2010 NORTHEASTERN NATURALIST 17(Monograph 7):1–32 Invasive Shrubs in Kentucky Richard L. Boyce* Abstract - I surveyed the distribution of invasive (non-native) shrubs in Kentucky, along with their properties, effects, and control measures. Kentucky's floral, physical geography, and climate are representative of a much broader region of the US, and the state has a large number of counties with available data. Invasive shrub species richness increases with county population and appears to be underreported in most of the state. The most widespread of the 68 species reported were Rosa multiflora (Multiflora Rose), Elaeagnus umbellate (Autumn Olive), Morus alba (Mulberry), Lonicera maackii (Amur Honeysuckle), Albizia julibrissin (Mimosa), Euonymus alatus, and Ligustrum sinense (Common Chinese Privet). An additional 17 were identified as ones that may become widespread in the future. Families with the largest number of species were Rosaceae, Caprifoliaceae, and Oleaceae. Most shrubs originated in eastern Asia, were introduced in the 19th century, have animal-dispersed fruit, reproduce vegetatively, are at least partially shade-tolerant, and tolerate a wide range of soils. Many have extended-deciduous leaf habits and tolerate drought. Mechanical and chemical control methods appear to be best for controlling them, but the use of fire and biological control has been studied for only a few species. Invasive shrub impact is difficult to assess from distribution alone, and further work is needed to determine current and future impact of the species identified in this study. Introduction Invasive plant species are now recognized as a major problem in ecosystems across the US, including those in Kentucky. Many of them crowd out native species, including the ones that are desired for regeneration after disturbance. Others may change forest ecosystem function in such a way that successful tree regeneration no longer occurs. In the past, invasive species were viewed as occupying niches created by human disturbance of natural ecosystems (e.g., Mooney and Drake 1989, Rejmánek 1989). However, more recent work has shown that relatively undisturbed ecosystems can be successfully invaded (e.g., Gordon 1998, Horvitz et al. 1998). This vulnerability to invasion is due to characteristics possessed by most successful invaders, including 1) a high rate of reproduction and dispersal, 2) superior competitive ability, 3) few herbivores or diseases, 4) an ability to occupy a “vacant” niche, and 5) the capability of altering site characteristics (Gordon 1998). For the purposes of this study, I define any shrub species that has been called non-native, naturalized, alien, exotic, or introduced as an invasive species. Some reserve the term “invasive” for introduced plants that are actively expanding their range and abundance. However, many alien plants that escape from cultivation undergo a substantial “lag” phase before their spread *Department of Biological Sciences, Northern Kentucky University, Nunn Drive, Highland Heights, KY 41099; boycer@nku.edu. 2 Northeastern Naturalist Vol. 17, Monograph No. 7 begins (Mack et al. 2000). Thus, non-native plants that may appear to be wellbehaved at present are included in this study, as they may be in their lag phase. In this review, I will focus on the effects of invasive shrub species in Kentucky, particularly on forest tree regeneration. Results from Kentucky can be extrapolated to a fairly large region of the US, as its flora, physical geography, and climate are similar to much of the seven states that border it. Furthermore, whereas Kentucky is only a moderate-sized state, its 120 counties allow a fine degree for resolution for species distribution. While shrub data directly applicable to Kentucky ecosystems would be most useful, such data for most species included in this study are rare, and so I also include data from other regions. Shrubs can have particular effects on trees not caused by other plant forms. They are relatively tall and long-lived, so they compete against tree seedlings longer than herbaceous vegetation. Miller (2005) has identified a number of other effects. By forming monotypic stands, invasive shrubs reduce biodiversity and hinder forest tree regeneration. This effect is clearly evident where I live and work, in the Ohio River valley region, where the invasive Lonicera maackii (Rupr.) Herder (Amur Honeysuckle) successfully keeps the dominant oak-hickory forests from regenerating in many places, due to its extended leaf-out period and the resulting dense shade (Luken and Thieret 1995), as well as its allelopathic effects on other plants (Cipollini et al. 2008, Dorning and Cipollini 2006). Invasive shrubs can destroy habitat for other organisms and disrupt important ecological processes, such as fire frequency and intensity, nitrogen cycling, and soil pH equilibrium. Many invasive shrubs take advantage of disturbance to initially become established. They tend to be prolific seed and fruit producers, and their seed is spread by animals, wind, and water. Seeds of many species can remain viable in the seed bank for many years. Invasive shrubs often also reproduce vegetatively, and they can come to dominate a stand via the production of root sprouts, stem sprouts, and other forms of vegetative reproduction. The objective of this review is to survey the extent of invasive shrubs in Kentucky. I look at shrub distribution, nativity, physiological characteristics, habitat preferences in the US, effects on forest trees (if known), and control measures. Recommendations for recognition and control of current and potential invasive shrubs follows, as well areas that require further research. Methods Data for this study were collected primarily from the USDA PLANTS database (USDA NRCS 2008) and EDDMapS (2009), with additional references cited in Supplemental Table 1 (available online at http://www. eaglehill.us/NENAonline/suppl-files/n17-2-Boyce-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/N840.s1). Invasive species were included only if they were listed in at least one Kentucky county by USDA PLANTS, EDDMapS, or other sources. In addition, the growth habit listed in the USDA PLANTS database had to include the term “shrub,” i.e., a perennial, multi-stemmed woody plant that is usually less than 4 to 5 m in height (USDA 2010 R.L. Boyce 3 NRCS 2008). Exceptions were made for species included in the genera Rosa and Rubus. In the USDA PLANTS database, they are not listed as shrubs, but rather as subshrubs, i.e., low-growing shrubs less that 0.5 m tall, never exceeding 1 m. However, other references included in this study state that they all reach more than 1 m in height, and thus they are included. Maclura pomifera (Raf.) C.K. Schneid (Osage-orange) was not included because it grows as a tree in Kentucky. Species nomenclature follow USDA PLANTS (USDA NRCS 2008). The 2004 estimated Kentucky county human population data were obtained from the US Census Bureau (2005), and total number of invasive shrub species in each county was regressed against the logarithm of county population. I hypothesized that counties with herbaria, and those adjacent, would have better invasive shrub collections than other counties due to the presence of botanists adding to herbaria collections. Thus, a multiple regression of species number in each county was performed on both the logarithm of county population and a dummy