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Historic land use influences contemporary establishment of invasive plant species

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The legacy of agricultural land use can have widespread and persistent effects on contemporary landscapes. Although agriculture can lead to persistent changes in soil characteristics and plant communities, it remains unclear whether historic agricultural land use can alter the likelihood of contemporary biological invasions. To understand how agricultural land-use history might interact with well-known drivers of invasion, we conducted factorial manipulations of soil disturbance and resource additions within non-agricultural remnant sites and post-agricultural sites invaded by two non-native Lespedeza species. Our results reveal that variation in invader success can depend on the interplay of historic land use and contemporary processes: for both Lespedeza species, establishment was greater in remnant sites, but soil disturbance enhanced establishment irrespective of land-use history, demonstrating that contemporary processes can help to overcome legacy constraints on invader success. In contrast, additions of resources known to facilitate seedling recruitment (N and water) reduced invader establishment in post-agricultural but not in remnant sites, providing evidence that interactions between historic and contemporary processes can also limit invader success. Our findings thus illustrate that a consideration of historic land use may help to clarify the often contingent responses of invasive plants to known determinants of invasibility. Moreover, in finding significantly greater soil compaction at post-agricultural sites, our study provides a putative mechanism for historic land-use effects on contemporary invasive plant establishment. Our work suggests that an understanding of invasion dynamics requires knowledge of anthropogenic events that often occur decades before the introduction of invasive propagules.
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COMMUNITY ECOLOGY - ORIGINAL RESEARCH
Historic land use influences contemporary establishment
of invasive plant species
W. Brett Mattingly
John L. Orrock
Received: 15 March 2012 / Accepted: 11 December 2012
Ó Springer-Verlag Berlin Heidelberg 2012
Abstract The legacy of agricultural land use can have
widespread and persistent effects on contemporary land-
scapes. Although agriculture can lead to persistent changes
in soil characteristics and plant communities, it remains
unclear whether historic agricultural land use can alter the
likelihood of contemporary biological invasions. To
understand how agricultural land-use history might inter-
act with well-known drivers of invasion, we conducted
factorial manipulations of soil disturbance and resource
additions within non-agricultural remnant sites and post-
agricultural sites invaded by two non-native Lespedeza
species. Our results reveal that variation in invader success
can depend on the interplay of historic land use and con-
temporary processes: for both Lespedeza species, estab-
lishment was greater in remnant sites, but soil disturbance
enhanced establishment irrespective of land-use history,
demonstrating that contemporary processes can help to
overcome legacy constraints on invader success. In con-
trast, additions of resources known to facilitate seedling
recruitment (N and water) reduced invader establishment in
post-agricultural but not in remnant sites, providing
evidence that interactions between historic and contem-
porary processes can also limit invader success. Our find-
ings thus illustrate that a consideration of historic land use
may help to clarify the often contingent responses of
invasive plants to known determinants of invasibility.
Moreover, in finding significantly greater soil compaction
at post-agricultural sites, our study provides a putative
mechanism for historic land-use effects on contemporary
invasive plant establishment. Our work suggests that an
understanding of invasion dynamics requires knowledge of
anthropogenic events that often occur decades before the
introduction of invasive propagules.
Keywords Agriculture Disturbance Lespedeza
Longleaf pine savanna Soil compaction
Introduction
The legacy of agricultural land use can shape many con-
temporary ecological patterns and processes (Foster et al.
2003; Flinn and Vellend 2005; Cramer et al. 2008). For
example, post-agricultural lands often exhibit substantial
reductions in plant diversity and abundance (Vellend 2004;
Flinn and Vellend 2005; Hermy and Verheyen 2007;
Vellend et al. 2007), altered soil microbial communities
and nutrient availability (Fraterrigo et al. 2005, 2006), and
lasting changes in soil properties, including reductions in
organic matter and water-holding capacity (Foster et al.
2003; McLauchlan 2006). These effects of historic agri-
culture may be particularly relevant for understanding the
forces that shape the success of non-native plant invasions
because resident plant diversity and productivity (Knops
et al. 1999; Levine 2000; Symstad 2000; Hector et al.
2001), microbial associates (Callaway et al. 2004; Mitchell
Communicated by Bryan Foster.
Electronic supplementary material The online version of this
article (doi:10.1007/s00442-012-2568-5) contains supplementary
material, which is available to authorized users.
W. B. Mattingly J. L. Orrock
Department of Zoology, University of Wisconsin,
Madison, WI 53706, USA
Present Address:
W. B. Mattingly (&)
Department of Biology, Eastern Connecticut State University,
Willimantic, CT 06226, USA
e-mail: mattinglyw@easternct.edu
123
Oecologia
DOI 10.1007/s00442-012-2568-5
et al. 2006), and soil resources (Huenneke et al. 1990;
Davis and Pelsor 2001; Maron and Marler 2007) can all be
important determinants of invasion success. Indeed, the
potential for the legacy of agricultural land use to affect
plant invasions is underscored by recent observational
studies documenting that post-agricultural lands often have
a greater abundance and diversity of invasive non-native
species (reviewed in Vila and Ibanez 2011).
