The forests of Western North Carolina are threatened by a wide variety of environmental stressors and disturbances, such as insects, disease, invasive species, drought, fire, hurricanes, tornadoes, and ice storms. A stressor is any kind of event or action which, at certain levels, causes stress to organisms; for example, a period of drought. A disturbance is a relatively discrete event in time that disrupts ecosystem, community, or population structure and changes resources, substrate availability, or the physical environment; for example, a wildfire. Organisms may adapt to a level of disturbance, but when another threshold is exceeded degradation occurs. Degradation is the destruction of complex natural environments.