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Tree leaf litter composition and nonnative earthworms influence plant invasion in experimental forest floor mesocosms

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Dominant tree species influence community and ecosystem components through the quantity and quality of their litter. Effects of litter may be modified by activity of ecosystem engineers such as earthworms. We examined the interacting effects of forest litter type and earthworm presence on invasibility of plants into forest floor environments using a greenhouse mesocosm experiment. We crossed five litter treatments mimicking historic and predicted changes in dominant tree composition with a treatment of either the absence or presence of nonnative earthworms. We measured mass loss of each litter type and growth of a model nonnative plant species (Festuca arundinacea, fescue) sown into each mesocosm. Mass loss was greater for litter of tree species characterized by lower C:N ratios. Earthworms enhanced litter mass loss, but only for species with lower C:N, leading to a significant litter×earthworm interaction. Fescue biomass was significantly greater in treatments with litter of low C:N and greater mass loss, suggesting that rapid decomposition of forest litter may be more favorable to understory plant invasions. Earthworms were expected to enhance invasion by increasing mass loss and removing the physical barrier of litter. However, earthworms typically reduced invasion success but not under invasive tree litter where the presence of earthworms facilitated invasion success compared to other litter treatments where earthworms were present. We conclude that past and predicted future shifts in dominant tree species may influence forest understory invasibility. The presence of nonnative earthworms may either suppress of facilitate invasibility depending on the species of dominant overstory tree species and the litter layers they produce.
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ORIGINAL PAPER
Tree leaf litter composition and nonnative earthworms
influence plant invasion in experimental forest floor
mesocosms
R. Travis Belote ÆRobert H. Jones
Received: 29 May 2008 / Accepted: 16 June 2008
ÓSpringer Science+Business Media B.V. 2008
Abstract Dominant tree species influence commu-
nity and ecosystem components through the quantity
and quality of their litter. Effects of litter may be
modified by activity of ecosystem engineers such as
earthworms. We examined the interacting effects of
forest litter type and earthworm presence on invasi-
bility of plants into forest floor environments using a
greenhouse mesocosm experiment. We crossed five
litter treatments mimicking historic and predicted
changes in dominant tree composition with a treat-
ment of either the absence or presence of nonnative
earthworms. We measured mass loss of each litter
type and growth of a model nonnative plant species
(Festuca arundinacea, fescue) sown into each meso-
cosm. Mass loss was greater for litter of tree species
characterized by lower C:N ratios. Earthworms
enhanced litter mass loss, but only for species with
lower C:N, leading to a significant litter 9earthworm
interaction. Fescue biomass was significantly greater
in treatments with litter of low C:N and greater mass
loss, suggesting that rapid decomposition of forest
litter may be more favorable to understory plant
invasions. Earthworms were expected to enhance
invasion by increasing mass loss and removing the
physical barrier of litter. However, earthworms typ-
ically reduced invasion success but not under invasive
tree litter where the presence of earthworms facili-
tated invasion success compared to other litter
treatments where earthworms were present. We
conclude that past and predicted future shifts in
dominant tree species may influence forest understory
invasibility. The presence of nonnative earthworms
may either suppress of facilitate invasibility depend-
ing on the species of dominant overstory tree species
and the litter layers they produce.
Keywords Ailanthus altissima Castanea dentata
Decomposition Earthworms Invasional meltdown
Leaf litter Lumbricus terrestris
Plant invasions
Introduction
Dominant species control many community and
ecosystem processes (Wardle 2002). In forests, leaf
litter inputs to the forest floor serve as an important
mechanism by which trees regulate ecosystem func-
tions including nutrient and energy cycling, tree
regeneration, and the maintenance of biological
diversity (Gilliam and Roberts 2003; Sayer 2006).
The type and quality of dominant leaf litter controls
these processes by mediating temperature, moisture,
and nutrient inputs, and serving as a physical barrier to
plant establishment (Facelli and Pickett 1991; Beatty
2003). Therefore, when humans directly or indirectly
R. T. Belote (&)R. H. Jones
Department of Biological Sciences, Virginia Tech,
Blacksburg, VA 24061, USA
e-mail: rtbelote@vt.edu
123
Biol Invasions
DOI 10.1007/s10530-008-9315-1
alter dominant tree species via disturbance, climate
change, extinction, or facilitation of various biological
invasions, additional biological invasions may be
facilitated or resisted, depending on the properties of
the dominant trees’ litter. An understanding of how
dominant tree species influence forest invasibility
could prove very useful for land managers interested
in minimizing nonnative plant invasions.
Several well-known changes in dominant tree
species have taken place in the temperate forests of
eastern North America. American chestnut (Castanea
dentata (Marsh.) Borkh.) was once a dominant canopy
tree (Russell 1987), but experienced widespread
mortality when the nonnative chestnut blight fungus
(Cryphonectria parasitica) was introduced to eastern
North America. The functions that American chestnut
provided within ecosystems are not fully understood,
but it may have served as a ‘‘foundation species’’ by
controlling the composition of understory species and
mediating nutrient dynamics in soils and streams
(Ellison et al. 2005). Other ongoing changes in these
forests include the introduction of nonnative, invasive
trees such as tree-of-heaven (Ailanthus altissima
(P. Mill.) Swingle, hereafter Ailanthus), and distur-
bance-driven shifts in native species compositions
favoring early successional species (Johnson et al.
