Preface: J.M. Kimble, Linda S. Heath, Richard A. Birdsey, & R. Lal

The U.S. has vast areas of fertile soils that are used as cropland, grazing lands, forestlands, and other uses that are too numerous to mention. In 1999 a book on carbon sequestration, The Potential of U.S. Cropland to Sequester Carbon and Mitigate the Greenhouse Effect, was published. The second book in the series, The Potential of U.S. Grazing Lands to Sequester Carbon and Mitigate the Greenhouse Effect, was published in 2001. This third book in the series, The Potential of U.S. Forest Soils to Sequester Carbon and Mitigate the Greenhouse Effect, addresses soil found in forest areas of the U.S., including Hawaii, Alaska, and Puerto Rico.

Soil is the component of the Earths' surface the supports our agricultural crops, grazing lands, and forest production. In most cases, soils are only one to two meters thick, but within that zone are found most of the nutrients that are necessary to support all terrestrial life, the one major exception being carbon dioxide, which is taken from the atmosphere through photosynthesis. Mitigating the increase in atmospheric carbon dioxide is the focus of this book, with particular emphasis on how improved forest management can reduce the concentration of atmospheric carbon and increase the amount of soil carbon. Over time, some of the carbon fixed by the vegetation is converted into soil organic carbon. This book summarizes what is known about the characteristics of soil organic carbon and suggests management opportunities for diverse forested ecosystems. The broad range of forest ecosystems includes high alpine areas in the mountains, permafrost-affected areas in the North, tropical and subtropical systems in Hawaii and Puerto Rico, large areas of natural and highly managed temperate forests, wetlands, as well as the increasing area of urban forests.

The information contained in this book, when linked to the previous works, will provide the information that is needed to develop policies and options that will allow soil C sequestration to be considered as a serious option in developing mitigation policies to address global climate change. Soil management can lower the levels of greenhouse gases by increasing sequestration while providing many other positive benefits such as improving crop yields, reducing erosion, lowering needs for external inputs, and increasing environmental or societal benefits. This is a classic "win-win" scenario.

In April 2001 the authors of this book came together in Charleston, South Caroline, to go over drafts of their chapters, identify gaps, and discuss changes. Over the last 10 months the authors have spent considerable time and energy revising their chapters, and we thank them for this effort. They have put together an outstanding summary of information that clearly demonstrates the importance of soils in forested ecosystems.

Recent work published in the Proceedings of the National Academy of Sciences (December 18, 2001, edition at http://www.pnas.org/current.shtml) and the related overview article from Goddard Space Flight Center (December 11, 2001, edition at http://ww.gsfc.nasa.gov/topstory/2011204carbonsink.html) concluded that forests in the U.S., Europe, and Russia have been storing nearly 700 million metric ton of carbon per year during the 1980s and 1990s. This conclusion refers primarily to carbon in biomass; however, in most forest systems the soil pool is the largest carbon poll. Uptake of 700 million metric tons by forests is a significant factor in the global carbon budget. We now need to look at how much carbon can be taken up by soils in addition to the carbon going into the biomass.

Thanks are due to the staff of Lewis Publishers/CRC Press for their timely efforts in publishing this information and making it available to both the scientific and policy communities. We especially thank Lynn Everett from the The Ohio State University for her efforts in organizing the conference and in handling all of the papers that are included in this book from the first draft through the peer review process to providing the information to the publisher. She kept the pressure on to get the work done in a timely manner

Many times the comments made that you cannot see the forest for the tress, but this lack of vision also applies to the soils in forested ecosystems. We can see the trees, even at times the forest, but the material below the litter --the soil-- contains one of the largest carbon pools, is teeming with life, and yet is an ecosystem that most people never observe or understand. We hope this book will improve the understanding of the role of forest soils have on the overall environment. Soils are important to forest growth and the overall sustainability of our environment.