INFLUENCE OF ARTIFICIAL GAPS IN TROPICAL FOREST ON SURVIVAL, GROWTH, AND PHYTOLYMA-LATA ATTACK ON MILICIA-EXCELSA

Milicia excelsa and M. regia are important timber species in moist tro pical areas of Africa. They have not been successfully grown largely b ecause of attacks by gall-forming psyllids in the genus Phytolyma. Our objectives were to evaluate the growth of planted Milicia seedlings a nd incidence of psyllid attack in small (4.2 m(2)), medium (18.5 m(2)) and large (>500 m(2)) artificial gaps in the Bobiri Forest Reserve in the Moist Semi-Deciduous Forest of Ghana. After 13 months, height and diameter growth of Milicia seedlings were significantly greater in th e medium and large gaps than in the small gaps. Insect attacks occurre d first and most severely in the large gaps, but spread to gaps of all sizes between the 11th and 13th months after planting. While gap size significantly affected the susceptibility of seedlings to psyllid att ack, it is not the only factor important in determining susceptibility of Milicia excelsa under field conditions. We conclude that gap sizes in the range of 10-50 m(2), where irradiances are from 30-60% of full sunlight, in forests similar to those at the study site, seem to be m ost suitable for regeneration of Milicia. (C) 1998 Elsevier Science B. V.