Trees crown structure

Technical Nature. Wood is a complex plant tissue composed of several distinct types of cells. In the trees discussed in this text, wood is easily recognized as that tissue located to the inside of the tree bark and forming the interior bulk of all major stems, branches, and roots. Technically, wood is the main conductive and mechanical (or supportive) tissue of the tree, and is largely responsible for the upward translocation of water and dissolved minerals from the root system to the active tree crown (buds and functioning leaves) (J). The histological and cellular structure of wood and how it serves conductive, mechanical, and storage functions in the tree will be dealt with later in this chapter. 

If we draw an analogy between the structure of battery plates and the structure of a tree with a large crown, the plate grid would play the role of the tree trunk. The trunk spUts into several thick branches, which develop further into a system of thinner branches from which the leaves and buds grow. In the case of a battery plate, the AMCL plays the role of the thick branches from which the tree crown grows. That is why the skeleton of the AMCL should be built of thick branches so as to have low ohmic resistance. Otherwise, the AMCL of the plates will get strongly polarized when the high formation current is switched on. 

In the present paper firstly general methodical problems of vitality assessments of deciduous trees are discussed and also existing disparities or contradictions are pointed out if assessments based on "leaf loss" and those based on crown structures are compared. The necessity of a consideration of branching is substantiated and methods which have been developed until now are presented. 

Therefore, in the following paper the branching and the crown structure of trees in the assessment of tree vitality is considered. This is also important for the interpretation of aerial photographs. 

Stress symptoms of tree crowns leaf loss versus crown structure... 

For this reason it is not surprising if considerable disagreements between so called "leaf loss" and the crown structure, which will be discussed later, do occur if vitality assessments of the same beech trees are compared (fig. 1). The assessments may differ by up to 2 damage or vitality classes and agreement is only achieved for about 50% of the assessed trees (HESS.FORSTL.VERS.ANST. 1988, ATHARI KRAMER 1989a). 

Fig. 1 Disagreements between a vitality assessment of beech trees based upon leaf loss damage classes (SS L Verl.) and crown structure vitality classes (VS Kr Str.) after investigations of a) ATHARI KRAMER 1989a,b and b) HESS. FORSTL.VERS.ANST. 1988 the black columns mark the share of trees which are in the same vitality/damage class in accordance with both methods of assessment...

Fig. 2 Disagreement between a vitality assessment based upon crown transparency and crown structure (vc = vitality class according to ROLOFF 1989a) in many tree species (here wild cherry) the crown becomes more transparent with better growth...

In the following, tree vitality is discussed in terms of growth potential, which in trees is expressed in shoot growth. Although various branching structures within one tree crown have long been... 

Genetical consequences are presented by MOLLER-STARCK HATTEMER (1989). In beech trees he found (on the basis of crown structure) a decreasing genetic variety with decreasing vitality of the tree (heterozygotic grade, genetic diversity, respectively). 

Finally, changes of the crown structure of stressed beech trees may also have silvicultural consequences (DOBLER et al. 1988, HESS.FORSTL.VERS.ANST. 1988). As the canopy becomes more transparent after thinning, it is difficult to selectively regulate natural regeneration of beech stands. A modification of thinning approaches and methods have been suggested. 

Forests collect more pollutants than do surrounding surfaces with lower vegetation. For example, the forest edge will disturb the vertical wind profde and induce air turbulence that will in turn increase the dry deposition. The deposition at the front is considerably higher compared to that in the open field (by a factor of between 5 and 20), and also to that within the forest (a factor of 2 to 4). The increased deposition affects the vitality of the trees at the edge. Forest structures (tree species, crown density, stem density) differ widely in terms of aerodynamic roughness and leaf area, and these factors will each influence deposition. 

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