2002). For example, timber harvesting can shift an
oak (Quercus spp.) dominated to a yellow-poplar
(Liriodendron tulipifera L.) dominated forest on
mesic upland sites (Loftis and McGee 1992). Addi-
tional changes in dominant species composition are
predicted in the future because of changes in climate,
further invasions, growing demands for timber
resource extraction, fire suppression, and potential
interactions between these factors (Reich and Frelich
2002). These shifts in dominant tree composition will
also change the litter layers of forests.
Changes in litter can also occur through the action of
animals. Earthworms in particular have gained much
attention because of their dramatic effects on litter
layers and subsequent changes to structure and func-
tion of terrestrial ecosystems (Bohlen et al. 2004;
Hobbie et al. 2006; Hendrix 2007). Earthworms are
considered ecosystem engineers because of their
ability to modify habitats, alter pools and fluxes of
nutrients, and change understory community species
composition (Jouquet et al. 2006). The introduction of
nonnative earthworms into forested habitats that
naturally lack them often dramatically changes the
composition and diversity of the forest floor by
removing the litter layer and exposing mineral soil
(Hale et al. 2005; Frelich et al. 2006). Observational
studies suggest that nonnative earthworms may be
introduced following disturbance (Kalisz and Dotson
1989) and may facilitate nonnative plants through
‘invasional meltdown’’––the process where invasion
by one species facilitates additional invasions (Sim-
berloff and Von Holle 1999; Heneghan et al. 2007).
Mechanistic experiments that test this hypothesis are
lacking.
The direct effects and potential interactions
between changes in dominant tree species (through
‘extinction’’, invasions, and disturbance) and inva-
sions of nonnative earthworms on the invasibility of
temperate deciduous forests are poorly understood.
While whole-stand manipulations to test the influence
of changes in dominant species and earthworm
invasions on ecosystem function or community com-
position are difficult, and impossible for certain
species (e.g., American chestnut), it is possible to
experimentally investigate these changes by manipu-
lating leaf litter and monitoring subsequent changes in
forest floor function and recruitment of plant species.
After considering historic, ongoing, and potential
future changes to dominant species of forested
ecosystems, we formulated and tested several hypoth-
eses in a study using experimentally created forest
floor mesocosms. First, we hypothesized that litter
from different species (representing dominant tree
compositional changes) would have different impacts
on invasibility because of variation in litter quality
(e.g., N content) leading to differences in decompo-
sition rate and subsequent differences in physical
barriers to plant establishment (Sayer 2006). Second,
we hypothesized that plant invasion would also
depend on the presence of nonnative earthworms
because earthworms consume and bury litter (Frelich
et al. 2006) or seeds (Milcu et al. 2006). Finally, we
hypothesized that litter type and earthworm presence
would have interacting effects on plant invasion
reflecting variation in earthworm consumption or
burial of different litter types.
Methods
To test our hypotheses, we conducted a greenhouse
study between 16 April and 16 June 2007. Simulated
R. T. Belote, R. H. Jones
123
forest floor mesocosms were established by filling
18 liter plastic tubs with silt loam soils (classified as a
Typic Dystrudepts) collected from the A and AB
horizons of forested areas located in Montgomery
County, Virginia, USA. Soil was sieved with a coarse
metal screen (5 mm) to remove rocks, large root
fragments, and macro-invertebrates (including earth-
worms) prior to filling the tubs. We filled the soil to a
depth of 17 cm, leaving a 10 cm barrier to prevent
earthworm escape from the top of the mesocosms.
Each mesocosm included five drainage holes screened
to allow drainage but prevent soil loss and earthworm
escape. We added 0.5 l of water to each mesocosm
every day for the first 4 weeks, and then reduced the
watering frequency to every other day for the last half
of the study. Average greenhouse temperature was
maintained at 21°C throughout the experiment.
We collected senesced leaves from American
chestnut, Ailanthus, yellow-poplar, and northern red
oak (Quercus rubra L.) in October of 2006. Litter
was collected from at least 12 individuals per species
after senescence and before or immediately after
abscission. American chestnuts still occur as stump
sprouts in its native range and can overtop other tree
species following canopy disturbance on certain sites
before the blight induces mortality of the stem and
tree crown (McCament and McCarthy 2005). We
took advantage of one of these sites (a 10-year-old
clearcut in Craig County, VA, USA where *4 m tall
trees were relatively abundant) to collect litter of
American chestnut trees. To mimic litter mass of
typical hardwood forests of the area (Grigal and
Grizzard 1975), we added 18.25 grams of air-dried
litter to each mesocosm. These litter treatments
represent past, current, and possibly future changes
in dominant tree species and litter composition of the
forest floor. A fifth treatment included the absence of
litter as a control.
We added the nonnative anecic earthworm, Lum-
bricus terrestris to half of the mesocosms to cross
litter treatments with presence or absence of earth-
worms. Earthworm densities of three individuals per
mesocosm were chosen to mimic densities observed
in earthworm-invaded habitats (Kalisz and Dotson
1989). Mesocosms were randomly relocated on the
greenhouse bench every 2 weeks during the experi-
ment. At experiment termination, we investigated
each mesocosm containing earthworms for the pres-
ence of castings on the soil surface and burrows
below the soil surface to ensure that earthworms were
active where they were added. Each treatment
combination was randomly assigned to mesocosms
and replicated 5 times resulting in a fully crossed
multi-factorial completely randomized design (5 litter
treatments 92 earthworm treatments 95 reps =50
mesocosms).
