of the propagule may vary substantially
among introduction events. It is likely that larger
pieces of rhizomes or stem fragments (higher quality)
would be beneficial for species with vegetative
reproduction because greater mass would mean higher
carbon stores to support initial establishment and
growth. Furthermore, a higher quality propagule may
be especially important in low resource environments,
such as low light, where establishment might rely
heavily on energy stores of the vegetative fragment.
However, only a single study (Quinn and Holt 2009)
has investigated the influence of propagule quality on
the performance of an invasive plant species with
vegetative reproduction. Additionally, while they
reported that propagule mass contributed positively
to invader shoot height and performance, the relation-
ship did not exist at all study sites. Thus, further
research to empirically evaluate the effects of propag-
ule quality on invasive plant establishment is needed.
In this study we used an outdoor mesocosm
experiment to test the relative contribution of propag-
ule size and quality to the establishment success and
performance of cogongrass (Imperata cylindrica, (L.)
P. Beauv., hereafter cogongrass), a highly invasive,
rhizomatous C
4
grass. Cogongrass is native to Asia
and has invaded a wide variety of habitats (e.g., natural
areas, pine plantations, pastures) throughout the
eastern US from Texas to Florida and as far north as
Virginia (USDA, NRCS 2005). It is considered a
2326 J. A. Estrada et al.
123
primary threat to native biodiversity and ecosystem
functions (Brewer 2008; Estrada and Flory 2015;
MacDonald 2004) and is a federally listed noxious
weed (USDA, NRCS 2005). The accidental transport
of cogongrass rhizome fragments (e.g., via fill dirt or
transport on machinery, Willard et al. 1990) is thought
to be a common means of introduction throughout
much of the invasive range. Since both the number and
quality of rhizome fragments likely varies substan-
tially among introduction events, we tested whether
increasing propagule size (number of propagules) and
quality (length/mass of rhizome fragments) would
enhance cogongrass establishment. We were inter-
ested in evaluating a single introduction event, thus
propagule number was not manipulated. As with many
plant species, cogongrass establishment is highly
influenced by light availability (Ayeni and Duke
1985), so we also evaluated whether greater propagule
quality would improve establishment probability in
lower light environments. We predicted that both
greater propagule size and quality would positively
influence cogongrass performance, and that higher
quality propagules would better establish and perform
under low resource, shaded conditions.
Methods
Experimental design
To evaluate the contributions of propagule size and
propagule quality to cogongrass establishment and
performance under sun and shade, we established an
outdoor mesocosm experiment at the Bivens Arm
Research Site (BARS) in Gainesville, FL (29.628489°
N, -89.353370°W). We introduced three propagule
sizes (one, three, and five rhizome fragments) and
three propagule quality treatments (one, three, and five
nodes) in a factorial design (nine total treatment
combinations) nested within two light treatments with
ten replicates (180 mesocosms total). Since the
diameters of cogongrass rhizomes vary, we standard-
ized the treatments by mass, with one, three, and five
node segments weighing 0.17 ±0.02, 0.46 ±.04,
and 0.76 ±0.07 g (mean ±SD) respectively. We
obtained the ranges by calculating a 15 % interval
around the mean mass of each quality treatment.
Rhizome fragments were planted 2–3 cm deep in 3.8L
round, plastic pots filled with a heterogeneous mixture
of screened local topsoil (Florida Green Keepers,
Alachua County, FL). We then arranged the pots into
20 plots and randomly assigned each plot to either full
sun (n =10) or 60 % shade cloth (n =10). The
experiment was conducted for a period of 12 weeks
(August through November 2013). All pots were
watered daily and a 50 % concentration of 24-8-16
water-soluble fertilizer (Scotts Miracle-Gro Products,
Inc. Marysville, OH) was applied during the 7th week
of the experiment. Rhizome fragments were collected
from an existing cogongrass population at BARS.
Data collection
We recorded the total number of tillers and height of
the tallest tiller in each mesocosm twice per week for
the first 10 weeks of the experiment and once per week
for the final 2 weeks. We scored mesocosms as having
‘established’’ cogongrass if live shoots were present
in the mesocosm at the conclusion of the experiment.
All biomass was harvested in November 2013 and
aboveground and belowground portions were sepa-
rated. During the harvest we located and removed the
originally introduced rhizome segments to ensure that
final belowground values only reflected biomass
produced during the course of the experiment. Root
and rhizome materials were washed to removed soil,
and all plant materials were dried at 60 °C to constant
mass and weighed.
Statistical analysis
We analyzed four response variables using general-
ized linear mixed effects models: establishment
(presence of tillers at the conclusion of the experi-
ment), final tiller count, aboveground biomass, and
belowground biomass. For all models, we included
categorical predictor variables for fixed effects of light
treatment (sun/shade), propagule size (one, three, or
five propagule fragments), and propagule quality (one,
three, or five nodes), alongside plot as a random effect
to account for the blocking of mesocosms within light
treatments in our experimental design. For statistical
inference, we examined the posterior distributions of
the fixed effects predictors to determine if the 95 %
confidence intervals excluded zero (analogous to a
Wald-Z or a likelihood ratio test, Bolker et al. 2009).
Propagule quality mediates invasive plant establishment 2327
123
For categorical predictors, these parameter estimates
represent contrasts to an estimated intercept term that
serves as the baseline (i.e., reference) level. These
results are displayed graphically in coefficient plots to
facilitate ready interpretation and comparison of both
effect size and uncertainty across predictors.