While the patterns revealed by these observational
studies (e.g., Von Holle and Motzkin 2007; Mosher et al.
2009) often reflect the culmination of a long history of
invasive plant establishment and spread, the actual timing
of invasive propagule arrival relative to the abandonment
of agriculture may be a critical determinant of invasive
plant success. For example, an immediate consequence of
soil disturbances, such as those associated with agricultural
activities, is the disruption of resident plant community
structure, often resulting in decreased plant species rich-
ness and productivity at local scales (Sousa 1984). Because
invasive plant performance is often negatively correlated
with each of these community properties (Levine and
D’Antonio 1999; Levine et al. 2004), soil disturbances that
disrupt resident plant communities may facilitate invasive
plant establishment in otherwise competitive environments.
However, as the time since the disturbance event increases
(e.g., as in the course of old-field succession), resident
communities may change in ways that reduce the likeli-
hood that newly arrived propagules will establish. Thus,
soil disturbance, whether from a historic or contemporary
event, can provide a window of opportunity for invasive
plant establishment; however, if propagule arrival does not
coincide with the disturbance event, then over time previ-
ously disturbed habitat could become more resistant to
plant invasions. This dynamic requires evaluation.
Despite the potential for the legacy of agricultural land
use to affect invasion success, there is no experimental
confirmation of the link between historic land-use patterns
and invasive plant performance, making it difficult to
evaluate whether past agricultural disturbance is a defini-
tive driver of contemporary invasions. Moreover, because
land-use legacies may interact with other common
anthropogenic factors that affect invasive plant performance
(e.g., changes in resource addition rates and disturbance
regimes), factorial experiments that couple land-use pat-
terns with factors known to affect invader success are
necessary to fully understand the relationship between past
land use and contemporary invasions. For example, agri-
cultural land use may affect invader success by increasing
soil compaction (Kyle et al. 2007; Parker et al. 2010), but
this legacy effect may be countered by contemporary soil
disturbances. As such, the lack of an experimental
approach that explicitly considers agricultural land-use
history and other important determinants of invasion
success is a primary impediment to understanding the
potentially widespread effect of historic agricultural land
use on biological invasions.
In this study, we use experimental additions of two
invasive Lespedeza species (Lespedeza bicolor and
Lespedeza cuneata) to evaluate how past agricultural land
use affects the likelihood of contemporary plant invasions.
Further, we explicitly examine how contemporary eco-
logical correlates of invasion success (i.e., soil resource
availability and localized disturbance) might interact with
past land use in determining invasive plant performance.
By coupling a mechanistic multifactor experiment with
variation in underlying land-use history, we test the fol-
lowing predictions:
1. Post-agricultural lands, by virtue of historic distur-
bances, will be less resistant to invasion than habitat
lacking an agricultural history.
2. Contemporary soil disturbances and resource addi-
tions, by lessening the competitive environment, will
heighten invasive plant performance.
3. The effects of contemporary disturbances will be
contingent on land-use history, whereby invader
responses to disturbance will be more pronounced in
habitats lacking an agricultural history.
Materials and methods
Study system and site selection
We conducted this study at Fort Bragg, a military instal-
lation that occupies more than 73,000 ha of longleaf pine
savanna in the Sandhills region of North Carolina, USA
(Sorrie et al. 2006). Fort Bragg encompasses a mosaic of
upland habitat with distinct land-use histories, including
areas that were formerly cultivated and areas that lack
a history of agriculture, hereafter referred to as post-
agricultural and remnant habitats, respectively. Agriculture
was abandoned when the military installation was established
in 1918 (Aragon 2004
), and former agricultural fields
were then naturally reforested. As such, post-agricultural
habitat is nearly a century old and has mature longleaf
overstories similar to those of remnant habitat. In our study,
tree canopy cover did not differ between post-agricultural
(48.3 ± 4.8 %) and remnant (54.3 ± 2.0 %) sites (t =-1.16,
P = 0.28).
Sites were selected using a Geographic Information
System that contained installation boundaries, a digitized
historic topographical map depicting the perimeters of
cultivated fields in 1919, USDA soil series information,
and annual prescribed and wildfire records from 1991 to
2009. We used the historic map to identify the locations of
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remnant and post-agricultural habitat across the landscape.
We then narrowed our selection of sites by standardizing
for soil type and fire management. Across all selected sites,
soils belonged to the Blaney-Gilead-Lakeland soil unit,
which is noted for well-drained soils with a high sand
content (Wyatt 1995). All sites have experienced a 2.7- to
4.8-year fire-return interval since 1991. For each post-
agricultural site, we selected a nearby (\1.5 km) remnant
stand that met the soil and fire management criteria. All
study sites were located in upland longleaf pine savanna
throughout the western half of Fort Bragg (35°8
0
21
00
N,
78°59
0
57
00
W; Moore and Hoke Counties, North Carolina,
USA).
