THE NATIONAL ACADEMIES PRESS 500 Fifth Street, N.W. Washington, DC 20001
NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the panel responsible for the report were chosen for their special competences and with regard for appropriate balance.
Support for this study was provided by the Department of the Interior under contract no. 80221-A-G100. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.
International Standard Book Number 13: 978-0-309-21231-1
International Standard Book Number 10:0-309-21231-6
Photo on the cover is courtesy of David Policansky.
Additional copies of this report are available from the National Academies Press, 500 5th Street, N.W., Lockbox 285, Washington, DC 20055; (800) 624-6242 or (202) 334-3313 (in the Washington metropolitan area); Internet, http://www.nap.edu.
Copyright 2011 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America.