PARENT SESSION
Poster Session #41: Invasive Species Ecology: Woodlands.
Wednesday, August 7. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Juvenile mortality as a function of growth under low light for exotic Norway maple (Acer platanoides L.) and native sugar maple (Acer saccharum L.).

Eickwort, Jeffrey^*,1, Kobe, Richard¹, ¹ Michigan State University, East Lansing, MI

ABSTRACT- Norway maple (Acer platanoides L.) is an exotic tree species that has been shown capable of invading northern hardwoods forests and excluding native tree species under its canopy. However, the mechanisms behind its competitive advantage are not well understood. To explore the differences in life-history traits between this invasive exotic and a native congener, we developed field-calibrated models of sapling mortality as a function of recent radial growth for Acer platanoides and Acer saccharum where they co-occur in a low-light, closed-canopy environment in central lower Michigan. These species-specific models characterize an individual's probability of mortality as a function of recent radial growth (a surrogate for whole-plant carbon balance). Light availability (measured with hemispherical canopy photos) for the two species was similar, ranging from 1.2% to 10.5% full sun and averaging approximately 5% (p=0.37). Average yearly radial growth rates (measured through analysis of stem cross-sections) were also similar for A. platanoides and A. saccharum (0.25 and 0.28 mm respectively, p=0.34). However, the results of our Likelihood Ratio Tests show that Norway maple has a significantly lower probability of mortality per unit of radial growth than sugar maple (p<0.05). These results suggest that one explanation for Norway maple's ability to invade late-successional forests and competitively exclude native species may be its greater ability to survive under suppressed growth.

KEY WORDS: invasion, Acer platanoides, mortality