Experimental design
Within each remnant and post-agricultural stand, we
imposed a soil-disturbance treatment, manipulated soil
nutrient and water availabilities, and separately introduced
two non-native N
2
-fixing Lespedeza species (L. bicolor and
L. cuneata) into the experimental plots in a fully factorial
design (Online Resource 1). Although both of these species
may be invasive in southern pine forests (Norden and
Kirkman 2006), neither species was present at the study
sites prior to experimental introductions. All treatment
combinations were replicated 8 times, yielding 128
experimental units per Lespedeza species (2 land-use lev-
els 9 2 disturbance levels 9 2 nutrient levels 9 2 water
levels 9 8 replicates). Within our split–split-plot design,
historic land use provided the largest experimental unit,
soil disturbance was applied within the land-use treatment,
and the nutrient 9 water factorial treatments were applied
within the disturbance treatment. Plot assignments were
randomly determined at each of the lower levels of the
split–split-plot design.
At each site we established two 1.5 9 1.5-m plots,
separated by a 1-m-wide buffer, randomly oriented, and
positioned within the interior of the stand at least 100 m
from the nearest road or drainage. In January 2010, we
imposed a soil disturbance treatment at each site by
excavating the soil from one of the paired plots to a depth
of 15 cm, removing all coarse above- and belowground
vegetation, and returning the homogenized soil to the plot.
Soil within the adjacent plot remained undisturbed.
We split each 1.5 9 1.5-m plot into four 0.75 9 0.75-m
experimental units, each of which received a unique
combination of levels (i.e., ambient vs. enriched) of the soil
nutrient and water treatments (Online Resource 1). In
March 2010, two adjacent 0.75 9 0.75-m units were fer-
tilized with slow-release fertilizer (N–P–K, 10–10–10) at a
rate of 24 g N m
-2
year
-1
, a rate characteristic of the higher
end of experimental nutrient gradients (Tilman 1993;
Thompson et al. 2001). Two arenas were established within
each experimental unit; we added 20 seeds of L. bicolor
into one arena and 20 seeds of L. cuneata into the other.
Each arena consisted of a clear plastic ring (21-cm diam-
eter, 12-cm height) covered with hardware cloth and
affixed to the ground with landscape staples. These arenas
prevented seeds from washing out of the experimental units
and minimized consumer pressure (all arenas were
removed in May 2010). The water treatment was also
initiated in March 2010, immediately following seed
additions, wherein 15 mm of water was provided directly
to the arenas twice a week for 10 weeks, totaling an
additional 300 mm water year
-1
(i.e., a 25 % increase in
mean annual precipitation) for those arenas assigned to the
water-addition treatment level. We did not add water to
arenas assigned to the ‘ambient water’ treatment level.
Data collection
In September 2010, seven months following seed addi-
tions, we evaluated the performance of each Lespedeza
species both in terms of establishment and growth because
the factors most crucial to invader success can vary across
life history stages (Huston 2004). For each experimental
unit, individuals were counted, clipped at the stem base,
dried to a constant weight at 65 °C, and weighed. We
defined invasive plant establishment as the proportion of
individuals alive during this final census period and growth
as the measure of per capita aboveground biomass per
experimental unit (see also Gurevitch et al. 2008; Hooper
and Dukes 2010). To evaluate the competitive environment
localized within each experimental unit, we quantified the
richness and aboveground biomass of the resident under-
story plant community within a 32-cm-diameter neigh-
borhood centered on each sampling arena. All resident
plants rooted within this area were grouped by species,
clipped at the stem base, dried, and weighed. For each
neighborhood, this census yielded measures of resident
species richness and community productivity.
We measured several environmental variables that
might contribute to differences in the success of invasive
plant species between remnant and post-agricultural sites
(Kirkman et al. 2001; Bassett et al. 2005; Walker and
Silletti 2006). Forest canopy cover was quantified for each
site by taking the mean of four measurements from a
spherical crown densiometer (Forestry Suppliers, Jackson,
MS) held at 1.37-m height. To further quantify forest
structure, we measured the distance between study plots
and the three nearest canopy trees at each site. We also
measured the diameter of these trees at 1.37 m above the
ground. Soil moisture holding capacity was quantified for
each 1.5 9 1.5-m plot, wherein 12 soil cores (each 2.5 cm
in diameter and 15 cm in depth) were collected, homoge-
nized, and processed as in Brudvig and Damschen (2011).
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123
Soil compaction was quantified for each plot by taking the
mean of six measurements from a cone penetrometer
(Dickey-John, Auburn, IL) inserted to a 15-cm depth.
