Relationships between forest structure and tree's dimensions with physiographical factors in Armardeh forests (Northern Zagros)

The study was carried out to investigate relationships between physiographical factors and some tree's characteristics and forest structure at Kurdistan province of Iran. For this reason, effects of slope (five levels), aspect (four levels) and elevation (four levels) on tree's characteristics (dbh, total height and crown area) and forest structure (diameter distribution curve, density and basal area) were investigated. The trees were sampled, using 77 plots (1000m2 area) under systematic randomized sampling method, based on completely randomized design. Results showed that the physiographical factors affected the tree's characteristics significantly. The greatest tree's diameter, total height and crown cover were found on low slopes, eastern and northern aspects and high altitudes. The interaction analysis showed that slope had important role on most of the tree's performance. The diameter distribution patterns at all physiographical conditions were uneven-shaped normal and Kortiusis and low tree density at low diameter classes, indicated poor regeneration at past. The diameter distribution curves at intermediate slopes and altitude and northern slopes showed an adequate condition, in which density indices (number and basal area per hectare) were also at best conditions. In contrast, sites with southern aspects and low slopes had poor density indices, for this reason they need high attention and preference in forest management projects. It could be concluded that difference in species composition and human intervention are main sources of tree's characteristics and forest structure variation at physiographical units.