Does money grow on trees? With the growing interest in market-based trading systems to reduce carbon emissions, including their embrace by the Republican and Democratic presidential candidates, there is an increased likelihood that farmers in the Chesapeake Bay drainage may soon cash in on the sale of carbon offsets by planting and protecting trees on their land.

Trees remove carbon dioxide from the atmosphere as they grow and are one of nature's ways of capturing a portion of the carbon dioxide produced by burning fossil fuels.

This stored carbon may have cash value today because the global strategy to reduce carbon emissions and slow the surge of future climate change has spurred strong interest in market-based systems.

In a market-based system for carbon dioxide, government regulators would force a "cap" or limit, on the amount of carbon dioxide a company or industry could legally emit. Companies could meet their carbon emission caps through the increased use of lower-emissions or no-emissions energy, energy conservation or increased efficiency. Those companies that reduce their emissions below their required cap could sell their surplus reductions as credits-or emission allowances-to companies willing to buy them.

Carbon sequestration, what trees and other plants do as they lock up carbon dioxide in their growth, can be a component of a carbon cap and trade strategy.

Theoretically, companies or landowners could create and protect carbon sequestering sources, such as forests and wetlands, and sell carbon emission credits based on the tons of carbon sequestered-captured by the plants rather than released into the atmosphere. An acre of wooded buffer, for example, captures about 3,000 pounds of carbon per year. A power plant needing to offset 600 tons of carbon dioxide emissions could purchase 400 acres of such buffer to offset their emissions.

While in their embryonic stages, several voluntary carbon markets, such as the Chicago Climate Exchange, do exist. The number of organizations supplying carbon credits to the market has grown200 percent since 2002.

Europe has the only regulated carbon market. There, tons of carbon are bought and sold on an exchange and the price of carbon has risen steadily the last several years.

Given the increasing interest by individuals and companies to be carbon neutral and foster a green image, analysts see the appeal of carbon offsets growing for companies, municipalities and individual investors.

Proponents argue that carbon offsets create flexibility and allow a smoother transition to a carbon-free economy by helping companies meet more aggressive carbon-reduction targets and controlling the overall costs of reducing greenhouse gas emissions.

A viable carbon offset program in the United States could enlist agriculture in the global effort to reduce greenhouse gas emissions. Essentially, paying farmers and landowners to grow and protect trees and vegetation to lock up carbon would help utilities and manufacturers meet their greenhouse gas emission goals.

Perhaps most attractive to those concerned about water quality and the ecological health of the Chesapeake Bay are the many ecosystem benefits that would accrue from creating a monetary value for carbon sequestered by reconstructing wetlands and planting and protecting vegetation on riparian lands and flood plains.

Re-establishing native trees, shrubs and grasses along water bodies and sensitive wetlands reduces erosion and sediment delivery to the Bay; captures nitrogen and phosphorus that would otherwise pollute the water; and provides critical fish and wildlife habitat.

A successful market for carbon dioxide might encourage markets for these valuable ecosystem services. Voluntary markets for all of these already exist within the United States, although the trading of these respective credits has been sparse or nonexistent.

Whether federal, regional or watershed-based, challenges exist to successfully developing and implementing a carbon offset market. They include the need for rigorous accounting standards; reliability of monitoring, calculating and verifying carbon offset values; and dealing with lands already set aside and "valued" in conservation programs.

Yet, several major forces support the need for a market: Companies and governments show increasing interest in market-based cap and trade programs as a way to tackle the massive challenge of reducing global greenhouse gas emissions; and society is increasingly valuing and demanding more sustainable management of our natural resources.

If we find a market mechanism to pay landowners to restore trees, install streamside buffers and protect water quality, we will have taken a critical step in figuring out a greener future for the beleaguered waters of the Chesapeake Bay. And we will have shown that money can grow on trees.