Dendroclimatological Analysis of Pinus brutia Ten. Grown in Swaratoka, Kurdistan Region-Iraq

It is well known that there is a strong relationship between the amount of precipitation and radial growth of the trees, but it is not known up to which extent they depends on each other. On the other hand, the data about the amount of precipitation is available from 1976 in Duhok governorate in general. One of the problems studied here is to estimate the quantity of the precipitation using the width of annual ring for the periods prior to 1976, in order to see the trend of rain and snow fall in the region. The data used in this study came from 387 sample pairs of precipitation and diameter growth. These data were undergone data processing for the purpose of developing of regression equations between the width of diameter growth as dependent variable and the amount of yearly precipitation as independent variables in regression equations. Accordingly, thirteen regression equations were developed; two of them were simple regression equations, one polynomial, and the rest of equations were nonlinear. These equations were undergone several measures of precision for the purpose of selecting the most appropriate one which fits our data set. Ultimately the non-linear regression equation: Dg = 0.293781 + 0.0000371 x p(1.40698) was selected, with an adjusted R-2 of 76.22, standard error of estimate of 0.1283 and DW of 1.88 The selected equation can be used to estimate the amount of radial growth of a tree in the region by substituting the amount of precipitation in the equation.