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This research has been supported by the Leverhulme Trust (grant no. RC-2018-023), the European Research Council (grant no. 694481), the German Research Foundation (grant no. FE-1096/6-1), the Swiss Government Excellence Postdoctoral Scholarships (grant no. FIRECO 2016.0310), the National Science Centre of Poland (grant no. 2015/17/B/ST10/01656), the SCIEX Scholarship Fund (grant no. PSPB-013/2010), and the Estonian Research Council (grant no. MOBJD313)., Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using IntCal20 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1676 records (entities) from 1480 sites worldwide. The database (RPDv1b – Harrison et al., 2021) is available at https://doi.org/10.17864/1947.000345., Leverhulme Trust RC-2018-023, European Research Council (ERC) European Commission 694481, German Research Foundation (DFG) FE-1096/6-1, Swiss Government Excellence Postdoctoral Scholarships FIRECO 2016.0310, SCIEX Scholarship Fund PSPB-013/2010, Estonian Research Council MOBJD313

Outbreaks of conifer bark beetles in Europe and North America have increased in scale and severity in recent decades. In this study, we identify existing fossil records containing bark beetle remains from the end of the Last Glacial Maximum (~14,000 cal. yr BP) to present day using the online databases Neotoma and BugsCEP and literature searches, and compare these data with modern distribution data of selected tree-killing species. Modern-day observational data from the Global Biodiversity Information Facility (GBIF) database was used to map recorded distributions from AD 1750 to present day. A total of 53 fossil sites containing bark beetle remains, from both geological and archeological sites, were found during our searches. Fossil sites were fewer in Europe ( n = 21) than North America ( n = 32). In Europe, 29% of the samples in which remains were found were younger than 1000 cal. yr BP, while in North America, remains were mainly identified from late Glacial (~14,000–11,500 cal. yr BP) sites. In total, the fossil records contained only 8 of 20 species we consider important tree-killing bark beetles in Europe and North America based on their impacts during the last 100 years. In Europe, Ips sexdentatus was absent from the fossil record. In North America, Dendroctonus adjunctus, Dendroctonus frontalis, Dendroctonus jeffreyi, Dendroctonus pseudotsugae, Dryocoetes confusus, Ips calligraphus, Ips confusus, Ips grandicollis, Ips lecontei, Ips paraconfusus, and Scolytus ventralis were absent. Overall, preserved remains of tree-killing bark beetles are rare in the fossil record. However, by retrieving bulk material from new and existing sites and combining data from identified bark beetle remains with pollen, charcoal, tree rings, and geochemistry, the occurrence and dominance of bark beetles, their outbreaks, and other disturbance events can be reconstructed.

Temperate mountain forests have experienced an increase in frequency and severity of natural disturbances (e.g., droughts, fires, windstorms and insect outbreaks) in recent decades due to climate and environmental change. Outbreaks of bark beetles have caused significant dieback of conifer forests in Central Europe and it is essential to model and predict the potential severity of future bark beetle outbreaks. However, to predict future bark beetle activity, historical baseline information is required to contextualize the magnitude of current and potential future outbreaks. A fossil beetle record from a forest hollow in the Tatra Mountains, Slovakia; one of the best-preserved national parks in Central Europe, was produced to identify insect outbreaks during the last millennia. Sub-fossil bark beetle remains were compared with parallel pollen and charcoal to assess whether peaks in conifer bark beetle remains correspond with indications of disturbance documented in historical or sedimentary fossil records. Three peaks in bark beetle remains were detected (1) post-2004, (2) AD 1140–1440, and (3) AD 930–1030. The abundance of species Pityogenes chalcographus and Pityophthorus pityographus in the two top samples can be linked directly to large bark beetle outbreaks in the High Tatra Mountains after 2004. P. chalcographus and P. pityographus are also the abundant species in the second peak (AD 1140–1440) while the third peak (AD 930–1030) consists of the species Polygraphus poligraphus. The most prominent conifer bark beetle in Central Europe, Ips typographus, was found to be present in most of the samples but always at very low numbers. It is plausible that P. chalcographus and P. pityographus fossils might be useful proxies for past conifer bark beetle outbreaks in Central Europe, as they occur together with fossils of I. typographus but appear to be well-preserved. A significant correlation was found between primary bark beetles and macroscopic charcoal densities in the sediment, highlighting the complex interactions between disturbance agents, bark beetles and fire, in this long-term regime of natural disturbances. Our 1400-year disturbance record shows how bark beetle outbreaks have been an important component of the regional natural disturbance regime for over a millennium and have intensified with increasing anthropogenic activity. Bark beetle outbreaks are likely one of the drivers promoting the future ecological stability of the temperate conifer ecosystem over decades to centuries.

