Total Charcoal Research Articles

Experimental study of improved cookstove with primary and secondary sources

Improved cookcookstoves are cooking devices using biomass such as wood and charcoal. Although existing improved cookcookstoves contribute to reducing wood consumption, this consumption is still considerable, and the smoke produced is a source of many illnesses. It is therefore necessary to work on further improving these "improved cookstoves". The present work concerns the construction of an improved cookstove with primary and secondary sources. The device is essentially made from recycled materials. Boiling tests were carried out, the mass of charcoal consumed recorded and the efficiency of the cookstove calculated. The results obtained from the water boiling test experiments show that the boiling time with the secondary-source cookstove is faster than with the primary-source cookstove alone. The secondary-source cookstove has an overall thermal efficiency of 38%, while the improved single-primary-source cookstove has an overall thermal efficiency of 11%. In terms of total charcoal consumption, the primary-source cookstove consumed 1.19 kg throughout the test, while the secondary-source cookstove consumed just 0.38kg.

Reproducible protocol for the extraction and semi-automated quantification of macroscopic charcoal from soil.

Charcoal fragments preserved in soils or sediments are used by scientists to reconstruct fire histories and thereby improve our understanding of past vegetation dynamics and human-plant relationships. Unfortunately, most published methods for charcoal extraction and analysis are incompletely described and are therefore difficult to reproduce. To improve the standardization and replicability of soil charcoal analysis, as well as to facilitate accessibility for non-experts, we developed a detailed, step-by-step protocol to isolate charcoal from soil and to efficiently count and measure charcoal fragments. The extraction phase involves the chemical soaking and wet sieving of soils followed by the collection of macrocharcoal (≥500 μm). The analysis phase is performed semi-automatically using the open-source software ImageJ to count and measure the area, length, and width of fragments from light stereo microscope images by means of threshold segmentation. The protocol yields clean charcoal fragments, a set of charcoal images, and datasets containing total charcoal mass, number of fragments, and morphological measurements (area, length, and width) for each sample. We tested and validated the protocol on 339 soil samples from tropical savannas and forests in eastern lowland Bolivia. We hope that this protocol will be a valuable resource for scientists in a variety of fields who currently study, or wish to study, macroscopic charcoal in soils as a proxy for past fires.

Potential critical sources of error in the analysis of microcharcoal in Greenlandic palynological samples – an initial study

AbstractIt is common practice to count charcoal particles alongside pollen and non‐pollen palynomorphs in palynological samples. The classification of material as charcoal is dependent upon a number of morphological criteria which, in certain geological zones, could be misclassified. In a preliminary study we tested the effects of different preparation techniques on the count result of charcoal from the same samples of Greenland lake sediments. We demonstrate that the use of hydrofluoric acid has a major impact on the number of recorded charcoal particles. We show that detrital biotite is responsible for a large fraction of the particles misclassified as charcoal and suggest that by using a neodymium magnet any inaccuracy can be minimised. This protocol was then applied to further samples which removed the biotite fraction from the total charcoal count.

Wildfire history of the boreal forest of south-western Yakutia (Siberia) over the last two millennia documented by a lake-sediment charcoal record

Abstract. Wildfires, as a key disturbance in forest ecosystems, are shaping the world's boreal landscapes. Changes in fire regimes are closely linked to a wide array of environmental factors, such as vegetation composition, climate change, and human activity. Arctic and boreal regions and, in particular, Siberian boreal forests are experiencing rising air and ground temperatures with the subsequent degradation of permafrost soils leading to shifts in tree cover and species composition. Compared to the boreal zones of North America or Europe, little is known about how such environmental changes might influence long-term fire regimes in Russia. The larch-dominated eastern Siberian deciduous boreal forests differ markedly from the composition of other boreal forests, yet data about past fire regimes remain sparse. Here, we present a high-resolution macroscopic charcoal record from lacustrine sediments of Lake Khamra (south-west Yakutia, Siberia) spanning the last ca. 2200 years, including information about charcoal particle sizes and morphotypes. Our results reveal a phase of increased charcoal accumulation between 600 and 900 CE, indicative of relatively high amounts of burnt biomass and high fire frequencies. This is followed by an almost 900-year-long period of low charcoal accumulation without significant peaks likely corresponding to cooler climate conditions. After 1750 CE fire frequencies and the relative amount of biomass burnt start to increase again, coinciding with a warming climate and increased anthropogenic land development after Russian colonization. In the 20th century, total charcoal accumulation decreases again to very low levels despite higher fire frequency, potentially reflecting a change in fire management strategies and/or a shift of the fire regime towards more frequent but smaller fires. A similar pattern for different charcoal morphotypes and comparison to a pollen and non-pollen palynomorph (NPP) record from the same sediment core indicate that broad-scale changes in vegetation composition were probably not a major driver of recorded fire regime changes. Instead, the fire regime of the last two millennia at Lake Khamra seems to be controlled mainly by a combination of short-term climate variability and anthropogenic fire ignition and suppression.

