The effect of forest treefall gap on humus forms in a mixed Fagus orientalis Lipsky (Oriental Beech) forest

Gap formation affects environmental conditions in forest ecosystems. In this study, the effect of forest gap on humus form in a mixed Fagus orientalis Lipsky (Oriental Beech) forest was investigated by comparing the humus forms found in gaps with those in parts of the stand with closed canopies in a temperate mixed forest in northern Iran. In total, 32 gaps were selected from which 160 humus profiles were considered within gaps, and a further 160 within adjacent closed canopies. In each profile, humus forms were determined based on their morphological characteristics. Results indicated that gap significantly affected humus forms. The humus forms in gaps differed significantly from those in adjacent areas of closed stand. Mull order type humus was the most commonly found in the study site (70% of all profiles). The results also showed that forest floor thickness was lower in gaps than in adjacent closed areas. The suborder eumull was the most common in gaps, whereas dysmull was found to be the most common within closed areas.