Sedimentary charcoal records are widely used to reconstruct regional changes in fire regimes through time in the geological past. Existing global compilations are not geographically comprehensive and do not provide consistent metadata for all sites. Furthermore, the age models provided for these records are not harmonised and many are based on older calibrations of the radiocarbon ages. These issues limit the use of existing compilations for research into past fire regimes. Here, we present an expanded database of charcoal records, accompanied by new age models based on recalibration of radiocarbon ages using INTCAL2020 and Bayesian age-modelling software. We document the structure and contents of the database, the construction of the age models, and the quality control measures applied. We also record the expansion of geographical coverage relative to previous charcoal compilations and the expansion of metadata that can be used to inform analyses. This first version of the Reading Palaeofire Database contains 1681 records (entities) from 1477 sites worldwide. The database (DOI: 10.17864/1947.319) is available from https://researchdata.reading.ac.uk/id/eprint/319.

The ability of natural resource agencies to act before, during, and after outbreaks of conifer bark beetles (Coleoptera: Curculionidae) is important to ensure the continued provision of ecosystem services. Adaptive capacity refers to the capability of an agent or system to adapt to change, regardless of whether it is examined as an independent social or ecological entity, or as a coupled social–ecological system. Understanding the components of a disturbance and the associated effects to ecosystem services, social systems, and natural resource management increases the ability to adapt to change and ensure continued resilience. This paper presents a definition and conceptual framework of adaptive capacity relevant to bark beetle disturbances that was developed through an interdisciplinary workshop held in 2016. The intent is to assist natural resource managers and policy-makers in identifying important adaptation characteristics to effectively address bark beetle disturbances. The current state of knowledge regarding institutional, social, and environmental factors that influence adaptive capacity are identified. The mountain pine beetle (Dendroctonus ponderosae) in the western USA is used as a specific example to discuss several factors that influence adaptive capacity for increasing resilience. We hope that our proposed framework serves as a model for future collaborations among both social and physical scientists and land managers to better address landscape-level disturbances that are being exacerbated by climate change.

© 2019, Institute of Zoology, Slovak Academy of Sciences. The Bohemian Forest lakes, situated along the Czech-German-Austrian border, were strongly affected by atmospheric acidification between the 1950s and the late 1980s. The subsequent chemical recovery of the lake water should precede and enable a biological recovery, including changes in caddisfly (Insecta: Trichoptera) assemblages. Nevertheless, local pre-acidification data and detailed knowledge of the lake district history are missing, making evaluation of lake recovery difficult. We performed high-resolution analysis of caddisfly remains in a 2.2 m long sediment profile from Prášilské Lake covering the complete history of the lake-catchment evolution. Caddisfly larvae are good indicators of environmental conditions and their subfossil remains are well preserved in unconsolidated waterlaid sediments. A total of 10 caddisfly morpho-taxa were found providing a record from 11,400 cal. yr. BP to the present. With the exception of Athripsodes aterrimus, all identified species are currently present in the Bohemian Forest glacial lakes or their inflow streams but not all of them are documented in Prášilské Lake. The caddisfly fauna consisted of acid-resistant, acid-tolerant and eurytopic species since the Early Holocene. Based on our results, the acid, dystrophic state of Prášilské Lake has been occurring since the lake formation. We conclude that the first signs of natural acidification appeared not later than during the Holocene onset in the Bohemian Forest region. Furthermore, we did not detect any abrupt changes in the species composition connected to the period of anthropogenic acidification during the twentieth century. This study provides for the first time a record of postglacial succession of caddisfly assemblages in a central European mountain lake.