We modeled establishment as a Bernoulli random
variable (0/1) related to our predictor variables via the
logit-link function. The subsequent analyses (tiller
count, biomass) were conducted using data only from
mesocosms where cogongrass had emerged after
4 weeks (i.e., removing the zeroes due to establish-
ment failure). The above and belowground biomass
data were analyzed with a normal distribution. The
tiller production data were assigned a Poisson distri-
bution, including a random effect term for overdis-
persion (Gelman and Hill 2006) and given the standard
log-link.
We were specifically interested in the effect of
propagule quality on tiller counts since we observed a
notable advantage of three and five node rhizome
segments over single node segments in the sun
treatment. Therefore we created a set of six test
statistics (T
test
) that contrasted predictions of expected
tiller count under all six combinations of propagule
size and light treatment among mesocosms with three
or five node segments versus mesocosms with the
same propagule size and light treatment but with
single node segments. Under the Poisson model, these
expectations are simply the exponentiated sum of our
fitted fixed effects parameters (Gelman and Hill 2006).
We computed the probability that the T
tests
were
positive, indicating an advantage for a higher quality
propagule, by sampling their posterior distributions
(i.e., computing proportion of draws above zero). We
graph the mean and the 50 and 95 % credible intervals
for the T
test
and highlight the results where the 95 %
intervals exclude zero.
All models were estimated via Gibbs-sampling
Markov Chain Monte Carlo methods, using 5 chains of
12,000 iterations each, discarding the first 2000
iterations, and thinning by a factor of 50, leading to
1000 draws from the posterior distribution for each
parameter. Convergence was assessed via the Gelman-
Rubin diagnostic (R-hat \1.1, Gelman et al. 2013)
and by visually checking for well-blended chains. All
models were programmed in R (v. 3.1.0, R Core
Development Team) and JAGS (v.3.4.0), linked via
the ‘‘R2jags’’ package.
Results
Establishment
We found strong evidence for the role of both propagule
size and quality in predicting establishment (presence
of tillers after 12 weeks). The main effects indicators
for three and five propagule treatments were significant
and positive (mean: 2.59, 95 % CI 018–5.343; 4.79,
2.003–7.995, respectively), while the main effect
indicator for the three node quality treatment was also
significant and positive (2.54, 1.359–5.343, Fig. 1a).
Neither light treatment nor the five node treatment were
significant, nor were any of the higher-order
interactions.
Tiller count
Tiller count was most strongly driven by propagule
size, with the five propagule coefficient significant and
positive (1.25, 0.462–2.093, Fig. 1b). Our test statis-
tics, which contrasted tiller count predictions for three
node as opposed to single node rhizome segments
under all combinations of propagule size and light
treatments, predicted an advantage (median) for a
higher quality propagule in sun treatments when
propagule size was above one (Fig. A1). Unlike the
emergence model, the light treatment was significant
and negative (-1.382, -2.694 to -0.101) indicating
that tiller count was suppressed by shading. This result
can also be seen in the raw data on tiller counts, which
indicated a 200 % increase in tillers for plants in the
sun compared to shade treatment across all propagule
size and quality measures (Fig. A2).
Biomass and plant height
Aboveground biomass was determined almost exclu-
sively by propagule size, with the main effect indictor
for the five propagule treatment being the only positive
and significant coefficient (1.71, 0.717–3.171, Fig. 2a).
While the three node treatment suggested a net positive
result, the considerable overlap with zero precludes
making a solid statistical inference. Neither the light
environment nor propagule quality had a discernible
impact on final aboveground biomass. There was,
however, a significant difference in plant height, with
those in full sun (mean ±SD: 0.54 ±0.63 cm) being
2328 J. A. Estrada et al.
123
shorter than those in shaded treatments
(1.12 ±1.13 cm) (t =13.75, p\0.0001).
Similar to the aboveground biomass model, below-
ground biomass was also driven by propagule size, with
no significant influence from the propagule quality
treatments (Fig. 2b). Both the three and five propagule
treatments showed positive and significant main effect
indicators (1.30, -0.011 to 2.516; 1.76, 0.631–2.929,
respectively) demonstrating that introductions of three
or five rhizome fragments produced significantly more
belowground biomass than single rhizome introduc-
tions. Belowground biomass was also influenced by
light environment, with reduced rhizome production
under the shade treatment (-1.312, -2.890 to 0.154).
Total belowground biomass for plants in the sun
(mean ±SD: 1.11 ±0.13 g) was on average twice
as high as for those in the shaded treatment
(0.54 ±0.07 g).
Fig. 1 Coefficient plots for establishment (a) and tiller count
(b). Each coefficient represents positive or negative treatment
effects as compared to a reference level of one propagule with
one node in the sun. We consider coefficients with confidence
intervals (95 %) excluding zero to be significantly positive or
negative, with those above zero being positive and below being
negative
Fig. 2 Coefficient plots for aboveground (a) and belowground
(b) biomass. Each coefficient represents positive or negative
treatment effects as compared to a reference level of one
propagule with one node in the sun. We consider coefficients
with confidence intervals (95 %) excluding zero to be signif-
icantly positive or negative, with those above zero being
positive and below being negative
Propagule quality mediates invasive plant establishment 2329
123
Discussion
Here we report on the first experimental evaluation of
the relative influence of propagule pressure and
propagule quality on the establishment and perfor-
mance of an invasive plant species. Our finding that
propagule size was the most influential factor across
all treatments supports previous studies indicating that
propagule pressure is a primary driver of non-native
plant establishment (reviewed in Lockwood et al.