To investigate how litter and earthworm treatment
combinations influenced invasibility, 1000 seeds of a
model invasive plant species (Festuca arundinacea
Schreb., hereafter fescue) were sown into each of the
mesocosms by evenly scattering onto soil surface
prior to adding leaf litter and earthworms. We
determined end of season production of fescue by
harvesting above and belowground biomass as our
measurement of invasion success. To test the predic-
tion that decomposition would vary among treatment
combinations, we collected litter from the soil surface
at experiment termination and calculated per cent
mass loss from initial litter mass. To investigate
potential species-specific chemical characteristics of
litter that might influence decomposition, five litter
samples per species were drawn prior to establishing
mesocosms and analyzed for initial percent C and N
using a FlashEA 1112 Series Elemental Analyzer
(CE Elantech, Lakewood, NJ); we used these data to
calculate C:N ratios.
Statistical analysis
We used a two-way analysis of variance (PROC
GLM; SAS 9.1) to test for main and interactive
effects of litter treatment and earthworm treatment on
two response variables, litter mass loss and fescue
biomass. Data were tested for normality and homo-
geneity of variance using Shapiro-Wilk’s W statistic
and Levene’s test, respectively (Levene 1960; Shap-
iro and Wilk 1965). Data not meeting assumptions
were log or arc-sin square root transformed. Post-hoc
mean comparisons within treatments were performed
using least square mean contrasts. One litter and
earthworm control mesocosm (i.e., no litter or
earthworms present) was eliminated from analyses
because it was a statistical outlier where fescue grew
very poorly, the result of clogged drainage holes
causing standing water. To investigate how litter C:N,
mass loss, and invasion success were related we
performed three pairwise regressions. Specifically,
we regressed mass loss on litter C:N ratios, fescue
Tree leaf litter composition and nonnative earthworms influence plant invasion
123
biomass on C:N, and fescue biomass on mass loss
rates. Because we did not measure percent C and N of
litter in each mesocosm, the two regressions involv-
ing C:N were conducted using mean values per
treatment combination; for the remaining regression,
individual data points for each mesocosm were
included. We employed a critical alpha value of
0.05 for statistical significance.
Results
Earthworm castings and burrows were observed in all
of the mesocosms where we added earthworms. Litter
mass loss depended on an interaction between species
of litter and the presence of nonnative earthworms
(Fig. 1). Specifically, percent mass loss tended to be
higher in litter of invasive Ailanthus and early-
successional yellow-poplar than in American chest-
nut or northern red oak. Percent mass loss of
Ailanthus and yellow-poplar were nearly twice as
much and 1.4 times greater in the presence versus
absence of earthworms, respectively, but mass loss
rates of American chestnut and northern red oak did
not differ between earthworm treatments (Fig. 1).
Litter mass loss tended to be lower for litter of
species with lower percent leaf N and higher C:N
ratios (Table 1; Figs. 1and 2).
Successful invasion by fescue was mediated by an
interaction between the litter treatments and earth-
worm presence (Fig. 3). Biomass of fescue tended to
be highest in the absence of litter and under Ailanthus
and yellow-poplar litter and lower under chestnut and
red oak litter (Figs. 3and 4). Earthworms decreased
the success of fescue in the absence of litter and
presence of yellow-poplar litter, but had no signifi-
cant effect in the other three treatments. In the
presence of earthworms, the greatest fescue biomass
occurred under litter of the invasive tree Ailanthus
(Table 2; Fig. 3). The effect of litter on invasion
success (i.e., biomass of fescue) was related to litter
C:N ratios and mass loss (Fig. 2). Specifically,
invasion success increased with increasing litter mass
loss.
Discussion
Results of this study supported all three of our
hypotheses; i.e., that litter, earthworms, and their
interactions can influence success of nonnative plant
invasion into forest understories. The quality of the
litter appeared to be driving these results. The effect of
litter quality and recalcitrance from dominant species
is known to influence multiple community and
ecosystem components across diverse habitats (Fa-
celli and Pickett 1991; Wardle 2002;Ha
¨ttenschwiler
et al. 2005; Sayer 2006). In our study, results suggest
that litter layers of forests dominated by species with
recalcitrant litter (i.e., slow decomposition rates) and
high C:N ratios may be more resistant to understory
plant invasions even if nonnative earthworms are
introduced. Alternatively, forested stands with rapidly
decomposing litter (and lower C:N ratios) may be
particularly vulnerable to invasions by understory
plant species. These results confirm predictions that
changes in litter layers simulating historic, ongoing, or
future shifts in tree composition may influence the
resistance of forest floor ecosystems to invasions by
nonnative plant species.
Recent studies suggest that ‘‘functionally extinct’’
American chestnut trees were a foundation species
and that their litter played an important role in stream
and soil nutrient dynamics (Ellison et al. 2005;
Rhoades 2007). Our study suggests that chestnut litter
may have served as a barrier to nonnative understory
plant species compared to litter from species with
faster decomposition rates. However, in many forests,
oak species likely replaced chestnuts following blight
mortality (Abrams et al. 1997) and we detected no
Fig. 1 Mean percent mass loss of litter (-SE) from four
species in mesocosms with or without nonnative earthworms,
Lumbricus terrestris.P-values above graphs indicate contrasts
between earthworm treatments within each litter treatment
R. T. Belote, R. H. Jones
123
significant difference between the main effects of
chestnut litter and red oak litter on invasion success.
