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RHODORA, Vol. 110, No. 943, pp. 345–353, 2008 E Copyright 2008 by the New England Botanical Club

NEW ENGLAND NOTE FIFTEEN WOODY SPECIES WITH POTENTIAL FOR INVASIVENESS IN NEW ENGLAND CHRISTOPHER T. MARTINE Department of Biological Sciences, State University of New York at Plattsburgh, 101 Broad St., Plattsburgh, NY 12901 e-mail: [email protected]

STACEY LEICHT-YOUNG Lake Michigan Ecological Research Station, USGS Great Lakes Science Center, 1100 North Mineral Springs Road, Porter, IN 46304

PATRICK HERRON1

AND

ANDREW LATIMER2

Department of Ecology and Evolutionary Biology, University of Connecticut, 75 North Eagleville Rd., Storrs, CT 06269-3043 1 Current Address: Rowland Institute at Harvard, 100 Edwin H. Land Blvd., Cambridge, MA 402142 2 Current Address: Department of Plant Sciences, University of California Davis, One Shields Ave., Davis, CA 95616

In a recent paper (Herron et al. 2007), we published a statistical model for predicting invasiveness of exotic woody plant species in New England. A dataset was compiled of 28 biological/ecological characters for each of 248 exotic trees, shrubs, and lianas currently available in the nursery trade in northeastern North America. We applied a Bayesian hierarchical analysis to explore 1) what set of plant traits confer invasive success on non-native plants in New England, and 2) which currently non-invasive species share important traits with the 33 woody species listed by the Invasive Plant Atlas of New England (Mehrhoff et al. 2003). Using this approach we were able to compare non-native species that are known invaders to non-native species that are not currently considered invasive in New England. One benefit of the hierarchical approach is that we could measure the responses of distinct growth forms, a crucial advantage not only for more robust predictions, but also for determining whether different invasion strategies are employed by each woody growth form (tree, shrub, liana). 345

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The model identified a suite of biological/ecological traits that may be useful in predicting invasiveness. In our analyses of growth form we found a number of differences, including a stronger correlation between invasiveness and wind-dispersed seeds in trees than in shrubs or lianas. The most effective predictors across growth forms were: a) whether or not a species is invasive in another part of the world, b) the native latitudinal range, c) the rate of growth, and d) growth form. Of the 248 species we analyzed, the model identified a set of 15 species as being potentially invasive in New England. Our conclusion is that these species warrant further study and ought to be monitored in the field. Because our previous paper (Herron et al. 2007) focused on the modeling methods and performance, and did not discuss in detail the 15 species the model predicted to pose potential problems for New England, it is useful to publish a more detailed discussion of species-level results and their implications. Doing this provides the opportunity to synthesize model results with additional botanical and field information about these species, and to discuss their current status and potential for spread. Some of these species are already under investigation. The intention of this publication is to bring the rest of these species to the attention of the botanical community, and to stimulate further study and observation of these species before they become widespread. This is particularly important because while many of these species are well-known as widespread naturalized species, some are currently not appreciated as potential invaders, or even widely known at all. The identification of potential invaders is an important step in early detection efforts focused on stopping biological invasions before they begin. For the following treatment the primary scientific names listed are those currently accepted by the Integrated Taxonomic Information System (ITIS; http://www.itis.gov; retrieved 15 Nov 2007). Where distribution data are attributed to the PLANTS Database (USDA, NRCS 2007), it is prudent to recall that PLANTS distributions are based on herbarium records and label data that are not always clear with regard to whether specimens were made from cultivated plants or from escaped/naturalized populations. Because of this, we also checked for records of these species in the herbarium collections at NEBC and CONN. Where specimens have been deposited and are clearly identified as escaped or naturalized, the states of origin are noted in brackets. Unless otherwise stated, we were able to identify New England merchants

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offering each of these species. Every one of these species is available through on-line sale and/or mail order. EXPANDED TREATMENTS OF EXOTIC WOODY SPECIES PREDICTED TO BE INVASIVE IN NEW ENGLAND BY HERRON ET AL. (2007)