variable that was set to either 1, if the county included or was adjacent to an herbarium, or 0 otherwise. Because this analysis indicated that invasive shrub species presence was undercounted in counties away from herbaria, quantile regression was also performed, using the statistical package R (R Development Core Team 2008), to better estimate the most likely occurrence of invasive shrubs. In addition to tallying the total number of counties where each invasive species occurred, I also collected and tabulated physiological characteristics and habitat preferences, effects on forests, control measures, and nativity. In order to assess the potential of species that are currently not widespread in Kentucky to become so, I performed a fuzzy set ordination (FSO) on the data set (Boyce and Ellison 2001; Roberts 1986, 2008). A number of species characteristics were used to construct a similarity matrix among species. These characteristics were: origins from either eastern Asia or western Eurasia; open-canopy forest habitat; riparian habitat; a heavy, conspicuous, or persistent fruit crop; distribution of seed by birds; vegetative reproduction; shade tolerance; leaf habit (deciduous, extended-deciduous, or evergreen); drought tolerance; and nitrogen fixation. Most of these factors were binary (0 or 1); shade and leaf habit were assigned three levels. Ružička’s index was used to calculate similarities (Boyce and Ellison 2001), as it gave the best fit. FSO was performed on the species similarity index, using the number of counties (breadth of occurrence) as the factor. Ordination scores were then normalized to the same range as the actual number of counties, i.e., the apparent number of counties. The minimum apparent number of counties for widespread species (actual number of counties ≥40) were then calculated; other species that had apparent number of counties scores equal to or higher than this minimum were classified as of concern for becoming widespread in the future. Results Number and distribution Sixty-eight invasive shrub species occur in Kentucky (Appendix 1). The occurrences in the 120 counties in Kentucky are listed in Supplemental 4 Northeastern Naturalist Vol. 17, Monograph No. 7 Figure 1. Number of invasive shrubs species vs. logarithm of estimated 2004 Kentucky county populations. The light dashed line shows the results of a linear regression (No. Spp. = -15.091 + 4.873 x log10[2004 county population]; R2 =0.1472, P < 0.0001). The inclusion of a dummy variable for the presence of an herbarium in the county or adjacent to it resulted in the following multiple linear regression equation: No. Spp. = - 12.8727 + 4.1834 x log10(2004 county population) + 2.0307 x (Herbarium presence [1 or 0]); R2 = 0.1886, Herbarium presence P = 0.0160. The heavy dashed line and the solid line show the 90% and 95% quantile regression lines (No. Spp. = -18.148 + 7.040 x log10[2004 county population] and No. Spp. = -15.913 + 6.978 x log10[2004 county population], respectively) and are discussed in the text. All labeled counties (except Jefferson) have active herbaria. Table 1 (available online at https://www.eaglehill.us/NENAonline/supplfiles/n17-2-Boyce-s1, and, for BioOne subscribers, at http://dx.doi. org/10.1656/N840.s1). An additional 6 species are listed by Jones (2008) as occurring in Kentucky, but I was either unable to find county occurrences and/or there is some doubt as to whether they are spreading from introduced sites (Jones 2008); these include Ribes aureum Pursh var. villosum DC. (Golden Currant), R. rubrum L. (Cultivated Currant), Rosa gallica L. (French Rose), R. rugosa Thunb. (Rugosa Rose), Spiraea thunbergii Siebold ex Blume (Thunberg’s Meadowsweet), and Tamarix parviflora DC. (Smallflower Tamarisk). The most widespread species (≥40 counties) are Rosa multiflora (Multiflora Rose; 84), Elaeagnus umbellata (Autumn Olive; 52), Morus alba (Mulberry; 48), Lonicera maackii (Amur Honeysuckle; 47), Albizia julibrissin (Mimosa; 46), Euonymus alatus (46), and Ligustrum sinense (Common Chinese Privet; 40). The number of invasive shrub species showed a linear increase with the logarithm of Kentucky county population (Fig. 1). Six counties with active herbaria (Calloway, Campbell, Fayette, Madison, Rowan, and Warren) are found well above the linear regression line. Jefferson County, which contains Louisville and is Kentucky’s most populous county, is also above the regression line. A multiple linear regression with a dummy variable for herbarium presence in or adjacent to the county also showed significance (P = 0. 0160), indicating that invasive shrubs are more likely to be undercounted in counties remote from herbaria, i.e., most of Kentucky. The 0.90 and 0.95 2010 R.L. Boyce 5 quantile regression lines include 90 and 95%, respectively, of the data points under them (Fig. 1). Most of the points that lie close to the quantile regression lines are for counties with or near herbaria or with recently published checklists (data not shown). Thus, these lines are likely to be truer estimates of shrub abundance than the linear regression line. Taxonomy Shrubs from the families Rosaceae have been the most successful in invading Kentucky (18 species), followed by Caprifoliaceae (14) and Oleaceae (8) (Fig. 2). The large number of species in the genera Rosa, Lonicera, and Ligustrum are responsible for these trends (Appendix 1). Elaeagnaceae and Rhamnaceae have 4 and 3 species, respectively. Aceraceae, Celastraceae, Hydrangeaceae, Salicaceae, and Verbenaceae each have 2. The families Aquifoliaceae, Araliaceae, Berberidaceae, Cupressaceae, Fabaceae, Grossulariaceae, Hippocastanaceae, Malvaceae, Moraceae, Taxaceae, and Ulmaceae are each represented by 1 species. Timeframe of introduction A few shrubs (13) were introduced into the US before 1800 (Appendix 1). However, most (45) were introduced in the 19th and 20th centuries—with introductions likely still occurring now in the 21st century. Despite recognition Figure 2. Classification of Kentucky invasive shrub species by family. 6 Northeastern Naturalist Vol. 17, Monograph No. 7 of the problem of invasive species, a large number—88%—of these shrubs are still distributed by vendors in the US (Appendix 1). Virtually all of these species can be purchased on the web from international vendors. Native ranges of exotic shrubs Most invasive shrubs in the US are from two regions of the world— eastern Asia and western Eurasia (including Europe, north Africa, and western Asia; Fig. 3). Kentucky has a climate similar to eastern Asia, so it is unsurprising that Asian shrubs do well in this part of the country. Europe is well-represented because US gardeners often follow European gardening traditions and use European plants, and the Kentucky climate is similar enough to that of Europe for many European shrubs to survive. Habitats in the US Most invasive shrubs in Kentucky live in a variety of different habits in the US (and therefore presumably in Kentucky); the specific habitats are described in Supplemental Table 2 (available online at http://www. eaglehill.us/NENAonline/suppl-files/n17-2-Boyce-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/N840.s1). By grouping these habitats into broad categories, however, we can see what kinds of habitats invasive shrubs generally select. More than 95% invade disturbed and/or open habitats (Fig. 4). This finding is not surprising, given that invasive plants are often found in resource-rich disturbed habitats (e.g., Drake et al. 1989, Hobbs and Huenneke 1992). Almost half also invade riparian zones, probably because these areas often are also disturbed and are rich in other resources. Almost two-thirds will invade open-canopy forests, while less Figure 3. Regions of the world where Kentucky invasive shrubs are native. 