What types of ecosystems have been changed?

What types of ecosystems have been changed?

Virtually all of Earth’s ecosystems have been significantly transformed through human actions. In the second half of the 20^th century ecosystems changed more rapidly than at any other time in recorded human history. Some of the most significant changes have been the conversion of forests and grasslands into cropland, the diversion and storage of freshwater behind dams, and the loss of mangrove and coral reef areas.

The most rapid changes are now taking place in developing countries, but industrial countries experienced comparable changes in the past. However, current transformations seem to occur at a faster pace than changes prior to the industrial era.  The structure of the world’s ecosystems changed more rapidly in the second half of the twentieth century than at any time in recorded human history, and virtually all of Earth’s ecosystems have now been significantly transformed through human actions. The most significant change in the structure of ecosystems has been the transformation of approximately one quarter (24%) of Earth’s terrestrial surface to cultivated systems. More land was converted to cropland in the 30 years after 1950 than in the 150 years between 1700 and 1850.

Between 1960 and 2000, reservoir storage capacity quadrupled; as a result, the amount of water stored behind large dams is estimated to be three to six times the amount held by natural river channels (this excludes natural lakes).  In countries for which sufficient multiyear data are available (encompassing more than half of the present-day mangrove area), approximately 35% of mangroves were lost in the last two decades. Roughly 20% of the world’s coral reefs were lost and an additional 20% degraded in the last several decades of the twentieth century.

Although the most rapid changes in ecosystems are now taking place in developing countries, industrial countries historically experienced comparable rates of change. Croplands expanded rapidly in Europe after 1700 and in North America and the former Soviet Union, particularly after 1850. Roughly 70% of the original temperate forests and grasslands and Mediterranean forests had been lost by 1950, largely through conversion to agriculture. Historically, deforestation has been much more intensive in temperate regions than in the tropics, and Europe is the continent with the smallest fraction of its original forests remaining. However, changes prior to the industrial era seemed to occur at much slower rates than current transformations.