Abstract
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.
Highlights
Mixed forests composed of Fagus sylvatica L., Abies alba Mill. andPicea abies (L.) Karst. (Norway spruce) represent one of the most ecologically and economically important forest categories of European mountainous regions [1]
The high share of conifers in comparison to other Dinaric mixed old-growth forests in Slovenia and Croatia could be attributed to the higher altitude and continental climate
Other Bosnian mixed old-growth forests (Igman, Lom and partly Perucica) are in a similar altitudinal belt and exhibit fewer conifers; past natural or anthropogenic disturbances may have influenced the high share of conifers
Summary
Mixed forests composed of Fagus sylvatica L. (hereafter beech), Abies alba Mill. (fir) andPicea abies (L.) Karst. (Norway spruce) represent one of the most ecologically and economically important forest categories of European mountainous regions [1]. (Norway spruce) represent one of the most ecologically and economically important forest categories of European mountainous regions [1]. They grow in the relatively humid and cold climates of the mountains [2]. There are many reports of synchronous regression of conifers, especially of silver fir in old-growth forests (e.g., [4,5,6,7]) as well as in managed forests [8,9,10,11]. Natural and anthropogenic, influence the coexistence of beech, fir and spruce, making this topic challenging to study [12,13,14,15]
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