The Study of Important Quantitative Parameters and Biological Conditions of Alnus Species in Gombol Forests of Lahijan District

To know and study the measure of tree characteristics can be a good guide to adopt forestry ways and correct methods in their culture to attain the objectives of tending of forests. In the region of Gombol from the Lahijan forests, 121 trees from the Alnus species were randomly Selected and their characteristics such as log diameter, diameter at breast height, whole height, height and diameter of crown, were measured. Results of this study showed that the relationship between diameter at breast height and crown height was increasing but it was decreasing from the layer of 70 cm. Also from the statistical point of view there is a Significantly difference between diameter at breast height and crown diameter of Alnus trees in the region studied. By increasing diameter at breast hight, the slenderness coefficient is decreased. Based on this coefficient, nearly 14 percent of trees were unstable and 86 percent of them had partial and suitable stability. Also Alnus species in this region was very unstable over the diameter of 35 cm and it is stable from the diameter of 35 cm or so. The relationship between diameter at breast height and trunk diameter is linearly increasing. As a biological conditions, Alnus species in this region contains 4. 8 6. 4 soil pH and it lives in the soil texture that is heavy to half heavy without slip and contains safe lower layer.