|Honeysuckle Management and Deer
Amur Honeysuckle (Lonicera maackii) Management Method Impacts Restoration of Understory Plants in the Presence of White-Tailed Deer (Odocoileus virginiana)
Kendra Cipollini, Elizabeth Ames and Don Cipollini*
*First and second authors, Assistant Professor and Undergraduate Student, Wilmington College, Wilmington, OH 45177. Third author, Professor, Wright State University, Department of Biological Sciences, Dayton, OH 45435. Current address of second author, 1967 Beatty Rd, Wilmington, OH 45177. Corresponding author’s email: KAL143@alumni.psu.edu.
Management methods for invasive species may vary in their restoration success in the presence or absence of herbivores. We investigated the performance of understory plants after management of the invasive shrub Amur honeysuckle using two herbicide-based methods (cut/paint and basal application) in fenced and unfenced plots. The cut/paint method resulted in the removal of above-ground stems, while the basal application resulted in the dead stems remaining in place. Light level in the cut/paint treatment was higher than in the basal application treatment, which was higher than in the control (no management) treatment. Across fencing treatments, fruit production, height and subsequent recruitment of transplanted jewelweed were greater in the cut/paint treatment. Across management treatments, jewelweed plants were taller in the fenced treatment. Native species richness was generally higher in the cut/paint and basal application treatments than in the control treatment. There were more jewelweed recruits, more jewelweed fruits and greater species richness in the cut/paint treatment than in the basal application treatment in fenced plots, but these measures were similar in both management treatments in unfenced plots. Thus standing dead stems of Amur honeysuckle offered some protection from damage in the presence of herbivores, offsetting the overall advantage of the cut/paint method seen in the fenced plots. There was a trend for more leaves of transplanted wild ginger in the basal application treatment. There were more invasive garlic mustard and more Amur honeysuckle seedlings in the cut/paint treatment than in the control treatment. Our results illustrate the complexities involved in selecting appropriate restoration management techniques given herbivore pressure, differential species response and presence of multiple invasive species.
Nomenclature: triclopyr; garlic mustard, Alliaria petiolata (Bieb.) Cavara & Grande; honeysuckle, Lonicera maackii (Rupr.) Maxim.; jewelweed, Impatiens capensis Meerb.; white-tailed deer, Odocoileus virginiana Zimmermann; wild ginger, Asarum canadense L.
Key words: Forest restoration, herbivore, herbivory, touch-me-not
Invasive plants can have major impacts on native plant populations, communities, and ecosystems around the world (Sakai et al. 2001; Pimentel et al. 2005). Once an invasive plant has become established in an ecosystem, restoration practitioners frequently seek to reduce populations of the invasive species through a variety of methods, from mechanical to chemical (e.g., Carlson and Gorchov 2004; Hartman and McCarthy 2004; Milligan et al. 2004, Krueger-Mangold et al. 2006). Another threat to native ecosystems and their successful restoration is browsing or other forms of damage by herbivores. Sweeney and Czapka (2004) suggest that protecting seedlings from herbivory should be given higher priority than protection from competition during restoration. In Midwestern and eastern forests in the United States, a primary herbivore threatening understory plants is the white-tailed deer, Odocoileus virginiana Zimmermann, which is considered a keystone herbivore due to its direct and indirect effects on both plants and animals (Rooney 2001; Rooney and Waller 2003; Cote et al. 2004). Herbivores may not only have direct impacts but may also have indirect impacts; for example, forest areas where deer had been excluded had lower numbers of invasive species (Webster et al. 2005), thus implicating deer in the spread of invasive plants.
