Big old cottonwoods

Abstract

In studying riparian woodlands along streams across western North America, we observed a grove of exceptionally large and old black cottonwoods, Populus trichocarpa Torr. & A. Gray, along the Elk River in southeastern British Columbia. Situated in a floodplain forest dominated by western red cedar, Thuja plicata Donn ex D. Don, the cottonwoods were up to 2.2 m in diameter, and although heart rot prevented precise aging, increment cores indicated ages of up to 400 years. This demonstrated the potential for substantial longevity of section Tacamahaca cottonwoods (including Populus angustifolia James and Populus balsamifera L.) compared with section Aigeiros species (Populus deltoides Bartr. and Populus fremontii Wats.), which are shorter lived (about 150 year maximum). Very old cottonwoods make distinctive contributions to habitat structure of riparian woodlands and reveal stable floodplain locations that have not been eroded by the river channel for the duration of the trees' lives.Key words: aging, poplars, riparian, trees.