Effects of Red Cedar on Invertebrate Abundance and Morphospecies Richness Jenna Noble, Todd Tracy,...
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O ak G rove Invertebrate A bundance 20 25 30 35 40 45 50 55 60 C edar Non-C edar N um berofinvertebrates Effects of Red Cedar on Invertebrate Effects of Red Cedar on Invertebrate Abundance and Morphospecies Richness Abundance and Morphospecies Richness Jenna Noble, Todd Tracy, Jesse Nieuwenhuis, and Jonathan Gesink Northwestern College, Orange City, IA ABSTRACT Although native to the eastern US, the Eastern red cedar Juniperus virginiana is taking over grasslands, oak savannas, and natural prairies in the Midwest. In this study, we used pitfall traps to examine the effects of the presence and removal of red cedar on invertebrate abundance and species richness, with particular focus on ants and carabid beetles. In September 2007 we performed 24-hour trapping sessions in: a) cedar-invaded, cedar-removed, and cedarless areas within a riparian mixed-grass prairie habitat along the Niobrara River at the Nature Conservancy’s Niobrara Valley Preserve in north-central Nebraska, and b) cedar-invaded and cedarless areas within an upland remnant tallgrass prairie at Oak Grove County Park near Hawarden, Iowa. We found greater invertebrate abundance and carabid beetle abundance in non-cedar plot than traps in the cedar-infested plot, and more ants in the cedar-removed plot than either non-cedar or the cedar-infested plot. Conversely, we found higher invertebrate richness in cedar-infested areas of Oak Grove than non-cedar areas, and we found no differences in abundance between cedar and non-cedar areas. We tentatively conclude that red cedar negatively impacts invertebrate communities and discuss possible reasons for the differences in results between study sites. INTRODUCTION Eastern red cedar Juniperus virginiana is generally classified as an invasive species in the central U.S., despite the fact that it is a native tree. This species has become problematic in that it is spreading (via birds passing seeds through their digestive tracts) across the grasslands and rangelands of the central U.S., areas that historically have burned frequently enough and/or been sufficiently trampled by buffalo to prevent woody species from taking hold. Until recently, red cedar’s range was limited to river bottoms and cliff faces where trampling and fires were less likely to have occurred. The facilitation of the spread of the trees into upland areas has been greatly aided by farmers, ranchers, and state Departments of Transportation planting the species as a windbreak. Although the species is useful for windbreaks and building material, economic losses from lost rangeland and lost hunting leases, decreased stream water quality, and lowered water tables appear to outweigh the benefits of the species in many areas (Drake & Todd 2002). The effects these cedars have on native plant diversity is fairly easily seen, but what is not so apparent are the effects on upland invertebrates communities. Studies done in Nebraska on the endangered American Burying Beetle Nicrophorus americanus (family Silphidae) showed that the presence of cedar affected where the insect ranged. Mark/recapture experiments showed that although the beetles did not completely avoid the invasive, there were significantly fewer beetles ranging under the cedar trees (Walker and Hobak 2007). While providing some insight into the potential effects of cedar on invertebrates, this study focused on only one species, and thus we still lack a broader understanding of the effects of these cedars and their removal on invertebrates communities in general. In our study, we hypothesized that the presence of red cedar influences the overall species richness and abundance of invertebrates in an area, and we predicted that invertebrate abundance and species richness would be lower in cedar-infested areas than cedar-free areas, with areas recently cleared of cedars showing intermediate values. MATERIALS AND METHODS Our pitfall-trapping in Nebraska took place on September 14 -15, 2007, at the Nature Conservancy’s Niobrara Preserve in north-central Nebraska, in a riparian zone along the Niobrara River. The research area was relatively flat with sandy soil and typical mixed-grass prairie grasses and forbs. Our test plots were the following: cedar-present, cedar-removed (in a controlled burn the previous winter), and non-cedar (area never invaded). We marked and flagged 10 separate sample points a minimum of 15m apart within each of the three test plots. Pitfall cups were then placed at ground level beside each flag, and cups were filled with ~2cm of DeathJuice, a combination of 70% ethanol and dish soap, used to trap and kill the insects that fall into the