Norway Maple (Acer platanoides) Invasion of a Natural Forest Stand: Understory Consequence and Regeneration Pattern

Norway maple (Acer platanoidesis) is invasive in a natural stand in suburban Ithaca, NY. To determine the understory pattern and consequences of a Norway maple invasion, I compared density and species richness under Norway maples and sugar maples (Acer saccharum). Mean sapling density was significantly lower (P<0.0027) under Norway maples (3.64/100 m2±1.6 SE) than under sugar maples (19.4/100 m2±4.4 SE). Mean sapling species richness was significantly lower (P<0.0018) under Norway maples (0.7/32 m2±0.18 SE) than under sugar maples (2.6/32 m2±0.48 SE). Likewise, Norway maple regeneration is more frequent under sugar maples than sugar maple regeneration: 57% of sugar maple plots had Norway maple saplings while 0% of Norway maple plots had sugar maple saplings. Two significant plot effects were found for presence–absence: Norway maple saplings grow under Norway maples with a significantly lower frequency (P<0.03) than under sugar maples; sugar maple saplings grow under Norway maples with a significantly lower frequency (P<0.000) than under sugar maples. Across the site, Norway maple saplings were the most abundant (29 saplings for 480 m2). The success of Norway maple regeneration and the reductions in total stem density beneath Norway maples is most likely the result of its strong competitive abilities, notably its high shade tolerance and abundant seed crops.