Indigenous Fire-Managed Landscapes in Southeast Australia during the Holocene—New Insights from the Furneaux Group Islands, Bass Strait

Indigenous land use and climate have shaped fire regimes in southeast Australia during the Holocene, although their relative influence remains unclear. The archaeologically attested mid-Holocene decline in land-use intensity on the Furneaux Group islands (FGI) relative to mainland Tasmanian and SE Australia presents a natural experiment to identify the roles of climate and anthropogenic land use. We reconstruct two key facets of regional fire regimes, biomass (vegetation) burned (BB) and recurrence rate of fire episodes (RRFE), by using total charcoal influx and charcoal peaks in palaeoecological records, respectively. Our results suggest climate-driven biomass accumulation and dryness-controlled BB across southeast Australia during the Holocene. Insights from the FGI suggest people elevated the recurrence rate of fire episodes through frequent cultural burning during the early Holocene and reduction in recurrent Indigenous cultural burning during the mid–late Holocene led to increases in BB. These results provide long-term evidence of the effectiveness of Indigenous cultural burning in reducing biomass burned and may be effective in stabilizing fire regimes in flammable landscapes in the future.

Vegetation history and human impacts from Thong Pha Phum, western Thailand during the past 700 years

Palaeoecological analyses including pollen and charcoal analyses on a sediment core (NP3) collected from Nong Pling freshwater spring area in Thong Pha Phum, western Thailand are used to reconstruct past environmental change. The results demonstrate that there were changes in plant composition over the past 700 years resulting from interactions between hydrological conditions in relation to rainfall variability, and anthropogenic activity. Open vegetation such as grasses and lowland forest were established in Nong Pling freshwater spring forest from at least around ad 1300 suggesting drier conditions than present until around ad 1460. After that, decreased lowland forest and increased freshwater spring taxa together with the low charcoal contents indicate wetter conditions than during the former period, which allowed freshwater spring taxa to establish until around ad 1800. There were some fluctuations between freshwater spring taxa and lowland forest with open vegetation, probably due to rainfall fluctuations particularly after ad 1800 until the present. Moreover, recent increases in total charcoal accumulation, especially in large particles and the appearance of domesticated grass pollen may be related to recent human interaction within the ecosystems in Thong Pha Phum.

Sedimentary charcoal proxy records of fire in Alaskan tundra ecosystems

Extensive burning of Arctic tundra landscapes in recent years has contradicted the conventional view that fire is a rare, spatially limited disturbance in tundra. These fires have been identified as harbingers of climate change, despite our limited understanding of Arctic fire frequency and climatic controls. Much of this understanding relies upon sedimentary charcoal-based fire reconstructions, yet the controls on sedimentary charcoal abundance need to be rigorously tested in tundra ecoregions. We compile published charcoal-based tundra fire reconstructions in Alaska and compare them with historical, limnological, and spatial data to: (1) evaluate the spatial and temporal characteristics of tundra fires, (2) identify the primary controls of charcoal accumulation in lake sediments, (3) assess the accuracy of peak analysis in identifying local (<1 km) fire events, and (4) constrain charcoal source area. We find that tundra fires are spatially and/or temporally dichotomous in the historical (observational) period (1940–2015 CE), a characteristic which is mimicked by charcoal accumulation rates. We show that, despite methodological differences in published studies, analyses of charcoal peaks accurately identified local (<1 km) fire events in the historical period. Further, we find that lake properties (e.g. depth and surface area) have weak influences on charcoal accumulation in the tundra and that charcoal source areas in the Alaskan tundra are much broader than in forest and grassland ecosystems. We conclude that the unique nature of tundra fire regimes allows for the reliable use of total charcoal accumulation as a fire proxy.

