Keywords:stand dynamics / forest-forming process / tree age structure / succession / nature-based management Abstract• This review summarizes early stand-scale studies of pristine forest structures, disturbance regimes and successional patterns carried out in boreal Eurasia. We attempt to reveal, characterize and classify stand dynamic types that can be used as templates for nature-based forest management.• The studies reviewed demonstrate multiple successional pathways in stand development in all types of pristine forests. All-aged stands driven by small-scale disturbances are formed over successional development of several hundreds of years. This endogenous development can be interrupted by standreplacing or partial disturbances leading to successions with even-aged or cohort-structured stands, respectively. In Western Europe, the most common disturbances are windthrows, surface fires and fluctuations in moisture regime; in Eastern Europe and Siberia, the most common disturbances are crown and surface fires and insect outbreaks. Type, return interval and severity of disturbances are strongly influenced by the site conditions and successional stage of a stand.• Based on characteristics of forest stands and disturbance regime, four main types of pristine boreal forest stand dynamics can be distinguished: (1) even-aged, compositional change dynamics, (2) evenaged, mono-dominant dynamics, (3) cohort dynamics and (4) fine-scale gap dynamics. These types can be mimicked in developing scenarios of ecological sustainable forest management in Eurasian boreal forests. Mots-clés :dynamiques forestières / succession forestière / structure d'âge / sylvigénèse / gestion durable Résumé -Structure des peuplements, régimes de perturbation et dynamiques de succession dans les forêts boréales eurasiennes : une revue basée sur des travaux russes.• Cette revue bibliographique résume les résultats de nombreuses études anciennes sur la structure des peuplements forestiers, sur les régimes de perturbation et sur les dynamiques de succession en forêt boréale eurasienne. Une typologie des modes de succession est proposée pour servir de cadre à une gestion forestière proche de la nature.• Les études analysées montrent l'existence de multiples modes de succession et de développe-ment des peuplements dans tous les types de forêts vierges analysées. Des peuplements mélangés comportant des arbres de tous âges se développent en réponse à des perturbations locales avec des dynamiques de plusieurs siècles. Ce développement endogène peut être interrompu par des renouvellements massifs ou des perturbations partielles qui conduisent à des successions basées sur des peuplements équiennes ou structurés en cohortes, respectivement. En Europe occidentale, les perturbations les plus fréquentes sont les chablis, les incendies de surface et des fluctuations des régimes hydriques ; en Europe oriental et en Sibérie, ce sont les incendies de surface et de canopée, et les attaques massives par des insectes.• En se basant sur les caractéristiques des peuplem...

Abstract. The condition of forest ecosystems depends on the temporal and spatial pattern of management interventions and natural disturbances. Remnants of previous conditions persisting after disturbances, or ecosystem legacies, collectively comprise ecosystem memory. Ecosystem memory in turn contributes to resilience and possibilities of ecosystem reorganization following further disturbance. Understanding the role of disturbance and legacies is a prerequisite for maintaining resilience in the face of global change. Several legacy concepts discussed in the peer-reviewed literature, including disturbance, biological, soil, land-use, and silvicultural legacies, overlap in complex ways. Here, we review these established legacy concepts and propose that the new terms "material legacy" (individuals or matter, e.g., survivors, coarse woody debris, nutrients left after disturbance) and "information legacy" (adaptations to historical disturbance regimes) cut across these previous concepts and lead to a new classification of legacies. This includes six categories: material legacies with above-and belowground, and biotic and abiotic categories, and information legacies with above-and belowground categories. These six legacies are influenced by differential patterns of editing and conditioning by "legacy syndromes" that result from natural or human-manipulated disturbance regimes that can be arranged along a gradient of naturalness. This scheme is applied to a case study of hemiboreal forests in the Baltic States of Estonia, Latvia, and Lithuania, where natural disturbance, traditional clearcut silviculture, and afforestation of abandoned agricultural lands constitute the three main legacy syndromes. These legacy syndromes in turn influence forest response to management actions and constrain resilience, leading to a mosaic of natural, manipulated, and artificial (novel) ecosystems across the landscape, depending on how the legacies in each syndrome affect ecological memory.

