Charcoal Abundance Research Articles

Relationship between extreme species richness and Holocene persistence of forest-steppe grasslands in Transylvania, Romania

The most species-rich grasslands worldwide are known from the Carpathian Mts and their periphery in East-Central Europe. They occur in forest-steppe regions, transitional between temperate forest and arid steppe biomes. Their climate, largely suitable for forests, raises questions about the origin of these grasslands. Have they been forested in the past, or locally maintained through a disturbance regime? We addressed these questions to contribute to the broader understanding of Holocene dynamics of open habitats in temperate Europe. We employed soil charcoal analysis and soil morphology to reconstruct past representation of woody species with fine spatial resolution. Our study area was Romanian Transylvania, a region renowned for a well-developed forest-steppe. Six soil profiles along a climatic gradient were assessed: four in forest-steppe grasslands, two in grasslands in adjacent forest region (forest grasslands). The results revealed profound differences between forest-steppe and forest grasslands. Forest-steppe profiles showed Phaeozems with low specific anthracomass of woody species and continuous dominance by Juniperus, suggesting a long-term presence of grasslands. Forest grasslands showed Luvisols with higher anthracomass and abundant charcoal of broad-leaved trees, indicating establishment after deforestation. The high radiocarbon ages of charcoals in basal soil horizons point to a glacial origin of soils and the link of forest-steppe grasslands to glacial forests. Siberian hemiboreal forests and related grasslands may be modern analogues of the reconstructed ecosystems, sharing many species with present day forest-steppe. We suggest that disturbances such as fire, herbivore grazing, and human activities have played an important role in shaping the forest-steppe over time, contributing to the formation of today’s richest grasslands.

The optimum fire window: applying the fire–productivity hypothesis to Jurassic climate states

Abstract. Present-day fire frequency is related to a productivity–aridity gradient on regional and global scales. Optimum fire conditions occur at times of intermediate productivity and aridity, whereas fire is limited at the high productivity (moisture) and aridity (no fuel) endmembers. However, the current global fire activity pattern is reinforced by the predominant burning of grasslands. Here we test the intermediate fire–productivity hypothesis for a period on Earth before the evolution of grasses, the Early Jurassic, and explore the fire regime of two contrasting climatic states: the cooling of the Late Pliensbachian Event (LPE) and the warming of the Sinemurian–Pliensbachian Boundary (SPB). Palaeo-fire records are reconstructed from fossil charcoal abundance, and changes in the hydrological cycle are tracked via clay mineralogy, which allows inference of changes in fuel moisture status. Large fluctuations in the fossil charcoal on an eccentricity timescale indicate two modes of fire regime at the time. Wildfires were moisture-limited in a high-productivity ecosystem during eccentricity minima for both the SPB and the LPE. During eccentricity maxima fires increased, and an optimum fire window was reached, in which periodically greater seasonality in rainfall and temperatures led to intermediate states of productivity and aridity. The LPE experienced more extreme climatic endmembers compared to the SPB, with the fire regime edging closer to “moisture limitation” during eccentricity minima, and experienced more pronounced seasonality during eccentricity maxima, explained by the overall cooler climate at the time. This study illustrates that the intermediate-productivity gradient holds up during two contrasting climatic states in the Jurassic.

First palynological results from Spila nad Procjepom cave, Mljet island (Croatia)

This paper presents the first results of palynological research from the Spila nad Procjepom cave, situated in the Mljet National Park, Croatia. The palynological data obtained, enables a partial insight into the local vegetation cover, temporal changes in the vegetation during the accumulation of studied deposits (at ca. 3500 cal years BP), and post-depositional processes that influenced the palynomorph assemblage. Results of palynofacies analysis indicate changes from fluvial (channel deposits), through palustrine to terrestrial environments. Although the interpretation of changes in plant cover, due to the lack of statistical significance, should be taken with caution, preserved pollen types confirm the dominance of the Mediterranean evergreen forest vegetation on Mljet island. Moreover, a high proportion of non-arboreal pollen (NAP) indicates some level of forest degradation, ranging from Mediterranean open forest to degraded maquis. Abundant charcoal additionaly confirms that the cave was inhabited by humans.