Amur honeysuckle (Lonicera maackii (Rupr.) Maxim.) is an Asian shrub that is invasive in Midwestern and northeastern U. S. forests (Luken and Thieret 1995; USDA/NRCS 2007). Amur honeysuckle has extended leaf phenology (Trisel 1997) and bird- and mammal-dispersed fruit (Vellend 2002; Bartuszevige and Gorchov 2006), both of which contribute to its invasive success. Amur honeysuckle reduces native plant species richness (Collier et al. 2002), and the performance of a wide range of both understory and overstory plants (Gould and Gorchov 2000; Gorchov and Trisel 2003; Miller and Gorchov 2004; Hartman and McCarthy 2007). Effects of Amur honeysuckle on other plants can be mediated directly through such factors as shading and allelopathy (e.g., Gorchov and Trisel 2003; Cipollini et al. 2008a) but it may also have indirect effects (Meiners 2007). The impact of Amur honeysuckle is not limited to plant communities; its presence also affects birds and herptiles (Schmidt and Whelan 1999; McEvoy and Durtsche 2004).
Control of Amur honeysuckle is a major focus of natural resource agencies and conservation organizations within its invaded range. Due to these efforts, much information has been gained on how to effectively kill Amur honeysuckle in natural environments (Nyboer 1992; Conover and Geiger 1993; Hartman and McCarthy 2004). Management techniques include the cut-and-paint, or cut/paint, method, where Amur honeysuckle is cut at the base and removed; herbicide is subsequently applied to the cut stump (McDonnell et al. 2005). Two other herbicide-based methods, the foliar spray method and the injection method (Conover and Geiger 1993, Hartman and McCarthy 2004, respectively), result in the killing of Amur honeysuckle with the dead stems left standing in place.
Standing dead stems of Amur honeysuckle could affect restoration success in a number of ways. Standing stems may continue to shade the understory, which may delay the development of plant communities for as long as stems remain standing. Amur honeysuckle produces allelopathic compounds in its tissues (Trisel 1997; Dorning and Cipollini 2006; Cipollini et al. 2008a, 2008c) and thus standing dead stems could continue to contribute allelochemicals to the understory until they decompose completely. In contrast, the presence of standing dead stems may have some positive effects, analogous to the protection from herbivory offered by so-called “nurse plants” (Garcia and Obeso 2003; Bakker et al. 2004). There is some evidence that standing dead stems of Amur honeysuckle may provide protection of transplanted plants from herbivore browsing (Gorchov and Trisel 2003), but this effect has not been quantified adequately. Hartman and McCarthy (2004) followed survival of transplanted tree seedlings after different methods of Amur honeysuckle management, but deer impact was insufficient to examine for protective effects. The response of the native herb community to the presence of standing dead stems has not been examined.
Another challenge to forest restoration is the response of invasive plants to restoration efforts (Loh and Daehler 2007). Although poorly replicated, McConnell et al. (2005) found an increase in species richness after management of Amur honeysuckle using the cut/paint method, but Amur honeysuckle seedlings and other invasive species also increased in abundance in the cut/paint treatment. Runkle et al. (2007) also found an increase in species richness eight years after removal of Amur honeysuckle; however, this increase was primarily the result in the increase of species with high dispersal ability, such as vines and other weedy species. Luken et al. (1997) found the vine Vitus vulpina responded positively to Amur honeysuckle management. No comparisons of the effects of honeysuckle management method on invasive plant responses have been published, but the presence of standing dead stems may slow the response of invasive plants.
The objectives of this study were to determine the effect of the presence or absence of standing dead Amur honeysuckle, the presence or absence of deer, and their interaction on understory plants. We followed the success of transplanted jewelweed (Impatiens capensis Meerb.), and transplanted wild ginger (Asarum canadense L.) in basal application and cut/paint management treatments. We also followed the natural recruitment of species in basal application, cut/paint and control treatments. We predicted that in the absence of deer, the cut/paint management method would best benefit plant performance, due to the increase in light and the removal of potentially allelopathic stem and leaf material. We predicted that in the presence of deer, the basal application method, which leaves the dead stems standing, would best benefit plant performance due to the protection conferred by the stems against deer damage.