Sea-level budgets account for the contributions of processes driving sea-level change, but are predominantly focused on global-mean sea level and limited to the 20th and 21st centuries. Here we estimate site-specific sea-level budgets along the U.S. Atlantic coast during the Common Era (0–2000 CE) by separating relative sea-level (RSL) records into process-related signals on different spatial scales. Regional-scale, temporally linear processes driven by glacial isostatic adjustment dominate RSL change and exhibit a spatial gradient, with fastest rates of rise in southern New Jersey (1.6 ± 0.02 mm yr−1). Regional and local, temporally non-linear processes, such as ocean/atmosphere dynamics and groundwater withdrawal, contributed between −0.3 and 0.4 mm yr−1 over centennial timescales. The most significant change in the budgets is the increasing influence of the common global signal due to ice melt and thermal expansion since 1800 CE, which became a dominant contributor to RSL with a 20th century rate of 1.3 ± 0.1 mm yr−1., Sea-level rise is an important part of climate change, but most sea-level budgets are global and cannot capture important regional changes. Here the authors estimate sea-level budgets along the U.S. Atlantic coast, finding a faster rate of rise during the 20th century than any time in the past 2000 years.

Disentangling the long-term changes in forest disturbance dynamics provides a basis for predicting the forest responses to changing environmental conditions. The combination of multidisciplinary records can offer more robust reconstructions of past forest disturbance dynamics. Here we link disturbance histories of the central European mountain spruce forest obtained from dendrochronological and palaeoecological records (fossil pollen, sedimentary charcoal, bark beetle remains and geochemistry) using a small glacial lake and the surrounding forest in the Sumava National Park (Czech Republic). Dendrochronological reconstructions of disturbance were created for 300-year-long records from 6 study plots with a minimum of 35 trees analyzed for the abrupt growth increases (releases) and rapid early growth rates, both indicative of disturbance events. High-resolution analysis of lake sediments were used to reconstruct 800-year long changes in forest composition and landscape openness (fossil pollen), past fire events (micro- and macroscopic charcoal), bark beetle occurrence (fossil bark beetle remains), and erosion episodes (geochemical signals in the sediment) potentially resulting from disturbance events. Tree-ring data indicate that disturbances occurred regularly through the last three centuries and identify a most intensive period of disturbances between 1780 and 1830 CE. Geochemical erosion markers (e.g. K, Zr, % inorganic) show greater flux of catchment sediment and soils in the periods 1250–1400 and 1450–1500 CE, before a substantial shift to a more erosive regime 1600–1850 and 1900 CE onwards. Pollen records demonstrate relatively small changes in forest composition during the last 800 years until the beginning of the 20th century, when there was decrease in Picea. Fossil bark beetle remains indicate continuous presence of bark beetles from 1620s to 1800s, and charcoal records suggest that more frequent fires occurred during the 18th century. Each of the dendrochronological, palaeoecological and sedimentological records provide a unique perspective on forest disturbance dynamics, and combined offer a more robust and complete record of disturbance history. We demonstrate that sedimentary proxies originating from the lake catchment mirror the forest disturbance dynamics recorded in the tree-rings. The multidisciplinary records likely record forest disturbances at different spatial and temporal scales revealing different disturbance characteristics. Integrating these multidisciplinary datasets demonstrates a promising way to obtain more complete understanding of long-term disturbance dynamics. However, integrating datasets with variable spatial and temporal influence remains challenging. Our results indicated that multiple disturbance factors, such as windstorms, bark beetle outbeaks and fires, may occur simultaneously creating a complex disturbance regime in mountain forests, which should be considered in forest management and conservation strategies.

Montane biomes are niche environments high in biodiversity with a variety of habitats. Often isolated, these non-continuous remnant ecosystems inhabit narrow ecological zones putting them under threat from changing climatic conditions and anthropogenic pressure. Twelve sediment cores were retrieved from a peat bog in Tatra National Park, Slovakia, and correlated to each other by wiggle-matching geochemical signals derived from micro-XRF scanning, to make a reconstruction of past conditions. A fossil beetle (Coleoptera) record, covering the last 1000 years at 50- to 100-year resolution, gives a new insight into changing flora and fauna in this region. Our findings reveal a diverse beetle community with varied ecological groups inhabiting a range of forest, meadow and synanthropic habitats. Changes in the beetle community were related to changes in the landscape, driven by anthropogenic activities. The first clear evidence for human activity in the area occurs c. 1250 CE and coincides with the arrival of beetle species living on the dung of domesticated animals (e.g. Aphodius spp.). From 1500 CE, human (re)settlement, and activities such as pasturing and charcoal burning, appear to have had a pronounced effect on the beetle community. Local beetle diversity declined steadily towards the present day, likely due to an infilling of the forest hollow leading to a decrease in moisture level. We conclude that beetle communities are directly affected by anthropogenic intensity and land-use change. When aiming to preserve or restore natural forest conditions, recording their past changes in diversity can help guide conservation and restoration. In doing so, it is important to look back beyond the time of significant human impact, and for this, information contained in paleoecological records is irreplaceable.