2010 R.L. Boyce 7 than 1/4 can invade closed-canopy forest, which appears to be due to differences in shade tolerance (see below). Physiological characteristics Seed reproduction and vectors. More than three-quarters of invasive shrubs have a heavy, conspicuous, or persistent fruit crop (Fig. 5), which is attractive to a variety of animals (Fig. 6; see also Supplemental Table 3, available online at https://www.eaglehill.us/NENAonline/ suppl-files/n17-2-Boyce-s1, and, for BioOne subscribers, at http:// dx.doi.org/10.1656/N840.s1). While most of the other shrubs for which data are available do not produce attractive fruits, they do produce heavy seed crops. These findings are not surprising, because many of these shrubs have escaped from gardens, where they are often grown for their flowers, fruit, or both, and gardeners usually prefer plants that bloom and/or yield prolifically. It is common for shrubs to produce large numbers of small fruits, so birds are responsible for spreading more than 30 of these species (Fig. 6). A number of other animals also spread these plants. Wind, human activities, water, and seed are also responsible for spreading some species. Vegetative reproduction. Almost three-quarters (47 of 68) of these species can reproduce vegetatively or asexually (Supplemental Table 3, available online at https://www.eaglehill.us/NENAonline/suppl-files/n17-2-Boyce-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/N840.s1). This trait allows some species to dominate an area more quickly than would be pos- Figure 4. Habitat type in which Kentucky invasive shrubs can grow. Many species can grow in more than one habitat type, and thus percentages total to more than 100%. 8 Northeastern Naturalist Vol. 17, Monograph No. 7 Figure 5. Sexual reproduction modes used by Kentucky invasive shrubs. “Fruit crop” means an attractive fruit that is consumed by animals, whereas “seed crop” means that fruits are not usually consumed, and therefore seeds are spread by other vectors. ND = no data. Species with multiple fruit classifi- cations were placed in the “heavy fruit crop” category. Figure 6. Dispersal agents used by Kentucky invasive shrubs. Many species use more than one agent. ND = no data. 2010 R.L. Boyce 9 sible if they relied only on sexual reproduction. It also means that special care needs to be taken during control, as plant parts left on a site may regenerate. Shade tolerance. A total of 46 invasive shrub species are partially shade tolerant (Fig. 7, Appendix 2), allowing them to invade partially open, undisturbed forests, as well as more open areas. Eight species are intolerant and are restricted to open and/or disturbed areas. Only 13 species are considered to be shade tolerant; these species often have the ability to invade closedcanopy forest. Leaf habit. More than half of invasive shrubs are classified as deciduous (Fig. 8, Appendix 2). Few are evergreen, but many (≈30%) have an extended leaf period, i.e., they leaf out early and/or retain leaves longer than native woody plants. In the literature, these plants are referred to by a variety of terms, including semi-deciduous, tardy-deciduous, extended-deciduous, and semi-evergreen; here, I classify them as “deciduous-extended”. Soil and water requirements. Since invasive shrubs grow in a wide variety of habitats, it is not surprising that soil and water requirements are quite variable (Appendix 2). More than 95% grow on what is defined as a “wide range” of soil types, which may aid in the initial establishment of invasive species. While water requirements are more variable, close to one-third grow under a wide range of availabilities, and almost 15% are drought tolerant or resistant (Fig. 9). This plasticity in water requirements no doubt also aids in the initial establishment of these species. Effects Almost all shrubs can directly suppress other plants via competition, so here I focus on more indirect effects of invasive shrubs. The indirect Figure 7. Shade tolerance of Kentucky invasive shrubs. ND = no data. 10 Northeastern Naturalist Vol. 17, Monograph No. 7 effects of more than one-third of these shrubs have not been determined (Fig. 10; Supplemental Table 4, available online at http://www.eaglehill. us/NENAonline/suppl-files/n17-2-Boyce-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/N840.s1); clearly, much more study is required. Some of the common indirect effects include decreased community richness, alteration of nutrient cycling, allelopathy, competition for pollinators, and restriction of wildlife use (Fig. 10; Supplemental Table 4, available online at https://www.eaglehill.us/NENAonline/suppl-files/n17-2-Boyce-s1, and, for BioOne subscribers, at http://dx.doi.org/10.1656/N840.s1). Some species can change (usually enhance) soil N, an ability common to all the N-fixing species, i.e., all members of Elaeagnaceae and Fabeaceae (Appendix 2). Other effects include being a host for diseases that affect other plants, changes in fire regimes, and interbreeding with native species (Fig. 10). Control Physical control. The most effective form of physical control involves uprooting (Fig. 11, Appendix 3). This approach is used most often on young shrubs, as they are easier to uproot. It is also easier to extract their whole root systems, which is important because most of the shrubs for which data are available will resprout after cutting (Appendix 3). Cutting alone is effective on only about one-quarter of all species (Fig.11) and often needs to be repeated. The effectiveness of physical control for a substantial fraction of invasive shrubs has not been determined. Fire control. More than two-thirds of the species have not been evaluated (Fig. 12, Appendix 3). Of the ones that have, only a few show complete Figure 8. Leaf habit of Kentucky invasive shrubs. Deciduous- extended includes a variety of terms including semi-evergreen or semi-deciduous. Deciduous or evergreen includes plants that can exhibit either strategy, depending on location. 