Microscopic Charcoal Analyses Research Articles

Stable hydrogen isotope evidence of late-Holocene precipitation variability on the Caribbean slope of the Cordillera Central, Costa Rica

In Central America and the Caribbean, periods of increased aridity that correspond to the Terminal Classic Drought (TCD; 1200–850 cal yr BP) and the Little Ice Age (LIA; 500–100 cal yr BP) have been documented in many paleoclimate records. Compound-specific hydrogen (δDalkane) and carbon (δ13Calkane) isotopic compositions of n-alkanes in lake sediment can be used to interpret changes in paleoprecipitation and terrestrial paleovegetation, respectively. To assess the climate forcing mechanisms that drove the TCD and LIA, we established a multidecadal to centennial-scale late-Holocene reconstruction of precipitation variability and vegetation change at mid-elevation on the Caribbean slope of Costa Rica, developed from new δDalkane, δ13Calkane, and geochemical analyses and previous pollen and microscopic charcoal analyses from a sediment core from Laguna María Aguilar. Laguna María Aguilar is a freshwater lake located at 770 m elevation on the Caribbean slope of the Cordillera Central. During the TCD, δDalkane data for María Aguilar indicate relatively wet conditions compared to the mean δDalkane value for the entire record. Other proxy records for the TCD indicate that the Pacific slope of Costa Rica and sites above 3400 m near the continental divide experienced generally drier conditions than mid- and low-elevations on the Caribbean slope. We conclude that the TCD may have been driven by both Pacific and Atlantic climate-forcing mechanisms. During the LIA, the Laguna María Aguilar δDalkane record indicates an increase in hydroclimate variability, with some of the highest recorded δDalkane values (driest conditions) during the earliest portions of the LIA, but conditions were not persistently dry for the entirety of the LIA. Based on regional paleoclimate records overall, the LIA drought appears to be more clearly expressed on the Caribbean slope than on the Pacific slope of Costa Rica, indicating that the LIA was perhaps driven primarily by Atlantic Ocean conditions and climate dynamics.

Disturbance and Succession in Early to Mid-Holocene Northern English Forests: Palaeoecological Evidence for Disturbance of Woodland Ecosystems by Mesolithic Hunter-Gatherers

Forest succession can be monitored in the present, modelled for the future, but also reconstructed in the past on the records of forest history, including through the use of palaeo-ecological techniques. Longer-term records from pollen data can show changes over centennial and millennial timescales that are impacted by climate, migration or soil development. Having knowledge of previous phases of post-disturbance seral stages of woodland regeneration however, as after fire, can provide insights regarding successional process and function over short-term decadal timescales. The aim of this paper is to test the high-resolution pollen record as a source of new insights into processes of succession, assisted by the supplementary data of microscopic charcoal analyses. On short-term timescales, multiple phases of forest disturbance and then recovery have been identified in early to mid-Holocene peat records in northern England, many from the uplands but also from lowland areas. We identify and describe a typology of recovery patterns, including the composition and rate of recovery, and then test the processes and factors that impacted on different seral trajectories, concentrating on fire disturbance which might have had a natural origin, or might have been caused by pre-agricultural Mesolithic hunter-gatherers. Factors considered include the spatial location and intensity of the fire event, the duration of the disturbance phase, the structure and dynamics of the successional regeneration vegetation communities and the pre-disturbance tree cover. Data from examples of fire disturbance of woodland have been examined from both upland and lowland sites in northern England and indicate that they had different successional pathways after disturbance. Fire disturbances in the denser lowland forests were mostly single burn events followed by natural successions and regeneration to forest, whereas fire disturbances in the upland woods usually showed continued or repetitive fire pressure after the initial burning, arresting succession so that vegetation was maintained in a shrub phase, often dominated by Corylus, for an extended period of time until disturbance ceased. This creation of a kind of prolonged, almost plagioclimax, ‘fire-coppice’ hazel stage suggests controlled rather than natural successional pathways, and strongly suggests that Mesolithic foragers were the fire starters in the upland English woodlands where hazel was naturally common and could be maintained in abundance in later-stage successions, along with other edible plants, for human use. All post-fire seral stages would have been attractive to game animals, providing a reliable food source that would have been of great benefit to hunter-gatherer populations.

