ON THE IMMINENT DECLINE OF RIO-GRANDE COTTONWOODS IN CENTRAL NEW-MEXICO

Increment cores from 144 Fremont cottonwoods (Populus fremontii var. wislizeni) were taken at three riparian woodland sites along the Rio Grande in New Mexico. Trees at two study sites averaged 38.8 and 43.2 years old. All trees fewer than 26 years old at those sites were root suckers from older trees whose primary trunks had decayed. The third site, one of few known locations where young trees are present, had 75% of the trees between 5 and 25 years old. Cottonwood recruitment generally (but not always) could be associated with years of overbank flooding. The combination of a paucity of cottonwood regeneration over the last 30 years, the rapid colonization during this century of Russian-olive (Elaeagnus angustifolia) and salt cedar (Tamarix chinensis) into the valley, and current river channel management practices suggests that the Rio Grande riparian woodland will become dominated by the exotic shrubs over the next 50 to 100 years. To assure the continued survival of the cottonwood riparian community along the Rio Grande, resource managers need to implement strategies to enhance cottonwood regeneration and survival and to control the spread of exotics.