2010 R.L. Boyce 11 Figure 9. Water requirements of Kentucky invasive shrubs. ND = no data. Figure 10. Indirect effects of Kentucky invasive shrubs. ND = no data. 12 Northeastern Naturalist Vol. 17, Monograph No. 7 control by fire alone, and that is only if it is repeated. More studies have reported that fire control is partially effective, and it often works best when combined with other treatments (Appendix 3). Some species, of course, are actually stimulated by fire, either through resprouting, heavy seed germination, or a combination. Chemical control. Control with herbicides is currently the most effective way to control invasive shrubs, 40 of which can be controlled by the application of at least one herbicide (Appendix 3). Effectiveness has still not been determined on 28 out of the 68 species, however. Herbicides are often combined with cutting, where herbicide is painted or sprayed onto freshly cut stumps. Specific herbicides and their methods of application will not be discussed here, but can be found in the cited references. Some of the most effective herbicides, e.g., glyphosate, are broad-spectrum and will kill desired species as well, and so they must be used carefully. Land managers may also hesitate to use a chemical agent for an infestation over a wide area, due to possible detrimental environmental effects and costs of herbicide applications. Biological control. More than half of the shrub species have not been evaluated (Fig. 13, Appendix 3). Grazing animals, such as goats, sheep, cattle, and chickens, have shown some promise for controlling a few species. Six species show potential for control by biological agents, while no biological agent has been found so far for 13 species. Species likely to become widespread All of the eight most widespread species have high ordination scores, i.e., high apparent number of counties (Appendix 1, Fig. 14). The FSO is statistically significant (P = 0.0135), showing that shrub occurence is correlated to the suite of physiological characteristics chosen for the similarity Figure 11. Physical or mechanical control methods that have been found to be effective in controlling shrubs that are invasive in Kentucky. 2010 R.L. Boyce 13 matrix. A total of 17 other species also have high ordination scores, higher than the minimum of the seven species currently most widespread. These species are Aesculus parviflora, Berberis thunbergii, Crataegus monogyna, Elaeagnus angustifolia, E. pungens, Kerria japonica, Ligustrum ovalifolium, Figure 12. Fire control methods for shrubs that are invasive in Kentucky. Figure 13. Types of biological control agents found for Kentucky invasive shrubs. NK = report that none are known. ND = no report of either an effective agent or a lack of one. 14 Northeastern Naturalist Vol. 17, Monograph No. 7 L. vulgare, Lonicera tatarica, Lonicera x bella, Rhamnus cathartica, Rhodotypos scandens, Rubus armeniacus, R. phoenicolasius, Salix purpurea, Ulmus pumila, and V. opulus var. opulus. Species with high ordination scores are similar to widespread species, while not similar to less commonly occurring species (Roberts 1986). Thus, these 17 species have characteristics of species already widespread and could in turn become widespread (found in ≥40 counties) over time. As these species increase their range, the strength of their ordination scores is expected to increase. Discussion The number of invasive shrubs in Kentucky is substantial; there are 68 with good documentation, while there are probably others that have not yet Figure 14. Fuzzy set ordination (FSO) of invasive shrub species in Kentucky. The similarity matrix used in the ordination was drawn from invasive shrub characteristics, as described in the text, and the factor used in the ordination was the number of counties in which the species were found. The ordination is statistically significant (Spearman r = 0.298, P = 0.014). Points with abbreviations (first two letters of generic and specific epithets) and in boldface indicate species already widely distributed. The 17 points with abbreviations in plain text indicate species with high normalized ordination scores (apparent number of counties) that are greater than the minimum ordination score for already-widespread species. Note that three species are clustered tightly together. 2010 R.L. Boyce 15 been recognized. The USDA PLANTS Database (USDA NRCS 2008) lists some of the species included here as having life forms of both a shrub and a tree. It is often difficult to decide exactly how to classify larger woody plants, as some can grow as a tree (i.e., with a single stem) under some circumstances, while they can grow as a shrub (i.e., with many stems) under others. For example, Morus alba can occur as a tree as well as a shrub in Kentucky (R.L. Boyce, pers. observ.). Some of the species listed here were not described in the recent catalog for Kentucky woody plants by Clark and Weckman (2008). However, even with the more liberal criteria employed in the current study, it is clear that that invasive shrubs are undercounted in most regions of the state. Madison County is home to Eastern Kentucky University and Berea College, both with very active taxonomists (Ross Clark, Ron Jones, Ralph Thompson, and Timothy Weckman), and it lies well above even the quantile regression lines (Fig. 1). Jefferson County, which includes Louisville, Kentucky's second largest city, also lies near the quantile regression lines. The University of Louisville no longer has an active herbarium, but its collection was incorporated into the Western Kentucky University Herbarium (SERNEC 2010). In addition, many academic institutions as well as natural resource agencies are located in Louisville, and professionals from these organizations may have reported sightings to the USDA PLANTS and EDDMapS databases. Thus, even these quantile regressions appear to be underestimates of the true number of invasive shrubs that occur in Kentucky. The most well-represented families of invasive woody plants in the Czech Republic were Rosaceae, Caprifoliaceae, and Oleaceae, as they are in the current study (Křivánek and Pyšek 2008). These three families also account for 12 of the 22 invasive shrub species listed on the IPANE database for New England (Mehrhoff et al. 2004). Frappier and Eckert (2003) found that the factors which were the best predictors of invasiveness for woody plants in New Hampshire were resprouting ability, lower shade tolerance, tolerance of low soil fertility, and being an angiosperm. Herron et al. (2007) also found that invasive shrubs in New England were not evergreen and did not have wind-dispersed seeds; however, there was no association with shade tolerance nor possession of bird-dispersed fruits. The results from the current study also show strong associations with deciduousness/nonevergreenness, resprouting, and tolerance of low soil fertility. While some of the other traits, such as bird-dispersed fruits and lower amounts of shade tolerance, may also be important predictors of invasiveness in Kentucky, Herron et al. (2007) cautioned that these traits may not sufficiently distinguish invasive shrubs from non-invasive ones. Some of the included species are not currently having much impact. However, lag phases for introduced shrubs can be quite long. Křivánek and Pyšek (2008) showed that the average lag phase for invasive shrubs in the Czech Republic, i.e., the time between introduction and escape, was 110 years, ranging from 20 to 257 years. As a large proportion of the species listed here have been present in Kentucky, with a similar temperate climate, for that time or less, 16 Northeastern Naturalist Vol. 17, Monograph No. 7 even species with very restricted distributions should be closely monitored, as they may still be in the lag phase. The FSO suggests that 17 species may currently be in lag phases; these species should be monitored closely and perhaps be treated most aggressively at present. Some of these species, such as Berberis thunbergii, Elaeagnus spp., Lonicera spp., and Rhodotypos scandens, are already recognized as major problems in other states. Others, such as Aesculus parviflora and Kerria japonica, are not, but they do have the same set of characteristics as species already widespread in Kentucky. It is clear that the most heavily populated areas of the state are serving as sources of invasive shrubs, probably most of which have escaped from cultivation. Thus, we need both a better tally of those