Fire-derived charcoal affects fine root vitality in a post-fire Gmelin larch forest: field evidence

Fine roots are only a small part of total ecosystem biomass, but substantially contributing to soil carbon accumulation in boreal forests. Wildfires may influence fine root dynamics directly via heating and indirectly via interactions with wildfire-deposited charcoal. We tested if the presence of charcoal in a recently burned larch forest affected fine root vitality. This study was stratified across vegetation type (understorey and overstorey), soil depth (upper and lower layers), and root diameter classes: fine (≥0.5 mm but <2 mm diameter), and very fine (diameter < 0.5 mm) in a recently surface-burned Gmelin larch (Larix gmelinii (Rupr.) Rupr.) forest in the Russian Far East. Charcoal content and fine root vitality were positively correlated for overstorey vegetation, but negatively correlated for understorey vegetation. On the other hand, total charcoal content did not significantly correlate with very fine root vitality, biomass or necromass. Our study provides the first field evidence that fine root dynamics are influenced by fire-derived charcoal in frequently burned boreal forest. Furthermore, the effect of charcoal on fine root vitality depends on the vegetation type, root diameter, and soil depth, which indicates the necessity of complicated modeling of soil organic carbon derived from fine roots in post-fire boreal forests.

Fire history reconstruction in grassland ecosystems: amount of charcoal reflects local area burned

Fire is one of the most prevalent disturbances in the Earth system, and its past characteristics can be reconstructed using charcoal particles preserved in depositional environments. Although researchers know that fires produce charcoal particles, interpretation of the quantity or composition of charcoal particles in terms of fire source remains poorly understood. In this study, we used a unique four-year dataset of charcoal deposited in traps from a native tallgrass prairie in mid-North America to test which environmental factors were linked to charcoal measurements on three spatial scales. We investigated small and large charcoal particles commonly used as a proxy of fire activity at different spatial scales, and charcoal morphotypes representing different types of fuel. We found that small (125–250 μm) and large (250 μm–1 mm) particles of charcoal are well-correlated (Spearman correlation = 0.88) and likely reflect the same spatial scale of fire activity in a system with both herbaceous and woody fuels. There was no significant relationship between charcoal pieces and fire parameters <500 m from the traps. Moreover, local area burned (<5 km distance radius from traps) explained the total charcoal amount, and regional burning (200 km radius distance from traps) explained the ratio of non arboreal to total charcoal (NA/T ratio). Charcoal variables, including total charcoal count and NA/T ratio, did not correlate with other fire parameters, vegetation cover, landscape, or climate variables. Thus, in long-term studies that involve fire history reconstructions, total charcoal particles, even of a small size (125–250 μm), could be an indicator of local area burned. Further studies may determine relationships among amount of charcoal recorded, fire intensity, vegetation cover, and climatic parameters.

A classification for macroscopic charcoal morphologies found in Holocene lacustrine sediments

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 &gt;100,000 macroscopic charcoal fragments &gt;150 µm. 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.

Postglacial climate and fire‐mediated vegetation change on the western Olympic Peninsula, Washington (USA)

The mode and tempo of forest compositional change during periods of rapid climate change, including the potential for the fire regime to produce nonlinear relationships between climate and vegetation, is a long‐standing theme of forest ecological research. In the old conifer forests of the coastal Pacific Northwest, fire disturbances are sufficiently rare that their relation to climate and their ecological effects are poorly understood. We used a 14 700‐year high‐resolution sediment record from Yahoo Lake on the Olympic Peninsula, Washington, USA, to examine vegetation (landscape vegetation from pollen and local vegetation from macrofossils) and fire (landscape fire from total charcoal and local fire from charcoal peaks) in conjunction with independent records of climate. We hypothesized that the successional stage of the local forest will exhibit alternate stable states over a range of fire activity, that species turnover will increase abruptly above a certain level of fire activity and that both responses would be more gradual at the landscape scale than the local scale. Supporting these hypotheses, at the local scale, we found strong evidence for alternate stable states of late vs. early successional communities and inertia of species turnover to changing fire activity. At the landscape scale, vegetation responded more gradually to changing fire activity. From 14 700 to 7000 years ago, high landscape vegetation turnover occurred along with high landscape fire activity, especially during the warm summers of the early Holocene. In several instances, local species turned over completely following fire events but several centuries after climate change. In contrast, during the last 7000 years, the local forest composition was dominated by late‐successional species with little species turnover, despite periods of moderate fire activity. We suggest that the relatively minor climate fluctuations of the past 7000 years were not sufficient to cause large‐scale species turnover after fire. The Yahoo Lake fire and vegetation record of the early Holocene provides a model for dramatic ecosystem change following an anticipated shift to warmer summer temperatures.

