Abstract
In the conditions of ongoing climate change, the old-growth forest remnants of the Western Carpathians provide a unique possibility to study the structural changes in forests undisturbed by human activity. In four subalpine primary spruce forests in Slovakia, we analysed the temporal variability of basic stand characteristics, the dynamics of diameter structures and the development of tree species composition. The study was conducted in a series of 10 permanent research plots with the size of 0.5 ha. Within each plot, we recorded all living trees (dbh > 8 cm) as well as the recruitment individuals (dbh 0.1−8.0 cm). Old-growth spruce forests Babia hora, Kotlový žľab and Pilsko showed continuous reduction of stem density, basal area and growing stock during the investigated period. In the last two decades, the negative interdecadal changes of basal area and stand volume even exceeded the rate 35% as a consequence of severe disturbances caused by the windstorms and bark-beetles. Breakdown of these stands affected also their diameter structure and the unimodal distributions were replaced by the more differentiated structures of rotated sigmoid shape. Such significant change was followed by a massive increase in stem density of spruce and rowan recruitment. Stable bimodal diameter structure was observed only in old-growth forest Zadná Poľana, that was characterized by the small-scale gap dynamics. The results documented the intense breakdown of natural spruce stands with unimodal structure and the key role of the existing seedlings and saplings bank of spruce and rowan for their regeneration after the disturbance events.