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Seasonal variation in light availability and canopy structure of invasive Norway maple and native sugar maple and American beech

Ryan M. Esquejo and José-Luis Machado. Swarthmore College, Swarthmore, PA 19081

Abstract (submitted to ESA, Montreal, 2005)

The introduction and uncontrollable dispersal of invasive species create serious ecological and economic disruptions. The invasive Norway maple (Acer platanoides L.) was introduced initially in the northeastern United States from Europe as an ornamental shading tree. Several studies have suggested that the Norway maple reduces the availability of photosynthetic light in the understory limiting the establishment, growth and survival of native tree species. We compared the photosynthetic light availability in the understory and canopy structure for the period between leaf budburst of the invasive Norway maple and natives species: sugar maple (Acer saccharum Marshall.) and American beech (Fagus grandifolia Ehrh.) We took black and white digital hemispherical photographs each month from April 2003 through May 2004. We estimated percent canopy openness, photosynthetic photon flux density (PPFD) and leaf-area index (LAI). Early in spring, the Norway maple understory showed significantly lower percent canopy openness and PPFD with higher LAI compared to that of sugar maple and American beech. However, this pattern was not maintained during the summer months when the sugar maple and the American beech understories showed higher leaf area index with lower percent canopy openness and PPFD. Our study confirms that the invasive Norway maple has an early leaf budburst resulting in a marked reduction of light in the understory. Physiological studies are needed to determine the effect of this early spring reduction in light on the establishment, growth and survivorship of native tree species.

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