Search

The vascular cambium of trees is a secondary meristem and is responsible for the formation of the xylem and phloem. The main focus of this chapter is on the xylem, specifically on the following three topics, demonstrating that the cambium is not only responsible for the quantitative side of xylem formation, but also for the expression of stable anatomical features essential for wood identification. In this complex process, we first describe the seasonal cambial activity and its environmental control. Second, we discuss the cambium’s involvement in the restoration of tissues after injuries. Third, we examine the cambium-dependent shaping of taxa-specific wood anatomical characteristics. The results are mainly based on light microscopy; however, electron microscopy was also occasionally used to reveal structural features on the cellular level.

Nach mechanischer Verletzung eines Baumes bis in den Holzkorper hinein wird die Wunde von den Seiten aus uberwallt. Ziel der Untersuchungen war es, die Entwicklungsstufen der Uberwallung am Wundrand bei Buche (Fagus sylvatica L.) und Eiche (Quercus robur L.) licht- und elektronenmikroskopisch darzustellen. Bereits nach etwa zehn Tagen war eine deutliche Reaktion zu beobachten, ausgelost durch Zellteilungen der wundnahen Kambial- und Holzstrahlzellen. Als Folge entstand ein junger Kallus aus isodiametrischen parenchymatischen Zellen mit zumeist grosen Vakuolen. In den Vakuolen waren zum Teil dunkel gefarbte Inhaltsstoffe eingelagert. Sechs Monate spater hatte sich aus diesem undifferenzierten Kallusgewebe ein deutlich vom Wundrand hervortretender Uberwallungswulst gebildet. Dieser enthielt die spezifischen Gewebe Wundholz, Wundkambium, Wundrinde und Wundperiderm, deren strukturelle Entwicklung diskutiert wird.

Trees in urban areas are pruned for several reasons. Each pruning cut causes a wound, which leads at least in the exposed wood at the wound surface to discoloration and decay. The extension of the resulting defect depends on wound diameter, tree species, time of wounding, wound treatment, and last but not least the attachment of the branch to the stem. The effects of different pruning cuts on urban trees has been investigated in Hamburg, Germany, since 1985. The study of 750 different pruning wounds on typical urban tree species lead to the Hamburg Tree Pruning System (Hamburger Schnitt- methode). The system is described in this paper and answers the following questions: How should branches with and without a branch collar be removed? How should dead branches be removed? How should branches with included bark or codominant stems be removed? What are the differences between tree species in wound response? What is the maximum wound size which will be effectively compartmentalised by the tree?

Eine bislang wenig beobachtete Wundreaktion von Baumen ist die Bildung eines Flachenkallus auf dem freigelegten Holzkorper. Unterhalb dieses Wundgewebes entsteht weder eine Verfarbung noch eine Faule im Holz. Die Literatur der letzten ca. 250 Jahre sowie die ersten Ergebnisse aus eigenen Untersuchungen an kunstlich angelegten Stammwunden an funf verschiedenen Baumarten werden vorgestellt. Danach konnen offenbar alle Laubbaumarten einen Flachenkallus ausbilden. Verstarkt wird dies, wenn nach der Verletzung moglichst sofort eine Wundbehandlung erfolgt, z. B. mit einem Wundverschlussmittel oder mit schwarzer Kunststofffolie. Warum bei gleicher Behandlung derselbe Baum vereinzelt vollflachig, z. T. gar nicht mit der Bildung eines Flachenkallus reagiert, ist bisher ungeklart. Bereits jetzt lasst sich die Empfehlung geben, an oberflachigen Rucke- und Anfahrschaden jegliches mechanische Bearbeiten mit schneidenden Geraten zu unterlassen, da dies die Bildung eines Flachenkallus verhindert.

Breaking-off of crown parts and large branches is a common type of tree failure and can result in substantial damage to objects and persons. The trees are often irreversibly damaged as well. Reasons for this type of failure are usually included bark in forks and decay or cracks in branches. As an alternative to topping or felling hazard trees, a tree crown stabilization system was developed for the protection of crowns endangered by possible failure. The System Osnabriick consists of at least two double belts, each strapped around the stem or branch and connected by wire cables. Wood-biological investigations on beech trees with six-year-old double-belt systems showed that neither discoloration nor fungal attack occurred in the wood and bark under the belts. The cambium beneath the belts apparently was not impaired either. The double-belt system makes it possible to maintain old trees with severe defects in urban areas by safeguarding their natural crown architecture as well as providing maximum safety to the public.

Holes from increment borings create wounds that lead to discoloration and may result in a colonization of the wood by fungi. There are various opinions about the damage caused by such borings and about the efficacy of wound dressings. For this reason, 78 differently treated boreholes in large-leaved lime (Jilia platyphyllos Scop.) and small-leaved lime (Tilia cordata Mill.), as well as in horsechestnut (Aesculus hippocastanum L.) and silver birch (Betula pendula Roth), were examined macroscopically and microscopically with regard to the wound reactions nearly 10 years after boring. Obvious differences in wound reactions were observed among the tree species. Both species of lime compartmentalized the wounds very effectively. Horsechestnut, on the other hand, revealed more extensive discoloration. Silver birch had the weakest compartmentalization, with discoloration up to 2 m (6.6 ft) in length. Cambial dieback around all borings, except for those plugged with creosote-impregnated wood dowels, was approximately the same for all species. Fungi occurred only within the discoloration. Cell wall disintegration was rarely observed. Treatment with LacBalsam® or polyurethane had little or no influence on the wound reactions. Boreholes sealed with impregnated wood dowels had far-reaching discoloration and cambial dieback as a result of the toxic effect of creosote.

Es wurden die Wundreaktionen nach Astring- und stammparallelem Schnitt an neun bzw. zehn Jahre alten Astungswunden an zwei unterschiedlich effektiv kompartimentierenden Baumarten, Linde und Roskastanie, untersucht.