How Much of the Earth Do Trees Cover?

Total Coverage

• Trees cover 30 to 31 percent of the land on Earth. Of this percentage, the majority of trees are in forests and rainforests. That percentage is dwindling quickly due to deforestation. Because the number of trees on Earth is so vast, it is measured easily in hectares rather than acres. One hectare is equal to 2.47 acres. Therefore, the number of trees across the planet cover about 4 billion hectares. Multiplying that figure by 2.47 reveals that trees cover roughly 9.88 billion acres worldwide.

Vital Function

• Trees perform a vital function for all life on Earth, removing carbon dioxide from the atmosphere and expelling life-giving oxygen. This process takes place during photosynthesis. A single acre of trees is capable of providing enough oxygen to support as many as 18 people for one year, according to the U.S. Department of Agriculture. Trees also act as cleaners of the environment, removing dust particles and other harmful pollutants from the atmosphere.

  It is estimated that human beings expel roughly 9 billion tons of carbon -- mostly in the form of carbon dioxide -- into the atmosphere each year through their burning of fossil fuels and their alteration of landscape. Of the carbon expelled, most ends up in the oceans or atmosphere, contributing to the greenhouse effect, which is believed to be responsible for global climate change. About 3 billion tons of the expelled carbon end up in land ecosystems. "As much as 45 percent of the carbon stored on land is tied up in forests," according to a National Aeronautics and Space Administration Earth Observatory website article.

Loss

• With each passing year, more of Earth's natural, old-growth forests are lost to deforestation. Land is cleared of trees to make way for construction, road-building and agriculture. Trees also are harvested for their raw materials, such as timber, to make tools and paper. Deforestation reached an all-time high during the 1990s. During those 10 years, the net loss of forests and trees worldwide was 83 million hectares. The following decade, 2000 through 2010, net tree loss was less, about 52 million hectares.

  When new trees are planted to make up for those lost to logging and land-clearing, biodiversity is rarely considered. Planting the same species of tree over a large area results in monoculture. Monoculture in any instance, whether in a forest or garden, is considered a poor choice because an entire forest or crop may be wiped out if pests or diseases invade.

Other Important Functions

• In addition to creating oxygen, trees perform many other important functions in the environment. They act as a natural climate adjuster, keeping areas warmer than they would be otherwise in winter by shielding them from wind and keeping areas cooler in summer by providing shade and absorbing the sun's radiant heat. Trees conserve water by filtering and absorbing runoff during rainstorms and releasing the water into the atmosphere through transpiration. Additionally, trees keep soil intact by preventing erosion, and they add nutrients and enrich the soil through the decomposition of their fallen leaves.