Interdependences between Smallholder Farming and Environmental Management in Rural Malawi: A Case of Agriculture-Induced Environmental Degradation in Malingunde Extension Planning Area (EPA)

The objective of this article was to develop a deeper understanding of the interdependences between smallholder farming and the state of environmental management in rural Malawi. We examined the agricultural local governance framework in Malingunde Extension Planning Area (EPA), its contribution to food security and how it conflicts with overall land and forest resources management. The charcoal production process was discussed in line with its implications for agricultural production and environmental sustainability. The smallholder households employ inappropriate land management practices, engage in agricultural production on unsuitable land and use fertile soils, timber and firewood for brick production and construction and secondly engage in charcoal production (deforestation) as a coping mechanism against food deficiency. However, while detrimental in its own right, this environmental degradation in the area cannot be explicitly pinned to, for instance, the total charcoal supply being out of balance with wood stocks or insufficient land. It is, rather, usually due to failures to provide incentives to manage land and forest resources in a manner that allows regeneration of both the soils and wood stocks in the area. An improvement in the quality and quantity of the smallholder agriculture sector production would promote significantly the environmental management efforts.

Economic contribution and the potential use of wood charcoal for soil restoration: a case study of village-based charcoal production in Central Laos

Wood charcoal production provides affordable energy in many developing countries and has substantially contributed to the economy through the provision of rural incomes. In several countries, charcoal production leads to overexploitation of forests due to inefficiencies in processing. This study was undertaken in central Laos to (1) examine and document traditional charcoal production systems; (2) investigate the production capacity, recovery efficiencies and economic gains of existing traditional charcoal production methods; (3) characterize the chemical properties of wood charcoal and investigate the potential for soil restoration and (4) investigate local charcoal producers' perception on forest degradation and their species preferences. Through a socio-economic survey, a cost-based method for economic valuation was undertaken on a range of charcoal production methods currently being used. Laboratory chemical analyses were performed on wood charcoal samples. Results indicated that the traditional mud charcoal mound was used by the majority (82%) of charcoal producers. Total charcoal production per production cycle varied between 400 (produced from 2.7 m3 of wood) and 1600 kg (produced from 18 m3 of wood), with a mean of 938 kg (±120) for traditional mud charcoal mounds. The volume of the traditional mud charcoal mounds correlated positively and significantly with total charcoal production (R 2 = 0.45, p = 0.03), whereas correlated negatively and significantly with the recovery efficiency (R 2 = 0.58, p = 0.01). On average, the local producers receive a total net benefit of 457,272 Lao kip (USD 57.2) in 17 days. We also identified a rice husk mound method of charcoal production, which may not encourage further deforestation while producing rice husk biochar that can be used for soil restoration. Furthermore, we found that there are significant differences (p < 0.05) between the sampled wood charcoals in chemical properties, indicating that the potential of using wood charcoal for the restoration of degraded soils varies from charcoal to charcoal.

Climate - fire interactions during the Holocene: a test of the utility of charcoal morphotypes in a sediment core from the boreal region of north-western Ontario (Canada)

Charcoal accumulation rates and fire-return intervals were calculated from total charcoal and charcoal morphotypes over the Holocene, from a well-dated sediment core from Lake 239 located in north-western Ontario, and compared with previously published independent climate reconstructions. Both total and morphotype analysis show a two-to-three fold increase in accumulation rates in the early-to-mid Holocene (range: 1 to 6 pieces cm–2 year–1) compared with the early and late Holocene (range: 0 to 2 pieces cm–2 year–1). Fire-return intervals and fire frequencies calculated during these periods, based on peak analysis, showed very different trends. The fire-return interval based on Type M charcoal, a morphotype associated with primary charcoal deposition, was high during the early and late Holocene, and low from ~7500 to 4000 cal year BP, with high inferred fire frequency during the warm mid-Holocene (~12.5 fires per 1000 years), compared with &lt;5 fires per 1000 years over the rest of the Holocene, whereas fire-return interval and fire frequency based on total charcoal did not show patterns consistent with climate. These results suggest that a two- to three-fold increase in fire frequency would not be unexpected in the future under a predicted warmer climate.

