Reconstruction Of Fire History Research Articles

Scales of plant stewardship in the precontact Pacific Northwest, USA

Numerous oral histories and substantial ethnographic evidence illustrate how plant species, communities, and even landscapes were extensively managed and cared for by ancestral communities in the Pacific Northwest. Camas ( Camassia spp.) is one such cultural keystone plant, common from the Pacific Ocean to the Rocky Mountains, with numerous records describing its role as a staple food for many Northwest peoples. Supporting deep time archeological evidence for such management or stewardship practices, however, has remained elusive. In this paper we analyze archived collections of archeological camas bulbs from 11 sites across the Willamette Valley, Oregon to demonstrate people began preparing camas within earth ovens by approximately 8000 calendar years before present and deliberately harvesting sexually mature camas plants circa 3500 calendar years before present. We compare these findings with climatological, palynological, and fire history reconstructions to discuss stewardship strategies for camas and associated plant communities through time at the population, community, and landscape levels. These findings confirm and expand upon Indigenous knowledges as well as offer time-tested methods for cultural keystone conservationists seeking to revitalize traditional plant stewardship practices throughout this region and beyond. This “camas case study” also offers another example of a human-plant symbiotic relationship, expanding our knowledge of plant food pathways, processes, and mutualisms.

Late Holocene high-resolution paleoenvironmental reconstruction from Beaver Lake in the northwest lowlands of the Olympic Peninsula, Washington (USA)

Fire is an essential component of the landscapes and forests of the Pacific Northwest, including the temperate rainforests of the Olympic Peninsula. Previous fire history reconstructions from the peninsula show that fire return intervals varied throughout the postglacial period, primarily in response to climatic changes and corresponding shifts in vegetation. However, much less is known about the fire history of the low-elevation forests of the Olympic Peninsula and the role of cultural fire regimes in these environments. The purpose of this study was to reconstruct the paleoenvironmental history of a low-elevation study site, Beaver Lake, located in the northwestern part of the peninsula. Using macroscopic charcoal, pollen, and sedimentological analyses of a ca. 3440-year-long record, we reconstructed a high-resolution record that shows fire activity was remarkably high during the late Holocene for an area considered part of a temperate rainforest. However, patterns of burning varied throughout the record, with the first third (ca. 3440 to 2350 cal yr BP) and last third (ca. 800 cal yr BP to the present day) recording much higher amounts of fire activity compared to the middle portion (ca. 2350 to 800 cal yr BP), which recorded very little fire activity. Larger and/or more severe fires that likely burned during multi-year droughts correlate with peaks in magnetic susceptibility and pollen trends that indicate substantial geomorphic responses and successional changes in forest structure following these events. Cooler temperatures and a wetter climate, indicated by nearby glacial advancements, may have staved off fire activity during the period of low fire activity. Cultural burning by the Indigenous tribes of the Olympic Peninsula likely contributed to the observed fire activity at Beaver Lake as nearby prairies were managed for resource procurement, indicated in particular by an increase in herbaceous morphotype charcoal during the past 800 years.

Monitoring Intra-Annual Wood Formation of Pinus nigra J.F. Arnold (Black Pine) to Understand the Fire Seasonality in Western Anatolia

Recent climate and societal changes have increased wildfire activity and prolonged the fire season in many regions of the world. The precision of fire seasonality analysis from tree-ring records can be improved by complementing the subjectively determined intra-ring position of fire scars with more precise studies of wood formation. With this aim, we monitored the wood formation dynamics of Pinus nigra J.F. Arnold (black pine) trees along a climatic gradient in western Anatolia to better understand the wood formation for the interpretation of fire seasonality. Wood microcores were collected from April to November 2021 from trees at four sites across (from north; the Black Sea climate in Bolu to the south; and the Mediterranean climate in Isparta) the areas where previous fire history reconstructions were conducted. These previous studies showed that most fires occurred during the latewood formation period. We found that matured latewood tracheids were observed between September (August) and November, thus suggesting that these fires occurred during late summer and fall. Our results show the importance of temperature and water availability for the timing of earlywood and latewood formations. These findings can be used to better inform planning activities for fire management and as a proxy to reconstruct past fire seasonality.