Human-activity modified vegetation composition at Hangzhou Bay, Zhejiang Province, China over the last 10,000 years

Vegetation composition has been greatly modified by human activity since Neolithic times, providing valuable insights into the evolution of human-landscape relationships. In this paper, we integrated 26 pollen records from the Zhejiang Province of China where a Neolithic culture of rice farming existed at an early date, to examine the dynamics of agricultural development and its impact on vegetation. Firstly, we synthesized the relative abundance of Oryza pollen and charcoal (Cpeak) using generalized additive models, to produce a record of agricultural development and the intensity of human activities. We found that changes in Oryza abundance and Cpeak were positively correlated, and identified three phases as follows: agricultural initiation before 8000 cal yr BP, agricultural development between 8000 and 6000 cal yr BP and the onset of intensive rice farming after 6000 cal yr BP. Pearson correlation between each pollen taxon and Oryza indicates that arboreal taxa exhibit an overall negative correlation with Oryza, but terrestrial herbs and ferns show a positive correlation, indicating that deforestation accompanied agricultural development. Rosaceae, Castanea, Fagus and Typha display positive correlation with Oryza during the earliest stage dominated by hunter-gathering, reflecting the protection and cultivation of food-producing vegetation. During the intensive farming stage, the Liangzhu ancestors reclaimed more farmland and began to pay attention on farmland management including clearing the fields of weeds. This is the main reason for the enhanced negative correlation between Artemisia, Chenopodiaceae, Brassicaceae, Asteraceae and Lamiaceae with Oryza at 6000–5000 cal yr BP. Finally, we confirm the potential of integrated Oryza abundance in pollen records as a human-impact index in the Zhejiang region, and emphasize that temporal dynamics in vegetation and human activities should be critically pre-examined when applying relevant human-impact indices.

Charcoal abundance measurements are affected by freeze-drying

Fire has been a part of Earth system processes for millions of years, and its use has been accelerated once hominins and humans entered landscapes. Charcoal amounts, usually measured by the number of particles or surface area of particles per sample, are used to reconstruct aspects of fire history in sedimentary records. Freeze-drying is commonly performed on sediment cores and soils that will undergo geochemical analysis, and the process is known to affect outcomes. We compared charcoal abundances in paired freeze-dried and non-freeze-dried samples from lake sediment cores to test the hypothesis that freeze drying reduces the amount of recoverable charcoal in paleoecological reconstructions. Wilcoxon Rank Sum tests showed that particle counts and surface area measurements of charcoal are significantly higher in non-freeze-dried samples compared with freeze-dried samples. Our results indicate that sediments should not be freeze-dried prior to charcoal analysis, and if it necessary, that subsamples of fresh material should be collected first.

Repeated fires in forested peatlands in sporadic permafrost zone in Western Canada

Wildfires play a crucial role in northern boreal peatland ecosystems, influencing the functioning of these ecosystems by affecting vegetation composition and biomass, peat accumulation patterns, and soil carbon stocks. Northern peatland ecosystems are under pressure due to climate warming and increasing anthropogenic stress. The frequency and severity of wildfires is predicted to increase in the coming years. Therefore, understanding long-term natural fire dynamics and their effect on peatland functionality will provide crucial information for peatland management and preservation policies. To investigate the long-term fire history of Western Canada and its effect on peat accumulation and vegetation succession, we analyzed macroscopic plant remains and charcoal within peat cores taken from five peatlands in the region. Records of the most recent fire events were derived from fire scars and documented fires in the study area. Regional long-term peatland fire patterns were examined by pooling together macroscopic charcoal records and calculating 100 year moving averages. All studied sites, except the northernmost one, demonstrated repeated fires throughout the past 1500 years, suggesting that fires have been an integral part of the peatland ecosystem in Western Canada. Compiled charcoal records indicated a peak in fire activity, with the highest abundance of charcoal for the period from the 1300s to the 1550s and decreasing fire activity during recent centuries. The clear and consistent post-fire increase in the abundance of Sphagnum mosses suggests a relatively rapid recovery of peatland ecosystems after burning. The regeneration pattern, where pre-fire vegetation repeatedly re-establishes, suggests that from a long-term perspective, fires do not necessarily have a negative effect on peatland functioning and peat accumulation. In conclusion, peatlands could remain as effective carbon sinks if their natural state is secured.

