Investigation of the relationship between diameter growth of Alder species and climatic parameters in Neka-Zalmarud forests of Mazandaran province

Obtaining information about the impact of climatic variables on the growth of trees in the long run can be obtained through retrospective analysis of annual tree rings and using the tree chronology method. The aim of this study was to investigate the effect of climatic variables on the diameter growth of alder species along an altitude gradient in undisturbed Hyrcanian forests (Neka-Zalmorud forests of Mazandaran province).   

For this purpose, three altitude regions (low land, middle land and high land) in sample parcels were selected. In each area, 10 trees and totally 30 trees were selected using seleted sampling method. Necessary samples were prepared from using increment borer. 50-year (1965-2014) climatic data of temperature, precipitation and relative humidity were prepared from related sources and the SPI index was calculated.  

The results showed that there is a correlation between acceptable the time series and a strong relationship between growth and climatic variables. There was a significant difference between all three regions and the highest diameter growth was obtained in the middle land. The study of the relationship between climatic variables and the growth also showed that in the low land region, temperature and relative humidity factors have a significant negative correlation (-0.571) and positive (0.734), respectively. The same variables were significant in the middle land area. In high land region, none of the climatic variables showed a significant relationship with growth. 

 Growth at low and middle lands has shown more dependence on climate and growth of this species has decreased during the study period.