The myth of the resilient forest: Case study of the invasive Norway maple (Acer platanoides)

In a New Jersey Quercus-Fagus-Acer saccharum forest (Drew University Forest Preserve), the exotic tree Norway maple (A. platan oides) is a major and growing presence in all size classes. Norway maple, long one of North America's favorite shade trees, is invading nature preserves in New Jersey and elsewhere. Research in the Drew Forest Preserve shows that the forest is not a tight, resilient unit that repels invasions. Norway maple does not rely upon disturbance or edges. Norway maple seedlings are shade tolerant and abundant, far outnumbering sugar maple and beech seedlings in the heart of the forest preserve. An analysis of population size and age struc ture shows that Norway maple trees date back to 1915 or earlier and are present in all subsequent age classes. Spatial studies show clumped distri butions for Norway maples as for other plant species but show no restriction to edges. In the understory, species richness is significantly lower beneath Norway maple than under sugar maple or beech, and most stems under Nor way maple are additional Norway maples. A restoration experiment (with tree removal plots and seedling removal plots) was begun in 1998 in a patch of 75-year-old sugar and Norway maples; this unusually simple two-species area will elucidate the competitive interaction over time. Other invasive spe cies also penetrate relatively undisturbed forest; Lonicera japonica, Alliaria petiolata, Berberis thunbergii, and Wisteria floribunda are present alongside Norway maple in the Drew Forest Preserve. Nor is disturbance needed to admit exotic pathogens or insect pests that attack native trees. The threat to the eastern deciduous forest is grave. If the forest is not sufficiently resilient to weather the onslaught of intentional and accidental introductions, then intervention is urgently needed.