Search

Mixed-severity disturbance regimes are prevalent in temperate forests worldwide, but key uncertainties remain regarding the variability of disturbance-mediated structural development pathways. This study investigates the influence of disturbance history on current structure in primary, unmanaged Norway spruce ( Picea abies ) forests throughout the Carpathian Mountains of central and eastern Europe, where windstorms and native bark beetle outbreaks are the dominant natural disturbances. We inventoried forest structure on 453 plots (0.1 ha) spanning a large geographical gradient (>1,000 km), coring 15–25 canopy trees per plot for disturbance history reconstruction (tree core total n = 11,309). Our specific objectives were to: (1) classify sub-hectare-scale disturbance history based on disturbance timing and severity; (2) classify current forest structure based on tree size distributions (live, dead, standing, downed); (3) characterize structural development pathways as revealed by the association between disturbance history and current forest structural complexity. We used hierarchical cluster analysis for the first two objectives and indicator analysis for the third. The disturbance-based cluster analysis yielded six groups associated with three levels of disturbance severity (low, moderate, and high canopy loss) and two levels of timing (old, recent) over the past 200 years. The structure-based cluster analysis yielded three groups along a gradient of increasing structural complexity. A large majority of plots exhibited relatively high (53%) or very high (26%) structural complexity, indicated by abundant large live trees, standing and downed dead trees, and spruce regeneration. Consistent with conventional models of structural development, some disturbance history groups were associated with specific structural complexity groups, particularly low-severity/recent (very high complexity) and high-severity/recent (moderate complexity) disturbances. In other cases, however, the distribution of plots among disturbance history and structural complexity groups indicated either divergent or convergent pathways. For example, multiple disturbance history groups were significantly associated with the high complexity group, demonstrating structural convergence. These results illustrate that complex forest structure – including features nominally associated with old-growth – can be associated as much with disturbance severity as it is with conventional notions of forest age. Because wind and bark beetles are natural disturbance processes that can induce relatively high levels of tree mortality while simultaneously contributing to structural complexity and heterogeneity, we suggest that forest management plans allow for the stochastic occurrence of disturbance and variable post-disturbance development trajectories. Such applications are especially appropriate in conservation areas where biodiversity and forest resilience are management objectives, particularly given projections of increasing disturbance activity under global change. [ABSTRACT FROM AUTHOR]

In order to gauge ongoing and future changes to disturbance regimes, it is necessary to establish a solid baseline of historic disturbance patterns against which to evaluate these changes. Further, understanding how forest structure and composition respond to variation in past disturbances may provide insight into future resilience to climate-driven alterations of disturbance regimes. We established 184 plots (mostly 1000 m 2 ) in 14 primary mountain Norway spruce forests in the Western Carpathians. On each plot we surveyed live and dead trees and regeneration, and cored around 25 canopy trees. Disturbance history was reconstructed by examining individual tree growth trends. The study plots were further aggregated into five groups based on disturbance history (severity and timing) to evaluate and explain its influence on forest structure. These ecosystems are characterized by a mixed severity disturbance regime with high spatiotemporal variability in severity and frequency. However, periods of synchrony in disturbance activity were also found. Specifically, a peak of canopy disturbance was found for the mid-19th century across the region (about 60% of trees established), with the most important periods of disturbance in the 1820s and from the 1840s to the 1870s. Current stand size and age structure were strongly influenced by past disturbance activity. In contrast, past disturbances did not have a significant effect on current tree density, the amount of coarse woody debris, and regeneration. High mean densities of regeneration with height >50 cm (about 1400 individuals per ha) were observed. Extensive high severity disturbances have recently affected Central European forests, spurring a discussion about the causes and consequences. We found some evidence that forests in the Western Carpathians were predisposed to recent severe disturbance events as a result of synchronized past disturbance activity, which partly homogenized size and age structure and made recent stands more vulnerable to bark beetle outbreak. Our data suggest that these events are still part of the range of natural variability. The finding that regeneration density and volume of coarse woody debris were not influenced by past disturbance illustrates that vastly different past disturbance histories are not likely to change the future trajectories of these forests. These ecosystems currently have high ecological resilience to disturbance. In conclusion, we suggest that management should recognize disturbances as a natural part of ecosystem dynamics in the mountain forests of Central Europe, account for their stochastic occurrence in management planning, and mimic their patterns to foster biodiversity in forest landscapes. [ABSTRACT FROM AUTHOR]

Disturbances, both natural and human induced, influence forest dynamics, ecosystem functioning, and ecosystem services. Here, we aim to evaluate the consequences of natural disturbances on the magnitude and dynamics of tree- and stand-level biomass accumulation from decadal to centennial scales. We use tree-ring data from 2301 trees and biometric data from 4909 trees sampled in 96 plots (each 1000 m 2 ) to quantify the influence of mixed severity disturbance regimes on annual aboveground biomass increment (AGBI) and total aboveground biomass accumulation (AGB) across a mountainous monotypic Norway spruce ( Picea abies (L.) Karst.) primary forest. We hypothesise that the multiple internal and external factors constraining tree growth will cause differences in tree and stand-level biomass trajectories in these natural forests. Although we found that tree-level AGB growth increases with tree size, we also found that tree age and disturbance legacies plays a crucial role for AGB in the investigated Norway spruce forests. Importantly, while younger trees of the same diameter class have an average current AGBI rate that is ∼225% higher than older trees (300–400 years), we find trees that have been suppressed for up to 120 years can respond vigorously when competition is reduced. On average, post disturbance AGBI was ∼400% greater than pre-disturbance AGBI. Growth of suppressed trees, independent of their age, followed similar trajectories after canopy accession. While aboveground biomass generally increased through time, the time since disturbance and disturbance severity are important co-predictors for stand-level AGBI and AGB. These forests regained most of the above ground living biomass over short interval (∼50 years) after low intensity disturbances. The highest stand-level living AGB was observed on plots that experienced >40% canopy removal 160–190 years ago, whereas the highest AGBI occurred in plots disturbed recently within the past 40–50 years. Our results emphasize the importance of including both individual tree age and disturbance legacies to accurately characterize biomass dynamics and trajectories in forest ecosystems. Importantly, the period of time that a tree is in the canopy, and not tree age, modulates the trajectory of tree level AGBI. Growth rates begin to decline after ∼30 years (tree-rings width) and ∼100 years (AGBI) in the canopy. We demonstrate that even late-seral forests can rapidly regain biomass lost to low intensity disturbance. [ABSTRACT FROM AUTHOR]

