Figure 2.

The hypothetical optimal tree size for vines (tree size includes both tree diameter and height) should vary with the climbing mechanism: tendril-bearers, stem twiners and root climbers. Benefits (∼ energy values) are assumed to increase with tree height because light harvest by climbing plants increases with height; the curve is further assumed to flatten out because most vines are not able to climb up to the top of canopy trees. Costs (∼ handling times) increase with tree diameter particularly for tendril-bearers and stem twiners because of biomechanical constraints: they fail to attach to thick trunks (see text); root climbers are free from this constraint but costs are assumed to increase slightly in very thick trunks—and hence old trees—because of the expected greater competition with other vines or epiphytes. Therefore, the optimal tree size, determined at the maximum distance between the cost and benefit curves, should be largest for root climbers and smallest for tendril-bearers.