Reconstruction of local fire history, example of peat deposits of the Mokhovoe mire (Northern Altai)

Reconstruction of local fire history, example of peat deposits of the Mokhovoe mire (Northern Altai)

The history of fire, human and climate in black pine forests of western Anatolia: The Taurus mountains

The interactions between fire occurrence-human-climate are highly complex to understand and also difficult to predict due to having many sources of variations in fire regimes. However, we can gather information about the effect of human influence on the regional fire regimes where human influence is high, and the history of locations is well-known by conducting retrospective fire history studies in locations. Here, we present the impact of human settlements on fire occurrence by comparing and discussing the previous drought-driven tree-ring-based fire history reconstruction sites in western Anatolia. For this purpose, we collected cross-sections from Miyarcık highland, Antalya, and developed a 519–y long (1503–2021 CE) composite fire chronology using dendrochronological methods. Our study site location is known for the seasonal inhabitants of “Yörüks”, who led a nomadic life in the Taurus Mountains for centuries, and forests were used for livestock grazing. Since the temperatures increase significantly at the beginning of spring in the lower elevations of Antalya, the yörüks move towards the upper highlands with their animals from May to November. We found lower fire frequency and no fire-climate association compared to other sites that experienced drought-driven wildfires, even though this site is located in a high-fire-risk region. Low-frequency fires might be due to moderate-level livestock grazing by yörüks in this area. Grazing contributes to reducing the amount of accumulated combustible materials, causes discontinuity of fuel in the understory of forests, and affects the dynamics of the spatial distribution of wildfires. This study showed that moderate-level grazing might support effective fire management activities as fuel management because of modifying the fuel properties, changing the fuel-fire interaction (e.g., the fuel continuity and amount of accumulated fuel), and reducing the wildfire probability over space and time.

What burned the forest? Wildfires, climate change and human activity in the Mesolithic – Neolithic transition in SE Iberian Peninsula

Climate variability such as higher or lower temperatures, changing precipitation patterns, shifts in plant communities and other climate-related changes have particularly affected areas with Mediterranean-type climates. A multi-proxy analysis including pollen, sedimentary charcoal, mineralogy and Summed Probability Distributions (SPD) of archaeological 14C dates, allowed the reconstruction of landscape change, geomorphological evolution and fire history at the Laguna de Villena, in the southeastern Iberian Peninsula, during the Mesolithic-Neolithic transition. The Villena paleolake was sensitive to Early Holocene and Middle Holocene regional climatic variability that included several arid phases (around 8.2 ka cal BP, 6.8 ka cal BP and 5.9 ka cal BP) according to geochemical and pollen data. During this period, landscape dynamics show the degradation of oak forests and expansion of pyrophytic pine forests and shrublands, as well as open spaces predominated by grasses. The charcoal record shows a decreasing trend of biomass burned from 8.5 ka cal BP onwards, although fire peaks occurred recurrently during the Early and Middle Holocene. The most intense phase of fire activity was experienced in the last millennia of the Early Holocene, with five fire episodes from 9.1 to 8.4 ka cal BP, coinciding with a phase of higher archaeological evidence in the area. A decrease in archaeological evidence coincides with a gap in fire episodes during the Early Holocene-Middle Holocene transition, suggesting an effect of the abrupt 8.2 ka cal BP event on human activity and on landscape dynamics. After 8.0 ka cal BP, lowerer biomass burned is explained by the configuration of a more open landscape due to the combination of climate (increasing aridity) and increasing human activities in the region. The mineralogical and palynological data highlighted the interaction between human activities, climate and fire dynamics. The sedimentary charcoal record evidenced how most of the fire peaks did not occur in the context of dry episodes, as often assumed, deriving on an anthropogenic explanation related to Early and Late Mesolithic burning practices during a phase of higher archaeological evidence in the Villena paleolake surroundings. Afterwards, combined agropastoral activities from the Early Neolithic onwards and increasing aridity during the Middle Holocene maintained the forest clearances, in the context of fire episodes characterised by decreased biomass burned. This study shows how Middle Holocene palaeoecological records reflect complex histories blending climate and anthropogenic processes that derived in major landscape changes explaining the origin of current landscapes.

