No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
The comparative use of charcoal frequency, area and morphology to reconstruct fire history in a late Holocene peat sequence from NW Romania
Abstract
Ombrotrophic peatlands are ideal archives for reconstructing charcoal fluxes resulting from vegetation burning. This is because they are sensitive to local environmental changes and the deposition of allochthonous material is exclusively atmospheric. This article presents a charcoal analysis in which two generally accepted research methods were compared, namely (i) quantification of the frequency of occurrence (number), and (ii) quantification of the size (area) of charred particles. The peat cores were extracted from the ombrotrophic bog of Tăul Mare in the Eastern Carpathian Mountains (northern Romania). The two methods for quantifying the occurrence of charcoal yielded similar results showing increasing variability of fire activity during the last ~ 3000 years. Charcoal peaks were best defined in the charcoal area dataset and indicated an increase in charcoal particle size during periods of high charcoal abundance, which points to local fires. Analysis of charcoal morphology showed that, during time intervals with high charcoal abundance, there was a gradual increase in the proportion of burnt wood. This suggests that episodes of high and/or low intensity burning, on both long and short timescales, may play an important role in determining the charcoal signature of these events. The high level of detection of high intensity fires suggests that charcoal records may be most useful in systems with high intensity fires.
ResearchGate has not been able to resolve any citations for this publication.
Although our understanding of key drivers of fire activity (climate, vegetation and humans) has improved, considerable uncertainty remains regarding the relative importance of these drivers and how they vary across spatial and temporal scales. Notably missing from our use of sedimentary charcoal records as a way to reconstruct past fire activity is the role of local controls on burning, and the relationships between different charcoal sizes, source area and types of depositional environment. To address these issues, we used seven sedimentary charcoal records within a small climatically homogeneous area, but with heterogeneous vegetation and human history in the Eastern Romanian Carpathians. On a temporal scale, we found more homogeneous fire histories during the early and mid Holocene (11000-6000 cal yr BP), which became more heterogeneous thereafter. This suggests that climate exerted a stronger influence on fire activity during the early Holocene, whereas local controls (vegetation type and load, land cover and - use) became more important over the mid and late Holocene. On an elevation gradient, we found discrepancies in trends in fire activity between the coniferous forest, treeline and subalpine vegetation that could have resulted from variability in fuel availability in response to changes in the elevational climate gradient and degree of anthropogenic impact. For the coniferous forests, anthropogenic activities enhanced biomass burning from ca 2000-1500 cal yr BP through the use of fire to open up the forests. For the treeline – subalpine areas, humans enhanced fire activity earlier, i.e., from 8000 and 4500 cal yr BP, and reduced burning activity through clearance and hence decrease in fuel load, from ca. 3000 cal yr BP. Our determination of macro-charcoal size-classes show that the 150-300 μm fraction is present in the highest proportion at all sites, with most of this fraction perhaps connected to a combination of local and regional fires, and not strictly to local fire activity. Lakes provide higher charcoal influx and larger sizes of charcoal particles than peat, and this suggests that peat - lake sediment lithological transitions within the same record can contribute to a taphonomic change in apparent rates of charcoal deposition.
Aim
We provide the first European‐scale geospatial training set relating the charcoal signal in surface lake sediments to fire parameters (number, intensity and area) recorded by satellite moderate resolution imaging spectroradiometer (MODIS) sensors. Our calibration is intended for quantitative reconstructions of key fire‐regime parameters by using sediment sequences of microscopic (MIC from pollen slides, particles 10–500 µm) and macroscopic charcoal (MAC from sieves, particles > 100 µm).
Location
North–south and east–west transects across Europe, covering the mediterranean, temperate, alpine, boreal and steppe biomes.
Time period
Lake sediments and MODIS active fire and burned area products were collected for the years 2012–2015.
Methods
Cylinder sediment traps were installed in lakes to annually collect charcoal particles in sediments. We quantitatively assessed the relationships between MIC and MAC influx (particles/cm ² /year) and the MODIS‐derived products to identify source areas of charcoal and the extent to which lake‐sediment charcoal is linked to fire parameters across the continent.
Results
Source area of sedimentary charcoal was estimated to a 40‐km radius around sites for both MIC and MAC particles. Fires occurred in grasslands and in forests, with grass morphotypes of MAC accurately reflecting the burned fuel‐type. Despite the lack of local fires around the sites, MAC influx levels reached those reported for local fires. Both MIC and MAC showed strong and highly significant relationships with the MODIS‐derived fire parameters, as well as with climatic variation along a latitudinal temperature gradient.
Main conclusions
MIC and MAC are suited to quantitatively reconstructing fire number and fire intensity on a regional scale. However, burned area may only be estimated using MAC. Local fires may be identified by using several lines of evidence, e.g. analysis of large particles (> 600 µm), magnetic susceptibility and sedimentological data. Our results offer new insights and applications to quantitatively reconstruct fires and to interpret available sedimentary charcoal records.
