AN ASSESSMENT OF EDGE EFFECT ON GROWTH AND TIMBER EXTERNAL QUALITY OFAYOUS (TRIPLOCHITON-SCLEROXYLON K-SCHUM) UNDER CAMEROON RAIN-FOREST CONDITIONS

An investigation was conducted in order to assess the edge effect on g rowth characteristics and timber external quality of ayous (Triplochit on scleroxylon K, Schum). Average bore height and diameter at breast h eight (Dbh) were compared for trees growing on the edge and inside the plantation. Only the average Dbh differed significantly between trees of the 2 positions. The external quality of timber was found to decli ne from bottom to top of the tree, irrespective of the position. This decline was more pronounced in the upper part of the interior trees as compared to the border trees. Finally, a segmented polynomial functio n comprising a sloping line and a plateau fitted fairly well the decre ase in Dbh measured at regular 5 m intervals from the border. The bord er effect thus appeared to be considerable, though limited to within 1 0 m of the edge where a 50% decrease in Dbh occurred. This suggests th at a guard area of at least 10 m wide should be allowed when sampling an old stand of ayous.