J. D. Sauerländer's Verlag, Bad Orb

There is a long tradition in forest sciences to concentrate on the investigation of aggregated processes. The aim was according to Alexander v. Humboldt “to find out the mean state around which because of the seeming freedom of nature all phenomenon oscillate within narrow limits”. Especially this approach has been used in the construction of yield tables. In this contribution the important role of the height of the tree Xm and the age tm at the maximum of the increments is shown for the analysis of the tree height growth. The used method of the determination of these parameters by the help of growth data series is described.With the help of examples it will be shown, that the growth curves for mean values of the height of spruces and also the growth curves for stand heights of spruces become nearly identically after a simple transformation of the axes independent of the site quality. After this transformation the age is practically measured in units of the age reached when the maximum of increments appears and the height is measured in units of that height which was reached at the entrance of the maximum of increments. This speaks for a unique growth principle of spruces independent from the site. Furthermore it follows that the influence of different characteristics of sites on the growth of the height of trees leads essentially only to a change of the age tm and the height Xm at the entrance of the maximum of the increments. An equal result has been obtained for red oaks. Their transformed growth curve is nearly in agreement with the unique transformed growth curve for spruces. For additional tree species (fir, red beech and douglas fir) indications have been found that their transformed growth curves also are in rough agreement with the corresponding unique growth curve for spruces. This indicates possibly an additional unique growth principle which only weakly depends on the tree species. The important role of the time tm at which the maximum of increments appears for description of the growth of tree heights was already pointed out by Backman in 1943. But for the second important parameter he used the value of the maximum of the increments max(dX/dt) instead of the height of the tree Xm reached at the moment tm when the maximum of increments appears. The findings reported here may be used in different ways for forestry and for forest science. But first of all they should be checked by the help of additional growth data on trees and stands. Having this in mind just a few possible examples for an application of the mentioned findings shall be mentioned:1. The data collected on different test areas may be integrated after the         transformation (1).2. It seems to be hopeful to find out the future growth curve of a site using step by step the growth data in the early growth period by looking for a couple of tm and Xm which transforms the data by (1) to the state independent growth curve.3. Stable sites may be distinguished from influenced sites (e.g. by climate change) by comparing their transformed growth data series.4. Looking for a relation between tm and Xm one may try to characterize a site influence on the growth of tree heights only by one parameter.5. First attempts indicate that transformation (1) may be successful applied to other growth indicators also.For the precise determination of the transformation parameters tm and Xm a sufficient number of measurements of the growth indicator before and after tm are necessary. This should be taken into account for further applications of the described transformation.

Download