Within the undisturbed plot at each site, we also measured
the depth at which 2 MPa was attained, a level of soil
compaction beyond which plant performance is generally
constrained (Bassett et al. 2005).
Data analysis
To examine the proportion of added seeds that became
established as plants, we used a generalized linear mixed
model with a binomial response distribution (SAS version
9.1; SAS Institute, Cary, NC). We used a separate analysis
for each Lespedeza species, treating land-use history, soil
disturbance, nutrient addition, and water addition as fixed
effects. We treated replicate sites as a random effect.
Our model and subsequent significance tests explicitly
incorporated the multi-level split-plot structure of our
experimental design. We used the Kenward–Rogers approxi-
mation to estimate variance components and denominator df,
as recommended by Littell et al. (2006). Because our
hypotheses allow for multiple, interactive effects, we
evaluated all possible interactions in our model.
We used linear mixed models to evaluate the following
response variables: invader growth following establish-
ment, resident species richness, and total resident biomass.
The structure of these models with regard to fixed and
random effects was identical to the model for invader
establishment. Based on examination of residuals from
preliminary analyses, a natural-log transformation was
applied to the resident biomass data to improve normality.
Examination of residuals following analyses suggested that
residuals from all final models exhibited no patterns con-
sistent with heteroscedasticity or non-normality.
To evaluate site-level environmental differences
between land-use categories, we used t-tests that employed
the Cochran and Cox approximation method to account for
unequal group variances. To evaluate plot-level environ-
mental differences, we used linear mixed models that
treated land-use history and soil disturbance as fixed effects
and replicate plots as a random effect. Finally, we used
correlation analyses to evaluate relationships between
Fig. 1 Effects of soil disturbance on a, b establishment and c, d
biomass production of Lespedeza bicolor and Lespedeza cuneata in
post-agricultural and remnant habitats. Establishment is defined as the
proportion of individuals alive at the final census, and biomass
production as the measure of per capita aboveground biomass per
arena. Invasive plant responses are averaged across levels of the soil
nutrient and water-addition treatments. Biomass data are presented on
a log scale for readability, but analyses were conducted on non-
transformed data. Data represent mean ± 1SE
0.0
0.1
0.2
0.3
0.001
0.01
0.1
1
10
Establishment (proportion)
0.0
0.1
0.2
0.3
undisturbed soil
disturbed soil
L.bicolor
L.cuneata
Biomass production (g)
0.001
0.01
0.1
1
10
L.bicolor
L.cuneata
Establishment (proportion)
Post-agricultural
Remnant
Biomass production (g)
(a)
(b)
(c)
(d)
c
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123
invader performance, resident species richness and pro-
ductivity, and environmental variables.
Results
Invasive plant establishment
For both species of Lespedeza, the proportion of seeds that
established as plants was greater in remnant than in post-
agricultural habitats (main effect of land use: L. bicolor,
F
1,33.4
= 10.2, P = 0.003, 100 % greater establishment in
remnant plots, Fig. 1a; L. cuneata, F
1,18.8
= 6.3, P = 0.022,
138 % greater establishment in remnant plots, Fig. 1b).
Regardless of land-use history, soil disturbance promoted the
establishment of both Lespedeza species (main effect of
disturbance: L. bicolor, F
1,33.4
= 26.4, P \ 0.001, 200 %
greater establishment in disturbed plots; L. cuneata,
F
1,18.8
= 26.2, P \ 0.001, 352 % greater establishment in
disturbed plots). For L. bicolor, responses to nutrient and
water additions were contingent on land-use history (land
use 9 nutrient, F
1,46.9
= 4.4, P = 0.042; land use 9 water,
F
1,112
= 5.2, P = 0.024). In particular, nutrient and water
additions both reduced L. bicolor establishment in post-
agricultural habitats (linear contrasts: nutrient, F
1,65.5
= 6.7,
P = 0.012, 56 % reduction in establishment with nutrient
addition; water, F
1,112
= 6.6, P = 0.012, 48 % reduction in
establishment with water addition) but not in remnant habi-
tats (nutrient, F
1,31.2
\ 0.1, P = 0.88, Fig. 2a; water,
F
1,112
