Damage and landscape change provide scientists with a view of how life recovers after extreme events. For example, the recovery of life around Mount St Helens has been and continues to be actively studied. Volcanism also responsible for major release of gases and particulate matter that may influence weather and climate. Cosmic disturbance- results could be very local or a global catastrophe. May be the causative mechanism in major extinction events.
Some workers believe that there is periodicity to asteroidal and meteoric impacts.
Dutch elm disease. AIDS epidemic in Africa. Plague in Middle Ages. Herbivory- over grazing, introduction of new and different herbivores, effect of elephants on African plains landscape. Many others such as ants, burrowing animals, exotic grazers and browsers.