regions of the state that have not been well-surveyed, as well as closer monitoring of more populated regions that are serving as sources for new introductions. One of the first steps needed to deal with invasive shrubs is to recognize the scope of the problem. Some states, notably Florida (Invasive Species Working Group; http://iswgfla.org/) and California (Department of Fish and Game; http://www.dfg.ca.gov/invasives/), have state agencies that monitor the presence and spread of invasive species. Other states, such as Tennessee (Tennessee Exotic Pest Plant Council; http://www.tneppc.org/), have wellestablished nongovernmental organizations that play a similar role. The University of Montana INVADERS database (http://invader.dbs.umt.edu/) plays a similar role in five northwestern states. Kentucky is a member of the Southeast Exotic Pest Plant Council (http://www.se-eppc.org/) and has an active state chapter (http://www.se-eppc.org/ky/). This organization needs to be supported in its efforts to monitor and control the spread of invasive plants in Kentucky. State (and federal) governments need to consider greater regulation of plants that are both known and suspected to be invasive. Most of the shrubs described in this study are known to be invasive yet can be purchased on the web and/or local nurseries. While Kentucky and many other states do have noxious-plant laws, few invasive shrubs are included. For example, only Rosa multiflora is on Kentucky’s list (Kentucky Revised Statutes 1990). Thus, vendors and purchasers are unlikely to know that they are dealing with invasive plants. Clearly, both vendors and consumers need to be educated about invasive plants. Stronger regulations, both at the state and federal levels, would also help control the spread of invasive shrubs in particular and invasive plants in general. We may also want to consider regulating plants that currently are not widespread, but have traits common to invasives that may make them problematic in the future. From this survey, it is clear that most invasive shrubs in Kentucky share a number of properties, including resprouting ability, partial shade tolerance, a heavy fruit crop that is attractive to birds, and extended deciduous or deciduous habit. Certain families, such as Rosaceae, Caprifoliaceae, and Oleaceae, also contain a large number of invasive shrubs and thus should be regarded with suspicion. Not all of these properties may be good predictors of invasiveness, but shrubs that fall in several of these categories appear to be at 2010 R.L. Boyce 17 high risk of becoming invasive, and regulation may be merited before these shrubs become a problem. More research of all kinds is also needed for the invasive shrubs that we do recognize at present. The physiological requirements of many species are known either poorly or not at all. The potential habitats of some shrubs also need more study. Clearly, much more work needs to be put into discovering better control methods. Both fire and biological control methods merit much more work than they have received to date. Also, more work needs to be done on the direct and indirect effects of invasive shrubs. We know that in many cases, invasive shrubs displace or prevent the establishment of native tree species. It is clear, however, that shrubs do this in a variety of ways (e.g., Gordon 1998). It is also clear that they can have numerous indirect effects on forest ecosystems (e.g., Horvitz et al. 1998). Knowledge of these effects is critical if we are to successfully control invasive species and restore native forests. Other steps need to be taken as well (Webster et al. 2006). This study shows that certain shrubs, such as Rosa multiflora and Elaeagnus umbellata, are quite widespread. However, a wide distribution does not always translate into a large impact, especially if shrub density remains low. Local shrub density is probably a better indication of impact to local ecosystems, but these data are generally lacking. An enhanced understanding of their local impact would allow us to rank shrubs by the threat they represent and would allow control methods to be prioritized. Because timber harvests and other human activities that disturb forests aid in the spread of many of these invasive shrubs, invasive treatment and monitoring efforts need to be included in these activities. This approach will also mean more cooperation between public and private sectors. Finally, the best control methods need to be communicated and used. Acknowledgments I would like to thank Maggie Whitson, both for permission to use the John W. Theriet Herbarium at Northern Kentucky University and for her extraordinary job of reviewing this manuscript. Literature Cited ABC. 2008. Gardening Australia – Fact Sheet: Pete’s Garden. Available online at http:// www.abc.net.au/gardening/stories/s1298518.htm. Accessed 14 January 2010. Adams, D.W. 2004. Restoring American Gardens: An Encyclopedia of Heirloom Ornamental Plants, 1640–1940. Timber Press, Portland, OR. 420 pp. Albrecht, L.A. 2001. Jetbead: A new invasive threat. Northeastern Weed Science Society Newsletter. April 2001:7. 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Available online at http://www.census.gov/popest/counties/tables/CO-EST2004-01-21.xls. Accessed 14 January 2010. USDA Natural Resources Conservation Service (NRCS). 2008. The PLANTS Database. National Plant Data Center, Baton Rouge, LA 70874-4490 USA. Available online at http://plants.usda.gov/. Accessed December 8, 2008. Van Clef, M. 2008. Invasive Species Phenology and Treatment Recommendations. Friends of Hopewell Valley Open Space, Pennington, NJ. 4 pp. Available online at http://www.fohvos.org/pdfs/CJISSTPhenology_and_Treatment_Target_Species_ 2008.pdf. Accessed 14 January 2010. Victoria Department of Primary Industries (DPI). 2009. Invasiveness Assessment – Purple Osier (Salix purpurea) in Victoria (Nox). Available online at http:// www.dpi.vic.gov.au/dpi/vro/vrosite.nsf/pages/invasive_purple_osier. Accessed 14 January 2010. Washington State University (WSU) Clark County Extension. 2010. Leatherleaf viburnum – Viburnum rhytidophyllum – PNW Plants. Available online at http://www.pnwplants.wsu.edu/PlantDisplay.aspx?PlantID=129. Accessed 14 January 2010. Weakley, A.S. 2008. Flora of the Carolinas, Virginia, and Georgia, and Surrounding Areas. The University of North Carolina Herbarium, Chapel Hill, NC. 1015 pp. Available online at http://herbarium.unc.edu/flora.htm. Accessed 14 January 2010. Webster, C.R., M.A. Jenkins, and S. Jose. 2006. Woody invaders and the challenges they pose to forest ecosystems in the eastern United States. Journal of Forestry 104:366–374. Weeds Australia. 2010. Weeds Australia—Weed identification. Available online at http://www.weeds.org.au/cgi-bin/weedident.cgi?tpl=ibra.tpl&ibra=all. Accessed 14 January 2010. Welch, W.C. 2001, Jan–Feb. Winter honeysuckle, Lonicera fragrantissima. Horticulture Update (Texas Agr. Ext. Service). Available online at http://aggie-horticulture. tamu.edu/extension/newsletters/hortupdate/jan01/art1jan.html. Accessed 14 January 2010. 26 Northeastern Naturalist Vol. 17, Monograph No. 7 Wieseler, S. 2009a. PCA Alien Plant Working Group—Common Buckthorn (Rhamnus cathartica). Available online at http://www.nps.gov/plants/alien/fact/rhca1. htm. Accessed 14 January 2010. Wieseler, S. 2009b. PCA Alien Plant Working Group—Siberian Elm (Ulmus pumila). Available online at http://www.nps.gov/plants/alien/fact/ulpu1.htm. Accessed 14 January 2010. Williams, C.E. 2009. PCA Alien Plant Working Group – Exotic Bush Honeysuckles (Lonicera spp.). Available online at http://www.nps.gov/plants/alien/fact/loni1. htm. Accessed 14 January 2010. Wilson, L., J. Davison, and E. Smith. 