= 0.1, P = 0.72, Fig. 2b). Moreover, water addition
and disturbance interacted to affect L. bicolor establishment
(disturbance 9 water, F
1,112
= 7.5, P = 0.007), such that
water addition decreased L. bicolor establishment in undis-
turbed habitats only (linear contrasts: undisturbed,
F
1,112
= 7.1, P = 0.009; disturbed, F
1,112
= 0.7, P = 0.39;
52 % reduction in establishment with water addition,
Fig. 3a). L. cuneata establishment was reduced by nutrient
addition (main effect of nutrient: F
1,53.6
= 7.3, P = 0.009,
57 % reduction in establishment with nutrient addition) but
not by water addition (main effect of water: F
1,112
= 3.2,
P = 0.076). The responses of L. cuneata to these resource
additions were independent of land-use history and soil
Establishment (proportion)
0.0
0.1
0.2
0.3
ambient nutrients
nutrient addition
0.0
0.1
0.2
0.3
ambient water
water addition
Remnant
Establishment (proportion)
Post-agricultural
(a)
(b)
Fig. 2 Effects of land-use history on L. bicolor establishment in
response to a soil nutrient and b water additions. Establishment is
a averaged across levels of the soil-disturbance and water-addition
treatments and b averaged across levels of the soil-disturbance and
nutrient-addition treatments. Data represent mean ± 1SE
Establishment (proportion)
0.0
0.1
0.2
0.3
ambient water
water addition
Undisturbed soil
Biomass production (g)
0.001
0.01
0.1
1
10
ambient nutrients
nutrient addition
Disturbed soil
(a)
(b)
Fig. 3 Effects of soil disturbance on L. bicolor responses to a water
and b soil nutrient addition. Establishment is averaged across land-use
and nutrient-addition treatments, and biomass production is averaged
across land-use and water-addition treatments. Biomass data are
presented on a log scale for readability, but analyses were conducted
on non-transformed data. Data represent mean ± 1SE
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123
disturbance. For both species of Lespedeza, all other higher-
order interactions describing the proportion of seeds estab-
lishing were non-significant (Online Resource 2). The
proportions of individuals alive in May and September 2010
were highly correlated for both L. bicolor (r = 0.68,
P \ 0.0001) and L. cuneata (r = 0.55, P \ 0.0001).
Invasive plant productivity
For both species of Lespedeza, average per capita biomass
production was independent of land-use history (main
effect of land use: L. bicolor, F
1,16.2
= 1.1, P = 0.31,
Fig. 1c; L. cuneata, F
1,12.2
= 0.8, P = 0.38, Fig. 1d). Soil
disturbance enhanced the growth of L. bicolor (main effect
of disturbance: F
1,16.4
= 13.6, P = 0.002, 200 % biomass
increase in disturbed plots, Fig. 1c) but not of L. cuneata
(F
1,11.1
= 2.8, P = 0.12, Fig. 1d). For L. bicolor, nutrient
addition enhanced productivity (main effect of nutrient:
F
1,35.6
= 10.5, P = 0.003), but this effect was detected
only in disturbed habitats (disturbance 9 nutrient,
F
1,35.6
= 10.0, P = 0.003, 817 % biomass increase with
nutrient additions, Fig. 3b; linear contrasts: undisturbed,
F
1,40.4
\0.1, P = 0.96; disturbed, F
1,30.5
= 23.2, P \ 0.001).
In contrast, resource additions did not affect L. cuneata
productivity. For both species of Lespedeza, all other
higher-order interactions describing per capita growth were
non-significant (Online Resource 2).
Resident richness and productivity
Resident species richness and productivity differed among
undisturbed post-agricultural and remnant plots (land
use 9 disturbance interaction: species richness, F
1,14
=
11.8, P = 0.004; productivity, F
1,14
= 19.3, P \0.001;
Online Resource 2). In particular, post-agricultural habitats
had fewer resident species than remnant habitats in
undisturbed plots (linear contrast: F
1,20.5
= 9.7, P =
0.005) but not in disturbed plots (F
1,20.5
\ 0.1, P = 0.95).
Similarly, post-agricultural habitats were less productive
than remnant habitats in undisturbed plots (linear contrast:
F
1,21.5
= 19.9, P \ 0.001) but not in disturbed plots
(F
1,21.5
= 0.1, P = 0.78). Soil disturbance reduced resi-
dent species richness and productivity in remnant plots
only (Online Resource 3). Neither resident species richness
nor productivity was correlated with the establishment or
productivity of either non-native Lespedeza species (Online
Resource 4).
Environmental characteristics
Fire-return intervals were similar between remnant and post-
agricultural plots (3.7 ± 0.3 years in remnant plots vs.