High-latitude fire activity of recent decades derived from microscopic charcoal and black carbon in Greenland ice cores

Warming temperatures and prolonged drought periods cause rapid changes of fire frequencies and intensities in high-latitude ecosystems. Associated smoke plumes deposit dark particles from incomplete combustion on the Greenland ice sheet that reduce albedo but also provide a detailed record of paleofire history. Here, we apply an emerging microscopic charcoal technique in combination with established black carbon and lead pollution measurements to an array of 10 ice cores from southern to central Greenland that span recent decades. We found that microscopic charcoal deposition is highly variable among sites, with a few records suggesting recently increasing biomass burning possibly in response to growing fire activity in boreal forest ecosystems. This stands in contrast to decreasing trends in black carbon measured in the same ice cores, consistent with contributions from industrial fossil fuel emissions. Decreasing trends of lead pollution and occurrence of microscopic spheroidal carbonaceous particles (SCP), a microfossil tracer of fossil fuel emissions, further support our interpretation that black carbon in this region is influenced by industrial emissions during recent decades. We conclude that microscopic charcoal analyses in ice may help disentangle biomass burning from fossil-fuel emissions during the industrial period and have potential to contribute to better understanding of regional high-latitude fire regimes.

Holocene wildfire and vegetation dynamics in Central Yakutia, Siberia, reconstructed from lake-sediment proxies

Wildfires play an essential role in the ecology of boreal forests. In eastern Siberia, fire activity has been increasing in recent years, challenging the livelihoods of local communities. Intensifying fire regimes also increase disturbance pressure on the boreal forests, which currently protect the permafrost beneath from accelerated degradation. However, long-term relationships between changes in fire regime and forest structure remain largely unknown. We assess past fire-vegetation feedbacks using sedimentary proxy records from Lake Satagay, Central Yakutia, Siberia, covering the past c. 10,800 years. Results from macroscopic and microscopic charcoal analyses indicate high amounts of burnt biomass during the Early Holocene, and that the present-day, low-severity surface fire regime has been in place since c. 4,500 years before present. A pollen-based quantitative reconstruction of vegetation cover and a terrestrial plant record based on sedimentary ancient DNA metabarcoding suggest a pronounced shift in forest structure toward the Late Holocene. Whereas the Early Holocene was characterized by postglacial open larch-birch woodlands, forest structure changed toward the modern, mixed larch-dominated closed-canopy forest during the Mid-Holocene. We propose a potential relationship between open woodlands and high amounts of burnt biomass, as well as a mediating effect of dense larch forest on the climate-driven intensification of fire regimes. Considering the anticipated increase in forest disturbances (droughts, insect invasions, and wildfires), higher tree mortality may force the modern state of the forest to shift toward an open woodland state comparable to the Early Holocene. Such a shift in forest structure may result in a positive feedback on currently intensifying wildfires. These new long-term data improve our understanding of millennial-scale fire regime changes and their relationships to changes of vegetation in Central Yakutia, where the local population is already being confronted with intensifying wildfire seasons.

Tracing human impact on a mountainous plant landscape in Rhodopi Mt (N. Greece) during the last 1100 years

