Dendroecological reconstruction of disturbance history of an old-growth mixed sessile oak-beech forest.

Questions What are the stand development patterns and successional processes occurring in a Quercus petraea-Fagus sylvatica old-growth forest? Do these two sympatric species have different recruitment and canopy accession strategies? How do they respond to disturbance? Location Old-growth Q. petraea- F. sylvatica forest in Runcu Grosi Natural Reserve, Romania. Methods Increment cores were taken from 110 similarly sized pairs of standing dead and living sessile oak trees, and additionally from the 110 most competitive neighbouring living beech trees, growing in the best-preserved part of the reserve. Release events were detected using the boundary line method. Recruitment and canopy accession strategies were defined using tree juvenile growth rate, overall growth patterns and the presence or absence of a major crown release. Results Sessile oak establishment occurred between 1800 and 1859, while beech have regenerated continuously, with greater in-growth after 1860. Tree recruitment followed species-specific requirements, with most sessile oak having a gap origin (82%) and many beech regenerating in the understorey (41%). Release events occurred continuously during the period analysed (1820-2003), but the percentage of trees per decade that showed releases was <15%. A larger number of releases were recorded in beech compared to sessile oak. Living and dead sessile oak originated under similar conditions, but after the 1900s they experienced different canopy disturbances regimes. Conclusions The investigated stand appears to originate after a large-scale disturbance that promoted sessile oak recruitment. Thereafter, regular small-scale disturbances favoured beech, which became a competitor to sessile oak and achieved faster growth despite a less favourable initial canopy position. Mortality started to occur in oak. Stand maturation and increasing competition could favour the occurrence of large-scale windthrow, which would again promote sessile oak. [ABSTRACT FROM AUTHOR]