Abstract
Mixed mountain forests of silver fir (Abies alba Miller), beech (Fagus sylvatica L.), and spruce (Picea abies (L.) Karst.) are widespread in Europe and have a high ecological and socio-economic value. In the upcoming decades, these forests will likely undergo substantial restructuration due to climate change and altered disturbance regimes. In this context, knowledge of species responses to variations in climate and disturbance regimes (e.g. fire and human impact) may offer critical information to infer the vulnerability of a large part of European mountain forest ecosystems. Since environmental changes generally occur on multiple spatial scales and their effects on forests operate on long-time scales, integrative methodological approaches are required. A high naturalness of forests is key prerequisite to study natural species-environmental interactions. While many European forests were deeply transformed since the Neolithic (around 6500 years ago), the Dinaric Alps still host some of the last remnants of primary and old-growth forests. This study combined the assessments of contemporary forests structure and composition, remote sensing analyses and multi-proxy palaeoecological records in two forests located in the central Dinaric Alps (Montenegro) to provide insights on the long-term vegetation dynamics. The results supported the high naturalness of some mountain forest ecosystems located in the central Dinaric Alps. However, land-use pressure (agriculture and grazing) as well as fires (probably mainly human-induced) likely played an important role in reducing the area of fir-spruce-beech old-growth forests during the Middle Ages. Legacies of past land-use activities are still visible both in tree species composition and structure of current forest stands. Fire was confirmed to be an important disturbance agent during the Holocene. Although further research from European mixed forests is necessary to validate the responses of spruce, beech, and fir to fire, climate, and human impacts, our results suggest that A. alba may be well adapted to warmer-than-present summers and could be resistant to low frequency and low severity fires or even rare high-severity fires. However, it is a species highly sensitive to human impact. F. sylvatica may be sensitive to increasing summer temperatures and could be favored by low biomass burning whereas it is insensitive to human impact. P. abies may be insensitive to variations in summer temperature, human impact, and biomass burning and can persist under fire-return intervals of c. 200-300 years or even after rare high-severity fires. Our study shows that combining integrative methodological approaches can generate valuable insights able to support the definition of protection, restoration, and management strategies of European mixed spruce-beech-fir mountain forests.