Reducing carbon by increasing trees.

To most people, climate seems relatively constant. Ups and downs in temperature and rainfall are merely fluctuations, not indications of climatic shifts that could significantly affect us now or in the future. But a growing body of research conducted experts around the world concludes that this is an illusion. Global warming is a real threat, caused by carbon dioxide and other greenhouse gases we humans release into the atmosphere.

Global warming is expected to affect everything from the natural environment to human health, mostly for the worst. Fortunately, research also shows many opportunities to mitigate these undesirable changes. Many of the opportunities to reduce carbon dioxide emissions can benefit us socially, environmentally, and economically. And many of those opportunities are linked to trees and forests.

Those opportunities are discussed in a new book produced by AMERICAN FORESTS. Forests and Global Change, Volume 2: Forest Management Opportunities for Mitigating Carbon Emissions is a collection of 14 papers on topics ranging from forest management options to alternative product uses for wood. Some of the ideas presented in the book are discussed here.

AMERICAN FORESTS in 1989 began studies to quantify the potential role of trees and forests in mitigating the effects of global warming in the U.S. Our work looked at how trees and forests could help control the amount of carbon released into the atmosphere annually as molecules of carbon dioxide.

And what role could trees play in reducing global warming? An important one when you consider that about half the dry weight of wood is carbon. The vegetation, litter, humus, woody debris, and soils of the nation's 737 million acres of forest land contain 60 billion tons of carbon - about 40 times the country's annual carbon emissions. In addition, large volumes of carbon are stored in products made solely or in part from wood (houses, furniture, and books) and in landfills and dumps.

We can greatly increase the amount of carbon stored in forests. There are 116 million acres of private land, most small parcels, that are marginally successful as crop and pasture land but could be suitable forestland. There are also 211 million acres of public and private forest land where timber growth, inventories, and harvests could increase with more intensive tree planting. These changes could mean large increases in both number of trees and amount of carbon stored.

The net annual timber growth could eventually rise by about two-thirds - from slightly less than 22 billion cubic feet to more than 35 billion. That means larger harvests. The products created from some of that wood would offer more opportunities to increase carbon storage.

Timber cut 100 years ago still retains two-thirds of its carbon in long-lived products such as buildings, furniture, and books, and when discarded in landfills. Additionally, wood fuel can be used in place of fossil fuels, allowing the fossil fuels to continue to retain their carbon.

And what about the investment necessary to put these suggestions into practice? Our research shows they would yield returns comparable to those received on other types of investments. Implementing these economic opportunities could increase carbon storage by about 188 million tons a year. That's some 13 percent of the carbon now being released each year.

Using short-rotation woody crops for fuel could also have a substantial impact on carbon storage. In the studies connected with this work it was estimated that as much as 70 million acres of cropland could be made available for planting to woody crops. The role of these short-rotation crops in storing carbon could vary widely depending on the amount of land used for woody crops, the vegetative yields, and just how efficient the technology is in converting the harvested biomass to energy.

Opportunities also exist for controlling atmospheric carbon through planting trees and increasing canopy cover in urban areas. The additional trees would help, but most of the impact would come from energy conservation and continued storage of the displaced carbon in fossil fuels.

Properly placed trees that shade homes and other small structures from direct sunlight can reduce the energy used for air conditioning by as much as 50 percent. The urban heat island effect has increased city temperatures an average of several degrees above those in the surrounding countryside. Trees that shade parking lots, streets, and other heat-absorbing areas can reduce temperatures and the need for energy for cooling.

By providing an effective windbreak, trees can also reduce the energy needed for heating in winter. A well-placed windbreak, which does not also shade the home, can lower energy used for heating by as much as 15 percent.

Although it is difficult to quantify the carbon-storing effects of tree planting in urban areas, AMERICAN FORESTS estimated that a modest planting program (planting an estimated 17 million trees annually nationwide) could increase carbon storage by about 12 million tons a year. A substantial planting program (planting 42 million trees annually nationwide over a 10-year period) could increase storage by 32 million tons a year.

