|Agro-forestry in the African Humid Tropics (UNU, 1982, 162 pages)|
|Taungya systems from biologiocal and production viewpoints|
From the papers presented, and subsequent discussion, it was clear that taungya systems have met with widely varying success in different countries and-at least in the case of Nigeria-in different sections of the same country. In large part this has not been due to technical or even economic problems, but more to basic political decisions and social acceptance. In particular, lack of continuity was cited as a problem. In Togo taungya has generally failed because the government has claimed forests as its property. This has led to widespread discontent and the destruction of timber trees in favour of fruit trees, which provide regular income after a relatively short period of establishment. In Kenya the taungya system is being phased out because labour costs are relatively high, there is a problem with the labourers or their relatives trying to settle in the forest, and very large areas need to be planted as industrial plantations.
With regard to the experiments on taungya in Sierra Leone, it was clarified that the plantations are used for food crops for the first one or two years, and then the farmers must stay out of the area until the final thinning is carried out. The farmers are then allowed to return and plant tree crops such as cola, citrus, coffee, and cocoa. It is expected that the timber crop will mature and the tree crops will decline in yield at about the same time (about 30-35 years after planting the timber crop), and the area will be clearfelled in order to begin a new cycle. It was noted that in Nigeria a similar system had been tried but had failed because the farmers began to think the forest reserve belonged to them and acted accordingly. The importance of crown shape and density on the yields of the tree crops was raised, but long-term data were not available.
The long-term effect of tree plantations was also discussed, although there was, again, a lack of decisive evidence. It was noted that fertilization may well be necessary when establishing second or third generation tree crops, depending on the inherent soil fertility, and that an initial dose of fertilizer at an early stage of growth could be far more effective than fertilization at establishment. The type and frequency of the products removed are also important. The export of timber, for example, might remove large quantities of calcium, while palm oil is almost pure carbohydrate. In most cases the harvesting and removal of forest products would remove far fewer nutrients than represented by the harvesting of food crops on an annual basis.