Clark explored the Yellowstone River in a boat made of lashed
cottonwood trees. These trees, which grow along many plains
rivers, proved invaluable throughout the journey, providing
shade and shelter as well as transportation. To commemorate
the tree, Clark named the site where he constructed the boats
Camp Cottonwood. But the massive groves have been dying out
because of dams, which block the seasonal flooding of the
riverbanks. Cottonwoods, both this species and black cottonwood,
Populus trichocarpa, which occurs further west, require the
rich silt deposited by high springtime water in order to germinate.
Since dams have altered the rivers' flow, no new trees are
taking root to replace the old ones. Along the Garrison Reach
of the Missouri River, the Sierra Club is planting cottonwoods
and working to restore the river to its natural flow patterns.
Black cottonwood (subspecies) is state threatened.