cup. We collected the cups 24 hours later and poured their contents into individually labeled bags, which were then taken back to Northwestern College, where identification of samples to the morphospecies level was performed using dissecting microscopes. Our pitfall-trapping in Iowa took place on September 19-20, 2007, in an upland oak savanna at Oak Grove County Park, where tallgrass prairie species are found interspersed with woody plants and shrubs, including eastern red cedars (Fig. 2). The same trapping method was used, but with only infested and non-cedar areas being tested, as no cedar-removed areas were available. We paired cedar and non-cedar traps by placing one pitfall cup under the outer branches of a cedar tree and the corresponding non-cedar cup anywhere from 5 to 10m away from the tree in a clear, grassy area. Ten pairs of cups were placed. These were harvested 24 hours later, and their contents were poured into labeled baggies and taken to the lab for analysis. Invertebrate abundance and richness values were determined for each sample point at both sites. For the Niobrara Preserve data, we performed an ANOVA and pairwise t-tests comparing both the abundance and the richness among treatment plots. For the Oak Grove data, we performed t-tests comparing abundance and richness between cedar and non-cedar samples. RESULTS At the Niobrara Preserve, samples from the non-cedar area exhibited significantly higher species abundance than either the cedar-infested samples (p=0.007) or the cedar-removed samples (p=0.046), and cedar-removed areas showed significantly higher species abundance than cedar- infested areas (p=0.0005; Fig. 3a). No significant differences in species richness were found among the Niobrara sites (ANOVA p=0.086), although there was marginally significantly greater richness in cedar-removed samples than cedar-infested samples (p=0.059; Fig. 4a) . Conversely, in our Oak Grove data we found significantly higher overall richness in cedar-infested areas than non-cedar areas (p=0.015; Fig. 4b), but no differences in species abundance, although the difference in overall abundance was almost significant (p=0.092; Fig. 3b). With regard to ant abundance, we found significant differences among the three areas at the Niobrara site (ANOVA p=0.006; Fig. 3a), with the cedar-removed area showing significantly greater ant abundance than both the cedar-infested (p=0.003) and non-cedar areas (p=0.002). No difference was found between the non-cedar and cedar-infested areas (p=0.33), and no differences in ant abundance were seen in the Oak Grove data (p= 0.90). To determine whether the differences in abundance among the three Niobrara plots could be attributed solely to differences in ant numbers, we ran t-tests comparing the mean abundance of invertebrates at both sites, excluding the ants (Fig. 3a). We found no differences in non-ant abundance between non-cedar and cedar-removed plots (p=0.14) but found that both non-cedar and cedar-removed plots showed significantly greater non-ant abundance than the cedar-infested plot (p=0.0001 and 0.022, respectively). We also examined the abundance of carabid (Fig. 5a&b) and staph (Fig. 6a&b) beetles at both study sites and found that the Niobrara data showed a significantly higher abundance of carabid beetles in the non-cedar area than the cedar-infested area (p=0.01; Fig. 5a) and marginally significantly more staph beetles in the cedar-infested area than cedar-removed area (p=0.057; Fig. 6a). In Oak Grove no significant differences in carabid (Fig. 5b) and staph (Fig. 6b) beetle abundance were found, although we did find marginally significantly more staph beetles in cedar-infested samples than non-cedar samples (p=0.092; Fig. 6b). DISCUSSION In this study, we examined the effects of invasive eastern red cedar on invertebrate communities by pitfall-trapping in a riparian area along the Niobrara River at the Nature Conservancy’s Niobrara Valley Preserve in north-central Nebraska and in an upland savanna at Oak Grove Park near Hawarden, Iowa. Our Niobrara data showed that the presence of red cedar had an adverse effect on ant abundance and overall invertebrate abundance (both including and excluding ants) but not invertebrate richness. We also found that ants preferred the cedar-removed plot to either the cedar-infested plot or the non-cedar plot and that carabid beetles, often used in studies as an indicator of larger community structure, were found in significantly greater numbers in non-cedar areas than cedar-infested areas. Conversely, at Oak Grove we found significantly greater invertebrate richness in cedar-infested than non-cedar areas but no significant difference in overall, ant, carabid, or staph beetle abundance. Results from our Niobrara site support our hypothesis