High intensity fire accelerates accumulation of a stable carbon pool in permafrost peatlands under climate warming

Peatland carbon pools store one-third of global soil carbon, but are increasingly threatened by wildfires, particularly high intensity wildfires, as a consequence of climate warming. However, with only a limited understanding of fire history reconstruction available, the long-term impacts of fire intensity on the stability of the peatland carbon pool remains poorly understood. Here, based on Fourier transform infrared spectroscopy and chemical analysis of PyC and organic matter in Hongtu (HT) peat core in the northern Great Khingan Mountains (China), historical fire intensity and fuel sources during the last 700 years were reconstructed and their effects on carbon stability evaluated. Our results showed that the major stable carbon pool (i.e. aromatics) and the retained labile carbon pool (i.e. iron-bound organic carbon, Fe-OC) in HT peatland are 278.1 ± 6.2 mg·g−1 and 6.78 ± 3.85 mg·g−1, respectively. High-intensity herb fires in peatlands occurred more easily under wet conditions and caused more PyC accumulation than shrub fires. Both climate warming and high-intensity fire promoted more aromatics and Fe-OC accumulation, increasing the overall stability of peatland carbon pool. High-intensity fire under warm climate conditions resulted in Fe-OC accumulation rates threefold higher (ca. 0.02 mg·cm−2 yr−1 to ca. 0.06 mg·cm−2 yr−1) but had no marked effects on the aromatic and PyC accumulation rates. Overall, our results suggest that high-intensity fires can accelerate stable carbon pool accumulation in peatlands during climate warming.

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.

Climate forcing of regional fire years in the upper Great Lakes Region, USA

Background Drivers of fire regimes vary among spatial scales, and fire history reconstructions are often limited to stand scales, making it difficult to partition effects of regional climate forcing versus individual site histories. Aims To evaluate regional-scale historical fire regimes over 350 years, we analysed an extensive fire-scar network, spanning 240 km across the upper Great Lakes Region in North America. Methods We estimated fire frequency, identified regionally widespread fire years (based on the fraction of fire-scarred tree samples, fire extent index (FEI), and synchronicity of fire years), and evaluated fire seasonality and climate–fire relationships. Key results Historically, fire frequency and seasonality were variable within and among Great Lakes’ ecoregions. Climate forcing at regional scales resulted in synchronised fires, primarily during the late growing season, which were ubiquitous across the upper Great Lakes Region. Regionally significant fire years included 1689, 1752, 1754, 1791, and 1891. Conclusions We found significant climate forcing of region-wide fire regimes in the upper Great Lakes Region. Implications Historically, reoccurring fires in the upper Great Lakes Region were instrumental for shaping and maintaining forest resilience. The climate conditions that helped promote widespread fire years historically may be consistent with anticipated climate–fire interactions due to climate change.

The reconstruction of Holocene northwestern Mongolian fire history based on high-resolution multi-site macro-charcoal analyses

In palaeoecology, multi-site macro-charcoal analyses provide information on climate–fire–vegetation linkages, their spatial and temporal extent, and the impact of prehistoric human practices. Our multi-site study comprises eight macro-charcoal records from two highly continental forest-steppe regions in western and north-central Mongolia, covering the Holocene. In addition to reviewing macro-charcoal influxes and comparing macro-charcoal morphotype results with arboreal/non-arboreal pollen ratios, our dataset provides the first fire frequency synthesis for two regions in Mongolia. During the early and mid-Holocene, the fire history in western and north-central Mongolia was controlled by the regional climate variability, whereas the fire intensities were higher in the Mongolian Altai. In general, fire frequencies are lower in northern Khangai. Increases in the fire frequency correlate with the potential beginning of a rise in the nomadic population of the Mongolian Altai after 1,100 cal yr BP. In both areas, individual macro-charcoal peaks, a marked site-to-site variability, and a generally very low impact on the forest-steppe distribution may mostly be explained by a strictly local nomadic disturbance.

Late-Holocene vegetation and fire history in Western Putorana Plateau (subarctic Siberia, Russia)

We present a reconstruction of vegetation dynamics and fire history from the western part of the Putorana Plateau during the Late-Holocene. The study area is located in the remote and poorly investigated region of Central Siberia, which represents an important area for understanding climate and environmental changes in the Russian Subarctic. Pollen and macroscopic charcoal data from three closely located lakes along an altitudinal transect in the Khantaika River basin show no major changes in vegetation in the study area during the last 3.9 ka BP. However, a detailed analysis of the data reveals an extension of forest coverage in lake catchments at about 3.1 ka BP followed by a gradual degradation of woodlands, and an expansion of shrubs and tundra vegetation at around 2.7–2.5 ka BP. Fire activity was relatively high between 3.0 and 2.0 ka BP compared to all but the most modern part of the record, while macroscopic charcoal accumulation reaches a maximum in the most recent surface sediments. This suggests an increase in the frequency and area of fires in the region since the end of the 19th century, which has no analog during the Late-Holocene.