Materials and Methods
Experimental Design. We established experimental plots during the first week of April in 2005 in Hamilton County Park District’s Sharon Woods, located in Sharonville, Ohio, USA (39°16'40” N, 84°23'56”W). We chose two sites impacted by Amur honeysuckle approximately 0.75 km apart from each other. Each site is located in mixed oak-maple-ash forest community with a relatively large amount of Amur honeysuckle, yet still contained some degree of native understory vegetation. Deer density at Sharon Woods was approximately eight deer/km2, which is the management goal at this site (J. Klein, personal communication). Within each site, we selected three subsites, with paired 8 by 6 m experimental plots at each subsite, for a total of 12 paired plots. Within each subsite, we used a split-split plot experimental design, with the split plot factor of deer exclusion and the split-split plot factor of Amur honeysuckle management method (see Figure 1). We fenced one plot of each pair at each subsite, placing metal fence posts into the ground and attaching plastic deer fencing (1.8m-tall with five-cm mesh) to the posts. Within each paired plot (fenced and unfenced), we created eight 2 by 3 m subplots. For three of the adjacent subplots, we removed Amur honeysuckle using the cut/paint method, i.e. cutting off the Amur honeysuckle with a handsaw approximately 10 cm from the soil surface, removing the Amur honeysuckle, and painting the stump with the herbicide triclopyr1 to prevent resprouting. For three of the adjacent subplots, we removed Amur honeysuckle using the basal application method, i.e. applying triclopyr in a band around the entire circumference of the base of each stem. On subsequent visits, we controlled the minimal amount of living or sprouting Amur honeysuckle with the same method as the rest of the subplot. We did not remove any Amur honeysuckle in the remaining two adjacent subplots and these served as our controls. For two of the three management method subplots (i.e., basal application and cut/paint), one subplot was designated as the “transplant subplot” and one was designated as the “natural recruitment subplot” for further treatment and measurements. No further measurements were made on the third management method subplot.
Study Species and Measurements. On May 5, 2005, we transplanted four two-leaved rhizomes of the perennial wild ginger and six seedlings of the annual jewelweed into our “transplant subplots.” Transplants were collected locally. Wild ginger is a shade-tolerant rhizomatous perennial that typically expands into a large clump through asexual reproduction. Wild ginger has been shown to be impacted by Amur honeysuckle (Dorning 2004), and appears to be largely resistant to deer browsing (D. Cipollini, personal observation). Plants were collected by first excavating rhizomes, which were often several internodes in length with a pair of leaves at each node. Single transplants, each containing one leaf pair, were then created by clipping the rhizome several cm on each side of a node. Jewelweed is an annual herb that is found in a range of light conditions, from forest clearings to closed woodlands (von Wettberg and Schmidt 2005) and reproduces exclusively by seed. Jewelweed is sensitive to deer browsing (Williams et al. 2000; Asnani et al. 2006). Seedlings were transplanted from local populations when they were approximately 5-10 cm tall. Transplants were not placed in the control treatment, since we expected survival to be low (see Cipollini et al. 2008b). In 2005, we measured survival and fruit number of transplanted jewelweed on 2 June and 30 June, and both height and fruit number on 21 July. We measured survival and leaf number of each clump of wild ginger on 25 April 2006 and 4 May 2007. On 4 May 2007, we measured the width of the largest leaf in each clump of wild ginger.
In a 1-m2 area of each of the transplant subplots (where jewelweed and wild ginger had been transplanted in 2005), we counted the number of seedlings of jewelweed on 26 April 2006 and on 24 April 2007. We were confident that most, if not all, of the seedlings of jewelweed were from fruits of plants that we had transplanted the previous year as there were almost no jewelweed in the plots except for the ones we transplanted. On 26 April 2006 and 24 April 2007, in one haphazardly-chosen control subplot and in both natural recruitment subplots, we counted the number of plants of each species in a 1-m2 area of the subplot and species richness was determined. In all the subplots, we measured light levels2 at 1 m height on July 6 2006, which was a bright and mostly cloudless day. All light measurements were made within 65 min of each other.
