Regeneration patterns, dendroecology, and forest-use history in an old-growth beech-oak lowland forest in Northern Spain

Past regeneration patterns of Quercus robur L. and Fagus sylvatica L. and their relationship to canopy structure, disturbances and forest-use history were investigated in an old-growth, lowland forest in Cantabria, Northern Spain. Dendroecological techniques were used to estimate tree ages and reconstruct disturbance histories in four representative stands which differed in composition and structure. Age estimates and tree locations were used to reconstruct patterns of tree establishment. Documentary sources were also used to report on changes in land-use during the past 250 years. Age structures of both species were discontinuous in time and space, and revealed two main cohorts distributed in even-aged, spatially segregated patches. Juveniles showed a clumped spatial pattern at varying distances, indicating an establishment: in more or less extensive patches. Establishment site analyses revealed that Q. robur regenerated in canopy gaps, while F. sylvatica recruited throughout the forest floor, but it displayed inhibition near mature conspecifics. A lack of tree establishment from the 1840s to the 1920s coincided with an intense grazing pressure from domestic animals. F. sylvatica exhibited continuous recruitment in periods of forest protection against grazing, such as from the 1740s to the 1830s and from the 1920s. By contrast, Q. robur recruitment was dependent on both low grazing intensities and disturbances that resulted in the expansion of existing canopy openings, as occurred in 1943, 1956 and 1967. Past selective cuttings, canopy closure and forest protection could be responsible for the increasing decline of oak dominance. Planting Q. robur and controlling F. sylvatica regeneration are therefore advisable to prevent the complete domination of beech in the future forest canopy. (C) 2003 Elsevier Science B.V All rights reserved.