2005; Simberloff 2009). We also showed that propag-
ule quality significantly enhanced both establishment
and performance. However, in contrast to our predic-
tions, greater propagule quality did not increase
establishment or performance in the shade compared
to sun treatment. Thus, cogongrass is likely to
establish in habitats with a wide range of light
conditions, but performance will be greatest for large
propagule sizes and high quality propagules under full
sun. More generally, our data suggest that propagule
quality may play an important but underappreciated
role in the invasion process.
Although we found that higher propagule quality
(Cthree node rhizome fragment) enhanced establish-
ment, there was no additional benefit of five compared
to three nodes. This result was unexpected because the
presence of additional nodes (i.e., potential growth
sites) should presumably increase the likelihood of
establishment. Additionally, it was assumed the larger
five node rhizome segments would contain more
stored energy (Decruyenaere and Holt 2001; Dong and
Pierdominici 1995; Quinn and Holt 2008), thereby
promoting establishment. The advantage of the three
node segments was driven by extremely high estab-
lishment ([98 %) across both light treatments when
more than one propagule was introduced, indicating
that rhizome fragments of this quality present a
considerable invasion risk. Yet, nearly 50 % of single
rhizome fragments with one node established. It is
possible that the incorporation of additional stressors
(e.g., drought, competition) may have reduced the
viability of the single node fragments, but our results
suggest that even a very small propagule may result in
establishment and potentially invasions.
While our data are in general agreement with
previous work on propagule quality, our findings
provide two novel insights. First, propagule quality
had a larger influence over establishment success than
the light environment. This finding is important because
light availability is a well-known driver of plant
performance and can dictate establishment success for
many non-native species (Canham et al. 1990; Val-
ladares 2003). However, there is evidence suggesting
that established cogongrass populations might tolerate
reduced light environments. For example, studies
conducted by Patterson (1980) suggest that cogongrass
is able to persist in up to 50 % shade and rapidly adapt
to changes in light levels by altering specific leaf area
and leaf area ratio. Gaffney (1996) and Ramsey et al.
(2003) also found cogongrass to have a low light
compensation point (32–35 lmol m
-2
s
-1
), indicating
that it could thrive as an understory species. Establish-
ment in shaded habitats has been reported for other
invasive grasses, including giant cane (Arundo donax,
Quinn and Holt 2009) and stiltgrass (Microstegium
vimineum, Schramm and Ehrenfeld 2010;Wilsonetal.
2015), but in general, reduced light availability is
thought to inhibit the survival and spread of invasive
grasses (Funk and McDaniel 2010;LohandDaehler
2007). The long-term fate of newly established
cogongrass in shaded habitats has not been evaluated
so it is unclear whether these populations will ulti-
mately spread or die off once energy stores in the
propagule are depleted. Our second important conclu-
sion is that even ‘‘low quality’ (i.e., one node)
propagules may present a substantial invasion risk
under favorable environmental conditions. While high
light availability did not increase establishment success,
it significantly enhanced tiller production relative to the
shade treatment. Thus, although the introduction of a
single node rhizome segment presents considerably less
risk than larger fragments, those that do survive and
establish are expected to rapidly spread in full sun
habitats.
Light availably has been shown to drive below-
ground production in grasses, often resulting in
rhizome proliferation under high light levels (Dong
and Pierdominici 1995; Wills 1975). Accordingly, our
results show a significant increase in rhizome biomass
in the sun treatment. Accumulation of belowground
biomass in cogongrass may be an important compo-
nent of invasion success since vast rhizome assem-
blages have been linked to its ability to rapidly regrow
and dominate landscapes after disturbances such as
mowing or fire (Lippincott 2000), making control
difficult. Additionally, enhancement of belowground
biomass likely explains the dramatic increase in tiller
counts in the sun treatment since this pattern of growth
2330 J. A. Estrada et al.
123
would also generate more nodes for shoot develop-
ment. We therefore conclude that invasions in habitats
with high light availability are likely to rapidly spread
and complicate management efforts.
Our results demonstrate that propagule size was the
most influential factor in determining establishment
and performance of a highly invasive grass species,
but that propagule quality also plays an important role
in cogongrass invasions. Furthermore, we showed that
propagule quality might be a more influential deter-
minant of establishment than light availability. Given
the relative lack of studies that have examined
propagule quality in the invasion process we urge that
future research efforts be focused on: (1) measuring
natural variations in propagule quality in the field, (2)
experimental introductions of different propagule
qualities across variable habitat characteristics (i.e.,
resource availability, resident species diversity and
density, disturbance level) to help improve predictions
of invasion success, and (3) determining the extent to
which propagule quality mitigates environmental or
demographic stochasticity during introductions. In
conclusion, our study shows that the introduction of
high quality propagules can enhance invasive plant
establishment, even at low propagule sizes, suggesting
that propagule quality is an important component of
predicting invasive plant establishment.
Acknowledgments We thank Deah Lieurance, Christina
Alba, and members of the Flory Lab for helpful discussions
and revisions on earlier versions of the manuscript. Support was
provided in part by the Florida Fish and Wildlife Conservation
Commission.
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... their quality). For example, establishment success of rhizome fragments of the invasive cogongrass, Imperata cylindrica, increased with fragment size (Estrada, Wilson, NeSmith, & Flory, 2016). Similarly, shoot height and survival of the invasive giant cane, Arundo donax, in Southern California riparian habitats were positively correlated with the weight of transplanted rhizomes (Quinn & Holt, 2008). ...
... For example, fragments of the clonal seaweed, Caulerpa cylindracea, lacking rhizoids performed as well as intact fragments and better than fragments lacking fronds, but only when sediments were enriched in organic matter . Likewise, in the cogongrass, positive effects of increased fragment size on tiller production and growth were modulated by light levels (Estrada et al., 2016). As a consequence of disturbance, land-or seascapes often consist of mosaics of habitats differing in environmental conditions and resource availability. ...