Statistical Analyses. For all analyses, we used a nested split-split plot Analysis of Variance (ANOVA) or Multivariate Analysis of Variance (MANOVA) with site as a fixed factor, subsite as the main plot factor (nested within site), fencing as the split plot factor and management method as the split-split plot factor (SAS 1999). For MANOVAs, when significance was found using Wilk’s λ, separate univariate analyses of variance were performed on each separate date, followed by Tukey’s test to determine significance between treatment levels. We analyzed jewelweed fruit production in 2005 and number of seedlings in 2006-7, and number of wild ginger leaves using separate MANOVAs, with each date as a separate variable in the model (von Ende 1993). We analyzed jewelweed height, jewelweed survival, wild ginger leaf width and wild ginger survival separately using ANOVA. We analyzed native species richness and number of invasive garlic mustard (Alliaria petiolata (Bieb.) Cavara & Grande) plants using separate MANOVAs, using each date as a separate variable in the model. We analyzed number of Amur honeysuckle seedlings in spring 2007 using ANOVA. Data were transformed as necessary to meet model assumptions. For light levels, data could not be transformed to meet model assumptions of normality, and a Kruskal-Wallis Rank Sum test was then used. The α-level used for all tests was 0.05.
Results and Discussion
Management of Amur honeysuckle increases the light reaching the forest floor. Light levels were significantly affected by management treatment (F 2, 76 = 47.10, p < 0.001); light levels in the cut/paint treatment was significantly higher than the light levels in the basal application treatment which were in turn significantly higher than the light levels in the control treatment (Figure 2). Controlling Amur honeysuckle and leaving the dead stems in place increased light levels over eight times of light levels in the control. In comparison, the cut/paint treatment increased light levels over 24 times of the light levels in the control. A smaller (~10 times) increase in light after Amur honeysuckle removal was reported in previous work (Luken et al. 1997).
Plants were taller in the cut/paint treatment than in the basal application treatment on July 21 (F1,55 = 21.53, p < 0.0001; Figure 3). In the field, height and reproduction were related in previous work (Cipollini et al. 2008b). In the MANOVA for transplanted jewelweed fruit production across three dates, there was a significant effect of management treatment (F3,42 = 4.19, p = 0.0111). On 30 June, there were significantly more fruits on plants in the cut/paint treatment than on plants in the basal application treatment (F1,44 = 11.77, p = 0.0013; Figure 4). In the MANOVA for the number of jewelweed seedlings across two years, there was a significant effect of management method (F2,9 = 4.86, p = 0.0370; Figure 5). In both years, there were more jewelweed seedlings in the cut/paint treatment than in the basal application treatment across fencing treatments (F1,10 = 4.97, p = 0.0499 and F1,10 = 10.58, p = 0.0087, respectively). In the MANOVA across two years, species richness was significantly affected by management method (F4,38 = 3.70, p = 0.0122; Figure 6). The effect of management method on species richness approached significance in 2006 (F2,20 = 3.11, p = 0.0667) and was significant in 2007 (F2,20 = 7.62, p = 0.0035), with greater richness in the cut/paint and basal application treatment compared to the control treatment. There were no significant treatment effects on survival of jewelweed in the ANOVA.
Previous studies have found that Amur honeysuckle exerts strong aboveground effects on native species (Gorchov and Trisel 2003; Miller and Gorchov 2004; Cipollini et al. 2008b). The positive effects of the cut/paint method on species richness, jewelweed fruit production, jewelweed height and jewelweed recruitment is likely due to the increased light intensity. However, alleviation of allelopathy by removal of Amur honeysuckle stems may have contributed to the beneficial effects of this treatment (Trisel 1997; Dorning and Cipollini 2006; Cipollini et al. 2008c). Regardless of mechanism, native plants benefited from control of Amur honeysuckle, with a trend for greater success using the cut/paint method.