3.8 ± 0.2 years in post-agricultural plots, t = 0.22,
P = 0.83). Proximity of canopy trees to study plots was
independent of land-use history (5.4 ± 0.3 m in post-agri-
cultural plots vs. 5.4 ± 0.5 m in remnant plots, t = 0.04,
P = 0.97). These neighboring trees were also similar in
diameter between the land-use categories (41.4 ± 1.4 cm in
post-agricultural plots vs. 37.7 ± 2.4 cm in remnant plots,
t = 1.31, P = 0.21). Soil moisture-holding capacity was
independent of land-use history, although there was a trend
of greater moisture-holding capacity in remnant plots
(0.386 ± 0.014 in post-agricultural plots vs. 0.438 ± 0.015
in remnant plots, main effect of land use: F
1,14
= 3.8,
P = 0.072). Disturbance reduced soil moisture holding
capacity independent of land-use history (0.434 ± 0.014 in
undisturbed plots vs. 0.390 ± 0.016 in disturbed plots, main
effect of disturbance: F
1,14
= 24.9, P \ 0.001). The upper
soil horizons were more compacted at post-agricultural than
at remnant sites (depth at which 2 MPa was attained:
8.3 ± 2.9 cm at post-agricultural sites vs. 40.1 ± 9.6 cm at
remnant sites, t =-3.17, P = 0.016). Despite this differ-
ence, soil disturbance reduced compaction to similar levels
in both post-agricultural and remnant plots (land
use 9 disturbance, F
1,14
= 14.4, P = 0.002, Fig. 4a; linear
contrasts: undisturbed, F
1,25.9
= 20.5, P \ 0.001; dis-
turbed, F
1,25.9
\ 0.1, P = 0.99). For each Lespedeza spe-
cies, measures of both establishment (L. bicolor, r =-0.62,
P \ 0.001, Fig. 4b; L. cuneata, r =-0.65, P \ 0.001;
Fig. 4c) and productivity (L. bicolor, r =-0.50,
P = 0.004; L. cuneata, r =-0.43, P = 0.013) were nega-
tively correlated with soil compaction; invader performance
was not correlated with the other environmental variables
measured in our study (Online Resource 4).
Discussion
In a recent review, Gurevitch et al. (2011) surmise that
‘different mechanisms may contribute to the invasion of
different species, or to the same species in different places
or at different times.’ Our results illustrate that historic land
use can provide an important lens through which to view
this contingency in biological invasions because agricul-
tural legacies consistently affected the establishment of two
invasive species in our study. Our results also demonstrate
that historic and contemporary disturbance regimes can
have additive and complementary effects on invasion
success. Further, our study points to soil compaction as a
putative mechanism capable of creating persistent land-use
effects on invasion success (see also Kyle et al. 2007;
Parker et al. 2010) and mediating interactions between
historic land use and contemporary disturbance: soil com-
paction was significantly greater in post-agricultural sites
relative to remnant sites, but this difference was eliminated
by contemporary soil disturbances (Fig. 4a).
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123
Land-use legacies and the greater success of invasive
species in remnant habitats
By coupling a multifactor experiment with variation in
underlying land-use history, our results reveal that the
establishment of both invasive Lespedeza species is greater
in habitats that lack an agricultural history. In contrast to
our results, the patterns revealed in recent observational
studies reflect the culmination of a long history of invasive
plant establishment and spread following agricultural
abandonment in the nineteenth century (e.g., DeGasperis
and Motzkin 2007; Von Holle and Motzkin 2007;
McDonald et al. 2008; Mosher et al. 2009), where it is
likely that the disturbance associated with former agricul-
tural practices initially facilitated the establishment of
invasive plants which then persisted in the landscape dur-
ing the course of old-field succession. In our study, the
resistance of post-agricultural habitats to invasive plant
establishment *90 years after agricultural abandonment
suggests that timing of propagule introduction is important,
especially relative to the timing of agricultural activities.
Supporting this notion, studies have also shown that non-
native species richness and abundance in post-agricultural
lands can vary with the time since introduction (Aragon
and Morales 2003; Wilson et al. 2007), demonstrating in
some cases that the relative abundance of non-native plants
declines over time (e.g., Meiners et al. 2002). As with our
study location, the abandonment and subsequent refores-
tation of former agricultural fields has widely occurred
throughout Europe and eastern North America (Flinn and
Vellend 2005). As such, understanding the influence of
historic land use may provide insight into contemporary
invasion dynamics in a broad range of human-modified
landscapes.
Additionally, the relative absence of invasive plants in
remnant forests, as documented by observational studies,
may reflect inherent differences in propagule pressure
between remnant and post-agricultural habitats (Martin
et al. 2009) and the tendency for non-native species to be
seed-limited in undisturbed habitats (Clark et al. 2007),
differences that we overcame with our experimental
approach. Indeed, by imposing an experimental framework
over a historic landscape, our study demonstrates that
contemporary disturbance can set the stage for the invasion
of otherwise resistant post-agricultural habitats, thereby
helping to reconcile the seemingly conflicting results of our
experimental study with those of observational studies.
