Abstract
Trees are large engineering structures that have to withstand major wind and static forces and translocate considerable volumes of water. Natural selection has over millions of years optimised tree structure to maximise survival of the species. Naturally this process does not necessarily optimise the properties of the resultant lumber such as hardness, stiffness and strength. Such wood properties can now be improved by genetic engineering and tree breeding. If this is done without understanding the contribution of wood structure to tree survival, this can lead to increased susceptibility to windthrow, splitting and branch damage in the standing tree and internal checking and collapse during wood drying. As a first step to quantifying these potential problems this paper reviews latest findings on the nanostructure of the cell wall of softwoods and then discusses the probable relationships between microfibril directions in the secondary cell wall layers and potential threats to the survival of trees such as excessive vibration and crack propagation.
Zusammenfassung
Bäume können als große Holzkonstruktionen aufgefaßt werden, die starken statischen und Windbelastungen ausgesetzt sind sowie große Mengen an Wasser transportieren. Die natürliche Selektion hat über Jahrmillionen die Holzstruktur und damit das Überleben der Arten optimiert. Dieser Prozess optimierte nicht notwendigerweise die resultierenden Eigenschaften von Schnittholz wie Härte, Steifheit und Festigkeit. Solche Holzeigenschaften können inzwischen durch Züchtung und genetische Manipulation verbessert werden. Werden diese Versuche unternommen, ohne die Bedeutung der Holzstruktur für das Überleben des Baumes zu kennen, so kann das zu verstärkter Anfälligkeit für Windbruch, Risse und Astschäden am stehenden Baum sowie zu Rißbildung und Kollaps während des Trocknens führen. Als ersten Schritt zur Quantifizierung dieser möglichen Probleme gibt diese Arbeit einen Überblick über jüngste Erkenntnisse zur Nanostruktur der Zellwand in Nadelholz. Daran anschließend erfolgt eine Diskussion wahrscheinlicher Beziehungen zwischen der Orientierung der Mikrofibrillen in den Sekundärwänden und möglichen Gefahren für das Überleben des Baumes wie übermäßige Vibrationen und Rißfortpfianzung.
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Booker, R.E., Sell, J. The nanostructure of the cell wall of softwoods and its functions in a living tree. Holz als Roh-und Werkstoff 56, 1–8 (1998). https://doi.org/10.1007/s001070050255
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DOI: https://doi.org/10.1007/s001070050255