Invasion of an old-growth forest in New York by Ailanthus altissima:: sapling growth and recruitment in canopy gaps

The exotic tree Ailanthus altissima is known to invade open and disturbed sites. As a shade-intolerant species, it is not generally identified as a potential invader of forests. Nevertheless, Ailanthus saplings dominate several natural gaps within Montgomery Place South Woods, a small old-growth hemlock-hardwoods forest in the Hudson Valley region of New York State. Within these gaps, the height, diameter, and extension growth of the tallest Ailanthus saplings are significantly greater than those of the tallest native competitors. Although Ailanthus is absent from fully shaded areas, relative radial growth rates of saplings throughout Montgomery Place are not strongly affected by light availability. Pole-sized Ailanthus within South Woods exhibit a history of high annual radial growth, with means for individual trees ranging from 1.96-3.70 mm/yr. These results support the hypothesis that Ailanthus established in old-growth gaps can reach the canopy by virtue of rapid growth during a single period of release. Ailanthus thus exhibits a gap-obligate strategy of forest recruitment.