The mechanical architecture of the trunk of Aralia spinosa during the crown building phase is described. All of the trunks sampled exhibited continuous taper along their length, and taper was dependent on ramet age and size. The trunks of older, larger ramets were more tapered than those of younger, smaller ramets. Trunk specific gravity was positively correlated with both ramet age and size. Specific gravity declined acropetally in 73% of the trunks sampled. Bark thickness exhibited an acropetal decline in 93% of the trunks, while only 60% exhibited a significant decrease in the percentage of the cross-sectional area of the trunk composed of bark. Sixty seven percent of the trunks exhibited an acropetal decline in the percentage of the cross sectional area composed of wood, while all trunks exhibited an acropetal increase in the percentage of pith. On average, 47% of the variation in specific gravity could be attributed to the percentage of wood, while 77% could be attributed to the percentage of pith. The percentage of the cross sectional area composed of bark accounted for only 14% of the variation in specific gravity. Wood specific gravity was generally unrelated to ramet age, size or position along the length of the trunk. The mechanical architecture of the trunk of Aralia spinosa exhibits considerable ontogenetic variation. We suggest that trunk construction imposes constraints on the maximum size attainable and the crown form of this species.

Key words: Aralia spinosa, biomechanics, specific gravity, trunk anatomy