Gap recruitment and partitioning in an old-growth beech forest of the Dinaric Mountains: Influences of light regime, herb competition and browsing

Canopy gap recruitment in beech (Fagus sylvatica L.) old-growth forests is influenced by the interplay of the canopy gap disturbance regime, site factors, and stand history. Persistent seedling and sapling banks of beech and other shade tolerant species often play a major role in canopy gap closure. To gain more insight into interactions between medium-sized gaps and pre-gap ground vegetation patterns, we studied beech regeneration over a 10-year period on a site rich in wild garlic (Allium ursinum L.) in a Dinaric beech old-growth forest. In 1999 we selected the five largest newly created gaps (∼200 m2) and systematically established 13 permanent plots (1 × 2 m) in each gap. In 1999, 2004, and 2009, we sampled tree species regeneration (density, cover, and growth), ground vegetation (composition and cover), and light climate. Beech regeneration slowly increased in density and cover despite an overall decrease in light (11.0–5.7%). The same was not true for maple. While beech was present in all regeneration classes, dominant maple seedlings rarely reached 50 cm. Beech also had a significantly greater height increment. Regeneration of both species was negatively affected by Allium cover, low light levels, and ungulate browsing. Gap partitioning was observed among shade tolerant Allium, which preferred microsites under closed canopy and low light levels, beech regeneration, which preferred gap periphery, and other less shade tolerant herbs, which favoured gap centres. The slow development of the regeneration indicated the importance of several gap releases. The high maple seedling density and less abundant beech advance regeneration in this study site compared to other beech sites suggests that Allium dominated managed forests might present an opportunity for growing less shade-tolerant species, if managed with a gap-oriented silvicultural system (e.g. irregular shelterwood).

► We studied tree regeneration and vegetation in medium-sized gaps over a decade.
► Decrease in diffuse light (11.0–5.7%) indicated importance of several gap releases.
► Gap partitioning among herbs, beech and sycamore maple regeneration was observed.
► Beech advance regeneration under closed canopy was hindered by Allium ursinum.
► In similar conditions gap periphery seems advantageous for beech establishment.