Model Humus forms changes in the beech and hornbeam stands in the old growth and managed forest (Case study: Shast-kalate forest of Gorgan)

The aim of this study was to investigate the effect of environmental factors and stand properties on changes of humus forms in the managed and old growth forest of Gorgan. First we superimposed geological, soil, topography and tree type maps to producing homogeneous units. In each unit, three sample plots (20 × 20 meters) were selected and five humus profiles were described in each plot. Main and secondary humus forms were identified based on new European classification. Environmental factors and stand characteristics were investigated in each sample as factors influencing the changes in the humus form. Kruskal-Wallis test and random forest algorithm were used based on the Gini index for analysis. Three main humus forms and eleven secondary forms were identified in the research area, so that the main humus of the MULL (49%) and the secondary humus of the Oligomul (26%) were the most abundant humus forms. There was a significant difference between the main (p<0.01) and secondary (p<0.001) humus forms between the managed and old growth forest. The effect of most environmental variables and stand characteristics were significant on the changes of humus forms. The effective important variables in the main and secondary humus forms classification were thickness of H horizon, altitude from sea level, geographic direction and tree basal area.