ESSAI
Volume 4
Article 23
Spring 2006
The Relationship Between Europe Buckthorn
(Rhamnus cathartica) and Macroinvertebrate
Decomposers in a Forested Habitat
Emily N. Hansen
College of DuPage
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Recommended Citation
Hansen, Emily N. (2006) "The Relationship Between Europe Buckthorn (Rhamnus cathartica) and Macroinvertebrate Decomposers
in a Forested Habitat," ESSAI: Vol. 4, Article 23.
Available at: http://dc.cod.edu/essai/vol4/iss1/23
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Hansen: Europe Buckthorn and Macroinvertebrate Decomposers
The Relationship Between Europe Buckthorn (Rhamnus cathartica) and Macroinvertebrate
Decomposers in a Forested Habitat
by Emily N. Hansen
(Honors Biology 1110)
The Assignment: Write a paper following a professional format that describes the
author’s research experiment.
ABSTRACT
T
he introduction of exotic species to new habitat often results in unregulated growth, which
pushes out native species and disrupts balanced relationships within the ecosystem. The study
done examines how the exotic species European buckthorn (Rhamnus cathartica L.) thrives in
habitat foreign to its origins by determining the effect of buckthorn’s leaf litter on soil
macroinvertebrates in comparison to two native species’ litter. Leaf packs from the buckthorn and the
native species, Slippery elm (Ulmus rubra) and Box elder (Acer negundo), were placed on the forest
floor near the parent species in the study area, a restored forest in Glen Ellyn, IL. Macroinvertebrate
species of the leaf packs were counted and physical measurements of the soil taken. Results indicate
macroinvertebrate communities are potentially affected by buckthorn’s greater nitrogen content,
evidenced by a greater Oribatid population, greater species richness, and greater leaf pack weight
loss in European buckthorn leaf packs. Increased soil macroinvertebrate activity returns greater
nutrient levels to buckthorn soil. Buckthorn did not appear to affect soil condition, as indicated by
little variance in physical soil measurements (temperature, moisture, pH).
INTRODUCTION
Exotic species notoriously enter habitats foreign to them and replace native species of the
same niche, thereby altering the ecosystem’s balance (Cunningham et al., 2005). This invasiveness is
the result of ecological release from control agents that regulated species’ population size in their
native habitats (Cunningham et al., 2005). Without limiting agents, exotic species grow unchecked to
unhealthy numbers and disrupt ecosystem processes such as nutrient cycles and community structure.
European buckthorn (Rhamnus cathartica L.) is an exotic species known for its invasiveness
and detrimental impact on forest ecosystems following successful invasion and propagation (Swink
and Wilhelm, 1994). Originally from Eurasia and Northern Africa, European buckthorn was
introduced to North America in the 1880’s as an ornamental shrub and has since taken over natural
habitat within the woodlands of the northeastern and midwestern United States and southeastern
Canada, replacing native plant species and affecting ecosystems (Heneghan et al., 2005; Preston,
2002). I sought to determine the affect of this exotic species on soil macroinvertebrates by studying
its leaf litter and soil characteristics in comparison with two native species, Slippery elm (Ulmus
rubra) and Box elder (Acer negundo). By centering on soil macroinvertebrates and thereby the
process of decomposition of which they are involved, a better understanding of the effect of this
exotic species on the Midwest forest ecosystem and its widespread success in invasion of similar
habitats can be determined.
Key Words: exotic species, European buckthorn, soil macroinvertebrates, leaf packs, nitrogen
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Decomposition, especially pertaining to that of leaf litter, is essential to nutrient cycling,
plant growth, and the food web (Heneghan et al., 2002). Involvement of macroinvertebrates in this
process is of great importance because their decomposition rates are directly related to their
consumption of organic matter (Vasconcelos and Laurence 2005; Cárcamo et al., 2001). These
populations are needed to fragment leaf litter, exposing more surface area for microfloral
colonization and the completion of decomposition (Cárcamo et al., 2001). This key role grants their
importance as the focus of this study.
METHODS
The study location was a 1ha wooded plot on the campus of College of DuPage, Illinois
(41o45’00” N, 88o00’00”). The plot was previously farmed prior to College acquisition in 1965 and
has since been left to undergo ecological succession.
Leaves were collected early September of 2005 from trees in the study area of European
Buckthorn, Slippery Elm, and Box Elder. Prior to placing in galvanized mesh, leaves were dried at
60o C to a constant weight in a drying oven. Leaves were placed in galvanized chicken wire having a
mesh size of 2.54 cm by species. The packs were distributed randomly over the study area on
September 6, 2005.