Light conditions and allelopathy are not the only consideration during restoration, as deer can greatly impact restoration success (e.g., Ruhren and Handel 2003; Sweeney and Czapka 2004). Deer damage observed in this study included not only herbivory, but also physical damage by trampling. Although our fences excluded other herbivores aside from deer, we observed that deer were responsible for the majority of damage observed in unfenced plots. The density of deer at this site was high enough to have statistically significant main effects on jewelweed height only. On 21 July 2007 transplanted jewelweed were significantly taller when they were fenced (F1,3 = 10.25, p = 0.0493; Figure 3). Due to the nature of our statistical split-split plot design, small differences in the split-plot factor of fencing can not be easily detected (Neter et al. 1996). The experimental design does allow better detection of differences between the split-split plot factor of management method and its interaction with fencing, which was of primary interest in this study.
In the MANOVA for transplanted jewelweed fruit production across three dates, the interaction of fencing and management treatment was significant (F3, 42 = 3.34, p = 0.0280). On 30 June, there was a significant interaction between management method and fencing (F1,44 = 9.58, p = 0.0034; Figure 4). In the MANOVA for the number of jewelweed seedlings across two years, the interaction of fencing and management method was significant (F2,9 = 9.09, p = 0.0069). In 2007, there was a significant interaction between fencing and management (F1,10 = 7.91, p = 0.0184; Figure 5). The interaction between fencing and management method on species richness was significant in the MANOVA (F4,38 = 2.87, p = 0.0358). The interaction of fencing and management was significant in 2007 (F2,20 = 5.61, p = 0.0116; Figure 6). For jewelweed fruit production, jewelweed recruitment and species richness, there was a more strongly positive effect of fencing in the cut/paint treatment than in the basal application treatment. In basal application plots, measurements were similar whether they were fenced or not.
We therefore found that leaving the dead stems standing provided some protection from deer damage. This is inferred from the less positive effect of fencing on jewelweed fruit production and recruitment and native species richness in the basal application treatment than in the cut/paint treatment. For example, in plots protected from herbivores, jewelweed recruitment in 2007 was twice as high in cut/paint treatments compared to basal the basal application treatment. In plots exposed to herbivores, jewelweed recruitment was nearly identical in the two management treatments (Figure 5). Thus, the general advantage of using the cut/paint treatment was not seen in the presence of deer. Interestingly, we found that species richness was higher in our unmanaged control plots when they were not fenced. However, the overall interaction of fencing and management method on species richness was significant even if the control treatment was removed from the statistical analysis. It is important to note that although differences in species richness were statistically significant, differences were small.
Despite a protective effect from deer, the benefit of using the basal application method in the presence of deer was not great enough to fully recommend its use over the cut/paint method in terms of benefits to native plant performance; in our study, even in unfenced plots, native plants generally performed better or the same with the cut/paint method. Due to deer management efforts, the deer density at our study site is only slightly above the carrying capacity of 4-6 deer/km2 recommended from studies in Wisconsin and Illinois (Alverson et al. 1988; Anderson 1994; Balgooyen and Waller 1995). In areas where deer density is high, a method that leaves the dead stems standing may be more beneficial than the cut/paint method. Since dead stems start to fall after approximately 2-3 years (K. Cipollini, personal observation), it is unclear how long the protective effect will persist. At the very least, the short-term protection from deer damage allows time for a deer management program to be implemented before deer can impact restoration efforts after Amur honeysuckle control. Additionally, the costs of each management method in terms of labor and materials must be weighed during consideration of restoration strategy. Clearly, relying on dead stems for protection from herbivores is more cost effective than the installation of deer fencing, though admittedly the restoration benefits may be not as great. The injection method, which leaves the dead stems in place, is faster and therefore cheaper than the cut/paint method for larger stems (Hartman and McCarthy 2004). Similarly, the foliar spray method is cost effective (T. Borgman, personal communication).
