•Past land use and management influence disturbance probability in mountain forests.•Forests established after 1920 are more susceptible to natural disturbances.•Recent management may increase ...stands’ susceptibility to disturbances.
Mountain forests provide a wide range of ecosystem services, including carbon sequestration and protection from natural hazards. Forest cover in the European Alps has increased over the last century, but in recent years, these forests have experienced an increasing rate of natural disturbances by agents such as windthrow, bark beetle outbreaks, and forest fires. These disturbances pose a challenge for forest management, making it important to understand how site and stand characteristics, land use legacies and recent management influence disturbance probability. We combined a dataset of forest disturbances detected from space with in-situ forest management records, allowing us to differentiate between different types of disturbances for the Canton of Graubünden, Switzerland, in the years 2005–2018. The resulting dataset of over 28′000 attributed disturbance patches (corresponding to a disturbed forest area of ca. 23′600 ha) was combined with information on topography, forest structure, and historical forest cover. A machine-learning approach was used to investigate the non-linear and interacting relationships between potential drivers and disturbance occurrence. Natural disturbances (especially windthrow and bark beetle outbreaks) were most common at lower elevations, on shallow and south-facing slopes, and in even-aged, spruce-dominated stands with a closed canopy. Forests established in the 20th century were significantly more susceptible to natural disturbances than forests that were already present before 1880, which may be due to the uniform age and vertical structure of secondary forests, as well as legacy effects of former agricultural use. On the other hand, forest management more often took place in forests present before 1880. Management interventions (such as thinning) in turn increased the susceptibility to natural disturbances in the short term. This finding emphasizes the need to balance short-term increases in disturbance susceptibility with long-term benefits in forest resilience when planning management interventions in mountain forests. Our findings highlight the importance of considering multiple interactive drivers, including management and land-use history, for understanding forest disturbance regimes.
•Regional-scale dendroecological study of primary mixed beech-fir forests.•Low-and intermediate-severity disturbances were the prevailing type of events.•Plot-level events of high and very-high ...disturbance severities were also detected.•Overall, the forest was driven by a mixed-severity disturbance regime.
Natural disturbances are key factors in the formation of forest ecosystem structure. Evaluation of the spatial and temporal extent of disturbance regimes is critical for understanding forest dynamics, forest structural heterogeneity, and biodiversity habitats. Quantifying disturbance regimes is therefore imperative for appropriate management of forests and protected areas. However, natural disturbance regimes have rarely been assessed using dendrochronological methods on a regional scale across primary mixed beech-fir forest stands - one of the dominant forest vegetation types in Europe. To study the natural disturbance regimes of beech-dominated mixed-forest stands, we established 42 permanent study plots with an area of 0.1 ha across three primary forest stands in the Western Carpathians, a region that still contains large areas of primary forest. We reconstructed each stand-level disturbance history using a tree-ring based approach. The temporal synchronicity of disturbance events was then evaluated by delineating stand-level disturbance events using a kernel density function, and through the detection of plot-level disturbances with severities greater than 10 percent. The results obtained from the chronologies showed substantial variability in time and space, especially in the mid-19th century. Low- and moderate-severity plot-level disturbance events were most common, but high- and extremely high-severity plot-level disturbance events also occurred. The observed spatial and temporal variability suggests that the beech-dominated forests were primarily driven by mixed-severity disturbance regimes, with windstorms as the main disturbance agent.
This reconstruction of the disturbance regime provided unique insight into the scale of mortality processes in these beech-dominated mixed forests. This information can help guide ecological forestry in areas where both wood production and biodiversity preservation are simultaneous goals, such as by employing more spatiotemporally-complex silvicultural systems that resemble natural disturbance patterns and facilitate heterogeneous forest structures.
