University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Nebraska Cooperative Fish & Wildlife Research Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications Unit 2006 When landscaping goes bad: the incipient invasion of Mahonia bealei in the southeastern United States Craig R. Allen U.S. Geological Survey, [email protected] Ahjond S. Garmestani South Carolina Cooperative Fish and Wildlife Research Unit, [email protected] Jill A. LaBram South Carolina Cooperative Fish and Wildlife Research Unit Amanda E. Peck South Carolina Cooperative Fish and Wildlife Research Unit Luanna B. Prevost Clemson University Follow this and additional works at: https://digitalcommons.unl.edu/ncfwrustaff Part of the Other Environmental Sciences Commons Allen, Craig R.; Garmestani, Ahjond S.; LaBram, Jill A.; Peck, Amanda E.; and Prevost, Luanna B., "When landscaping goes bad: the incipient invasion of Mahonia bealei in the southeastern United States" (2006). Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications. 18. https://digitalcommons.unl.edu/ncfwrustaff/18 This Article is brought to you for free and open access by the Nebraska Cooperative Fish & Wildlife Research Unit at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Nebraska Cooperative Fish & Wildlife Research Unit -- Staff Publications by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Biological Invasions (2006) 8: 169–176 Ó Springer 2006 DOI 10.1007/s10530-004-2896-4 When landscaping goes bad: the incipient invasion of Mahonia bealei in the southeastern United States Craig R. Allen1,*, Ahjond S. Garmestani2, Jill A. LaBram2, Amanda E. Peck2 & Luanna B. Prevost3 1USGS – South Carolina Cooperative Fish and Wildlife Research Unit; 2South Carolina Cooperative Fish and Wildlife Research Unit; 3Department of Biological Sciences, Clemson University, Clemson, SC 29634, USA; *Author for correspondence (e-mail: [email protected]; fax: +1-864-656-1034) Received 8 July 2004; accepted in revised form 3 September 2004 Key words: horticulture, landscaping, Mahonia bealei, non-indigenous species, ornamentals, woodlots Abstract Woodlots are forest islands embedded within an urban matrix, and often represent the only natural areas remaining in suburban areas. Woodlots represent critical conservation areas for native plants, and are important habitat for wildlife in urban areas. Invasion by non-indigenous (NIS) plants can alter eco- logical structure and function, and may be especially severe in remnant forests where NIS propagule pressure is high. Woody shrubs in the Family Berberidaceae have been well documented as invaders of the forest–urban matrix in North America. Mahonia bealei (Berberidaceae) is a clonal shrub native to China, and is a popular ornamental in the Southeastern United States. Mahoni bealei is listed as ‘‘pres- ent’’ on some local and state floras, but almost nothing is known regarding its invasion potential in the United States. We sampled 15 woodlots in Clemson, South Carolina, to assess the invasion of M. bealei and other woody non-indigenous species (NIS). M. bealei invaded 87% of the woodlots surveyed and species richness of NIS on these woodlots varied from 5 to 14. Stepwise-multiple regression indicated that less canopy cover and older M. bealei predicted greater abundance of M. bealei, and that not all subdivisions were equally invaded (P < 0.0001; r2 ¼ 0.88). The impact of M. bealei on native flora and fauna may be considerable, and it is likely to continue to spread in the Southeastern United States. M. bealei should be recognized as an aggressive invader in the Southeastern United States, with the potential for negative impacts on native flora and fauna. Introduction sinense; Japanese honeysuckle, Lonicera japonica; Nandina, Nandina domestica). L. sinense has been Invasion by non-indigenous (NIS) plants can characterized as an aggressive invader in the alter ecological structure and function, and is one southeastern USA, with the ability to reduce of the primary threats to rare and endangered growth of native species (Merriam and Feil species (Gordon 1998). The majority of woody 2002). Lonicera japonica is tolerant of shade and invasive plants in the United States were intro- can overwhelm forest edges once established duced for horticultural purposes, including land- (Robertson et al. 1994). scaping (Reichard and White 2001). Many NIS The southern Piedmont region of the United plants were introduced into the United States as States, 161,430 km2 between the Appalachian ornamentals (e.g., Chinese privet, Ligustrum Mountains and the Coastal Plain, extends from 170 Virginia in the northeast to east-central Alabama create a shift in forest under- and mid-story com- in the southwest. Regional