Windbreaks and shelterbelts in rural areas can also help lower carbon emissions. As in urban areas, most of the impact would come from a reduced dependence on fossil fuels due to increased productivity from cropland and livestock, from reduced energy needs for heating and cooling on farmsteads, and by preventing some of the buildup of drifting snow, lessening the impact of operating snow removal equipment.

Two other options exist for reducing carbon emissions, although quantitative estimates of their impact have not been developed. The first would substitute wood for other materials, recycle wood products, and improve wood use. A substantial portion of the potential increases in carbon storage discussed here would come from substituting wood biomass for fossil fuels. We can also reduce our reliance on other forms of energy by substituting wood for steel and plastics and by recycling the millions of tons of paper and solid wood that are hauled away to landfills and dumps each year. Simple practices such as improving the design of structures and more vigilant upkeep and maintenance to increase service life, would reduce the demand for materials and energy needs.

Better management and release of carbon from our existing forests is another option. Millions of tons of carbon go back into the atmosphere each year from the decay of forest vegetation. Some forests, particularly those in the Inland West, are heavily overloaded with biomass, increasing the risk of fires that would release enormous amounts of carbon and cause major environmental economic damage (see "Wildfire: Carbon Threat Heats Up," page 27).

Carbon storage could increase by 300 million to 600 million tons a year when all the opportunities described above are considered. This is enough to offset somewhere between 20 and 40 percent of the carbon the U.S. emits annually.

These changes would do more than just reduce carbon emissions, providing many positive benefits to the natural environment, our quality of life, and the economy. For example, converting marginal crop and pasture land to forests would reduce soil erosion and flooding, improve water quality and wildlife habitat, and increase recreational use and owner income. Planting trees in urban areas would improve residents' quality of life and reduce cooling and heating costs. Jobs would increase as more people were needed to plant trees, manage resources, and process wood products.

Forestry opportunities are not a panacea. It will take much action - including energy conservation and the development of alternative energy sources - to control carbon emissions. But tree and forest programs can make a substantial contribution. They should be included in any comprehensive effort to slow global warming.

RELATED ARTICLE: The Carbon Trip or How our trees and forests affect the global - and local - climate

Carbon dioxide, the major greenhouse gas, is essential for photosynthesis in plants but a potential health and environmental threat when excessive amounts are produced by burning fossil fuels. This traps heat in the atmosphere and causes the planet to slowly warm. Trees and forests, together with increased energy conservation and alternative energy sources, can reduce carbon dioxide production and build-up - and slow global warming. The U.S.'s 737 million acres of forestland store 60 billion tons of carbon - about 40 times our annual carbon emissions. Planting more trees would allow us to increase carbon storage by 300 million to 600 million tons a year. Here's how:

* 16 million acres of private land, mostly small parcels marginally successful as crop and pasture land, could be forested.

* Sustainably grown wood fuel used in place of fossil fuels keeps carbon stored in fossil fuels. Up to 70 million acres of crop-land could be planted to woody, fossil fuel-replacing crops.

* About 30% of rural forest carbon is stored in trees, 60% in soil, and 10% in other plants and on the forest floor.

* 211 million acres of public and private forests could be more intensively planted with trees.

* Carbon makes up about half the dry weight of trees.

* Increasing tree cover and tightening dark, heat-absorbing surfaces can decrease city temperatures by 6 to 12 [degrees] F.

* Large city trees store 90 times more carbon per year than small ones.

* These trees store carbon but save even more as natural air conditioners, cooling our communities without burning fossil fuels.

* Property placed shade trees reduce the energy used for home air conditioning by as much as 50%.

* Plant trees on the east and west sides of homes, especially to shade air conditioners and windows.

* 800 million tons of carbon are stored as building materials in the nation's 121 million housing units. Furniture and landfills also store carbon.

Want To Know More?

Most actions that involve trees and forests in reducing the build-up of carbon dioxide will produce numerous other sociaL, environmental, and economic benefits. To learn about planting and caring for trees to slow global warming and improve the environment, contact AMERICAN FORESTS' Global ReLeaf 2000 campaign, PO Box 2000, Washington, DC 20013; 202/667-3300 or visit our Web site: http://www.amfor.org.