that invertebrate abundance is adversely affected by the presence of red cedar, while results from Oak Grove suggest otherwise. Differences between the two sites can be accounted for perhaps by the different terrain, substrate, and slope exposure, as our Nebraska site was sandy and flat, while our Iowa site was grassy and sloped. Furthermore, our Iowa site is heavily invaded by downy brome Bromus tectorum and leafy spurge Euphorbia esula, two invasives not directly studied in this experiment. Most of our non- cedar pitfall traps at Oak Grove were placed in the ground where one or both of these species were present, and thus an apparent preference for cedar-infested areas over non-cedar areas at Oak Grove may be an avoidance of these two invasives rather than an actual preference for cedar. Neither of these two invasives was found at the Niobrara site, and no other invasives were apparent in any of the Niobrara plots, and thus results at Niobrara are less likely to reflect an avoidance of something other than cedar. While the presence of cedars clearly relates to a decreased abundance of invertebrates at our Nebraska site, cedars do not seem to impact morphospecies richness. In general, all morphospecies collected at the Niobrara site were found in greater numbers in non-cedar areas than infested areas, but species still used cedar-infested areas in low numbers, which supports the conclusions of Walker and Hoback (2007) in their Nebraska beetle study. More sampling dates and sampling over multiple years are necessary to fully understand the effects of cedar and its eradication on invertebrate communities. For example, long-term monitoring will elucidate the effects of the restoration process. The vast numbers of ants in the cedar-removed area may be the result of the burning of cedars in the cedar-removed plot, and repeated sampling of the area over a period of several years will reveal whether the invertebrate community gradually becomes more like the non-cedar area. Moreover, we know from our reeserach of the European buckthorn at Northwestern College’s Alton forest and at Oak Grove that patterns in invertebrate abundance and richness between areas of high and low buckthorn density vary from one season to the next, and without repeated sampling in our present study we can only draw tentative conclusions about the effects of cedar in the fall. The results of our present study can help us more fully understand the impacts of red cedar on its surroundings. Not only can cedars displace native plants, alter soil properties, lower water tables, and decrease the quality of pastureland, they also appear to displace many of REFERENCES Drake, B., and Todd, P. 2002. A strategy for control and utilization of invasive juniper species in Oklahoma: Final report of the redcedar taskforce. Oklahoma Department of Agriculture, Food, and Forestry. Jennings, V., and Tallamy, D. 2006. Composition and abundance of ground-dwelling coleoptera in a fragmnented and continuous forest. Environmental Entomology 35:1550-1560. Walker, T., and Hoback, W. 2007. Effects of invasive eastern redcedar on capture rates of Nicrophorus americanus and other Silphidae. Environmental Entomology Fig. 1. Niobrara Valley Preserve study site. Non-cedar area is in foreground, with cedar-removed area in the middle (yellow arrow) and cedar-infested area in background (red arrow). Fig. 2. Oak Grove study site. O ak G rove Invertebrate R ichness 8 9 10 11 12 13 14 15 16 C edar Non-C edar # ofm orphospecies Niobbrara C arabid B eetle A bundance 0 2 4 6 8 10 12 14 16 C edar N on-C edar R em oved A bundance (# ofcarabid beetles) O ak G rove C arabid B eetle A bundance 0 2 4 6 8 10 12 14 16 C edar Non-C edar N um berofB eetles Niobrara Staph B eetle A bundance 0 0.5 1 1.5 2 2.5 3 3.5 4 C edar N on-C edar R em oved N um berofstaph beetles O ak G rove Staph B eetle A bundance 0 0.5 1 1.5 2 2.5 3 3.5 C edar Non-C edar N um berofB eetles Niobrara Invertebrate R ichness 4 5 6 7 8 9 10 11 12 C edar N on-C edar R em oved N um berofm orphospecies A A A A B B B B Fig. 3. Invertebrate abundance at A) Niobrara, and B) Oak Grove. Overall abundance, ant abundance, and non-ant abundance are shown for Niobrara, while only overall abundance is shown for Oak Grove. Bars connect means that are significantly different at alpha = 0.05. Fig. 4. Invertebrate richness at A) Niobrara, and B) Oak Grove. Differences were not significant at Niobrara but were significant at Oak Grove. Bar connects means that are significantly different at alpha = 0.05. Fig. 5. Carabid beetle abundance at A) Niobrara, and B) Oak Grove. Bar connects means that are significantly different at alpha = 0.05. Fig. 6. Staphylinidae (staph) beetle abundance at A) Niobrara, and B) Oak Grove. No significant differences were detected.
