Spatiotemporal Recruitment Patterns of Two Introduced Magnolia L. Species in a Disturbed Oak Forest

ABSTRACT Although nearly half of all Magnolia species are threatened globally, human-assisted movement and cultivation of some species has led to their escape within non-indigenous ecosystems. The ongoing naturalization of select Magnolia taxa has been associated with climate change and variously characterized as assisted-migration, range shift/expansion, or biological invasion. This study documented recruitment patterns in space and time for two species of introduced ‘umbrella’ magnolias, which have become increasingly prolific in New England. A census was conducted that identified a total of 388 Magnolia macrophylla (SE US.) and M. obovata (Japan) individuals that escaped from cultivation and colonized an adjacent oak forest. Seedling recruitment occurred rapidly in response to forest disturbance, and mean tree age was significantly different as a function of three discrete disturbance events. M. obovata was a more successful colonizer overall, yielding more individuals (326 vs. 62), and recruiting further (90% quantile = 388 ± 91 vs. 228 ± 44 m) than M. macrophylla, given founding populations that were of identical size (n = 3) and similar age. This study represents the first documented escape of M. obovata in North America, while M. macrophylla has been documented elsewhere in New England and linked to increased temperature and precipitation patterns.