Albizia julibrissin Durazz. (Fabaceae) – Known to escape from cultivation on the East Coast (Gleason and Cronquist 1991), this Asian native (known commonly as mimosa or silk-tree) is now listed as an invasive species in ten states from Florida to New Jersey (Miller et al. 2006). Its fast growth rate, wind-dispersed fruits/seeds, and the ability to fix atmospheric nitrogen may all contribute to its success in disturbed habitats and along edges and roadsides (Martine 2007). The species is also able to move along riparian corridors through water dispersal of fruits (Remaley 2006c). Over much of New England winter temperatures appear to limit recruitment in this species, but coastal populations in Connecticut (Connolly 2008) have the potential to spread inland if warming trends continue. [CONN: Connecticut] Ampelopsis aconitifolia Bunge (Vitaceae) – Monkshood vine, a native of China, is available in the nursery trade, though to a limited extent in New England. It shares many characteristics with its invasive congener, A. brevipedunculata (porcelainberry or Amur peppervine), including bird-dispersed seeds. Fruit color is a potentially important difference between the species, the berries of A. aconitifolia mature to dull orange or yellow and A. brevipedunculata to a brilliant blue (Dirr 1998). According to PLANTS, monkshood vine has been recorded in at least six U.S. states, including Connecticut and Massachusetts. [CONN, NEBC: no specimens seen] Caragana arborescens Lam. (Fabaceae) – Siberian peashrub is a northern Asian species known to occur in at least 18 states (USDA, NRCS 2007) as well as southern Canada (Henderson and Chapman 2006; Moffatt et al. 2004). It is considered invasive in Minnesota (Department of Natural Resources Trails and Waterways 2003), Manitoba (Moffatt et al. 2004), and Alberta (Henderson and Chapman 2006). This nitrogen-fixing species is extremely adaptable to poor soils, alkalinity, salt, winds, and cold temperatures (Dirr 1998). In addition, it is a prolific seed producer that can spread from plantings into adjacent natural areas (Henderson and

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Chapman 2006). Henderson and Chapman (2006) reported that approximately 50 planted individuals of C. arborescens grew to approximately 60,000 plants in 75 years. It is planted as a hedgerow plant in New England, but so far, the species has been known to escape cultivation in the region only on rare occasions, despite heavy fruit production (B. Connolly, Univ. Connecticut, pers. comm.). [NEBC: Maine, Massachusetts] Colutea arborescens L. (Fabaceae) – Bladder senna, a Mediterranean legume, is known from 16 U.S. states, including Massachusetts, Connecticut, and Rhode Island (USDA, NRCS 2007), although large-scale incursions are apparently still rare. The species is considered a potential invader in the U.S. (Swearingen 2005), Japan (Yoshioka 2005), and Ireland (Reynolds 2002). It is apparently moving northward in Europe, perhaps as a consequence of global climate change (Sukopp and Wurzel 2003). Like Caragana arborescens and other legumes listed here, the ability for Colutea arborescens to fix nitrogen likely confers an advantage on disturbed or infertile sites. [CONN: Connecticut; NEBC: Massachusetts] Euonymus europaeus L. (Celastraceae) – Recorded from 17 U.S. states (USDA, NRCS 2007), European spindletree is considered an invasive shrub in seven U.S. states (Swearingen 2005) and it has been collected from at least five states in New England. As in other members of the genus Euonymus, the arillate seeds have the potential for biotic dispersal. Movement of seeds by birds may be contributing to the current spread of this species and others (such as E. fortunei and E. atropurpureus) in New England. The tracking of European spindletree can be complicated by the fact that wingless forms of E. alatus (burningbush or winged euonymus) are sometimes misidentified as E. europaeus (L. Mehrhoff, Univ. Connecticut, pers. com.). [CONN: Connecticut, Massachusetts, Vermont; NEBC: Connecticut, Massachusetts, New Hampshire, Rhode Island, Vermont] Halimodendron halodendron (Pallas) Voss (Fabaceae) – Listed as a noxious weed in California, Russian salttree is also present in at least five other western states (USDA, NRCS 2007). A thorny native of central Asia, the species is drought- and salt-tolerant, and has the ability to reproduce vegetatively by roots and to fix nitrogen (Dirr 1998). Although this species withstands winter temperatures as cold as those occurring in New England (Dirr 1998), it is