... This mechanism may explain the greater ability of −F+R fragments in regenerating fronds in bare sediments, but not on sediments from which both below-and above-ground Z. growth, but only when exposed to full sun light (Estrada et al., 2016). ...
Article
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Propagule pressure is acknowledged as a key determinant of invasion success. Nonetheless, the role of morphological or physiological attributes of propagules (i.e. their quality) in regulating invader establishment has been little explored. In particular, no study has investigated how the presence of propagules differing in quality within an inoculum influences establishment across heterogeneous landscapes. We experimentally tested the hypothesis that the quality (+Fronds+Rhizoids; +Fronds−Rhizoids; −Fronds+Rhizoids) and the diversity (1, 2 and 3 fragment types) of vegetative fragments of the seaweed Caulerpa taxifolia determine their establishment success across seascapes consisting of bare sediments and patches of the seagrass Zostera muelleri exposed to different disturbance intensities (control, seagrass canopy clipping and total removal). After 6 weeks, seaweed biomass, stolon and frond length, frond and rhizoid number were generally greater in unvegetated habitats (bare sediments and total seagrass removal) than full or reduced seagrass canopies. The type and the diversity of types of fragments inoculated had significant effects on the final biomass and morphological features of C. taxifolia only in vegetated habitats. In control plots, inocula of fragments retaining both fronds and rhizoids achieved higher biomass, developed longer stolons and more fronds. In canopy clipping plots, mixed inocula of +Fronds+Rhizoids and −Fronds+Rhizoids fragments had the greatest biomass and stolon length. Synthesis. Assessing how propagules differing in quality perform in different habitats might be not sufficient to draw a comprehensive picture of invasion risk, as their establishment can be modulated by both negative and positive interactions among them. Propagule composition should be, therefore, considered as a further dimension of propagule pressure. Our results also suggest that the relevance of specific propagule traits for invader establishment decreases from intact to degraded habitats. Considering propagule size in terms of amount of competent propagules, rather than an absolute measure, would refine our ability of predicting invasion risk across habitats differing in biotic or abiotic conditions.
... Propagule pressure-a function of the number of individuals released into a new region per introduction event and number of discrete introduction events-has been widely shown to influence the establishment and spread of non-native plants (Lockwood et al. 2005;Simberloff 2009). By contrast, the role of propagule quality (referred to as the physical condition of a propagule, following Estrada et al. 2016) has received less attention (Rejmánek and Richardson 1996;Smith and Walters 1999;Quinn and Holt 2009;Lange and Marshall 2016). ...
... In particular, the role of propagule quality has been little explored in clonal plants with vegetative reproduction, a trait often associated with high invasiveness in both terrestrial and marine environments (Ceccherelli and Cinelli 1999;Kolar and Lodge 2001;Renoncourt and Meinesz 2002). To date, few studies have experimentally assessed how propagule quality influences the invasion success of these plants, showing that fragment characteristics, such as their size and number of internodes, are key determinants of plant performance (Smith and Walters 1999;Quinn and Holt 2009;Estrada et al. 2016). In addition, how the performance of vegetative propagules differing in quality varies across heterogeneous landscapes is yet to be explored (but see Uyà et al. 2018). ...
... Our study shows that both fragment quality and sediment characteristics influence C. cylindracea fragment survival and, hence, are likely to influence long-term spreading dynamics of this seaweed. More generally, it supports previous evidence of propagule quality to be a determinant of invasion success (Smith and Walters 1999;Quinn and Holt 2009;Estrada et al. 2016;Lange and Marshall 2016), but also brings novel evidence by demonstrating that these effects are likely context-dependent. Organic loading, promoting fragment survival, may sustain the persistence and spread of this seaweed in sedimentary environments. ...
Article
Full-text available
Although propagule pressure is recognized as an important determinant of invasion dynamics, the role of propagule quality (i.e. the physical condition of a propagule) has received little attention. In particular, how the performance of vegetative propagules differing in quality varies across heterogeneous landscapes is yet to be explored. Caulerpa cylindracea is a clonal, invasive seaweed, widely distributed in the Mediterranean. By means of a laboratory experiment, we investigated how variation in the quality of seaweed fragments (intact vs. frond-removal vs. rhizoid-removal) influenced their survival on control versus sediments enriched with detritus from the native seagrass, Posidonia oceanica. The survival of seaweed fragments was low on non-enriched sediments, irrespective of their characteristics. On enriched sediments, survival was high in control and rhizoid-removal fragments, but low in frond-removal fragments. Our study shows that both fragment quality and sediment characteristics influence the survival of C. cylindracea propagules and, hence, long-term spreading dynamics of this seaweed. More generally, it brings novel evidence showing that the effects of propagule quality on invasion success are context-dependent.
... Cogongrass is a highly invasive, rhizomatous C 4 grass that is of management concern throughout much of the Southeast US due to its impacts on biodiversity and ecosystem processes (see Estrada and Flory 2015). While there are a variety of explanations for the invasive success of cogongrass, the ability to reproduce and spread rapidly via rhizomes is a commonly cited mechanism (Patterson 1980, Lippincott 2000, Holzmueller and Jose 2012, Estrada et al. 2016. Additionally, it has been suggested that cogongrass invasion in low resource environments (e.g., shade) is augmented by photosynthate transfer (Estrada et al. 2017). ...
... 'This article is protected by copyright. All rights reserved.' a size that elicits high emergence rates (Estrada et al. 2016). Rhizome fragments were grown in the greenhouse until new rhizome formation was noted (~ 4 weeks). ...