Evidence that modern fires may be unprecedented during the last 3400 years in permafrost zone of Central Siberia, Russia

Recent climate change in Siberia is increasing the probability of dangerous forest fires. The development of effective measures to mitigate and prevent fires is impossible without an understanding of long-term fire dynamics. This paper presents the first multi-site palaeo-fire reconstruction based on macroscopic charcoal data from peat and lake sediment cores located in different landscapes across the permafrost area of central Siberia. The obtained results show similar temporal patterns of charcoal accumulation rates in the cores under study, and near synchronous changes in fire regimes. The paleo-fire record revealed moderate biomass burning between 3.4 and 2.6 ka BP, followed by the period of lower burning occurring from 2.6 to 1.7 ka BP that coincided with regional climate cooling and moistening. Minimal fire activity was also observed during the Little Ice Age (0.7–0.25 ka BP). Fire frequencies increased during the interval from 1.7 to 0.7 ka BP and appears to be partly synchronous with climate warming during the Medieval Climate Anomaly. Regional reconstructions of long-term fire history show that recent fires are unprecedented during the late Holocene, with modern high biomass burning lying outside millennial and centennial variability of the last 3400 years.

Late Holocene climate variability in central Korea indicated by vegetation, geochemistry, and fire records of the Yongneup moor

In many cases, proxy-based palaeoclimatic and palaeoenvironmental reconstructions in East Asia have shown mixed signatures of summer temperature and precipitation, driven by the predominant regional impact of the East Asian Summer Monsoon. Although these studies have contributed significantly to understanding the past variability in East Asian summer climate during the Holocene period, relatively little has been learned about climatic conditions in other seasons, such as winter and spring, and variations in the individual climatic elements of temperature and precipitation. To address these issues, in this study, we present a reconstruction of a 3000-year fire and vegetation history of the Yongneup moor, central Korea, during the late Holocene based on multi-proxy analyses of pollen, geochemistry, and macrocharcoal. Our data identify two fire episodes at Yongneup during ca. 2900–2700 and 2400–2300 cal yr B.P., possibly caused amid deteriorated climatic conditions not only in summer but also in winter–spring during contemporaneous grand solar minima. During the last two millennia, Yongneup likely experienced cold weather conditions at ca. 1420–1230 and 1000–590 cal yr B.P. and warm conditions at ca. 1850–1420 and 1230–1000 cal yr B.P., as well as wet conditions during ca. 1530–1400, 1220–1000, and 890–700 cal yr B.P. and drier conditions during ca. 1750–1530, 1400–1220, 1000–890, and 700–530 cal yr B.P. The dry periods were coincident with an increased El Niño–Southern Oscillation in the Tropical Pacific Ocean, which supports its role in controlling the hydroclimate of the Korean Peninsula. Our results also emphasise the potential value of further research on the “Millennium Eruption” of Mount Paektu/Changbaishan (946 CE), whose climatic consequences in the East Asian region remain poorly understood. • Late Holocene climate variability in Korea reconstructed from the Yongneup moor • Fire events coincident with solar minima at ca. 2900–2700 and 2400–2300 cal yr B.P. • Potential impact of climate deterioration on Mumun (Bronze Age) societies in Korea • Fluctuations in cold–warm and dry-wet conditions during the last two millennia • Implication on the volcanic impact of the “Millennium Eruption” of Mount Paektu

Climate and landscape change favouring early rice agriculture and appreciable human impact: Evidence from sediment [formula omitted]13C in eastern China

Kuahuqiao site, famous for its early rice cultivation, is taken to be a typical case of how agriculture emerged in a littoral environment in the early Holocene. However, the lack of fire history and local climatic reconstruction has hindered the detailed picture of agricultural origins and development. Here we report new records of TOC, BC, δ13CTOC, δ13CBC, and C/N, alongside published pollen and charcoal data. Our δ13CTOC and C/N confirm the previously-proposed formation of wetlands, which offered favorable landscapes for rice paddy agriculture, prior to the appearance of the Kuahuqiao culture. Based on BC, δ13CTOC, and δ13CBC records we suggest a hotter but drier climate that would have benefited rice agriculture by augmenting the distribution of wild rice and C4 herbs. In addition, δ13CTOC shows a decreased C3/C4 ratio as a signal of human occupation with manipulation of forest for hunting-gathering or/and land clearance for agriculture. Combined δ13CBC and BC records oppose the proposal of intense fire use in early agriculture and suggest that fire use was constrained to domestic purposes. Flood events which seem to have terminated the Kuahuqiao culture left impressions in TOC, BC, δ13CTOC, δ13CBC.

