Canopy gaps in an old-growth fir-beech forest remnant of Western Carpathians

Abstract

The old-growth forest remnants of Western Carpathians provide a unique possibility to study the disturbance regimes of forest ecosystems without human influence. This study investigated the gap dynamics in beech-dominated old-growth forest Badínsky prales in Central Slovakia. Considering the decline of silver fir in last decades, the study analyzed the main characteristics of disturbance regime with the emphasis on the role of fir. On a 5-ha research plot, the dominant tree species was beech, the proportion of fir reached about 10%. However, a significantly higher proportion of fir ([30%) was observed in the coarse woody debris. In total, 45 canopy openings were recorded. Canopy gaps and expanded gaps covered 11.3 and 37.9% of the forest area, respectively. Despite the highest frequency of small gaps \100 m 2 , their proportion of the overall gap area reached only 20%, what suggests the important role of intermediate and large gaps in the gap dynamics as well. The analysis of gapmakers' crown projections confirmed a rather low contribution of fir (14.6%) to the gap formation despite its relatively intensive mortality. A high variability of the next generation age between the gaps (6-44 years) was recorded what suggests a large temporal variation of the disturbance events. The lateral expansion of adjacent trees was found to be the determining process for the closure of small canopy openings. The intermediate and large gaps are more likely closed by the height growth of natural regeneration and understory trees that are present on the majority of the area.

Structural Diversity in a Mixed Spruce-Fir-Beech Old-Growth Forest Remnant of the Western Carpathians

“…The proportion of land area in canopy gaps in NNR Dobročský prales reached 18% and was higher than values reported from European common beech-dominated [18,[74][75][76] and mixed common beech-silver fir or common beech-silver fir-Norway spruce forests [38,76] with the proportions rarely exceeding 11%. On the other hand, a fraction of the expanded gaps (39%) was nearly the same as that observed in old-growth common beech-dominated forest Badín in Slovakia [18] and common beech-silver fir forest Perucica in Bosnia-Herzegovina [38], both reaching 38%. The larger extent of canopy gaps was also confirmed by the median canopy gap size (91 m 2 ) that was one of the highest values reported from Europe.…”

“…In recent studies (e.g. [8,18]), the impact of ungulates and the expansion of common beech were similarly considered to be the most important factors that currently limit silver fir regeneration in forest reserves of the Carpathians. The reduction of silver fir in the lower and middle layer observed in our study is the direct consequence of this lack of saplings and virtually no ingrowth into these layers.…”

“…Responses to natural and anthropogenic disturbances in mixed stands are usually very complicated and each tree species can respond to similar disturbances with different intensities [15,16]. The dynamic of natural mixed forests is driven by disturbances of smaller scale and higher frequency, that remove single or eventually small groups of trees and favour multi-layered stand structure, but also by less frequent disturbances of intermediate or large scale, that allow shade-intolerant species to establish and survive [17][18][19][20]. Small-scale disturbances favour silver fir because of its high tolerance to shade, but on the other hand, silver fir is negatively affected by high deer browsing [21,22], the expansion of beech [8,18] and in the past also by air pollution [23,24].…”

“…The dynamic of natural mixed forests is driven by disturbances of smaller scale and higher frequency, that remove single or eventually small groups of trees and favour multi-layered stand structure, but also by less frequent disturbances of intermediate or large scale, that allow shade-intolerant species to establish and survive [17][18][19][20]. Small-scale disturbances favour silver fir because of its high tolerance to shade, but on the other hand, silver fir is negatively affected by high deer browsing [21,22], the expansion of beech [8,18] and in the past also by air pollution [23,24]. Intermediate disturbances promote both common beech and Norway spruce establishment [25]; however, currently we can observe different development trends of these tree species.…”

“…The minimal stage area should be a compromise between the minimal size of the canopy gap that allows for natural regeneration, since such a canopy gap is a prerequisite for a new development stage, and practicability of field work [35]. Although the most common disturbance regime in beech-dominated natural forests is very small in scale [5,18,38], to capture the full range of development stages within the forest succession cycle requires a fairly large research plot [2,39]. Therefore, when studying development dynamics, it is recommended to conduct the surveys on sufficiently large research plots segmented at an appropriate scale according to the local disturbance regime [40].…”