Conservation efforts to protect forested landscapes are challenged by climate projections that suggest significant restructuring of vegetation and disturbance regimes in the future. In this regard, paleoecological records that describe ecosystem responses to past variations in climate, fire and human activity offer critical information for assessing present landscape conditions and future landscape vulnerability. We illustrate this point drawing on eight sites in the northwest U.S., New Zealand, Patagonia, and central and southern Europe that have experienced different levels of climate and land-use change. These sites fall along a gradient of landscape conditions that range from near-pristine (i.e., where vegetation and disturbance have been significantly shaped by past climate and biophysical constraints) to highly altered (i.e., landscapes that have been intensely modified by past human activity). Position on this gradient has implications for understanding the role of natural and anthropogenic disturbance in shaping ecosystem dynamics and assessments of present biodiversity, including recognizing missing or overrepresented species. All the study sites reveal dramatic vegetation reorganization in the past as a result of postglacial climate variations. In nearly-pristine landscapes, like Yellowstone, climate has remained the primary driver of ecosystem change up to the present day. In Europe, natural vegetation-climate-fire linkages were broken ∼6000-8000 years ago with the onset of Neolithic farming, and in New Zealand, natural linkages were first lost ∼700 years ago with arrival of the Māori people. In the northwestern U.S. and Patagonia, greatest landscape alteration has occurred in the last 150 years with Euro-American settlement. Paleoecology is sometimes the best and only tool for evaluating the degree of this alteration and the extent to which landscapes retain natural components. Information on landscape-level history thus helps assess current ecological change, clarify management objectives, and define conservation strategies that seek to protect both "natural" and "cultural" elements. This article is protected by copyright. All rights reserved.
To investigate Holocene vegetation and fire-disturbance histories in the treeline ecotone, macroscopic charcoal, plant-macrofossil, and pollen records from two lacustrine sediment records were used. Lake Lia is on the southern slope and Lake Brazi is on the northern slope of the west-east-oriented Retezat Mountain range in the Romanian Carpathians. The records were used to reconstruct Holocene fire-return intervals (FRIs) and biomass burning changes. Biomass burning was highest at both study sites during the drier and warmer early Holocene, suggesting that climate largely controlled fire occurrence. Fuel load also influenced the fire regime as shown by the rapid biomass-burning changes in relation to timberline shifts. Overall, the number of inferred fire episodes was smaller on the northern than on the southern slope. FRIs were also comparatively longer (1000–4000 years) on the northern slope where Picea abies-dominated woodlands persisted around Lake Brazi throughout the Holocene. On the southern slope, where Pinus mugo was more abundant around Lake Lia, FRIs were significantly shorter (80–1650 years). A period of frequent fire episodes occurred around 1900–1300 cal yr BP on the southern slope, when chironomid-inferred summer temperatures increased and the pollen record documents increased anthropogenic activity near the treeline. However, the forest clearance by burning to increase grazing land was subdued in comparison to other European regions.
Climate, vegetation and humans act on biomass burning at different spatial and temporal scales. In this study, we used a dense network of sedimentary charcoal records from eastern Canada to reconstruct regional biomass burning history over the last 7000 years at the scale of four potential vegetation types: open coniferous forest/tundra, boreal coniferous forest, boreal mixedwood forest and temperate forest. The biomass burning trajectories were compared with regional climate trends reconstructed from general circulation models, tree biomass reconstructed from pollen series, and human population densities. We found that non-uniform climate, vegetation and human drivers acted on regional biomass burning history. In the open coniferous forest/tundra and dense coniferous forest, the regional biomass burning was primarily shaped by gradual establishment of less climate-conducive burning conditions over 5000 years. In the mixed boreal forest an increasing relative proportion of flammable conifers in landscapes since 2000 BP contributed to maintaining biomass burning constant despite climatic conditions less favourable to fires. In the temperate forest, biomass burning was uncoupled with climatic conditions and the main driver was seemingly vegetation until European colonization, i.e. 300 BP. Tree biomass and thus fuel accumulation modulated fire activity, an indication that biomass burning is fuel-dependent and notably upon long-term co-dominance shifts between conifers and broadleaf trees.
Macroscopic charcoal analysis of lake sediment stratigraphies is a widely used approach to reconstruct past
biomass burning patterns of ecosystems. The development of fire records often relies on a single quantification method of charcoal in a sediment subsample; however, recent studies have shown that additional paleoecological information can be obtained by classifying charcoal morphologies. The morphologies and diagnostic features of charcoal yields information about fuel sources, fire type, and charcoal taphonomy, and can aid in calibrating sediment records to known historical fires. This additional information enhances paleoecological inferences by providing more paleoenvironmental information than studies of total charcoal as the only metric. Here we present a classification of 27 macroscopic charcoal morphologies observed in Holocene sediments of lakes located in the mixed-conifer forests of southeastern British Columbia, Canada. This classification system builds on other morphological classifications that have been previously utilized, but is more inclusive of the morphological variability observed and is flexible to modification for use when applied to other study settings. The morphological classification presented here was developed following the observation of >100,000 macroscopic charcoal fragments >150 mm. This paper focuses on the observed morphological classes, their identification, potential fuel sources, and the morphotype assemblage stratigraphy from one site as an example. The charcoal assemblages varied throughout the mid-to-late Holocene contemporaneously with known regional scale hydroclimatic changes in British Columbia. Major changes in fire frequency were also concomitant with morphotype assemblage changes. Future work focusing on linking fuel types with charcoal morphotypes, post-fire observations of charcoal taphonomy, and the analysis of multiple attribute charcoal data sets from a variety of ecosystems will improve our understanding of biomass burning and long-term fire ecology.