Article
While many clonal plants are highly successful invaders, the contribution of clonal integration (i.e., the translocation of resources among ramets) to invasion is often unknown. We used model simulations to ask if clonal integration would facilitate photosynthate translocation, if the performance of daughter ramets might be enhanced by clonal integration, and if shaded ramets benefited relatively more from transferred photosynthate. Then, to test if photosynthate translocation augmented performance of emerging daughter ramets for a globally invasive grass (Imperata cylindrica ), we combined a ¹³CO2 pulse‐chase experiment with a greenhouse experiment manipulating light levels and rhizome attachment. We found that acropetal photosynthate transfer occurred between all sampled parent‐daughter ramet pairs and that this resource sharing led to higher biomass and tiller production when rhizomes between parent and daughter ramets were intact. We also found that the benefits of integration to recipient clones outweighed the costs to donors, since there was no reduction in parent plant performance due to sharing. Additionally, our data analyses show that photosynthate transfer was likely of greater benefit in overcoming growth constraints in shade than in full sun (posterior probability ~ 96.5%), a result that is further supported by our numerical simulations from a basic growth model. Thus, resource sharing among clonal plants may be a critical but underappreciated trait of invasive species. More generally, photosynthate transfer is a probable mechanism that explains why clonal integration can be particularly beneficial in heterogeneous resource environments. This article is protected by copyright. All rights reserved.
... The reproductive traits of plants are positively correlated with their invasive ability (Williamson and Fitter 1996;Estrada et al., 2016), and the biological characteristics of propagules play a crucial role in the successful colonization of invasive plants (Estrada et al., 2016). Normally, higher quantities of propagules increase the possibility of survival during transport (Kolar and Lodge 2001;Lockwood et al., 2005). ...
... The reproductive traits of plants are positively correlated with their invasive ability (Williamson and Fitter 1996;Estrada et al., 2016), and the biological characteristics of propagules play a crucial role in the successful colonization of invasive plants (Estrada et al., 2016). Normally, higher quantities of propagules increase the possibility of survival during transport (Kolar and Lodge 2001;Lockwood et al., 2005). ...
Article
High reproductive and dispersal capacity allow invasive plant species to spread and establish, out-compete and occupy new niches. Sonneratia apetala, a species used in afforestation projects in southern China, was introduced from Bangladesh in 1985. This species has the capacity to colonize in mangrove mudflats and invade natural mangrove community of China. However, its effectiveness to do so may change with latitude. Aiming to provide reproduction evidence on S. apetala invasiveness from the perspective of fruit and seed properties, we conducted in situ observations of fruit and seed properties of 12 S. apetala populations across the latitudinal gradient from Haikou (19.60°N) to Quangang (25.25°N, current latitudinal limit for this species). Fruits per tree decreased with increasing latitude (R² = 0.47; p < 0.0001); fruit weight (R² = 0.28; p < 0.0001) and volume (R² = 0.27; p < 0.0001) varied quadratically relative to latitude. However, seed quantity per fruit, weight and volume were not correlated with latitude. The relationship between fruit and several climatic factors showed that mean annual precipitation, mean annual low temperature and mean annual irradiance had significant effects on these properties. Fruit floating percentages suggested decreases with time but was markedly site specific. Accordingly, the dispersing potentials were high in low latitude regions with small and light fruits but with big quantity; while they were weak in high-latitude regions where medium size fruits might resist the cold in winter. The mid-latitude sites with large fruits and great germination percentage resulted in good performance and establishment, where the species invasiveness should be noted.
... Each growth cycle entailed 3 months of growth, where newly formed rhizomes were harvested and used for the next growth cycle. Rhizomes from the third growth cycle were introduced directly into the experiment as three-node rhizome segments, a propagule size shown to have high emergence rates (Estrada et al., 2016). ...
... Phenotypic plasticity may contribute to the establishment or spread of Imperata by enhancing phenotype-environment matching across heterogeneous resource conditions. For example, a plastic Imperata population that establishes along a forest edge in full sun conditions could also spread into nearby forests with shaded conditions by altering functional traits such as (plant height, increasing LMR, and/or increasing SLA) (Estrada et al., 2016;Estrada et al. 2017;this study). Under such a scenario, a plastic population would ultimately occupy a larger area and would, therefore, be considered to have greater invasiveness than a less plastic population that is restricted to full sun conditions. ...
Article
Full-text available
Phenotypic plasticity can promote plant invasions and enhance impacts on native species, but little is known about variation in plasticity among invader populations compared with native species. Variation in plasticity among invader populations could inform more precise predictions of invader spread and impacts across heterogeneous resource environments. We used a common garden experiment with sun and shade treatments to test for variation in plasticity among 12 populations of an invasive grass (Imperata cylindrica), and to determine whether the invader exhibited greater plasticity than six native species that co‐occur in the Southeast USA. Principal component analysis revealed that invader populations from different native ranges consistently varied from each other and native species in traits linked to more favorable phenotypes under resource limitation. Overall, the invader exhibited greater plasticity than native species did, as demonstrated by higher plasticity index values for traits such as plant height, leaf mass ratio, and root : shoot ratio. Variation in phenotypic plasticity among invader populations suggests the potential for evolution of plasticity, and greater plasticity of invader populations than native species may underlie invader dominance. Differences in plasticity among populations appears to play an important role in predictions of the spread and potentially the impacts of invasive species.
