Comparing the Various Interpolation Techniques of Climatic Data for Determining the Most Important Factors Affecting the Trees Growth in the Elevated Areas of Chaharbagh, Gorgan

The dendroclimatology science reconstructs the past climates through studying the relationship between climatic indices and tree rings which is a pre-requisite of agricultural and natural resources studies. Basically، the tree species of highland regions are more sensitive to the climatic conditions. Unfortunately، in the highland forest regions like Chaharbagh، Gorgan (case study) there is nometeorological station. In order to solve this problem، in this study various interpolation methods of temperature and precipitation data from the area understudy were compared and the best methods were determined. Then، through using the best interpolation methods، monthly temperature and precipitation variables in the period 1982-2006 were calculated in the tree ring sampling points for two tree species (i. e.، Juniperus polycarpus and Quercus macranthera). Finally the correlation between yearly tree rings and monthly temperature and precipitation، Standardized Drought Index (SPI)، and Reconnaissance Drought Index (RDI) were evaluated. The results show that among various interpolation methods the 3D linear gradient and linear and nonlinear hybrid methods are the best interpolation methods for temperature and precipitation، respectively. Correlation coefficient analyses showed that the effective meteorological factors on the growth of Quercus macranthera trees are the positive effect of the SPI of June and the negative effect of the March temperature. The July precipitation and the pre-growth September temperature have a negative effect on the growth of the Juniperus polycarpus trees.