The IntCal09 and Marine09 radiocarbon calibration curves have been revised utilizing newly available and updated data sets from 14C measurements on tree rings, plant macrofossils, speleothems, corals, and foraminifera. The calibration curves were derived from the data using the random walk model (RWM) used to generate IntCal09 and Marine09, which has been revised to account for additional uncertainties and error structures. The new curves were ratified at the 21st International Radiocarbon conference in July 2012 and are available as Supplemental Material at www.radiocarbon.org. The database can be accessed at http://intcal.qub.ac.uk/intcal13/. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.
Fire is well recognized as a key Earth system process, but its causes and influences vary greatly across spatial and temporal scales. The controls of fire are often portrayed as a set of superimposed triangles, with processes ranging from oxygen to weather to climate, combustion to fuel to vegetation, and local to landscape to regional drivers over broadening spatial and lengthening temporal scale. Most ecological studies and fire management plans consider the effects of fire-weather and fuels on local to sub-regional scales and time frames of years to decades. Fire reconstructions developed from high-resolution tree-ring records and lake-sediment data that span centuries to millennia offer unique insights about fire's role that cannot otherwise be obtained. Such records help disclose the historical range of variability in fire activity over the duration of a vegetation type; the role of large-scale changes of climate, such as seasonal changes in summer insolation; the consequences of major reorganizations in vegetation; and the influence of prehistoric human activity in different ecological settings. This paleoecological perspective suggests that fire-regime definitions, which focus on the characteristic frequency, size and intensity of fire and particular fuel types, should be reconceptualized to better include the controls of fire regimes over the duration of a particular biome. We suggest that approaches currently used to analyze fire regimes across multiple spatial scales should be employed to examine fire occurrence across multiple temporal scales. Such cross-scale patterns would better reveal the full variability of particular fire regimes and their controls, and provide relevant information for the types of fire regimes likely to occur in the future with projected climate and land-use change.
Interpretations of charcoal records from small hollows lack a strong theoretical and empirical foundation, and thus their potential for providing useful fire-history records is unclear. To evaluate this potential, we examined charcoal records in 210 Pb-dated cores from 12 small hollows and looked for evidence of 20 local fires reconstructed with tree-ring records from the surrounding forest. Using all charcoal/0.15 mm wide we established an optimum threshold that identified charcoal peaks corresponding to known fires while minimizing charcoal peaks identified that were not associated with known fires (i.e., false positives). This threshold detected four of four high-severity fires, five of 10 moderate-severity fires, and three of six low-severity fires. Analysis of larger charcoal alone (/0.50 mm wide) yielded nearly identical temporal patterns and detection rates, but four false positives were identified, twice as many as identified using all charcoal/0.15 mm wide. Charcoal peak magnitude was highly variable within severity classes: although half of the low-and moderate-severity fires left no detectable peaks, others left peaks larger than some high-severity fires. Our results suggest that fire detection depends strongly on fire severity and that fine-scale spatial patterns of lower-severity burns play an important role in determining the charcoal signature of these events. High detection rates for high-severity fires and low false-positive rates indicate that charcoal records from small hollows will be most useful in systems where fires are large, severe and infrequent.
_______________________________________________________________________________________ SUMMARY The abundance of charcoal in sediments has been interpreted as a 'fire history' at about 1,000 sites across the globe. This research effort reflects the importance of fire in many ecosystems, and the diversity of processes that can be affected by fire in many landscapes. Fire appears to reflect climate through the intermediary of vegetation, but arguably responds faster than vegetation to climate change or variability. Fire and humans are also intricately linked, meaning that the activity of fire in the past is also of relevance to prehistoric and historic human transitions and to contemporary natural resource management. This article describes recent advances in the analysis of charcoal in peat and other sediments, and offers a simple method for the quantification of larger charcoal fragments (>100 µm) and a standardised method for the quantification of microscopic charcoal on pollen slides. We also comment on the challenges that the discipline still faces.