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Transcript of Effects of Red Cedar on Invertebrate Abundance and Morphospecies Richness Jenna Noble, Todd Tracy,...
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Effects of Red Cedar on Invertebrate Abundance and Effects of Red Cedar on Invertebrate Abundance and Morphospecies RichnessMorphospecies Richness
Jenna Noble, Todd Tracy, Jesse Nieuwenhuis, and Jonathan GesinkNorthwestern College, Orange City, IA
ABSTRACTAlthough native to the eastern US, the Eastern red cedar Juniperus virginiana is taking over grasslands, oak savannas, and natural prairies in the
Midwest. In this study, we used pitfall traps to examine the effects of the presence and removal of red cedar on invertebrate abundance and species richness, with particular focus on ants and carabid beetles. In September 2007 we performed 24-hour trapping sessions in: a) cedar-invaded, cedar-
removed, and cedarless areas within a riparian mixed-grass prairie habitat along the Niobrara River at the Nature Conservancy’s Niobrara Valley Preserve in north-central Nebraska, and b) cedar-invaded and cedarless areas within an upland remnant tallgrass prairie at Oak Grove County Park
near Hawarden, Iowa. We found greater invertebrate abundance and carabid beetle abundance in non-cedar plot than traps in the cedar-infested plot, and more ants in the cedar-removed plot than either non-cedar or the cedar-infested plot. Conversely, we found higher invertebrate richness in cedar-
infested areas of Oak Grove than non-cedar areas, and we found no differences in abundance between cedar and non-cedar areas. We tentatively conclude that red cedar negatively impacts invertebrate communities and discuss possible reasons for the differences in results between study sites.
INTRODUCTIONEastern red cedar Juniperus virginiana is generally classified as an invasive species in the central U.S., despite the fact that it is a native tree. This species has become problematic in that it is spreading (via birds passing seeds through their digestive tracts) across the grasslands and rangelands of the central U.S., areas that historically have burned frequently enough and/or been sufficiently trampled by buffalo to prevent woody species from taking hold. Until recently, red cedar’s range was limited to river bottoms and cliff faces where trampling and fires were less likely to have occurred. The facilitation of the spread of the trees into upland areas has been greatly aided by farmers, ranchers, and state Departments of Transportation planting the species as a windbreak. Although the species is useful for windbreaks and building material, economic losses from lost rangeland and lost hunting leases, decreased stream water quality, and lowered water tables appear to outweigh the benefits of the species in many areas (Drake & Todd 2002). The effects these cedars have on native plant diversity is fairly easily seen, but what is not so apparent are the effects on upland invertebrates communities. Studies done in Nebraska on the endangered American Burying Beetle Nicrophorus americanus (family Silphidae) showed that the presence of cedar affected where the insect ranged. Mark/recapture experiments showed that although the beetles did not completely avoid the invasive, there were significantly fewer beetles ranging under the cedar trees (Walker and Hobak 2007). While providing some insight into the potential effects of cedar on invertebrates, this study focused on only one species, and thus we still lack a broader understanding of the effects of these cedars and their removal on invertebrates communities in general. In our study, we hypothesized that the presence of red cedar influences the overall species richness and abundance of invertebrates in an area, and we predicted that invertebrate abundance and species richness would be lower in cedar-infested areas than cedar-free areas, with areas recently cleared of cedars showing intermediate values.
MATERIALS AND METHODSOur pitfall-trapping in Nebraska took place on September 14 -15,
2007, at the Nature Conservancy’s Niobrara Preserve in north-central Nebraska, in a riparian zone along the Niobrara River. The research area was relatively flat with sandy soil and typical mixed-grass prairie grasses and forbs. Our test plots were the following: cedar-present, cedar-removed (in a controlled burn the previous winter), and non-cedar (area never invaded). We marked and flagged 10 separate sample points a minimum of 15m apart within each of the three test plots. Pitfall cups were then placed at ground level beside each flag, and cups were filled with ~2cm of DeathJuice, a combination of 70% ethanol and dish soap, used to trap and kill the insects that fall into the cup. We collected the cups 24 hours later and poured their contents into individually labeled bags, which were then taken back to Northwestern College, where identification of samples to the morphospecies level was performed using dissecting microscopes.