Stepwise deforestation during the Permian-Triassic boundary crisis linked to rising temperatures

Although the trajectory of the marine mass extinction at the ∼252-Ma Permian-Triassic (P-Tr) boundary has been well studied, details of the coeval collapse of terrestrial ecosystems remain murky. Here, we use hydrocarbon biomarker compositions and other geological records (i.e., organic carbon isotopes (δ13Corg), charcoal abundance, and Hg content) from a tropical peatland succession in southwestern China to reconstruct in detail the history of terrestrial ecosystem collapse during the P-Tr crisis. Our high-resolution hydrocarbon biomarker records reveal that this collapse proceeded in a stepwise manner with increasing intensity as the crisis unfolded. We recognize three discrete crisis stages: Stage I within the uppermost Xuanwei Formation and Stages II and III within the lowermost Kayitou Formation. Stage I, the early crisis stage, is marked by a significant decline in terrestrial biomass (continuing into the later stages), as recorded by reduced C29 steranes relative to total steranes and a concomitant reduction in the ratio of pristane to phytane (Pr/Ph). Stage II, the main crisis stage, records intensified soil erosion and sediment flux as revealed by rising dibenzofuran (DBF) content and high hopane/sterane ratios, the disappearance of coal seams, a sharp negative shift in δ13Corg, and peak concentrations of charcoal reflecting increased wildfire incidence. Stage III, the late crisis stage characterized by enhanced soil erosion, corresponds to peak values of Hg and Hg/TOC but no charcoal peak, suggesting intensified volcanism and a return to a humid climate. These stages closely follow temperature records, which show a stepwise rise during the crisis interval, implying that the deforestation process was strongly influenced by punctuated rises in temperature and/or its attendant effects (e.g., climate aridification). This P-Tr transition scenario suggests that global warming can trigger deforestation and reduce terrestrial carbon storage, thus serving as a positive climate feedback, with important implications for present-day climate change.

Charcoal and biological activity in formiguer soils of Catalonia (Spain): Application of a micromorphological approach

The "formiguers" (earth mounds to burn woody plant residues) constituted a common practice of fertilization of soils in many regions of Spain in the past. The result of combustion is the formation of char, charcoal, soot, graphitic carbon and black carbon, which increased soil fertility. We applied a micromorphological approach to study the relationship between charcoal and features due to biological activity on some soils of Catalonia where “formiguers” were traditionally applied. Five sites with different land uses were selected in the north and south of Catalonia, and soil thin sections were obtained from undisturbed samples. The micromorphological characterization and the quantification of the total porosity, biopores, charcoal and biospheroids due to earthworms were determined. Samples from horticultural fields showed higher total porosity (15%) than those from other fields (9%). A similar pattern appeared in relation to charcoal abundance, 1.3% in horticultural plots compared to near null presence in other plots. The biopore percentage was approximately twice (11.2%) in the north sites with respect to the south sites, and biospheroids were absent in the latter while their mean abundance was 1% in the former. Our results suggest that the presence of charcoal fragments have significantly influenced bioporosity in the studied soils. The micromorphological techniques proved useful to study of the distribution and abundance of charcoal and biospheroids in formiguer soils in Catalonia.

Warming, drought, and disturbances lead to shifts in functional composition: A millennial-scale analysis for Amazonian and Andean sites.

