Experience with the tropical shelterwood system of regeneration in natural forest in Nigeria

Abstract

The Nigerian tropical shelterwood system (T.S.S.) was a major management preoccupation of the Forestry Service in western and mid-western Nigeria during the 1950s, and altogether about 200 000 hectares of forest were treated under this system. The method was developed in response to what, at the time, was regarded as a need for an extensive system of regeneration which could keep up with, and be financed from, the earnings from forest exploitation. It was intended to obtain sustained or improved yields, particularly of the primary economic species, to supply mainly export markets. The system consisted of canopy opening, by poisoning unsaleable trees with sodium arsenite to promote survival and growth of seedlings of valuable species, and also climber cuttings and cleanings in order to control climbers and herbaceous weeds. The treatments were begun 5 years before exploitation. Originally the felling cycle was fixed at 100 years, and a final crop of 25 fully grown trees per hectare was regarded as acceptable, compared with actual removals at the time of about 5 trees per hectare on average. Satisfactory regeneration was regarded as a minimum of 100 well grown seedlings and saplings of listed economic species per hectare. The system was abandoned primarily because it did not make sufficiently intensive use of the land to compete with other forms of land use, such as cocoa, oil palm, or arable crops. Something more obvious than natural regeneration methods had to be done with the land if it was to remain in forestry use, and during the 1960s the emphasis changed to artificial regeneration, particularly by ‘taungya’. In the 1970s it has become apparent that, owing to Nigeria's limited area of high forest estate, intensive forestry would be required to meet future home requirements. It now seems that the system could not be economic because of the paucity of valuable regeneration and because of the relatively slow growth rates in natural forest. Silviculturally there was the difficulty of reconciling the need to open the canopy and yet at the same time to control growth of climbers and herbaceous weeds. Natural forest is not adapted to withstand heavy exploitation nor to maintain high increments. Though timber crops can produce high increments in the humid tropics, they may need to be established by planting and considerable capital investment may be required for the purpose.