Physiology of Tropical Vines and Hemiepiphytes: Plants that Climb Up and Plants that Climb Down

Abstract

Vines climb up. From a starting point in the forest understory, vines use the mechanical competence of neighboring plants in their ascent towards the bright sun of the forest canopy. Hemiepiphytes climb down. They begin life in the treetops and extend earthward to form permanent and often substantial connection with the soil (Figure 13.1). Vines and hemiepiphytes hold in common a period of mechanical dependence, yet the physiological consequences and constraints associated with this reliance upon external support differs substantially between the two groups. In vines, adaptations essential for effective climbing constrain their outward form and thus influence the uptake, transport, and storage of energy and materials. For hemiepiphytes, in contrast, the major constraints may not be the particular rigors associated with life as either an epiphyte or a tree, but rather in the plasticity required to succeed as both. Our discussion of tropical vine physiology is morphologically organized, considering in turn the function of stems, leaves, and roots. With hemiepiphytes, we focus primarily on the nature of the transition between the epiphytic and tree growth forms. We draw upon the roles of vines and hemiepiphytes in tropical forest communities only as such discussion provides insights into their physiology.

Plants become climbers, in order ... to reach the light, and to expose a large surface of their leaves to its action and to that of the free air. This is effected ... with wonderfully little expenditure of organized matter ...

— Darwin, 1867, The Movements and Habits of Climbing Plants

And the whole life history of these outlandish trees seems beautifully contrived to accomplish this objective: — to seize a place in the sun in the midst of a dense tropical forest.

— Dobzhansky & Murca-Pires, 1954, Strangler Trees