Tropical forests are changing in composition and productivity, probably in response to changes in climate and disturbances. The responses to these multiple environmental drivers, and the mechanisms underlying the changes, remain largely unknown. Here, we use a functional trait approach on timescales of 10,000 years to assess how climate and disturbances influence the community-mean adult height, leaf area, seed mass, and wood density for eight lowland and highland forest landscapes. To do so, we combine data of eight fossil pollen records with functional traits and proxies for climate (temperature, precipitation, and El Niño frequency) and disturbances (fire and general disturbances). We found that temperature and disturbances were the most important drivers of changes in functional composition. Increased water availability (high precipitation and low El Niño frequency) generally led to more acquisitive trait composition (large leaves and soft wood). In lowland forests, warmer climates decreased community-mean height probably because of increased water stress, whereas in highland forests warmer climates increased height probably because of upslope migration of taller species. Disturbance increased the abundance of acquisitive, disturbance-adapted taxa with small seeds for quick colonization of disturbed sites, large leaves for light capture, and soft wood to attain fast height growth. Fire had weak effects on lowland forests but led to more stress-adapted taxa that are tall with fast life cycles and small seeds that can quickly colonize burned sites. Site-specific analyses were largely in line with cross-site analyses, except for varying site-level effects of El Niño frequency and fire activity, possibly because regional patterns in El Niño are not a good predictor of local changes, and charcoal abundances do not reflect fire intensity or severity. With future global changes, tropical Amazonian and Andean forests may transition toward shorter, drought- and disturbance-adapted forests in the lowlands but taller forests in the highlands.

Holocene relationships between climate, waterfowl, and lacustrine nutrient cycling at Kettle Lake, North Dakota, USA

Avian populations can substantially influence lacustrine nutrient loading and biogeochemical cycling through guano deposition. Here, we examine the influence of climate-forced avian migration throughout the Holocene on Kettle Lake, North Dakota, using stable nitrogen and carbon isotope values (δ15N, δ13C) of lake sediment organic matter. Carbon content and δ13C values are negatively correlated with δ15N and appear to be driven by changes in charcoal abundance and watershed vegetation, respectively. We find enriched δ15N values when the guano mineral struvite is present in the lake sediment core in the early to Mid-Holocene. A strong δ15N-percent Nitrogen content relationship during periods with struvite, relative to periods without struvite, indicates that guano deposition from mass bird visitations altered past nitrogen cycle processes, likely through enhanced denitrification. These results attest to the ability of waterfowl to alter lacustrine N-cycling in a mid-continental North American lake, and indicate that paleo-N data in this particular lake are recording a unique history that does not necessarily represent regional paleoenvironmental conditions. However, a significant, positive relationship between δ15N and Ambrosia and Amaranthaceae pollen abundance suggests avian visitation and its impacts on the N-cycle occurred during periods of anomalously wet summers superimposed on the background conditions of early to Mid-Holocene drought.

Fire history of the western Amazon basin recorded by multiple pyrogenic carbon proxies

Charcoal abundance has been used as a fire proxy to reconstruct human settlement and climate records, but analyses of pyrogenic carbon (PyC) have become more widespread. To compare these proxies, fire records spanning the past 3000 y of Western Amazon Lakes Ayauchi, Gentry and Parker region soil and sediments were determined by visually identified charcoal, chemical-thermal oxidation (CTO) and benzene polycarboxylic acid (BPCA) markers. Charcoal represented the smallest portion of PyC and, with its irregular distribution, it likely indicated only local or large fires. PyC via CTO concentrations were highest and most uniform, suggesting lower sensitivity in detecting fire. BPCA-derived PyC distributions in soils were consistent with more human occupation and higher temperature fires in the Lake Ayauchi region and, in lake sediments, BPCA-derived PyC bore the closest resemblance to patterns of climate and human influence. Thus, BPCAs were more sensitive indicators of fire over regional scales. The combined information from multiple fire proxies revealed a history of frequent fires in western Amazon. Lake Ayauchi region had greater fire frequency and higher temperature fires than the Gentry/Parker region, suggesting greater human occupation. The greater fire frequency in wetter periods and regions of western Amazon, suggest a major influence of human activity on PyC production over the past 3000 years. Each fire proxy examined in this study had strengths and weaknesses and the use of a combination of fire proxies can provide a fuller picture of fire history than any single approach.

THE COMPLEMENTARY USE OF CHARCOAL NUMBER AND MORPHOLOGY TO RECONSTRUCT FIRE HISTORY IN A LATE HOLOCENE PEAT SEQUENCE FROM NW ROMANIA

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.

