The methods used to value tropical forests have the potential to influence how policy makers and others perceive forest landsforestlands. A small number of valuation studies achieve real impact. These are generally succinct accounts supporting a specific perception. However, such reports risk being used to justify inappropriate actions. The end users of such results are rarely those who produced them and misunderstanding of key details is a concern. One defence is to ensure that the ultimate users appreciate shortcomings and common pitfalls.

Several traditional methods of maintaining soil fertility in bean-based cropping systems are reviewed as follows: visoso, large- scale chitemene, ngoro or matengo pit (Mbinga District, Tanzania), mambwe land-use system of northern Zambia (fundikila), mounds of the Wafipas (SW Tanzania), tumba land-use system (southern Tanzania), guie (central highlands of Ethiopia), mafuku in Zaire, termite mounds, agroforestry, relay intercropping systems, coffee- banana-bean cropping system of the Wahayas of Bukoba (Tanzania), removal of maize tassels (northern Malawi), and storage of nutrients in weeds (

In Colombia coffee production is facing risks due to an increase in the variability and amount of rainfall, which may alter hydrological cycles and negatively influence yield quality and quantity. Shade trees in coffee plantations, however, are known to produce ecological benefits, such as intercepting rainfall and lowering its velocity, resulting in a reduced net-rainfall and higher water infiltration.

Throughout Africa the importance of land use issues in relation to tsetse control planning has been emphasized consistently in the tsetse literature. Because of inappropriate land use, concerns for the environment in tsetse-freed areas have been expressed frequently. This debate is very relevant to Zimbabwe, where extensive tsetse control operations in recent years have confined the remaining area of tsetse infestation to parts of the Zambezi valley, a semi-arid region of the country with a fragile eco-system and limited agricultural potential.

This audiotutorial unit (cassette, printed script, 76 color slides, study guide, self-evaluation test), prepared by the Communications Support Unit at CIAT, is available for use with a manually or automatically synchronized slide projector/cassette tape reccorder. Each unit is a vailabIe from the Distribution Office at a cost of US$ 50; photocopies of the study guide alone can be obtained from the Cassava Information Center. The objective of this unit is to present some of the results of research conducted by the physiology Section of CIATs Cassava Program.