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Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001–2014, aiming to 1) quantify their within‐ and between‐biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 × 106 ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite‐based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter–area‐ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within‐biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.

During two measurement campaigns, from August to September 2008 and 2009, we quantified the major ecosystem fluxes in a hemiboreal forest ecosystem in Järvselja, Estonia. The main aim of this study was to separate the ecosystem flux components and gain insight into the performance of a multi-species multi-layered tree stand. Carbon dioxide and water vapor fluxes were measured using the eddy covariance method above and below the canopy in conjunction with the microclimate. Leaf and soil contributions were quantified separately by cuvette and chamber measurements, including fluxes of carbon dioxide, water vapor, nitrogen oxides, nitrous oxide, methane, ozone, sulfur dioxide, and biogenic volatile organic compounds (isoprene and monoterpenes). The latter have been as well characterized for monoterpenes in detail. Based on measured atmospheric trace gas concentrations, the flux tower site can be characterized as remote and rural with low anthropogenic disturbances. Our results presented here encourage future experimental efforts to be directed towards year round integrated biosphere-atmosphere measurements and development of process-oriented models of forest-atmosphere exchange taking the special case of a multi-layered and multi-species tree stand into account. As climate change likely leads to spatial extension of hemiboreal forest ecosystems a deep understanding of the processes and interactions therein is needed to foster management and mitigation strategies.

Global forest area is declining rapidly, along with degradation of the ecological condition of remaining forests. Hence it is necessary to adopt forest management approaches that can achieve a balance between (1) human management designs based on homogenization of forest structure to efficiently deliver economic values and (2) naturally emerging self-organized ecosystem dynamics that foster heterogeneity, biodiversity, resilience and adaptive capacity. Natural disturbance-based management is suggested to provide such an approach. It is grounded on the premise that disturbance is a key process maintaining diversity of ecosystem structures, species and functions, and adaptive and evolutionary potential, which functionally link to sustainability of ecosystem services supporting human well-being. We review the development, ecological and evolutionary foundations and applications of natural disturbance-based forest management. With emphasis on boreal forests, we compare this approach with two mainstream approaches to sustainable forest management, retention and continuous-cover forestry. Compared with these approaches, natural disturbance-based management provides a more comprehensive framework, which is compatible with current understanding of multiple-scale ecological processes and structures, which underlie biodiversity, resilience and adaptive potential of forest ecosystems. We conclude that natural disturbance-based management provides a comprehensive ecosystem-based framework for managing forests for human needs of commodity production and immaterial values, while maintaining forest health in the rapidly changing global environment.

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, smallsized and buried dead material, forest floor, and mineral soil.

Changes in climate, land use, and land management impact the occurrence and severity of wildland fires in many parts of the world. This is particularly evident in Europe, where ongoing changes in land use have strongly modified fire patterns over the last decades. Although satellite data by the European Forest Fire Information System provide large-scale wildland fire statistics across European countries, there is still a crucial need to collect and summarize in-depth local analysis and understanding of the wildland fire condition and associated challenges across Europe. This article aims to provide a general overview of the current wildland fire patterns and challenges as perceived by national representatives, supplemented by national fire statistics (2009–2018) across Europe. For each of the 31 countries included, we present a perspective authored by scientists or practitioners from each respective country, representing a wide range of disciplines and cultural backgrounds. The authors were selected from members of the COST Action “Fire and the Earth System: Science & Society” funded by the European Commission with the aim to share knowledge and improve communication about wildland fire. Where relevant, a brief overview of key studies, particular wildland fire challenges a country is facing, and an overview of notable recent fire events are also presented. Key perceived challenges included (1) the lack of consistent and detailed records for wildland fire events, within and across countries, (2) an increase in wildland fires that pose a risk to properties and human life due to high population densities and sprawl into forested regions, and (3) the view that, irrespective of changes in management, climate change is likely to increase the frequency and impact of wildland fires in the coming decades. Addressing challenge (1) will not only be valuable in advancing national and pan-European wildland fire management strategies, but also in evaluating perceptions (2) and (3) against more robust quantitative evidence.