Deforestation and fragmentation of forests worldwide are negatively impacting biodiversity. The capercaillie ( Tetrao urogallus ) is an endangered umbrella species of montane forests in central Europe. Despite its status, it has largely been overlooked in forest management planning in the Carpathian Mountains, a biodiversity hotspot within the European Union. Previous investigations of timber management effects on capercaillie have shown contradictory results within Europe; habitat loss and fragmentation due to intensive forest management have been implicated in population declines, while other studies have suggested neutral or positive effects. In Romania, recent changes in forest management have shifted from extensive, selective logging to intensive clearcutting; this change provides the opportunity to assess the effects of harvesting on capercaillie numbers across a full range of forest management intensities, thereby addressing discrepancies in the literature. Across the Southern and Eastern Carpathian mountains from 2009–2011, we used spring counts of capercaillie males at leks to evaluate the impact of forest management, other human activities, and habitat at two spatial scales – stand (∼2 ha) and landscape (∼300 ha). At the landscape level, the proportion of forest clearcuts and intensity of tourism had significant negative effects on the number of capercaillie males in the lek. In contrast, low intensity selective logging had a positive effect at the local stand (lek) level. Large scale (landscape level) forest clear-cutting had a negative effect on the capercaillie population – areas comprised of clearcuts of 30% reduced male lek counts by 76%. The protection of intact mature and old-growth forests, and forest management practices that emulate natural disturbance processes are recommended to support habitat of this critical umbrella species and associated biodiversity. [ABSTRACT FROM AUTHOR]

Good understanding of forest productivity and carbon (C) storage capacity is essential for better understanding of C dynamics and climate modeling. Studies of old-growth forest C dynamics from central and eastern Europe are rare and the few remaining pristine forests represent a unique opportunity to study natural forest dynamics in an otherwise managed landscape. We studied protected old-growth Norway spruce ( Picea abies L.) stands in the Bohemian Forest, Czech Republic, to explore total ecosystem C pool (live and dead biomass and soil) variability in forest ecosystem as a function of stand age and elevation. These old-growth forest ecosystems store very high amounts of C, up to 570 t C ha −1 , and 393 t C ha −1 on average. Live biomass is the dominant C pool followed by mineral soil, forest floor and dead biomass. We found that total C significantly decreased with increasing elevation (1025–1338 m a.s.l) from 456 to 294 t C ha −1 , predominantly driven by decreases in live biomass and forest floor C pools. Significant changes take place in individual pools based on age and elevation gradients, but total C was not significantly different between stands age 116–145 years. Contrary to some recent findings that old-growth forest ecosystems continue to sequester C long after maturity, our data supports the hypothesis that old-growth forests reach a steady state and become C neutral. They accumulate same amount of C through photosynthesis than is lost by decay and leaching. This study provides a detailed overview of C pools of old-growth Bohemian Forests and highlights the importance of including all major C pools in forest ecosystem C studies. [ABSTRACT FROM AUTHOR]

• We studied live and dead biomass carbon accumulation in primary uneven-aged forest. • We used 9610 tree cores from 400 plots from spruce forest in Carpathian mountains. • More severe disturbance resulted longer accumulation than less severity disturbance. • Disturbance driven stand structural diversity partly explained accumulation patterns. • Results can be used as a reference in uneven-aged forest management. Accurate estimations of changes in the forest carbon (C) pools over time are essential for predicting the future forest C balance and its part in the global C cycle. While the overall understanding of global forest C dynamics has improved, some significant forest ecosystem processes have been largely overlooked, resulting in possible biases. As an example, the effects of low and moderate severity disturbances have received disproportionately little attention. In this study, we use an extensive database of 9610 tree increment cores from 400 plots in primary uneven-aged Norway spruce (Picea abies) forests in the Carpathian Mountains, to explore the dynamics of live and dead wood C after disturbance. The data represents a chronosequence of more than 250 years since disturbance, varying highly in severity. We found that disturbance severity had a substantial impact on the post-disturbance long-term accumulation of C. Initially, live tree C accumulated at a similar rate independent of disturbance severity. However, the increase in C leveled off earlier after low disturbance severity while the most heavily disturbed forests continued to accumulate C to the latest stages of stand development. These results stress the importance of taking disturbance severity into account when predicting the long-term dynamics of C storage in forests under climate change. The results also highlight the importance of these forests as significant C pools. If harvested and turned into managed forest they would not reach their maximum C storing capacity. [ABSTRACT FROM AUTHOR]