D

   of the biological sciences

that serves to determine the age of wooden objects. The method,

while employed primarily for dating archaeological and architec-

tural artifacts, is also used to solve art-historical problems (Baillie 1982;

Fletcher 1978; Eckstein, Wrobel, and Aniol 1983; Eckstein, Baillie, and

Egger 1984; Schweingruber 1988; Klein and Eckstein 1988). As such, it is

the discipline’s principal goal to give at least a terminus post quem for the

creation of a painting by determining the felling date of the tree that pro-

vided the wood for the panel.

This article presents the current state of the application of den-

drochronology as an aid for solving art-historical problems; also discussed

are tree growth patterns and the dendrochronological methods employed.

Atree grows by both elongation and radial increments. The elongation

takes place at the terminal portions of the shoot, branches, and roots. The

radial increment is added within a particular zone of living cells between

the wood and the bark. This layer, called the cambium, envelopes the

woody portion of the stem, branches, and roots.

Dendrochronology focuses primarily on the annual periodicity of

growth that is controlled by the climate (e.g., temperature and rainfall).

Inthe cool and temperate climatic belt, a dormant season occurs from

autumn to spring, and a growth season occurs during the summer. When

the vegetative period begins in May, new cells form to conduct water from

the roots to the treetop. These large cells are the earlywood cells. During

the summer, around the end of June, the latewood formation starts;

around the middle of September, the radial growth of the tree stops for

seven months. The result is the gradual accumulation of growth during

one growing season, forming an annual ring, or tree ring.

Conifers and hardwood species have different tree ring structures.

In conifers—such as pine, fir, and spruce (Fig. 1a)—the wood is more or

less uniformly composed of one cell type, the tracheids, and the growth

ring is distinguished by differences in both cell size and cell-wall thickness

between elements produced during the early and late parts of the growing

season. The hardwood trees can be divided into two groups. In one, tree

rings are evident because of the formation of a band of large earlywood

vessels for water conduction, followed by the formation of a more com-

pact latewood with smaller vessels and an increase in fibers, the cell

Biological Base of

Dendrochronology

39

Peter Klein

Dendrochronological Analyses of Panel Paintings