Mediterranean mountain ecosystems have been attractive to human societies due to their valuable resources, but are also susceptible to environmental and climate changes. The Rhodope Mountain Range hosts one of the least disturbed natural forests of Europe and is a conservation priority area in the Southern Balkans. Located in the borderlands of the plain of Macedonia, the forest ecosystem development of Rhodope Mountains was shaped not only by Late Holocene climatic variability, but also by changes in human activities since Byzantine times. Palynological and microscopic charcoal analysis of the Livaditis ombrotrophic bog record offers unique insights into vegetation and landscape evolution under the influence of human land-use practices in the south Rhodope area during the last c.a. 1100 years. The findings show a forested landscape, with well-developed Pinus and Abies forests of in the montane zone and mixed deciduous oak forests below that flourished in the area until 900 AD. The expansion of human activity in mountainous areas during the period of Byzantine economic growth (ca. 1000 AD) is evidenced by forest clearance through fire, affecting mainly the Abies populations. The Livaditis record bears evidence about both, arboriculture and cereal cultivation as well as animal husbandry during the first period of human activities in the uplands, while a shift towards pastoralism is most likely associated with the establishment of the Vlach population in the region (ca. 1200 AD). Subsequently, a short-lived expansion of the Pinus percentages could be attributed to the afforestation of abandoned pasture land during the Little Ice Age. Finally, a further intensification of pastoralism is most likely concurrent with the population expansion documented during the Ottoman period (after 1500 AD). The Livaditis pollen record shows significant vegetation shifts in the upland area of southern Rhodope Mountains that could be associated with changes in climate, population mobility and density, as well as evolving land-use practices.

Late Holocene transformations of lower montane forest in the Beskid Wyspowy Mountains (Western Carpathians, Central Europe): a case study from Mount Mogielica

This article presents a reconstruction of Late Holocene vegetation changes within the lower montane forest zone in the Beskid Wyspowy Mountains (Western Carpathians, Central Europe). Pollen, non-pollen palynomorphs, loss on ignition, and microscopic charcoal analyses were applied to a profile collected from the deposits of the rich fen which developed in the landslide depression. The results reveal that during the period between ca. 4800 ± 70 and 4160 ± 60 cal. BP, Picea abies dominated in the local forests. Between ca. 4800 ± 70 and 4660 ± 60 cal. BP, Acer was an important component in local woodlands, which distinguishes the study site from others in the Western Carpathians. At ca. 4100 ± 60 cal. BP, forests dominated by Abies alba and Fagus sylvatica expanded. Nowadays, this type of vegetation is characteristic of the lower montane zone in the Polish Western Carpathians. This expansion was probably a consequence of environmental disturbances related to the cold and wet ‘4.2 ka BP’ event. The spread of these forests was preceded by a short episode of expansion of Tilia (Tilia cordata and/or Tilia platyphyllos) which was a very local event. The area of the Beskid Wyspowy Mountains provided suitable habitats for the occurrence of T. baccata, which has not been recorded in pollen data spanning the Middle and beginning of the Late Holocene from this mountain range. A significant increase in the percentages of Kretzschmaria deusta, a parasitic fungus, reveals that A. alba–F. sylvatica forests provided an optimal habitat for such species during the period from 4070 ± 60 to 47 cal. BP. Since ca. 2640 ± 110 cal. BP, pollen of pioneer trees, such as Pinus sylvestris and Betula, as well as human activity indicators (Cerealia type and Plantago lanceolata) have become more frequent. Nonetheless, it is highly probable that this section of deposits also includes the presence of one or more sedimentary gaps.

Anthracological and morphological analysis of soils for the reconstruction of the forest ecosystem history (Meshchera Lowlands, Russia)

Pedoanthracological methods have never been used for studying natural and anthropogenic factors of ecosystem dynamics in the area of the Middle Russian Upland. The article presents results of the first study of soil charcoal stratigraphy, taxonomy, and radiocarbon dating combined with morphological analysis of soil profiles performed for sandy soil (Podzols and Arenosols) in the Meshchera Lowlands. Charcoal samples from different soil patterns and horizons were taken from 19 soil pits in four forest sites. The taxonomic identification of charcoals was performed for 24 soil samples; 12 charcoal samples were radiocarbon-dated. The following three patterns of ancient pedoturbations were studied in the soil profiles: arable layers, root channels, and pits formed after treefalls with uprooting. Results of soil charcoal analysis were compared with pollen and microscopic charcoal analysis of the cores taken in the surrounding peats. Pinus charcoals of various age prevailed in all charcoal samples. Charcoal of Betula and Sorbus also occurred. The oldest charcoal fragments were 2610 cal. BP. The remaining charcoal samples were mainly grouped into three clusters: about 2200, about 900–1000, and later 500 cal. BP. We assume that most charcoal samples were associated with burning and subsequent plowing which provided the upper layer of the soil (arable layers and sometimes root channels) with charcoal fragments. Charcoals were most abundant in the deepest pits formed after ancient treefalls. Periods of accumulation of charcoals in the peatlands and in the soil did not coincide for the last several millennia in the study region: intensive mixing of charcoals into the soil began after a decrease in the flow of charcoals into the peats. We associate this with the changing dynamics of landscapes under the influence of anthropogenic factors.

