The effect of size and origin of canopy gaps on plant composition and soil seed bank in the mixed and pure beech (Fagus orientalis Lipsky) stands

To study the effect of canopy gaps on aboveground plant composition and permanent soil seed bank in mixed and pure stands of oriental beech (Fagus orientalis lipsky), artificial and natural canopy gaps with different sizes considered at the Hajikola-Tirankli forest plan, Sari. All canopy gaps were grouped in different classes including small (less than 150 m2), medium (150-350 m2), and large (350-500 m2) sizes. The variation of aboveground vegetation composition in response to the gap characteristics was surveyed by Detrended correspondence analysis (DCA), and similarity of the aboveground vegetation with soil seed bank in the two depths was compared using the Jaccard similarity index. In total, 71 plant species were identified in the region, from which 26 belonged to above ground, 24 species to soil seed banks and 21 species were similar for both sections. Species such as Carex sylvatica Huds. Carex riparia Curtis, Rubus hyrcanus Juz. and Hypericum androsaemum L. were dominant in the soil seed bank. In addition, results showed that plant composition in vegetation differed with a soil seed bank. The Jaccard similarity index indicated that the similarity rate of aboveground vegetation and the corresponding seed banks under large gaps was higher than those of small/medium gaps and control plots. Moreover, the similarity rate between soil seed bank in the upper layer (0-5 cm) with above-ground vegetation composition was higher compared with the deeper layer (5-10 cm). These differences, especially with regard to the variation of similarity between the soil seed bank and vegetation across a range of gap sizes calls for increased attention to management and rehabilitation measures that are appropriate for each of the microhabitats created by the canopy gaps.