Structure and regeneration patterns of pedunculate oak and European beech in an old-growth lowland forest in Cantabria, Spain

Abstract

The composition and structure of four stands of old-growth forest located in the Cantabrian lowlands, were described. The regeneration patterns of the dominant tree species as well as their relationships with the forest history were analysed. Age distributions and canopy history were reconstructed by using dendroecological techniques, and the spatial dimension of tree regeneration was studied by quantitative spatial analysis. The forest under study is composed of two dominant tree species, Fagus sylvatica L. and Quercus robur L., along with a shade-tolerant understory tree (Ilex aquifolium L.) and a group of five pioneer species. Both dominant species showed balanced populations, with monotonic-descendent or compound diameter distributions. All tree populations under study comprised two cohorts: young trees 20-70 years old and mature trees 155-260 years old. Both cohorts were separated by a period of 100-140 years lacking regeneration. F. sylvatica and Q. robur establishment showed a significant clumped pattern, with a significant repulsion from adult trees at a small spatial scale. The recruitment of Q. robur took place mainly in open space and canopy gaps, while the main limiting factor for F. sylvatica regeneration was the presence of mature trees of their own species. Tree establishment along the 20th century started in the 1930s, coinciding with a disturbance period, a reduction in forest density, and a decrease in grazing intensity.