Modelling the growth of tree plantations and agroforestry systems in South and East Africa: proceedings of the meeting in Finland, 24-28 August 1998 (Research notes / University of Joensuu, Faculty of Forestry ; 80 , Tiedonantoja / Joensuun yliopisto, Metsätieteellinen tiedekunta; 80; , Tiedonantoja.; 80, 1998)