... 3)(2004), 16 of the 24 in the recorded areas (Ren et al. 2009) of introduction were located in the latitudinal zone from Shenzhen (22°46′ N) to Zhanjiang (21°27′ N) (Fig. 3a), which was also the main area of S. apetala distribution in China in this study. The biology of propagules plays a crucial role in plant dispersal (Williamson and Fitter.1996;Estrada et al., 2016). Propagule characteristics of mangroves are particularly critical in the colonization of new habitats (Stocken et al. 2019). In our previous study, we conducted a systematic study of fruit and seed features of S. apetala at different latitudes in China, and found the fruit properties with significant variation in latitudinal gradients ( ...
Article
The non-native mangrove species, Sonneratia apetala, was widely planted in coastal restoration projects of China in the past three decades, and dispersed in mangrove habitats in some introduction areas, which aroused wide attention from scientists and forest managers. Therefore, it is an urgent need to investigate their distributing patterns and build a dataset with basic information for natural mangrove conservation and restoration. The techniques combined field survey and visual interpretation based on sub-meter spatial resolution imagery from Google Earth (GE). The results showed that the boundary of stable S. apetala populations was ranged from 18°15′ N to 25°36′ N, with a total area of 3,804.86 ha in China in 2020. Guangdong had the largest distribution area of 3,217.34 ha, accounting for 84.56% of the total S. apetala populations in China, within which Zhanjiang (20°35'-21°30' N) took the largest amount. The spatial distribution of S. apetala in China followed the following three characteristics, 1) S. apetala was concentrated in the mid-latitude region (20°00'-23°00' N) of the southeast coast of China, especially along the coasts of Leizhou Bay (20°35'-21°30' N) in Guangdong; 2) S. apetala populations were commonly found in the middle to low tidal zones and at the seaward edges of native mangroves; 3) the dispersal S. apetala populations were found along rivers, tidal creeks, and other water systems, which also concentrated in estuaries or bays with freshwater inflow, on the coastal zones with low salinity, and in bare mudflat or low-shading forest edges, and forest gaps as well.
... seedlings grown in plastic tubes) 2.5 weeks before the experimental fires (Southern Habitats, LLC) because these species often resprout from below-ground buds after fires. Cogongrass rhizome fragments, each with three nodes (Estrada et al., 2016), were planted the day before fires. The number of seeds sown ranged from 13 to 40 seeds for species with larger seeds and 175 to 350 seeds for species with smaller seeds (Table S2). ...
Article
Full-text available
Non‐native invasive grasses are driving intense fires across the globe but the impacts of native versus invader‐fuelled fires on community assemblages are poorly understood. By increasing fire intensity, grass invasions might increase below‐ground mortality of heat‐sensitive seeds and buds, thereby shifting community composition. We compared fuel loads in native and non‐native invasive (cogongrass, Imperata cylindrica) plant‐dominated areas of pine savannas in Florida. Then, we conducted a field experiment to examine how fuel loads and native and invasive fuel types affected soil heating and seedling emergence or resprouting of native and invasive plant species. Average fuel loads in invaded communities were 152% greater than that in native communities. Soil heating, including heating duration >60°C, maximum temperature and heat flux >60°C, increased, and seedling emergence and resprouting decreased with greater fuel loads; these relationships were similar across the overlapping range of native and invasive fuel loads. However, longer durations of soil heating at the higher average fuel loads of invaded communities resulted in 23% lower predicted probability of seedling emergence compared to average fuel loads of native communities. Invasive cogongrass resprouting was not affected by fuel loads, indicating that cogongrass tolerates the intense fires it generates. In contrast, seedling emergence and resprouting of most other species was reduced by greater fuel loads. Synthesis and applications. By increasing fuel loading and soil heating, grass invasions may alter post‐fire community assemblages and facilitate invasive grass dominance at the expense of native species via an invasion‐fire cycle. Fuel loads can be used to predict soil heating duration and depth, and these data, combined with information on species tolerances to heating, can be used to forecast the impacts of invasions on post‐fire community composition. To maintain fire regimes that promote native communities and resist invader dominance, it is critical to manage invasive species that increase fuel loads.
... Many of the world's most invasive macrophytes spread vegetatively via asexual fragmentation (Wright, 2005;Williams and Smith, 2007). The recruitment success of macroalgal fragments (i.e., propagules) can be influenced by their quality (van Kleunen et al., 2015;Estrada et al., 2016), the recipient environment Gribben et al., 2018), and the interaction between the two (Bulleri et al., , 2019. For example, larger, more intact fragments such as those with intact rhizoid structures generally show higher recruitment potential (Khou et al., 2007;Wu et al., 2007;Uyà et al., 2018). ...
Article
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A species’ ability to spread is in part governed by the extent to which recipient habitats either resist, tolerate or promote the species’ recruitment. In disturbed marine environments, there is a general trend for the loss of algal canopies, thought to resist invasion, toward algal turf or rock barrens habitat. This study tested whether the spread of the range-expanding native macroalga Caulerpa filiformis was resisted by algal canopies but facilitated by algal turf or barrens habitats. Large-scale field surveys generally supported the predicted recruitment patterns, with C. filiformis recruits being most abundant on turf (but not barrens) and absent under kelp canopies. However, a discrepancy existed between different structural forms of turf, with the positive association holding true only for geniculate corallines, not filamentous turf. Secondly, a laboratory experiment tested whether the physical structure and/or the sediment-trapping properties of coralline turf influenced the recruitment success of C. filiformis. Whilst the structural complexity of turf aided overall recruitment performance (i.e., increased rhizoid production, attachment speed, success, and strength), a positive influence of turf-derived sediment on recruits’ growth was less obvious, at least over 10 days. The high morphological plasticity of C. filiformis propagules resulted in possible benefits of faster or stronger attachment of more developed propagules being only temporary, and that recruitment may be regulated in accordance with habitat preference. Finally, a field experiment confirmed the observed positive role of turf and the negative influence of algal canopies in the short-term, however, adverse environmental conditions in the longer-term resulted in the loss of most fragments. In conclusion, this study demonstrated the importance of both positive and negative species interactions for the recruitment success of a native alga, suggesting that a shift from kelp to turf algae can initiate further community change.
