Search

Climate change is challenging conservation strategies for protected areas. To summarise current guidance, we systematically compiled recommendations from reviews of scientific literature (74 reviews fitting inclusion criteria) about how to adapt conservation strategies in the face of climate change. We focussed on strategies for designation and management of protected areas in terrestrial landscapes, in boreal and temperate regions. Most recommendations belonged to one of five dominating categories: (i) Ensure sufficient connectivity; (ii) Protect climate refugia; (iii) Protect a few large rather than many small areas; (iv) Protect areas predicted to become important for biodiversity in the future; and (v) Complement permanently protected areas with temporary protection. The uncertainties and risks caused by climate change imply that additional conservation efforts are necessary to reach conservation goals. To protect biodiversity in the future, traditional biodiversity conservation strategies should be combined with strategies purposely developed in response to a warming climate.

Boreal forests store 30% of the world's terrestrial carbon (C). Consequently, climate change mediated alterations in the boreal forest fire regime can have a significant impact on the global C budget. Here we synthesize the effects of forest fires on the stocks and recovery rates of C in boreal forests using 368 plots from 16 long‐term (≥100 year) fire chronosequences distributed throughout the boreal zone. Forest fires led to a decrease in total C stocks (excluding mineral soil) by an average of 60% (range from 80%), which was primarily a result of C stock declines in the living trees and soil organic layer. Total C stocks increased with time since fire largely following a sigmoidal shape Gompertz function, with an average asymptote of 8.1 kg C m−2. Total C stocks accumulated at a rate of 2–60 g m−2 yr−1 during the first 100 years. Potential evapotranspiration (PET) was identified as a significant driver of C stocks and their post‐fire recovery, likely because it integrates temperature, radiation, and the length of the growing season. If the fire return interval shortens to ≤100 years in the future, our findings indicate that many boreal forests will be prevented from reaching their full C storage potential. However, our results also suggest that climate warming‐induced increases in PET may speed up the post‐fire recovery of C stocks. Published version

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.

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 m2) 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.

Litterfall is a fundamental process in the nutrient cycle of forest ecosystems and a major component of annual net primary production (NPP). Despite its importance for understanding ecosystem energetics and carbon accounting, the dynamics of litterfall production following disturbance and throughout succession remain poorly understood in boreal forest ecosystems. Using a replicated chronosequence spanning 209 years following fire and 33 years following logging in Ontario, Canada, we examined the dynamics of litterfall production associated with stand development, overstory composition type (broadleaf, mixedwood, and conifer), and disturbance origin. We found that total annual litterfall production increased with stand age following fire and logging, plateauing in post-fire stands approximately 98 years after fire. Neither total annual litterfall production nor any of its constituents differed between young fire- or logging-originated stands. Litterfall production was generally higher in broadleaf stands compared with mixedwood and conifer stands, but varied seasonally, with foliar litterfall highest in broadleaf stands in autumn, and epiphytic lichen litterfall highest in conifer stands in spring. Contrary to previous assumptions, we found that the contribution of litterfall production to net primary production increased with stand age, highlighting the need for modeling studies of net primary productivity to account for the effects of stand age on litterfall dynamics.

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.

A generic regression model for above-ground biomass of forest stands was constructed based on published data (R2= 0.88,RSE= 32.8 t/ha). The model was used 1) to verify two allometric regression models of trees from Scandinavia applied to repeated measurements of 275 sample plots from database of Estonian Network of Forest Research (FGN) in Estonia, 2) to analyse impact of between-tree competition on biomass, and 3) compare biomass estimates made with different European biomass models applied on standardized forest structures. The model was verified with biomass measurements from hemiboreal and tropical forests. The analysis of two Scandinavian models showed that older allometric regression models may give biased estimates due to changed growth conditions. More biomass can be stored in forest stands where competition between trees is stronger. The tree biomass calculation methods used in different countries have also substantial influence on the estimates at stand-level. A common database of forest biomass measurements from Europe in similar to pan-tropical tree measurement data may be helpful to harmonise carbon accounting methods.

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.

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.

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.