The correct interpretation of charcoal records in a palaeoecological context requires the understanding of the sources and transport of charcoal particles. Conventionally, it is assumed that macroscopic charcoal particles are not transported far from fires (c. 200 m). Therefore macroscopic charcoal records are used to reconstruct local fire frequencies. However, the general scarcity of empirical and experimental evidence impedes a thorough check of this assumption. In this study we present the first unambiguous evidence of kilometre-scaled macroscopic charcoal transport in Europe. During the hot summer of 2003 an intensive crown fire occurred in Leuk, central Swiss Alps. It affected 300 ha of forest as well as 10 ha of pasture and fallow land. Litter traps and nets had been located approximately 5 km west and east of the burned area. The downwind site in the east (Jeizinen) recorded a strong charcoal fallout at 5.3 km from the fire edge. The observed charcoal influx of fragments with a size up to 1.3 cm reached average values of 0.144 and 0.098 mm 2 /cm 2 per fire (or yr) in five traps and two nets, respectively. These values are comparable with charcoal accumulations measured at only c. 50 m from large fires, suggesting that macroscopic charcoal transport does not decay rapidly to zero with increasing distance from the fire. We suggest a long-distance dispersal model for transport of macroscopic charcoal during large fire events. Reconstructions of local fire regimes may be affected by long-distance transport of macroscopic charcoal, although this problem is mitigated by the tendency of most macroscopic charcoal particles to be deposited within very short distances (B/50 m) from the fire edge.
Fire-history reconstructions that extend beyond the age of living trees and subfossil wood are based on an analysis of particulate charcoal and other fire proxies preserved in the sediments of lakes and wetlands. The goal of such research is to document the long-term fire history with enough temporal and spatial resolution to complement and extend reconstructions provided by dendrochronological and historical records. Long-term records also provide an opportunity to examine how fire regimes were affected by periods of major climate change and vegetation reorganization in the past. Such insights are critical for understanding the legacy of past fires in present ecosystems, as well as the role of fire with projected climate changes as a result of increased greenhouse gases in the future (e.g., Overpeck, Rind, and Jones 1990; Price and Rind 1994; Bartlein, Whitlock, and Shafer 1997). In the last decade several advances have been made in the analysis of lake and wetland sediment records for fire history reconstructions. These advances reflect a growing interest within the paleoecological community to consider fire as an ecosystem process operating on long and short time scales, as well as an increasing need on the part of resource managers to understand prehistoric fire regimes. In this chapter we review the theoretical and empirical basis for charcoal analysis, including assumptions about the charcoal source area and the processes that transport and deposit charcoal into lakes and wetlands. We discuss issues of site selection, chronology, and data analysis. In an effort to standardize procedures and establish greater confidence in inter-site comparisons, we suggest a research protocol for long-term fire history studies in the western Americas
It is widely accepted, based on data from the last few decades and on model simulations, that anthropogenic climate change will cause increased fire activity. However, less attention has been paid to the relationship between abrupt climate changes and heightened fire activity in the paleorecord. We use 35 charcoal and pollen records to assess how fire regimes in North America changed during the last glacial-interglacial transition (15 to 10 ka), a time of large and rapid climate changes. We also test the hypothesis that a comet impact initiated continental-scale wildfires at 12.9 ka; the data do not support this idea, nor are continent-wide fires indicated at any time during deglaciation. There are, however, clear links between large climate changes and fire activity. Biomass burning gradually increased from the glacial period to the beginning of the Younger Dryas. Although there are changes in biomass burning during the Younger Dryas, there is no systematic trend. There is a further increase in biomass burning after the Younger Dryas. Intervals of rapid climate change at 13.9, 13.2, and 11.7 ka are marked by large increases in fire activity. The timing of changes in fire is not coincident with changes in human population density or the timing of the extinction of the megafauna. Although these factors could have contributed to fire-regime changes at individual sites or at specific times, the charcoal data indicate an important role for climate, and particularly rapid climate change, in determining broad-scale levels of fire activity.
Fires influence basic ecosystem processes, including the distribution, the structure and the composition of vegetation, as well as the carbon cycle and climate at the global scale. Long-term knowledge (i.e., centuries or millennia) of fire regime history and forest fire ecology and dynamic in local environments is necessary for sustainable ecosystem management and biodiversity conservation strategies. Charcoal is a widely used proxy for reconstructing fire regime history and vegetation burning. Charcoal analysis is based on the accumulation of charred particles in depositional environments such as lakes and bogs, during and shortly after the occurrence of fire events. Ombrotrophic peat bogs are sensitive to local environmental changes and, given that the deposition of allochthonous material is exclusively atmospheric, they are ideal archives for reconstructing charcoal fluxes resulting from biomass burning. This study quantifies charcoal abundance (number) in a peat sequence extracted from Tăul Mare ombrotrophic peat bog (Văratec Massif, Lăpuş Mts, north-western Romania) aiming to reconstruct local fire history over the last 3000 years and to explore potential drivers. As a novelty, observations concerning the morphology of charred fragments are added to provide additional information on the type of material burnt (woody vegetation or herbs), fire severity and charcoal source area, thus strengthening the interpretation of the charcoal record. Results showed moderate fire activity between 3000 and 2300 cal yr BP, which slightly decreased between 2300 and 700 cal yr BP and varied considerably throughout the last 700 years. Several major fire episodes were further identified around 2500, 1700, 1300, 900 and 500 cal yr BP. Of these, the first four overlapped two phases of progressive landscape opening and extension of pastoral activities, while the latter was unprecedented in the entire history of the bog and was likely associated with the development of mining activities in the area. This study provides the first complementary use of charcoal morphologies in fire history reconstruction in Romania and adds a valuable perspective on the extent of past human impact on the mid-elevation mountain landscape.
