RADIAL AND VERTICAL WOOD SPECIFIC-GRAVITY IN OCHROMA-PYRAMIDALE (CAV EX LAM) URB (BOMBACACEAE)

Radial (pith-to-bark) wood samples from Ochroma pyramidale sampled at breast height and at subsequent five meter height intervals were analyzed to determine basic specific gravity. Specific gravity increased linearly with radial distance at any given height. In multiple regressions both radial distance and height proved to be equally important independent variables in explaining variation in specific gravity. However, when radial distance was measured centripetally (bark-to-pith) rather than centrifugally (pith-to-bark), the importance of height diminished drastically. These results suggest that the secondary xylem produced at any one time along the bole exhibits the same specific gravity. This time-constant model is contrasted with the alternative extreme, the radius-constant model, where xylem at a given radial distance (pith-to-bark) would exhibit the same specific gravity. Both models present alternative developmental patterns for tropical wet forest species which commonly exhibit increases in specific gravity with distance from the pith.