Corresponding with the increasing global resource demand, harvesting now affects millions of hectares of boreal forest each year, and yet our understanding of harvesting impacts on boreal carbon (C) dynamics relative to wildfire remains unclear. We provide a direct comparison of C stocks following clearcut harvesting and fire over a 27-year chronosequence in the boreal forest of central Canada. Whereas many past studies have lacked measurement of all major C pools, we attempt to provide complete C pool coverage, including live biomass, deadwood, forest floor, and mineral soil C pools. The relative contribution of each C pool to total ecosystem C varied considerably between disturbance types. Live biomass C was significantly higher following harvesting compared with fire because of residual live trees and advanced regeneration. Conversely, most live biomass was killed following fire, and thus post-fire stands contained higher stocks of deadwood C. Snag and stump C mass peaked immediately following fire, but dramatically decreased 8 years after fire as dead trees began to fall over, contributing to the downed woody debris C pool. Forest floor C mass was substantially lower shortly after fire than harvesting, but this pool converged 8 years after fire and harvesting. When total ecosystem C stocks were examined, we found no significant difference during early stand development between harvesting and fire. Maximum total ecosystem C occurred at age 27 years, 185.1 ± 18.2 and 163.6 ± 8.0 Mg C ha−1 for harvesting and fire, respectively. Our results indicate strong differences in individual C pools, but similar total ecosystem C after fire and clearcutting in boreal forests, and shall help improve modeling terrestrial C flux after stand-replacing disturbances.

Boreal forests are critical to the global carbon (C) cycle. Despite recent advances in our understanding of boreal C budgets, C dynamics during compositional transition to late-succession forests remain unclear. Using a carefully replicated 203-year chronosequence, we examined long-term patterns of forest C stocks and net ecosystem productivity (NEP) following stand-replacing fire in the boreal forest of central Canada. We measured all C pools, including understorey vegetation, belowground biomass, and soil C, which are often missing from C budgets. We found a slight decrease in total ecosystem C stocks during early stand initiation, between 1 and 8 years after fire, at -0.90 Mg C ha -1 y -1 .A s stands regenerated, live vegetation biomass increased rapidly, with total ecosystem C stocks reaching a maximum of 287.72 Mg C ha -1 92 years after fire. Total ecosystem C mass then decreased in the 140- and 203year-old stands, losing between -0.50 and -0.74 Mg Ch a -1 y -1 , contrasting with views that old-growth forests continue to maintain a positive C balance. The C decline corresponded with canopy transition from dominance of Populus tremuloides, Pinus banksiana ,a nd Picea mariana in the 92-year-old stands to Betula papyrifera, Picea glauca ,a ndAbies balsamea in the 203-yearold stands. Results from this study highlight the role of succession in long-term forest C dynamics and its importance when modeling terrestrial C flux.

Aboveground deadwood, consisting of downed woody debris (DWD), snags, and stumps, is an important component of boreal forest ecosystem structure. Accurate deadwood density estimates are essential for evaluating ecosystem biomass and carbon stocks. The objective of this study was to examine the relationships between deadwood density, tree species, and decay status, identified in the field by morphological character- istics. We sampled DWD, snags, and stumps of trembling aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) B.S.P.), and balsam fir (Abies balsamea (L.) Mill.) in the boreal forest of central Canada. A total of 240 samples (99 DWD, 94 snags, and 47 stumps) were collected. Decay class and tree species explained 80% of the variation in wood density of all deadwood types. Wood density decreased consistently from the lowest to the highest decay class. Tree species identity was also important in determining the relationships between wood density and field- assigned decay class for snags and stumps, but not for DWD, probably because of the five-class system used for DWD, rather than the three-class system used for snags and stumps. These results indicate that decay class and tree species are adequate predictors of deadwood density. FOR .S CI. 59(3):261-266.

