Print PageNorway maple (Acer platanoides) populations are rapidly displacing sugar maple (Acer saccharum) in forest stands across the Northeastern United States. Earlier studies have suggested that Norway maple trees develop deeply shaded understories that influence the performance of other tree species while other studies have suggested that Norway maple alters the chemistry of the soil by producing allelochemicals to minimize competition from other species. Our study sought to separate the influence of canopy structure from the influence of allelochemicals in the soil by evaluating the physiological performance of Norway and sugar maple seedlings grown in conspecific soils but transplanted under both conspecific and heterospecific canopies. Fenced-4.5x4.5 m plots were built around six mature trees of each species and 148 seedlings were transplanted with their conspecific soil. We measured in-situ photosynthetic light response curves between 8 AM and 2 PM using a LI-6400 infrared gas analyzer equipped with blue-red photodiode.
Results/Conclusions
Contrary to our expectations, sugar maple seedlings outperformed Norway maple seedlings when growing under Norway maples canopies. They showed higher maximum photosynthetic rates (3.15 mmol m-2 s-1 for sugar and 2.89 mmol m-2 s-1 for Norway), lower dark respiration rates (-0.193 mmol m-2 s-1 for sugar and -0.299 mmol m-2 s-1 for Norway) and lower light compensation point (3.94 mmol m-2 s-1 for sugar and 5.65 mmol m-2 s-1 for Norway). Similar results were found for both species growing under sugar maple canopies. Our results do not support previous studies and suggest that shade tolerance adaptations alone cannot explain the effective invasion mechanism of Norway maple seedlings. Future experiments need to investigate the specific role of soil resources and/or allelochemicals in the establishment, growth and survival of sugar maple seedlings under Norway maple canopies.
