managing these areas. As new national policies are instituted, however, they can sometimes have unintended effects. In the wake of severe floods in 1988, for example, the government of Thailand instituted a ban on commercial logging. The subsequent rise in timber prices led to increased illegal cutting and failed to check the forces behind forest encroachment by shifting cultivators (Myers, 1989).

Efforts to review policies that contribute to deforestation are a prerequisite to sustainable land use in the humid tropics, and they merit expansion. At national and regional levels, policy reviews should respond to the specific biophysical, social, and economic circumstances that affect land use patterns within countries and regions. These reviews should also focus on the in-country effects of international trade, lending, and debt-reduction policies. At the international level, the review process will vary from institution to institution, depending on its size and objectives and the range of its activities.

Although the policy review process will necessarily vary, the following considerations are generally applicable.

• Given the complexity of the socioeconomic and ecological aspects of land use in the humid tropics, reviews should be undertaken by multidisciplinary teams.

• Economic policies that encourage large-scale logging and agricultural clearing should be identified and evaluated in terms of their externalized costs, social and ecological costs, and availability of transport infrastructure, such as roads and bridges. For example, the fees charged loggers for the right to cut standing timber seldom come close to the costs of replacing the volume removed with wood grown in plantations (World Bank, 1992). In general, these policies discourage long-term interest and investments in forest management (both in the public and private sectors), undervalue the full economic and environmental benefits of conserving primary forests, and hinder the adoption of sustainable land use alternatives.

• New methods of assessing and assigning value to the forests should be sought. Reviews should assist in recognizing the full range of the forests' economic benefits, the key environmental services they provide, the potential for sustainable use of their resources, the opportunity costs involved in forest conversion, and the rights of future generations to forest services and products. When possible, values should be expressed in standard economic terms, such as financial costs and returns, with cost and benefit streams discounted to a common base. Those that cannot, such as aesthetic values and environmental services secured through conserving biological diversity, should nonetheless be explicitly noted in all economic analyses (Barbier et al., 1991; Norgaard, 1992; Randall, 1991).