2006. Grazing and browsing guidelines for invasive rangeland weeds. Pp. 142–167, In K. Launchbaugh (Ed.). Targeted Grazing: A Natural Approach to Vegetation Management and Landscape Enhancement. American Sheep Industry Association, Englewood, CO. 199 pp. Available online at http://www.cnr.uidaho.edu/rx-grazing/Handbook/Chapter_15_Targeted_Grazing. pdf. Accessed 14 January 2010. Wisconsin Department of Natural Resources (WDNR). 2009. Invasive Species: Plants. Available online at http://dnr.wi.gov/invasives/plants.asp. Accessed 14 January 2010. Woods, K.D. 1993. Effects of invasion by Lonicera tatarica L. on herbs and tree seedlings in four New England forests. American Midland Naturalist 130:62–74. Zheng, H., Y. Wu, J. Ding, D. Binion, W. Fu, and R. Reardon. 2004. Invasive Plants of Asian Origin Established in the United States and their Natural Enemies. Volume 1. USDA Forest Service FHTET-2004-05. 147 pp. Available online at http:// www.invasive.org/weeds/asian/. Accessed 14 January 2010. 2010 R.L. Boyce 27 Appendix 1. Invasive shrubs found in Kentucky. Data are taken from the PLANTS database (USDA NRCS 2008) and from the noted references. Botanical, common, and family names follow the PLANTS database (USDA NRCS 2008). Native range and introduction date, if known, are also given. Some introduction dates, especially those attributed to Rehder (1986), may refer to introductions to Europe. A species is noted as currently distributed if described as such in the literature or found for sale on the internet by a US distributor. Note that almost all species are available internationally. Date = US introduction date, # = number of counties in which species was found, and Current? = currently distributed in Kentucky. Numerical superscript references to sources: 1. Rehder 1986. 2. Browne 1846. 3. PFAF 2008. 4. FHP Invasive Plants 2010. 5. Miller 2003. 6. SE-EPPC 2003. 7. Remaley 2009b. 8. Mehrhoff et al. 2004. 9. Swearingen et al. 2002. 10. Rhoads and Block 2002. 11. WDNR 2009. 12. Bargeron et al. 2003. 13. Alverson and Sigg 2005. 14. Muzika and Swearingen 2009. 15. Deiter 2005. 16. Tu 2003. 17. Smith 1997. 18. Sather and Eckhart 1987. 19. Martin 2005. 20. Brand 2001. 21. Frappier et al. 2004. 22. Christman 2008. 23. Batcher 2000. 24. Zheng et al. 2004. 25. Urbatsch 2000. 26. Langeland and Burks 1998. 27. Welch 2001. 28. Batcher and Stiles 2000. 29. Luken and Thieret 1995. 30. Gorchov and Trissel 2003. 31. Hutchinson and Vankat 1997. 32. Gould and Gorchov 2000. 33. Woods 1993. 34. Converse 1984. 35. Gooseberry Limited 2010. 36. Hedgerowmobile 2010. 37. Amrine 2002. 38. Eckardt 1987. 39. Hoshovsky 1989. 40. Hoshovsky 2005. 41. Johnson and Hoagland 1999. 42. Weakley 2008. 43. Spencer 2009. 44. GRIN 2009. 45. Tucker 1996. 46. Remaley 2009a. 47. Tenaglia 2007. 48. Adams 2004. 49. Cochran 2000. 50. Wieseler 2009b. Species Common name Family Native range Date # Current? Acer campestre L. Hedge Maple Aceraceae Europe, N Africa, W Asia1 18222 1 Yes A. ginnala Maxim. Amur Maple Aceraceae N China, Korea, Japan1 ≈18601 1 Yes Aesculus parviflora Walter Bottlebrush Buckeye Hippocastanaceae S Carolina, Alabama to Florida1 17851 1 Yes Albizia julibrissin Durazz. Silktree Fabaceae S to E Asia3 17451, 3–7 46 Yes Berberis thunbergii DC. Japanese Barberry Berberidaceae Japan1, 8–12 18641, 8–11 25 Yes Callicarpa dichotoma (Lour.) Purple Beautyberry Verbenaceae China, Japan1 18571 1 Yes K. Koch Caryopteris x clandonensis Bluebeard Verbenaceae Hybrid between C. incana 19331 1 Yes hort. ex Rehder and C. mongholica1 Chaenomeles speciosa Flowering Quince Rosaceae China1, 3 Before 18001 13 Yes (Sweet) Nakai Crataegus monogyna Jacq. Oneseed Hawthorn Rosaceae Europe, N Africa, S Asia3, 13 1800s13 2 Yes Deutzia scabra Thunb. Fuzzy Pride-of-Rochester Hydrangeaceae Japan, China1, 3–4 18221 6 Yes Elaeagnus angustifolia L. Russian Olive Elaeagnaceae Europe, W Asia1, 5, 14–16 Late 1800s14 10 No E. pungens Thunb. Thorny Olive Elaeagnaceae Japan1 18301 1 Yes E. umbellata Thunb. Autumn Olive Elaeagnaceae China, Korea, Japan1, 5–6, 9, 17–18 18301, 5, 9, 17–18 52 Yes Eleutherococcus pentaphyllus Ginseng Araliaceae Japan1 18591 4 Yes (Siebold & Zucc.) Nakai 28 Northeastern Naturalist Vol. 17, Monograph No. 7 Species Common name Family Native range Date # Current? Euonymus alatus (Thunb.) Winged Burning Bush Celastraceae NE Asia, Japan, central ≈18605, 9, 19 46 Yes Siebold China1, 3, 5, 9, 19 E. europaeus L. European Spindletree Elaeagnaceae Europe, W Asia1 ND 1 Yes E. kiautschovicus Loes. Creeping Strawberry Bush Celastraceae China1, 20 ≈18491 1 Yes Forsythia suspensa (Thun.) Weeping Forsythia Oleaceae China1 18331 2 Yes Vahl F. viridissima Lindl. Green-stemmed Forsythia Oleaceae China1 19171 1 Yes Frangula alnus Mill. Glossy Buckthorn Rhamnaceae Europe, W Asia, N Africa1, 8, 21 Before 18001, 8 4 Yes Hibiscus syriacus L. Rose of Sharon Malvaceae E Asia1, 3–4, 22 1600s?1, 22 18 Yes Ilex cornuta Lindl. & Paxton Chinese Holly Aquifoliaceae E China1 18461 1 Yes Kerria japonica (L.) DC. Japanese Rose Rosaceae China, Japan1 18341 4 Yes Ligustrum amurense Carrière Amur Privet Oleaceae China1, 23 18601 5 Yes L. obtusifolium Siebold & Border Privet Oleaceae Japan1, 8, 23 18858 17 Yes Zucc. L. ovalifolium Hassk. California Privet Oleaceae Japan1, 21 18471 4 Yes L. sinense Lour. Chinese Privet Oleaceae China1, 5, 8, 23–26 18521, 25–26 40 Yes L. vulgare L. European Privet Oleaceae Europe, N Africa1, 5, 23 Mid-1800s5 22 Yes Lonicera fragrantissima Sweet Breath of Spring Caprifoliaceae China24, 27 After 18451, 27 3 Yes Lindl. & Paxton L. maackii (Rupr.) Amur Honeysuckle Caprifoliaceae China, Korea, Japan1, 5, 8, 24, 28–32 1890s8, 28–32 47 Yes Herder L. morrowii A. Gray Morrow’s Honeysuckle Caprifoliaceae Japan1, 6, 8, 28 ≈18751, 6, 8, 28 8 Yes L. standishii Jacques Standish’s Honeysuckle Caprifoliaceae Europe, Asia1, 9 ≈18451 2 Yes L. tatarica L. Tatarian Honeysuckle Caprifoliaceae C Asia, S Russia1, 6, 8, 28, 33 17521, 6, 8, 28, 33 4 Yes L. xylosteum L. Dwarf Honeysuckle Caprifoliaceae Europe, Asia1, 8 Before 19611 3 Yes Lonicera x bella Zabel Bell’s Honeysuckle Caprifoliaceae Hybrid between L. morrowii Before 18781, 4 1 Yes and L. tatarica1, 4, 8, 28 Lonicera x minutiflora Zabel Small-flowered Honeysuckle Caprifoliaceae Hybrid between L. morrowii 18781 2 No and L. xylosteoides1 Lonicera x xylosteoides Tausch Fly Honeysuckle Caprifoliaceae Hybrid between L. tatarica Before 18381 1 Yes and L. xylosteum1 Malus baccata (L.) Borkh. Siberian Crab Apple Rosaceae E Asia1, 3 17841 2 Yes 2010 R.L. Boyce 29 Species Common name Family Native range Date # Current? Morus alba L. White Mulberry Moraceae E Asia1, 9, 24 1700s9 48 Yes Philadelphus coronarius L. Sweet Mock Orange Hydrangeaceae Europe1 Before 17701 2 Yes Platycladus orientalis (L.) Oriental Arborvitae Cupressaceae N China, Korea1 Before 17371 1 Yes Franco Prunus cerasus L. Sour Cherry Rosaceae SE Europe to W Asia1, 3 ND 7 Yes P. mahaleb L. Mahaleb Cherry Rosaceae Europe, W. Asia1 Before 18462 20 Yes Pyracantha crenulata Nepalese Firethorn Rosaceae Himalayas1 ≈18441 1 Yes (D. Don) Roem. Rhamnus cathartica L. Common Buckthorn