Historic and contemporary processes generate
contingency in invasion success
Our study highlights the importance of considering historic
land use as well as contemporary disturbances as deter-
minants of invasive plant success. The general importance
of soil disturbance in facilitating invasions is widely rec-
ognized and may operate through several pathways,
including changes to the physical, chemical, and biological
properties of disturbed soil (Lozon and MacIsaac 1997;
D’Antonio et al. 1999). In post-agricultural landscapes,
Soil compaction (MPa)
0
1
2
3
undisturbed soil
disturbed soil
01 23
Establishment (proportion)
0.0
0.2
0.4
0.6
0.8
Soil compaction (MPa)
01 23
Establishment (proportion)
0.0
0.2
0.4
0.6
0.8
L. cuneata
L. bicolor
R = 0.39
2
P < 0.001
R = 0.42
2
P < 0.001
Post-agricultural Remnant
(a)
(b)
(c)
Fig. 4 a Effects of soil disturbance on soil compaction in post-
agricultural and remnant sites. Data represent mean ± 1 SE. The
relationships between soil compaction and the establishment of b
L. bicolor and c L. cuneata. Plant performance is generally constrained
when soil compaction exceeds 2 MPa (Bassett et al. 2005)
Oecologia
123
however, disturbance-induced changes in soil compaction
may be of particular relevance to invasive plant perfor-
mance. Increased soil compaction is indeed a persistent
legacy of historic agriculture (Compton et al. 1998;
Maloney et al. 2008; Parker et al. 2010) and one that has
been shown to constrain plant performance through a
variety of mechanisms, including reductions in porosity,
nutrient mineralization rates, and oxygen and water avail-
ability (Unger and Kaspar 1994; Bassett et al. 2005). Soil
compaction levels that exceed 2 MPa are generally con-
sidered to limit plant performance (Bassett et al. 2005).
In our study, soil compaction was 44 % greater in post-
agricultural (2.30 MPa) than in remnant (1.60 MPa) habitats.
This considerable difference in soil compaction, combined
with the positive invader responses elicited by disturbance-
induced decreases in soil compaction and the strong neg-
ative relationship between soil compaction and invader
establishment (Fig. 4) all suggest that an agricultural leg-
acy effect on soil compaction is a probable cause for the
observed differences in the proportion of seeds establishing
for invasive Lespedeza plants between post-agricultural
and remnant habitats.
Few studies have explicitly examined the influence of
soil compaction on invasion success. As with our study,
Kyle et al. (2007) use experimental seed additions and
demonstrate that increased soil compaction reduces non-
native plant performance. In contrast, Parker et al. (2010)
reveal a positive correlation between compaction and non-
native species richness. These equivocal results may be
explained in part by the timing of analysis relative to
propagule introductions: in contrast to seed-addition
experiments, observational studies often evaluate the out-
come of plant recruitment that occurred in the past and
under conditions that may have differed from those
observed at the time of the study. Nonetheless, the over-
arching importance of soil compaction in our study is
suggested by the significant reductions in non-native plant
establishment as well as in native richness and productivity
on compacted soils of post-agricultural lands (Online
Resource 3) as well as the negative relationships between
soil compaction and both the establishment and growth of
each non-native Lespedeza species. Although levels of soil
compaction differed significantly between post-agricultural
and remnant sites, other key environment characteristics
that are known to affect plant performance in our study
system (e.g., canopy cover, tree density, and soil water
holding capacity) did not, nor were they significantly cor-
related with the performance of either invasive species
(Online Resource 4). Further, the relative lack of under-
story vegetation in post-agricultural sites likely minimized
competitive interactions between the invasive and resident
plants, a factor that has otherwise been shown to constrain
invasive species performance in more productive and
diverse communities (Levine and D’Antonio 1999; Levine
et al. 2004). Indeed, that invader performance was
heightened in remnant habitats, which were more produc-
tive and diverse than post-agricultural habitats in our study,
also suggests that factors other than competitive interac-
tions, such as soil compaction, are driving patterns of
invader success. Together, this evidence points to soil
compaction as a likely mechanism for historic land-use
effects on invasive plant establishment in contemporary
landscapes. It is important to note, however, that even
following disturbance-induced reductions in soil compac-
tion, the performance of each non-native Lespedeza species
was greater at remnant than at post-agricultural sites
(Fig. 1). Our results thus show that the effects of agricul-
tural legacies on plant establishment and growth extend
beyond issues of soil compaction. A profitable area of
future research would be to examine whether agricultural
land use leads to persistent changes in soil pathogens and
mutualists that may have detrimental effects on plant
establishment and growth, even after compaction is alle-
viated by soil disturbances.
Although invader establishment was lower in post-
agricultural than in remnant habitats, nutrient and water
additions further reduced L. bicolor establishment in post-
agricultural sites. This response was counterintuitive since
the post-agricultural sites in our study provided a relatively
competitor-free environment and since these resource
additions have been shown to stimulate legume germina-
tion and facilitate seedling establishment (Williams et al.
2003; Van Klinken et al. 2008; Luna and Moreno 2009).
However, in light of the considerable difference in soil
compaction between remnant and post-agricultural sites, it
is possible that L. bicolor establishment is reduced because
land-use history and resource additions interact to produce
an evolutionary trap (Schuler and Orrock 2012). In evo-
lutionary time, resource-rich microsites were likely suitable
for seedling establishment, but anthropogenic soil com-
paction uncouples the typical relationship between
resources and establishment, where, to the detriment of the
seedling, germination is prompted in an otherwise inhos-
pitable microsite. Previous studies indeed demonstrate that
seedlings are particularly vulnerable to the adverse effects
of soil compaction (Smith et al. 2001; Bassett et al. 2005).
