The research leading to this paper was supported by the Forestry Policy and Planning Division of the Food and Agriculture Organization of the United Nations, by Agriculture Cooperative State Research Service grant 95-37400-1851, by McIntire-Stennis grant 3986, and by the School of Natural Resources, University of Wisconsin-Madison. We thank P. A. Wardle and M. E. Chipeta for their help in defining the problem and setting the study objectives, and C. Brown and anonymous reviewers at FAO for their comments on an earlier draft.