Are circumpolar hunter-gatherers visible in the palaeoenvironmental record? Pollen-analytical evidence from Nunalleq, southwestern Alaska

Identifying evidence for hunter-gatherers in the palaeoenvironmental record is far from simple. Despite decades of research, few studies have demonstrated unambiguous palynological evidence of hunter-gatherers. This paper presents the results of high-resolution palaeoecological analyses of a peat sequence located within the vicinity of the pre-historic Yup’ik village of Nunalleq in southwestern Alaska. The aim of this research was to examine whether there are any discernible palaeoenvironmental impacts associated with the 15th–17th century occupation of the site. Presuming an ephemeral character to any palaeoecological signal, this study selected a sampling location approximately 30 m east of the limit of archaeological remains. Pollen, non-pollen palynomorphs and microscopic charcoal analysis were then used to generate a highly resolved (contiguous 1 cm) environmental history for the site. The results are striking and indicate that the activities of prehistoric Yup’ik hunter-gatherers at Nunalleq did lea...

Holocene history of landscape development in the catchment of Lake Skogstjern, southeastern Norway, based on a high-resolution multi-proxy record

A high-resolution multi-proxy record from sediments of a small-sized lake situated in Telemark, southeastern Norway, was used to reconstruct the local landscape development of the past c. 10,500 years. Our data demonstrate that changes in vegetation composition and structure in the first two-thirds of the Holocene are principally attributable to climatic changes and high erosion rates, as deduced from geochemical and physical (loss-on-ignition) proxy analyses. The highest signals of erosional inputs to the lake (c. 8030–5760 cal. BP) can be correlated with the first part of the Holocene Thermal Maximum. Nevertheless, evidence from pollen, non-pollen palynomorphs and microscopic charcoal analyses indicates the presence of nutrient-rich and disturbed environments already during the middle Mesolithic (c. 10,050–9400 cal. BP). It also shows traces of animal husbandry (c. 5580 cal. BP) and small-scale cereal cultivation (c. 5520 cal. BP) in the early Neolithic. In subsequent periods, human impact remains at a relatively low level and does not generate significant palaeo-environmental changes. Not until the second half of the Bronze Age (c. 2840 cal. BP) is some intensification in animal husbandry recorded, whereas crop cultivation continues to play a minor role in the second millennium BP. The establishment of a full farming economy took place during the Roman Iron Age (c. 1790 cal. BP), characterised by extensive forest clearance and local fires, crop cultivation in permanent fields and the presence of open pastures. This establishment is associated with advanced soil degeneration and increased erosion rates.

Vegetation and fire history of coastal north-eastern Sardinia (Italy) under changing Holocene climates and land use

