Toward a definition of the range of variability of central European mixed Fagus-Abies-Picea forests: the nearly steady-state forest of Lom (Bosnia and Herzegovina)

Knowledge on the range of variability of montane European forests is hampered by limited data on the natural disturbance regime and by the small size of old-growth remnants. We studied the mixed Fagus-Abies-Picea Lom forest reserve (55.8 ha) in Bosnia and Herzegovina at three different scales: a grid of 40 sampling points to describe the structural characteristics and their range of variability, three transects to analyse gap size and gap fraction, and a 1.1 ha permanent plot to reconstruct age structure and disturbance history. The forest is characterized by a high volume of living trees (763 m(3).ha(-1) in the 55.8 ha core area and 1160 m(3).ha(-1) in the permanent plot) and of coarse woody debris (327 and 383 m(3).ha(-1), respectively). The percentages of forest area in canopy and expanded gaps are 19% and 41%, respectively. The median canopy gap size is 76.9 m(2) and ranges from 11.1 to 708.0 m(2). There are large (up to 120 cm diameter at breast height) and very old trees (441, 432, and 416 years for silver fir (Abies alba Mill.), Norway spruce (Picea abies (L.) Karst.), and European beech (Fagus sylvatica L.), respectively). During the last three centuries, the disturbance patterns have been characterized by single-tree or small group mortality. In central Europe, this forest is at the end of a gradient from forests characterized by intermediate disturbances to those where very small-scale processes predominate.