Vegetative life history of a dominant rain forest canopy tree

Tetramerista glabra has a remarkable combination of life history traits. it is a dense-wooded, large, common canopy tree in primary pear swamp rain fo rest. Its seedlings, although shade tolerant, can grow rapidly in high ligh t conditions, but frequently lack structural stability Most juvenile stems (94% in the understory and 38% in canopy gaps) collapse under their own wei ght or from branchfalls. Fallen stems then ramify into vegetative sprouts, which in turn may collapse, perpetuating a vegetative juvenile cycle. Most recruitment is from sprouts rather than from seed. Structural analysis of s tem dimensions shows that stems 2-8 cm DBH (diameter at breast height) are dose to the theoretical buckling limit, especially for those dependent on n eighboring vegetation to maintain vertical form. Trees > 4 cm DBH persistin g as upright stems develop stilt root support and become structurally indep endent at ca 8 cm DBH. Eventually, as stems thicken, stilt roots anastamose and trees adopt the cylindrical growth form of mature canopy trees (up to 150 cm DBH). Thus, the vegetative life history strategy of the species is t o: (i) regenerate a large "ramet bank" from the majority of juveniles that fail structurally while suppressed in the understory, and (ii) to maximize height growth at the expense of diameter growth in high light conditions. T he growth pattern and plastic form of I:glabra shows how a shade tolerant s pecies may adapt to utilize the ephemeral light resource in canopy gaps. Th e growth strategy of this species allows it to circumvent the normal trade- off between shade tolerance and rapid growth in Canopy gaps.