Rhamnaceae Europe, N Africa, N and Before 18008, 34 9 No W Asia1, 3–4, 9, 34 R. davurica Pall. Dahurian Buckthorn Rhamnaceae E Asia1, 3 18171 7 Yes Rhodotypos scandens Jetbead Rosaceae China, Korea, Japan1, 9 18661, 9 5 Yes (Thunb.) Makino Ribes uva-crispa L. European Gooseberry Grossulariaceae Europe, NW Africa, SW Asia3, 35 ND 1 Yes Rosa canina L. Dog Rose Rosaceae Europe1, 3, 36 ND 10 Yes R. eglanteria L. Sweetbriar Rose Rosaceae Europe1, 3 ND 21 Yes R. micrantha Borrer ex Sm. Smallflower Sweetbrier Rosaceae Europe, Mediterranean1, 3 ND 3 No R. multiflora Thunb. Rambler Rose Rosaceae Japan, Korea, China6, 8–9, 37–38 Before 18686, 8–9, 38 84 Yes R. wichuraiana Crép. Memorial Rose Rosaceae E Asia1, 3 18911 17 Yes Rubus armeniacus Focke Himalayan Blackberry Rosaceae W Europe1, 39–40 18851, 39–40 2 No R. bifrons Vest ex Tratt. Himalayan Berry Rosaceae Europe3, 41–42 ND 2 No R. phoenicolasius Maxim. Wineberry Rosaceae Japan, Korea, China1, 8–9, 43 18761, 8–9, 43 18 Yes Salix atrocinerea Brot.A Large Gray Willow Salicaceae Europe, N Africa, Asia1, 3, 44–45 ND 5 No S. purpurea L. Purpleosier Willow Salicaceae Europe, central Asia, N Africa, ND 2 Yes Japan1, 3, 20 Spiraea japonica L. f. Japanese Meadowsweet Rosaceae Japan, Korea, China1, 3–4, 6, 46 18706, 8, 46 12 Yes S. prunifolia Siebold & Zucc. Bridalwreath Spirea Rosaceae E Asia1, 3, 20, 47 18641 3 Yes Syringa vulgaris L. Common Lilac Oleaceae SE Europe42, 44 1700s1, 48 7 Yes Taxus baccata L. English Yew Taxaceae Europe, N Africa, W Asia1 early 1900s49 1 Yes Ulmus pumila L. Siberian Elm Ulmaceae N China, E Siberia, Manchuria, 18601 13 Yes Korea1, 3, 50 30 Northeastern Naturalist Vol. 17, Monograph No. 7 Species Common name Family Native range Date # Current? Viburnum lantana L. Wayfaringtree Caprifoliaceae Europe, W. Asia1 ND 1 Yes V. opulus L. var. opulus European Cranberrybush Caprifoliaceae Europe, N Africa, N Asia1, 3–4, 44 After 16501 8 No V. rhytidophyllum Hemsl. Leatherleaf Arrowwood Caprifoliaceae C and W China1 19001 1 Yes V. setigerum Hance Tea Viburnum Caprifoliaceae China1 19011 2 Yes V. sieboldii Miq. Siebold’s Arrowwood Caprifoliaceae Japan1 18801 1 Yes AThe USDA PLANTS database (USDA NRCS 2008) classifies Salix cinerea L. ssp. oleifolia (Sm.) Macreight as a synonym for S. atrocinerea and S. cinerea L. ssp. cinerea as a synonym for S. cinerea L. Clark and Weckman (2008) classified both as subspecies of S. cinerea and mapped them together, so some of the listed county occurrences may not be S. atrocinerea. 2010 R.L. Boyce 31 Appendix 2. Physiological characteristics and soil and moisture requirements of invasive shrubs. For shade tolerance, T = totally shade tolerant, P = partially tolerant, and I = intolerant. For leaf habit, E = evergreen, DE = deciduous-extended, and D = deciduous. Under soils requirements, WR = wide range. Nitrogenfixing species are also noted. ND = no data were found. Numerical superscript source references: 1. PFAF 2008. 2. FHP Invasive Plants 2010. 3. Remaley 2009b. 4. Miller 2003. 5. SE-EPPC 2003. 6. Swearingen 2009. 7. Swearingen et al. 2002. 8. Rhoads and Block 2002. 9. Randall and Marinelli 1996. 10. Mehrhoff et al. 2004. 11. MBG 2009. 12. Evans 2003. 13. Brand 2001. 14. Alverson and Sigg 2005. 15. Muzika and Swearingen 2009. 16. Brusati 2005. 17. Deiter 2005. 18. Tu 2003. 19. Sather and Eckardt 1987. 20. Martin 2005. 21. BackyardGardener 2010. 22. Converse 1984. 23. Plant Information Databases 2010. 24. Faucon 2005. 25. Bushes and Shrubs 2003. 26. Horticopia 2004. 27. Urbatsch 2000. 28. Williams 2009. 29. Zheng et al. 2004. 30. Welch 2001. 31. Batcher and Stiles 2000. 32. Boiteau et al. 2009. 33. Woods 1993. 34. Kling 2010. 35. Timberline Landscaping 2010. 36. Wieseler 2009a. 37. Hoch 2001. 38. Albrecht 2001. 39. Bergmann and Swearingen 2009. 40. Eckardt 1987. 41. Dana and Lerner 2006. 42. Langeland and Burks 1998. 43. Hoshovsky 1989. 44. Hoshovsky 2005. 45. Spencer 2009. 46. Rhodus 2002. 47. Remaley 2009a. 48. Paghat’s Garden 2005. 49. Wieseler 2009b. 50. Invasive Species 2009. 51. Kline 2010. 52. WSU Clark County Extension 2010. Shade Species tolerance Leaf habit Soil requirements Moisture requirements N-fixer Acer campestre P1 D1 WR, tolerates calcareous1 Moist1 No Acer ginnala P1 D1 WR1 Moist1 No Aesculus parviflora T1 D1 WR1 Moist well-drained1 No Albizia julibrissin P1–5 D1–2, 4 WR1–3 WR1–2, 4 Yes1–2, 4 Berberis thunbergii T5–9 E or D5–8, 9–10 WR1, 9 Drought-tolerant1, 5–6 No Callicarpa dichotoma P11-12 D11-12 WR12 WR12 No Caryopteris x clandonensis I11, 13 D11, 13 Average11 Drought-tolerant11 No Chaenomeles speciosa T1 D1 WR, not high pH1 Drought-tolerant11 No Crataegus monogyna P1, 9 D1, 9, 14 WR1, 14 Drought-tolerant1 No Deutzia scabra P1 D1–2 WR1 WR2 No Elaeagnus angustifolia P15–16 D4, 9, 17 WR, pH 6–99–10, 15–18 Dry to moist9–10, 15–18 Yes4, 10 E. pungens T1, 4 E1, 4 WR, tolerates salt1, 4 Drought-tolerant1, 4 Yes1 E. umbellata I19 DE4, 9, 19 Tolerates poor soils, low pH10, 19 Drought-tolerant4–5, 7, 10, 19 Yes4–5, 7, 10, 19 Eleutherococcus pentaphyllus P1, 11, 13 DE13 WR1, 11, 13 Drought-tolerant11, 13 No Euonymus alatus T1, 9–10, 20 D1, 4, 9–10, 20 WR1, 10, 20 Well-drained, dry to moist1, 9–10 No E. europaeus P1, 13 DE13 WR1, 13 WR but well-drained1, 13 No E. kiautschovicus P13, 21 DE13, 21 WR13, 21 Well-drained13, 21 No Forsythia suspensa T1, 11 D1, 11 WR1 Moist well-drained1 No F. viridissima P1, 11, 13 D1, 11, 13 WR1, 11, 13 Moist well-drained1, 11 No 32 Northeastern Naturalist Vol. 17, Monograph No. 7 Shade Species tolerance Leaf habit Soil requirements Moisture requirements N-fixer Frangula alnus I10, 22 DE22 WR22 Tolerates high moisture2, 22 No Hibiscus syriacus P1, 23 D1–2, 23 WR1, 23 Well-drained1–2, 23 No Ilex cornuta P1, 11 E1, 11 WR1, 11 Moist well-drained1, 11 No Kerria japonica T1, 11, 13 D1, 11, 13 WR1 Moist well-drained1, 11, 13 No Ligustrum amurense P24 DE24 WR24 Well-drained24 No L. obtusifolium P1, 26 E, DE1, 10 WR1 Moist well-drained1, 26 No L. ovalifolium T1 E1 WR1 WR1 No L. sinense T4, 27 E, DE1, 4, 9, 27 WR1, 26 Mesic best1, 26 No L. vulgare P1 DE27 WR1 WR1 No Lonicera fragrantissima P4, 28 DE4, 28–30 WR, including acidic and poor30 Drought-tolerant30 No L. maackii P4, 10, 28, 31 DE1, 4, 9–10, 28, 30 WR, prefers calcareous10, 31 WR13 No L. morrowii P4, 28, 31 DE4–5, 32 WR, prefers calcareous10, 31 Mesic best10, 31 No L. standishii P28 DE, D28, 32 WR28 Mesic best28 No L. tatarica P4–5, 10, 28 DE4–5, 28–29, 31, 33 WR31 WR31 No L. xylosteum P10, 28 D28 WR10 WR10 No Lonicera x bella P2, 10, 31 DE5, 28 WR31 WR31 No Lonicera x minutiflora ND ND ND ND No Lonicera x xylosteoides P34–35 DE34 WR34–35 Moist well-drained35 No Malus baccata P1 D1 WR1 Moist well-drained1 No Morus alba P1 D1 WR1 Drought-tolerant1 No Philadelphus coronarius P13 D13 WR13 WR34 No Platycladus orientalis P11. 13. 23 E11. 13. 