The riparian vegetation along the Bighorn River in Wyoming forms a complex mosaic comprised of cottonwood (Populus deltoides) groves, meadows, marshes, and several kinds of shrubland. Changes in the riparian mosaic during the last 50 years were reconstructed using tree ring analysis and aerial photos taken over the river in 1938, 1944, 1954, 1961, 1967, 1979, and 1981. The mosaic is dynamic, changing in relation to channel shifting and fire, with one of the more notable trends being a decrease in the area of woodland and an increase in the area of shrublands. The decrease in woodland can be attributed to fire and changes in river characteristics brought about by upstream dam construction. A large portion of the disturbed woodland has been converted to shrublands dominated by the native Rhus trilobata and the introduced Tamarix chinensis. © by the Ecological Society of America. Abstract reproduced by permission