Over the past few decades, mean summer temperatures within the Carpathian Mountains have increased by as much as 2 °C leading to a projected increased forest fire risk. Currently, there are no paleofire records from the Western Carpathians that provide the long-term range of natural variability to contextualise the response of upper-montane forests to future environmental change and disturbance regimes. We present the first high-resolution Holocene fire history record from the upper-montane ecotone from the High Tatra Mountains, Slovakia, as well as provide a regional synthesis of pan-Carpathian drivers of biomass burning in upper-montane forests. Our results illustrate that forest composition and density both greatly influence biomass burning, creating two different climate-fuel feedbacks. First, warmer conditions in the early Holocene, coupled with generally higher abundances of Pinus sp., either P. cembra and/or P. mugo/sylvestris, created a positive climate-fuel relationship that resulted in higher amounts of biomass burning. Second, cooler and wetter late Holocene conditions led to denser Picea abies upper-montane forests, creating a negative climate-fuel feedback that reduced biomass burning in upper-montane forests across the Carpathians. Given that warmer and drier conditions are expected across the entire Carpathian region in the future, our results illustrate how future climate change could potentially create a positive climate-fuel relationship within upper-montane forests dominated by Picea abies and Pinus cembra and/or P. mugo/sylvestris.

Investigating past changes in temperate mountain spruce forest ecosystems and the processes behind them can provide valuable information for understanding present and future ecosystem dynamics. To assess the late Holocene ecosystem change and disturbance history in mountain spruce forests, we sampled four small forest hollows from the High Tatra mountains in Slovakia. We use pollen analysis to reconstruct changes in forest composition over the last circa 5000 cal. yr BP. Fire history is analysed using macroscopic charcoal counts and charcoal area measurements. As disturbance is one of the key factors shaping mountain forest dynamics, the analysed pollen records will be processed with a new method quantifying disturbance based on plant ecological indices (Kuneš et al. 2019). These indices for disturbance will be attributed to pollen taxa and then disturbance frequency and severity for the whole community will be calculated. We assess the role of climate and human impact as potential drivers on the past forest and disturbance dynamics. The climate variable will be constructed from modelled climate data for the last 4000 years and for the past 1000 years we will use climate reconstruction from the tree-ring records from the region. We use human indicator pollen taxa as the variable for human influence on ecosystem dynamics, and to indicate human activity in the region.Preliminary results demonstrate opening of the landscape circa 800-500 cal. yr BP in connection with a change in the disturbance regime as indicated by the disturbance indices. The presence of human indicator pollen taxa in all small hollow records suggest landscape opening in connection with anthropogenic activity in the region. In addition, the charcoal records demonstrate periods of fire, which coincide with the opening of landscape and it is plausible that change in the fire regime is connected to the intensified human activity in the region. These results will be discussed further in the presentation in the light of climate data and further data analysis.Reference:Kuneš, P. Abraham, V. & Herben, T. 2019. Changing disturbance-diversity relationships in temperate ecosystems over the past 12 000 years. Journal of Ecology 107:1678–1688.

Last millennium relative sea-level (RSL) changes along the U.S. Atlantic coast are spatially variable. Glacial isostatic adjustment (GIA) has been a significant driving factor in RSL rise during the last millennium, producing maximum rates of vertical land motion in the mid-Atlantic region due to its proximity to the margin of the former Laurentide Ice Sheet. However, there is uncertainty surrounding the influence of other regional and local processes on RSL changes such as ocean and atmosphere circulation dynamics; gravitational, rotational, and deformational signals associated with ice mass and distribution changes; sediment compaction; and tidal range change.Here, we examined the high spatial density of high-resolution RSL records along a ~200 km stretch of coastline from New York City to southern New Jersey to distinguish between local, regional, and global scale drivers. We produced a new high-resolution (decimeter vertical, decadal temporal) RSL record of the last millennium in northern New Jersey and integrated it into an updated global database of instrumental and proxy sea-level records of the Common Era. We used a spatiotemporal empirical hierarchical model to estimate past RSL and rates of RSL change and their associated uncertainties in the context of broader regional changes by decomposing the records into global, regional linear, regional non-linear, and local components.We found that RSL in northern New Jersey continuously rose over the last 1000 years at a rate of 1.2 ± 0.2 mm/yr (2σ) from 1000 to 1700 CE before increasing to 1.3 ± 0.7 mm/yr from 1700-1800 CE to 1.8 ± 0.6 mm/yr from 1800-1900 CE to 3.0 ± 0.6 mm/yr from 1900-2000 CE. Most of the RSL rise during the past 1000 years is attributed to regional-scale linear processes that we interpret primarily as GIA. The linear component of the RSL records exhibits a north to south gradient, with a greater contribution of RSL rise in southern New Jersey and a smaller contribution in New York City. The regional-scale non-linear contribution from the records have a magnitude