This study also confirms personal observations that
oak-dominated forests, which may be declining in
abundance due to low rates of oak regeneration,
altered disturbance regimes, and timber harvesting
practices (Loftis and McGee 1992; McShea et al.
2007), appear particularly resistant to understory plant
invasions, while forest stands dominated by yellow-
poplar or invasive Ailanthus may be more vulnerable
to understory plant invasions.
Nonnative earthworms had mixed effects on the
success of plant invasions in this study. Earthworms
typically reduced fescue biomass within litter treat-
ments, but tended to have no negative influence under
Ailanthus or northern red oak litter. Within litter
treatments, earthworms likely buried or consumed
seeds or new sprouts of fescue (Brown et al. 2004;
Eisenhauer and Scheu 2008), which reduced its
overall success. However, earthworms consumed or
buried nearly 100% of the N-rich Ailanthus litter,
which removed the physical barrier that litter creates.
Table 1 Mean percent C, N, and C:N ratios (±SE, n=5 samples) from initial litter prior to addition to mesocosms, and notes on
ecology and abundance, for species used in a greenhouse test of invasibility of forest understories
Species Common name C (%) N (%) C:N Current or historic trends
Ailanthus altissima Tree-of-heaven 49.2 ±0.2
a
2.24 ±0.04
a
22.0 ±0.4
a
Invasive in disturbed habitats
Liriodendron tulipifera Yellow-poplar 47.9 ±0.4
b
0.77 ±0.02
b
62.4 ±1.7
b
Early successional and
dominant, can replace
Q. rubra on mesic upland
sites following disturbance
Castanea dentata American chestnut 50.9 ±0.2
c
0.62 ±0.01
c
82.8 ±0.7
c
Functionally extinct because of
blight invasion, mostly
replaced by oak and other
hardwood species
Quercus rubra Northern red oak 51.7 ±0.6
c
0.69 ±0.02
d
75.1 ±1.6
d
Dominant canopy tree; local
abundance can decline
because of harvesting and
gypsy moth defoliation; can
be replaced by L. tulipifera
following disturbance
Means with different letters represent significant differences (P\0.05)
Fig. 2 Pairwise regressions between litter C:N and mass loss
(R
2
=0.73, P=0.007), litter C:N and invasion success
(R
2
=0.70, P=0.01), and litter mass loss and invasion
success (R
2
=0.30, P\0.001). Square symbols represent
values of litter of northern red oak, triangles are values for litter
of American chestnut, circles are values for litter of yellow-
poplar, and 9represents values from litter of Ailanthus. Filled
symbols indicate values for mesocosms that included additions
of nonnative earthworms; open symbols are values where
earthworms were absent. C:N values were estimated based on
litter sampled from the leftover pool of litter and not from litter
used in each mesocosm
Tree leaf litter composition and nonnative earthworms influence plant invasion
123
This led to fescue biomass tending to be greater under
Ailanthus litter than other litter treatments where
earthworms were present. Under highly recalcitrant
northern red oak litter and where overall invasion
success was lowest (main effect of litter), earthworms
did not have a negative effect on invasion success.
The fact that earthworms preferentially consume or
bury litter of certain species is well known (Darwin
1881; Perel and Sokolov 1964; Curry and Schmidt
2007). Litter from oak species has been observed to
be relatively unpalatable to Lumbricus terrestris
(Satchell 1983; Heneghan et al. 2007).
Ecologists have often observed that nonnative
earthworms and nonnative plants frequently occupy
the same habitats, suggesting potential facilitation
between earthworm and plant invaders (Kourtev
et al. 1999; Heneghan et al. 2007). However, under-
standing causality of these patterns has been limited
by the observational nature of the studies. Some
ecologists have suggested that nonnative plants may
change soil characteristics, which allows for nonna-
tive earthworms to invade (Ehrenfeld et al. 2001).
Other hypotheses suggest that earthworms facilitate
plant invasions, or that both nonnative earthworms
and nonnative plants respond similarly to covarying
factors such as disturbance or proximity to agricul-
tural land use (Kalisz and Dotson 1989). While we
did not test the hypothesis that plant invasions
facilitate earthworm invasion, results from our study
do suggest that invasion by a nonnative tree and the
litter layer it produces, coupled with invasion by
nonnative earthworms might directly facilitate further
understory plant invasions.
The long-term effects of litter differences on
earthworm populations or nonnative plants is
Fig. 3 Invasion success of fescue (grams of biomass per
mesocosm +SE) in mesocosms receiving crossed treatments of
litter and earthworms. P-values above graphs indicate contrasts
between earthworm treatments within each litter treatment. P-
values for contrasts between litter treatments within earthworm
treatments are in Table 2
Fig. 4 Sample photos of
mesocosms showing main
effects of each litter
treatment on invasion
success of fescue. Photos
were taken during the last
week of the experiment
R. T. Belote, R. H. Jones
123
not clear. Our experiment lasted only 2 months, which
was insufficient to investigate treatment effects on
humic and mineral soil layers and composition.