Estimates of historical disturbance patterns are essential to guide forest management aimed at ensuring the sustainability of ecosystem functions and biodiversity. However, quantitative estimates of ...various disturbance characteristics required in management applications are rare in longer-term historical studies. Thus, our objectives were to (1) quantify past disturbance severity, patch size, and stand proportion disturbed and (2) test for temporal and subregional differences in these characteristics. We developed a comprehensive dendrochronological method to evaluate an approximately two-century-long disturbance record in the remaining Central and Eastern European primary mountain spruce forests, where wind and bark beetles are the predominant disturbance agents. We used an unprecedented large-scale nested design data set of 541 plots located within 44 stands and 6 subregions. To quantify individual disturbance events, we used tree-ring proxies, which were aggregated at plot and stand levels by smoothing and detecting peaks in their distributions. The spatial aggregation of disturbance events was used to estimate patch sizes. Data exhibited continuous gradients from low- to high-severity and small- to large-size disturbance events. In addition to the importance of small disturbance events, moderate-scale (25–75% of the stand disturbed, >10 ha patch size) and moderate-severity (25–75% of canopy disturbed) events were also common. Moderate disturbances represented more than 50% of the total disturbed area and their rotation periods ranged from one to several hundred years, which is within the lifespan of local tree species. Disturbance severities differed among subregions, whereas the stand proportion disturbed varied significantly over time. This indicates partially independent variations among disturbance characteristics. Our quantitative estimates of disturbance severity, patch size, stand proportion disturbed, and associated rotation periods provide rigorous baseline data for future ecological research, decisions within biodiversity conservation, and silviculture intended to maintain native biodiversity and ecosystem functions. These results highlight a need for sufficiently large and adequately connected networks of strict reserves, more complex silvicultural treatments that emulate the natural disturbance spectrum in harvest rotation times, sizes, and intensities, and higher levels of tree and structural legacy retention.
•We assess the association between forest disturbance history and current structure.•Carpathian spruce forests illustrate multiple pathways of structural development.•Complex structure is associated ...as much with disturbance as it is with stand age.•Unmanaged forests can inform adaptive management intended to foster resilience.
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 (0.1ha) spanning a large geographical gradient (>1,000km), 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 200years. 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.
•Forests can shift to alternate states where regeneration fails post-disturbance.•Empirical experiments can help to quantify alternate states in forests.•Acacia woodland replaces ash-type eucalypt ...forest where regeneration fails.•Transition to alternate states can compromise the functional integrity of forests.•Management changes and intervention must mitigate the risk of regeneration failure.
Under the current trajectory of accelerated climatic and environmental change, many forests are at risk of regeneration failure and subsequent transition to alternate stable states including non-forests or grassland. These regimes shifts can have severe ecological impacts and compromise carbon stores, undermine climate change mitigation, and create conditions incompatible with the survival of biodiversity. However, detailed empirical-based understanding of the alternative states associated with disturbance regime shifts is limited. Here, using a manipulative experiment, and controlling for seed application, we document temporal patterns of vegetation structure and composition associated with regeneration failure after clearcut logging in the ash-type eucalypt forests in south-eastern Australia. Our findings clearly demonstrate that in the absence of direct seed input, frequent stand-replacing disturbance can result in regeneration failure in these forests leading to them being replaced by low species diversity Acacia woodland. These insights can be extrapolated to scenarios of post-fire regeneration failure, where frequent fire precludes the development of adequate seed-stores (<21 years). Such shifts to alternative stable states can have severe ecological implications which require management intervention to circumvent and conserve the functional integrity of these forests. Our case study demonstrates the value of manipulative empirical experiments in quantifying the potential aftermath of forest regeneration failure. Such experiments may be useful to support theories and models in quantifying the ecological implications of regeneration failure, and to guide the application of management interventions for restoration where empirical-based knowledge of these states is limited.
Aim
Natural disturbances influence forest structure, successional dynamics and consequently, the distribution of species through time and space. We quantified the long‐term impacts of natural ...disturbances on lichen species richness and composition in primary mountain forests, with a particular focus on the occurrence of endangered species.