Little is known about the vegetation and fire history of Sardinia, and especially the long-term history of the thermo-Mediterranean belt that encompasses its entire coastal lowlands. A new sedimentary record from a coastal lake based on pollen, spores, macrofossils and microscopic charcoal analysis is used to reconstruct the vegetation and fire history in north-eastern Sardinia. During the mid-Holocene (c. 8,100–5,300 cal bp), the vegetation around Stagno di Sa Curcurica was characterised by dense Erica scoparia and E. arborea stands, which were favoured by high fire activity. Fire incidence declined and evergreen broadleaved forests of Quercus ilex expanded at the beginning of the late Holocene. We relate the observed vegetation and fire dynamics to climatic change, specifically moister and cooler summers and drier and milder winters after 5,300 cal bp. Agricultural activities occurred since the Neolithic and intensified after c. 7,000 cal bp. Around 2,750 cal bp, a further decline of fire incidence and Erica communities occurred, while Quercus ilex expanded and open-land communities became more abundant. This vegetation shift coincided with the historically documented beginning of Phoenician period, which was followed by Punic and Roman civilizations in Sardinia. The vegetational change at around 2,750 cal bp was possibly advantaged by a further shift to moister and cooler summers and drier and milder winters. Triggers for climate changes at 5,300 and 2,750 cal bp may have been gradual, orbitally-induced changes in summer and winter insolation, as well as centennial-scale atmospheric reorganizations. Open evergreen broadleaved forests persisted until the twentieth century, when they were partly substituted by widespread artificial pine plantations. Our results imply that highly flammable Erica vegetation, as reconstructed for the mid-Holocene, could re-emerge as a dominant vegetation type due to increasing drought and fire, as anticipated under global change conditions.

Long-term variability and rainfall control of savanna fire regimes in equatorial East Africa.

Fires burning the vast grasslands and savannas of Africa significantly influence the global carbon cycle. Projecting the impacts of future climate change on fire-mediated biogeochemical processes in these dry tropical ecosystems requires understanding of how various climate factors influence regional fire regimes. To examine climate-vegetation-fire linkages in dry savanna, we conducted macroscopic and microscopic charcoal analysis on the sediments of the past 25000years from Lake Challa, a deep crater lake in equatorial East Africa. The charcoal-inferred shifts in local and regional fire regimes were compared with previously published reconstructions of temperature, rainfall, seasonal drought severity, and vegetation dynamics to evaluate millennial-scale drivers of fire occurrence. Our charcoal data indicate that fire in the dry lowland savanna of southeastern Kenya was not fuel-limited during the Last Glacial Maximum (LGM) and Late Glacial, in contrast to many other regions throughout the world. Fire activity remained high at Lake Challa probably because the relatively high mean-annual temperature (~22°C) allowed productive C4 grasses with high water-use efficiency to dominate the landscape. From the LGM through the middle Holocene, the relative importance of savanna burning in the region varied primarily in response to changes in rainfall and dry-season length, which were controlled by orbital insolation forcing of tropical monsoon dynamics. The fuel limitation that characterizes the region's fire regime today appears to have begun around 5000-6000years ago, when warmer interglacial conditions coincided with prolonged seasonal drought. Thus, insolation-driven variation in the amount and seasonality of rainfall during the past 25000 years altered the immediate controls on fire occurrence in the grass-dominated savannas of eastern equatorial Africa. These results show that climatic impacts on dry-savanna burning are heterogeneous through time, with important implications for efforts to anticipate future shifts in fire-mediated ecosystem processes.

Vegetation history and landscape management from 6500 to 1500 cal. b.p. at Lac d’Antre, Gallo-Roman sanctuary of Villards d’Héria, Jura, France

The lake sediment record was used to reconstruct past vegetation dynamics and human impacts from the middle Neolithic (6500 cal. b.p.) to the Middle Ages (1500 cal. b.p.) around Lac d’Antre in the southern Jura mountains of France. This lake was surrounded by the Gallo-Roman sanctuary of Villards d’Heria, which has been widely investigated by archaeologists and enables a comparison between palaeoenvironmental proxies and archaeological data. Pollen and microscopic charcoal analyses were conducted on a 500 cm sediment core with eleven radiocarbon dates providing the chronological control. In a mixed oak woodland context, the successive development of Taxus, Fagus and Abies were mainly caused by climatic variations during the Neolithic, in which there was weak human impact. The first significant signs of human activity were detected during the Bronze Age from 3900 cal. b.p., followed by an increase of human pressure and woodland clearances during the Iron Age, from 2700 cal. b.p. The occupation of the Gallo-Roman sanctuary was continuous with the Iron Age occupation. All the analysed palaeoenvironmental data indicate that the strongest human impact occurred during the Gallo-Roman period, which matches the occupation of Villards d’Heria previously dated by archaeologists from 2000 to 1700 cal. b.p., 1st to 3rd century a.d. Moreover, there appears to have been a new period of human settlement close to the lake at the beginning of the Middle Ages. The low charcoal accumulation rate (CHAR) recorded during the Bronze and Iron Ages suggests that fire was not the main agent used to clear the dense woods to create new cultivated fields and pastures. High CHAR values recorded during the Roman period may represent fire use for domestic and agro-pastoral activities.

