August 5, 2019

Last week, on July 29, in the northeastern African nation of Ethiopia, citizens worked with conservation groups, business leaders, and the government to plant more than 350 million trees in a single day. Part of Ethiopia’s Green Legacy Initiative to combat deforestation and climate change, the highly organized event resulted in the planting of 353,633,660 seedlings in just 12 hours. Believed to be a world record, the number far exceeded the original goal of planting 200 million trees in one day. The Green Legacy Initiative hopes to brighten the ecological future of a nation prone to such climate-related problems as drought, famine, and soil erosion.

Prime Minister Abiy Ahmed plants one of more than 350 million trees planted in Ethiopia on July 29, 2019. Credit: Office of the Prime Minister

For the record tree-planting day, many schools and government offices were closed to allow more people to participate. Ethiopian Prime Minister Abiy Ahmed joined in the effort, planting trees in the capital city of Addis Ababa. The tree-planting drive targeted areas that have been stripped of forests over the years, and the types of new trees varied from region to region. The United Nations estimates that just 4 percent of Ethiopia is currently covered by forest, down from about 30 percent in 1900. Ethiopia’s ever-growing population, the need for more farmland, unsustainable forest use, and climate change are cited as the major causes for the nation’s drastic deforestation.

Illinois Senator (and future United States President) Barack Obama plants a tree in Uhuru Park in Nairobi, Kenya, with environmental activist and Nobel Peace Prize winner Wangari Muta Maathai in 2006. Every tree planted helps counteract the effects of climate change. Credit: © Green Belt Movement

The Green Legacy Initiative, launched in May 2019, aims to help reverse Ethiopia’s environmental decline by providing tree seedlings, encouraging tree-planting groups, and asking every citizen to plant at least 40 trees by the end of October. (The seedlings have a better chance of surviving in Ethiopia during the wetter months from May to October.) With a population of about 114 million people, this puts the initiative’s goal at more than 4 billion newly planted trees. More than 2.6 billion trees have been planted so far. Aside from ordinary counting methods, the Ethiopian government is using satellites and special computer software to keep track of the immense number of planted seedlings. The Green Legacy Initiative is also cleaning waterways and making agriculture more sustainable.

The planting of carbon dioxide-absorbing trees—along with recycling and reducing the use of plastics, fossil fuels, and other environmentally damaging materials—is a highly effective way to counteract the effects of global warming and climate change. India set the previous world record for the most trees planted in one day (50 million) on July 11, 2016.

January 17, 2014

A long-held biological assumption about living things–that growth slows or stops with age–has been disproven, report scientists in the latest issue of the journal Nature. Like most living things on Earth, animals, including humans, grow until they reach maturity, the point at which they stop growing. Then, over a lifetime, cells change and break down, eventually leading to death, a process called senescence. But trees have been found to be free from this growth limit.

A worldwide study of trees has led to the discovery that trees continue to grow even as they grow old. “We didn’t think that things could have unlimited growth potential,” commented Nathan Phillips of Boston University. “There’s been a long history of that kind of thinking.” In fact, the growth rate of trees not only does not slow with age but actually accelerates. “This finding contradicts the usual assumption that tree growth eventually declines as trees get older and bigger,” stated Nate Stephenson, the study’s lead author and a forest ecologist with the U.S. Geological Survey. “What we found was the exact opposite. Tree growth rate increases continuously as trees get bigger and bigger.”

The world's largest tree, according to volume of wood, is the General Sherman Tree in Sequoia National Park in California. This giant sequoia ranks as one of the oldest living things on the earth. It is between 2,200 and 2,500 years old. (Richard C. Burns, National Park Service)

An international team of scientists surveyed nearly 700,000 trees in tropical, subtropical, and temperate zones across 6 continents. Scientists from 16 nations compiled the mass growth rates of more than 400 tree species. They found that for most species, mass growth rate increases continuously with tree size. The scientists found while trees do stop growing taller, they continue to pack on more and more mass by growing wider. The lifetime of a tree appears to be limited only by disease, drought, fire, high winds, or human destruction.

“It also means that big, old trees are better at absorbing carbon [dioxide] from the atmosphere than has been commonly assumed,” declared Stephenson. That means that the oldest members of a forest absorb more carbon dioxide from of the air than younger trees. “Not only do they hold a lot of carbon, but they’re adding carbon at a tremendous rate,” noted Stephenson, pointing out the importance of old-growth forests. “And that’s going to be really important to understand when we’re trying to predict how the forests are going to change in the future–in the face of a changing climate or other environmental changes.”