Location
Ten primary mountain spruce forest stands across five mountain chains of the Western Carpathians, a European hotspot of biodiversity.
Methods
Living trees, snags and downed logs were surveyed for epiphytic and epixylic lichens in 57 plots. Using reconstructed disturbance history, we tested how lichen species richness and composition was affected by the current forest structure and disturbance regimes in the past 250 years. We also examined differences in community composition among discrete microhabitats.
Results
Dead standing trees as biological legacies of natural disturbances promoted lichen species richness and the occurrence of threatened species at the plot scale, suggesting improved growing conditions for rare and common lichens during the early stages of recovery post disturbance. However, high‐severity disturbances compromised plot‐scale species richness. Both species richness and the number of old‐growth specialists increased with time since disturbance (i.e., long‐term uninterrupted succession). No lichen species was strictly dependent on live trees as a habitat, but numerous species showed specificity to logs, standing objects or an admixture of tree species.
Conclusions
Lichen species richness was lower in regenerating, young and uniform plots compared with overmature and recently disturbed areas. Natural forest dynamics and its legacies are critical to the diversity and species composition of lichens. Spatio‐temporal consequences of natural dynamics require a sufficient area of protected forests for provisioning continual habitat variability at the landscape scale. Ongoing climatic changes may further accentuate this necessity. Hence, we highlighted the need to protect the last remaining primary forests to ensure the survival of regionally unique species pools of lichens.
We documented that natural forest dynamics and its legacies are critical to the diversity and species composition of lichens in primary spruce mountain forests. Both species richness and the number of old‐growth specialists increased with time since disturbance. Spatio‐temporal consequences of natural dynamics require a sufficient area of protected forests for provisioning continual habitat variability at the landscape scale.
Global change has been accompanied by recent increases in the frequency and intensity of various ecological disturbances (e.g., fires, floods, cyclones), both natural and anthropogenic in origin. ...Because these disturbances often interact, their cumulative and synergistic effects can result in unforeseen consequences, such as insect outbreaks, crop failure, and progressive ecosystem degradation. We consider the roles of biological legacies, thresholds, and lag effects responsible for the distinctive impacts of interacting disturbances. We propose a hierarchical classification that distinguishes the patterns and implications associated with random co-occurrences, individual links, and multiple links among disturbances that cascade in chains or networks. Disturbance-promoting interactions apparently prevail over disturbance-inhibiting ones. Complex and exogenous disturbance cascades are less predictable than simple and endogenous links because of their dependency on adjacent or synchronous events. These distinctions help define regional disturbance regimes and can have implications for natural selection, risk assessment, and options for management intervention.
Constructing disturbance regimes is key to understanding current forest conditions and anticipating future changes. Many disturbance regimes, however, can only be constructed over large areas and ...long time-spans to capture the stochasticity of individual disturbance events. Typically, field-based approaches can go sufficiently back in time but are limited to small areas (e.g., several hectares), while remote-sensing-based approaches can cover large areas but are limited to relatively short-time spans (e.g., several decades). In this study, we developed a framework that combines contemporary and pre-remote-sensing disturbances to construct a disturbance regime for a large region. Specifically, we extracted the contemporary disturbances (1984–2021) from remote-sensing data, from which we trained machine-learning models (XGBoost algorithm) to predict key disturbance attributes, including the elapsed time since disturbance and spatial contraction distance, which were used to derive the occurrence time and original extent of individual disturbance events. We then extracted pre-remote-sensing disturbances from the earliest remote-sensing images (1980s) and used the machine-learning models to extrapolate the pre-remote-sensing disturbance attributes and thus expanded the timespan to 1900. Our approach incorporates ecological factors key to characterizing spatiotemporal dynamics in post-disturbance forest recovery, including vegetation index to represent recovery stage, disturbance pattern (shape and size of disturbed patches), distance to the edge of disturbed patches to reflect the effects of seed dispersal, and topography and forest type to capture the effects of spatial heterogeneity in environment and vegetation. We tested the framework in a wind-prone region of Changbai Mountain, northeast China. We showed that our approach can derive spatially-explicitly severe wind disturbance events for a large region over a long time-span while capturing the spatiotemporal stochasticity of the wind disturbance regime. The framework represents a process in constructing disturbance regimes over large areas, and it is transferable to other forest regions and other types of disturbances such as fire. The derived disturbance regime could fill the information gap of forest restoration and management.