Pleistocene megafaunal extinction in the grasslands of Junín‐Peru

AbstractAimTo determine the timing of megafaunal extinction in the high plains of Peru and also to determine if the timing was delayed in grasslands compared with previously published forested settings to dissociate the effects of succession from human or climatic impacts.LocationThe Junín Plateau, Peru.TaxonFlowering plants and Ascomycetes.MethodsThe sediments used in this analysis were collected from the edge of Lake Junín, Peru. Eleven ages derived from 14C accelerator mass spectrometry provide a chronology. We provide a paleoecological reconstruction of past climate and vegetation change, fire history and megafaunal herbivore presence from c. 20,000–7000 years ago based on fossil pollen, charcoal and Sporormiella spores. Data were analysed using multivariate analysis and Bayesian change point analysis.ResultsMegafaunal populations appear to have been positively impacted by dry climatic oscillations until c. 15,200 years ago. A reduction in Sporormiella abundance between 13,000 and 12,300 years before the present coincides with increased charcoal abundance and is identified as the period of megafaunal population collapse leading to extinction. The timing of the extinction does not differ substantially from that observed in wooded Andean settings.Main ConclusionThe timing of the collapse of megafaunal populations in high grasslands was very similar to that of lower, now‐forested settings. Upticks in fire activity, during what is generally seen to be a wet period, formed the backdrop to extinction and are strongly associated with human activity.

Boron isotopes and FTIR spectroscopy to identify past high severity fires

Bushfires have played a crucial role in shaping the landscape and biodiversity for millennia. As fire regimes continue to alter with climate change, greater understanding becomes critical in mediating future events. Existing records are largely historically limited or do not accurately identify fire severity; therefore, there is a need to develop new proxies that can extend our fire records significantly. Here, we test whether changes in carbon (C) and nitrogen (N) content, boron (B) isotopes and Fourier Transform Infrared (FTIR) spectra in sediment deposits can identify past fire events. To achieve this, we investigated sediments deposited in small order creek beds of the Upper Nepean Catchment in southeastern Australia. In each deposit, layers associated with past fire events were independently identified based on visual inspection of higher charcoal abundance. Radiocarbon dating of charcoal fragments was used to approximate the age of the fire events.Neither C and N abundances nor C/N ratios show association with charcoal-rich layers, suggesting they are not useful proxies to identify past fires. Conversely, FTIR spectra show increased aromatic/aliphatic ratios in sediment layers recording past fire events. This observation suggests that those fires were hot enough to reduce long-chain aliphatic compounds to more temperature- and decomposition-resistant aromatics. In each deposit, an increase in δ11B by 2–7 ‰ is associated with charcoal-rich sediment layers. Leaves and fine branches, which burn only during high severity fires, are enriched in 11B, possibly causing the increase in the δ11B value of the sediment clay size fraction. These results suggest that, even in these small order creek beds which are typically transient environments, both FTIR spectra and B isotopes are potentially useful proxies to identify past fire events.

Intensive peatland wildfires during the Aptian–Albian oceanic anoxic event 1b: Evidence from borehole SK-2 in the Songliao Basin, NE China

The Cretaceous has been considered a “high-fire” world accompanied by widespread by-products of combustion in the rock record. The mid-Cretaceous oceanic anoxic event 1b (OAE1b) is marked by one of the major perturbations in the global carbon cycle characterized by deposition of organic-rich sediments in both marine and terrestrial settings. However, our understanding is still limited on changes in wildfire activity during OAE1b period. Here, we carried out a comprehensive analysis, including organic carbon isotope (δ13Corg), total organic carbon (TOC), coal petrology, trace elements, and pyrolytic polycyclic aromatic hydrocarbons (pyroPAHs), of coal seams of the middle Aptian to early Albian Shahezi Formation from borehole SK-2 in Songliao Basin, Northeast China. Two negative δ13Corg excursions in the Shahezi Formation can be corresponded with the 113/Jacob and Kilian sub-events of OAE1b. Moreover, the intensive peatland wildfires have been identified during the sub-event periods of OAE1b based on the co-occurrence of high abundance of charcoal and pyroPAHs at that time. In addition, Sr/Ba, Sr/Cu and Sr/Rb ratios demonstrate that enhanced peatland wildfires were controlled by dryer climate conditions owing to episodic northward migration of arid zones in East Asia related with rising global temperature during the sub-events of OAE1b. The climate-driven extensive wildfire activity in the mid-latitude terrestrial ecosystems can be a contributing factor for OAE1b through the increased flux of nutrients fuelling primary producers in the lake and marine environments and leading to more speculative anoxia to allow the deposition of organic-rich sediments. Our results provide essential understanding of the importance of wildfires in driving mechanism of oceanic anoxic events (OAEs) in Earth's history.

