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Regression of conifers in European mixed old-growth mountain forests has been observed for a long period and studied from different aspects. Old-growth (OG) forests in Bosnia and Herzegovina (BiH) have not experienced heavy air pollution and chronic overbrowsing that have affected many other European OG forests, while climatic and anthropogenic disturbances have been well documented. We analysed stand structure in the Janj OG forest, compared it with inventories of Lom and Perucica OG forests (BiH) and with earlier inventories of the same reserves. At present, OG forest Janj is characterized by a high growing stock (1215 m3·ha-1). This is due to good site quality, prevalence of conifers (84%) and dominant endogenous processes in recent decades. In all three OG forests, indicators of structural change exhibited progression of European beech over time. Historical evidence revealed the occurrence of warm summers and droughts followed by bark beetle outbreaks in the 1920s, 1940s and early 1950s, which in turn influenced a marked conifer decline. It seems likely that repeated canopy opening released waves of European beech regeneration. These stand structural changes have delayed the rejuvenation of conifers and can help explain the early observations of conifer decline. [ABSTRACT FROM AUTHOR]

Norway spruce is one of the most important conifer tree species in Europe, paramount for timber provision, habitat, recreation, and protection of mountain roads and settlements from natural hazards. Although natural Norway spruce forests exhibit diverse structures, even-aged stands can arise after disturbance or as the result of common silvicultural practice, including off-site afforestation. Many even-aged Norway spruce forests face issues such as senescence, insufficient regeneration, mechanical stability, sensitivity to biotic disturbances, and restoration. We propose the use of Density Management Diagrams (DMD), stand-scale graphical models designed to project growth and yield of even-aged forests, as a heuristic tool for assessing the structure and development of even-aged Norway spruce stands. DMDs are predicated on basic tree allometry and the assumption that self-thinning occurs predictably in forest stands. We designed a DMD for Norway spruce in temperate Europe based on wide-ranging forest inventory data. Quantitative relationships between tree- and stand-level variables that describe resistance to selected natural disturbances were superimposed on the DMD. These susceptibility zones were used to demonstrate assessment and possible management actions related to, for example, windfirmness and effectiveness of the protective function against rockfall or avalanches. The Norway spruce DMD provides forest managers and silviculturists a simple, easy-to-use, tool for evaluating stand dynamics and scheduling needed density management actions. [ABSTRACT FROM AUTHOR]

Questions: What is the structure of the anthropogenic upper forest-grassland ecotone and are there differences in the spatial relationships between the tree species involved? Location: Valfurva Valley, Italian central Alps. Methods: We conducted a spatial distribution and structure analysis in three 1-ha permanent plots along an altitudinal gradient, from the treeline to the sub-alpine forest. We reconstructed the age structure from cores from each individual with diameter > 4 cm at 50 cm height. Results: All tree species and age classes examined had a clumped structure. The cluster tendency was more evident at the treeline where the environmental conditions are more severe. In the sub-alpine forest there was a repulsion between Pinus cembra and Pious mugo but at the treeline P. cembra was frequently found downslope from P. mugo. Conclusions: Although human influence has been the main driving force in shaping the present forest structure, in the last few decades natural dynamics have become the predominant force acting on forest structure and processes, showing a higher magnitude as altitude increases. Our results emphasize the existence of facilitating and interfering mechanisms between different species. P. cembra seems to be favoured compared to the other tree species. [ABSTRACT FROM AUTHOR]

Abstract: Regeneration of non fire-adapted conifers following crown fires on the European Alps is often delayed or unsuccessful. Fire may limit establishment by eliminating seed trees, altering soil properties, or modifying microsite and soil conditions via disturbance legacies. However, the effect of soil legacies on post-fire establishment has rarely been discussed. We analyzed the abundance of Scots pine regeneration in a 257ha wildfire in an inner-alpine forest. Our aims were (1) to model fire intensity at the soil surface and topsoil heating along a gradient of increasing fire severities; (2) to assess the differences in soil properties along the fire severity gradient; (3) to model the effect of disturbance and soil legacies on the density of pine seedlings. We reconstructed fire behavior and soil heating with the First Order Fire Effects Model (FOFEM), tested the effect of fire severity on soils by nonparametric distributional tests, and modeled seedling density as a function of site, disturbance and soil legacies by fitting a GLM following a variable selection procedure. Topsoil heating differed markedly between the moderate and high severity fires, reaching temperatures high enough to strongly and permanently alter soil properties only in the latter. High fire severity resulted in decreased soil consistency and wet aggregate stability. Burned soils had lower organic matter and cations than those unburned. Pine seedlings favored low-fertility, eroded, and chemically poor sites. Establishment was facilitated by the presence of coarse woody debris, but hampered by increasing distance from the seed source. These results suggest that in dry, inner-alpine valleys, fire residuals and soil legacies interact in determining the success of Scots pine re-establishment. High severity fire can promote favorable soil conditions, but distance from the seed source and high evaporation rates of bare soils must be mitigated in order to ensure a successful restoration. [Copyright &y& Elsevier]