Canopy gaps in a Carpathian subalpine spruce forest

The size, number, and enlargement of gaps as well as the process of gap formation were analyzed in a subalpine spruce forest in the Babia Gora massif, one of the highest in the western Carpathian Mountains. Openings in the forest canopy of up to one hundred square meters are typical structural elements of subalpine spruce forests. Gaps comprised 34% of the studied forest area of 14.4 ha. There were 38 gaps per ha, most of them < 100 m(2). Average gap size was 92 m(2). Most gaps were environmentally heterogeneous as a result of their progressive and ongoing enlargement, which was evidenced in many gaps by snags and logs representing a wide spectrum of decomposition classes. The density of logs and the area covered by them were about two times larger in gaps than under spruce canop. Logs in gaps were of greater diameter. The mean gap size has increased in recent years. At the same time establishment of new gaps became rarer and enlargement of existing aps took place more often. This suggests that the average area of gaps will further increase in the future. The closure of gaps resulting from the elongation of spruce branches on adjacent trees and through the development of young trees did not keep pace with the process of gap creation. it yielded a 0.3-0.4% increase of total gap area per year.