engleski

Long-term changes in tree species composition in old-growth Dinaric beech-fir forest

Successive inventories of individual old-growth beech– fir forests from Dinaric mountains show structural changes during the last half a century. To be aware of these trends is important for general understanding of regeneration processes in old-growth forests, as well as for stating appropriate silvicultural aims. However, no study comparatively investigated data sets from several old-growth forests. We analyzed data from 31 inventories of growing stock in seven old-growth forests representing large area stretching from the north-west of the Dinaric mountain range in Slovenia to the central part in Croatia. All forests experienced a decrease in the proportion of silver fir in the growing stock. The decrease was of a different magnitude in individual old-growth forests. However, the overall growing stock in the majority of old-growth forests didn't fluctuate as expected due to the silver fir decline. The diameter distribution of five selected forests was closer to a rotated sigmoid than to a negative exponential distribution in spite of relatively large areas which were inventoried. The curves for growing stock according to dbh revealed, that beech and silver fir occupy different niche within ecosystem. In the lower diameters beech is more frequent and competitive, while silver fir compensates for this in larger diameters (and heights). Both curves from most reserves were not stable in time. The most apparent and worrying trend in Slovenia was the decrease of the silver fir curve over the entire range of the diameter distribution, with peaks in the lowest and largest diameters. Moreover, the silver fir regeneration > 20 cm was almost completely absent due to high densities of large herbivores. While Čorkova Uvala appears to be a very balanced reserve in regard to all sampled parameters. The results revealed a general synchronous trend of silver fir replacement by beech on a broader geographical scale. The complex reasons for this are discussed and some general guidelines for the silviculture in managed beech fir forests are given.

old-growth forest; beech-fir forest; virgin forest; diameter distribution; growing stock; species composition; alternation of tree species; long-term inventories

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