Gap regeneration and replacement patterns in an old-growth Fagus–Abies forest of Bosnia–Herzegovina

Abstract

We examined the influence of small-scale gap disturbances on stand development and tree species coexistence in an old-growth Fagus sylvatica-Abies alba forest in the Dinaric Mountains of Bosnia-Herzegovina. The structure and composition of tree regeneration in gaps were compared to the forest as a whole, and the influence of gap size on the density and composition of regeneration was assessed. Transition probabilities were also calculated from gapfillers in different life stages to examine canopy replacement patterns. The structure and composition of tree regeneration were similar between gaps and the forest as a whole, and there was no relationship between overall regeneration density and gap size, indicating most individuals established prior to gap formation. Likewise, there was no strong evidence of gap-size partitioning for shade tolerant F. sylvatica and A. alba, although less tolerant Acer pseudoplatanus only recruited to taller life stages in larger gaps. Transition probabilities calculated from the seedling and sapling data suggest that most gaps will be captured by F. sylvatica, while probabilities based on pole-sized gapmakers indicate both A. alba and F. sylvatica will be maintained in the canopy. We suggest that gaps primarily play a role in reorganizing advance regeneration, and that coexistence of shade tolerant F. sylvatica and A. alba is more likely related to their differential ability to tolerate shaded understory conditions, particularly during larger life stages, rather than gap-size partitioning.

Comparative Structural Dynamics of the Janj Mixed Old-Growth Mountain Forest in Bosnia and Herzegovina: Are Conifers in a Long-Term Decline?

“…Coexistence of spruce, fir and beech is a complex subject [12,13,17,19,46]. It is driven by the interaction of many factors, anthropogenic and natural.…”

“…It is driven by the interaction of many factors, anthropogenic and natural. While small scale endogenous disturbance favours fir, intermediate disturbance promotes beech, spruce and admixed broadleaved species [5,19]. Regarding site conditions, conifers are for example more susceptible to competition from ground vegetation than broadleaves and are therefore more successful in the regeneration on rockier sites or acidic soils and on CWD with less abundant ground flora [16].…”

“…Regarding disturbance events in BiH from the 1920s to the early 1950s, it is also important that early summer drought is a strong masting predictor for beech [84]. Large-scale synchronous regeneration of beech has probably delayed the regeneration of conifers, lasting for several decades [19]. Documented climatic events, likely coupled with anthropogenic disturbances, are indicated in this study by the following: (1) beech dominance among small trees in all inventories and its increase overall dbh classes in recent inventories; (2) the future decrease of the beech middle-story modelled with transition probabilities; (3) the IQ shape of dbh frequency distribution in the 1950s for conifers in all old-growth forests and (4) changes in dbh frequency distributions.…”

“…These forests therefore represent an excellent resource for the study of interactions of climatic fluctuations and indirect anthropogenic disturbances, both of which are well documented in the literature [33,[37][38][39][40][41]. The Janj old-growth forest has received less scientific attention [42,43] than the forests of Perucica (e.g., [5,19,[44][45][46]) and Lom [32,47,48]. The aims of this study were (1) to describe the structural changes over a 60-year period in the Janj old-growth forest and (2) to compare and contrast the changes with those in the Lom and Perucica (Bosnia and Herzegovina) old-growth forests and other similar old-growth forests in Europe.…”

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

“…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. While common beech seems to be favoured by climate change, resulting in more frequent seed crops, lower sensitivity to competition from ground vegetation or a prolonged growing season [12], Norway spruce suffers from longer drought periods, bark-beetle outbreaks and more frequent and stronger wind disturbances [11].…”