Conclusions

Twining climbers that attach firmly to the host support eventually require substantial compliance to escape stresses. Most of the climbing strategies require a stiff initial development to (a) get off the ground, (b) locate host supports, and (c) span distances between host supports. A twining strategy would therefore require an initial phase of stiff development followed by a later stage of compliant development. This requires a relatively sophisticated change in stem development and is mostly observed among dicotyledonous angiosperms that possess a bifacial vascular cambium and produce a specialized type of highly compliant wood during later growth. Many of these wood types have been termed "anomalous wood" (or more recently, variant cambia), and produce a wide range of vascular configurations that often incorporate enhanced hydraulic conductance, wound repair, and mechanical compliance properties. Is high compliance necessary for all climbing habits? For firmly attached twining plants that produce large diameter climbing axes, the answer is probably yes. However, some kinds of hook climbing may require relatively stiff stems so that the plant stem will be more likely to sway onto another neighboring support rather than buckle and collapse.

In summary, climbing plants can show many types of attachment from firmly attached twiners to less well attached hook climbers and to leaning plants. Bending mechanical properties of the stem and its change during development can differ between these categories: Twining climbers tend to produce lower values of Estr in older stages of development than other more loosely attached climbers. This is probably because firm attachment to host plants requires high compliancy to survive movement of the host plant. Other niches linked to more loosely attached climbing modes are open to a wider range of plant groups and do not require high compliancy in older growth stages. This type of climbing strategy has been adopted by a wide range of plant groups, notably monocotyledons.

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