We found few treatment effects on wild ginger, which would be expected based on its relative resistance to deer damage and its shade tolerance. On the other hand, the study may have been too short to detect responses in this perennial species. In the MANOVA for wild ginger leaf number, there were no significant treatment effects, yet the effect of management method approached significance (F2,44 = 2.83, p = 0.070). We performed ANOVAs for each separate date to determine the nature of this non-significant trend. On 25 April 2006, there were leaves on plants in the basal application treatment (3.28 ± 0.27, mean ± SE) than in the cut/paint treatment (2.53 ± 0.15, mean ± SE; F1,45 = 5.68, p = 0.0214). In the ANOVAs for wild ginger leaf width and survival, there were no significant effects. The trend for greater leaf number in the basal application treatment could be due to the propensity of this species to perform better in later successional habitats that have lower light levels (Damman and Cain 1998). We found that wild ginger is a good candidate for restoration, as rhizome fragments are easy to collect and transplant and they survived (75% survival on average) and grew well (5 leaves on average after two years) during our study, consistent with the transplant success found by Mottl et al. (2006). Ruhren and Handel (2003) found that wild ginger had poor transplant success; since their transplants were grown from seed, they may have been much smaller than the rhizome fragments that we transplanted.
Amur honeysuckle management also affected invasive species. There was a significant effect of management method on number of garlic mustard in the MANOVA (F4,38 = 3.34, p = 0.0194). In both years, there were significantly more garlic mustard in cut/paint treatment than in control treatment, with the number of garlic mustard in basal application treatment intermediate between the two (F2, 20 = 4.29, p = 0.0282; F2, 20 = 4.99= 0.0174 respectively; Figure 7). The effects of management method on Amur honeysuckle seedlings in 2007 were significant (F2, 20 = 4.11, p = 0.0319) and similar to the effects seen for garlic mustard (Figure 8). Luken et al. (1997) found that garlic mustard was one of the most important species in Amur honeysuckle thickets, yet it did not respond positively to gap formation. Runkle et al. (2007) found a slight but significant increase in garlic mustard on one sampling date after Amur honeysuckle management. In comparison, we found strong responses of garlic mustard to Amur honeysuckle management, as there were seven times more garlic mustard plants in cut/paint treatments than in control treatments in the second year after Amur honeysuckle management. We also found increases in Amur honeysuckle seedlings with control of Amur honeysuckle, similar to the results of McConnell et al. (2005). Therefore, the benefits of using the cut/paint method are diminished when other invasive species are present.
Our results indicated that in determining the best method for restoration success, restoration practitioners need to take into account deer populations and the presence of other invasive species. The cut/paint method increases light and facilitates greater plant performance but it can contribute to the reinvasion of other invasive species. The cut/paint method is not as successful when deer are present. Methods that leave the dead stems standing may provide temporary protection from browsing and may delay the expansion of invasive species, allowing native species to have higher growth, survival and reproduction. Our results indicate that there are differences between restoration management methods in successful understory restoration and that the management method, the effect of deer, the species of interest and the presence of invasive species must be weighed together in devising restoration strategies. The restoration species of interest must also be considered, as jewelweed and wild ginger responded differently to management methods.
Sources of Materials
1Pathfinder II®, 13.6% triclopyr, Dow Agrosciences, Indianapolis, IN.
2Li-Cor Quantum Sensor, Lincoln, NB.
We thank the Hamilton County Park District for providing funding for this project and permission to perform the research at Sharon Woods. We thank Tom Borgman of the Hamilton County Park District in particular for all his assistance. We thank Jim Rosenberger for statistical advice. We thank Elizabeth Cipollini, Emmett Cipollini, Caitlin Combs, Georgette McClain, Rob Murphy, Jana Reser, Adam Roe and Yvonne Vadeboncoeur for assisting with field research. Doug Burks, Don Troike, Doug Woodmansee, and the WC students of BIO 440/441 provided valuable comments throughout this experiment.
