Strategies to balance between light acquisition and the risk of falls of four temperate liana species: to overtop host canopies or not?

Abstract

Summary 1. Lianas face a dilemma: how can they achieve a balance between the benefits they gain from light capture in their host canopies and the risk of falls resulting from the deleterious effects they have on the growth and survival of their host trees? To address this issue, we investigated leaf distribution patterns, canopy dynamics and the impact of four liana species on the growth of their hosts. 2. In the forest canopy, the majority of the leaves of Actinidia arguta (Actinidiaceae) received >80% irradiance relative to the canopy top. The leaf mass and the length of the canopy framework of this species increased linearly with time after it had reached the forest canopy (estimated from the number of growth rings in the main liana stem at 8 m height). In contrast, a much lower percentage irradiance was received by leaves of the three other species, Celastrus orbiculatus (40–80%, Celastraceae), Schisandra repanda (<40%, Schisandraceae) and Schizophragma hydrangeoides (<20%, Hydrangeaceae). In these species, canopy sizes did not change markedly with time. Species that intercepted more light acquired a larger number of host trees. 3. Growth-ring widths of the host trees of A. arguta and C. orbiculatus were smaller than those of liana-free trees; this difference was not significant in the two species that intercepted less light. The length of the basal stem between the rooting point and the point of attachment to the current host tree was greater in species that intercepted more light, suggesting the successful movement of these lianas to new hosts following the death of previous host trees. 4. Synthesis. Lianas have various ecological strategies for resolving their dilemma. They may be aggressive and rapidly spread in host canopies, intercepting much light, but reducing the risk of falls by acquiring many host trees to balance their top-heavy architecture. Alternatively, they may be commensal, whereby small liana canopies in lower positions in their host canopies acquire less light, but do not negatively affect the current hosts. Such variations reflect niche differentiation among species, and could be an important mechanism underlying the diversification and coexistence of liana species.