The hook climbers show a more variable range of shifts in mechanical properties compared with twiners and tendril climbers (Table 2.1; Figure 2.3 and Figure 2.4). The woody dicotyledonous liana Strychnos (Figure 2.6d and 2.6e) shows the highest value of Estr of all plants tested in young stages of development, i.e., over 12,000 MNm-2, followed by a large reduction in Estr (Table 2.1). In older stages, its value of Estr is also rather higher than most twining and tendril-climbing species. The two woody hook-climbers Bougainvillea and Rosa do not show a noticeable drop in Estr during development; rather, they retain relatively high values in old stages or increase them.
Monocotyledonous hook climbers (Figure 2.5) also show variable trends, depending on the taxonomic group they belong to. Species of Calamus (Figure 2.5b) show decreases in Estr to values of 1830 and 2300 MNm-2, equivalent to the highest values of old twining species (Lonicera and Secamone) (Table 2.1; Figure 2.3 and Figure 2.4). Old stages of these Calamus species are canelike and have lost the leaf sheath that contributed to relatively high values of Estr in young stages of growth. In Daemonorops jenkinsiana, old stages included stems, which are still surrounded by leaf sheaths. For this species, very old and long stems were not available in the studied area. In Plectocomia himalayana, the older stages measured show no changes in mechanical properties compared with young stages (Table 2.1; Figure 2.3 and Figure 2.4). For this species, values of Estr remain high, around 3000 to 4000 MNm-2 (Table 2.1). The South American climbing palm Desmoncus (Arecoideae) (Figure 2.5a and 2.5f) shows a quite different trend. Interestingly, both species show a marked increase in Estr in older stages of development, for which the leaf sheath has senesced and, in the case of D. orthacanthos, was finally lost. Values in young stages of around 4000 to 5000 MNm-2 are in the similar range, with higher values found among twiners and tendril climbers, whereas values in older stages of 8000 to 9000
Secamonopsis madagascariensis _ Secamone ligustrifolia _ Secamone geayii Secamone cristata Secamone buxifolia Secamone bosserii Pervillaea philipsonii Maripa scandens Machaerium sp. _ Lonicera sempervirens Lonicera reticulata Lonicera periclymenum Lonicera alseuosmoides Gnetum cf. guianensis Gnetum bucholzianum Gnetum africanum Fallopia albertii Doliocarpus sp. Condylocarpon guianense Aristolochia macrophylla Aristolochia gigantea Aristolochia brasiliensis
Smilax aspera Passiflora glandulifera _ Clematis vitalba Clematis flammula var. maritima Bauhinia guianensis
Strychnos sp. Rosa canina Plectocomia himalayana Desmoncus polyacanthos Desmoncus orthacanthos Daemonorops jenkinsiana Calamus tetradactylus Calamus acanthospathus Bougainvillea glabra
Lycopodiella cernua _ Ischnosiphon centricifolius Croton pullei Croton nuntians
Lonicera xylosteum Lonicera myrtillus Clematis recta
Branch angle climbers
□ Leaning climbers
2000 4000 6000 8000 10000 12000 14000 16000 18000
Structural Young's modulus (MNm 2)
FIGURE 2.3 Mean structural Young's modulus and one standard deviation of young stages of development of climbing plants with different modes of attachment. Black bars = dicotyledons, grey bars = gymnosperms, white bars = monocotyledons, striped bar = lycopod.
MNm-2 are higher than all other plants tested with the exception of the monocotyledon Ischnosiphon and the leaning species Lonicera xylosteum (Table 2.1).
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