The significance of pyrogenic polycyclic aromatic hydrocarbons in Borneo peat core for the reconstruction of fire history.

The reconstruction of fire history is essential to understand the palaeoclimate and human history. Polycyclic aromatic hydrocarbons (PAHs) have been extensively used as a fire marker. In this work, the distribution of PAHs in Borneo peat archives was investigated to understand how PAHs reflect the palaeo-fire activity. In total, 52 peat samples were analysed from a Borneo peat core for the PAH analysis. Pyrogenic PAHs consist of 2–7 aromatic rings, some of which have methyl and ethyl groups. The results reveal that the concentration of pyrogenic PAHs fluctuated with the core depth. Compared to low-molecular-weight (LMW) PAHs, the high-molecular-weight (HMW) PAHs had a more similar depth variation to the charcoal abundance. This finding also suggests that the HMW PAHs were mainly formed at a local fire near the study area, while the LMW PAHs could be transported from remote locations.

Exploring the past of Mavrovouni forest in the\xa0Pindus Mountain range (Greece) using tree rings of Bosnian pines

Key messageLong Bosnian pine chronologies from different mountains are shaped by different climatic parameters and can help identify past drought events and reconstruct landscape histories.We developed a 735-year-long Pinus heldreichii chronology from the southern distribution limit of the species, expanding the available database of long Bosnian pine chronologies. Tree-ring growth was mainly positively correlated with growing degree days (GDD: r1950–2018 = 0.476) while higher temperatures during both winter and growing season also enhanced growth (TWT: r1950–2018 = 0.361 and TGS: 0.289, respectively). Annual precipitation, during both calendar and water years, had a negative but weaker impact on annual tree growth. The newly developed chronology correlates well with chronologies developed from the neighboring mountains. The years with ring width index (RWI) lower than the average were found to correspond to cool years with dry summers. Still, the newly developed chronology was able to capture severe drought events, such as those in 1660, 1687, and 1725. Several old living trees had internal scars presumably caused by fires. Therefore, old mature trees could be used for fire history reconstruction in addition to climate reconstruction. Although the presence of lightning scars indicates an important natural agent of fire ignition, human activities associated with animal grazing could also be an underlying reason for fires in the region.

Holocene Fire Regime Changes in the Southern Lake Baikal Region Influenced by Climate-Vegetation-Anthropogenic Activity Interactions

Catastrophic fire years that have taken place during the last decade in Siberia, and more generally within the boreal forest, have been directly linked to global warming and had strong repercussions on boreal ecosystems and human populations. In this context the study of the past dynamics of these fires is essential for understanding their links with climate, vegetation and human activity changes on longer time scales than the last few decades. However, few studies on fire dynamics are available for Siberia, and none have been conducted for the entire Holocene period. This study presents the first fire history reconstruction of this area during the Holocene based on charcoals sequestered in sediments of two lakes located on the southern shore of Lake Baikal, in Siberia. The results show a similar trend in the two lakes, with high frequency and high peak magnitude during the Early Holocene and low magnitudes after 6500 cal. yr BP. This difference is interpreted as crown fires versus surface fires. According to pollen records (Dulikha, Vydrino, Ochkovoe) available near the studied lakes, a vegetation transition occurred at the same time. Picea obovata, which has a tree structure prone to crown fires, was dominant during the Early humid Holocene. After 6500 cal. yr BP, conditions were drier and Pinus sylvestris and Pinus sibirica became the dominant species; their tree structure favors surface fires. In addition to vegetation dynamics, the nearby pollen sequence from Dulikha has been used to provide quantitative estimates of past climate, indicating an Early to Middle Holocene climatic optimum between 8000 and 5000 cal. yr BP and an increase in temperatures at the end of the Holocene. These results have been compared to outputs from regional climate models for the Lake Baikal latitudes. Fire dynamics appear to have been more linked to the vegetation than climatic conditions. Over the past 1500 years, the greater presence of human populations has firstly resulted in an increase in the fire frequency, then in its maintenance and finally in its suppression, which may possibly have been due to very recent fire management, i.e., after ca 500 cal. BP.

