Population dynamics of woody plants on a river island

Abstract

The woody plant population on a small, frequently flooded, river island was studied. The island occurs on the Chippewa River near Eau Claire, Wisconsin, U.S.A. The major species included sandbar willow (Salix interior, Rowlee), a small shrub; Cottonwood (Populus deltoides Marsh.) and river birch (Betula nigra L.), both early successional species in river bottoms; and silver maple (Acer saccharinum L.), green ash (Fraxinus pennsylvanica Marsh), and American elm (Ulmus americana L.) which are later successional species. Seedling input is sporadic and unpredictable. However, mortality rates of successfully established plants are quite low because of their ability to sprout following damage. The resultant clones may exhibit differing growth patterns. Willow extends laterally into adjacent unoccupied areas, thereby increasing its cover. It tends to be most abundant in the low, frequently flooded parts of the island and is predicted to continue to increase in abundance. Others, such as elm and silver maple, produce fewer sprouts which grow directly from the root crown and attain greater heights but do not spread into new areas. These species occur at higher elevations and are also predicted to increase in numbers. Still other species, such as green ash and Cottonwood, are so severely damaged by recurring beaver cutting that their normal growth form is greatly modified and their future uncertain.