Tracheid dimension (tracheid length, tracheid diameter, cell wall thickness, and lumen diameter), morphology properties (Runkel index, flexibility ratio, slenderness coefficient) and mechanical strength properties (modulus of rupture and modulus of elasticity) variations of Pinus eldarica wood (eldar pine) were determined on three sites with different soil fertility in Iran. Nine normal trees of pine wood were selected from three different sites in the western part of the Mazandaran region: Benafshde site (site 1), Kelardashat site (site 2) and Marzanabad site (site 3). Logs and discs were cut at breast height. Wood specimens were taken along radial direction from the pith to the bark (six distances from pith) to determine tracheid features and from mature wood to determine static bending properties. The analysis of variance indicated that site, radial direction and interactions between site and radial position had a significant effect on tracheid dimensions and morphology properties. In addition, the effect of site was significant on modulus of elasticity (MOE) and modulus of rupture (MOR) in mature wood. The highest of tracheid length, tracheid diameter, lumen diameter, flexibility coefficients, MOE and MOR were found on site 2, the highest of cell-wall thickness and Runkel were found on site 3, and the highest of slenderness coefficients were found on site 1. Variations of tracheid length, cell wall thickness, slenderness coefficients and Runkel coefficients increased along radial direction from the pith to the bark, while the flexibility coefficients decreased. A rapid increase of tracheid diameter and lumen diameter was observed from the pith to about 60% of radial direction, and it decreases up to the bark in eldar pine wood. Results based on the morphological properties analysis indicated that the fibers obtained from three different sites are suitable for paper production.
