Cambial Cell Production and Structure of Xylem and Phloem as an Indicator of Tree Vitality: A Review

Abstract

One third of Europe’s land surface is covered by forests, with important economic and social value. They constitute the most natural ecosystems of the continent. Natural biotic and abiotic disturbances affect their structure and composition. Sustainable forest management and environmental policies rely on the sound scientific resource provided by long-term, large scale and intensive monitoring of forests. Long-living trees and ecosystems are suitable for studying the impact of human factors as opposed to the effects of natural system variability. Forest monitoring helps to improve our knowledge of the state of forests and to quantify changes that are taking place within forests and related ecosystems. Information about forest ecosystem functions and processes is, however, also necessary to gain an understanding of the causes underlying such changes and, subsequently, to model the future effects of natural and anthropogenic stress factors on our forests and understand the adaptation potential of forests to the effects of environmental change and air pollution (UNECE, 2008). The vitality of trees is one of the most important indicators of forest condition and can be characterized by different parameters, such as assessment of the crown condition, tree growth etc. (UN-ECE, 2008). However, the latest studies show that cambium activity and increments of its products – secondary phloem and secondary xylem (wood) – reflect the vitality of trees (Gricar et al., 2009). In the different vitality of silver firs (Abies alba Mill.), it has been demonstrated that data on phloem increment structure, the relationship between the phloem and wood increment and the number of cambial cells in the dormant state are very useful in the assessment of the health condition of trees. This review focuses in particular on presenting the potential of structure and width of xylem, phloem and cambium in the case silver fir and pedunculate oak, as indicators of the vitality status of trees. Forest monitoring and indicators of tree vitality status will be briefly summarized. Growth ring patterns have proved to be an appropriate tool for quantifying the response of a forest stand to changing environmental factors, so wood formation processes that determine the structure of wood and its quality will be described in more detail. Finally, tree vitality has a major influence on wood quality. Two examples, silver fir and pedunculate oak, will therefore be demonstrated.