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apparently still unknown as a wild plant in the region. [CONN, NEBC: no specimens seen]. Ligustrum amurense Carrie`rre (Oleaceae) – Considered an occasional escape in the Northeast (Gleason and Cronquist 1991) and an invasive species in Virginia (Swearingen 2005), Amur privet has been recorded in 14 states (USDA, NRCS 2007). Like the privets already considered invasive in New England (L. obtusifolium, L. ovalifolium, L. sinense, L. vulgare), L. amurense has fruits that are dispersed by birds, which could aid its spread across the landscape. Problems in taxonomy and identification have made it difficult to clearly assess the abundance and distribution of Ligustrum species in New England, and L. amurense might already be more prevalent than thought. Identification of Ligustrum species requires flowering specimens and more of these collections are needed. [NEBC: Massachusetts] Polygonum baldschuanicum Regel [syn.: P. aubertii L. Henry, Fallopia baldschuanica (Regel) Holub; Polygonaceae] – Bukhara fleeceflower, or silver lace vine, has been identified as a potential problem in a number of U.S. states including Massachusetts (Weatherbee et al. 2005), South Carolina (Miller et al. 2006), and Washington (Zika 2005). Escaped populations have been reported in at least 11 states (USDA, NRCS 2007). A fast-growing vine, the species has the potential to smother native vegetation. Unmanaged cultivated specimens easily overtake adjacent plantings (Martine, pers. obs.). Polygonum baldschuanicum is known to hybridize with P. cuspidatum (Japanese knotweed; Bailey 2004), a notorious congener already listed as invasive in New England (Mehrhoff et al. 2003). [CONN: Connecticut; NEBC: Massachusetts] Robinia hispida L. (Fabaceae) – Bristly locust, or rose-acacia, is a native shrub of the Mid-Atlantic and Southeast. According to Gleason and Cronquist (1991), the species escapes cultivation as far north as Maine, and established populations are known from coastal Connecticut and Orange County, Vermont (B. Connolly, pers. comm.). A nitrogen-fixer with the ability to colonize poor soils, the species is listed as invasive in five U.S. states: Missouri, New Jersey, Pennsylvania, Ohio, and Washington (Swearingen 2005). Robinia hispida can hybridize with R. pseudoacacia (black locust), a listed invasive in New England. The resultant cross, Robinia 3 margarettiae, has been recorded in four southeastern states (USDA, NRCS