Our results suggest that historic and contemporary pro-
cesses can create evolutionary traps for seeds and that this
effect may depend upon the plant species under
consideration.
Historic land use had similar effects on both inva-
sive Lespedeza species in our study: for L. bicolor and
L. cuneata, the proportion of seeds establishing was greater
in remnant than in post-agricultural habitats, but plant
growth was independent of land-use history. However, the
manner in which land-use history influenced invader
Oecologia
123
responses to resource additions differed between these two
Lespedeza species. Nutrient and water additions both
reduced L. bicolor establishment in post-agricultural but not
in remnant habitats, whereas these resources did not interact
with land-use history in affecting L. cuneata success. These
species-specific responses could be attributed to the fact
that L. bicolor, a woody species with larger seeds than
L. cuneata, exhibited greater establishment rates, was more
productive, and thus achieved a greater range of variation in
plant responses to resource additions. Our study only
evaluated the responses of invasive non-native legumes,
and thus it will be important to assess the manner in which
historic land use influences the success of invasive plant
species in other functional groups.
Implications for conservation and restoration
Remnant habitats often represent areas of conservation
concern, particularly in the threatened longleaf pine eco-
system: these habitats typically exhibit high levels of plant
diversity, contain endemic and otherwise rare species, and
often provide the reference communities that are used to
judge conservation and restoration goals (Frost 2006;
Walker and Silletti 2006). Our results inform the man-
agement of invasive species in this threatened ecosystem:
despite the low abundance of invasive plants currently in
upland habitat at our study site (W. B. Mattingly and
J. L. Orrock, unpublished data), our study demonstrates that
remnant habitats are particularly suitable for invasive plant
establishment. As a result, effective management to pre-
vent invasion of these habitats will require special attention
to the flow of propagules. In this system, dispersal limita-
tion, at least in the case of invasive non-native Lespedeza
species, seems the most likely explanation for their absence
in remnant habitats. In support of this notion, Clark et al.
(2007) find that non-native species are more likely to be
dispersal-limited than native species in undisturbed habi-
tats. In the longleaf pine ecosystem, in particular, research
indicates that many species are indeed limited by seed
availability (Myers and Harms 2009), suggesting that
established plant communities in these highly diverse
systems may not provide an effective barrier to the estab-
lishment of non-native Lespedeza species, a notion further
supported by our study (Online Resource 3). Moreover, in
light of the positive effects of soil disturbance on the
success of invasive Lespedeza species, instances where
increased propagule supply intersects with contemporary
soil disturbance could increase community susceptibility to
invasion, especially in remnant habitats. Importantly, pro-
cesses that produce contemporary disturbance may also be
associated with increased input of invasive propagules. For
example, logging commonly creates soil disturbances, and
vehicle traffic associated with logging machinery can
provide a source of invasive plant propagules (Veldman
and Putz 2010). Once invasive plant species colonize
remnant habitats, the increased rates of establishment and
growth that they experience in these areas may make
eradication difficult.
In finding a role for historic land use in affecting inva-
sive plant establishment, our study highlights the need for
additional research into the mechanisms that create and
maintain the effects of land-use legacies on biological
invasions. For example, although multiple lines of evi-
dence implicate soil compaction as being important in our
system, other differences in soil conditions (e.g., microbial
communities, Fraterrigo et al. 2006) could play an impor-
tant role in affecting invasibility of post-agricultural lands,
and future studies are needed to understand how agricul-
tural land use may create long-lasting changes in soils that
foster contemporary invasions. Moreover, we focus on
N-fixing invasive species in this study, as they are often
important in terrestrial systems (Richardson et al. 2000).
However, future work that examines the degree to which
other plant traits (e.g., seed size, dispersal ability, or
growth form) contribute to invasibility in habitats that
differ in their land-use history will also provide important
information for fully characterizing the nature of biological
invasions.
Acknowledgments We thank A. Powell for assistance in the field,
J. Gray, L. Carnes-McNaughton, and J. Monroe for providing logis-
tical support at Fort Bragg, and L. Brudvig and N. Reif for providing
helpful comments on this manuscript. This study was supported by
the Strategic Environmental Research and Development Program
(project SI-1695) and complied with the current laws of the United
States.
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Supplementary resource (1)

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... www.nature.com/scientificreports/ invasion even after many years from the ceased of agricultural activities 30 . Semi-natural habitats are usually more resistant to plant invasion 23,31 and a different landscape composition and disturbance seem to determine their degree of invasion 32 . ...
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... Past land use is known to cause long-lasting changes in soil properties, which in turn affects plant communities ( Brudvig et al., 2013;Dupouey et al., 2002;Freschet et al., 2014;Isbell, Tilman, Polasky, Binder, & Hawthorne, 2013;Mattingly & Orrock, 2013). ...
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