Abstract: Almost everyone knows that ecosystems and species all over the world are endangered because of ever-growing disturbance by human activity. It is less well known that some ecosystems and species are disappearing because humans have *halted* disturbance, interfering with natural disturbance regimes or modifying patterns of human disturbance that prevailed for thousands of years. A striking example of a disturbance-dependent ecosystem is serpentine grassland. Occurring in only a few scattered locations in southeastern Pennsylvania and elsewhere in the northern Piedmont, it is a globally rare natural community type, harboring a rich assemblage of rare species. It has declined severely during the last 60 years due to the suppression of wildfire. In collaboration with The Nature Conservancy, Dr. Latham is conducting a series of experiments to test hypotheses about the origin and maintenance of these unique eastern North American savannas, and to devise effective methods for their restoration.