Reconstruction of the fire history in the Siedlungskammer Burgweinting (Bavaria, Germany) in relation to settlement and environmental history

Abstract Palaeoenvironmental investigations were carried out in the Siedlungskammer (prehistoric settlement area) Burgweinting (Regensburg, Bavaria, Germany) to reveal past settlement conditions and human impact on the environment. Two sequences were obtained from the Islinger Mühlbach Fen, in close proximity to the archaeological excavation site in Burgweinting, which documents an almost continuous settlement history since the Neolithic Period. The analyses of the sequences comprise stratigraphic, geochemical and microscopic charcoal analyses. For chronological information, radiocarbon dating was conducted on a total of 10 samples. Thus, the first long-term fire record was reconstructed for the investigation area, and the results were correlated, based on radiocarbon dating, with the available environmental information and settlement history in the Siedlungskammer Burgweinting. The fire record reveals an almost continuous, but alternating fire history. Furthermore, it shows that fire played an important role in the Siedlungskammer Burgweinting and that most probably as early as the Mesolithic hunterer–gatherers deliberately used fire.

Long‐term interactions between Mediterranean climate, vegetation and fire regime at Lago di Massaciuccoli (Tuscany, Italy)

Summary A Holocene sedimentary sequence from a coastal lake in the Mediterranean area (Lago di Massaciuccoli, Tuscany, Italy, 0 m a.s.l.) was sampled for pollen and microscopic charcoal analyses. Contiguous 1‐cm samples represent an estimated time interval of c. 13 years, thus providing a high‐resolution sequence from 6100 to 5400 cal. years bp. Just before 6000 cal. years bp, sub‐Mediterranean and Mediterranean forests were present together with fir (Abies alba), a submontane species that is today absent at low altitudes in the Mediterranean. A sharp vegetational change occurred after 6000 cal. years bp involving a drastic decline of Abies alba around the site. Time‐series analyses suggest that increased fire activity at this time caused a strong decline in Abies alba, a highly fire‐sensitive species. During 100 years of higher fire incidence, diverse (predominantly evergreen) forest communities were converted to low‐diversity fire‐prone shrub communities. Cross‐correlations reveal that fire during the mid‐Holocene hindered the expansion of holm oak (Quercus ilex), the most common tree species today in Mediterranean environments. While the factors that triggered the Holocene expansion of this species in the Mediterranean area are unclear, our results do not support the hypothesis that fire was key for holm oak expansion. Diatom analyses of the same sediment core provide an independent palaeoenvironmental proxy for palaeoclimatic reconstruction. A change in the eutrophy and salinity of the lake occurred just before 6000 cal. years bp, suggesting that a climatic shift towards aridity may have triggered the observed change in hydrology and possibly also in fire regime. Over the millennia fire has decisively contributed to the establishment of the present fire‐adapted vegetation type (macchia). Native fire‐sensitive species were displaced or repressed, and arboreal vegetation became less diverse. Combined ecological and palaeoecological data may help to assess possible future scenarios of biosphere responses to global change. Our results imply that the forecasted global warming and fire increase may trigger irrecoverable biodiversity losses and shifts in vegetational composition within a few decades or centuries at most. In particular, fire and drought‐sensitive vegetation types, such as the relict forests of Abies alba in the Apennines, seem particularly threatened by large‐scale displacement.

