Dendrochronological studies of common cypress (Cupressus sempervirens L. var. horizontalis) to determine its annual diameter growth rate and identify the oldest trees in the Hyrcanian habitats, Iran

In temperate regions, the one-year life cycle forms observable growth rings influenced by the genetic, physiological, climatic, and physiographic structures of trees that consider in dendrochronology. Common cypress (Cupressus sempervirens L. var. horizontalis) is a precious Mediterranean species that grows in the Hyrcanian regions, as the only native cypress in Iran. In order to determine the annual diameter growth of this species and to identify the oldest trees, a sample of 92 aging woods was selected in the Hyrcanian habitats of Iran. Samples were collected by an increment borer with a length of 50 cm and measured in the dendrochronology laboratory by Lintab 6 device, and the obtained data were automatically recorded for time matching in TSAP-Win software and time series analysis. After comparative dating and eliminating any measurement error, the mean values of the vegetative ring width of all specimens were calculated and the average growth of the cypress was obtained. The relationship between the width of growth rings in each cypress tree, and the difference in tree growth of the three provinces viz. Gilan, Mazandaran and Golestan was evaluated using R software. The results showed that a tree in Viaeyeh, Rudbar county is the oldest tree in existence reaching an age of 1519 years. The annual diameter growth of cypress is reported as 0.95 mm. The growth rate curve in Mazandaran province during the last 450 years showed milder characteristics in the arrangement, uniformity and slope of change compared to the other two provinces. This indicates the stability of climatic and habitat conditions in Hassanabad, Mazandaran province, compared with the two other areas and sufficient evidence that this area is very close to the Mediterranean climate.