... Here, propagule pressure was positively associated with both the likelihood of establishment and population growth rates (thus abundances) after three years (Grevstad 1999) as well as population persistence to year ten postintroduction (Grevstad 2006); unfortunately, abundance in year ten was not reported. Thus, for these two examples propagule pressure appears to have been similarly related to establishment and post-establishment abundances (see also Fauvergue et al. 2007, Burgess and Marshall 2011, Britton and Gozlan 2013, Estrada et al. 2016, Lange and Marshall 2016. Whether this pattern is general remains to be seen, but increased demographic stochasticity in small populations should yield a positive association between abundance and the likelihood of population persistence over time and thus a similar relationship between propagule pressure and both metrics (although see Memmott et al. 2005 for a contrary example). ...
Article
Full-text available
Colonization is a critical filter, setting the stage for short‐term and long‐term population success. Increased propagule pressure (e.g., more founding individuals) usually enhances colonization; however, this pattern may be driven by purely numeric effects, population genetic diversity effects, or both. To determine the independent and interactive effects of propagule pressure and genetic diversity, we conducted a seed addition experiment in the field using the ruderal annual Arabidopsis thaliana. Propagule pressure treatments spanned five levels, from 32 to 960 seeds per 0.25‐m² plot. Founder populations were composed of one, four, or eight genotypes and exposed to ambient or reduced levels of interspecific competition. Genotype monocultures were included to quantify additive vs. non‐additive effects. Populations were followed for three generations, with abundance, population persistence and genotype retention (the proportion of introduced genotypes persisting over time) as the major response variables. Increased propagule pressure enhanced abundance immediately following introduction, particularly where nutrient availability was high and competition reduced. Greater propagule pressure also increased the likelihood of population persistence and genotype retention through three generations. However, most populations experienced rapid abundance declines over time, yielding no relationship between propagule pressure and third‐generation abundance across persisting populations. Under reduced competition, increased genetic diversity led to a marginal increase in persistence through the third generation that was more pronounced, and statistically significant, in low nutrient conditions. Genetic diversity did not affect persistence through the first generation, thus indicating that genetic diversity effects strengthened over time. Nevertheless, genotypic mixture populations fell short of expectations based on performance in monocultures (negative non‐additive effects). Increased genetic diversity was also associated with abundance declines, largely due to one particularly high‐performing genotype in the lowest diversity treatments (i.e., genotypic identity effects). Overall, our results indicate that increases in both propagule pressure and genetic diversity can enhance colonization success but are highly context dependent. They also highlight novel ways in which both factors can impact the retention of introduced genetic diversity over time. Our findings pinpoint the determinants of a fundamental population process and have key implications for applications where enhanced or suppressed colonization is desired, including ecological restoration and invasive species management.
... The initial size of A. donax rhizomes was found to be related to the level of sprouting (Santín-Montanyá et al. 2014) and yield biomass (Copani et al. 2013). Estrada et al. (2016) and Peng et al. (2017) found that rhizome segments containing three or more nodes significantly enhanced the establishment of invasive species such as alligator weed [Alternanthera philoxeroides (Mart.) Griseb.] and cogongrass [Imperata cylindrica (L.) P. Beauv.]. ...
Article
Giant reed ( Arundo donax L.) has recently shown great potential as a feedstock for the bioenergy industry. However, before A. donax can be grown commercially, due to its invasive nature, management strategies must be developed to reduce the risk of unintended spread. This research was conducted in northeastern Oregon (USA) during two growing seasons. Nine control strategies were evaluated in a field that previously had A. donax as a crop. The control strategies included mechanical practices (stem cutting and rhizome digging), physical practices (covering with an opaque tarp), chemical practices (glyphosate applications at different rates and timings), and a combination of these practices. Spring samplings of A. donax regrowth in the season following treatments indicated that stem cutting in the spring without follow-up control practices provided no control. Covering plants with a tarp after cutting them (either with or without a glyphosate treatment after cutting) resulted in 96% control. Application of glyphosate alone also resulted in excellent control, although timing of application was an important factor for maximizing efficacy. The best results were found when the maximum dose (10.2 L ai ha ⁻¹ ) was split among two or three applications (>99% of control) compared with the maximum dose applied once (75% to 94%). Control was lower (73% to 89%) for two of the strategies that included mechanical practices, stem cutting + glyphosate and rhizome digging, in comparison to other strategies involving tarps and/or glyphosate applications (88% to 100%). Results indicated that it is very difficult to eradicate volunteer A. donax in 1 yr, but very good control can be achieved with several of the strategies tested.
Article
Full-text available
Seed size and shape predict seed persistence in the soil for British and Argentinian herbaceous plant species. Those species with small, rounded seeds tend to have persistent seeds while those with larger, more elongate or flattened seeds usually lack persistence. It has been suggested that the mechanism underlying this pattern may be ease of burial, as small, rounded seeds are incorporated into the soil more easily than large, elongate or flattened seeds and are therefore less likely to be eaten by seed predators. We tested whether seed size and shape were related to persistence in the soil for 47 species native to New Zealand forests. There was a tendency for species with persistent seeds to have smaller seeds than species with transient seeds. However, species with large and/or elongate or flattened persistent seeds were relatively common. This indicates that seed size and shape are not related to persistence in New Zealand in the same way as in Britain and Argentina. A similar negative result has been found in Australia. The underlying cause of the patterns observed is unlikely to be ease of burial, since incorporation of seeds into the soil is likely to operate in all countries in a similar manner on seeds without specialised seed burial mechanisms. Data from all four floras studied to date also suggest that species with small, rounded seeds that do not germinate immediately must have the ability to survive periods of burial.
