The use of understorey heterogeneity, species diversity and stand structure for characterising Quercus suber forests in south-western Spain and Portugal - a methodological approach
Cork oak forests under different management regimes and different structure of the surrounding landscape from two study areas in Portugal and Spain were compared with regard to stand structure, understorey species diversity and vegetation heterogeneity. Direct ordination methods were used to detect the relationship within variables of forest structure on the one hand, and between parameters of forest and landscape structure on the other hand. Differences between the study areas with regard to forest structure and understorey heterogeneity can be attributed to the successional status of the cork oak forests. In the Spanish study area, forest conditions range from young, open stands intermingled with heathland vegetation to tall-growing forest with dense canopy cover. In Portugal, many cork oak forests consist of over-aged and declining stands where tallgrowing maquis formations fill the gaps between decaying trees. Landscape variables measured in circles of different radii around the forest sites, as well as abiotic parameters, and to a lesser extent also disturbance via forest management, show a close relationship to the main gradients in the data set. However, few indications of scale-dependence of this relationship can be found. The more time passes between disturbance events related to cork stripping, the higher is the number of herb species, and the lower is the number of maquis species in the forest understorey vegetation.