Our pitfall-trapping in Iowa took place on September 19-20, 2007, in an upland oak savanna at Oak Grove County Park, where tallgrass prairie species are found interspersed with woody plants and shrubs, including eastern red cedars (Fig. 2). The same trapping method was used, but with only infested and non-cedar areas being tested, as no cedar-removed areas were available. We paired cedar and non-cedar traps by placing one pitfall cup under the outer branches of a cedar tree and the corresponding non-cedar cup anywhere from 5 to 10m away from the tree in a clear, grassy area. Ten pairs of cups were placed. These were harvested 24 hours later, and their contents were poured into labeled baggies and taken to the lab for analysis.
Invertebrate abundance and richness values were determined for each sample point at both sites. For the Niobrara Preserve data, we performed an ANOVA and pairwise t-tests comparing both the abundance and the richness among treatment plots. For the Oak Grove data, we performed t-tests comparing abundance and richness between cedar and non-cedar samples.
Due to the large number of ants found in the cups of the Niobrara Preserve, we also ran the ANOVA and individual T-tests using the ant data for each of the three areas. After subtracting the number of ants from the total abundance of invertebrates, we reran the comparative abundance ANOVA and T-tests in order to determine whether differences in abundance could simply be attributes to differences observed in ant abundance among the three treatments. We also performed an ANOVA and t-tests on staphylinid (staph) and carabid beetles in each of our test sites, as carabid beetle abundance is often used as an indicator of larger community structure (e.g., Jennings and Tallamy 2006).
RESULTS At the Niobrara Preserve, samples from the non-cedar area exhibited significantly higher species abundance than either the cedar-infested samples (p=0.007) or the cedar-removed samples (p=0.046), and cedar-removed areas showed significantly higher species abundance than cedar-infested areas (p=0.0005; Fig. 3a). No significant differences in species richness were found among the Niobrara sites (ANOVA p=0.086), although there was marginally significantly greater richness in cedar-removed samples than cedar-infested samples (p=0.059; Fig. 4a) . Conversely, in our Oak Grove data we found significantly higher overall richness in cedar-infested areas than non-cedar areas (p=0.015; Fig. 4b), but no differences in species abundance, although the difference in overall abundance was almost significant (p=0.092; Fig. 3b). With regard to ant abundance, we found significant differences among the three areas at the Niobrara site (ANOVA p=0.006; Fig. 3a), with the cedar-removed area showing significantly greater ant abundance than both the cedar-infested (p=0.003) and non-cedar areas (p=0.002). No difference was found between the non-cedar and cedar-infested areas (p=0.33), and no differences in ant abundance were seen in the Oak Grove data (p= 0.90). To determine whether the differences in abundance among the three Niobrara plots could be attributed solely to differences in ant numbers, we ran t-tests comparing the mean abundance of invertebrates at both sites, excluding the ants (Fig. 3a). We found no differences in non-ant abundance between non-cedar and cedar-removed plots (p=0.14) but found that both non-cedar and cedar-removed plots showed significantly greater non-ant abundance than the cedar-infested plot (p=0.0001 and 0.022, respectively).
We also examined the abundance of carabid (Fig. 5a&b) and staph (Fig. 6a&b) beetles at both study sites and found that the Niobrara data showed a significantly higher abundance of carabid beetles in the non-cedar area than the cedar-infested area (p=0.01; Fig. 5a) and marginally significantly more staph beetles in the cedar-infested area than cedar-removed area (p=0.057; Fig. 6a). In Oak Grove no significant differences in carabid (Fig. 5b) and staph (Fig. 6b) beetle abundance were found, although we did find marginally significantly more staph beetles in cedar-infested samples than non-cedar samples (p=0.092; Fig. 6b).
DISCUSSIONIn this study, we examined the effects of invasive eastern red cedar on invertebrate communities by pitfall-trapping in a riparian area along the Niobrara River at the Nature Conservancy’s Niobrara Valley Preserve in north-central Nebraska and in an upland savanna at Oak Grove Park near Hawarden, Iowa. Our Niobrara data showed that the presence of red cedar had an adverse effect on ant abundance and overall invertebrate abundance (both including and excluding ants) but not invertebrate richness. We also found that ants preferred the cedar-removed plot to either the cedar-infested plot or the non-cedar plot and that carabid beetles, often used in studies as an indicator of larger community structure, were found in significantly greater numbers in non-cedar areas than cedar-infested areas. Conversely, at Oak Grove we found significantly greater invertebrate richness in cedar-infested than non-cedar areas but no significant difference in overall, ant, carabid, or staph beetle abundance.
