Exotic Species: There are two categories of exotic species which have had significant impact on park forests: pathogens and invasive plants. Chestnut Blight and Dutch Elm Disease have virtually eliminated American chestnut and American elm and a similar fungal disease is currently impacting the American Butternut tree. Invasive exotic plant species such as honeysuckle, garlic mustard, kudzu, Microstegium, silver poplar, and Ailanthus out-compete native species and are therefore spreading. With over 1,000 species of flowering plants - including 84 tree species - the potential for loss of biodiversity is great.