Pollen analysis supported by twenty-five AMS ¹⁴C dates from the Tăul Negru peat bog (1143 m) in the Lăpuş Mountains (Eastern Carpathians, Romania) is used to reconstruct the Holocene vegetation history of this mountain region. The vegetation record at Tăul Negru starts at c. 10500 cal yr BP with dense montane forests dominated by Picea abies (spruce) and Ulmus (elm). Corylus avellana (hazel) spread after 10000 cal yr BP and reached maximum frequencies between 9000 and 7000 cal yr BP before a reduction. Thereafter Picea prevailed in the forests with Carpinus betulus (hornbeam) expanding after 5700 cal yr BP attaining maximum representation at 4200 cal yr BP. Fagus sylvatica (beech) spread from 4800 cal yr BP onwards with a short decline around 3700 cal yr BP. Mass expansion resumed afterwards leading to the ultimate recession of Picea, Corylus and Ulmus. Fagus predominates the forests until today. Small-scale human influence on the landscape (Cereal-type pollen grains, Poaceae, and Plantago lanceolata) first appeared after 6000 cal yr BP. Further anthropogenic impact was detected after 5000 cal yr BP and slightly stronger between 2300 cal yr BP and the 12th century AD with regular and increased appearances of primary and secondary cultural indicators. Large-scale forest clearing in the lowlands and foothills with more agriculture led to the development of the modern cultural landscape in the last 500 years.
Fire is a natural component of global biogeochemical cycles and closely related to changes in human land use. Whereas climate-fuel relationships seem to drive both global and subcontinental fire regimes, human-induced fires are prominent mainly on a local scale. Furthermore, the basic assumption that relates humans and fire regimes in terms of population densities, suggesting that few human-induced fires should occur in periods and areas of low population density, is currently debated. Here, we analyze human-fire relationships throughout the Holocene and discuss how and to what extent human-driven fires affected the landscape transformation in the Central European Lowlands (CEL). We present sedimentary charcoal composites on three spatial scales and compare them with climate model output and land cover reconstructions from pollen records. Our findings indicate that widespread natural fires only occurred during the early Holocene. Natural conditions (climate and vegetation) limited the extent of wildfires beginning 8500 cal. BP, and diverging subregional charcoal composites suggest that Mesolithic hunter-gatherers maintained a culturally diverse use of fire. Divergence in regional charcoal composites marks the spread of sedentary cultures in the western and eastern CEL. The intensification of human land use during the last millennium drove an increase in fire activity to early-Holocene levels across the CEL. Hence, humans have significantly affected natural fire regimes beyond the local scale – even in periods of low population densities – depending on diverse cultural land-use strategies. We find that humans have strongly affected land-cover- and biogeochemical cycles since Mesolithic times.
This study investigated the long-term role and drivers of fire in the central European temperate spruce-beech forests from Pr a silsk e 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.
Disturbances by fire are essential for the functioning of boreal/hemiboreal forests, but knowledge of long-term fire regime dynamics is limited. We analysed macrocharcoal morphologies and pollen of a sediment record from Lake Lielais Svētiņu (eastern Latvia), and in conjunction with fire traits analysis present the first record of Holocene variability in fire regime, fuel sources and fire types in boreal forests of the Baltic region. We found a phase of moderate to high fire activity during the cool and moist early (mean fire return interval; mFRI of ∼280 years; 11,700–7500 cal yr BP) and the late (mFRI of ∼190 years; 4500–0 cal yr BP) Holocene and low fire activity (mFRI of ∼630 years) during the Holocene Thermal Optimum (7500–4500 cal yr BP). Charcoal morphotypes and the pollen record show the predominance of frequent surface fires, occasionally transitioning to the crown during Pinus sylvestris-Betula boreal forests and less frequent surface fires during the dominance of temperate deciduous forests. In contrast to the prevailing opinion that fires in boreal forests are mostly low to moderate severity surface fires, we found evidence for common occurrence of stand-replacing crown fires in Picea abies canopy. Our results highlight that charcoal morphotypes analysis allows for distinguishing the fuel types and surface from crown fires, therefore significantly advancing our interpretation of fire regime. Future warmer temperatures and increase in the frequency of dry spells and abundant biomass accumulation can enhance the fire risk on the one hand, but will probably promote the expansion of broadleaf deciduous forests to higher latitudes, on the other hand. By highlighting the capability of broadleaf deciduous forests to act as fire-suppressing landscape elements, our results suggest that fire activity may not increase in the Baltic area under future climate change.