•Develop framework to construct disturbance regime over large region and long timespan.•Use contemporary remote sensing and pre-remote-sensing disturbances events.•Incorporate ecological factors key to characterizing post-disturbance dynamics.•The framework is transferable to other regions and other types of disturbances.
Hurricane wind regimes for forests of North America Cannon, Jeffery B; Peterson, Chris J; Godfrey, Christopher M ...
Proceedings of the National Academy of Sciences - PNAS,
10/2023, Volume:
120, Issue:
42
Journal Article
Peer reviewed
Open access
Despite the ubiquity of tropical cyclones and their impacts on forests, little is known about how tropical cyclone regimes shape the ecology and evolution of tree species. We used a simple ...meteorological model (HURRECON) to estimate wind fields from hurricanes in the Western North Atlantic and Eastern North Pacific tropical cyclone basins from storms occurring between 1851 and 2022. We characterize how the intensity and frequency of hurricanes differ among geographically distinct hurricane regimes and define four hurricane regimes for North America (Continental, Inland, Coastal, and Fringe). Along this coastal-to-inland gradient, we found major differences in the frequency and intensity of hurricane wind regimes. The Fringe regime experiences category 1 winds relatively frequently return period (RP) 25 y, whereas the Inland regime experiences category 1 winds very infrequently (RP ~3,000 y). We discuss how species traits related to tree windfirmness, such as mechanical properties and crown traits, may vary along hurricane regime gradients. Quantitative characterization of forest hurricane regimes provides a critical step for understanding the evolutionary and ecological role of hurricane regimes in wind-prone forests.
•The results of studies from the Western Carpathian spruce forests are reviewed.•Disturbance regimes and resulted stand structures in spruce forests are recognised.•The regeneration niches of Picea ...abies, Sorbus aucuparia and Larix decidua are characterised.•Two models of the stand dynamics are proposed for the Western Carpathian spruce forest.
Disturbances of different spatial extent and intensity play an important role in the Western Carpathian Norway spruce forests. These forests are shaped mainly by severe winds, often followed by bark beetle infestations. Their intensity varies substantially, resulting in variability of disturbance regimes. Low- and moderate-severity disturbances create small-scale dynamics associated with small- and medium-sized gaps resulting from the death of individual trees or groups of them. Large stand-replacing disturbances are much less frequent but affect larger areas. In spite of such large variability of disturbance regimes, the structure of old-growth spruce stands varies less, with unimodal diameter distributions being the most common ones. In this review we discuss the possible natural mechanisms behind the relationship between the varied disturbance regimes and the rather uniform tree stand structures. We reviewed a large number of studies done in well preserved spruce stands throughout the Western Carpathians in Poland and Slovakia, which included analyses of the diameter and age distributions of stands and their short-term dynamics, as well as dendroecological reconstructions of disturbances over the last 200years. The regeneration niches of spruce and accompanying tree species are also analyzed. Two models of the relationship between stand dynamics and stand structure are proposed for Western Carpathian subalpine spruce stands. In the first one, severe stand-replacing disturbances hit forests over a large area, resulting in low variability of the age and size of trees recruited synchronously over extensive areas. In the second model, gap-phase dynamics produce spruce stands composed of distinct age cohorts of trees that originated over extensive areas. In our models, different trajectories of forest dynamics can yield similar stand structures, which will not be good indicators of disturbance regimes. We suggest that the abundance of rowan and European larch is a more reliable indicator of past disturbance regimes, because rowan benefits most from gap dynamics, while European larch is connected with extensive stand-replacing disturbances.
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