Journal Article

Brittleness of twig bases in the genus <i>Salix</i>: fracture mechanics and ecological relevance

Heike Beismann, Hiltrud Wilhelmi, Henri Baillères, Hanns‐Christof Spatz, Arno Bogenrieder and Thomas Speck

in Journal of Experimental Botany

Published on behalf of Society for Experimental Biology

Volume 51, issue 344, pages 617-633
Published in print March 2000 | ISSN: 0022-0957
Published online March 2000 | e-ISSN: 1460-2431 | DOI:
Brittleness of twig bases in the genus Salix: fracture mechanics and ecological relevance

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The twig bases within the genus Salix were investigated. Brittleness of twig bases as defined in the literature neither correlates with Young's modulus nor with growth strains, which were measured for S. alba, S. fragilis and S. ×rubens. For the species S. alba, S. appendiculata, S. eleagnos, S. fragilis, S. purpurea, S. triandra, S. viminalis, and Srubens, fracture surfaces of broken twigs were investigated and semi‐quantitatively described in terms of ‘relative roughness’ (ratio of rough area of fracture surface over whole area of fracture surface). The relative roughness clearly corresponds with the classification into brittle and non‐brittle species given in the literature. An attempt was made to quantify brittleness with mechanical tests. The absolute values of stress and strain do not correlate with the brittleness of the twig bases as defined by the relative roughness. However, the ‘index stress’ (ratio of stress at yield over stress at fracture) or the ‘index strain’ (ratio of strain at yield over strain at fracture), correlate well with the relative roughness. The graphic analysis of index stress against index strain reveals a straight line on which the eight species are ordered according to their brittleness. Depending on growth form and habitat, brittle twig bases of willows may function ecologically as mechanical safety mechanisms and, additionally, as a propagation mechanism.

Keywords: Growth strains; scanning electron microscopy; elasticity; fracture; plant ecology.

Journal Article.  8023 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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