ok, so i thogt this chapter is not that inteesting to post in blog originaly, but when u think better, why not?

next couple of posts will talk about tree and its biology. And most importantly tree diseases and things that affect tree look. Basically all stuff that makes trees visually interesting and which are not simulated in tree generators.

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Introduction:

When considering Virtual Tree Generation, it is important to understand what is the biological nature of a tree. In this chapter, important biological elements and processes related to trees will be discussed, which are important in some way for tree modeling.

1.1 Tree

A Tree is a woody plant and its’ main trunk is usually

un branched. Usually a tree is divided into three major parts those are the crown, trunk and the roots. The crown consists of branches, twigs, and leaves.

Trees do not heal their injured tissues; instead the cells of injured tissues change and become a barrier for diseases and further decay. The layers of new tree tissues usually cover a wound. The changed wood tissue is called a “reaction zone”. In many tree species it is easy to recognize, this wood as it is often darker in color compared to healthy wood tissue (Whiting et al. 2005).

A trunk is commonly defined as the main stem of a plant which serves as a support for leaves and a connection with the roots. The trunk also serves as a water storage tank, for example in the case of baobab trees. Water and minerals collected through roots are then transmitted through the trunk to the leaves. The trunk itself consists of two main types of wood. The Xylem is a supporting wood, and Phloem is wood for water transportation (Whiting et al. 2005).

tree structure

tree structure

Fig 4.Wood layer structures. Picture taken from: David Whiting, Robert Cox, and Carol O’Meara; 2005. Tree Growth and Decay. GardenNotes #611.

The bark of a tree serves as a protective layer from different types of damage and the Phloem is a tissue beneath the bark. The main purpose of the Phloem layer is to transport sugars and carbohydrates produced by leaves and to feed the roots. Xylem is a wood tissue which acts as a supporting material for the whole tree.

Wood which grows at the beginning of summer is used for water transportation inside the tree. If enlarged, its structure remains tubular in its shape, while tree tissue which grown at the end of summer is much more dense in its structure and serves as a support material for the overall tree (Whiting et al. 2005).

The “reaction zone“ does not always stop decay. Decay can easily advance in Xylem wood tissue which grows in early summer and serves as a water transportation system inside a tree. If the reaction zone would stop decay effectively, it would also plug Xylem tubes. As a result, the water supply inside a tree would be compromised and the tree would die (Whiting et al. 2005).

inside of tree

inside of tree

Fig 5. Decay creates a hole in the center of a tree. The darker area is a reaction zone. Picture taken from: David Whiting, Robert Cox, and Carol O’Meara; 2005. Tree Growth and Decay. GardenNotes #611.

When the wall of a trunk has a hole which leads to empty space in the center of the trunk, the tree becomes coincidentally weaker, and is considered hazardous. Tree holes are candidates for many flora and fauna species to use as a home.

Such inhabitants usually contribute to wood decay, and the death of the tree. Holes are sometimes filled with rainwater, which makes rotting possible. (Forest Resources Extension)

tre ee hole

tre ee hole

Figure 6. The strength of a tree is strongly reduced by a hole. Picture taken from: David Whiting, Robert Cox, and Carol O’Meara; 2005. Tree Growth and Decay. GardenNotes #611.

There are two main types of trees according to how new layers of wood grow. The first is “Exogenous” which are trees that grow outwards; meaning each year a new row of wood is being placed on the outside of the existing trunk beneath the bark. The other type is called “Endogenous” which, unlike the “Exogenous”, places new layers inside the trunk.

While most trees belong to the Exogenous category, others like Palms, Dragon trees and Cacti grow by extending themselves from inside. Usually each new layer of wood grows in one year, but that strongly depends on rain periods. A growth layer which is produced in one season is called an “Annual Ring” (Bodirlau et al. 2007). By counting the annual rings of a tree one can determine the trees age. The science of tree age determination is called “Dendrochronology.” Some trees in deserts might have a new layer after each rain season, which is not necessarily regular, and some trees may produce two layers of wood a year. In tropical areas where it is always wet, the annual rings on trees might be not seen at all.

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and see some “manually” modeled trees here

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