Fire frequency and severity are key parameters in evaluating fire-mediated changes in ecosystems, but these metrics are rarely reconstructed at extensive temporal scales. Notably our understanding of the role of fire regime dynamics in the functioning and biodiversity of Central Eastern European temperate forests is limited because investigation of the effect of fire has been neglected. To fill this gap in knowledge, we applied a multi-proxy approach (macrocharcoal, charred remains, pollen, plant macrofossils) to two sedimentary sequences spanning stands of closed canopy Picea abies to the P. abies treeline located in the northern Carpathians, Romania. We found that climate exerts a broad-scale influence, whereas vegetation feedbacks strongly modulate this fire-climate relationship. Fire has been almost continuously present throughout the Holocene with a remarkably stable mean fire rotation (∼250 yr) with fires of mostly low to mid severity and/or small to medium size. Humans have shifted the fire regime during the last 2800 years to slightly longer fire return intervals (mean 300 yr) and more biomass consumption per fire. We found that P. abies was favoured by low to moderate fire severity/area burned. The establishment of late-successional, shade tolerant Fagus sylvatica was facilitated by fire disturbances, but its expansion coincided with major gaps in fire events. This highlights the key role of fire in the expansion of F. sylvatica that seems only possible in a low/small to mixed severity/size fire regime with a sufficiently long fire return interval. High magnitude charcoal peaks negatively affected F. sylvatica. We found more diverse pollen assemblages, especially taxa linked to anthropogenic impact, at times of moderate fire disturbance corroborating the intermediate disturbance hypothesis. In terms of forest management, our results show that, contrary to current understanding, fire is a natural and important driver of vegetation change in this region. The anticipated increase in fire activity with the climate warming and/or augmented fuel accumulation may threaten the dominant forest ecosystems, given that these are adapted to low frequency and severity fires. We advise forestry to consider the effects of fire as part of climate-change conservation strategies. Diversifying the forest tree mixture with more fire-resistant native species is desirable in order to mitigate the effects of increased fire occurrence and severity.
If radiocarbon measurements are to be used at all for chronological purposes, we have to use statistical methods for calibration. The most widely used method of calibration can be seen as a simple application of Bayesian statistics, which uses both the information from the new measurement and information from the 14 C calibration curve. In most dating applications, however, we have larger numbers of 14 C measurements and we wish to relate those to events in the past. Bayesian statistics provides a coherent framework in which such analysis can be performed and is becoming a core element in many 14 C dating projects. This article gives an overview of the main model components used in chronological analysis, their mathematical formulation, and examples of how such analyses can be performed using the latest version of the OxCal software (v4). Many such models can be put together, in a modular fashion, from simple elements, with defined constraints and groupings. In other cases, the commonly used “uniform phase” models might not be appropriate, and ramped, exponential, or normal distributions of events might be more useful. When considering analyses of these kinds, it is useful to be able run simulations on synthetic data. Methods for performing such tests are discussed here along with other methods of diagnosing possible problems with statistical models of this kind.
Predictions of the extent of forest fires under warmer and drier conditions in boreal regions require knowledge of long-term relationships between fire and climate. However, many long-term studies that utilize the remains of total charcoal in lacustrine sediments fail to demonstrate a relationship between climate change and fire activity. A new approach to reconstruct the relative-area burned based on specific types of charcoal particles (the charcoal-morphotype (CM) fire index) has shown significant correlations to recorded forest fires. Here we assess the utility of the CM derived from an analysis of charcoal morphotypes in sediment cores from Opatcho Lake (British Columbia, Canada) using two independent paleoclimate proxies over the last 400 years, and since the mid Holocene. Over the past 400 years, significant correlations between the CM fire index and independent climate reconstructions (diatom-inferred salinity, dendroclimatic reconstructions of temperature and precipitation, and reconstructions of the Pacific Decadal Oscillation) range from 0.35 to 0.42. Similarly, since the mid Holocene the correlation between the CM fire index and independent proxies of past climate (diatom-inferred salinity and temperature inferences from chironomids from the southern interior of British Columbia) range from 0.70 to 0.76. These significant correlations strongly contrast with the very low and insignificant correlations between the CM fire index and total charcoal, suggesting that this approach provides paleofire information not available from traditional techniques. The CM fire index suggests that fires were at least two- and five-fold larger than those observed during the instrumental period, over the last 400 and 6000 years, respectively.
Fire-history reconstructions inferred from sedimentary charcoal records are based on measuring sieved charcoal fragment area, estimating fragment volume, or counting fragments. Similar fire histories are reconstructed from these three approaches for boreal lake sediment cores, using locally defined thresholds. Here, we test the same approach for a montane Mediterranean lake in which taphonomical processes might differ from boreal lakes through fragmentation of charcoal particles. The Mediterranean charcoal series are characterized by highly variable charcoal accumulation rates. Results there indicate that the three proxies do not provide comparable fire histories. The differences are attributable to charcoal fragmentation. This could be linked to fire type (crown or surface fires) or taphonomical processes, including charcoal transpor-tation in the catchment area or in the sediment. The lack of correlation between the concentration of charcoal and of mineral matter suggests that fragmentation is not linked to erosion. Reconstructions based on charcoal area are more robust and stable than those based on fragment counts. Area-based reconstructions should therefore be used instead of the particle-counting method when fragmentation may influence the fragment abundance.