After one month, the leaf packs were collected and dried to extract the colonizing
macroinvertebrates and final weight determination. Select physical measurements were taken where
each leaf pack had been placed. Soil pH was measured using a Kelway meter (Kelway Instruments
Co., Japan). Soil moisture was measured using and Aquaterr Instruments Moisture Meter (Aquaterr
Instruments Incorporated, Costa Mesa, CA).
Macroinvertebrate species diversity was measured using the Shannon index. Species richness
was equated as the number of species represented per sample. Species evenness was computed as the
quotient of (Shannon diversity)/(ln species richness). Student t-tests were used to compare Shannon
diversity of buckthorn to each of the other two species. Mann-Whitney tests were used to compare
species richness, species evenness, and physical measurements of buckthorn to each of the other two
species. Significance was determined where p≤0.05.
RESULTS
Macroinvertebrate populations (Table 1) varied little between European Buckthorn and the
two native tree species with few exceptions. Out of the fourteen soil macroinvertebrates present only
two appeared to have greater populations in the native species or exotic species; more Psocidae
(barklice) were present in the Slippery elm and Box elder leaf litter while Oribatid mite numbers
were greater in European buckthorn and not the other two. Physical measurements and
macroinvertebrate diversity calculations (Table 2) held little variation between the three trees. Only
species richness varied significantly between the macroinvertebrate fauna colonizing leaf packs of
European buckthorn versus those of slippery elm (Z = 2.11, P < 0.04). Physical characteristics were
basically the same in terms of soil temperature, soil moisture and soil pH. However, European
buckthorn’s leaf pack had a dramatically greater percentage of weight change than the native species,
again in even greater proportion to that of Slippery Elm at 13.4 percent difference compared to a
difference of 5.5 percent with Box Elder.
DISCUSSION
Oribatid mites are indicator species of nitrogen (Enami et al., 1999) so finding greater
numbers in the buckthorn litter suggests buckthorn leaves contain greater nitrogen content than
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Hansen: Europe Buckthorn and Macroinvertebrate Decomposers
Slippery elm and Box elder. Previous scientific research has also established European buckthorn
leaves as a source of higher nitrogen-content (Heneghan et al., 2002). Studies have also shown
earthworm density to be greater in soil closer to buckthorn, indicating more nutrient-rich soil
(Heneghan et al., 2005). This can explain the faster decomposition rate of buckthorn litter in
comparison to litter of native species, as indicated by the greater percentage of dry weight change of
leaf packs. Faster decomposition more likely occurred because greater nitrogen content promotes
growth of microflora which attracts mycophagous macroinvertebrates (Heneghen, 2002). The similar
physical soil levels of pH, moisture, and soil temperature around both the exotic and native species
indicate comparable soil quality. Generally, slightly alkaline pH levels promote low decomposition
rates (Killham, 1994), which potentially aids in buckthorn’s invasion.
European buckthorn’s origins in more fertile soil increases its favor in competition with
native plants that adapted to this less nutrient-rich soil with slower nutrient release for better survival
(Vasconcelos and Laurence, 2005; Ehrenfeld, 2003; Allison, 2004; Clark et al., 2005). Buckthorn’s
ability to use its naturally nitrogen-rich leaves to maintain its health by attracting soil
macroinvertebrates, as discussed earlier, gives insight into potential distress on the rest of the
ecosystem. Faster decomposition of buckthorn indicates a shorter duration of nutrient release, which
affects macroinvertebrates dependent on benefits of slower decomposition rates. Macroinvertebrates
may favor nutrient sources, but fast consumption of these sources results in longer time periods
during decreasing seasonal temperatures without nutrient or leaf sources that some cannot survive
(Killham, 1994; Heneghan, 2002). Psocidae (barklice), the species found in greater numbers in
Slippery elm and Box elder, is a soft-bodied macroinvertebrate that favors slower leaf litter
decomposition; its lifetime would be shortened without slow leaf decomposition in cold temperatures
(Borror et al., 1989; Gillot, 1995). This signifies how buckthorn’s fast decomposition could diminish
macroinvertebrate populations dependent on leaf litter for survival, thereby altering the forest food
web. The impact of changes in macroinvertebrate lifespan of species such as Psocidae on the
ecosystem is unknown but further tests could determine the extent of its impact. European
buckthorn’s affect on soil macroinvertebrate survival at different climates could be further tested by
isolating macroinvertebrates with European buckthorn leaf litter at each season, documenting
occurring effects. While more testing could be done, the direct and indirect damage of European
buckthorn’s influence on soil macroinvertebrates and their ecosystems should result in manual
removal of these invasive plants to maintain the health of the forests.
LITERATURE CITED
Allison, S.D., and P.M. Vitousek. 2004. Rapid nutrient cycling in leaf litter from invasive plants in
Hawai’i. Oecologia 141: 612-619.