Linking tree-ring and sediment-charcoal records to reconstruct fire occurrence and area burned in subalpine forests of Yellowstone National Park, USA

Reconstructing specific fire-history metrics with charcoal records has been difficult, in part because calibration data sets are rare. We calibrated charcoal accumulation in sediments from three medium (14—19 ha) and one large (4250 ha) lake with a 300 yr tree-ring-based fire-history reconstruction from central Yellowstone National Park (YNP) to reconstruct local fire occurrence and area burned within a 128 840 ha study area. Charcoal peaks most accurately reflected fires within 1.2—3.0 km of coring sites, whereas total charcoal accumulation correlated best with area burned within 6.0—51 km ( r2=0.22—0.62, p&lt;0.05). To reconstruct area burned for the entire study area, we developed a statistical model based on a composite charcoal record. The model explained 64—79% of the variability in area burned from AD 1675 to 1960 and was robust to cross-validation. Reconstructed area burned from AD 1240—1975 was significantly higher during periods including extreme annual drought ( p=0.05), and area burned varied significantly at ~ 60 yr timescales ( p&lt;0.05), similar to the variability in an independent precipitation reconstruction covering the same period. Widespread burning (&gt;10 000 ha) occurred at 150—300 yr intervals, and at the site level, fire probability increased with stand age (composite Weibull c parameter = 1.61 [95% CI 1.36—2.54]), both suggesting that post-fire stand development played an important intermediary role between climate and fire by increasing fuel abundance and probability of fire spread. Our study illustrates the possibility of reconstructing area burned with multiple charcoal records, and results imply that future fire regimes in YNP will be governed by direct impacts of altered moisture regimes and by vegetation dynamics affecting the abundance and continuity of fuels.

Wood Charcoal Supply to Addis Ababa City and its Effect on the Environment

Charcoal is a major source of energy for cooking, heating and lightening in sub-Saharan African countries. The livelihood of many rural and urban people also depends on the proceeds obtained from the sell of charcoal. Thus this, study was conducted with the objective to quantify the amount of charcoal supplied to Addis Ababa city, the capital of Ethiopia and its means of transportation. It is a result of a one week follow up study on the inlet of charcoal into the city. The data was analyzed using descriptive statistics and SAS software. The result indicated that about 7,549 different sizes and weights of bags of charcoal were supplied to the city in a day, suggesting an equivalent of about 68,886 tones of charcoal per year and about 899, 818 trees to being cut to this supply, releasing about 125,717 – 167,623 tones of carbon to the atmosphere. About 35% of the total charcoal flowing into the city enters in the morning between 6:00 a.m. and 11:59 a.m. While, about 34%, 21% and 10% enters the city in the afternoon, during the night and evening, respectively. Of the 9,822 vehicles encountered, entering in to the city in a day, about 2,148 of them were coming with loads of charcoal, Isuzus and heavy Trucks such as tank Truck, daf Tractor, Mercedes-Benz Truck etc. being the major ones. The finding of the study also indicated, the high dependency of the city on charcoal as an energy source, negatively affecting the environment.

CHARCOAL RECORDS OF HOLOCENE WILDFIRES AND ENVIRONMENTAL CHANGES IN THE WEIHE RIVER DRAINAGE

The Weihe River drainage is situated in semi-arid and sub-humid monsoon-sensitive areas in the north of China. Charcoal preserved in the loess-soil profile provided records of wildfire history and climatic changes during the late Holocene. Total organic carbon,magnetic susceptibility and charcoal analysis of two Holocene loess profiles in the study area have revealed the relationship between Holocene wildfire activity,human activity and climatic changes. The results show that the climate was arid and local wildfire occurred frequently during the late time of the last glacial period before 11 500 aBP when steppe vegetation expanded from the Inner Mongolian Plateau southerly over the Weihe River drainage. Conversely,wildfires were reduced during the early Holocene. During the Holocene climatic optimum between 8 500 and 3 100 aBP,natural wildfires were largely reduced. Pathogenic alteration to the accumulated dust processes was so active that forest-grassland formed under the humid-warm climate of the Holocene Megathermal. However,localized wildfires in connection with human activities frequently occurred in different patterns at the study sites. With the drier climate and more intensified historical land-use,human-set fires were more common than the natural fires. Very high levels of biomass burning and deteriorated land-use conditions caused a regional desertion by the arable farming communities and the invasion of nomads in the northern part of the Weihe River drainage during the last 3 100 years. After 1 500 aBP,the amount of charcoal sharply decreased and wildfire occurrence slowly disappeared,which may have resulted from totally cultivated land for farming and fully established agricultural landscape in the southern part of Weihe River drainage of the Loess Plateau; meanwhile,mixed agriculture of semi-cultivation and semi-animal husbandry was gradually developed in the northern part of the Weihe River drainage.