Differences in humic layers and mineral soil chemical
characteristics under litter layers may have longer term
effects on invasibility and direct effects on earthworm
populations. Moreover, while each tree species repre-
sented in our litter treatments can dominate forests on
similar sites, the abundance and likelihood of domi-
nance of the tree species in a particular area may
depend on soil and site characteristics, which can also
influence invasive plant establishment and nonnative
earthworm abundance (Frelich et al. 2006). For exam-
ple, yellow-poplar typically replaces red oaks
following disturbance only on mesic upland sites, but
not on drier, less productive sites (Carmean and Hahn
1983). The same environmental factors that influence
shifts in tree composition may also influence earth-
worm abundance and behavior.
The application of this study to natural systems is
somewhat limited because it was conducted in a high
light greenhouse environment using a model invasive
species not typical of an understory plant invader.
Our aim was to test specific mechanisms based on
how changing litter layers may interact with earth-
worms to influence invasive plant establishment.
However, differences in litter layers likely have
important effects on native understory species as well
(Gilliam and Roberts 2003). The effects of nonnative
earthworms on native understory species depend on
the traits or plant functional groups (Hale et al.
2005). Additionally, natural litter layers contain
mixtures of litter from various species and sup-
port complex detrital foodwebs (Facelli 1994;
Wardle 2002), which could also influence litter
decomposition and understory invasibility. Clearly,
more studies are needed to investigate the complex
interaction between litter quality, earthworm inva-
sions, native species, and nonnative plant invasions.
Acknowledgements We thank Debbie Wiley and Aaron
Teets for assistance in the greenhouse and lab. Bobbie
Niederlehner helped with the carbon and nitrogen analysis.
Erik Nilsen provided greenhouse space and helpful comments
on earlier drafts. Jessica Homyack, Aimee
´Classen, and Martin
Nun
˜ez provided helpful comments during manuscript
preparation. Cindy Hale, Carola Haas, Tom Fox, Nate
Sanders, and Dan Simberloff provided helpful comments and
ideas during project conception. The work was supported by
NSF-DBI grant # 0400684, USDA-NRI grant # 2005-35101-
15363 and a Virginia Tech WPI Environmental Fellowship.
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... Earthworm invasions fundamentally alter soil structure, litter decomposition, nutrient cycling, and microbial communities (Greiner et al. 2012;Resner et al. 2015;Paudel et al. 2016a). These changes can limit plant germination and growth (Eisenhauer et al. 2012;Nuzzo et al. 2015), reduce plant species richness (Holdsworth et al. 2007a;Craven et al. 2016), and facilitate plant invasion (Belote and Jones 2009;Dávalos et al. 2014;Whitfeld et al. 2014). Earthwormcaused changes to vegetation and the forest floor can influence behavior, abundance, and community composition of animals ranging from arthropods and other annelids (Snyder et al. 2013;Burtis et al. 2014;Schlaghamerský et al. 2014) to salamanders and birds (Cameron and Bayne 2012;Loss et al. 2012;Ransom 2012). ...
... Much of this vast area has some native earthworms (Fender 1995;James 1995); however, nonnative earthworms can still have adverse ecological effects even when native species are present (Snyder et al. 2011(Snyder et al. , 2013Szlavecz et al. 2011;Lobe et al. 2014). Furthermore, although extensive research has shown a positive, and likely facilitative, relationship between non-native earthworms and either non-native invasive plant species or native weedy species (Holdsworth et al. 2007a;Belote and Jones 2009;Nuzzo et al. 2009;Paudel et al. 2016b;Craven et al. 2016), no research has assessed the potential for a facilitative interaction between earthworms and woody plants encroaching into grasslands. Woody plant encroachment is a major anthropogenic change that is occurring globally and has broad impacts on multiple ecosystem components, including hydrology, nutrient cycling, plant and animal species composition, and biodiversity (Huxman et al. 2005;Eldridge et al. 2011). ...
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European and Asian earthworms have invaded much of North America with profound impacts to soils, plant communities, and animal populations. However, few studies have assessed local-scale correlates of earthworm distributions, and most invasive earthworm research has occurred in northern forests. Additionally, despite several studies showing facilitative relationships between invasive earthworms and invasive plants, no research has assessed a potential facilitative interaction between earthworms and woody plants encroaching into prairies. We conducted the first assessment of factors influencing local-scale distributions of native and non-native earthworms for the U.S. Great Plains in a tallgrass prairie-woodland mosaic experiencing eastern redcedar (Juniperus virginiana) encroachment. We documented both native and non-native earthworms, including non-native species from Eurasia (Aporrectodea spp.) and South America (Family Ocnerodrilidae). Native and non-native earthworm distributions were strongly correlated, yet local-scale predictors of distribution also differed between the groups. Native earthworms were more likely to occur near roads and in areas with moist soils. Contrary to expectation, we found no evidence that non-native earthworms occurred more frequently in areas with eastern redcedar-encroachment; instead, non-native earthworms were most likely to occur in tallgrass prairie. Our results suggest that, within prairies and woodlands of the Great Plains, native and non-native earthworms occur most frequently near roadways and in locations with moist soil. Because the few approaches for controlling invasive earthworms are only likely to be feasible on a small scale, findings from such local-scale studies are important for directing management to reduce earthworm impacts on biodiversity and ecosystem services.
... In general, earthworms increase litter mass loss for plant species with lower C:N ratios (Belote & Jones 2009), though both physical character and chemical attributes of the food resource may change during decomposition (Swift et al. 1979). Although the litter C:N ratio is of importance for earthworm action in soil organic matter stabilization, in some cases its optimized decomposition is a function of habitat characteristics (e.g. ...