Due to recent outbreaks of native bark beetles, forest ecosystems have experienced substantial changes in landscape structure and function, which also affect nearby human populations. As a result, land managers have been tasked with sustaining ecosystem services in impacted areas by considering the best available science, public perceptions, and monitoring data to develop strategies to suppress bark beetle epidemics, and in some cases to restore affected lands and ecosystem services. The effects of bark beetle outbreaks are often detrimental to the provision of ecosystem services, including degraded landscape aesthetics and diminished air and water quality. However, there have been instances where bark beetle outbreaks have benefited communities by, for example, improving habitat for grazing animals and enhancing real- estate values. As a consequence of the interaction of a warming climate and susceptible forest stand conditions, the frequency, severity, and extent of bark beetle outbreaks are expected to increase and therefore will continue to challenge many social–ecological systems. We synthesize experiences from recent outbreaks to encourage knowledge transfer from previously impacted communities to potentially vulnerable locations that may be at risk from future bark beetle epidemics

Building robust age-depth models to understand climatic and geologic histories from coastal sedimentary archives often requires composite chronologies consisting of multi-proxy age markers. Pollen chronohorizons derived from a known change in vegetation are important for age-depth models, especially those with other sparse or imprecise age markers. However, the accuracy of pollen chronohorizons compared to other age markers and the impact of pollen chronohorizons on the precision of age-depth models, particularly in salt marsh environments, is poorly understood. Here, we combine new and published pollen data from eight coastal wetlands (salt marshes and mangroves) along the Atlantic Coast of the United States (U.S.) from Florida to Connecticut to define the age and uncertainty of 17 pollen chronohorizons. We found that 13 out of 17 pollen chronohorizons were consistent when compared to other age markers (radiocarbon, radionuclide 137Cs and pollution markers). Inconsistencies were likely related to the hyperlocality of pollen chronohorizons, mixing of salt marsh sediment, reworking of pollen from nearby tidal flats, misidentification of pollen signals, and inaccuracies in or misinterpretation of other age markers. Additionally, in a total of 24 models, including one or more pollen chronohorizons, increased precision (up to 41 years) or no change was found in 18 models. Ministry of Education (MOE) National Research Foundation (NRF) Published version MC was funded by the National Science Foundation EAR 1624551. NSK, TS, and BPH were funded by the Ministry of Education Academic Research Fund MOE2018-T2-1-030 and MOE2019-T3-1-004, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centres of Excellence initiative. This article is a contribution to International Geoscience Program (IGCP) Project 639, “Sea Level Change from Minutes to Millennia”. This work is Earth Observatory of Singapore contribution 349. AP wishes to acknowledge the funding Science Foundation Ireland Career Development Award (17/CDA/4695); an investigator award (16/IA/4520); a Marine Research Programme funded by the Irish Government, co-financed by the European Regional Development Fund (Grant-Aid Agreement No. PBA/CC/18/01); European Union’s Horizon 2020 research and innovation programme under grant agreement No 818144; and SFI Research Centre awards 16/RC/3872 and 12/RC/2289_P2.

Summary 1. Recent bark beetle outbreaks in North America and Europe have impacted forested landscapes and the provisioning of critical ecosystem services. The scale and intensity of many recent outbreaks are widely believed to be unprecedented. 2. The effects of bark beetle outbreaks on ecosystems are often measured in terms of area affected, host tree mortality rates, and alterations to forest structure and composition. 3. Impacts to human systems focus on changes in property valuation, infrastructure damage from falling trees, landscape aesthetics, and the quality and quantity of timber and water resources. 4. To advance our understanding of bark beetle impacts, we assembled a team of ecologists, land managers and social scientists to participate in a research prioritization workshop. 5. Synthesis and applications. We identified 25 key questions by using an established methodology to identify priorities for research into the impacts of bark beetles. Our efforts emphasize the need to improve outbreak monitoring and detection, educate the public on the ecological role of bark beetles, and develop integrated metrics that facilitate comparison of ecosystem services across sites.