Charcoal Whirlwinds and Post-Fire Observations in Serengeti National Park Savannahs

Whirlwinds and visible dust devils occur over semi-arid ecosystems and entrain particles from the ground surface. Fires produce abundant charcoal across savannahs and the resulting blackened surfaces create a large albedo contrast. Whirlwinds have been observed associated with active fires; yet, there are few published observations on post-fire landscapes. Spatiotemporal patterns of whirlwinds have been documented for a limited number of regions and have not been made for the ecosystems of eastern Africa. From field-based sightings in the Serengeti National Park, Tanzania, we report on whirlwinds over burned savannah patches that entrained large quantities of charcoal to produce black coloured charcoal devils that lofted charcoal into the atmosphere. Two occurrences of charcoal devils were sighted and photographed, one each in the Western Corridor (Bunda District) and Lamai (Serengeti District), Mara Region. The observations were compared with regional scale meteorological data and remote sensing satellite imagery and albedo estimates of the land cover conditions. Although direct meteorological or particulate matter measurements were not made, the observations show that both charcoal devils differed in colour, funnel shape, height, and savannah land cover types (different woody to grass fuel canopies), and thus different charcoal morphologies. Charcoal laden whirlwinds require further study and characterization to analyse the contribution to local-scale redistribution of matter and regional-to-global fluxes of terrestrially derived atmospheric particulates. Future research focusing on the spatiotemporal patterns of whirlwinds over burned patches of savannah, the formation, duration and dissipation mechanisms, and characterisation of the entrained material would contribute to our understanding of the phenomena. The redistribution of organic and clastic material would contribute to understanding of detrital fluxes to depositional environments, such as lakes, wetlands, and snow.
 Keywords: Atmospheric boundary layer; Convection; Detritus; Dust devils; Fires; Particulate matter.

Reconstructing burnt area during the Holocene: an Iberian case study

Abstract. Charcoal accumulated in lake, bog or other anoxic sediments through time has been used to document the geographical patterns in changes in fire regimes. Such reconstructions are useful to explore the impact of climate and vegetation changes on fire during periods when human influence was less prevalent than today. However, charcoal records only provide semi-quantitative estimates of change in biomass burning. Here we derive quantitative estimates of burnt area from vegetation data in two stages. First, we relate the modern charcoal abundance to burnt area using a conversion factor derived from a generalised linear model of burnt area probability based on eight environmental predictors. Then, we establish the relationship between fossil pollen assemblages and burnt area using tolerance-weighted weighted averaging partial least-squares regression with a sampling frequency correction (fxTWA-PLS). We test this approach using the Iberian Peninsula as a case study because it is a fire-prone region with abundant pollen and charcoal records covering the Holocene. We derive the vegetation–burnt area relationship using the 31 records that have both modern and fossil charcoal and pollen data and then reconstruct palaeoburnt area for the 113 records with Holocene pollen records. The pollen data predict charcoal-derived burnt area relatively well (R2 = 0.44), and the changes in reconstructed burnt area are synchronous with known climate changes through the Holocene. This new method opens up the possibility of reconstructing changes in fire regimes quantitatively from pollen records, after regional calibration of the vegetation–burnt area relationship, in regions where pollen records are more abundant than charcoal records.