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2007), but is apparently not yet known outside of cultivation in New England. [CONN: Connecticut, Massachusetts] Rubus armeniacus Focke (syn.: R. discolor Weihe & Nees, R. procerus P.J. Mu¨ll. ex Genev.; Rosaceae) – A European species, Himalayan blackberry occasionally escapes from cultivation in the Northeast according to Gleason and Cronquist (1991), although cold New England winters may preclude its establishment over much of New England. It has been reported as invasive in six western states (Swearingen 2005) and is naturalized throughout the Northwest (Oppenheimer 2006). It is also invasive in New Jersey (Swearingen 2005). Introduced for its fruits in South Africa, Asia, Eastern Europe, and North America (Oppenheimer 2006), the species has been wild-collected from escaped populations in at least 21 U.S. states (USDA, NRCS 2007). Its fast growth rate, tolerance of shade, vegetative reproduction, and biotic dispersal make it a successful invader, and dense thickets of R. armeniacus can limit recruitment of native tree species on the West Coast (Williams et al. 2006). Taxonomic confusion exists in the treatment of this species and a number of current state/regional lists refer to Himalayan blackberry as R. discolor. [CONN, NEBC: no specimens seen] Spiraea japonica L. f. (Rosaceae) – Japanese meadowsweet often escapes from cultivation in the northeastern U.S. (Gleason and Cronquist 1991) and has been recorded from 18 states (USDA, NRCS 2007), including five in New England. It is considered invasive in seven states, most of them in the Mid-Atlantic (Swearingen 2005). Highly adapted to disturbed habitats, the species spreads by long-lived wind- or water-dispersed seeds (Remaley 2006b; SEPPC 2001) and vegetative reproduction. Spiraea japonica occurs as an escape throughout New England and appears to have the potential to be a serious problem in the future (L. Mehrhoff, pers. comm.). [CONN: Connecticut; NEBC: Connecticut, Massachusetts, New Hampshire, Rhode Island] Tamarix ramosissima Ledeb. (Tamaricaceae) – Saltcedar, or tamarisk, is known from 19 U.S. states (USDA, NRCS 2007) and is a notorious invasive in the desert Southwest where its high rate of seed production and tolerance of drought has allowed it to dominate riparian communities and displace native vegetation (Sher and Marshall 2003). The species is cold-tolerant and it is

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infrequently used as an ornamental in New England. Although reported to occasionally escape from cultivation in the Northeast (Gleason and Cronquist 1991), saltcedar has apparently not become established in natural communities and is currently not considered a problem. [CONN, NEBC: no specimens seen] Viburnum lantana L. (Adoxaceae) – Wayfaring-tree withstands calcareous or dry soils better than most viburnums and this is partly why the species sometimes escapes from cultivation (Dirr 1998; Gleason and Cronquist 1991). The species is listed as invasive in Illinois and Wisconsin (Swearingen 2005) and is considered worth monitoring in New England (L. Mehrhoff, pers. comm.). Typically a multibranched shrub, wayfaring-tree shows a tendency to spread vegetatively through adventitious rooting (Kollman and Grubb 2002). Wide ecological tolerance and heavy production of bird-dispersed fruits confer exotic viburnums like this one the potential for continued spread in New England. [NEBC: Connecticut, Maine, Massachusetts] Viburnum opulus L. var. opulus (Adoxaceae) – The Eurasian variety of the native V. opulus var. americanum (American cranberrybush) with which it shares many characters, European cranberrybush is known as an occasional escape in the Northeast (Gleason and Cronquist 1991). This variety has been recorded throughout the Great Lakes region (Leicht-Young, pers. obs.), and is considered invasive in Pennsylvania, Indiana, and Wisconsin (Hoffman and Kearns 1997). Like V. lantana, European cranberrybush tends to root adventitiously (Kollmann and Grubb 2002). Birds and animals accustomed to eating the fruits of the native variety may also disperse the seeds of the exotic variety. Telling the varieties apart is tricky, so the current distribution of V. opulus var. opulus in New England may be underreported. [CONN: Connecticut, Maine, Massachusetts, Vermont; NEBC: many collections but variety identifications uncertain] Wisteria sinensis (Sims) DC. (Fabaceae) – Cultivated as a woody flowering vine, Chinese wisteria has been recorded in 25 U.S. states (USDA, NRCS 2007). An aggressive invader, the species is considered an invasive in 16 states (Swearingen 2005; USDA, NRCS 2007), but appears to not move far from points of establishment in New England (B. Connolly, pers. comm.) and is not yet considered a regional problem. Chinese wisteria threatens native vegetation by climbing, strangling, and shading shrubs and

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trees (SEPPC 2001). Under severe infestations trees may be pulled down, creating gaps in the canopy that facilitate the recruitment of new wisteria seedlings (Remaley 2006c). [CONN: Connecticut, Rhode Island; NEBC: Connecticut, Massachusetts] ACKNOWLEDGMENTS. We thank Les Mehrhoff and Bryan Connolly for providing insightful comments on the species we have treated here. F. Daniel Vogt and two anonymous reviewers made helpful suggestions on the manuscript. Thanks to Stephanie Zabel of Harvard University Herbaria for assistance in accessing specimens in the NEBC herbarium.