The influence of different drivers on changes in North American and European boreal forests biomass burning (BB) during the Holocene was investigated based on the following hypotheses: land use was important only in the southernmost regions, while elsewhere climate was the main driver modulated by changes in fuel type. BB was reconstructed by means of 88 sedimentary charcoal records divided into six different site clusters. A statistical approach was used to explore the relative contribution of (a) pollen-based mean July/summer temperature and mean annual precipitation reconstructions, (b) an independent model-based scenario of past land use (LU), and (c) pollen-based reconstructions of plant functional types (PFTs) on BB. Our hypotheses were tested with: (a) a west-east northern boreal sector with changing climatic conditions and a homogeneous vegetation, and (b) a north-south European boreal sector characterized by gradual variation in both climate and vegetation composition. The processes driving BB in boreal forests varied from one region to another during the Holocene. However, general trends in boreal biomass burning were primarily controlled by changes in climate (mean annual precipitation in Alaska, northern Quebec, and northern Fennoscandia, and mean July/summer temperature in central Canada and central Fennoscandia) and, secondarily, by fuel composition (BB positively correlated with the presence of boreal needleleaf evergreen trees in Alaska and in central and southern Fennoscandia). Land use played only a marginal role. A modification towards less flammable tree species (by promoting deciduous stands over fire-prone conifers) could contribute to reduce circumboreal wildfire risk in future warmer periods.

This study investigated the long-term role and drivers of fire in the central European temperate spruce-beech forests from Prášilské jezero, Czech Republic. The results illustrate the complex relationship between broad-scale climate, vegetation composition, and local human activities on fire throughout the Holocene. Biomass burning was the highest (average 3 fires/1000 years) and most severe during the early Holocene when fire resistant taxa (Pinus, Corylus and Betula) dominated. Using a Generalized Additive Model to assess the response of dominant canopy taxa to changes in biomass burning and fire severity, response curves demonstrate a positive relationship (p < 0.01) between fire resistant taxa and increases in biomass burning. Norway spruce (Picea abies) established ∼10,000 cal yr BP and expanded during peak biomass burning. Response curves show a slight negative relationship with Picea and increasing biomass burning, and a positive relationship with increasing fire severity. This suggests that central European spruce forests may not be significantly impacted by fire. Regional biomass burning dramatically decreased with the expansion of fire sensitive taxa (e.g. Fagus sylvatica) ∼6500 cal yr BP, yet no dramatic reduction in local fire frequency occurred. This suggests either human activities or rare fire-promoting climatic events were important in shaping local fire regimes. Fire activity peaked (6 fires/1000 years) ∼2500 cal yr BP and paralleled increases in anthropogenic pollen indicators. Fagus response curves illustrates a negative (p < 0.01) relationship with increasing biomass burning and fire severity suggesting that natural Fagus forests may be increasingly vulnerable to projected increases in wildfire occurrence. © 2018 Elsevier Ltd

Understanding the processes behind long-term boreal forest dynamics can provide information that assists in predicting future boreal vegetation under changing environmental conditions. Here, we examine Holocene stand-scale vegetation dynamics and its drivers at the western boundary of the Russian taiga forest in NW Russia. Fossil pollen and conifer stomata records from four small hollow sites and two lake sites are used to reconstruct local vegetation dynamics during the Holocene. Variation partitioning is used to assess the relative importance of the potential drivers (temperature, forest fires and growing site wetness) to the long-term stand-scale dynamics in taiga forest. All the main tree taxa, including the boreal keystone species Picea abies (Norway spruce) and Larix sibirica (Siberian larch), have been locally present since 10,000 cal yr bp. The constant Holocene presence of L. sibirica at three small hollow sites suggests a fast postglacial immigration of the species in northern Europe. Picea was present but not dominant at all study sites until its expansion between 8,000 and 7,000 cal yr bp markedly changed the forest structure through the suppression of Betula (birch), Pinus (pine) and Larix. Our results demonstrate that in general, the Holocene forest dynamics in our study region have been driven by temperature, but during short intervals the role of local factors, especially forest fires, has been prominent. The comparison between sites reveals the importance of local factors in stand-scale dynamics in taiga forests. Therefore, the future responses of taiga forest to climate change will be predominantly modulated by the local characteristics at the site.

