Opposing Growth Trends Created by External Disturbances in Larch Forests of the Mongolian Altai

If tree-ring series from different trees are merged to a chronology, in order to for example make inferences on climate, these series must be checked for consistency. Statistical parameters, including the Gleichläufigkeit (GL = coefficient of agreement) and standard t value have been applied for this purpose and are usually combined to boost the informative value. We tested the hypothesis that low GL and t values can, in turn, be used as indicators of external disturbance in a case study in forests of Siberian larch (Larix sibirica) in the Mongolian Altai. Since these forests were known to have been subjected to considerable selective logging, we were interested as to whether opposing trends in the radial stem increment between different tree individuals of the same forest stand can be correlated with logging intensity. We found low GL and t values at high tree stump densities and basal areas. Furthermore, other factors which are interrelated with logging were also correlated with GL and t. These factors included tree age, the dominance type (dominant versus suppressed position), the competitive pressure by neighbouring trees and stand density. In conclusion, low GL and t values can be used as indicators of external disturbance. However, the prevailing type of disturbance can only be identified in combination with a study of structural stand traits. In the present case study, the tree stump density combined with GL and t values are assumed to be good proxies of selective logging intensity.