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The ingestion of organic and mineral materials by earthworms is a prominent functional role that has profound consequences for the decomposition and stabilization of soil organic matter. To investigate the litter consumption of the African nightcrawler earthworm Eudrilus eugeniae (Kinberg, 1867) under different tropical conditions, (i) we used DNA barcoding to identify specimens of E. eugeniae collected from sites across the Adamawa region in Cameroon, and (ii) studied the influence of habitat suitability (soil properties), soil moisture, litter type and population density on litter consumption. A total of four litter consumption experiments were carried out using soils collected from refuse disposal sites, agricultural lands and savannahs dominated by the Mexican sunflower Tithonia diversifolia (Hemsl). The results revealed that litter consumption significantly increased in the refuse disposal and agricultural soils as opposed to the Mexican sunflower (T. diversifolia) soil, a cow dung enriched substrate and a sterile soil horizon from the savannah (P < 0.05). The optimum moistures for litter consumption were between 24 and 50%. Litter type did not affect the consumption rate of the earthworms (P > 0.05). We observed a general positive density dependent consumption with litter mass loss increasing with increasing density. Our results suggest that E. eugeniae has a strong direct effect on the decomposition of plant materials than expected from previous estimations, and that litter consumption rates are determined by several habitat components and population density.
... As described by Wardle (2002), community and ecosystem processes are controlled by keystone species. In forests, trees play the role of ecosystem engineers and regulate ecosystem functions (Reich et al. 2001;Crooks 2002;Belote and Jones 2009). Consequently, ecosystem invasions by woody species can lead to serious changes in community functions, altering primary production, biomass distribution, litterfall and decomposition rates, energy balance or carbon storage Jackson et al. 2002;Yelenik et al. 2004). ...
... Earthworm species composition and total biomass of earthworms present in an area are important regulators of decomposition in eastern deciduous forests. Earthworm-mediated increased litter decomposition and reduced litter biomass likely have cascading effects forest ecosystems, including reduced habitat for ground-and litterdwelling invertebrates (Ferlain and others 2018; Mahon and others 2019), higher recruitment for invasive species (Belote and Jones 2009), and greater effects of deer browse on herbaceous plants (Frelich and others 2006). Deer, Honeysuckle, Earthworms, and Litter Decay Content courtesy of Springer Nature, terms of use apply. ...
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Herbivore overabundance and species invasions could alter decomposition rates in temperate forests, with consequent effects on carbon sequestration, nutrient retention, and other ecosystem processes. At local scales, herbivores, invasive plants, and soil macroinvertebrates can be important drivers of decomposition, but interactive effects among these different groups are unknown. We tested for the effects of white-tailed deer, Amur honeysuckle, and earthworm activity (manipulated via mesh exclusion) on litter decomposition rates and loss of litter nitrogen (N) in five hardwood forest sites in southwestern Ohio. Each site consisted of a 20 × 20-m deer exclosure paired with a deer access plot; honeysuckle was removed from half of each plot. Effects of earthworm activity were tested using paired litter boxes of fine mesh (0.25 mm; earthworms excluded) or coarse mesh (10 mm; earthworm access). Restriction of earthworm activity in fine mesh treatments slowed litter decomposition and increased retention of N in the litter layer compared to coarse mesh. Deer access interacted with mesh treatments, with faster decomposition occurring in deer access, coarse mesh treatments relative to others. Greater earthworm biomass in deer access plots relative to deer exclosure plots corresponded with more rapid litter decomposition. Honeysuckle presence did not affect litter decomposition, but did increase litter N retention. The interactions between deer and earthworm activity indicate that reductions in deer populations may slow litter decomposition rates, increasing complexity of habitat structure at the soil surface, which relates to habitat for plants and animals.
... Dominant species of earthworms such as Lumbricus terrestris (Anecic) and Allolobophora chlorotica (Endogeic) control many community and ecosystem processes (Wardle, 2002). In a forest, leaf litter inputs to the forest floor serve as an important mechanism by which trees regulate ecosystem functions including nutrient and energy cycling, tree regeneration and the maintenance of biological diversity (Gillian and Roberts, 2003;Sayer, 2006;Belote and Jones, 2009). This bulk of organic matter nutrients that are added to the soil are located in the topsoil. ...
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The effects of tree canopies and leaf litter on the chemical properties of earthworm casts were studied at Umudike, Nigeria. These studies were carried out under some multipurpose tree canopies such as cacao (Theobroma cacao L.), breadfruit (Treculia Africana Decne), avocado pear (Persea Americana Mill) and mango (Mangifera indica L.) and were compared with the casts of their open adjacent sites which were 10m away. Generally, casts under tree canopies had significantly (P<0.05) higher values of pH, organic carbon, organic matter, total N, exchangeable Ca, exchangeable K, exchangeable Na, effective cation exchange capacity (ECEC) and available phosphorus than the casts of their adjacent open sites. However, casts under cacao tree canopy had higher values of nutrient elements than those of mango, breadfruit and avocado pear, while casts outside tree canopies gave significantly (P<0.05) the least mean values. This study has shown that the integration of trees such as cacao on farms can help increase earthworm casts as well as the nutrient elements of the soils.
