Stand structure and plant species diversity in managed and abandoned silver fir mature woodlands

Although few undisturbed forests remain in Europe, forest reserves and deforested areas that are no longer profitable have the potential to develop stand structures similar to those which preceded human disturbances. The direct effects of management cessation on forest diversity are confounded by many factors that should be controlled when comparing managed and abandoned stands. In the European Alps, however, the high variability of habitats makes it nearly impossible to find comparable stands located within forests large enough to be independent from the surrounding land. The aim of this study was to investigate the use of mixed models to compare deadwood and plant diversity between matched managed and unmanaged pairs of forests, with the hypothesis that their differences were due to direct effect of abandonment. Two neighbouring watersheds that were large enough to be independent from the surrounding forests were chosen. These watersheds had a common history of use, but one was non-intensively managed, while the other was untouched since 1957. Ten plots were randomly selected from each forest. Mixed models confirmed their matched topography and stand structure, while a similarity index confirmed their assignment to the same plant community. The unmanaged stand had higher soil nitrogen, higher Fagus sylvatica dendrological composition, higher tree species richness, higher dead logs and a different composition of the tree and understory layers. These results suggest that silver fir woodlands abandoned for more than 50 years change spontaneously and that this approach may be an effective means for studying other forest communities.