A lake sediment–based paleoecological reconstruction of late Holocene fire history and vegetation change in Great Basin National Park, Nevada, USA

AbstractAnalyses of macroscopic charcoal, sediment geochemistry (%C, %N, C/N, δ13C, δ15N), and fossil pollen were conducted on a sediment core recovered from Stella Lake, Nevada, establishing a 2000 year record of fire history and vegetation change for the Great Basin. Charcoal accumulation rates (CHAR) indicate that fire activity, which was minimal from the beginning of the first millennium to AD 750, increased slightly at the onset of the Medieval Climate Anomaly (MCA). Observed changes in catchment vegetation were driven by hydroclimate variability during the early MCA. Two notable increases in CHAR, which occurred during the Little Ice Age (LIA), were identified as major fire events within the catchment. Increased C/N, enriched δ15N, and depleted δ13C values correspond with these events, providing additional evidence for the occurrence of catchment-scale fire events during the late fifteenth and late sixteenth centuries. Shifts in the vegetation community composition and structure accompanied these fires, withPinusandPiceadecreasing in relative abundance and Poaceae increasing in relative abundance following the fire events. During the LIA, the vegetation change and lacustrine geochemical response was most directly influenced by the occurrence of catchment-scale fires, not regional hydroclimate.

Integrating charcoal morphology and stable carbon isotope analysis to identify non-grass elongate charcoal in tropical savannas

Fire is inextricably linked to the vegetation that provides the fuel load. For palaeofire records to contribute meaningfully to the reconstruction of past landscape fire history, it is helpful to identify the vegetation that has been burnt, for example, grassy versus woody vegetation in tropical savannas. The morphological characteristics of charcoal particles can provide useful information on source vegetation type, and the aspect ratio of charcoal particles has been proposed to identify the contribution of grasses to environmental records. Stable carbon isotope analysis of pyrogenic carbon can also chemically identify the proportion of C3 and C4 biomass in charcoal samples but has yet to be widely applied alongside charcoal morphological analysis. Using carbon isotope analysis we demonstrate that C3 sedges contribute elongate charcoal to a fire record where C4 grasses are absent. These results challenge the widespread assumption that elongate charcoal is primarily or exclusively derived from grass, as most experimental studies demonstrating this relationship were conducted in environments where graminoids (grass-like forms) did not significantly contribute to available fuels. In turn, this complicates the simple interpretation of elongate aspect ratios for charcoal in fire records as direct proxies for the proportion of grasses in an environment, beyond differentiating temperate forests from grasslands. Minimal work to date has been done on separating charcoal derived from different graminoid types and future studies would benefit from the ability to differentiate graminoids including Poaceae and Cyperaceae in fire records. These results highlight the benefits of a multi-proxy approach to the interpretation of fire records in tropical savannas.

Holocene fire history reconstruction of a mid-elevation mixed-conifer forest in the Eastern Cascades, Washington, USA

Fire histories of mid-elevation mixed-conifer forests are uncommon in the eastern Cascades, limiting our understanding of long-term fire dynamics in these environments. The purpose of this study was to reconstruct the fire and vegetation history for a moist mid-elevation mixed-conifer site, and to determine whether Holocene fire activity in this watershed was intermediate to fire regimes observed at higher and lower elevations in the eastern Cascades. Fire activity and vegetation change was reconstructed using macroscopic charcoal and pollen analysis of sediment core from Long Lake. This site is located ~45 km west of Yakima, WA, and exists in a grand fir-dominated, mixed-conifer forest. Results show low fire activity from ca. 9870 to 6000 cal yr BP, after which time fire increased and remained frequent until ca. 500 cal yr BP. A woodland environment existed at the site in the early Holocene, with the modern coniferous forest establishing ca. 6000–5500 cal yr BP. A mixed-severity fire regime has existed at the site for the past ~6000 years, with both higher- and lower-severity fire episodes occurring on average every ~80–100 years. However, only one fire episode occurred in the Long Lake watershed during the past 500 years, and none within the past ~150 years. Based on a comparison with other eastern Cascade sites, Holocene fire regimes at Long Lake, particularly during the late Holocene, appear to be intermediate between those observed at higher- and lower elevation sites, both in terms of fire severity and frequency.