Natural calamities, such as floods, drought, forest fires, earth-quakes, volcanic eruptions, epidemics etc., sometimes take a heavy toll of plant and animal life. Floods are frequent in moist tropical regions of the world which inundate much of the ground vegetation, trap a large number of animals while leaching away soil nutrients to make the already poor tropical soil poorer.
Failure of monsoon, for example, in succession for two or three years dries up ground vegetation and as the subsurface water table recedes trees are also affected. With plant life animals also suffer. In such localities heavy seasonal downpour also causes extensive damages.
Forest fires in densely wooded localities often reduce to ashes a large number of plant and animal species and so do earth-quakes which, however, are not as frequent as floods or droughts. Volcanic eruptions may at times completely destroy plant and animal life in its surrounding areas. Such an eruption occurred in Columbia in November 1985.
The hot sulphur containing material coming out from the volcano melted ice on the mountain sides and formed thick black mud which swept down the slopes to cause enormous damage to plant, animal and human lives. The black mud now covers an area of 2800 sq-kms and has made the soil useless. No vegetation survives here. Fortunately such eruptions are not very frequent. It was 23rd eruption of the volcano since last four thousand years.
Epidemics sometimes destroy large portions of a natural population. Sporadic diseases are quit frequent in a natural community. However, at times virulent strains appear, cause diseases which put on the dimensions of an epidemic. A large number of organisms are killed. In nature such episodes are usually confined to specific plant or animal populations as the pathogen is often specific to particular species or group of species.
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