Article
Purple nutsedge ( Cyperus rotundus L.) from single tubers was grown for 3 months at 24, 32, and 40 C and 9, 13, and 19 klux illumination. Growth in number and dry weight of shoots, bulbs, and tubers were determined at monthly intervals. Maximum growth for all portions of the plant occurred after 3 months at 32 C and 19 klux illumination. Minimum growth occurred at 40 C and 9 klux illumination. Growth at 24 C was not significantly affected by increased illumination above 9 klux.
Article
The growth responses of cogongrass [ Imperata cylindrica (L.) Beauv.] were studied in a controlled-environment greenhouse with a day/night temperature of 29/23 C, under full available light and 56 and 11% of full light. The cogongrass plants were grown from stem and rhizome propagules originating from an interstate highway median, a pecan [ Carya illinoensis (Wangenh.) K. Koch] plantation, and a pine ( Pinus spp.) forest. After 89 days, the plants from all three populations produced, on average, three times as much total dry weight and leaf area in full available sunlight as in 56% full light and 20 times as much as in 11% full light. The distribution of plant biomass into rhizomes decreased with shading, whereas the distribution into leaves increased. The distribution of leaf biomass as leaf area also increased with shading, with the result that the plants grown in 11% full light had leaf area ratios about 2.5 times greater than those grown in full light. Reductions in dry matter production with shading were due to significant reductions in both net assimilation rate and leaf area duration or total amount of leaf area present. The plants from the shaded and exposed habitats generally did not differ significantly in their responses to shading. Thus, there is little evidence for the presence of sun and shade ecotypes in the populations of cogongrass studied.
Article
Data on the seed morphology of three pine species (Pinus pinea L., P. pinaster Ait., and P. radiata D. Don) in the south-western Cape Province are presented. The seeds of both P. pinaster and P. radiata are relatively small (50 and 20mg respectively) and have relatively large wings (190 and 110mm² respectively). Pinus pinea, on the other hand, has a relatively large (700mg) seed and a small wing (24mm²). We show that P. pinaster is capable of dispersal away from the parent trees, whereas P. pinea seedlings occur only under parent trees. This supports the hypothesis that P. radiata and P. pinaster tend to be invasive by virtue of possessing winged seeds adapted for long-range dispersal.
Article
A survey of Florida highway rights-of-way was conducted during 1984–85 to determine the occurrence and severity of cogongrass infestation. Florida Department of Transportation district maintenance engineers surveyed 8,200 km of limited-access and other major highways (22% of highway system). Cogongrass was distributed widely from the north central region southward through the central Florida ridge north of Lake Okeechobee. Highest frequencies were in counties where cogongrass was used for forage and soil stabilization during the 1950s. The large, widely scattered cogongrass infestations probably were established during extensive roadway construction and routine maintenance which used rhizome-contaminated fill soil.
Chapter
In this essay, we have provided a brief review of the rapidly expanding literature on biological invasions. Many of the hypotheses explored above are not mutually exclusive, and the processes that underlie them may act simultaneously, in concert or in opposition, to determine the ultimate success or failure of an invader at each invasion stage. Though we have tried to be thorough, experienced researchers in the field will no doubt formulate additional hypotheses that warrant investigation. To date, most experiments have focused on only a single hypothesis for a small subset of invasive species under particular environmental conditions. To arrive at a realistic understanding of the ecological processes underlying biological invasions, a more integrative approach is warranted — one that examines the relative importance of each processes for a variety of species under myriad environmental conditions. This will prove to be a daunting task indeed, but one that will perpetuate the expansion of the field of invasion ecology for years to come, thereby ensuring plenty of fruitful lines of research for the keen investigators of the future.
Article
Fire maintains structure and function in pyrogenic ecosystems. Invasive nonindigenous grasses have introduced fire cycles into nonpyrogenic ecosystems and altered the fire regime in pyrogenic ecosystems, changing structure and function of the invaded ecosystems. Sandhill, a pyrogenic pine savanna ecosystem, occurs on well-drained sands on the southeastern Coastal Plain of the United States. Sandhill sites are managed with relatively frequent low-intensity fires fueled by short caespitose grasses and pine needles ignited in the growing season. Imperata cylindrica (L.) Beanv. (cogongrass), a tall rhizomatous grass from Southeast Asia, is invading Florida sandhill. To determine if cogongrass is functionally equivalent to indigenous sandhill grasses, I compared fine-fuel attributes that contribute to fire behavior, a parameter of the fire regime, in uninvaded and invaded sandhill. Sandhill invaded by cogongrass had significantly greater fine-fuel loads, horizontal continuity, and vertical distribution. These fine-fuel changes in invaded sandhill resulted in fires that, compared to those in noninvaded sandhill sites, were more horizontally continuous and had higher maximum temperatures at greater heights. Fire-induced mortality of juvenile Pinus palustris Mill, (longleaf pine) was higher for pines growing in invaded sandhill. Rate of fuel accumulation after burning was greater in invaded sandhill. Over time, changes in sandhill fire behavior due to cogongrass invasion could result in higher mortality of native herbaceous and woody plants, shifting sandhill composition from a species-rich pine savanna to a grassland dominated by nonindigenous cogongrass.