An analysis of elm (Ulmus americana) mortality in a second-growth hardwood forest in southeastern Michigan

Abstract

A second-growth hardwood forest containing both wet lowland and mesic upland sites in southeastern Michigan was studied 24 years after the introduction of Dutch elm disease. American elm (Ulmus americana) surprisingly had the highest importance value (IV = 61/300) (IV = relative density + relative dominance + relative frequency). Two other species (Acer rubrum and Quercus macrocarpa) closely followed elm with IVs of 41/300 and 38/300. respectively. Mortality for all trees surveyed was 20.4%. Elm comprised 86.6% of this total. Although reduced, the present IV for elm and the percentage of living individuals in each diameter class indicate that elm is still an important species in the forest community. Elm mortality reached 100% only on the poorly drained lowland pockets where densities of elm exceeded 50%. Its high reproductive capacity and dispersal rate indicate that elm will continue to exist as an important species, even if not a canopy dominant, in some types of hardwood communities.