Results from our Niobrara site support our hypothesis that invertebrate abundance is adversely affected by the presence of red cedar, while results from Oak Grove suggest otherwise. Differences between the two sites can be accounted for perhaps by the different terrain, substrate, and slope exposure, as our Nebraska site was sandy and flat, while our Iowa site was grassy and sloped. Furthermore, our Iowa site is heavily invaded by downy brome Bromus tectorum and leafy spurge Euphorbia esula, two invasives not directly studied in this experiment. Most of our non-cedar pitfall traps at Oak Grove were placed in the ground where one or both of these species were present, and thus an apparent preference for cedar-infested areas over non-cedar areas at Oak Grove may be an avoidance of these two invasives rather than an actual preference for cedar. Neither of these two invasives was found at the Niobrara site, and no other invasives were apparent in any of the Niobrara plots, and thus results at Niobrara are less likely to reflect an avoidance of something other than cedar.
While the presence of cedars clearly relates to a decreased abundance of invertebrates at our Nebraska site, cedars do not seem to impact morphospecies richness. In general, all morphospecies collected at the Niobrara site were found in greater numbers in non-cedar areas than infested areas, but species still used cedar-infested areas in low numbers, which supports the conclusions of Walker and Hoback (2007) in their Nebraska beetle study.
More sampling dates and sampling over multiple years are necessary to fully understand the effects of cedar and its eradication on invertebrate communities. For example, long-term monitoring will elucidate the effects of the restoration process. The vast numbers of ants in the cedar-removed area may be the result of the burning of cedars in the cedar-removed plot, and repeated sampling of the area over a period of several years will reveal whether the invertebrate community gradually becomes more like the non-cedar area. Moreover, we know from our reeserach of the European buckthorn at Northwestern College’s Alton forest and at Oak Grove that patterns in invertebrate abundance and richness between areas of high and low buckthorn density vary from one season to the next, and without repeated sampling in our present study we can only draw tentative conclusions about the effects of cedar in the fall.
The results of our present study can help us more fully understand the impacts of red cedar on its surroundings. Not only can cedars displace native plants, alter soil properties, lower water tables, and decrease the quality of pastureland, they also appear to displace many of the invertebrates living in invaded areas. One encouraging finding in our Niobrara study is that within a year of the removal of cedars in an attempt to restore an area heavily invaded by cedars, the invertebrate populations have already shown signs of recovery in the restoration area.
REFERENCES Drake, B., and Todd, P. 2002. A strategy for control and utilization of invasive juniper species in Oklahoma: Final report of the redcedar taskforce. Oklahoma Department of Agriculture, Food, and Forestry. Jennings, V., and Tallamy, D. 2006. Composition and abundance of ground-dwelling coleoptera in a fragmnented and continuous forest. Environmental Entomology 35:1550-1560.Walker, T., and Hoback, W. 2007. Effects of invasive eastern redcedar on capture rates of Nicrophorus americanus and other Silphidae. Environmental Entomology 297-307.
Fig. 1. Niobrara Valley Preserve study site. Non-cedar area is in foreground, with cedar-removed
area in the middle (yellow arrow) and cedar-infested area in background (red arrow).
Fig. 2. Oak Grove study site.
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Fig. 3. Invertebrate abundance at A) Niobrara, and B) Oak Grove. Overall abundance, ant abundance, and non-ant abundance are shown for Niobrara, while only overall abundance is shown for Oak Grove. Bars connect means that are significantly different at alpha = 0.05.
Fig. 4. Invertebrate richness at A) Niobrara, and B) Oak Grove. Differences were not significant at Niobrara but were significant at Oak Grove. Bar connects means that are significantly different at alpha = 0.05.
Fig. 5. Carabid beetle abundance at A) Niobrara, and B) Oak Grove. Bar connects means that are significantly different at alpha = 0.05.
Fig. 6. Staphylinidae (staph) beetle abundance at A) Niobrara, and B) Oak Grove. No significant differences were detected.