LITERATURE CITED

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MILLER, J. H., E. B. CHAMBLISS, AND C. T. BARGERON. 2006. Invasive Plants of the Thirteen Southern States. The Budwork Network and U.S.D.A. Forest Service, Univ. Georgia, Dept. Entomology, Tilton, GA. Website (http:// www.invasive.org/seweeds.cfm). Last accessed Feb 2007. MOFFATT, S. F., S. M. MCLACHLAN, AND N. C. KENKEL. 2004. Impacts of land use on riparian forest along an urban-rural gradient in southern Manitoba. Pl. Ecol. 174: 119–135. OPPENHEIMER, H., ed. 2006. Rubus discolor. Global Invasive Species Database. IUCN Invasive Species Specialist Group, Auckland, New Zealand. Website (http://www.invasivespecies.net). Last accessed Feb 2007. REMALEY, T. 2006a. Exotic Wisterias. Fact Sheet. Plant Conservation Alliance, Alien Plant Working Group, Washington, DC. Website (http://www. invasivespecies.net). Last accessed Oct 2007. ———. 2006b. Japanese Spiraea. Fact Sheet. Plant Conservation Alliance, Alien Plant Working Group, Washington, DC. Website (http://www. invasivespecies.net). Last accessed Oct 2007. ———. 2006c. Silk Tree. Fact Sheet. Plant Conservation Alliance, Alien Plant Working Group, Washington, DC. Website (http://www.invasivespecies. net). Last accessed Oct 2007. REYNOLDS, S. C. P. 2002. A catalogue of alien plants in Ireland. Occasional Papers, National Botanic Gardens, Glasnevin, Ireland. Website (http:// www.botanicgardens.ie/glasra/aliens.htm). Last accessed Feb 2007. SEPPC. 2001. Invasive Exotic Pest Plants in Tennessee. South-East [Tennessee] Exotic Pest Plant Council. Web hosting: Signal Data, Chattanooga, TN. Website (http://www.tneppc.org). Last accessed Feb 2007. SHER, A. A. AND D. L. MARSHALL. 2003. Seedling competition between native Populus deltoides (Salicaceae) and exotic Tamarix ramosissima (Tamaricaceae) across water regimes and substrate types. Amer. J. Bot. 90: 413–422. SUKOPP, H. AND A. WURZEL. 2003. The effects of climate change on the vegetation of central European cities. Urban Habitats 1: 66–86. SWEARINGEN, J. 2005. Alien plant invaders of natural areas. Plant Conservation Alliance, Alien Plant Working Group, Washington, DC. Website (http:// www.nps.gov/plants/alien/list/a.htm). Last accessed Feb 2007. USDA, NRCS. 2007. The PLANTS Database. National Plant Data Center, Baton Rouge, LA. Website (http://plants.usda.gov). Last accessed Feb 2007. WEATHERBEE, P. B., P. SOMERS, AND T. SIMMONS. 2005. A guide to invasive plants in Massachusetts. The Massachusetts Biodiversity Initiative. Website (http://www.cyberonic.com/˜gwlt/invasive.html). Last accessed Feb 2007. WILLIAMS, K., L. J. WESTRICK, AND B. J. WILLIAMS. 2006. Effects of blackberry (Rubus discolor) invasion on oak population dynamics in a California savanna. Forest Ecol. Managem. 228: 187–196. YOSHIOKA, T. 2005. Preliminary Weed Risk Assessment of Landscaping Plants. Landscape Research Japan 68: 296–300. ZIKA, P. 2005. Existing herbarium documentation for Washington’s noxious weeds: A report to the Washington Native Plant Society. Washington Native Plant Society, Seattle, WA. Website (http://wnps.org/invasive_species/ InvasiveSpeciesDocumentationReport.rtf). Last accessed Feb 2007.

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