Paper discusses the influence of site quality on self−thinning process in silver birch stands growing on abandoned farmlands in Mazowieckie region (central Poland). Number of trees in a stand decreases with increasing age. The better the site (the higher site index value), the higher number of trees can be observed. However at the age of 10 difference between sites of various quality (site index) become insignificant. There is no need to include site index into the self−thinning models for young silver birch stands.
The paper describes evaluation of spruce radial growth variability, based on of synchronized individual increment sequences (dendroscales). The empirical material were increment samples from 215 trees, growing on ten research plots in the Silesian and Żywiec Beskids. For each plot in each year there was calculated the raw average chronology, indexed chronology and the coefficient of variation for incremental indexes. In addition, an analysis of the occurrence of pointer years was performed. The observed medium-term changes of the analyzed incremental indices lead to conclusion that in the second half of the twentieth century, a certain external factor influenced the growth of tested spruces. Both the obtained results and the existing studies provide a basis for an assumption that this factor was mainly air pollution.
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