population growth position, which in turn may alter primary pro- has contributed to the conversion of rural, for- duction, nutrient cycling, and carbon storage ested or agricultural land-uses and land-covers to (Jackson et al. 2002). Mahonia bealei urban and suburban uses in many areas. The (Berberidaceae) is a clonal shrub native to China. southern Piedmont is expected to experience a It is a popular ornamental because of its bright greater loss of forested land than other regions yellow, slightly fragrant flowers that appear in of the south (Wear and Greis 2001). High rates late winter or spring and its dark blue berries of forest fragmentation are expected to increase, that remain through the summer. M. bealei can as human population growth accelerates in grow to 4 m tall (Basinger 2001). The leaves are urban, suburban and rural communities (Wear pinnately compound with 9–15 spiny leaflets, giv- and Greis 2001). As human population growth ing the plant a width of approximately 1–2.5 m. and developmental sprawl continue in this M. bealei is recommended as a wildlife attractant region, concomitant changes in ecosystem integ- by several resource management agencies in the rity and the production of ecological goods and southeastern United States, yet the Southeast services can be expected, including losses in water Exotic Pest Plant Council (www.se-eppc.org) lists availability and quality, loss of native habitats, it as a rank 2 (significant threat) NIS plant. loss of biological diversity, and conversion of for- Plants of this rank possess characteristics of an est land to non-natural states. As the southern invasive species but are not currently considered Piedmont further fragments and suburbanizes, to spread easily into native plant communities. remnant woodlots may become increasingly M. bealei is listed as present on several local or important in maintaining the integrity and resil- state floras (Basinger 2001; Bowen et al. 2002; ience of the linked human-ecological system. Leidolf et al. 2002) and is readily available at Woodlots are characterized as forest islands nurseries, but almost nothing is known regarding within an urban matrix, and often represent the its invasion potential in the United States. A clo- only semi-natural areas remaining in suburban sely related congener, Mahonia aquifolium, is rec- areas (Levenson 1981; Boutin and Jobin 1998). ognized as an aggressive invader in central Forest ‘‘islands’’ and fragments may be more Europe (Auge and Brandl 1997). easily invaded than continuous forests (Fine Here we: (1) document the presence of 2002). However, empirical evidence for island M. bealei and NIS, (2) assess the abundance and invasibility is mixed (Lonsdale 1999). Woodlots structure of invasive M. bealei populations, and can have twice as many native plant species as (3) determine predictors of M. bealei abundance old fields, wooded fencerows, ditches, and hay and overall NIS richness in southern Piedmont fields (Freemark et al. 2002). A small patch of woodlots. forest (4 ha) may be sufficient to sustain native, forest-interior plants (Usher 1987). Therefore, woodlots represent critical conservation areas for Materials and methods native plants (Boutin and Jobin 1998). Addition- ally, woodlots represent important habitat for We randomly selected five woodlots in each of wildlife in urban areas (Matthiae and Stearns three suburban subdivisions in the city limits of 1981). Understanding the role of NIS plants in Clemson, South Carolina, USA. Between Janu- woodlots is especially important, as they may ary and April, 2003, we collected information on have a greater impact on remnant woodlots in the invasion of M. bealei and other woody NIS urbanized areas (Miller and Hobbs 2002) than in on these 15 replicates. For each replicate we more extensive patches. recorded the adjacent land use (house, road, or Woody shrubs in the Family Berberidaceae undeveloped) surrounding the lot in the four car- (Barberry family) have been well documented as dinal directions, the age of the oldest and newest invaders of the forest–urban matrix in North adjacent houses, size of the woodlot (ha), slope, America (Ehrenfeld 1997, 1999; Silander and aspect, species richness of NIS, and percent cover Klepeis 1999). Invasion by woody shrubs may of M. bealei and English ivy (Hedera helix). Lot 171 size was determined from GIS coverage of own- house, slope, abundance of M. bealei, canopy ership parcels, and land use was determined by cover, vertical structure, percent H. helix cover, observation. Adjacent land use was quantified and age of oldest M. bealei. Assumptions of categorically, by assigning a house or road a equal variance and normality were tested with a value