Understory influence of the invasive Norway maple (Acer platanoides).

Abstract

WYCKOFF, PETER H. AND SARA L. WEBB (Biology Department, Drew University, Madison NJ 07940). Understory influence of the invasive Norway maple (Acer platanoides). Bull. Torrey Bot. Club 123:197-205. 1996.Norway maple (Acer platanoides) is invasive within a Fagus grandifolia-Acer saccharum-Quercus spp. forest preserve in New Jersey. To assess the community-level consequences of this invasion, we compared understory composition, richness, and structure beneath canopies of invasive Acer platanoides and of native Acer saccharum and Fagus grandifolia. Understory species richness was significantly lower beneath Acer platanoides and highest beneath Fagus grandifolia. Stem densities were high beneath Acer platanoides but consisted primarily of its own seedlings and saplings. When these Acer platanoides stems were removed from the analysis, there was a trend toward lower stem densities beneath the exotic tree compared with the native canopies. Individual shrub and forb species were too patchy for any canopy affinities to demonstrate significance within this small forest preserve, with two exceptions: Epifagus virginiana, a beech (Fagus) root parasite, was less abundant under Acer platanoides than under either Fagus grandifolia or Acer saccharum; and the shrub Lindera benzoin was less abundant under Acer platanoides and Fagus grandifolia than under Acer saccharum. Among tree seedlings, the exotic Acer platanoides far outnumbered all others, beneath its own canopy and also beneath the two native trees. A surprising paucity of Fagus grandifolia reproduction seems unrelated to the biological invasion. Acer saccharum has some prospects for self-replacement judging from sapling distributions but has sparse reproduction under the other canopy species relative to its exotic congener.