An interdisciplinary study (cartographic and historical records, geomorphological, geological and
bathymetric survey, water analysis, sediment coring and analysis and AMS radiocarbon dating) of two
small and previously unreported lakes (Iezer and Bol�at�au) in Obcina Feredeului Mountains, northeastern
Romania, provides new data into the environmental history and possible human impacts over the last
millennium in this region. The first recorded historical reference to Iezer Lake dates to 1594 AD, and to
Bol�at�au Lake to 1806 AD. Two sediment cores (420 cm for Iezer and 540 cm for Bol�at�au) of finely banded
lake sediments and a radiocarbon age estimate at Iezer Lake suggest that this lake may represent the
oldest landslide lake in Romania. The geomorphological, geological, and morphometric surveys indicate
that these lakes’ origins relate to landslide activity. Coarse grained, lighter sediment bands are generally
characterized by higher values in magnetic susceptibility, Saturation Isothermal Remanent Magnetisation
(SIRM), as well in geochemical indicators such as Ti and Zr, and low organic content, possibly
indicating periods of increased runoff. Conversely, finer-grained, dark sediment bands show lower values
in magnetic susceptibility, SIRM, Ti and Zr and higher organic content, and are likely to suggest quieter
deposition periods. However, there are two significant episodes of markedly increased surface erosion. The
oldest occurs between 100 and 110 cm, and might be coincident with the terminal part of Little Ice Age
(LIA), whereas the youngest in the top 30 cm coincides with recent land use. These lakes hold significant
potential in providing an important perspective on the environmental conditions over the last millennium
and, more specifically, to supply new information about the MedievalWarm Period (MWP) and LIA signals
in the NE Romanian Carpathians. These two landslide-dammed lakes should be defined as scientific
reserves to ensure their protection and to enhance their use as a scientific and educational resource.
The study of macroscopic charcoal particles from peat bogs has led to a better understanding of climate, vegetation and fire history, and human impacts. To determine the relationship between human activities and the role of fire events in vegetation change during the last 3300 cal yr BP, we present the results of a multi-proxy approach based on the analysis of sediment characteristics, sedimentary charcoal, organic matter and pollen, as well as historical sources. This multi-proxy research permits high resolution palaeoenvironmental and fire history reconstruction of a mountain area located in the southern central Pyrenees (Spain). In the Pyrenees, fire is typically attributed to human activities since the beginning of the Bronze Age and may be correlated with slash-and-burn cultivation, metallurgy and pasturing activities.The data indicate a good linkage between high fire signals and Poaceae and Cerealia pollen, which reveals the impact of agro-pastoral practices. This study also shows two periods, 2900–2650 cal yr BP and 1850–1550 cal yr BP, for which higher frequencies of fire occurred, suggested by high arboreal pollen (AP) concentrations, and confirming the need for arboreal biomass to sustain fires. From the beginning of the Middle Ages, it seems that a change occurred in the anthropogenic use of fire, from a tool for agro-pastoral forest clearance to a means of maintaining open spaces.
Biomass burning and resulting fire regimes are major drivers of vegetation changes and of ecosystem dynamics. Understanding past fire dynamics and their relationship to these factors is thus a key factor in preserving and managing present biodiversity and ecosystem functions. Unfortunately, our understanding of the disturbance dynamics of past fires is incomplete, and many open questions exist relevant to these concepts and the related methods. In this paper we describe the present status of the fire-regime concept, discuss the notion of the fire continuum and related proxies, and review the most important existing approaches for reconstructing fire history at centennial to millennial scales. We conclude with a short discussion of selected directions for future research that may lead to a better understanding of past fire-regime dynamics. In particular, we suggest that emphasis should be laid on (1) discriminating natural from anthropogenic fire-regime types, (2) improving combined analysis of fire and vegetation reconstructions to study long-term fire ecology, and (3) overcoming problems in defining temporal and spatial scales of reference, which would allow better use of past records to gain important insights for landscape, fire and forest management.
Geografia României: Geografia fizică (Geography of Romania: Physical Geography)
- L Badea
- P Gâştescu
Badea, L., Gâştescu, P. (1983) Geografia României:
Geografia fizică (Geography of Romania:
Physical Geography). Publishing House of the
Romanian Academy, Bucharest, 518-661 (in
Romanian).
Carpaţii Orientali, Carpaţii Maramureşului şi Bucovinei (Eastern Carpathians, Maramures and Bukovina Carpathians)
- L Badea
- Gh Niculescu
- D Călin
Badea, L., Niculescu, Gh., Călin, D. (2012) Carpaţii
Orientali, Carpaţii Maramureşului şi Bucovinei
(Eastern Carpathians, Maramures and Bukovina
Carpathians). Unităţile de relief ale României,
vol. VI (The relief units of Romania, Volume VI),
Editura Ars Docendi, University of Bucarest,
p. 31 (in Romanian).
