Studying the diameter growth of Persian oak and its relationship with climatic parameters in Zagros forests (Case study: Sarab-Karzan forests of Ilam)

The aim of this study is to assess the effect of climatic parameters on diameter growth of Persian oak trees in Sarab-Karzan forests of Ilam. Climatic data of a 29-year period (1987-2014) was obtained from synoptic weather station of Ilam to extract some mean monthly parameters. For investigation of tree diameter growth, 15 individuals with diameter 20 to 25 cm were chosen and core samples were taken from north side of trees using increment borer. They were polishd with corse and soft sandpapers and dimater growth was measured using microscope model 1001. Pearson correlation was used to investigate the correlation between diameter growth and climate parameters. Independent sample t-test was conducted to evaluate the significance of the correlations. The results showed that mean diameter growth of trees was 2.44 mm over the 29-year period. The highest correlation was observed between diameter growth and relative humidity in July (Pearson coefficient of 0.501) and September (0.558) (P≤ 0.01). In general, higher correlations were observed between diameter growth with rainfall in May (0.273) and temperature in July (0.354).