Interactions Among the Fire, Vegetation, the North American Monsoon and the El Niño-Southern Oscillation in the North American Desert Southwest

Millennial-scale environmental histories from North American desert southwest (SW) ciénegas were examined with existing time series for the North American Monsoon (NAM) and El Niño, in concert with published long-term records of desert vegetation and climate. The goal was to better understand the relationships among fire, the seasonality of precipitation, effective moisture levels, and vegetation type. It was determined that without sufficient winter precipitation fires are rare in desert SW ecosystems. However, it was also determined that in addition to winter moisture, summer ignitions are critical for fire in southwestern deserts. A relationship between the abundance of woody fuels and charcoal abundance was identified, although further calibration on charcoal production in woody vs. grassy desert settings in necessary to fully understand this interplay. Finally, the impacts of climate change and invasive species were considered, with both likely increasing the frequency of fire in desert ecosystems.

Late Holocene archaeobotanical evolution of the Canale di Imbocco (Roman imperial port of Portus, Central Italy)

The Roman port of Portus was the most important in the Mediterranean during the imperial period (27 BC–476 AD). It was made up of an outer port or Claudius basin and an inner hexagon or Trajan's port, joined by the Canale di Imbocco. The archaeobotanical record obtained in a continuos sediment core taken in this channel is made up of 19 types of plant macroremains, with a predominance of fibers of the seagrass Posidonia oceanica L., replaced by fluvial sediments in the upper part of the core. Seeds, fruits and thorns of aquatic species from marine or brackish waters, halophyte species, edible species, freshwater riparian vegetation and remains of charcoal and wood also appear regularly. According to the inferred palaeoenviromental evolution of this core, Portus was an area of fluvial-marine interaction during the Roman Empire, with brackish water conditions interrupted by stormy periods deduced from the record of P. oceanica. The archaeobotanical and sedimentary evolution points to a restriction of marine contributions and a final implantation of a fluvial environment. In this evolution, a specific interval with abundant charcoal and caryopses of Triticum could correspond to a fire, which was followed by a possible period of greater construction activity linked with large fragments of wood.

Variations in geomorphological dynamics in the northern Khangai Mountains, Mongolia, since the Late Glacial period

In semi-arid central Mongolia, geomorphological dynamics and forest distribution are commonly regarded as a result of the climatic development over the Holocene. The aim of this study was to detect variations in geomorphological activity and related eolian, periglacial, colluvial and fluvial processes since the Late Glacial, triggered by climate changes and other factors such as regional lake-level changes, fire events, and human impact. For this purpose, we investigated sediment archives in various relief positions (slope, pediment, valley bottom, dune and lake shore) in a forest-steppe region at the northern edge of the Khangai Mountains. We used a combination of geomorphological mapping and sampling of sediments, soils, paleosols, and organic layers. The samples were subjected to sedimentological analysis, luminescence and radiocarbon dating.The ages obtained for the eolian sediments showed that intense eolian activity and periglacial processes occurred during the Last Glacial Period and mitigated after 11 ka. After the Younger Dryas, geomorphological processes decreased and intensified soil formation indicated a stabilization of the soil surface simultaneously when spreading of forests around 9.5 ka was previously shown in the Khangai Mountains. The early and mid-Holocene were characterized by minor geomorphological activity and low fire frequency, as documented by sparseness of charcoal fragments and paleosols in the sediments. Only between 8 ka and 7 ka, reactivation of eolian sand transport was recorded during a drier period.Widespread distribution of late Holocene colluvial, alluvial and eolian sediments containing abundant charcoal, and periglacial features point to a distinct turning point in the Holocene landscape development around 4.5 ka, when substantially enhanced geomorphological activity started. This enhanced geomorphic activity corresponds with a period previously shown to be more humid but also more unstable, and during which forests became more susceptible to severe fire events. After a forest fire, lack of vegetation cover favored intensive erosion. Enhanced geomorphological activity points to a trend towards desertification, which was increasingly aggravated by human impact, since pastoralism emerged latest in the early Bronze Age. Increased production of steppe biomass during humid periods led to growth of population and livestock. This growth in turn resulted in overgrazing in drier years. This mechanism probably amplified the aridity signals that were detected in proxies of various paleoenvironmental archives.