Additional World Book articles:

• Trees Under Threat (a special report)
• Why Forest Need to Burn (a special report)

August 29, 2013

Europe is losing one of its main defenses against rising carbon dioxide emissions linked to global warming, a team of researchers from the Netherlands, Finland, Switzerland, and Italy has reported. Their analysis of data from 29 European countries suggests that the ability of the continent’s trees to absorb and sequester (store) carbon dioxide (CO2), an important greenhouse gas, has nearly reached its limit. Forests, much like oceans, are important natural carbon sinks—that is, areas that sequester large amounts of atmospheric carbon. According to the researchers, the amount of carbon dioxide being absorbed by Europe’s forests has been falling since 2005. The scientists also said that the forests may reach a saturation point by 2030, earlier than previously expected.

The researchers, headed by Gert-Jan Nabuurs of Wageningen University and Research Centre in the Netherlands, listed a number of reasons for the trend. Europe’s trees are aging. Green plants absorb CO2 from the atmosphere as they grow and use the carbon for photosynthesis. However, a tree’s ability to sequester CO2 lessens as it ages. Many of Europe’s trees were planted after World War II (1939-1945), which ravaged the landscape.

Forests cover large parts of Europe, such as the sides of this valley in southern Austria. (© Johanna Huber, SIME/4Corners Images)

Aging trees are more susceptible to wildfires, disease, infestation, and other natural disturbances that return the trees’ sequestered CO2 to the atmosphere, the scientists reported. They also noted that Europe has lost forest because of urban sprawl and deforestation. When trees die or shed leaves, they deposit their trapped carbon into the soil. There, certain bacteria may break down some of the plant matter and release carbon back into the atmosphere as CO2. Trees that are cut down release their CO2 back into the atmosphere as they decay, though turning the wood into paper products delays the release for a a short time.

The researchers suggested that European countries should reevaluate their forestry and land-use policies. “I think policymakers at a national level and within the European Union have to be clear that in certain regions, with valuable habitats, that the focus is on old forests and biodiversity,” Nabuurs told the BBC. “But in other regions, maybe it’s time to concentrate more on continuous wood production again and rejuvenate forests again, so then you have growing forests and a continuous flow of wood products.”

Additional World Book articles:

• Carbon cycle
• The Ocean’s Changing Chemistry (a special report)

March 15, 2012

The area covered by trees in many United States cities is declining, reports the U.S. Forest Service, and that loss of trees–as many as 4 million annually–translates into an astronomical loss in energy efficiency. According to the Forest Service, urban trees greatly decrease heating and cooling costs, by as much as $2,500 over the lifespan of a mature tree; improve air and water quality; and help control water drainage and erosion. The Forest Service calculates that the financial loss of an urban tree is, thus, three times greater that the cost of maintaining it.

Forest Service researchers David Nowak and Eric Greenfield arrived at their conclusion by comparing aerial photographs of 20 urban areas from the years 2002 to 2010 and evaluating the differences in the canopy coverage. They found that the tree cover in 17 out of the 20 cities had declined. New Orleans, Louisiana, had the largest decrease. (The research suggests that much of the tree loss there was a result of Hurricane Katrina in 2005.) Only one of the 20 cities–Syracuse, New York–showed an increase in the amount of tree cover.

Many urban trees are lost to the artifically made objects in a designed landscape. This is known as “impervious cover,” which includes rooftops and pavement–streets, sidewalks, and parking lots.

Trees across North America are under attack by a number of different diseases and pests. Urban trees are especially threatened by the emerald ash borer, the Japanese beetle, and a number of fungal diseases, including the Dutch elm disease.

Ginkgo trees are popular for city plantings because they are largely resistant to air pollution as well as various tree diseases. (Atoz)

Tree-planting programs in many cities have helped to slow tree loss but have not been able to reverse the larger trend. In an effort to make city planning more tree-conscious, the Forest Service is providing cities with a free software program entitled i-Tree Canopy. The program lets users analyze changes in an area’s tree coverage by pairing aerial photographs from different time periods. U.S. Forest Service Chief Tom Tidwell hopes the tool will help communities plant and maintain trees more effectively.

Additional World Book articles:

• Conservation
• Green building
• Ecology
• Trees Under Threat (a special report)

New York City Mayor Michael R. Bloomberg has planted the 500,000^th tree–a pin oak–as part of the city’s Million Trees Campaign. Beyond beautifying the city, trees help clean the air by absorbing carbon dioxide and producing oxygen. They also lower surrounding temperatures and reduce storm water runoff.

Launched in 2007, the Million Trees Campaign is one year ahead of schedule. The campaign is a partnership between New York City and the New York Restoration Project, a nonprofit agency founded by entertainer Bette Midler. The city is planting trees on streets and in parks. The Restoration Project is focusing on the addition of trees to the grounds of cemeteries, churches, housing projects, and libraries. It is also offering free trees to encourage New Yorkers to plant in their own yards.

Additional Year Book article:

• Trees Under Threat (a special report)