Quaking aspen (Populus tremuloides), a member of the willow (Salicaceae) family, is the most widespread deciduous tree in North America. Aspen range from Alaska in the North to Mexico in the South, from the Atlantic to the Pacific, and from sea level to an altitude of 12,100ft (3,700m). Among other willow, poplar, and shrub species, quaking aspen are commonly considered to have been among the first pioneers after the retreat of continental and alpine glaciers in the Pleistocene. While the species' geographic range is large, aspen stand location is limited to areas where annual precipitation exceeds 10 inches (400 millimeters) because of its high water needs. Interestingly, each stand is a set of clones: all of the trees are genetically identical. While aspens produce large amounts of viable seed, few seeds actually germinate and the primary means of reproduction for aspens in the west is via vegetative root suckering – genetically identical new shoots grow out of the roots of older plants. Some scientists estimate that significant sexual reproduction has not occurred in aspen for the last 10,000 years! While individual trees may only live 100-150 years, the clonal colony may exist for thousands. However, as the prolonged moist conditions necessary for successful seed growth are exceedingly rare in the Intermountain West, an aspen clone lost from the landscape will not generally regenerate from seed.
Quaking aspen are less common than limber pine (Pinus flexilis) or juniper (Juniperus scopulorum and Juniper osteosperma), Craters of the Moon's most abundant trees, but still make up an important part of the local ecosystem. Quaking aspen groves are found primarily in upland sites away from permanent stream courses. A veritable oasis in an otherwise semi-arid environment each aspen stand is a biologically rich, ecologically relevant community. Stands of aspen clones are among the most biologically rich plant communities in the Intermountain West and the species has been noted as a keystone species for areas in which it occurs – one without which its ecosystem could hardly function.
Declining aspen habitat would lead to losses of invertebrate, vertebrate, and nonvascular organisms, and vascular plants. In addition, aspen stands provide forage for wildlife and domestic livestock and attract a large number of campers, naturalists, and recreationists each year. For this reason, quaking aspen is one of fourteen "priority park vital signs", or indicators of ecosystem health identified by the National Park Service. These indicators are monitored in a collective effort by the Department of Rangeland Ecology and Management at the University of Idaho, the National Park Service Upper Colombia Basin Network Inventory and Monitoring Program (UCBN), and of course Craters of the Moon National Monument and Preserve in an effort to better understand how to protect and preserve our natural resources and the ecosystems that make Craters of the Moon National Monument and Preserve so special.