Forest vegetation composition, including dominant keystone species and floristic diversity, is driven by natural and anthropogenic disturbances. Disentangling these complex interactions to identify the role of species competition, climate and disturbances in boreal forest dynamics is challenging. Here, pollen and charcoal data are used to reconstruct Holocene vegetation and fire history at the local stand-scale within an old-growth Picea abies (Norway spruce) forest hollow in southern Finland. The aim is to reconstruct vegetation history with specific emphasis on the mid-Holocene expansion of Picea and the decline in deciduous species in relation to fire history. Early-Holocene forest development and vegetation dynamics are primarily driven by climatic variations. The spread of Picea at approximately 5,200 cal bp does not coincide with local natural or anthropogenic disturbance or a decline in deciduous species and is consistent with its regional expansion, suggesting climate as the most likely control over the late establishment of this taxon. The mid-Holocene decline in deciduous species corresponds to an increased fire frequency suggesting a higher anthropogenic disturbance (also considered as the primary reason for the loss of floristic diversity in southern Finland). The ‘natural’ fire frequency in this local stand-scale boreal forest is lower than that observed in the recent past (i.e. the time of significant anthropogenic impact), yet the present-day absence or low frequency of fire remains within the range of natural variability observed during the early- and mid-Holocene.

Fossil pollen, conifer stomata, and charcoal records for the last 10,000 years were studied from three small hollow sites (Larix Hollow, Mosquito Hollow, and Olga Hollow) located at the modern western range limit of Siberian larch ( Larix sibirica) in northwestern Russia to investigate the role of forest fires in stand-scale dynamics of taiga vegetation. Wavelet coherence analysis was utilized to reveal the significance of fire on the vegetation composition at different timescales by assessing the phase and strength of the relationship between forest fires and most common boreal tree taxa in a time–frequency window. Pollen and stomata data show that all of the modern-day common tree taxa, including Norway spruce ( Picea abies) and Siberian larch, have been present in the study region since the early Holocene. The absence of charcoal layers at Mosquito Hollow suggests that this site has acted as a fire-free refugium with continuous dominance of spruce throughout the Holocene. Meanwhile, the Larix Hollow record indicates frequent local fire events and as a consequence, a more variable tree species composition. The wavelet coherence results show that the impact of forest fires on vegetation varies from short-term (

The alarming rate of ecosystem degradation has raised the need for ecological restoration throughout different biomes and continents. North European forests may appear as one of the least vulnerable ecosystems from a global perspective, since forest cover is not rapidly decreasing and many ecosystem services remain at high level. However, extensive areas of northern forests are heavily exploited and have lost a major part of their biodiversity value. There is a strong requirement to restore these areas towards a more natural condition in order to meet the targets of the Convention on Biological Diversity. Several northern countries are now taking up this challenge by restoring forest biodiversity with increasing intensity. The ecology and biodiversity of boreal forests are relatively well understood making them a good model for restoration activities in many other forest ecosystems. Here we introduce northern forests as an ecosystem, discuss the historical and recent human impact and provide a brief status report on the ecological restoration projects and research already conducted there. Based on this discussion, we argue that before any restoration actions commence, the ecology of the target ecosystem should be established with the need for restoration carefully assessed and the outcome properly monitored. Finally, we identify the most important challenges that need to be solved in order to carry out efficient restoration with powerful and long-term positive impacts on biodiversity: coping with unpredictability, maintaining connectivity in time and space, assessment of functionality, management of conflicting interests and social restrictions and ensuring adequate funding.

