Deforestation is the purposeful clearing of forested land. Throughout history and into modern timesforests have been razed to make space for agriculture and animal grazingand to obtain wood for fuelmanufacturingand construction.

Deforestation has greatly altered landscapes around the world. About 2,000 years ago80 percent of Western Europe was forested; today the figure is 34 percent. In North Americaabout half of the forests in the eastern part of the continent were cut down from the 1600s to the 1870s for timber and agriculture. China has lost great expanses of its forests over the past 4,000 years and now just over 20 percent of it is forested. Much of Earth’s farmland was once forests.

Todaythe greatest amount of deforestation is occurring in tropical rainforestsaided by extensive road construction into regions that were once almost inaccessible. Building or upgrading roads into forests makes them more accessible for exploitation. Slash-and-burn agriculture is a big contributor to deforestation in the tropics. With this agricultural methodfarmers burn large swaths of forestallowing the ash to fertilize the land for crops. The land is only fertile for a few yearshoweverafter which the farmers move on to repeat the process elsewhere. Tropical forests are also cleared to make way for loggingcattle ranchingand oil palm and rubber tree plantations.

Deforestation can result in more carbon dioxide being released into the atmosphere. That is because trees take in carbon dioxide from the air for photosynthesisand carbon is locked chemically in their wood. When trees are burnedthis carbon returns to the atmosphere as carbon dioxide. With fewer trees around to take in the carbon dioxidethis greenhouse gas accumulates in the atmosphere and accelerates global warming.

Deforestation also threatens the world’s biodiversity. Tropical forests are home to great numbers of animal and plant species. When forests are logged or burnedit can drive many of those species into extinction. Some scientists say we are already in the midst of a mass-extinction episode.

More immediatelythe loss of trees from a forest can leave soil more prone to erosion. This causes the remaining plants to become more vulnerable to fire as the forest shifts from being a closedmoist environment to an opendry one.

While deforestation can be permanentthis is not always the case. In North Americafor exampleforests in many areas are returning thanks to conservation efforts.