Niklas - Basic tree biomechanics

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Karl J. Niklas
School of Integrative Plant Sciences, Section of Plant Biology, Cornell University, Ithaca New York USA

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Key words: biomechanics, buckling, dynamic loading, maximum height, static loading, trees, wind.

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Abstract

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All structures, whether engineered or natural, obey the same physical laws and processes. Trees are particularly susceptible to these laws and processes because they are structures (composed mostly of wood) that begin and end their lives in the same location, which can experience dramatic changes in weather and soil conditions. The biomechanical behavior of trees is reviewed by presenting and discussing a few basic equations, with a particular emphasis on the effects of wind on branches, trunks, and roots. Limited space precludes a detailed review of these equations. Therefore, some basic references are listed to provide the necessary details. An important point is that unlike engineered objects (and engineering theory that deals with them), trees are growing biological entities (that violate many of the assumptions of engineering theory). Consequently, the equations presented here provide only a first order approximation of how trees will respond to static (self) and dynamic (wind) loadings. Understanding the limits of these equations, therefore, is a critical first lesson in dealing with the biomechanical behavior of trees. In the final analysis, every tree will ultimately fail. The challenge is to anticipate when and how.

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