Fire disturbance is considered paramount for regeneration and biodiversity in the boreal forest with prescribed burning widely advocated in present day forest management. Palaeoecological knowledge is beneficial in understanding the role of fire as a driver of past vegetation dynamics. We use a sedimentary pollen and charcoal record to reconstruct 5000 years of fire and vegetation history from a small forest hollow (approximate area 12 m2) in the Vesijako Strict Nature Reserve, currently one of the few remaining old-growth forest stands in southern Finland. Results indicate three distinct periods in the environmental history (1) 5000–2000 cal. yrs. BP; semi-natural low frequency (430 year return period), low intensity fires in a diverse mixed stand with little evidence of anthropogenic disturbance and an expanding Picea abies (Norway spruce) population (2) 2000–750 cal. yrs. BP; anthropogenic-driven high frequency (180 year return period), high intensity stand-replacing fires in a low diversity stand with evidence of slash and burn cultivation and a decline of Picea population, (3) 750 cal. yrs. BP to present day; fire absence through a reduction in human-induced fire or active fire suppression and the expansion of the currently dominant Picea forest. The changing fire frequency has had a major influence on the forest composition during the last 5000 years. The loss of floristic diversity is associated with an increase in the human use of fire and without this human interference the previously high biodiversity in the stand may have remained up until the present day. If fire remains absent in Vesijako then it is likely that the Picea population will continue to dominate in the stand supporting a negative feedback mechanism that will result in lower frequency, higher intensity fires in the future.

The relative importance of climate, forest fires and human population size on long-term boreal forest composition were statistically investigated at regional and local scales in Fennoscandia. We employ pollen data from lakes, reflecting regional vegetation, and small forest hollows, reflecting local vegetation, from Russia, Finland and Sweden to reconstruct the long-term forest composition. As potential drivers of the Holocene forest dynamics we consider climate, generated from a climate model and oxygen isotope data, past forest fires generated from sedimentary charcoal data and human population size derived from radiocarbon dated archaeological findings. We apply the statistical method of variation partitioning to assess the relative importance of these environmental variables on long-term boreal forest composition. The results show that climate is the main driver of the changes in Holocene boreal forest composition at the regional scale. However, at the local scale the role of climate is relatively small. In general, the importance of forest fires is low both at regional and local scales. The fact that both climate and forest fires explain relatively small proportions of variation in long-term boreal vegetation in small forest hollow records demonstrates the complexity of factors affecting stand-scale forest dynamics. The relative importance of human population size was low in both the prehistorical and the historical time periods. However, this is the first time that this type of data has been used to statistically assess the importance of human population size on boreal vegetation and the spatial representativeness of the data may cause bias to the analysis.

Jones (1945) was a milestone paper exploring the natural forest concept with examples from the temperate and boreal ecosystems. It has become a classic because of its use of field observation of regeneration, succession and structure to assess theories about disturbance and the dynamic properties of natural forests. His main aim was to review some of the features of the structure and reproduction of the north temperate virgin forests, and this article presents, discusses and evaluates the main features of this legendary paper. Jones had international experience of both the ecological and silvicultural research communities and combined long-term field observations with theory to develop a realistic assessment of natural forest properties that formed the basis for current understanding. He demonstrated that natural disturbance regimes could generate a variety of structures and that a stable, “climax” forest concept was often not supported by field data. He also showed that even-aged components are ...

Background Severe canopy-removing disturbances are native to many temperate forests and radically alter stand structure, but biotic legacies (surviving elements or patterns) can lend continuity to ecosystem function after such events. Poorly understood is the degree to which the structural complexity of an old-growth forest carries over to the next stand. We asked how pre-disturbance spatial pattern acts as a legacy to influence post-disturbance stand structure, and how this legacy influences the structural diversity within the early-seral stand. Methods Two stem-mapped one-hectare forest plots in the Czech Republic experienced a severe bark beetle outbreak, thus providing before-and-after data on spatial patterns in live and dead trees, crown projections, down logs, and herb cover. Results Post-disturbance stands were dominated by an advanced regeneration layer present before the disturbance. Both major species, Norway spruce (Picea abies) and rowan (Sorbus aucuparia), were strongly self-aggregated and also clustered to former canopy trees, pre-disturbance snags, stumps and logs, suggesting positive overstory to understory neighbourhood effects. Thus, although the disturbance dramatically reduced the stand’s height profile with ~100% mortality of the canopy layer, the spatial structure of post-disturbance stands still closely reflected the pre-disturbance structure. The former upper tree layer influenced advanced regeneration through microsite and light limitation. Under formerly dense canopies, regeneration density was high but relatively homogeneous in height; while in former small gaps with greater herb cover, regeneration density was lower but with greater heterogeneity in heights. Conclusion These findings suggest that pre-disturbance spatial patterns of forests can persist through severe canopy-removing disturbance, and determine the spatial structure of the succeeding stand. Such patterns constitute a subtle but key legacy effect, promoting structural complexity in early-seral forests as well as variable successional pathways and rates. This influence suggests a continuity in spatial ecosystem structure that may well persist through multiple forest generations.