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Figure 1. Diagram of experimental set-up of one paired plot. Fenced plots were fenced along the entire 8 by 6 m perimeter of the plot.
Figure 2. Mean (± SE) light levels in treatments where Amur honeysuckle was not removed (control) and where Amur honeysuckle was removed using either the cut/paint method or the basal application method. Management treatments with different letters are significantly different from each other based on Tukey’s test at p < 0.05.
Figure 3. Mean (± SE) height of transplanted jewelweed on 21 July 2005 in treatments with Amur honeysuckle removed using either the cut/paint method or the basal application method (top) and in fenced and unfenced treatments (bottom). Letters indicate significant differences between treatments using Tukey’s test at p < 0.05.
Figure 4. Mean (± SE) number of fruits on transplanted jewelweed fruits on 30 June 2005 in fenced and unfenced treatments, with Amur honeysuckle removed using either the cut/paint method or the basal application method. Letters indicate significant differences between management treatments using Tukey’s test at p < 0.05. The effect of the interaction between fencing and management treatments on fruit number was significant (p = 0.0034).
Figure 5. Mean (± SE) number of seedlings of jewelweed in 2006 and 2007 in fenced and unfenced treatments, with Amur honeysuckle removed using either the cut/paint method or the basal application method. Letters indicate significant differences between management treatments using Tukey’s test at p < 0.05. The effect of the interaction between fencing and management treatments on fruit number was significant in 2007 (p = 0.0184).
Figure 6. Mean (± SE) native species richness in 2006 and 2007 in fenced and unfenced treatments, with Amur honeysuckle not removed (control) and with Amur honeysuckle removed using either the cut/paint method or the basal application method. The effect of management treatment on species richness was approaching significance in 2006 (p = 0.0667). Letters indicate significant differences between management treatments using Tukey’s test at p < 0.05. The effect of the interaction between fencing and management treatments on richness was significant in 2007 (p = 0.0116).
Figure 7. Mean (± SE) number of invasive garlic mustard in treatments where Amur honeysuckle was not removed and where Amur honeysuckle was removed using either the cut/paint method or the basal application method. Management treatments with different letters are significantly different from each other based on Tukey’s test at p < 0.05.
Figure 8. Mean (± SE) number of Amur honeysuckle seedlings in treatments where Amur honeysuckle was not removed and where Amur honeysuckle was removed using either the cut/paint method or the basal application method. Management treatments with different letters are significantly different from each other based on Tukey’s test at p < 0.05.
Management methods for invasive species may vary in their restoration success in the presence or absence of herbivores. We managed Amur honeysuckle using the cut/paint method, which involves cutting and removing the stems, then painting the stump with herbicide. We compared the cut/paint management method to the basal application method, where we applied herbicide to the stems, which remained standing after death. We compared the success of these two methods in the presence of deer by using fencing to exclude deer from half of the plots of each management method. Light level in the cut/paint method was eight times higher than in the basal application treatment and 24 times higher than in the control (no management). We transplanted two native species, jewelweed and wild ginger into each plot and also followed natural recruitment of native species. Fruit production, height and subsequent recruitment of jewelweed were greatest using the cut/paint method. Jewelweed plants were taller when fenced. Native species richness was generally higher in when Amur honeysuckle was managed. There were more jewelweed recruits, more jewelweed fruits and greater species richness in the cut/paint treatment than in the basal application treatment in fenced plots, but measures were similar for both management methods in unfenced plots. Thus standing dead stems of Amur honeysuckle offered some protection from damage in the presence of herbivores, offsetting the overall advantage of the cut/paint method seen in the fenced plots. The positive effect of removing above-ground biomass trades off with the increased deer impact, increased recruitment of Amur honeysuckle and increased success of garlic mustard. The presence of deer and other invasive species should be weighed when selecting the most appropriate management method for Amur honeysuckle.