... Because trees act as ecosystem engineers and regulate ecosystem function (Crooks, 2002;Belote and Jones, 2009), invasion by non-native tree species often has profound impacts on recipient forest communities (Lamarque et al., 2011). Tree invasions in forests have been associated with hierarchical effects from changes in species diversity to altered ecosystem function (Jackson et al., 2002;Yelenik et al., 2004;Pyšek et al., 2012). ...
Article
Land-use and forest management practices may facilitate the invasion success of non-native plants in forests. In this study, we tested if agricultural land abandonment and subsequent forest management contributed to the invasion success of Chinese tallow (Triadica sebifera (L.) Small) in the maritime forest of Parris Island, SC. We compared the abundance of Chinese tallow between disturbed and remnant forests, described Chinese tallow establishment patterns in relation to forest management activities, and characterized the structure and composition of disturbed and remnant forests in order to better understand relationships between stand characteristics and invasibility as indicated by Chinese tallow abundance. We found that stands in agricultural land use in 1939 but reforested with slash pine (Pinus elliottii Englem.) since the 1970s (i.e., disturbed forests) had significantly more Chinese tallow stems than stands that remained forested since 1939 (i.e., remnant forests). Remnant forests had significantly greater woody species richness and were more variable in species composition and structure than disturbed forests. Disturbed forests were dominated by early successional, shade intolerant species with a denser woody understory, while remnant forests included species associated with late successional habitats. The number of forest management events was positively associated with Chinese tallow abundance, explaining 34% of the total variation in stem density. Chinese tallow individuals commonly established immediately after forest thinning and their numbers increased exponentially through time. Our findings support that Chinese tallow establishment was strongly related to anthropogenic disturbance including historical agricultural land-use and forest management. This suggests that Chinese tallow invasion may be a symptom, rather than the driver, of the ecological degradation induced by persistent human perturbations.
... Results regarding the relationship between invasive plants and invasive invertebrates are thus far mixed. For instance, Zelles (2012) found no relationship between invasive earthworms and garlic mustard, and Belote and Jones (2009) used a mesocosm experiment to show invasive earthworms did not aid in non-native plant invasion. Conversely, Nuzzo et al. (2009) andWurst et al. (2011) both saw a positive relationship between earthworm invasion and plant invasion. ...
Article
Environmental disturbances seem to be increasing in frequency and impact, yet we have little understanding of the belowground impacts of these events. Soil fauna, while widely acknowledged to be important drivers of biogeochemical function, soil structure and sustainability, and trophic interactions, are understudied compared to other belowground organisms such as archaea, bacteria, and fungi. In this review we summarize the current state of knowledge of soil fauna as it relates to and is influenced by various disturbances. We focus our review on three main natural and anthropogenic disturbance types: 1) natural disturbances, including damage from wind and flooding; 2) invasive species, including above and belowground flora and fauna; and 3) climate change impacts on the atmosphere and temperature. We do not address the impacts of wildfires, forestry, agricultural practices, mining, or human-caused pollution, as these topics have all been covered in other works. We highlight knowledge gaps and suggest future avenues of research, with hope that the importance of soil fauna and their influences on ecosystems will be given greater emphasis in future research.
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Ecosystem engineers have been widely studied for terrestrial systems, but global trends in research encompassing the range of taxa and functions have not previously been synthesised. 2.We reviewed contemporary understanding of engineer fauna in terrestrial habitats and assessed the methods used to document patterns and processes, asking: 1.Which species act as ecosystem engineers and with whom do they interact? 2. What are the impacts of ecosystem engineers in terrestrial habitats and how are they distributed? 3. What are the primary methods used to examine engineer effects and how have these developed over time? We considered the strengths, weaknesses and gaps in knowledge related to each of these questions, and suggested a conceptual framework to delineate ‘significant impacts’ of engineering interactions for all terrestrial animals. 3.We collected peer-reviewed publications examining ecosystem engineer impacts and created a database of engineer species to assess experimental approaches and any additional covariates that influenced the magnitude of engineer impacts. 4.One hundred and twenty-two species from twenty-eight orders were identified as ecosystem engineers, performing five ecological functions. Burrowing mammals were the most researched group (27%). Half of all studies occurred in dry/arid habitats. Mensurative studies comparing sites with and without engineers (80%) were more common than manipulative studies (20%). These provided a broad framework for predicting engineer impacts upon abundance and species diversity. However, the roles of confounding factors, processes driving these patterns, and the consequences of experimentally adjusting variables, such as engineer density, have been neglected. True spatial and temporal replication has also been limited, particularly for emerging studies of engineer reintroductions. 5.Climate change and habitat modification will challenge the roles that engineers play in regulating ecosystems, and these will become important avenues for future research. We recommend future studies include simulation of engineer effects and experimental manipulation of engineer densities to determine the potential for ecological cascades through trophic and engineering pathways due to functional decline. We also recommend improving knowledge of long-term engineering effects and replication of engineer reintroductions across landscapes to better understand how large-scale ecological gradients alter the magnitude of engineering impacts. This article is protected by copyright. All rights reserved.
