Introducing canopy gap optimum size for established regeneration of oriental beech (Fagus orientalis Lipsky) in the Hyrcanian mixed-forests

Establishment and growth of tree regeneration in association with the canopy gap (CG) and its related parameters such as topography and surrounding tree diversity guarantee turnover and dynamics of forest ecosystems. This research was conducted in the control parcel within the third district of Glandroud forests in Mazandaran province and aimed to clarify influences of gap area with respect to the species diversity of surrounding trees and physiography on the density and height responses for established regeneration of oriental beech (Fagusorientalis Lipsky) in various growth stages, in order to suggest an optimum gap size for the mentioned regenerations. After measuring and calculating area of each CG using radial method, the gap sizes were classified based on full census. The established regeneration was divided into three classes of 1.3–2.5 cm (saplings), 2.5–5 cm (thickets), and > 5 cm (pole- or advanced regenerations). Following statistical tests, results generally showed that the variation of density of saplings, thickets and poles was not significantly correlated with the CG size and other associated parameters. However, significant difference among the CG size classes was observed for height of saplings in relation with physiographic units and frequency of marginally surrounding trees. In addition, height of thickets and pole individuals were significantly affected by gap size and frequency of surrounding trees. The findings indicated that all CG size classes consisting of an area less than 200 m2 and the maximum area of 1000 m2 are the environmentally and ecologically optimum areas for beech regeneration based on establishment proportion of growth stages recruitment in the forest ecosystem, taking account of frequency of surrounding trees and physiographic units.