Structural dynamics and synchronous silver fir decline in mixed old-growth mountain forests in Eastern and Southeastern Europe

Abstract

Research on old-growth forests is essential for understanding forest ecosystem functioning and for the development of forest management strategies. Their structural dynamics depends on disturbance patterns (White and Pickett, 1985). In recent decades, much research in old-growth forests has focused on natural disturbances. However, over several centuries, the natural disturbance regime has been severely altered by forest fragmentation, changes in fire regime, fauna extinctions, the introduction of forest management into the forest matrix surrounding old-growth, forest road infrastructure, and, in the last few decades, by overbrowsing, air pollution and climate change (Nowacki and Abrams, 1994;Uotila et al., 2002;Oulehle et al., 2010). Present-day old-growth forest structures are often a result of complex interactions between natural and anthropogenic disturbances (McLachlan et al., 2000). In Europe, old-growth forests have been significantly influenced by millennia of civilization. Thus, studies of

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

“…Tree species composition according to growing stock in Janj comprised one of the highest shares of conifers (84%) when compared to other old-growth forests in the region [15,44,47,60]. A similar low percentage of beech (18%) was found in the Igman old-growth forest in BiH, which is located about 92 km in the southeast direction.…”

“…Namely, lower SO 2 emissions [36] and lower deer densities [35] may be responsible for the less pronounced silver fir decline in Bosnia. Diaci et al [15] indicated a synchronous silver fir decline in most studied southeast European mixed old-growth mountain forests, while the share of fir in BA increased in the Igman and Trstionica mixed old-growth mountain forests in Bosnia. The data from this study indicated a more pronounced spruce decline in comparison to fir, which may be attributed to its greater susceptibility to drought and high temperatures at the limit of its geographic range towards the Adriatic Sea [62], or its successional stage due to past (anthropogenic) disturbance.…”

“…For conifers, IQ distributions may indicate, due to increasing Q, a higher mortality rate in large-diameter trees and potentially past disturbance, while a unimodal shape (Janj) may indicate heavier past disturbance, a succession or insufficient recruitment [56,57]. NE and RS shapes are often reported as common in old-growth forests [15,56]. In old-growth northern hardwoods, Ducey et al [69] found deviations from the classic "balanced" exponential distribution on plots heavily stocked with beech; however, in our study beech was sub-dominant to conifers and exhibited a tendency towards NE and CO shapes in all inventories.…”

“…than today and unregulated management that included felling of individual trees for fuel wood or construction on site, forest grazing and charcoal burning was common [7,9,15,32,33]. On the other hand, in the forest matrix surrounding old-growth forests, conifers were favoured for economic reasons.…”

“…Old-growth forests in Bosnia (Perucica, Lom and Janj) have not experienced chronic overbrowsing by deer as have other European old-growth forests [15,35], and environmental pollution has also been less acute [36]. 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].…”