Norway maple (Acer platanoides) and other non-native trees in urban woodlands of central Massachusetts1

Abstract

Bertin, R. I., M. E. Manner, B. F. Larrow, T. W. Cantwell, and E. M. Berstene (Biology Department, College of the Holy Cross, Worcester, MA 01610). Norway maple (Acer platanoides) and other non-native trees in urban woodlands of central Massachusetts. J. Torrey Bot. Soc. 132: 225–235. 2005.—We investigated the contribution of non-native tree species to woodlands in and near Worcester, a city of 170,000 residents in central Massachusetts. We sampled species composition of canopy, sapling and seedling layers in 32 woodlands. At three additional sites, we collected additional information on Norway maple, including size/age data, abundance with respect to distance from woodland edge, and apparent mortality compared to that of other species. In all, we encountered 66 tree species, of which 28 were introduced. The most common non-native trees were Norway maple (Acer platanoides L.), black locust (Robinia pseudoacacia L.) and tree-of-heaven (Ailanthus altissima (Miller) Swingle). The last two are shade-intolerant, and there was little evidence that they invade intact woodland. Young Norway maples, in contrast, can persist for decades in the understory. Norway maple comprised 11% of all trees sampled, and 23% of all seedlings and saplings. Its wind-borne seeds dispersed tens and occasionally hundreds of meters away from seed sources into woodland. Because its mortality was lower than or equal to that of most competing species, it is likely to increase in abundance. Young Norway maples were more common on disturbed sites and those near seed sources. Norway maple trees were less common on wet and dry sites than on mesic sites. Because of its widespread use as an ornamental, its capacity to invade intact woodlands and its dense shade, Norway maple has the potential to profoundly alter native woodlands, especially on mesic sites. Mesic woodlands in Worcester are likely to see a decline of species with low to moderate shade tolerance, like white ash (Fraxinus americana L.), red oak (Quercus rubra L.) and black locust, and an increase in shade-tolerant species, including Norway maple. Dry woodlands are likely to remain dominated by a mixture of native oaks, especially black oak (Quercus velutina Lam.).