Investigation on increment of Fagus orientalis Lipsky using time series analysis

Fagus orientalis Lipsky accounted for 24 percent of stem number and 30 percent of total volume in northern forests of Iran. The aim of this research is finding the regularity in frequencies of diameter increment, determining the relationship between tree age and fluctuations in radial increment of beech trees. Several hypotheses including stationary, secular trend, cyclic and random variations in data series of the beech tree increment, were examined to find out the main effective factor on variations. Four sound beech trees with mean diameter of 10 cm and maximum age of 350 years were selected. One disk was prepared at breast height from each sample tree. Then rings width was measured and data processed with the Time Series analysis. Results showed that there is more than one trend (model) in radial increment diagram of the sample beech trees. Positive correlation was calculated between tree age and radial increment up to the age of 120 years, where as this correlation turns to negative after this age. The mean and distribution of radial increment differ in periods of tree life. Radial increment of the beech trees is fitted with cubic model along the two age periods. Volume trend of annual increment always is positive and is not inversed. Autocorrelation diagrams show one year periodicity for the fluctuations of radial increments. The other periodicities are irregular and the alterations are not statistically significant.