23 WR13, 23 WR13, 23 No Prunus cerasus P1 D1 WR1 Moist well-drained1 No P. mahaleb P1 D1 WR1 Moist well-drained1 No Pyracantha crenulata P1 E1 WR1 Moist well-drained1 No Rhamnus cathartica P1–2, 10, 22 DE10 WR, neutral-basic pH, WR1–2, 10, 36 No prefers calcareous1–2, 10, 22, 36 Rhamnus davurica P1 D1 WR1 Moist1 No Rhodotypos scandens T2, 11, 37–38 D2, 7, 11, 37–38 WR2, 11, 37–38 WR11, 37–38 No Ribes uva-crispa P1 D1 WR1 Moist well-drained1 No Rosa canina P1 D1 WR1 Moist or wet, well-drained1 No 2010 R.L. Boyce 33 Shade Species tolerance Leaf habit Soil requirements Moisture requirements N-fixer R. eglanteria P1 D1, 11 WR1 Moist well-drained1, 11 No R. micrantha P1 D1 WR, including high pH1 WR1 No R. multiflora T5, 7, 39–40 D15 WR, prefers deep, fertile soils5, 7, 39–40 WR, prefers well-drained and No moist5, 7, 39–40 R. wichuraiana P1 DE1, 41 WR1 Moist well-drained1 No Rubus armeniacus I42 DE43–44 WR43–45 Moist, tolerates flooding43–44 No R. bifrons P1 D1 WR1 Moist well-drained1 No R. phoenicolasius I1, 10, 45 D10, 42 WR1 Moist well-drained42, 45 No Salix atrocinerea I1 D1 WR1 Moist or wet1 No S. purpurea I1, 34 D1, 13 WR1, 46 WR1, 13, 34, 46 No Spiraea japonica P5, 47 D, DE2, 5, 47–48 WR2, 5, 7, 47 WR2, 5, 7, 47 No S. prunifolia P1, 13 D1, 13 WR1, 49 Moist, well-drained1, 13 No Syringa vulgaris I1 D1 WR, not acid1 Moist soil1 No Taxus baccata T1, 13 E1, 11, 13 WR1, 13 Moist well-drained 1, 11, 13 No Ulmus pumila P1 D1 WR1–2 WR1–2, 49–50 No Viburnum lantana P1, 11, 13 D1, 11, 13 WR1, 13 WR1, 11, 13 No V. opulus var. opulus P1 D1–2, 9, 51 WR, including high pH1–2, 9, 51 WR1–2, 9, 51 No V. rhytidophyllum T13 E13 WR52 Well-drained13 No V. setigerum P1, 11, 13 D1, 11, 13 WR1 Moist well-drained1, 11, 13 No V. sieboldii P1, 13 D1, 13 WR1, 13 Moist well-drained1, 13 No 34 Northeastern Naturalist Vol. 17, Monograph No. 7 Appendix 3. Control methods available for invasive shrubs. Documentation of resprouting after cutting is listed in footnotes after species names, as this affects efficiency of control methods. For biological control, NK = none known; this was used if references explicitly stated that no biological control methods were known. ND = no data were found. Numerical superscript source references: 1. ISSG 2010. 2. FHP Invasive Plants 2010. 3. Plant Information Databases 2010. 4. PFAF 2008. 5. Remaley 2009b. 6. SE-EPPC 2003. 7. Miller 2003. 8. Randall and Marinelli 1996. 9. Nature Conservancy Connecticut Chapter 2009. 10. Swearingen 2009. 11. Swearingen et al. 2002. 12. WDNR 2009. 31. Rhoads and Block 2002. 14. MSU Extension 1999. 15. MBG 2009. 16. Alverson and Sigg 2005. 17. Weeds Australia 2010. 18. Richardson 2004. 19. Holst and Simmonds 2001. 20. ABC 2008. 21. Tu 2003. 20. Brusati 2005. 23. Deiter 2005. 24. Moorhead 2005. 25. IPAMS 2010. 26. Mikowychok 2008. 27. Sather and Eckardt 1987. 28. Van Clef 2008. 29. Martin 2005. 30. Converse 1984. 31. Batcher 2000. 32. Ensbey 2004. 33. Munger 2003. 34. Langeland and Stocker 2001. 35. Williams 2009. 36. Smith 1997. 37. Batcher and Stiles 2000. 38. Center for Earth and Environmental Science 2005. 39. Wieseler 2009a. 40. Mehrhoff et al. 2004. 41. Heidorn 1990. 42. South Australia MDB NRMB 2007. 43. Tasmania DPIW 2002. 44. Eckardt 1987. 45. Amrine 2002. 46. Bergmann and Swearingen 2009. 47. Hoshovsky 1989. 48. Spencer 2009. 49. King County Noxious Weed Control Program 2005. 50. Wilson et al. 2006. 51. Biosecurity New Zealand 2008. 52. Anderson 2007. 53. Victoria DPI 2009. 54. Brand 2001. 55. Remaley 2009a. 56. CBCN 2010. 57. Thomas and Polwart 2003. 58. Wieseler 2009b. 59. Ohio State University 2010. 60. Oliver et al. 2001. 61. Natural Lands Trust 2007. 62. Pennsylvania DCNR 2010. 63. Cheltenham Township 2009. Species Mechanical control Fire control Chemical control Biological control Acer campestre ND ND ND ND A. ginnala1 Hand pulling, cutting2 Partially effective1 Yes2 ND Aesculus parviflora3 ND ND ND ND Albizia julibrissin2, 4–6 Repeated cutting, girdling, uprooting2, 4–6 ND Yes2, 5–7 Possible6 Berberis thunbergii8–10 Uprooting6, 8–13 Perhaps8, 12 Yes6, 8–13 NK13 Callicarpa dichotoma ND ND ND ND Caryopteris x clandonensis ND ND ND ND Chaenomeles speciosa14–15 ND ND ND ND Crataegus monogyna16–18 Pull seedlings16 ND Yes16 Some goat grazing19 Deutzia scabra20 Pull seedlings2 ND Yes2 ND Elaeagnus angustifolia8, 21–23 Pull seedlings8, 21, 23 With other methods, Yes7–8, 21, 23–24 NK21, 23 stump burning8, 21, 23 E. pungens25 Hand pull26 Yes7 Yes25–26 NK25 E. umbellata27 Pull seedlings6, 8, 11, 27 Not effective8, 27 Yes7–8, 11, 27 ND Eleutherococcus pentaphyllus Pulling, mowing28 ND Yes28 ND Euonymus alatus11 Pull seedlings11, 29 ND Yes7–8, 11, 24, 29 ND E. europaeus Hand pull26 ND Yes26 ND E. kiautschovicus ND ND ND ND 2010 R.L. Boyce 35 Species Mechanical control Fire control Chemical control Biological control Forsythia suspensa ND ND ND ND F. viridissima ND ND ND ND Frangula alnus2, 8, 30 Repeated cutting, girdling, uprooting2, 30 Usually not effective8, 30 Yes2, 8, 30 Perhaps2 Hibiscus syriacus Uprooting effective2 ND Yes2 ND Ilex cornuta ND ND ND ND Kerria japonica4 Cutting15 ND ND ND Ligustrum amurense31 Uprooting6, 31–32 Perhaps33 Yes6, 31–32 NK6, 31 L. obtusifolium11, 31 Uprooting6, 11, 31–32 ND Yes6, 11, 31–32 NK6, 31 L. ovalifolium31 Uprooting11, 31–32 ND Yes8, 31–32 NK6, 31 L. sinense8, 11, 31 Uprooting6, 8, 11, 31–32 Partially effective31 Yes6–8, 11, 24, 34–36 Goat grazing19 Ligustrum vulgare8, 11, 34 Uprooting6, 8, 11, 34–35 Partially effective34 Yes6–8, 11, 24, 31–32, 34 NK6, 31 Lonicera fragrantissima35 Repeated clipping, uprooting11, 35 Perhaps35 Yes11, 29, 35 NK11, 35 L. maackii6, 8, 37 Repeated clipping, uprooting6, 8, 11, 35, 37 Not effective alone8, 35–37 Yes6, 8, 11, 24, 35–37 Perhaps36 L. morrowii6, 8, 37 Repeated clipping, uprooting6, 8, 11, 35, 37 Not effective alone8, 35–37 Yes6, 8, 11, 24, 35, 37 Perhaps36 L. standishii35 Repeated clipping, uprooting1, 35 Perhaps35 Yes11, 35 NK11, 35 L. tatarica6, 8, 37 Repeated clipping, uprooting6, 8, 11, 31, 37 Not effective alone8, 36–37 Yes6, 8, 11, 36–37 NK10, 36–37 L. xylosteum35 Repeated clipping, uprooting7, 35 Perhaps35 Yes7, 35 NK7, 35 Lonicera x bella6, 37 Repeated clipping, uprooting2, 6, 11, 35, 37 Not effective alone35, 37 Yes2, 6, 11, 35, 37 NK11, 35, 37 Lonicera x minutiflora ND ND ND ND Lonicera x xylosteoides ND ND ND ND Malus baccata ND ND ND ND Morus alba38 Uprooting11 ND Yes11 ND Philadelphus coronarius ND ND ND ND Platycladus orientalis ND ND ND ND Prunus cerasus4 ND ND ND ND P. mahaleb ND ND ND ND Pyracantha crenulata ND ND ND ND Rhamnus cathartica8, 36, 39 Pull seedlings, repeated cutting8, 36, 39–40 Repeated burning8, 36, 39–40 Yes8, 36, 39–40 Perhaps2 R. davurica41 Repeated cutting, girdling41 Repeated burning41 Yes41 NK41 Rhodotypos scandens11 Uprooting2, 11 ND Yes32 ND Ribes uva-crispa ND ND ND ND Rosa canina4 Pull seedlings, plowing42 ND Yes42 Goat grazing19, 42 36 Northeastern Naturalist Vol. 17, Monograph No. 7 Species Mechanical control Fire control Chemical control Biological control R. eglanteria4, 43 Pull seedlings, plowing42–43 ND Yes42–43 Goat, sheep grazing19, 42–43 R. micrantha4 ND ND ND ND R. multiflora6–7, 44 Repeated mowing, uprooting6, 8, 10, 32, 44 Perhaps44 Yes6–8, 10, 24, 44 Possible6, 10, 44–46 R. wichuraiana4 ND ND ND ND Rubus armeniacus47–49 Uprooting, repeated cutting47–49 Not effective alone47–49 Yes47–49 Goat, sheep, chicken grazing47–49 R. bifrons4 ND ND ND Goat, sheep grazing50 R. phoenicolasius11, 49 Uprooting11, 48 ND Yes11 ND Salix atrocinerea51–52 ND ND ND ND S. purpurea17, 53–54 ND ND ND ND Spiraea japonica10, 55 Repeated cutting2, 10, 55 ND Yes2, 10, 55 ND S. prunifolia54 ND ND ND ND Syringa vulgaris11 Girdle56 ND Yes56 ND Taxus baccata57 ND ND ND ND Ulmus pumila4, 8 Pulled seedlings, shallow girdling8, 58 Regular burning8, 58 Yes8, 58 ND Viburnum lantana59 Hand pull26 ND Yes26 Goat grazing60 V. opulus var. opulus4, 8 Pull seedlings8 ND Yes2, 8 ND V. rhytidophyllum ND ND ND ND V. setigerum ND ND ND ND V. sieboldii Physical removal, mowing28, 61-62 ND Yes61-63 ND