Nature and reactivity of charcoal produced and added to soil during wildfire are particle-size dependent

Charcoal added to soil by wildfires is usually considered to be part of the most stable pool of soil organic matter (SOM). It consists of a continuum of slightly burned plant residues to completely charred material. We sampled the macroscopic charcoal pool produced by a moderate intensity wildfire in a pine coastal forest in Tuscany (Central Italy) with the aim of assessing the relationship between its particle size and chemical composition as well as its reactivity. Our conceptual approach included particle size separation by dry sieving and analysis of four size fractions (>2 mm, 2–1 mm, 1–0.5 mm and <0.5 mm) for elemental composition. The composition of the charcoal fractions was studied using solid-state 13C nuclear magnetic resonance (NMR) spectroscopy, diffuse reflectance Fourier transform infrared (DRIFT) spectroscopy, analytical pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS) and CuO oxidation. The reactivity of the fractions was assessed using acid dichromate oxidation, while the morphology was observed using scanning electron microscopy (SEM). There were clear differences in chemistry and reactivity between the fractions. The different fractions are probably the result of both type of original plant material and the fire conditions. In fact, wood-derived charcoal largely prevalent in the largest fraction, while pine needles and herbs were most probably precursors of charcoal in the smallest fractions. The degree of charring was greatest for the coarse fraction, which represented 56% of the total charcoal, and decreased gradually to the finest fraction. The composition was completely aromatic for the coarsest fraction, whereas the finest fraction showed a greater contribution from aliphatic C- and N-containing components. The greatest reactivity was found for the smallest fraction, which represented 24% of the total charcoal. It is particularly rich in N and potentially susceptible to microbial decomposition. The study demonstrates that properties of charcoal added to soil during wildfires may be reliably discriminated on the basis of particle size.

Holocene palaeovegetation of the Tigray Plateau in northern Ethiopia from charcoal and stable organic carbon isotopic analyses of gully sediments

A long history of supporting sophisticated but unsustainable kingdoms makes the Tigray Plateau of the northern Ethiopian highlands a promising region for the study of relationships between palaeoenvironmental change and the trajectories of human civilizations. The natural vegetation above 2200 m elevation is thought to be forests dominated by Juniperus procera. Nonetheless, this hypothesis is not supported in the vegetation cover now and is scarcely studied in the palaeorecord. To examine changes in vegetation, climate, and land use, we identified buried charcoalized wood and estimated the percentage of organic carbon from C 4 plants (% C 4 carbon) from δ 13C values of bulk organic matter in the soils of gully walls in the boundaries of the ancient Aksumite Empire. Charcoal ranged in age from ca. 13,700 to 110 cal yr BP. Juniperus procera occurred in even the youngest samples, although at lower percentages of the total charcoal than in older samples. Nevertheless, rapidly regenerating angiosperms usually dominated or co-dominated charcoal even in some of the oldest strata. A shift towards higher % C 4 carbon and % total organic carbon (%TOC) in soils younger than 3300 cal yr BP began during a period when agricultural uses of land may have increased in order to support the needs of growing societies. A shift towards higher % C 4 carbon but lower %TOC began at ca. 6000 cal yr BP, however, during a period when no charcoal was found and no changes in human societal complexity are known. These results indicate that juniper forest types have long been present at > 2200 m in the Tigray Plateau but that they have rarely been the dominant natural vegetation. Furthermore, lack of repeatable correspondence between factors suggests that the causes of similar shifts in vegetation composition were not always the same.

Extreme fires under warmer and drier conditions inferred from sedimentary charcoal morphotypes from Opatcho Lake, central British Columbia, Canada

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.