Borror, D.J., C.A. Triplehorn, and N.F. Johnson. 1989. An Introduction to the Study of Insects.
Saunders College Publishing, Philadelphia, PA, USA.
Cárcamo, H.A., C.E. Prescott, C.P. Chanway, and T.A. Abe. 2001. Do soil fauna increase rates of
litter breakdown and nitrogen release in forests of British Colombia, Canada? Canadian
Journal of Forest Research 31: 1195-1204.
Clark, B.R., S.E. Hartley, K.N. Suding, C. de Mazancourt. 2005. The Effect of Recycling on Plant
Competitive Hierarchies. The American Naturalist 165: 609-622.
Cunningham, W.P., M.A. Cunningham, and B. Saigo. 2005. Environmental Science: A Global
Concern, 8th ed. McGraw Hill, New York, NY, USA.
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Ehrenfeld, J.G. 2003. Effects of Exotic Plant Invasions on Soil Nutrient Cycling Processes.
Ecosystems 6: 503-523.
Enami, Y., H. Shiraishi, and Y. Nakamura. 1999. Use of Soil Animals as Bioindicators of Various
Kinds of Soil Management in Northern Japan. Japan Annual Research Quarterly 33: 85-90.
Gillot, C. 1995. Entomology, 2nd Ed. Phlenum Press, New York, NY, USA.
Heneghan, L., C. Constance, and C. Brundage. 2002. Rapid Decomposition of Buckthorn Litter may
change soil nutrient levels. Ecological Restoration 20: 108-111.
Heneghan, L., C. Rauschenberg, F. Fatemi, and M. Workman. 2005. European Buckthorn (Rhamnus
catharica) and its effects on some ecosystem properties in an urban woodland. Ecological
Restoration 22: 275-280.
Killham, K. 1994. Soil Ecology. Cambridge University Press, New York, NY, USA.
Preston, R.J. 2002. North American Trees. Iowa State Press, Ames, IO, USA.
Swink, F. and G. Wilhelm. 1994. Plants of the Chicago Region, 4th ed. Indiana Academy of Science,
Indianapolis, IN, USA.
Vasconcelos, H.L., and W.F. Laurence. 2005. Influence of habitat, litter type, and soil invertebrates
on leaf-litter decomposition in a fragmented Amazonian landscape. Oecologia 144: 456-462.
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Table 1. Invertebrates inventoried from leaf packs according to leaf type.
Taxon
Isopoda
Pseudoscorpion
Oribatid mite
Pink acari
White acari
Clubionidae A
Clubionidae B
Lithobiomorpha
Entomobryidae
Isotomidae
Psocidae
Reduviidae
European buckthorn
1
2
3
1
1
1
120
1
60
10
4
1
2
Slippery elm
4
5
1
2
Box elder
3
4
1
1
82
1
6
104
1
2
2
5
6
7
1
2
3
1
1
2
2
12
19
1
42
66
6
3
2
3
1
4
6
7
6
33
20
2
116
1
1
3
16
23
1
13
1
40
50
1
2
2
2
1
7
7
1
3
3
36
2
24
1
1
6
3
6
1
5
21
1
3
1
4
96
4
1
1
96
70
2
54
60
2
152
1
12
90
60
1
Cicadellidae
Microlepidopteran
Curculionidae
Hydrophilidae
Latridiidae
Staphyliniidae A
Staphyliniidae B
Tenebrionidae
Noctuidae
Drosophilidae
Tipulidae
Formicidae A
Solenopsis
Trichogrammatidae
5
1
1
1
2
1
1
1
2
1
2
1
2
2
3
1
1
1
1
3
1
1
1
4
1
2
1
3
1
1
1
1
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Table 2. Summary (mean ± standard deviation, all n= 7 unless noted otherwise) of macroinvertebrate
species calculations and physical measurements of leaf packs.
Parameter
European buckthorn
Slippery elm
Box elder
Shannon diversity
*1.01 ± 0.39
0.66 ± 0.47
0.91 ± 0.37
Species richness
*7.8 ± 1.30
4.6 ± 2.37
6.14 ± 2.19
Species evenness
*0.49 ± 0.17
0.43 ± 0.27
0.54 ± 0.22
Soil °C
16.9 ± 0.8
16.8 ± 0.7
17.1 ± 1.7
Soil moisture (%)
91.2 ± 10.3
92.3 ± 7.6
89.0 ± 15.8
Soil ph
6.6 ± 0
6.6 ± 0
6.6 ± 0
Dry weight change
of leaf pack (%)
99 ± 0.0(7)
85.6 ± 17.5
93.5 ± 10.4
*n = 5
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