Tracking recorded fires using charcoal morphology from the sedimentary sequence of Prosser Lake, British Columbia (Canada)
- M D Enache
- B F Cumming
Enache, M.D., Cumming, B.F. (2006) Tracking
recorded fires using charcoal morphology from
the sedimentary sequence of Prosser Lake, British
Columbia (Canada). Quaternary Research, 65(2),
282-292. 10.1016/j.yqres.2005.09.003
Last millennium hydro-climate variability in Central-Eastern Europe (Northern Carpathians, Romania). The Holocene
- A Feurdean
- M Galka
- E Kuske
- I Tantau
- M Lamentowicz
- G Florescu
- J Liakka
- S M Hutchinson
- A Mulch
- T Hickler
Feurdean, A., Galka, M., Kuske, E., Tantau, I.,
Lamentowicz, M., Florescu, G., Liakka, J.,
Hutchinson, S.M., Mulch, A., Hickler, T. (2015)
Last millennium hydro-climate variability in
Central-Eastern Europe (Northern Carpathians,
Romania). The Holocene, 25(7), 1179-1192.
https://doi.org/10.1016/j.foreco.2016.11.046
A guide to screening charcoal peaks in macrocharcoal-area records for fire-episode reconstructions. The Holocene
- W Finsinger
- R Kelly
- J Fevre
- E K Magyari
Finsinger, W., Kelly, R., Fevre, J., Magyari, E.K.
(2014) A guide to screening charcoal peaks in
macrocharcoal-area records for fire-episode
reconstructions. The Holocene, 24(8), 1002-1008. https://doi.org/10.1177/095968361453473
Holocene fire history of a coastal temperate rain forest based on soil charcoal radiocarbon dates
- D G Gavin
- L B Brubaker
- K P Lertzman
Gavin, D.G., Brubaker, L.B., Lertzman, K.P. (2003)
Holocene fire history of a coastal temperate rain
forest based on soil charcoal radiocarbon dates.
Ecology, 84(1), 186-201. https://doi.org/10.1890/
0012-9658(2003)084[0186:HFHOAC] 2.0.CO;2
Recent sediment accumulation rates in contrasting lakes in the Carpathians (Romania): impacts of shifts in socioeconomic regime
- S M Hutchinson
- F O Akinyemi
- M Mîndrescu
- R Begy
- A Feurdean
Hutchinson, S.M., Akinyemi, F.O., Mîndrescu, M.,
Begy, R., Feurdean, A. (2016) Recent sediment
accumulation rates in contrasting lakes in the
Carpathians (Romania): impacts of shifts in socioeconomic regime. Regional Environmental Change,
16, 501-513. 10.1007/s10113-015-0764-7
Subalpine fires: the roles of vegetation, climate and, ultimately, land uses
- B Leys
- C Carcaillet
Leys, B., Carcaillet, C. (2016) Subalpine fires: the
roles of vegetation, climate and, ultimately, land
uses. Climatic Change, 135(3-4), 683-697.
10.1007/s10584-016-1594-4
Interpretation of the charcoal record in forest soils: forest fires and their production and deposition of macroscopic charcoal. The Holocene
- M Ohlson
- E Tryterud
Ohlson, M., Tryterud, E. (2000) Interpretation of the
charcoal record in forest soils: forest fires and
their production and deposition of macroscopic
charcoal. The Holocene, 10(4), 519-525.
https://doi.org/10.1191/09596830066744255
Microscopic Wood Anatomy: Structural Variability of Stems and Twigs in Recent and Subfossil Woods from Central Europe
- F H Schweingruber
Schweingruber, F.H. (1978) Microscopic Wood
Anatomy: Structural Variability of Stems and
Twigs in Recent and Subfossil Woods from
Central Europe. Swiss Federal Institute of
Forestry Research, Birmensdorf, 226 pp.
Clima Republici populare Romine (Climate of the People's Republic of Romania)
- S M Stoenescu
- D Tistea
Stoenescu, S.M., Tistea, D. (1962) Clima Republici
populare Romine (Climate of the People's
Republic of Romania). Volume 1, Meteorological
Institute, Bucarest, 168 pp. (in Romanian).
Tracking Environmental Change Using Lake Sediments
- C Whitlock
- C Larsen
Whitlock, C., Larsen, C. (2001) Charcoal as a fire
proxy. In: Smol, J.P., Birks, H.J.B., Last, W.M.
(eds.) Tracking Environmental Change Using
Lake Sediments; Volume 3: Terrestrial, Algal,
and Siliceous Indicators, Kluwer Academic
Publishers, Dordrecht, The Netherlands, 75-97.
10.1007/0-306-47668-1_5
E-mail: ancuta.petras@usm.ro
- Romania Suceava
Suceava, Romania. E-mail: ancuta.petras@usm.ro