Stand dynamics of an insular population of an invasive tree, Acer platanoides

Acer platanoides L. (Norway maple) is an invasive exotic tree species in the eastern and central United States that poses a serious threat to native forests. In order to improve our understanding of how this species invades native forests, we conducted a retrospective analysis of the stand dynamics of an established population of A. platanoides in a natural area on a temperate forested island in Lake Huron, Michigan, USA. Tree ring analysis was used to reconstruct the canopy recruitment of contemporary A. platanoides overstory trees, and a simple gap capture method was used to investigate gap capture rates for A. platanoides and native species. Given the extreme shade-tolerance of A. platanoides, surprisingly few of the contemporary A. platanoides overstory trees in the forest showed evidence of past suppression suggesting that most established under relatively open canopy conditions and/or in canopy gaps. Height growth comparisons with native species suggest that A. platanoides should be able to capture canopy gaps at least a decade before most common tree species on the island. A. platanoides displayed rapid juvenile growth rates that declined significantly (P < 0.001) with age once trees reached the overstory. These results suggest that A. platanoides ability to form pure stands and dominate native forests is closely linked to its ability to successfully out compete and competitively exclude native shade-tolerant species. While our results suggest that initial establishment of A. platanoides may follow disturbance, once established, populations appear to be self-sustaining. Consequently, monitoring and control efforts in edge and recently disturbed environments may help prevent the spread of this species into intact forest communities; however, chance long distance dispersals into the forest matrix may be more problematic since rare individuals may go unnoticed until they have established a new population. (c) 2004 Elsevier B.V. All rights reserved.