Atmospheric pollution critically affects forest ecosystems around the world by directly impacting the assimilation apparatus of trees and indirectly by altering soil conditions, which subsequently also leads to changes in carbon cycling. To evaluate the extent of the physiological effect of moderate level sulfate and reactive nitrogen acidic deposition, we performed a retrospective dendrochronological analysis of several physiological parameters derived from periodic measurements of carbon stable isotope composition ((13)C discrimination, intercellular CO2 concentration and intrinsic water use efficiency) and annual diameter increments (tree biomass increment, its inter-annual variability and correlation with temperature, cloud cover, precipitation and Palmer drought severity index). The analysis was performed in two mountain Norway spruce (Picea abies) stands of the Bohemian Forest (Czech Republic, central Europe), where moderate levels of pollution peaked in the 1970s and 1980s and no evident impact on tree growth or link to mortality has been reported. The significant influence of pollution on trees was expressed most sensitively by a 1.88‰ reduction of carbon isotope discrimination (Δ(13)C). The effects of atmospheric pollution interacted with increasing atmospheric CO2 concentration and temperature. As a result, we observed no change in intercellular CO2 concentrations (Ci), an abrupt increase in water use efficiency (iWUE) and no change in biomass increment, which could also partly result from changes in carbon partitioning (e.g., from below- to above-ground). The biomass increment was significantly related to Δ(13)C on an individual tree level, but the relationship was lost during the pollution period. We suggest that this was caused by a shift from the dominant influence of the photosynthetic rate to stomatal conductance on Δ(13)C during the pollution period. Using biomass increment-climate correlation analyses, we did not identify any clear pollution-related change in water stress or photosynthetic limitation (since biomass increment did not become more sensitive to drought/precipitation or temperature/cloud cover, respectively). Therefore, we conclude that the direct effect of moderate pollution on stomatal conductance was likely the main driver of the observed physiological changes. This mechanism probably caused weakening of the spruce trees and increased sensitivity to other stressors.

Boreal forest carbon (C) storage and sequestration is a critical element for global C management and is largely disturbance driven. The disturbance regime can be natural or anthropogenic with varying intensity and frequency that differ temporally and spatially the boreal forest. The objective of this review was to synthesize the literature on C dynamics of North American boreal forests after most common disturbances, stand replacing wildfire and clearcut logging. Forest ecosystem C is stored in four major pools: live biomass, dead biomass, organic soil horizons, and mineral soil. Carbon cycling among these pools is inter-related and largely determined by disturbance type and time since disturbance. Following a stand replacing disturbance, (1) live biomass increases rapidly leading to the maximal biomass stage, then stabilizes or slightly declines at old-growth or gap dynamics stage at which late-successional tree species dominate the stand; (2) dead woody material carbon generally follows a U-shaped pattern during succession; (3) forest floor carbon increases throughout stand development; and (4) mineral soil carbon appears to be more or less stable throughout stand development. Wildfire and harvesting differ in many ways, fire being more of a chemical and harvesting a mechanical disturbance. Fire consumes forest floor and small live vegetation and foliage, whereas logging removes large stems. Overall, the effects of the two disturbances on C dynamics in boreal forest are poorly understood. There is also a scarcity of literature dealing with C dynamics of plant coarse and fine roots, understory vegetation, small-sized and buried dead material, forest floor, and mineral soil.

Live vegetation carbon (C) pool dynamics are central to understanding C sequestration of forest ecosystems. Despite its importance, how aboveground live C pools change with stand development in boreal mixedwoods is poorly understood. We quantified aboveground live C pools (i.e., trees, >4 m in height; saplings and shrubs, 1.3–4 m in height; and understory plants

Artificially created high-stumps (snags) are created regularly during forest felling operations in Swedish coniferous production forests. The saproxylic beetle fauna in high-stumps of spruce and birch, on 20 clearcuts in Southern Sweden, were sampled by bark sieving. Ten of the clearcuts were located in hotspot areas with documented occurrence of many red-listed saproxylic beetle species. The other ten clearcuts were located in a typical production forest landscape (i.e. the matrix). Our aim was to investigate whether the benefit of creating high-stumps differs if the clearcuts is located in a hotspot area or in the matrix. In total 4,179 saproxylic beetles were found, belonging to 66 species, 9 of which were red-listed. Birch high-stumps hosted more species, on average, than spruce high-stumps. In an ordination analysis, tree species had the strongest explanatory effect among the environmental variables. No difference in beetle fauna could be found between the hotspot and matrix clearcuts, for neither birch nor spruce, according to all parameters: species numbers, species composition and red-listed species. The study does not indicate that conservation efforts in coniferous production forests should be concentrated to hotspot areas.