Human impact during the Bronze Age on the vegetation at Lago Lucone (northern Italy)

Lake-sediment records were used to reconstruct human impact on the landscape around Lago Lucone (45°33′N, 10°29′E, 249 m a.s.l.), a former lake in the western amphitheatre system of the Lago di Garda. Presence of prehistoric human populations is attested by pile-dwelling settlements from the Early-Middle Bronze Age, with one settlement at a distance of only 100 m from the coring site. Pollen, plant-macrofossil and microscopic charcoal analyses were applied to a 250 cm sediment core with four dates providing the time control. A mixed oak forest that was important during the Early-Middle Holocene was cleared and replaced by open vegetation during the Bronze Age (∼2000–1100 b.c.) when open lands were estimated to have covered more than 60% of the total relevant pollen-source area. During a phase of high human impact, independent climatic proxies suggest warm and dry climatic conditions. Later, ca. 1100 b.c., palaeobotanical evidence indicates a sharp decrease in human pressure in the Lago Lucone area. The comparison with other sedimentary palaeocultural records shows that the period 1300–1100 b.c. was characterised by general declines of agricultural activities both south and north of the Alps. These declines have been previously attributed to a change towards wetter and colder climatic conditions in and around the Alps. However, the decline in human impact around Lago Lucone cannot be exclusively attributed to climatic variation. Therefore other forcing factors independent of climatic changes, such as cultural crises or changes in spatial organisation of the habitats, cannot be ruled out under the present state of knowledge.

Palaeoenvironmental evaluation of the importance of fire as a cause for Calluna loss in the British Isles

Pollen and microscopic charcoal analyses of sediment cores were used to reconstruct long-term vegetation and fire histories for seven moorland lake catchments in the UK and Ireland. In each of the seven catchments Calluna vulgaris cover has declined considerably over the last 100–150 years. Redundancy analysis was used to examine the relationship between declining Calluna cover and catchment fire histories to determine whether burning of catchment vegetation was associated with the onset of Calluna loss. The results suggest that burning may have been a significant factor contributing toward the decline in Calluna cover at two of the seven study sites, but no single causative factor could be shown to be responsible for the decline on a national scale.

A method for the preparation and quantification of microscopic charcoal from terrestrial and lacustrine sediment cores

Existing methods of microscopic charcoal analysis are briefly reviewed. A simple but effective alter-native method for preparing and quantifying fossil microscopic charcoal in sediment samples from terrestrial and lacustrine cores is outlined. Weak hydrogen peroxide (6%f/o H202) is used to partially digest and bleach organic material in sediment samples. Charcoal particles are not bleached by the hydrogen peroxide and are thus easily identified when counted under a binocular dissecting microscope. The sample preparation procedure is extremely gentle on charcoal particles, much more so than the majority of existing methods, ensuring that little particle fragmentation occurs during preparation.

Late Wisconsin paleoecologic record from Swamp Lake, Yosemite National Park, California

A 7.86-m sediment core from Swamp Lake in Yosemite National Park, California, provides a continuous record of environmental change over the last ca. 16,000 yr, as inferred from pollen, macrofossil, and microscopic charcoal analyses. The core stratigraphy documents late Wisconsin (Tioga stage) deglaciation between >16,000 and 13,700 yr B.P., approximately 6000-3500 yr earlier than higher-elevation Sierra Nevada records. The core includes five volcanic ash layers, chemically identified as four Mono Craters ashes and the Tsoyawata ash (Mt. Mazama, Oregon). The fossil record shows that herbs and sagebrush dominated the glacial environment at Swamp Lake. By 12,000 yr B.P., a mixed conifer forest composed of high- and mid-elevation conifers grew around the lake, suggesting a cool, wet late-glacial environment. The modern Sierra montane forest did not become established until ca. 10,400 yr B.P., when maximum charcoal concentrations and minimum fir pollen percentages indicate an early Holocene xeric period. The record suggests that a cooling trend began ca. 6500 yr B.P. and persisted until ca. 3700 yr B.P. when the modern climatic regime was established.