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Dendroecological techniques were used to investigate the dynamics and successional development spanning three centuries of two virgin, old-growth forests dominated by Quercus rubra L. (mesic site) and Quercus prinus L. (xeric site) on the Blue Ridge Mountains of west-central Virginia. In the e. rubra stand, a large increase in recruitment of this species between 1820 and 1850 was associated with a sharp increase followed by a larger decrease in the master tree ring chronology. The decrease in growth between 1837 and 1844 coincided with a predicted southward displacement of the summertime position of the polar front from eastern Canada (E.R. Cook and P. Mayes. 1987. Decadal-scale patterns of climatic change over eastern North America inferred from tree rings. In Abrupt climatic change. Edited by W.H. Berger and L.D. Labeyrie. D. Reidel Publishing Company, Dordrecht, Holland. pp. 61-65). There was a virtual cessation of tree recruitment between 1850 and 1910, suggesting that the Q. rubra stand went through a ''midlife'' stem exclusion stage. However, another period of peak recruitment between 1920 and 1940 coincided with chestnut blight (Endothia parasitica) and extreme drought in the region. Oak recruitment in the Q. prinus stand was fairly continuous and exhibited peaks from 1710 to 1730 and in the 1940s that were associated with releases in radial growth. An increase in e. rubra in this stand occurred between 1860 and 1950. There was also a trend of increasing growth in the oldest e. prinus trees from 1860 to the present, particularly between 1930 and 1960. The xeric Q. prinus stand had only a small component of potential oak replacement species and appears to represent an edaphic climax for this genus. The large increase of mixed-mesophytic species during the 1900s in the e. rubra stand indicates its transitional nature in the absence of periodic fire.
Chapter
As early as 1908, Arldt concluded from considerations of palaeographic changes in land and sea distribution ofpresent day earthworm species that terricole oligochaetes first appeared in the Upper Triassic. Michaelsen (1921), interpreting earthworm distribution in terms of Wegner’s theory of continental drift, put their origin in the Carboniferous period and Wilcke (1955), from considerations of earthworm ecology, concluded that mull-forming, soil-dwelling worms could not have evolved before deciduous forests existed in the late Cretaceous.
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Castanea dentata (Marsh.) Borkh. was a major forest tree in the eastern United States before an introduced blight killed the chestnut trees in the early 20th century. Its post-glacial migration, especially north of the Wisconsin terminal moraine, was apparently slower than other genera found in association with it in the 20th century. Analysis of historical documents indicates that chestnut trees were restricted to moist but well-drained, acid loam soils. Chestnut had little success on the coastal plain or where drainage was poor. In areas of its greatest dominance, many trees were of rootcrown sprout origin and seedling establishment was not common. This suggests that its slow migration, as indicated by the palynological record, may have been caused by a paucity of appropriate sites for seedling establishment north of the Wisconsin terminal moraine, before adequate leaching of lime and establishment of good drainage, especially near sites of pollen accumulation. The apparent anomaly in its migration rate may also arise from comparing the migration of this species north of the terminal moraine with that of other associated genera. The palatability of its fruits and the coincidence of its migration with the development of agriculture also suggest that its spread into New England may have been associated with cultural changes in native American populations.
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Assemblages composed entirely of native taxa are the norm on S Appalachian areas that have not been cleared of forest or otherwise severely disturbed. The exotic taxa Octolasion tyrtaeum, Lumbricus terrestris, L. rubellus, L. castaneus and Pheretima s.l. were found on relatively small and scattered sites which had been severely disturbed (eg cleared, cultivated, inhabited). The genus Diplocardia dominated native assemblages on slightly disturbed sites, and generally persisted despite severe disturbance and the introduction of exotic taxa. Populations of Komarekiona eatoni and Eisenoides carolinensis were much reduced or eliminated by forest removal, and were apparently then replaced by exotic species. Octolasion tyrtaeum occurred both in clearings and in forests, and was the most widely distributed and frequently encountered exotic species; it may directly compete with the native topsoil-inhabiting species, K. eatoni and E. carolinensis, when they co-occur on forested sites. -from Authors
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Litterfall was monitored for 1 year on Walker Branch Watershed (97.5 ha) in eastern Tennessee. Data were collected from 80 plots, each with a 1 m$sup 2$ litter trap, and were stratified in two alternate ways for analysis. In one case, a conventional cover-type map was used to separate the plots into one of four cover types. In the other case, plots were separated into four groups based on multivariate stratification of overstory basal-area data. Subtle differences among strata in seasonal dynamics, total annual quantity, and elemental concentration of litterfall were detected better under the multivariate stratification than under the cover-type stratification. This study demonstrates that analysis of the structure of an ecosystem using multivariate techniques provides a firm basis for subsequent analysis of functions within that system. (auth)
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The American chestnut ( Castanea dentata ( Marsh.) Borkh.) was once an important tree species in the eastern United States prior to its devastation by the chestnut blight. The American Chestnut Foundation will soon release seeds that are blight resistant. However, the necessary site requirements for restoration efforts have not yet been explored. The goal of this study was to evaluate the survival and growth of chestnut seedlings within a diverse forest management regime. Seedlings were experimentally grown for 2 years in three mixed-oak forests subjected to thinning, burning, thinning followed by burning, and an untreated control. Seedling biomass parameters were most influenced by treatments that increased light availability. Soil chemistry and texture parameters were also correlated ( p < 0.05) with chestnut biomass. Thus, site fertility should also be considered in reintroduction efforts. While site quality may influence growth, light conditions appear to be overwhelmingly important. Therefore, we recommend that American chestnut seeds be planted in areas with moderate to high light conditions ( recently disturbed), with low surrounding competing vegetation ( possibly after a burn) for optimal growth benefits.