concurrent decline of the native Celastrus scandens and spread of the non-native Celastrus orbiculatus in the New York City metropolitan area, The

Journal of the Torrey Botanical Society, Apr-Jun 2003 by Steward, Angela M, Clemants, Steven E, Moore, Gerry

STEWARD, A. M., S. E. CLEMANTS, AND G. MOORE (Brooklyn Botanic Garden, 1000 Washington Avenue, Brooklyn, NY 11225-1099). The concurrent decline of the native Celastrus scandens and spread of the non-native Celastrus orbiculatus in the New York City Metropolitan area. J. Torrey Bot. Soc. 130: 142-145. 2003.-Before 1950, native Celastrus scandens (American bittersweet) was rather common in the New York Metropolitan area. Celastrus orbiculatus (Oriental bittersweet) was introduced into the region in the late 1800s. Analyses of the distribution of both species since the time of the introduction of C. scandens into the flora indicate that the native C. scandens has declined considerably, while the non-native C. orbiculatus has significantly spread and increased in abundance. Possible reasons for the concomitant decline of C. scandens and spread of C. orbiculatus are discussed.

Key words: bittersweet, Celastrus orbiculatus, Celastrus scandens, New York Metropolitan Flora project.

In the New York Metropolitan area, Celastrus orbiculatus Thunb. (Oriental bittersweet) is a commonly occurring weed, whereas the native Celastrus scandens L. (American bittersweet) occurs occasionally. Prior to introduction of C. orbiculatus, C. scandens was widespread in the area. We documented the changing distribution of both species in the New York Metropolitan area from the early 1800's through the present. We suggest several factors that may have contributed to the decline of C. scandens and the spread of C. orbiculatus.

Celastrus scandens and C. orbiculatus, both deciduous woody vines, are widely distributed in the United States. C. scandens is native to the United States and Canada from Quebec south to Georgia, west to Wyoming, Montana and Manitoba (White and Bowden 1947; USDA 2002). It occurs in many habitats, including upland woods, swamps, roadsides, field edges, and sandy dunes (USDA 2002). C. orbiculatus is native to eastern Asia in China, Japan and Korea and adventive in Canada and the United States. In the United States, it ranges from Maine south to Georgia, west to Arkansas, and north to Iowa and Wisconsin. C. orbiculatus grows in a variety of habitats, including roadsides, thickets, fence rows, fields, sunny wooded areas and marsh areas; it occasionally co-occurs with C. scandens.

Celastrus orbiculatus was introduced into North America during the late 1860's and was later popularized for ornamental plantings by the Arnold Arboretum at Harvard University (Patterson 1973; Rehder 1940). In 1897, the New York Botanical Garden introduced C. orbiculatus onto the grounds from seed sent by the Royal Botanic Gardens, Kew, England. Nash (1919) who first reported its local spread from the original planting noted: "[the vine] was of accidental occurrence [in this locality], and perhaps originated from seed carried by birds from the large specimen in the viticetum." Plant collection records indicate that C. orbiculatus was becoming naturalized in the Northeast from 1910-1925 (Patterson 1973; Merhroff 1986).

Celastrus scandens and C. orbiculatus are morphologically similar and commonly confused. However, closer examination reveals that the two species can be distinguished by differences in the leaves and inflorescences. Leaves of C. scandens are twice as long as broad and the flowers are borne in terminal panicles. Leaves of C. orbiculatus are broader, and the flowers are borne in axillary cymes. It is important to clarify these differences so that correct identifications can be made and species' distributions continually tracked in the New York Metropolitan area and beyond.

Materials and Methods. We documented the historical and current distribution of Celastrus as part of the New York Metropolitan Flora project (NYMF) (for a description of the NYMF project see Moore et al. 2002). Distribution maps for C. orbiculatus and C. scandens were produced using records from the NYMF database. Plant records are derived from three sources: 1) field surveys conducted by the Brooklyn Botanic Garden (BBG) 2) herbarium records from the greater NYMF range (for a list of herbaria visited see Moore et al. 2002) and 3) bibliographic sources, including checklists from state and national park agencies and field trips of the Torrey Botanical Society and the Philadelphia Botanical Club. Plant records were divided into two categories, pre- and post-1989, to show current species distribution patterns. Data are presented as presence-absence data: one dot on the distribution map indicates the presence of Celastrux in a 5x5 km square block (the NYMF area is comprised of 964 5×5 km blocks). Maps were created using ArcView 3.2 (ESRI 1995-01).

Further analyses were conducted on restricted data sets from the NYMF database. Records were sorted by 10 year intervals from 1910-1999; for example, 1910-1919, 1920-1929 etc. The total number of Celastrus records for each 10 year interval was compared with the values for C. scandens and C. orbiculatus, expressed as a percentage to show the change in distribution through time after C. orbiculatus introduction.