Acer platanoides is a European native tree that, in North America, has become both a popular landscape tree and an invader of diverse forests where it suppresses native vegetation. To better understand the ability of Acer platanoides to invade established forests, we have scrutinized ten years of seedling demography using a network of 80 permanent plots within a New Jersey deciduous forest. When this study began, the site was carpeted by small (height <20 cm) seedlings of the invasive Acer platanoides and of the native Acer saccharum in a 50:50 mixture. We investigated seedling establishment, growth, and mortality; and we asked whether or not Acer platanoides establishes a shade-tolerant seedling bank like that of its congeneric native.

Results/Conclusions

Results reveal many similarities in life history characteristics of the two species. Like Acer saccharum, Acer platanoides forms a bank of long-lived seedlings despite deep shade; sustains heaviest mortality to youngest seedlings; responds with comparable upward growth to canopy openings; and reproduces sporadically during occasional years of heavy masting and seedling establishment. Ten years of record show that masting by the two maples was often synchronous (in 1999, 2004, 2007) but sometimes not (only Acer platanoides masted in 2003). Acer saccharum had one extraordinary year of new seedling establishment (in 2004; 10x any previous densities for either species) and, despite mortality since then, still numerically dominates the forest understory. Such shifting patterns and episodic events illustrate the difficulty of predicting forest dynamics from shorter-term studies. We conclude that Acer platanoides has key ecological similarities to Acer saccharum including a persistent, shade-tolerant seedling bank that facilitates invasion of intact native forests.